Prepared in cooperation with the

TRUCKEE–CARSON PROGRAM

River and Reservoir Operations Model, 

Truckee River Basin, California and Nevada, 1998

U.S. Department of the Interior

U.S. Geological Survey

Water-Resources Investigations Report 01-4017
RIVER AND OPERATIONS MODEL, TRUCKEE RIVER BASIN, CALIFORNIA AND NEVADA, 1998
River and Reservoir Operations Model, 

Truckee River Basin, California and Nevada, 1998

By Steven N. Berris, Glen W. Hess, and Larry R. Bohman

U.S. GEOLOGICAL SURVEY

Carson City, Nevada

2001

Prepared in cooperation with the

TRUCKEE–CARSON PROGRAM

Water-Resources Investigations Report 01-4017
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

CHARLES G. GROAT, Director

Any use of trade, product, or firm names in this publication is for descriptive

purposes only and does not imply endorsement by the U.S. Government

For additional information

contact:

District Chief

U.S. Geological Survey

333 West Nye Lane, Room 203

Carson City, NV 89706–0866

email: GS-W-NVpublic-info@usgs.gov

http://nevada.usgs.gov
CONTENTS III

CONTENTS

Abstract.................................................................................................................................................................................. 1

Introduction............................................................................................................................................................................ 2

Purpose and Scope ..................................................................................................................................................... 4

Previous Investigations .............................................................................................................................................. 5

Acknowledgments...................................................................................................................................................... 6

Description of Study Area ..................................................................................................................................................... 7

Lake Tahoe and Upper Truckee River Subunit.......................................................................................................... 8

Middle Truckee River Subunit................................................................................................................................... 10

Lower Truckee River and Pyramid Lake Subunit...................................................................................................... 12

Chronology and Background of Decrees, Agreements, and Laws Affecting Operations ..................................................... 14

Early History .............................................................................................................................................................. 14

Truckee River General Electric Decree ..................................................................................................................... 14

Truckee River Agreement .......................................................................................................................................... 14

Construction of Additional Storage Reservoirs in the 1930’s ................................................................................... 15

Donner Lake Agreement ............................................................................................................................................ 15

Orr Ditch Decree........................................................................................................................................................ 16

Sierra Valley Decree .................................................................................................................................................. 16

Construction of Prosser Creek and Stampede Dams.................................................................................................. 16

Tahoe–Prosser Exchange Agreement ........................................................................................................................ 16

Endangered Species Act............................................................................................................................................. 16

Stampede Reservoir Judgement ................................................................................................................................. 17

Newlands Project Operating Criteria and Procedures................................................................................................ 17

Preliminary Settlement Agreement ............................................................................................................................ 17

Public Law 101-618 ................................................................................................................................................... 17

Interim Storage Agreement ........................................................................................................................................ 18

Truckee River Water Quality Settlement Agreement ................................................................................................ 18

Construction of Truckee River Basin Operations Model ...................................................................................................... 19

Description of Hydrological Simulation Program–FORTRAN................................................................................. 20

Flow-Routing Model.................................................................................................................................................. 22

Data for Simulation of Streamflow and Operations................................................................................................... 23

Streamflow...................................................................................................................................................... 24

Evapotranspiration.......................................................................................................................................... 26

Climate............................................................................................................................................................ 26

Municipal and Industrial Demands................................................................................................................. 27

Lake Level and Streamflow Forecasts............................................................................................................ 27

Description and Simulation of Truckee River Basin Operations .......................................................................................... 27

Description and Simulation of Current Operations ................................................................................................... 32

Current Water Categories ............................................................................................................................... 32

Current Reservoir Operations......................................................................................................................... 32

Flood-Control Criteria......................................................................................................................... 32

Lake Tahoe .............................................................................................................................. 33

Donner Lake ............................................................................................................................ 34

Martis Creek Lake .................................................................................................................. 34

Prosser Creek Reservoir .......................................................................................................... 35

Independence Lake.................................................................................................................. 35

Stampede and Boca Reservoirs ............................................................................................... 36

Lahontan Reservoir.................................................................................................................. 36

Reservoir Storage Priorities and Pass-Throughs ................................................................................. 37

Storage Priorities ..................................................................................................................... 37

Reservoir Pass-Throughs and Releases to Meet Newlands Project Demands......................... 39

Reservoir Demands ............................................................................................................................. 41
IV RIVER AND OPERATIONS MODEL, TRUCKEE RIVER BASIN, CALIFORNIA AND NEVADA, 1998

Floriston Rates......................................................................................................................... 41

Minimum Instream Flows ....................................................................................................... 44

Pyramid Lake Fish................................................................................................................... 45

Privately Owned Stored Water................................................................................................ 48

Current Operational Exchanges .......................................................................................................... 50

Tahoe–Prosser Exchange......................................................................................................... 50

Donner–Boca Exchange .......................................................................................................... 51

Boca–Stampede Exchanges..................................................................................................... 52

Merge Reservoir Releases for Multiple Objectives ............................................................................ 53

Current River Operations................................................................................................................................ 54

Sierra Valley Diversion....................................................................................................................... 55

Truckee Meadows Diversions............................................................................................................. 57

Lower Truckee River Diversions........................................................................................................ 58

Truckee River Diversions to Newlands Project.................................................................................. 61

Losses and Gains to Reaches.......................................................................................................................... 66

Description and Simulation of Operations Under Draft Truckee River Operating Agreement and

Water Quality Settlement Agreement .................................................................................................................. 67

Proposed Water Categories ............................................................................................................................ 69

Proposed Reservoir Operations ...................................................................................................................... 70

Storage of Proposed Water Categories ............................................................................................... 70

California Municipal and Industrial Credit Water................................................................... 70

Power Company Municipal and Industrial Credit Water, Fish Credit Water, 

Water-Quality Credit Water, and Joint Program Fish Credit Water.................................. 72

Reservoir Releases to Meet Downstream Demands ........................................................................... 80

Floriston Rates......................................................................................................................... 80

Power Company Municipal and Industrial Credit Water ........................................................ 82

Fish Credit Water..................................................................................................................... 83

California Municipal and Industrial Credit Water................................................................... 84

Diversion of Water in Lake Tahoe and Donner and Independence Lakes

for Municipal and Industrial Use in California.................................................................. 85

Water-Quality Targets and Related Instream Flow Transfers................................................. 85

Mandatory Exchanges and Transfers.................................................................................................. 88

Enhanced Minimum Instream Flows....................................................................................... 88

Other Exchanges and Transfers............................................................................................... 93

Voluntary Exchanges .......................................................................................................................... 96

Preferred Instream Flows......................................................................................................... 97

Enhanced Storage Security and Access................................................................................... 101

Exchanges from Lake Tahoe or Prosser Creek Reservoir to Boca Reservoir.............. 102

Exchanges from Boca Reservoir to Stampede Reservoir ............................................ 102

Efficient Use of Releases for Precautionary Drawdowns....................................................... 104

Maintenance of Recreational Pools ......................................................................................... 105

Merge Reservoir Releases for Multiple Objectives ............................................................................ 108

Losses and Gains to Reaches.......................................................................................................................... 109

Forecasts Affecting Operational Decisions .................................................................................................... 112

Normal and Dry Season ...................................................................................................................... 112

Drought Situations .............................................................................................................................. 113

Runoff Index ....................................................................................................................................... 120

Comparison of Simulated and Observed Operations............................................................................................................. 120

Model Limitations, Assumptions, and Suggested Improvements ......................................................................................... 125

Summary................................................................................................................................................................................ 127

References Cited.................................................................................................................................................................... 133

Glossary ................................................................................................................................................................................. 134
CONTENTS V

PLATE

Map showing hydrologic features, model lake/reservoir and river/canal reaches, and selected data-collection sites of 

Truckee River, Truckee Canal, and Lahontan Reservoir, California and Nevada

FIGURES

1. Map showing location of study area, California and Nevada............................................................................................ 3

2. Map showing hydrologic features, river reaches, and hydrologic subunits of the Truckee River Basin .......................... 9

3. Schematic diagram showing the river and reservoir reaches, outflows, and inflows for the 

U.S. Geological Survey Truckee River Basin operations model........................................................................... 25

4. Generalized flowchart of U.S. Geological Survey Truckee River Basin operations model.............................................. 29

5. Determination of normal or dry seasons for Lake Tahoe, February–June ........................................................................ 113

6. Determination of normal or dry seasons for Donner Lake, Prosser Creek Reservoir, Independence Lake, 

Stampede Reservoir, and Boca Reservoir, February–June .................................................................................... 116

7. Observed and simulated monthly mean streamflows for the period October 1, 1988, through 

September 30, 1997, for Truckee River at Farad, Calif. (station 10346000) ......................................................... 122

8. Observed and simulated monthly mean streamflows for the period October 1, 1988, through 

September 30, 1997, for Truckee River at Vista, Nev. (station 10350000) .......................................................... 123

9. Observed and simulated monthly mean streamflows for the period October 1, 1988, through 

September 30, 1997, for Truckee River at Nixon, Nev. (station 10351700) ........................................................ 124

TABLES

1. Selected characteristics of major reservoirs...................................................................................................................... 8

2. Floriston rates as related to Lake Tahoe water-surface elevation and month................................................................... 15

3. June through December end-of-month storage objectives for Lahontan Reservoir from 1988 and Adjusted 

Operating Criteria and Procedures ........................................................................................................................ 18

4. Fish flow targets to optimize spawning success by regulation of flows at Truckee River near Nixon, Nevada.............. 47

5. Tagged and untagged releases from reservoirs for current operations ............................................................................. 55

6. Rank order of water categories assigned to untagged releases, by reservoir under current operations ........................... 56

7. Independence Lake enhanced minimum flow targets....................................................................................................... 90

8. Assumed preferred instream flow targets downstream of reservoirs................................................................................ 99

9. Rank order of water categories assigned to untagged releases under Truckee River Operating Agreement 

and Water Quality Settlement Agreement ............................................................................................................. 110
VI RIVER AND OPERATIONS MODEL, TRUCKEE RIVER BASIN, CALIFORNIA AND NEVADA, 1998

CONVERSION FACTORS, VERTICAL DATUM, AND ACRONYMS

Multiply By To obtain

cubic foot per second (ft3/s) 0.02832 cubic meter per second

cubic feet per second per day (ft3/s/d) 0.02832 cubic meter per second per day

acre 4,047 square meter

acre-foot (acre-ft) 1,233 cubic meter

acre-foot per year (acre-ft/yr) 1,233 cubic meter per year

foot (ft) 0.3048 meter

inch (in.) 25.4 millimeter

inches per year (in/yr) 25.4 millimeter per year

mile (mi) 1.609 kilometer

square mile (mi2) 2.590 square kilometer

Temperature: Degrees Celsius (°C) can be converted to degrees Fahrenheit (°F) by using the formula °F = [1.8 (°C)] + 32. Degrees 

Fahrenheit can be converted to degrees Celsius by using the formula °C = 0.556 (°F − 32).

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929, formerly called “Sea-Level 

Datum of 1929”), which is derived from a general adjustment of the first-order leveling networks of the United States and Canada.

ACRONYMS:

BOR: Bureau of Reclamation

CDWR: California Department of Water Resources

CMICW: California M&I credit water

EIS/EIR: environmental impact statement/environmental impact report

EPA: Environmental Protection Agency

ESA: Endangered Species Act

ESP: Extended Streamflow Prediction

ET: Evapotranspiration

FCW: Fish Credit Water

F-TABLE: Function table within Hydrological Simulation Program–FORTRAN

FWM: U.S. District Court Water Master (commonly referred to as the Federal Water Master)

GENSCN: Generation and Analysis of Model Simulation Scenarios

HSPF: Hydrological Simulation Program–FORTRAN

JPFCW: Joint Program Fish credit water

M&I: Municipal and industrial

MAD: Maximum allowable diversion

NDEP: Nevada Division of Environmental Protection

NRCS: Natural Resources Conservation Service

NWS: National Weather Service

OCAP: Operating Criteria and Procedures

PCEDS: Power Company emergency drought supply

PCMICW: Power Company M&I credit water

PCPOSW: Power Company privately owned stored water

P.L.: Public Law

PRMS: Precipitation–Runoff Modeling System

POSW: Privately owned stored water

PSA: Preliminary Settlement Agreement

RCHRES: Reach-reservoir block within Hydrological Simulation Program–FORTRAN

SPECL: Special actions block within Hydrological Simulation Program–FORTRAN

SPPC: Sierra Pacific Power Company

TCID: Truckee–Carson Irrigation District

TCIDPOSW: Truckee–Carson Irrigation District privately-owned stored water

TMUGL: Truckee Meadows ungaged gains and losses
CONVERSION FACTORS, VERTICAL DATUM, AND ACRONYMS VII

TMWRF: Truckee Meadows Water Reclamation Facility

TPEW: Tahoe–Prosser Exchange water

TROA: Truckee River Operating Agreement

UCI: User’s control input for Hydrological Simulation Program–FORTRAN

USCOE: U.S. Army Corps of Engineers

USFWS: U.S. Fish and Wildlife Service

USGS: U.S. Geological Survey

WCWCD: Washoe County Water Conservation District

WDM: Watershed Data Management

WQCW: Water-quality credit water

WQSA: Water Quality Settlement Agreement

NOTICE

The customized software application and supporting materials (data and documentation) presented herein are 

made available by the U.S. Geological Survey (USGS) to be used in the public interest and for the advancement 

of science. The authors, USGS, or the United States Government assume no liability for the contents or the use 

thereof. This documentation does not constitute a standard, specification, or regulation. 
VIII RIVER AND OPERATIONS MODEL, TRUCKEE RIVER BASIN, CALIFORNIA AND NEVADA, 1998
ABSTRACT 1

ABSTRACT

The demand for all uses of water in the 

Truckee River Basin, California and Nevada, 

commonly is greater than can be supplied. Storage 

reservoirs in the system have a maximum effective 

total capacity equivalent to less than two years of 

average river flows, so longer-term droughts can 

result in substantial water-supply shortages for 

irrigation and municipal users and may stress 

fish and wildlife ecosystems. Title II of Public 

Law (P.L.) 101-618, the Truckee–Carson–Pyramid Lake Water Rights Settlement Act of 1990, 

provides a foundation for negotiating and developing operating criteria, known as the Truckee River 

Operating Agreement (TROA), to balance interstate and interbasin allocation of water rights 

among the many interests competing for water 

from the Truckee River. In addition to TROA, 

the Truckee River Water Quality Settlement 

Agreement (WQSA), signed in 1996, provides 

for acquisition of water rights to resolve waterquality problems during low flows along the 

Truckee River in Nevada. Efficient execution of 

many of the planning, management, or environmental assessment requirements of TROA and 

WQSA will require detailed water-resources data 

coupled with sound analytical tools. Analytical 

modeling tools constructed and evaluated with 

such data could help assess effects of alternative 

operational scenarios related to reservoir and river 

operations, water-rights transfers, and changes 

in irrigation practices. 

The Truckee–Carson Program of the U.S. 

Geological Survey, to support U.S. Department of 

the Interior implementation of P.L. 101-618, is 

developing a modeling system to support efficient 

water-resources planning, management, and 

allocation. The daily operations model documented herein is a part of the modeling system 

that includes a database management program, a 

graphical user interface program, and a program 

with modules that simulate river/reservoir operations and a variety of hydrologic processes. The 

operations module is capable of simulating lake/ 

reservoir and river operations including diversion 

of Truckee River water to the Truckee Canal for 

transport to the Carson River Basin. In addition to 

the operations and streamflow-routing modules, 

the modeling system is structured to allow integration of other modules, such as water-quality and 

precipitation-runoff modules. 

The USGS Truckee River Basin operations 

model was designed to provide simulations that 

allow comparison of the effects of alternative management practices or allocations on streamflow or 

reservoir storages in the Truckee River Basin over 

long periods of time. Because the model was not 

intended to reproduce historical streamflow or 

reservoir storage values, a traditional calibration 

that includes statistical comparisons of observed 

and simulated values would be problematic with 

this model and database.

This report describes a chronology and 

background of decrees, agreements, and laws that 

affect Truckee River operational practices; the 

construction of the Truckee River daily operations 

model; the simulation of Truckee River Basin 

operations, both current and proposed under the 

draft TROA and WQSA; and suggested model 

improvements and limitations. The daily operations model uses Hydrological Simulation Program–FORTRAN (HSPF) to simulate flowrouting and reservoir and river operations. The 

operations model simulates reservoir and river 

operations that govern streamflow in the Truckee 

River and Reservoir Operations Model, 

Truckee River Basin, California and Nevada, 1998

By Steven N. Berris, Glen W. Hess, and Larry R. Bohman
2 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

River from Lake Tahoe to Pyramid Lake, including diversions through the Truckee Canal to 

Lahontan Reservoir in the Carson River Basin. A 

general overview is provided of daily operations 

and their simulation. Supplemental information 

that documents the extremely complex operating 

rules simulated by the model is available. 

INTRODUCTION

The Truckee River has had a long history of 

providing water to a variety of economic and environmental users. Truckee River water is used for power 

generation upstream from Reno, municipal and 

industrial (M&I; bold non-italicized words are defined 

in the glossary) supply for the Lake Tahoe vicinity, 

town of Truckee, and the Reno–Sparks vicinity (hereafter referred to as the Truckee Meadows), and irrigation in both the Truckee and Carson River Basins. The 

Truckee River discharges into Pyramid Lake (fig. 1), 

and thus sustains lake levels and provides flows for 

spawning of the endangered cui-ui lakesucker and the 

threatened Lahontan cutthroat trout. The diversity of 

user interests, each with a demand on the limited water 

resource, has resulted in long-standing and intense 

conflicts among various economic, political, ecological, and institutional entities. The diversity in interests 

also provides a wide range of alternatives for planning, 

allocating, and managing the water resources and operating the various reservoir and diversion facilities. 

The demand for all uses of water in the Truckee 

River Basin, California and Nevada, commonly is 

greater than can be supplied. Storage reservoirs in the 

system have a maximum effective total capacity equivalent to less than two years of average river flows. 

Droughts lasting several years, such as the recent 

drought of the late 1980’s and early 1990’s, can cause 

substantial water shortages for irrigation and municipal 

users and may stress fish and wildlife ecosystems. 

Title II of Public Law (P.L.) 101-618, the Truckee–Carson–Pyramid Lake Water Rights Settlement 

Act of 1990 (104 Statute 3289), provides direction, 

authority, and mechanisms for resolving conflicts over 

water and water rights in the Truckee and Carson River 

Basins. A major element of P.L. 101-618, known as 

the Truckee River Operating Agreement (TROA), 

provides a foundation for improving water management and for negotiating and developing operating criteria to balance interstate and interbasin allocation of 

water rights among the many competing interests 

for Truckee River water. In addition to TROA, the 

Truckee River Water Quality Settlement Agreement 

(WQSA), signed in 1996, provides for acquisition of 

water rights to aid in resolving water-quality problems 

in the Truckee River in Nevada during low-flow periods while simultaneously providing additional water 

for fish and wildlife resources. Efficient execution of 

many of the planning, management, or environmental 

assessment requirements of TROA and WQSA will 

require detailed water-resources data. Analytical modeling tools constructed and evaluated with such data 

could help assess effects of alternative management 

and operational scenarios related to Truckee River 

operations, including water-rights transfers, changes in 

irrigation practices, and changes in demand patterns.

Daily, physically based models capable of simulating alternative management policies for river and 

reservoir operations are needed to assess alternatives 

for water management. The interdependence of many 

of the water-management issues of the Truckee River 

Basin, such as allocation of streamflow and achieving 

instream water-quality standards, suggests a strong 

need for an overall data-management and modeling 

system within which individual issues can be addressed 

in an efficient and coordinated manner. In addition, 

there is a need for a model that can provide the riverhydraulics and daily-flow data to other quantitative 

tools, such as water-quality models. Such a model 

needs to be interbasin in scope, addressing the interrelated management issues of the Truckee River, 

the Carson River, and the Truckee Canal, which facilitates the diversion of water from the Truckee River to 

Lahontan Reservoir in the Carson River Basin. The 

model needs to be fully documented and in the public 

domain, so that all stakeholders are confident in the 

system and they can all work from a common base or 

point of reference.

The dynamic nature of certain operations and 

management issues along the Truckee River requires a 

model computation interval that is daily, rather than 

monthly. Water-quality problems cannot be examined 

satisfactorily on a monthly time step. Temperature, 

dissolved oxygen, and other water-quality parameters 

often require daily or even hourly temporal resolution. 

In order to reflect actual river and reservoir operations, 

models should be capable of simulating brief hydrologic “pulses” in the system. Such short-term opportunities resulting from storm runoff lasting one week or 

less may allow for storage or exchange of credit 
INTRODUCTION 3

Dry lake Dry lake

Dry lake

Dry lake

Dry lake

Dry lake Dry lake

Dry lake

Dry lake Dry lake Dry lake

Marsh Marsh

Marsh

Marsh

Marsh Marsh

40 ̊ 

39 ̊ 

120 ̊ 119 ̊ 118 ̊ 

0

0 10 20 30 40 KILOMETERS

10 20 30 40 MILES

EXPLANATION

Hydrographic basin boundary

Base from U.S. Geological Survey digital data, 1:100,000

UniversalTransverse Mercator projection

Zone 11

Sparks

Yerington

Reno

Truckee

CARSON CITY

Wadsworth

Nixon

Hazen

Fallon

Stillwater

Wildlife

Management

Area

Fernley

Wildlife

Management

Area

Stillwater

National

Wildlife

Refuge

Fallon

Indian

Reservation

Pyramid Lake

Indian

Reservation

Fallon

National

Wildlife

Refuge

Carson

Sink

Carson

Lake

Winnemucca

Lake

Lahontan

Reservoir

Carson

River

River Truckee

East Fork

Carson River

Lake

Tahoe

West Fork

Carson River

Pyramid

Lake

CALIFORNIA

NEVADA

NEVADA

CALIFORNIA

ALPINE

CO

MONO

CO TUOLUMNE

CO

CALAVERAS

CO

AMADOR

CO

EL DORADO

CO

PLACER

CO

NEVADA

CO

SIERRA

CO

PLUMAS

CO

WASHOE

CO

PERSHING

CO

CHURCHILL

CO

STOREY

CO

MINERAL

CO

NYE

CO

LYON

CO

DOUGLAS

CO

LASSEN

CO

Sparks

Yerington

Reno

Sutcliffe

Tracy

Truckee

Floriston

Carson

City

CARSON CITY

Wadsworth

Nixon

Lovelock

Hazen

Fernley

Fallon

Stillwater

Wildlife

Management

Area

Fernley

Wildlife

Management

Area

Anaho Island National

Wildlife Refuge

Stillwater

National

Wildlife

Refuge

Fallon

Indian

Reservation

Pyramid Lake

Indian

Reservation

Fallon

National

Wildlife

Refuge

Carson

Sink

Carson

Lake

Winnemucca

Lake

Lahontan

Reservoir

Truckee

Canal

Carson

River

River Truckee

East Fork

Carson River

Lake

Tahoe

West Fork

Carson River

Pyramid

Lake

CALIFORNIA

NEVADA

NEVADA

CALIFORNIA

ALPINE

CO

MONO

CO TUOLUMNE

CO

CALAVERAS

CO

AMADOR

CO

EL DORADO

CO

PLACER

CO

NEVADA

CO

SIERRA

CO

PLUMAS

CO

WASHOE

CO

PERSHING

CO

CHURCHILL

CO

STOREY

CO

MINERAL

CO

NYE

CO

LYON

CO

DOUGLAS

CO

LASSEN

CO

Spanish

Springs

Valley

Truckee

Meadows

Spanish

Springs

Valley

Truckee

Dayton

Valley

Eagle

 Valley

Churchill

Valley

Carson Valley

Pah Rah Range

Marble Bluff

Dam

Derby

Diversion

Dam

Marble Bluff

SIERRA

NEVADA

Anaho Island National

Wildlife Refuge

Area of inset

CARSON DIVISION,

NEWLANDS PROJECT

IRRIGATED AREAS

TRUCKEE DIVISION,

NEWLANDS PROJECT

IRRIGATED AREAS

Washoe

Lake

Stea mboat Creek

Lahonton

Valley

NEVADA

CALIFORNIA

TRUCKEE 

RIVER

BASIN CARSON

RIVER

BASIN

LOCATION OF TRUCKEE AND

CARSON RIVER BASINS

Little

Truckee

River

Independence

Creek

Independence

Lake Boca

Reservoir Sagehen

Creek

Donner Creek

Martis Creek

Martis

Creek

Lake

Donner

Lake

Prosser Creek

Reservoir

Stampede

Little

Reservoir Truckee

Truckee

River

River

Independence

Creek

Independence

Lake Boca

Reservoir Sagehen

Prosser

Creek

Creek

Donner Creek

Martis Creek

Martis

Creek

Lake

Donner

Lake

Prosser Creek

Reservoir

Stampede

Reservoir

Truckee

Figure 1. Location of study area, California and Nevada
4 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

water1 under the flexible and efficient policies proposed in the draft operating agreement being negotiated under Public Law 101-618. Such transactions may 

not be simulated in models where the flows are averaged out over an entire month and vice versa. Another 

source of potential differences in modeling results 

between monthly and daily models is the simulation of 

flood-control criteria at reservoirs, which are used to 

reduce the chances of downstream flooding. These 

criteria, by definition, establish daily constraints on 

reservoir storage levels. A sudden storm resulting in 

storages above an established rule curve would result 

in the subsequent release of that extra water on a daily 

basis, whereas a monthly model may allow that extra 

water to be stored. Similarly, credit storage cannot take 

place if daily flood-control criteria dictate that no 

reduction in a planned release can be made. There are 

many other examples, but the point is that, depending 

on the purpose and goals of the model user, the computation interval may be an important factor in selecting 

the most appropriate model.

The Truckee–Carson Program of the U.S. Geological Survey (USGS) was established by the Department of the Interior to support implementation of 

Public Law 101-618 by (1) compiling records from 

multiagency gaging stations into a consistent longterm data base to provide reliable data in support of 

modeling activities in the Truckee River and Carson 

River Basins, (2) establishing new streamflow and 

water-quality gaging stations for more complete waterresources information and more consistent support of 

river operations, and (3) developing a modeling system 

to support efficient water-resources planning, management, and allocation. Modeling activities within the 

USGS Truckee–Carson Program include the following.

• Flow-routing models of all or selected parts of the 

Truckee River and Carson Rivers, major tributaries, lakes/reservoirs, and the Truckee Canal.

• Precipitation-runoff models for the headwater 

source areas of both basins.

• Stream temperature and total dissolved-solids 

models of the Truckee River.

• Operation models that simulate lake/reservoir and 

river operations, including the Truckee Canal, for 

both basins.

Purpose and Scope

The purpose of this report is to describe (1) the 

chronology and background of legal decrees and agreements that affect Truckee River operational practices; 

(2) the construction of the Truckee River Basin daily 

operations model, including the flow-routing model 

and data required to simulate operations; (3) the simulation of Truckee River Basin operations, both current 

(19982

) and proposed as of February 1998 under the 

draft TROA and WQSA; (4) a comparison of simulated 

and observed operations; and (5) limitations and suggested improvements of the model.

The daily operations model simulates flow and 

operations for three options: (1) current (1998) operational practices, (2) current operations and those proposed in draft TROA and WQSA, and (3) WQSA 

without draft TROA, which is not described separately 

in this report. TROA operations, as considered in this 

model documentation, reflect operational rules and 

policies presented in the February 1998 draft TROA, 

evaluated in the Draft Environmental Impact Statement/Environmental Impact Report by the Bureau of 

Reclamation and others (1998), and will be referred to 

hereafter as draft TROA. The geographic extent of the 

model is the Truckee River Basin from Lake Tahoe to 

Pyramid Lake, the Truckee Canal, and Lahontan Reservoir in the Carson River Basin (fig. 1). The operations model simulates both reservoir operations—for 

Tahoe, Donner, Martis Creek, and Independence 

Lakes, and Prosser, Stampede, and Boca Reservoirs in 

the Truckee River Basin and for Lahontan Reservoir in 

the Carson River Basin—and river operations including diversion of water from the Truckee River for irrigation and municipal and industrial uses, as well as 

diversion at Derby Diversion Dam of Truckee River 

water to the Newlands Project via the Truckee Canal. 

1

Under provisions proposed in the February 1998 draft 

TROA, credit water would be created, in part, when water 

of specific ownership is stored by reducing releases from a given 

reservoir. It can also be created by storing privately owned water 

and then transferring that water to credit water. Once created, 

credit water stored in individual Truckee River reservoirs would 

be allowed to be exchanged with storage in other Truckee River 

reservoirs and used as prescribed in the draft operating agreement 

(see exchange and transfer in the Glossary). 2

As used in this report, “current” refers to 1998.
INTRODUCTION 5

This report documents the first Truckee River 

operations model to simulate current and proposed 

(draft TROA) operations using a daily computation 

interval. Certain operational procedures, either historically practiced or proposed, are not included in the 

river/reservoir operational logic for simulation, nor are 

they described in this report. The historically practiced 

operations not included in the model are not typical of 

normal daily operations and were often single-incident 

variances based on human decisions, special permits, 

or court decisions. Proposed operational procedures 

not included were being negotiated and were, therefore, 

uncertain. The river/reservoir operational logic presented for purposes of simulation is based on the 

authors’ best understanding of current regulations, 

decrees, and agreements. The authors’ interpretation 

should not be considered a substitute for definition by 

more appropriate administrative or legal authorities.

The rules governing operations for the Truckee 

River are complex and unique. A general overview of 

Truckee River daily operations is provided in this 

report. Supplemental documentation to this report consists of detailed flowcharts and model code, which contains extensive internal documentation. The flowcharts 

provide a diagrammatic representation of the logical 

sequence of the code. The model code contains the 

most detailed information on the logic used to simulate 

river/reservoir operations. A listing of variable names 

used in the operations model code and their definitions 

also is available to assist users of either the flowchart or 

model code in the understanding and use of the model.3

The USGS Truckee River Basin operations 

model was designed to provide simulations that allow 

comparison of the effects of alternative management 

practices or allocations on streamflow or reservoir storages in the Truckee River Basin over long periods of 

time. Because the model was not intended to reproduce 

historical values, a traditional calibration with statistical comparisons of observed and simulated values is 

not particularly insightful for this model and database. 

This model is complex, contains extensive detail, and 

has a daily computation interval. Depending on the 

length of the desired period of simulation and computer 

hardware capabilities unique to each user, run times 

may require from several minutes up to several hours. 

Although some simple changes to certain variables 

(dates, target flows or storages, and so forth) could be 

implemented by almost anyone, it would require 

months of training to become familiar enough with the 

programs in the modeling system to be able to implement major changes in the model code. As such, this 

first version of the model was not designed for use in 

making quick simulations of near-term operations that 

might aid day-to-day water-resource management 

decisions. Significant modifications would be required 

to transform the model for that purpose. To accommodate a quick response to new simulation criteria, a 

Truckee River operations model would have to compromise detail for simplicity.

Previous Investigations

Horton (1997a) compiled a pre-20th-century and 

20th-century chronological history of the Truckee 

River. Significant events were discussed back to the 

time before European and United States colonization. 

Many investigators have designed and constructed models to simulate the physical and operational characteristics of the Truckee River. The Desert 

Research Institute at University of Nevada, Reno, 

developed a model that simulated Truckee River flow 

using historical and reconstructed monthly streamflow 

data (Butcher and others, 1969). The Truckee River 

was divided into regulated upstream reaches; a reach 

through the Truckee Meadows; a reach from Vista, 

Nev., to Nixon, Nev. (including the Truckee Canal); 

and a reach representing Pyramid Lake. The model 

incorporated a monthly mass balance that transmitted 

flows and accounted for gains and losses through each 

reach. Fordham and Butcher (1970) and Fordham 

(1972) combined a flow model with an optimization 

routine to maximize the beneficial use of surface water. 

This model was expanded to include both the Truckee 

and Carson River Basins. Chiatovich and Fordham 

(1979) combined a water-quality model developed by 

Westphal and others (1974) with a model of monthly 

reservoir operations to simulate an optimum operating 

policy. This combined model represents the water 

stored in all reservoirs in the upper Truckee River 

Basin, other than Lake Tahoe, as one combined reservoir, and it was developed to maximize the beneficial 

3The flowchart, code, and variable listings are not included 

in this report because of their length and technical complexity. 

Interested readers can contact the USGS Nevada 

District Public Information Assistant at (775) 887-7649 to obtain 

information on how to procure electronic copies of the variable 

listing, model code, or flowcharts.
6 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

use of surface water by considering both downstream 

water rights and diversion policies as well as concentrations of constituents affecting water quality.

The Bureau of Reclamation (BOR) constructed a 

monthly mass-balance model to analyze both operation 

of reservoirs and allocation of water within the Truckee 

and Carson River Basins. The original BOR model was 

later modified by consultants for Sierra Pacific Power 

Company (SPPC) (Sierra Pacific Power Company, 

purveyor of water to municipal and industrial users in 

the Truckee Meadows) to include water-management 

alternatives discussed in the Preliminary Settlement 

Agreement (PSA) as modified by the Ratification 

Agreement (Pyramid Lake Paiute Tribe of Indians and 

SPPC, 1989). This agreement, between SPPC and the 

Pyramid Lake Paiute Tribe, provides for water storage 

for the Truckee Meadows during drought and for 

augmentation and modification of flow in the lower 

Truckee River during nondrought periods to improve 

spawning conditions for endangered and threatened 

fish species. The modified BOR model, referred to as 

the Negotiations Model, is not intended to simulate 

historical streamflow, but to make relative comparisons of the effects of alternative management practices 

on flows and allocations. The Negotiations Model is 

currently being used to examine the effects of operation 

and allocation changes addressed in P.L. 101-618 as 

well as other water management alternatives.

Cobb and others (1990) reviewed the BOR model 

and the Negotiations Model, both of which lacked 

formal documentation. The two models focused on 

the Truckee River system, and to a lesser degree, the 

Truckee Canal and the Carson River from Churchill 

Valley to Lahontan Valley. Both models are monthly 

mass-balance accounting-type models, as opposed to 

physically based flow-routing models. Both models 

use synthesized monthly average streamflow at various 

points in the Truckee–Carson River system. The data 

bases are composites of historical records and, when no 

historical records existed, estimated records. Both 

models (1) use streamflow and runoff data as input, 

(2) impose a complex set of legal constraints, operating 

criteria, and assumptions for effects of development 

on water use and surface-water/ground-water relations, 

and (3) incorporate an accounting procedure to simulate monthly average streamflow at several locations in 

the system. 

Yardas (1996) developed a model of the Carson 

River below Lahontan Reservoir to simulate streamflow and distribution of irrigation water in the Newlands Project. The Yardas model can be used as a tool 

to better understand the effects of water acquisitions 

and other variables on inter- and intra-basin water 

demands and supplies.

In 1992, the USGS began to develop analytical 

modeling tools to help evaluate management options 

in support of the U.S. Department of the Interior 

implementation of P.L. 101-618. Berris (1996) developed a physically based flow-routing model of the 

Truckee River. The model routed daily mean streamflow along 114 miles (mi) of the mainstem Truckee 

River from just downstream from Lake Tahoe, Calif., 

to just upstream from Pyramid Lake, Nev. Hess (1996) 

developed a similar flow-routing model for the Carson 

River from the gaging station at East Fork Carson 

River near Markleeville, Calif., (italicized words are 

formal names for data-collection sites) and the gaging 

station at West Fork Carson River at Woodfords, Calif., 

to the gaging station Carson River at Fort Churchill, 

Nev., just upstream from Lahontan Reservoir. Selected 

reservoir and river operations added to the Truckee and 

Carson River flow-routing models are described by 

Berris and others (1996) and Hess (1997), respectively. 

Acknowledgments

The authors gratefully acknowledge the support 

of many people and agencies who provided data or 

information used in this report. William D. Bettenberg 

and Jeffrey P. Zippin of U.S. Department of the Interior 

and Steven R. Alcorn, Minerals Management Service/Truckee-Carson Coordination Office provided the 

information, advice, and support necessary to construct 

and document the Truckee River Basin daily operations model. Thomas R. Scott, Al Olson, Bill Greer, 

and David Overvold of BOR, Roderick Hall of Sierra 

Hydrotech Consultants, Richard Moser of Sierra 

Pacific Power Company, John Sarna of California 

Division of Water Resources, Thomas Strekal of 

Bureau of Indian Affairs/Truckee-Carson Coordination 

Office, Chester Buchanan of the U.S. Fish and Wildlife 

Service, and several people in the office of the U.S. 

District Court Water Master, also called the Federal 

Water Master (FWM), notably Garry D. Stone, Jeff 

Boyer, Chad Blanchard, and Matthew Setty, provided 

insight into the complexities and operation of the 

Truckee River Basin through extensive interviews 

and written documentation.
DESCRIPTION OF STUDY AREA 7

DESCRIPTION OF STUDY AREA

This section describes the Truckee River, Carson 

River, and Truckee Canal as an overview that precedes 

a more detailed discussion on the Truckee River Basin. 

Truckee River operations include diversion of water 

at Derby Diversion Dam into the Truckee Canal, a 

transbasin canal that delivers water to benchlands in 

the Truckee division of the Newlands Project and to 

Lahontan Reservoir in the Carson River Basin for use 

in the Carson Division of the Newlands Project (fig. 1).

The Truckee River originates at the outlet of the 

dam at Lake Tahoe in the Sierra Nevada of California 

and flows eastward into a topographically closed desert 

lake in Nevada (fig. 1). Its headwaters, where altitudes

exceed 10,000 feet (ft) above sea level, flow into Tahoe 

—a mountain lake with a surface area of about 192 

square miles (mi

2

) and an average depth of about 990

ft (Jones and others, 1991a, p. 11). The terminus 

of the Truckee River is at Pyramid Lake—located in 

the Basin and Range Physiographic Province of western Nevada. Pyramid Lake is a sink, about 3,800 ft in 

altitude, where water cannot leave through a surfacewater outlet. Drainage area for the entire Truckee River 

Basin is about 3,120 mi2, but only about 1,430 mi2

contribute to the 114-mi length of the Truckee River 

mainstem between the outlet of Tahoe and Marble 

Bluff Dam, located about 3.5 mi upstream from its 

mouth at Pyramid Lake (fig. 1; Brown and others, 

1986, p. 81 and 125).

The Carson River also has its headwaters in the 

Sierra Nevada in California, just to the south of and 

adjacent to the Truckee River Basin, and flows generally to the northeast into a topographically closed 

desert sink in Nevada (fig. 1). Its headwaters, where 

altitudes also exceed 10,000 ft above sea level, are 

divided into the East and West forks. The East and 

West Forks of the Carson River flow north out of the 

Sierra Nevada to join in the broad Carson Valley in 

Nevada, where the altitude is approximately 4,700 ft. 

The river then flows to the northeast through Carson 

Valley and parts of Eagle, Dayton, and Churchill 

Valleys into Lahontan Reservoir—a manmade reservoir with a capacity of 317,300 acre-feet (acre-ft) with 

flashboards and 295,500 acre-ft without flashboards 

(table 1) (U.S. Geological Survey, 1998, p. 177; 

Thomas R. Scott, Bureau of Reclamation, oral commun., 1997). From that reservoir, the regulated lower 

river continues northeastward through the Newlands 

Project in Lahontan Valley and ultimately terminates in 

the vast Carson Sink (fig. 1), about 3,850 ft in altitude,

where water cannot leave through a surface-water outlet. Drainage area for the entire Carson River Basin is 

about 3,966 mi2

, but only about 1,799 mi2 contribute to 

the 152-mi length of the Carson River between the 

source of the East Fork Carson River (the longest of the 

two major forks of the Carson River) and Lahontan 

Dam, not including drainage area to the Truckee Canal 

outside of the Carson River Basin (Horton, 1997b, 

p. I-1 and U.S. Geological Survey, 1996, p. 184). This 

report describes reservoir operations and the operations 

model for only a small part (Lahontan Reservoir) of the 

Carson River Basin.

Most demands for water in both Truckee and 

Carson River Basins are from the Basin and Range 

Physiographic Province of western Nevada, whereas 

most precipitation that supplies water to these rivers 

falls within the Sierra Nevada of California. Additionally, most of the regulated water storage in the basins 

lies within the Truckee River Basin in the Sierra 

Nevada of California. There is little upstream storage 

in the headwaters of the Carson River Basin. The 

Truckee Canal provides an interbasin transfer of water 

to supplement the Carson River supply and to partially 

meet the large demand for irrigation water within the 

Newlands Project, the first Federal reclamation project 

in the United States. Construction of Derby Diversion 

Dam (hereafter referred to as Derby Dam) and the 

Truckee Canal began in 1903, and the project was 

operational in 1915 with the completion of Lahontan 

Dam in the Carson River Basin. Derby Dam, about 

25 mi downstream from Reno, diverts water from the 

Truckee River to the Truckee Canal for delivery to the 

Newlands Project. The 32-mi manmade Truckee Canal 

has a maximum capacity of about 1,100 cubic feet per 

second (ft3/s) and a normal operating capacity of about 

900 ft3

/s (Horton, 1997a, p. I-25 and I-48). Some of the 

diverted water carried by the canal provides water for 

current irrigation of about 3,500 acres of farmland 

within the Truckee Division of the Newlands Project 

near Fernley, Nev. The remainder of the water diverted 

to the canal is stored in Lahontan Reservoir for irrigation of about 56,500 acres in the Carson Division of the 

Newlands Project in the Carson River Basin near Fallon, Nev. (Alan Olson, Bureau of Reclamation, written 

commun., 1999). 

For discussion in this report, the Truckee River 

Basin—from Lake Tahoe to Pyramid Lake—is divided 

into three hydrologic subunits—Lake Tahoe and the 

upper Truckee River, the middle Truckee River, and 
8 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

the lower Truckee River including Pyramid Lake—on 

the basis of similarity in climate and streamflow characteristics, physiography, human activities, and water 

quality (fig. 2). The boundaries of these subunits generally conform to published hydrographic boundaries 

for consistency with previous work (Berris, 1996, and 

Brown and others, 1986).

Lake Tahoe and Upper Truckee River Subunit

The Lake Tahoe and upper Truckee River subunit 

consists of the 932-mi2 drainage area of the Truckee 

River upstream from the USGS gaging station Truckee 

River at Farad, Calif. (hereafter referred to as Farad 

gaging station), located near the California–Nevada 

State line (fig. 2 and pl. 1). This subunit includes the 

drainage area and surface of the lake, and the drainage 

area of the Truckee River between the outlet of the lake 

and the Farad gaging station. It is a combination of subunits previously described in Brown and others (1986) 

and Berris (1996): the 506-mi2

 Lake Tahoe subunit, 

which includes the drainage area and 192-mi2

 surface 

of the lake, and the 426-mi2 upper Truckee River 

subunit, which includes the drainage area of the Truckee River between the outlet of the lake and the Farad 

gaging station. Mean annual runoff at the Farad gaging 

station for water years 1909–97 is 554,500 acre-ft (U.S. 

Geological Survey, 1998, p. 344). The section of the 

Truckee River between the lake and the Farad gaging 

station is 34 mi long.

The mountainous Lake Tahoe and upper Truckee 

River subunit is the coldest and wettest part of the study 

area. The Sierra Nevada, with peaks ranging from 

8,000 to 10,000 ft in altitude in this subunit, is a major 

barrier to moist air from the Pacific Ocean. The average 

annual precipitation for this subunit ranges from about 

30 to 70 inches per year (in/yr,) mostly as snow from 

November through April (Jones and others, 1991a, 

p. 31). This mountain barrier causes a distinct rainshadow to the east. Thus, an average of only about 

12–16 in/yr of precipitation falls in the drier parts of the 

subunit at lower elevations near the Nevada State line 

(Jones and others, 1991a, p. 31). Vegetation ranges 

from dense coniferous forests in the wet areas of the 

subunit to drier, open forests mixed with grasses, sagebrush, and rabbitbrush in the drier areas.

Runoff generated in the Lake Tahoe and upper 

Truckee River subunit supplies most of the water to the 

Truckee River system. Truckee River flows are heavily 

dependent on the yearly snowpack characteristics of 

the Sierra Nevada. High flows in the Truckee River are 

generally produced by snowmelt when temperatures 

increase in the spring or early summer, or in direct 

Table 1. Selected characteristics of major reservoirs

[Abbreviations: SPPC, Sierra Pacific Power Company, TCID, Truckee–Carson Irrigation District; USCOE, U.S. Army Corps of Engineers; 

BOR, U.S. Bureau of Reclamation; WCWCD, Washoe County Water Conservation District]

Reservoir name Dam owner 1

1 From Jones, 1991a, p. 11 except as noted.

Dam operator1 Storage capacity1

(acre-feet)

Dam 

construction 

date1

Drainage area1 

(square miles)

Lake Tahoe SPPC TCID 744,600 1913 506

Donner Lake SPPC/TCID SPPC 9,500 21928

2 From U.S. Geological Survey, 1998, p. 318.

14

Martis Creek Lake USCOE USCOE 320,400

3 From Bureau of Reclamation and others, 1998, hydrology appendix, p. H-2.

1971 40

Prosser Creek Reservoir BOR BOR 629,800 1962 50

Independence Lake SPPC SPPC 6

17,500 1939 8

Stampede Reservoir BOR BOR 6226,500 1970 136

Boca Reservoir BOR WCWCD 40,900 41938

4 From U.S. Geological Survey, 1998, p. 338.

172

Lahontan Reservoir 5BOR

5 From Jones, 1996b, p. 26.

5

TCID 6, 7295,500

6 At spillway crest.

7 From U.S. Geological Survey, 1998, p. 176.

7

1915 7, 81,799

8 Does not include drainage area from Truckee Canal.

7, 917,300

9 With use of flashboards on the spillway crest.
DESCRIPTION OF STUDY AREA 9

40 ̊

39 ̊

120 ̊ 119 ̊

Base from U.S. Geological Survey digital data, 1:100,000, 1979-80

Universal Transverse Mercator projection, Zone 11

0

0 10 20 KILOMETERS

10 20 MILES

Lake

Tahoe

Pyramid

Lake

Washoe

Lake

CALIFORNIA

NEVADA

Truckee Canal

Truckee

River

Sparks

Reno

S I E R R A

N E V A D A

EXPLANATION

Hydrographic basin boundary

Hydrographic subunit boundary

Reach boundaries

U.S. Geological Survey

 gaging station

Lake Tahoe and

upper Truckee River

subunit

Middle

Truckee River

subunit

Lower

Truckee River

and Pyramid

Lake subunit

LakeTahoe and

upper Truckee

River subunit

Truckee River

at Farad, Calif.

10346000

Truckee River

below Tracy, Nev.

10350400

Truckee River

at Vista, Nev.

10350000

Truckee River

near Nixon, Nev.

10351700

Little

Truckee

River

Independence

Creek

Independence

Lake Boca

Reservoir Sagehen

Creek

Donner Creek

Martis Creek

Martis

Creek

Lake

Donner

Lake

Prosser Creek

Reservoir

Stampede

Little

Reservoir Truckee Truckee

River

River

Independence

Creek

Independence

Lake Boca

Reservoir Sagehen

Prosser

Creek

Creek

Donner Creek

Martis Creek

Martis

Creek

Lake

Donner

Lake

Prosser Creek

Reservoir

Stampede

Reservoir

Truckee

Stea mboat Cr eek

Figure 2. Hydrologic features, river reaches, and hydrologic subunits of the Truckee River Basin
10 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

response to warm rains, derived from subtropical air

masses, falling on winter snowpacks. When the relatively warm rains fall on large snowpacks, rain in

addition to large amounts of water from melting snowpacks act together to form large runoff events or even 

floods. In contrast, during late summer and fall after

the snowpack has melted, there is little water entering

the Truckee River and, as a consequence, low flows 

commonly result.

Seven dams are operated upstream from the Farad 

gaging station to minimize flood hazards and to augment the water supply during periods of low flow and 

high demand. A small dam regulates the upper 6.1 ft

of Lake Tahoe, the largest storage facility in the system. The other dams—at Donner, Martis Creek, and 

Independence Lakes—and Prosser, Stampede, and 

Boca Reservoirs were built on four tributary streams. 

Selected characteristics of the major reservoirs in the

Truckee River Basin, in addition to Lahontan Reservoir 

in the Carson River Basin, are summarized in table 1. 

These reservoirs are operated according to complex

legal decrees and agreements that specify conditions 

for the storage and release of water. The regulations

that govern reservoir operations, described later in this 

report and in the supplemental documentation, form an 

integral part of the operations model.

Urban and agricultural development is not extensive in the Lake Tahoe and upper Truckee River subunit and requires a small percentage of the available

surface water. Most of the urban areas are around the

lake and around the town of Truckee. The year-round

permanent population around the lake is estimated at

about 50,000, but tourism increases daily population by 

as much as double the permanent population (Jones and 

others, 1991a, p. 37). Adjacent to the lake in California, 

municipal water use from both ground water and surface water was estimated to be between 15,000 and 

17,000 acre-ft per year in 1992 (John Sarna, California 

Department of Water Resources, written commun., 

1997; Jones and others, 1991a, p. 76). Water diverted 

for use in areas adjacent to the lake in Nevada was estimated at 6,600 acre-ft per year in 1995 (Jim Crompton, 

U.S. Geological Survey, written commun., 1999). Because of concerns about lake clarity and other lake 

water quality issues, municipal effluent is sewered and 

exported from the basin to sites in the Truckee and 

Carson River Basins. Small communities centered 

around and including the town of Truckee, Calif., use

about 5,000–6,000 acre-ft/yr, primarily from ground 

water (Jones and others, 1991a, p. 76). Some small

water systems serve the ski resorts located between 

the town of Truckee and the lake. Use of water for 

snowmaking has been about 1,000 acre-ft/yr, but will

probably increase (Jones and others, 1991a, p. 84). 

Since 1980, effluent from the area around Truckee and 

the ski resorts, along with effluent from the north and 

west sides of the lake, receives tertiary treatment at the

Truckee–Tahoe Sanitation Agency Water Reclamation

Plant near the mouth of Martis Creek and is discharged

into a leach field. From the leach field, the effluent 

percolates to ground water and may indirectly contribute to flows in both Martis Creek and the Truckee River

after an estimated detention period of 3 to 6 months

(Brown and others, 1986). 

Developed agricultural land is negligible in this 

subunit because of the short growing season in the

mountainous terrain. Water diverted from the Little

Truckee River upstream from Stampede Reservoir for

irrigation in California outside of the Truckee River

Basin averaged about 5,900 acre-ft/yr for the period 

1959–97 (Ron Vanscoy, California Department of

Water Resources, oral commun., 1997). Fish and wildlife uses are non-consumptive, but threshold streamflows, called instream flows, have been established to 

provide viable habitat in this and all of the Truckee 

River subunits. In another non-consumptive use, water 

is temporarily diverted from the Truckee River near 

Floriston, Calif., close to the California–Nevada State 

line, transported by a wooden flume to a riverside powerplant, and returned to the river after passing through

penstocks and rotating turbines for power generation.

Middle Truckee River Subunit

The Middle Truckee Riversubunit consists of the

744-mi

2 drainage area to the Truckee River between

the Farad gaging station and Derby Dam (fig. 2 and pl. 

1). The section of the Truckee River contained in this 

subunit is about 46 mi long. Mean annual runoff at the 

USGS gaging station Truckee River below Tracy, Nev. 

(hereafter referred to as Tracy gaging station; fig. 2 and 

pl. 1), about 5 mi upstream from Derby Dam, for water 

years 1972–96 was 580,900 acre-ft (U.S. Geological 

Survey, 1997, p. 399). Many tributary streams and the 

seven major upstream reservoirs provide and regulate 

flow that reaches this subunit, and from this flow, large 

volumes of water are diverted for power generation, 

irrigation, and municipal and industrial water supply. 

This subunit has about 26 diversions, but not all may be 

in operation every day or even every year.
DESCRIPTION OF STUDY AREA 11

Although the middle Truckee River subunit is 

mostly in the drier Basin and Range Physiographic 

Province, the extreme southwestern part of this subunit 

consists of high mountain uplands. The precipitation in 

this subunit ranges from about 30 to 50 in/yr in the 

southwestern uplands to less than 8 in/yr in the Truckee 

Meadows and along the Truckee River corridor downstream (east) from the Truckee Meadows (Jones and 

others, 1991a, p. 31 and Hardman, 1965). The mountainous southwestern part of this subunit receives 

ample snowfall to provide perennial flows to small tributary streams. Flow from these small tributaries, 

directly as surface water or indirectly through irrigation 

systems, joins the Truckee River upstream from the 

USGS gaging station Truckee River at Vista, Nev. 

(hereafter referred to as Vista gaging station; fig. 2

and pl. 1). Downstream from this gaging station, the

drainage consists of arid terrain and all tributary 

streams are ephemeral.

Wooden flumes carry diverted water for power 

generation to three power plants between the Farad 

gaging station and Reno, Nev. Like the diversion for

power generation in the upper Truckee River subunit, 

the water returns to the river after passing through powerplants. Water also is diverted to a thermal powerplant 

for cooling purposes at Tracy, Nev. (fig. 1 and pl. 1), 

between the Vista gaging station and Derby Dam. 

Water not consumed by evaporation at the powerplant 

was, until recently, discharged to holding ponds, where 

it was later re-used or allowed to percolate into the river 

alluvium. Currently, the small amount of water 

diverted for cooling purposes is consumed by evaporation within the powerplant.

Urban and agricultural land use is extensive 

throughout the middle Truckee River subunit. The 

cities of Reno and Sparks, along with their adjacent 

valleys, make up the Truckee Meadows in Nevada—

the most populous area of the Truckee River Basin. 

Urban and suburban developments in this rapidly 

growing area have replaced large areas that had been 

devoted to agriculture. Rapid population growth in the 

Truckee Meadows has created a large municipal 

demand for the available supply of Truckee River 

water. The cities of Reno and Sparks, with a combined 

population of about 187,000 people in 1990, had a 

growth rate of about 32 percent from 1980 through 

1990 (Jones and others, 1991a, p. 40). As a consequence, the increasing water demands of the growing 

number of municipal and industrial users have largely 

been met by the acquisition and conversion of water 

rights previously used for irrigation. Highland Ditch, 

a ditch that used to supply water to irrigate agricultural 

areas only, now conveys a part of its flow to the municipal water-treatment plant at Chalk Bluff (pl. 1). Delivery of Truckee River water by Sierra Pacific Power 

Company (SPPC) to its Truckee Meadows municipal 

and industrial users was 41,440 acre-ft in 1980 and 

54,209 acre-ft in 1987, an increase of about 31 percent. 

SPPC is the sole purveyor of water to municipal and 

industrial users in the Truckee Meadows. Despite 

increased population growth, annual water deliveries 

of Truckee River water to these users have exceeded 

those of 1987 for only two years—1996 and 1997. 

Municipal water-use restrictions have been necessary 

to level demands in accordance with treatment capacities during periods of heavy use during the summer. 

Thus, in 1992, a year of extreme drought, delivery of 

Truckee River water to municipal and industrial users 

was 42,960 acre-ft; during the high runoff years of 

1996 and 1997, deliveries were 55,490 and 63,550 

acre-ft, respectively (Richard D. Moser, Sierra Pacific 

Power Company, written commun., 1998).

Water for municipal and industrial (M&I) use is 

currently treated at two locations, the Chalk Bluff and 

Glendale treatment plants (pl. 1). Water is supplied to 

the Chalk Bluff plant from Highland Ditch (near Verdi, 

Nev.) or from the pumping station near Orr Ditch close 

to the plant site. The Glendale facility diverts water 

from the Truckee River at a pumping station at the 

plant. The Chalk Bluff water-treatment plant went into 

service in April 1994, to replace the Idlewild, Hunter 

Creek, and Highland water treatment plants, which 

were removed from water-treatment service in March 

1994, September 1995, and May 1996, respectively 

(Richard D. Moser, Sierra Pacific Power Company, 

oral commun., 1997). About half of the M&I water 

distributed is consumptively used. The other half 

(wastewater from M&I uses) is returned through a sewage collection system to the Truckee Meadows Water 

Reclamation Facility (TMWRF), previously known as 

the Reno-Sparks Sewage Treatment Plant. The treated 

effluent is then discharged into Steamboat Creek near 

its confluence with the Truckee River near Vista, Nev.

 In the middle Truckee River subunit, Truckee 

River water is diverted to agricultural lands, primarily 

devoted to pasture and alfalfa in the outlying areas of 

the Truckee Meadows as well as along the Truckee 

River corridor to the east. The diverted water flows 

through intricate networks of lateral ditches and fields. 

Excess water not infiltrated to deep ground water or 
12 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

consumed by evapotranspiration (ET) may return to the 

river either (1) through drains or ditch returns at discrete locations, (2) by surface flow over wide areas 

where fields are adjacent to the river, or (3) by groundwater accretions. Drains typically intercept water 

applied to fields that either runs off the surface or 

infiltrates to shallow ground water. If diverted water 

is never applied to fields, such as stockwater or excess 

diverted water, it may return directly to the river 

through that same ditch or indirectly through tributaries 

to the river. Agricultural water also may return to the

river along fields immediately adjacent to the river. 

This water may run off the field at several locations 

or it may infiltrate to shallow ground water that subsequently may discharge along the river. Although 

agricultural returns may enter the river at several locations in the Truckee Meadows, most enter the Truckee 

River through North Truckee Drain from the north and 

Steamboat Creek from the south. These two major 

drainages also intercept urban runoff from the RenoSparks area. Steamboat Creek also receives runoff 

from tributary streams with headwaters in the high 

mountains southwest of the Truckee Meadows—

such as Galena, Whites, and Thomas Creeks (pl. 1). 

Downstream from the Truckee Meadows, local diversions carry water for irrigation of benchlands adjacent 

to the river. Agricultural water used on these benchlands returns to the river at scattered locations, and is 

frequently ungaged. 

At Derby Dam, the downstream boundary of the 

middle Truckee River subunit, a significant percentage 

of the total river flow may be diverted to the Truckee 

Canal for delivery to Newlands Project irrigators along

the canal and in the Carson River Basin near Fallon, 

Nev. (fig. 1). From 1973–96, the average annual diversion from the Truckee River to the Truckee Canal to 

supply the Newlands Project was about 166,000 acreft/yr, or about 29 percent of the annual average runoff 

at the Tracy gaging station (U.S. Geological Survey, 

1974–75, 1976–97). In years when Carson River runoff 

is below average, however, higher percentages of 

Truckee River flow are diverted, typically more than 

80 percent (U.S. Geological Survey, 1989–93). For 

example, in 1990, about 87 percent of the annual 

streamflow measured at the Tracy gaging station was 

diverted to the Truckee Canal (U.S. Geological Survey, 

1991, p. 271, 274). However, adjustments to the 1988 

Operating Criteria and Procedure (OCAP) were implemented in December 1997 that will reduce diversions 

to an average of about 90,000 acre-ft/yr.

Some of the water diverted into the Truckee 

Canal is spilled back to the Truckee River at the Gilpin 

Spill, located about 7.5 miles downstream from the 

canal headgates. Truckee–Carson Irrigation District 

(TCID) uses the spill to re-regulate or fine-tune diversions to the Newlands Project. The exact amount of 

the spill can vary significantly in time and has never 

been gaged.

Lower Truckee River and Pyramid 

Lake Subunit

The lower Truckee River and Pyramid Lake 

subunit consists of the 1,440-mi2 drainage area that 

includes the Truckee River downstream from Derby 

Dam, Pyramid Lake, and a topographically closed 

basin that includes a dry lake bed, known as Winnemucca Lake (fig. 1). This subunit is a combination of 

subunits previously described in Brown and others 

(1986) and Berris (1996): the 261-mi2 lower Truckee 

River subunit, which includes the drainage area of the 

mainstem Truckee River between Derby Dam and 

Marble Bluff Dam (about 3.5 mi upstream from Pyramid Lake; pl. 1), and the 1,180-mi

2 Pyramid Lake subunit downstream from Marble Bluff Dam. The Truckee 

River between Derby Dam and Marble Bluff Dam is 

about 34 mi long. Mean annual runoff for water years

1958–97 at the USGS gaging station Truckee River 

near Nixon, Nev. (hereafter referred to as Nixon gaging 

station; fig. 2 and pl. 1), about 9.5 mi upstream from 

Marble Bluff Dam, is 398,700 acre-ft (U.S. Geological 

Survey, 1998, p. 388). Downstream from Derby Dam, 

the Truckee River flows east to Wadsworth, Nev., and 

then north to Marble Bluff Dam. Prior to the 1930’s, 

the Truckee River split just upstream from the present 

site of Marble Bluff Dam, and the river flowed into 

either Pyramid Lake or Winnemucca Lake or both. 

Since diversions to the Newlands Project began at 

Derby Dam in 1905, average flow of the river diminished sufficiently to result in declines of the water levels in both lakes. By the early 1930’s, only Pyramid 

Lake received inflows from the river, and by 1938 

Winnemucca Lake went dry (Brown and others, 1986, 

p. 20). The Truckee River currently enters Pyramid 

Lake across a broad delta downstream from Marble 

Bluff Dam. The interface of the delta and the lake 

shoreline is migratory, depending on lake levels and 

the volume of flow from the Truckee River. This 

interface has shifted several miles during this century 

because of the varying lake levels. To provide a stable 
DESCRIPTION OF STUDY AREA 13

reference point for modeling and measurements, Marble Bluff Dam was chosen as the boundary between 

the lower Truckee River and Pyramid Lake subunits 

previously described in Brown and others (1986) and 

Berris (1996).

In the lower Truckee River and Pyramid Lake 

subunit, the Truckee River flows through arid desert 

terrain. Annual precipitation in this subunit ranges 

from about 16 in/yr in the northwest along the crest of 

the Pah Rah Range (fig. 1) to less than 8 in/yr along the 

Truckee River corridor (Hardman, 1965). As a result of 

the arid climate, tributaries of the Truckee River flow 

only intermittently. Therefore, when large amounts of 

water are diverted from the middle Truckee River subunit to the Truckee Canal, flows in the lower Truckee 

River can be reduced appreciably. Other than from 

ephemeral tributaries, inflows to the lower section of 

the river are from Gilpin Spill from the Truckee Canal 

and from ground-water discharge from the Fernley 

area, some of which may originate from seepage from 

the Truckee Canal (Van Denburgh and Arteaga, 1985, 

p. 10–11). 

Water is diverted from the river at 10 locations 

to irrigate land along the river corridor in the lower 

Truckee River and Pyramid Lake subunit. There currently are no power-generation or municipal and industrial diversions in the reach. Irrigation water may return 

to the river either as surface inflows through ditches, 

return drains, or along fields adjacent to the river, or 

as ground-water discharge.

As the Truckee River turns northward near 

Wadsworth, Nev., it enters the Pyramid Lake Indian 

Reservation. The reservation, created in 1859 by the 

Secretary of the Interior, follows the Truckee River 

corridor to Pyramid Lake and includes the entire lake 

and adjacent area. Within the reservation, water is 

diverted from the Truckee River to cultivate lands 

along the river corridor and adjacent benchlands. 

Reduced flow in the Truckee River downstream 

from Derby Dam since diversion of water from the 

Truckee River to the Newlands Project began caused a 

decline of water level in Pyramid Lake, the formation 

of a broad shallow river delta at Pyramid Lake, and 

periodic shallow water levels in the lower Truckee 

River. The reduced lake and river levels have hindered 

the ability of fish species to migrate upstream to spawn 

in the Truckee River. From the late 1800’s to September 30, 1997, Pyramid Lake levels declined from about 

3,870 ft above sea level to 3,808 ft, a net decline of 

about 62 ft. In response to the 1967 listing of the 

Pyramid Lake cui-ui lakesucker as an endangered species, the Bureau of Reclamation developed Operating 

Criteria and Procedures (OCAP) to maximize use of 

Carson River, substantially reducing diversions of 

Truckee River water to the Newlands Project. Partially 

as a result of OCAP, since the lowest level of 3,783.9 ft 

was measured at Pyramid Lake in 1967, Pyramid Lake 

levels have increased about 24.5 ft to 3,808.4 ft on 

September 30, 1997 (U.S. Geological Survey, 1998, 

p. 237). Water in the lower Truckee River is currently 

managed for the benefit of the endangered cui-ui lakesucker species and to facilitate the establishment of 

cottonwood trees to improve riparian canopy and fish 

habitat. Fish are important to the culture and economy 

of the Pyramid Lake Indian Reservation. The Pyramid 

Lake Paiute Tribe and the United States are attempting 

to secure more water and more water rights to conserve 

the cui-ui as well as the Lahontan cutthroat trout, a 

threatened species of fish that has been reintroduced to 

the lake since the original strain became extinct in the 

lake more than 50 years ago. 

The level of Pyramid Lake also is important to 

wildlife. Anaho Island National Wildlife Refuge, 

located within Pyramid Lake and the Indian reservation, is home to a colony of American white pelicans. 

At very low lake levels, a land bridge from the shore to 

Anaho Island forms allowing predators access to the 

nesting area (Jones and others, 1991a, p. 85). 

Marble Bluff Dam was built in 1975 to help 

reestablish certain fish species in Pyramid Lake and the 

Truckee River. A fishway leading from the dam to the 

lake allows some of the fish to migrate to fish-handling 

facilities at the dam where fish can be captured and 

eggs stripped for hatchery production, or fish can be 

bypassed upriver for spawning. Recovering cui-ui 

lakesucker and Lahontan cutthroat trout require more 

than just minimal Truckee River streamflows. Several 

interactive physical and chemical characteristics of the 

river—such as volume, timing, and temperature of 

flows during the spawning season and the volume/ 

quality of Pyramid Lake water—affect the productivity 

and viability of these fish.
14 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

CHRONOLOGY AND BACKGROUND OF 

DECREES, AGREEMENTS, AND LAWS 

AFFECTING OPERATIONS

Current and proposed operational practices are 

the result of a long history of construction and management of facilities used to regulate Truckee River water. 

The following sections, based on selected parts of the 

draft TROA environmental impact statement/environmental impact report (EIS/EIR), describe the chronology and background of the facilities that regulate 

Truckee River water and the rules and policies that 

govern their operations (Bureau of Reclamation and 

others, 1998).

Early History

The first facility to control the waters of the 

Truckee River for beneficial use was a private dam 

constructed at the outlet of Lake Tahoe in the late 

1800’s. That dam initiated a series of disputes over 

rights to the use of the waters of the lake and the 

Truckee River. The dam was used primarily to regulate 

flows in the Truckee River so that logs could be floated 

to sawmills in the town of Truckee, Calif. In 1902, the 

predecessor to Sierra Pacific Power Company (SPPC), 

the Truckee River General Electric Company (Electric 

Company), obtained title to the dam. Several small runof-the-river hydropower plants were also constructed 

on the Truckee River in California and Nevada around 

the turn of the century.

After Congress authorized construction of the 

Newlands Project in 1902, the Bureau of Reclamation 

(BOR) began construction of Derby Dam on the lower 

Truckee River and construction of the Truckee Canal. 

Derby Dam was completed in 1905, and the Truckee 

Canal was completed in 1906. In 1903, BOR made 

claim to rights to the water stored in Lake Tahoe for 

delivery to the Newlands Project. Following a series of 

negotiations, the Federal Government was granted an 

easement over Lake Tahoe Dam, which allowed for 

more reliable water deliveries to the Newlands Project. 

As part of these negotiations, the original “Floriston 

rates” were established in 1908, providing the first 

required instream flow criteria for the river.

The original Floriston rates established a minimum flow in the river of 500 ft3/s from March through 

September and 400 ft3/s for the remainder of the year, 

as long as water was available in Lake Tahoe for 

release to the river. Floriston rates were intended to 

provide sufficient streamflow for a pulp and paper 

mill near Floriston, Calif., and for operation of the 

hydropower plants, as well as to supply water for other 

Truckee River rights holders.

In 1913, BOR and the Truckee River General 

Electric Company reconstructed the original dam at 

Lake Tahoe to its current configuration that controls 

the top 6.1 feet of storage at the lake.

Truckee River General Electric Decree

Negotiations and litigation between BOR and 

the Truckee River General Electric Company (United 

States of America v. Truckee River General Electric 

Company) continued and involved property owners 

at Lake Tahoe who were concerned over property 

damage due to high lake water elevation. The disputes 

resulted in a 1915 Federal court decree known as the 

Truckee River General Electric Decree, which gave the 

United States an easement and the right to operate Lake 

Tahoe Dam and its controlling works. The easement 

and the right to operate the dam were subject to the 

requirement, among others, that sufficient water be 

released to maintain Floriston rates, as defined in 

1908. The decree set forth the operating constraints 

of the lake and granted BOR the right to use Lake 

Tahoe Dam to regulate streamflows for diversion to

the Newlands Project. It did not, however, resolve 

concerns of the property owners.

Truckee River Agreement

Drought situations in the late 1920’s and early 

1930’s resulted in extensive controversy among BOR, 

irrigators (both in the Newlands Project and in the 

Truckee Meadows area), and landowners at Lake 

Tahoe over water rights, low lake water elevation, and 

attempts to pump water from the lake to satisfy downstream water users. Negotiations resulted in the Truckee River Agreement of 1935. Parties to the agreement 

were the Federal Government, Sierra Pacific Power 

Company (SPPC), Truckee-Carson Irrigation District 

(TCID)4, and Washoe County Water Conservation 

District. Key points of the Truckee River Agreement 

include:

• Confirming and modifying the original 1908 Floriston rates (table 2). The modified rates are still

4

Quasi-municipal agency that is the contract operator for 

BOR of the Newlands Project and operator of Derby and Lahontan 

Dams, and Lake Tahoe.
CHRONOLOGY AND BACKGROUND OF DECREES, AGREEMENTS, AND LAWS AFFECTING OPERATIONS 15

in effect today. The rates were modified to supply 

M&I and irrigation demands, as well as to provide flows for hydropower generation. Under the 

agreement, the modified Floriston rates are met 

using unregulated streamflow and releases from 

Lake Tahoe (and, when it was later built, Boca 

Reservoir). As shown in table 2, the modified 

Floriston rates vary from 300 to 500 ft3/s at Farad, 

Calif., depending on the water-surface elevation 

of the lake and the month of the year. Hereafter, 

the term “Floriston rates” will refer only to 

modified Floriston rates.

• Providing operating criteria to prevent damage 

along the shoreline of Lake Tahoe from highwater. The operating criteria provide for release 

of water from the lake to prevent the water 

surface from exceeding 6,229.1 ft, as much 

as practicable.

• Defining interrelationships among SPPC’s 

privately owned water, natural (unstored) flow, 

and diverted flow as they pertain to the Newlands 

Project, the Washoe County Water Conservation 

District, and SPPC.

• Defining future water-storage facilities called 

pondage used for the purpose of regulating 

the flow of the Truckee River for the periods 

(1) April 1 to October 31 when Floriston rates 

are not exceeded, and (2) November 1 to March 

31 to the extent necessary in the operation of the 

Truckee River hydroelectric plants. 

• Providing for construction of a new Federal dam 

for a “supplemental reservoir” (later named Boca 

Reservoir), allocating the water right priority for 

filling the reservoir, and establishing operating 

criteria for the reservoir to satisfy the exercise of 

water rights by supplementing Floriston rates.

• Establishing conditions under which Lake Tahoe 

could be pumped.

Construction of Additional Storage 

Reservoirs in the 1930’s

During the 1930’s, additional water storage was 

developed to further control flows in the Truckee 

River system. The Donner Lake Company expanded 

Donner Lake Dam in 1929 to create 9,500 acre-ft of 

storage in the lake. The dam was later acquired by 

SPPC and TCID in 1943. In 1939, SPPC acquired 

Independence Lake and Dam and enlarged the dam 

to increase the lake’s usable storage capacity from 

3,000 to 17,500 acre-ft. Water stored in these reservoirs 

is considered privately owned water. SPPC water in the 

lake is released to satisfy the exercise of SPPC water 

rights. TCID’s water in Donner Lake, when released 

and diverted from the Truckee River to the Truckee 

Canal at Derby Dam, is used generally to satisfy the 

exercise of individual water rights for irrigation in the 

Newlands Project. Independence Lake water is 

released to satisfy the exercise of SPPC water rights. 

Releases from these reservoirs are not currently used to 

achieve Floriston rates.

After Congress authorized the Truckee Storage 

Project in 1935, BOR began construction of Boca Dam 

on the Little Truckee River. The dam was completed in 

1939. Releases from Boca Reservoir are used to 

achieve Floriston rates and to provide flood control. 

The dam is operated by the Washoe County Water 

Conservation District.

Donner Lake Agreement

The Donner Lake Agreement among TCID, 

SPPC, and the Donner Lake Company, signed in 

1943, governs the operation of Donner Lake to satisfy 

Table 2. Floriston rates as related to Lake Tahoe water-surface elevation and month 1

1 Based on Bureau of Reclamation and others (1998, table 1-1, p. 1–7)

Floriston rates: Flow at gaging station, Truckee River at Farad, 

Calif. (10346000), in cubic feet per second

Water-surface elevation at Lake Tahoe Dam

(feet, Lake Tahoe datum) October November–February March April–September

Below 6,225.25 400 300 300 500

Between 6,225.25 and 6,226 400 350 350 500

Above 6,226 400 400 500 500
16 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

the exercise of water rights of SPPC and Newlands 

Project. Withdrawals are limited during the summer 

recreation season.

Orr Ditch Decree

A 1944 Federal court decree, known as the Orr 

Ditch Decree, adjudicated the water rights of litigants 

in a 1913 suit filed by the United States (United States 

of America v. Orr Ditch Water Company) that sought to 

confirm water rights for use in the Newlands Project. 

The Orr Ditch Decree affirmed individual water 

rights—amount, place and type of use, and priority—

and included guidelines previously specified in the 

Truckee River Agreement for operating Lake Tahoe 

and Boca Reservoir to serve those rights. Parties to the 

Orr Ditch Decree include the Federal Government, 

SPPC, TCID, the Washoe County Water Conservation 

District, and individual water rights holders in Nevada, 

many of them agricultural water users in the Truckee 

Meadows area.

Based on the date of establishment of the Pyramid 

Lake Indian Reservation, the court recognized an 1859 

priority date for water rights for irrigation of reservation lands. Known as Claims 1 and 2, these are the most 

senior water rights on the Truckee River. The decree 

also incorporates a SPPC right for a continuous flow 

of 40 ft3/s for M&I demands in Reno, with a priority 

junior only to Claims 1 and 2.

Sierra Valley Decree

As a result of litigation (United States of America 

v. Sierra Valley Water Company), the Sierra Valley 

Decree of 1958 confirmed a water right for Sierra 

Valley Water Company, which has historically 

diverted water out of the Little Truckee River to the 

Feather River Basin in California for irrigation5. The 

diversion averages about 6,000 acre-ft/yr. The Sierra 

Valley Settlement Agreement of 1993 settled a dispute 

concerning the point at which diversions from the 

Little Truckee River will cease as a result of the Sierra 

Valley Decree.

Construction of Prosser Creek and 

Stampede Dams

After Congress authorized the Washoe Project in 

1958, BOR constructed Prosser Creek Dam on Prosser 

Creek. Prosser Creek Reservoir provides 29,800 acreft of storage. Construction was completed in 1962. In 

accordance with the Tahoe–Prosser Exchange Agreement, a portion of water stored in the reservoir may be 

used to achieve Floriston rates in lieu of release from 

Lake Tahoe. Historically, water stored in the reservoir 

in excess of storage under the Tahoe–Prosser Exchange 

Agreement has been referred to as “uncommitted 

water” and is used to benefit Pyramid Lake fish.

Under the same congressional authorization, 

BOR completed construction of Stampede Dam and 

Reservoir on the Little Truckee River in 1970. Stampede Reservoir has a capacity of 226,500 acre-ft. 

Flood-control criteria require a combined maximum 

of 30,000 acre-ft of storage space in Stampede and 

Boca Reservoirs.

Tahoe–Prosser Exchange Agreement

The Tahoe–Prosser Exchange Agreement of 1959 

provides additional criteria for operating Lake Tahoe 

and the facilities that became Prosser Creek Dam and 

Reservoir. The agreement is among BOR, SPPC, 

TCID, and the Washoe County Water Conservation 

District. The purpose of the Tahoe–Prosser Exchange 

Agreement is to maintain flows immediately downstream from the lake. During high runoff, releases from 

the lake for Floriston rates may be unnecessary. In such 

a case, unless the lake is spilling or being drawn down 

due to high lake level conditions, the flow in the Truckee River between the lake and Prosser Creek may be 

almost nil. Under these conditions, the Tahoe–Prosser 

Exchange Agreement allows water to be released from 

Lake Tahoe to sustain instream flows for fishes in the 

Truckee River between the lake and Prosser Creek in 

exchange for an equal amount of water to be stored in 

Prosser Creek Reservoir, if possible. This was the first 

agreement in the Truckee River Basin to exchange storage in one reservoir for storage in another reservoir to 

achieve multiple benefits.

Endangered Species Act

The Endangered Species Act (ESA) provides for 

the protection and conservation of plant and animal 

species designated by the Secretary (Secretary of the 

Interior) as “endangered” or “threatened.” Cui-ui was 

5Agricultural lands in the Feather River Basin that receive 

water from the Little Truckee River for irrigation are located in 

Sierra and Plumas Counties.
CHRONOLOGY AND BACKGROUND OF DECREES, AGREEMENTS, AND LAWS AFFECTING OPERATIONS 17

listed as an endangered species in 1967. Lahontan cutthroat trout was initially listed as an endangered species 

in 1970, but was reclassified as threatened in 1975.

Stampede Reservoir Judgement

As a result of litigation (Carson-Truckee Water 

Conservancy District v. Watt, 1982), a Federal court 

upheld a determination of the Secretary that his obligations under the ESA took precedence over his authority 

to contract for delivery of water for irrigation and M&I 

uses. The judgement requires all storage in Stampede 

Reservoir to be used to provide water for the threatened 

and endangered Pyramid Lake fishes.

Newlands Project Operating Criteria 

and Procedures

Diversions to the Newlands Project from the 

Truckee River were generally unregulated prior to the 

implementation of Newlands Project Operating Criteria and Procedures (OCAP). OCAP were first introduced in 1967 with the objective to maximize the use 

of Carson River water for the Newlands Project and 

minimize the diversion of Truckee River water via the 

Truckee Canal. A more stringent OCAP that imposed a 

limit on Project diversions was approved in 1973 as a 

result of litigation (Pyramid Lake Paiute Tribe of Indians v. Morton, 1973) in which a Federal court ruled that 

the Newlands Project was diverting too much water 

from the Truckee River. Other OCAP’s were implemented in 1988 and again in 1997 (Adjusted OCAP), 

which further control diversions from the Truckee 

River to the Newlands Project.

OCAP includes procedures for calculating the 

annual water demand of the Newlands Project and the 

diversions of Truckee River water to the Project. Major 

components of OCAP include provisions for a maximum annual diversion; implementation of conservation measures to improve project efficiency; and 

criteria for diverting Truckee River water to the Newlands Project based upon the forecasted Carson River 

supply for the Carson Division, Lahontan Reservoir 

storage objectives (table 3), seasonal Newlands Project 

demands, and current reservoir storage.

Preliminary Settlement Agreement

The PSA (Preliminary Settlement Agreement), 

entered into in 1989 by SPPC and the Pyramid Lake 

Tribe, is an agreement to change the operation of Federal reservoirs and the exercise of Truckee River water 

rights to (1) improve spawning conditions for the 

endangered and threatened Pyramid Lake fishes and 

(2) provide additional M&I water for the Reno–Sparks 

area during drought periods. Many provisions of the 

PSA have not yet been implemented and will be implemented only through TROA.

The PSA allows SPPC to store a certain amount 

of privately owned water and a portion of former 

agricultural water rights in Federal reservoirs for M&I 

drought relief. SPPC would obtain a priority right to 

store this water in Stampede Reservoir. In exchange, 

that portion of Floriston rate water required solely for 

hydropower generation by SPPC’s Truckee River 

hydropower plants would be retained in storage and 

released at a later date for the benefit of the Pyramid 

Lake fishes. This water would be stored as credit water 

with varying degrees of protection against evaporation 

and spillage. Under certain conditions, some categories 

of credit water could be exchanged with other categories of stored water.

Public Law 101-618

Public Law 101-618 was enacted by Congress in 

1990 to provide direction, authority, and mechanism 

for resolving disputes over water and water rights in the 

Truckee and Carson River Basins. The purposes of the 

mandatory and permissible actions as specified in section 202 of P.L. 101-618 are to:

• Provide for the equitable apportionment of 

the waters of the Truckee River, Carson River, 

and Lake Tahoe between the States of California 

and Nevada; 

• Authorize modifications to the purposes and 

operations of certain Federal Reclamation 

project facilities to provide benefits to fish and 

wildlife; municipal, industrial, and irrigation 

users; and recreation;

• Authorize acquisition of water rights for fish 

and wildlife;

• Encourage settlement of litigations and claims;

• Fulfill Federal trust obligations toward 

Indian tribes;

• Fulfill the goals of the ESA by promoting the 

enhancement and recovery of the Pyramid Lake 

fishes; and
18 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

• Protect significant wetlands from further degradation and enhance the habitat of many species of 

wildlife that depend on those wetlands.

To achieve these purposes, P.L. 101-618 directs, 

among other actions, negotiation of an operating agreement (i.e., TROA). Provisions of the law directly 

related to the draft TROA are discussed below. (The 

following provisions were selected from a larger list in 

the EIS/EIR according to their pertinence to the simulation of operations.)

• Section 204 (Interstate Allocation) reaffirms the 

Alpine Decree for Carson River waters and 

apportions the waters of the Truckee River and 

Lake Tahoe between California and Nevada. 

TROA may include criteria and procedures for 

implementing and monitoring this apportionment, which automatically enters into effect when 

TROA is adopted, and certain other conditions of 

the act are satisfied. Once TROA goes into effect, 

the Interstate Allocation will provide a permanent 

and final resolution to long-standing controversies over the States’ rights to these waters. If 

TROA does not go into effect, these allocations 

do not go into effect for the Carson River, the 

Truckee River, or Lake Tahoe.

• Subsection 205(b) authorizes the Secretary to use 

Washoe Project facilities, Truckee River Storage 

Project facilities, and Lake Tahoe Dam for the 

storage of nonproject water to fulfill the purposes 

of Title II of P.L. 101-618. This authorization 

forms the cornerstone of TROA. Allowing multiple use of Federal reservoirs may enhance the 

water supply available for the Sierra Pacific service area during drought situations and may also 

provide better control of streamflows for Pyramid 

Lake fishes. Subsection 205(b) also authorizes 

the Secretary to collect appropriate charges for 

such uses.

Interim Storage Agreement

As authorized under paragraph 205(b)(3) of 

P.L. 101-618, the Secretary, SPPC, the Washoe County 

Water Conservation District, and Pyramid Lake Tribe 

reached an agreement (Contract for Storage of Sierra 

Pacific Power Company Water in Stampede and Boca 

Reservoirs) in 1994 that allows SPPC to store additional water in Stampede and Boca Reservoirs. The 

agreement provides additional storage capacity for 

SPPC to meet domestic, municipal, and industrial 

needs in Truckee Meadows during drought situations. 

The initial term of the agreement is 25 years; however, 

it will be superseded by TROA and is, therefore, 

referred to as the interim storage agreement.

Truckee River Water Quality 

Settlement Agreement

The Water Quality Settlement Agreement 

(WQSA), signed in 1996, provides for acquisition of 

water rights to resolve major water quality problems in 

the Truckee River in Nevada, while simultaneously 

providing a major contribution to fish and wildlife 

Table 3. June through December end-of-month storage objectives for Lahontan Reservoir 

from 1988 and Adjusted Operating Criteria and Procedures (OCAP) 1

1 Modified from Bureau of Reclamation and others (1998, table 1–2, p. 1–10). The end-of-month Lahontan 

storage objectives for January through June are variable, with a goal of achieving a storage at the end of June of 

190,000 acre-feet or 215,000 acre-feet for Adjusted OCAP and 1988 OCAP, respectively. The 1988 OCAP was 

used from 1988 to 1997. Adjusted OCAP was implemented in December 1997.

1988 OCAP Adjusted OCAP

Month Lower storage objective 

(acre-feet)

Upper storage objective 

(acre-feet)

Storage objective 2

(acre-feet)

2 Storage objectives listed assume annual Carson Division demand of 271,000 acre-feet.

June1 215,000 — 190,000

July 160,000 162,400 160,000

August 140,000 142,200 100,000

September 120,000 122,000 64,000

October 80,000 81,500 52.000

November 160,000 162,400 74,000

December 210,000 213,600 101,000
CONSTRUCTION OF TRUCKEE RIVER BASIN OPERATIONS MODEL 19

resources of the Truckee River. Parties to the agreement are the Cities of Reno and Sparks, the Washoe 

County Water Conservation District, the Pyramid Lake 

Tribe, the U.S. Department of the Interior (Interior), the 

U.S. Department of Justice, the U.S. Environmental 

Protection Agency (EPA), and the Nevada Division of 

Environmental Protection (NDEP).

Key provisions (selected) and terms of the 

WQSA are as follows.

• Reno, Sparks, and Washoe County agree to 

provide $12 million to acquire Truckee River 

water rights.

• Department of the Interior agrees to provide $12 

million to acquire Truckee River water rights.

• As provided by draft TROA, all water associated with the acquired water rights will be stored 

in a jointly managed pool in Federal reservoirs 

and released according to agreed-upon management measures and schedules to (1) augment 

instream flows in the Truckee River from Reno 

to Pyramid Lake, (2) improve Truckee River 

water quality, and (3) maintain and preserve the 

lower Truckee River and Pyramid Lake for fish, 

wildlife, and recreation.

• A water supply will be established to benefit 

water quality of the Truckee River downstream 

from TMWRF by using Truckee Meadows sewage effluent rather than Truckee River water 

for irrigation of certain Orr Ditch water rights; 

the Truckee River water that would have been 

diverted to satisfy the exercise of those Orr Ditch 

water rights will either be stored in upstream reservoirs or left in the river to provide this water 

quality benefit.

CONSTRUCTION OF TRUCKEE RIVER 

BASIN OPERATIONS MODEL

A daily operations model was constructed to simulate river and reservoir operations and streamflow for 

the Truckee River Basin from Lake Tahoe to Pyramid 

Lake, the Truckee Canal, and Lahontan Reservoir. This 

model was constructed within a larger modeling system that includes a database management program 

(ANNIE, Lumb and others, 1990) and a program that 

simulates river/reservoir operations and a variety of 

hydrologic processes (Hydrological Simulation Program-FORTRAN (HSPF), Bicknell and others, 1993). 

The HSPF program is composed of a variety of

modules that are used to simulate operations or such

physical processes as streamflow-routing, stream 

temperature, precipitation-runoff, and water quality. 

Some of these HSPF modules can be used by 

themselves, but others must be used with one or 

more other modules. For example, the module used to 

simulate streamflow routing can be used by itself. The 

simulation of operations by HSPF, however, requires 

the use of a flow-routing module and an operations 

module within HSPF. Models are unique applications 

of generic programs such as HSPF. Once data and 

parameters unique to a particular basin are specified or 

input to the program, a model results that cannot be 

used in another river or basin. 

The modeling system uses the time-series data 

management program ANNIE. ANNIE is an interactive program designed for management of data, which 

includes file creation, data set management, data analysis, and data display. ANNIE is used for the storage 

and management of the daily time-series data required 

to simulate various processes within a hydrologic system. HSPF simulation modules draw input from and 

write output to binary, direct-access files called Watershed Data Management (WDM) files.

The complex operational rules and data requirements of the comprehensive river-basin model 

described in this report require advanced computerprocessing capabilities to facilitate the creation of new 

scenarios and for summarizing and analyzing large 

volumes of input and output data. An interactive 

computer program, GENSCN (GENeration and analysis of model simulation SCeNarios), developed by Kittle and others (1998), can be used in conjunction with 

the operations model described in this report. GENSCN was developed to create simulation scenarios, 

analyze results of the scenarios, and compare scenarios. A variety of standard tabular, graphical, and statistical tools are provided, including animation. Readers 

interested in further details on the GENSCN program 

are referred to the documentation for that program.

The following sections describe (1) the HSPF 

program that contains flow-routing and operations 

modules, (2) the flow-routing and operations modules 

within HSPF to simulate daily streamflow, and (3) the 

data used by the daily model to simulate flow routing 

and operations.
20 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

Description of Hydrological Simulation 

Program–FORTRAN

HSPF is a computer program that can simulate 

hydrologic and associated water-quality processes on 

pervious and impervious land surfaces, within the soil 

profile, and in drainage networks and well-mixed lakes 

and reservoirs (Bicknell and others, 1993). Recently, 

logical capabilities were added to HSPF to allow the 

simulation of reservoir and river operations (Thomas 

Jobes, Aqua Terra Consultants, written commun., 

1998). HSPF was chosen to simulate Truckee River 

operations primarily because it can (1) simulate continuous, long periods of time, including periods of storm 

runoff and low flows, (2) simulate at a daily time interval, (3) simulate the hydraulics of complex natural and 

manmade drainage networks, (4) produce simulation 

results for many locations along a river and its tributaries, (5) simulate reservoir and river operations, and (6) 

compute a detailed water budget that accounts for 

inflows and diversions as well as different categories of 

water in the river and associated reservoirs. HSPF is an 

internationally used non-proprietary program maintained by the Environmental Protection Agency.

A category of water is any parcel of water that is 

individually accounted for in an observed or simulated 

water budget. A single river, reservoir, lake, or diversion ditch may contain several categories. Water within 

a category may have specific ownership, such as “privately owned stored water,” or have a designated use, 

such as “pooled water” (used to meet a minimum-flow 

requirement known as Floriston rates).

The user’s control input (UCI) file contains 

information the user must provide to run functional 

modules within HSPF. Modules describe discrete 

physical processes that may be added to the UCI. The 

UCI provides instructions to HSPF by defining the 

required modules to simulate a particular modular 

objective, such as streamflow routing. The Truckee 

River Basin operations model contains modules 

describing flow routing and operations. The flowrouting module determines the conveyance and storage 

characteristics for the stream channels and reservoirs, 

whereas the operations module is structured to allow 

development of rules that simulate human decisions 

and control over inflows and outflows to the hydrologic 

network. The HSPF operations module for the Truckee 

River must be run in combination with the HSPF daily 

flow-routing module developed by Berris (1996).

The modules in HSPF include one or more 

“blocks” that group the computations needed by each 

module. The streamflow-routing module uses only one 

block, the RCHRES (reach-reservoir) block. The module used in simulating operations contains two blocks, 

the SPECIAL ACTIONS (SPECL) block and the CATEGORY block. As previously stated, both modules, 

and therefore all three blocks, are required to fully 

simulate operations using HSPF. The SPECL block 

contains the model code that simulates river and reservoir operations. The code developed for the Truckee 

River Basin operations model in the SPECL block was 

further subdivided for organizational clarity into “subblocks,” which usually deal with specific reservoir or 

river operational functions such as flood-control criteria, minimum instream flows, and so forth. 

The RCHRES block of HSPF can simulate 

streamflow for long periods of time by numerically 

representing inflow, outflow, and the hydraulics of 

channels, reservoirs, and lakes. Channel inflow and 

outflow may be simulated in HSPF or provided to 

HSPF by external time series. Channel inflow is routed 

as streamflow through the drainage network by a modified kinematic-wave algorithm that is a component of 

HSPF. The drainage network may include any natural 

or manmade flow-conveyance system, but hydraulic 

properties of individual reaches must be held constant. 

Water lost from the drainage network is represented by 

evaporation, channel outflow as seepage to ground 

water, or discharge (diversion) out of the modeled 

drainage network.

The SPECL and CATEGORY blocks of HSPF 

can simulate reservoir and river operations over long 

periods of time by the designation of water categories 

in the CATEGORY BLOCK and model code in the 

SPECL block (Thomas Jobes, Aqua Terra Consultants, 

written commun., 1998). The separation of water into 

specific categories is handled by defining water categories in the CATEGORY block of the UCI file. Each category has a “tag” that is used throughout the UCI as a 

method to specify ownership of a given water quantity. 

Reservoir and river operations are governed by complex rules in legal agreements, decrees, and regulations 

that specify logical conditions for the use of water categories in the SPECL block. Variables are used in the 

code of the SPECL block to store numerical values 

necessary in the simulation processes that evaluate 

these logical conditions. Accordingly, if certain conditions are met during a simulation, then certain actions 

are taken. The Truckee River Basin operations model 
CONSTRUCTION OF TRUCKEE RIVER BASIN OPERATIONS MODEL 21

simulates reservoir and river operations by evaluating 

these conditions and executing the appropriate operations in the model code. Conditions that are typically 

evaluated during simulations include the time of year; 

reservoir stage, reservoir storage, or volume of a given 

water category in a reservoir; streamflow magnitude; 

and fulfillment of water demands. Thus, for example, 

release from the Lake Tahoe category pooled water to 

satisfy Floriston rates could be programmed to occur if 

the date is from April 1 through October 31 of a given 

year, if the elevation of the lake is within the range 

6,223.0 to 6,225.5 ft, and if the demand for additional 

water at the Farad gaging station has not been met. 

HSPF simulates operations and streamflow using 

a computational time interval of one day. Within each 

time interval, the operations are simulated in the 

SPECL block, then the results are input to the 

RCHRES block where flow routing is simulated. For 

the first time interval of a model run, the model evaluates initial conditions, simulates operations accordingly, and inputs the results to the RCHRES block for 

flow routing. For each following time interval, conditions of flow and reservoir storage existing after the 

final calculations for the previous time interval are the 

same as the conditions at the beginning of the next time 

interval. Based on the evaluation of these conditions, 

the model simulates operations, and, again, inputs the 

results to the RCHRES block for flow routing. Because 

inflows are simulated within the RCHRES block, the 

inflows and reservoir storages evaluated for the simulation of operations in a time interval are from the 

flow routing results of the previous time interval. Using 

this method of simulation provides operational decisions at the beginning of a computational time interval 

based on the inflows and storages from the previous 

time interval. This is not unlike actual operations, in 

which the runoff for a particular day is unknown at the 

beginning of the day, dictating the use of the previous 

day’s inflow to guide current operations, instead of a 

perfect forecast.

The previous discussion provided a general overview of the features of the method HSPF uses to route 

streamflow and perform operations. The following discussion on the HSPF flow-routing module provides 

description of (1) the HSPF drainage network segments 

called reaches, (2) the HSPF parameters used to characterize reaches, (3) how reach outlets allow delivery 

of water to specific destinations, such as a downstream 

reach or a diversion ditch, and (4) how HSPF routes 

streamflow from reach to reach in a drainage network.

HSPF requires that the linked network of river 

channels, lakes, and reservoirs be divided into segments called reaches. A reach must have relatively uniform hydraulic properties. For this study, hydraulic 

properties were generalized for reach segmentation to 

simulate only the essential properties that determine 

streamflow and volume in the drainage network. It was 

not necessary to simulate streamflow through every 

pool, riffle, or diversion dam.

HSPF model parameters in the RCHRES block 

represent hydraulic properties of all designated reaches 

in a drainage network. Function tables of the RCHRES 

block, referred to as F-tables, contain relations 

between hydraulic properties of channel reaches, lakes, 

and reservoirs. The hydraulic properties of channels, 

which include channel shape, channel roughness, channel slope, and channel length, determine the relation of 

streamflow to the volume of water stored in a reach. Ftables for unregulated channel reaches contain the relation between the two parameters streamflow at the 

downstream end of a reach and volume of water contained in a channel reach. Water volume in storage and 

corresponding streamflow are the parameters that 

define how water is routed through a channel from a 

reach to a downstream reach. F-tables for lakes 

and reservoirs contain the relations between three 

parameters—depth, surface area, and volume. These 

relations for lakes and reservoirs determine the depth, 

surface area, and volume of water in storage at the end 

of a simulated time interval after all inflows (for 

example, inflows from upstream reaches, tributaries, 

or precipitation) and all outflows (for example, regulated releases, diversions, or evaporation) have 

been simulated. 

A reach can have up to five outlets in HSPF. 

HSPF can produce simulation results for each outlet of 

a given reach. Typically, a reach outlet represents the 

downstream boundary of a reach and enables delivery 

of water from that reach to the next downstream reach. 

Reach outlets also allow diversion of water from a 

reach to ditches or canals, or seepage of water from 

river or lake bed to ground water. When water is 

diverted from a reach to a ditch or canal, that ditch or 

canal may or may not be a part of the modeled drainage 

network. If the ditch or canal is a part of the modeled 

drainage network, flow can be routed through reaches 

defined for that ditch or canal system. If the ditch or 

canal is not a part of the modeled drainage network, the 

water diverted from a given reach is not routed through 

the ditch or canal and is simply lost from the network.
22 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

HSPF can route flow through a drainage network, 

from reach to reach, to the designated downstream 

boundary of a drainage basin. A water budget is determined for the total volume of water as well as each 

water category in each reach by accounting for total 

volume of water and volume of water categories entering a reach, total volume of water and volume of water 

categories stored in a reach, and total volume of water 

and volume of water categories leaving a reach during 

a given time interval. The total volume of water entering a reach over a given time interval is the sum of the 

volumes from all inflows of all water categories during 

that interval. Inflows to a reach consist of all connected 

upstream reaches, tributaries, precipitation, and runoff 

and ground water from contributing subbasin areas that 

drain to the reach. In turn, the total water stored in a 

reach in a given interval is the sum of all volumes of 

all water categories draining into the reach from all 

connected reaches and drainage areas, plus the initial 

volume stored in the reach, minus the volume discharged from the reach during the time interval. The 

total volume of water leaving a reach over a given time 

interval is the sum of the volumes from all outflow of 

all categories during that interval. 

In HSPF, outlet discharge from a reach is a function of volume, a function of time, or a combination 

of both functions of volume and time. When outlet 

discharge is a function of volume, the total volume of 

water in the reach determines the outlet discharge as 

specified by model parameters. The volume function is 

most useful when a stage-discharge relation can characterize outlet discharge. When outlet discharge is a 

function of volume, water categories typically discharge from a reach in proportion to their stored 

volume within that reach. When outlet discharge is a 

function of time, an external or internally generated 

time series governs the outlet discharge for specific 

water categories. The time function is useful when a 

control structure governs outlet discharge, such as regulated releases from a reservoir or regulated diversions 

to meet agricultural or municipal and industrial 

demands. For example, model code within the SPECL 

block may internally generate a time series of Lake 

Tahoe releases from specific categories to meet Floriston rates, the minimum-flow requirement measured at 

the downstream Farad gaging station. The numerical 

value generated by the model code for a simulated time 

interval will govern the simulated release from specific 

lake water categories for that time interval as a function 

of time. When a reach has more than one outlet, then 

the priority of outflow demands for each outlet can 

be specified.

Water volumes may change categories when 

discharged from a reach. For example, uncommitted

water from Prosser Creek Reservoir will change to 

fish water upon release. These and other categories are 

defined in a later section, “Current Water Categories.”

Flow-Routing Model

The Truckee River flow-routing model is a 

necessary module for the operations model. The flowrouting module characterizes the movement of water 

into and through the reaches of the drainage network 

while the operations module simulates the manmade 

regulation of water movement within and out of the 

drainage network. The HSPF operations module for the 

Truckee River must be run in combination with the 

HSPF daily-flow routing module.

Berris (1996) developed a physically based flowrouting model constructed to simulate streamflow at 

daily time intervals along the Truckee River from the 

outlet of Lake Tahoe to just upstream from Pyramid 

Lake. Daily streamflow data for water years 1978–92 

for the mainstem of the Truckee River, tributaries, irrigation ditches, and the Truckee Canal were obtained 

from several agencies and compiled into a comprehensive data base using WDM files. (A water year is the 

12-month period beginning October 1 and ending 

September 30, and designated by the calendar year of 

the ending date.) Where streamflow data were unavailable or incomplete, flows were estimated. The Truckee 

River and two tributaries, Donner Creek and Martis 

Creek, were divided into 47 reaches, each with fairly 

uniform hydraulic characteristics. Hydraulic characteristics defined for the 47 reaches were based on crosssectional survey data obtained from field surveys and 

previous studies. 

Model testing demonstrated that hydraulic characteristics of the Truckee River are adequately represented in the model (Berris, 1996) for a range of flow 

regimes. Most of the differences between observed and 

simulated streamflow resulted from inadequate data 

describing inflow to and outflow from the Truckee 

River, rather than from inadequate data characterizing 

the hydraulic properties of the reaches. Inflow and 
Data for Simulation of Streamflow and Operations 23

outflow data were considered inadequate for reaches 

where, and periods when, measurements were inaccurate or data were not available.

The scope of the flow-routing model described 

above was expanded from 47 reaches to 72 reaches 

for use with the operations model. The additional 

25 reaches include 7 reaches defined for lakes and 

reservoirs in the Sierra Nevada (Lake Tahoe, Donner, 

Martis Creek, and Independence Lakes, and Prosser, 

Stampede, and Boca Reservoirs); 7 for channel segments along the Little Truckee River, and Independence and Sagehen Creeks; 1 for Pyramid Lake; 1 for 

Lahontan Reservoir in the Carson River Basin; and 

9 for the Truckee Canal (fig. 3 and pl. 1). 

The RCHRES block of HSPF routes streamflow 

along connected reaches of a drainage network based 

on the hydraulic characteristics of reaches (Berris, 

1996). For channel reaches where outlet discharge is 

a function of volume, F-tables represent the relation 

of surface-water volume temporarily stored in the 

reach to surface-water discharge at the downstream 

end of the reach. Hydraulic properties, measured or 

estimated at cross sections, were used to determine 

volume-discharge relations for these types of reaches. 

Most reaches were characterized using at least 3 cross 

sections, but reaches in the Truckee Meadows were 

characterized using between 12 and 18 cross sections 

(Berris, 1996). Reach characteristics along the Truckee 

Canal were computed using only 1 cross section in 

some cases because of the fairly uniform channel 

geometry of the canal (Carol Grenier, Bureau of Reclamation, written commun., 1994). For lakes and reservoirs where outlet discharge from a reach is a function 

of time, F-tables represent the relations between depth, 

surface area, and volume. F-tables were based on 

hydraulic properties obtained from tables and graphs 

relating depth and volume, and tables and graphs relating depth and surface area for the following reservoirs: 

Lake Tahoe (A.M. Piper, U.S. Geological Survey, written commun., 1993); Donner and Independence Lakes 

(Sierra Pacific Power Company, written commun., 

1980); Prosser Creek Reservoir (Bureau of Reclamation, written commun., 1962 and U.S. Army Corps of 

Engineers, 1985); Martis Creek Lake (U.S. Army 

Corps of Engineers, 1985); Boca Reservoir (Bureau 

of Reclamation, written commun., 1970 and 1980); 

Stampede Reservoir (Bureau of Reclamation, written 

commun., 1974 and 1980); Pyramid Lake (Harris, 

1970); and Lahontan Reservoir (Alan Olson, Bureau 

of Reclamation, written commun., 1989). 

Data for Simulation of Streamflow 

and Operations

Data necessary for streamflow and operations 

simulations are provided to the model either from 

external time series or from within the model code of 

the SPECL block. External time series are accessed 

directly by the model during simulations or can be 

accessed by the interactive programs ANNIE or 

GENSCN during pre- or post-simulation analyses. 

Data within the model code of the SPECL block are 

considered to be numerical assignments to model 

variables. Default values are provided, but the model 

user may modify the values to create different model 

scenarios through the use of the interactive computer 

program GENSCN or through any standard editor 

program. Descriptions and discussions of the many 

types and uses of data used for numerical assignments 

to model variables are provided in the two succeeding 

sections—”Description and Simulation of Current 

Operations” and “Description and Simulation of Draft 

TROA and WQSA Operations”—and in the flowchart, 

code, and variable listings provided in the supplemental documentation that was described in the “Purpose 

and Scope” section. 

In addition to data used for variable assignments 

within the SPECL block, the following types of external time series of daily data are required input to run the 

operations model for all or part of the period covering 

water years 1933 to 19976. 

• Streamflow data:

– Reservoir inflows:

• Lake Tahoe (net inflow);

• Donner Lake;

• Martis Creek Lake;

• Prosser Creek Reservoir;

• Independence Lake;

• Stampede Reservoir;

• Boca Reservoir.

– River inflows:

• Ungaged tributaries to the Truckee River 

upstream from Farad gaging station;

• Sagehen Creek;

• Dog Creek;

6

The period of data, water years 1933–97, was chosen 

because a sufficient amount of observed data were available for 

use by the operations model. The period represents a wide range 

of hydrologic conditions.
24 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

• Hunter Creek;

• Carson River near Fort Churchill.

– Tributaries and channel seepage losses between 

the Farad and Vista gaging stations other than 

Dog and Hunter Creeks.

• Evapotranspiration (ET) losses from phreatophytes 

downstream from Vista gaging station.

• Climate Data:

– Precipitation:

• Six major lakes and reservoirs upstream 

from Farad gaging station7 not including 

Lake Tahoe;

• Pyramid Lake;

• Truckee River precipitation from Vista 

gaging station to Marble Bluff Dam.

– Evaporation:

• Six major lakes and reservoir upstream; 

from Farad gaging station6 not including 

Lake Tahoe;

• Pyramid Lake;

• Truckee River evaporation from Vista gaging 

station to Marble Bluff Dam;

• M&I demand data for the Truckee Meadows;

• Forecast Data:

– Lake Tahoe April-to-peak closed-gates rise;

– Little Truckee River above Boca Reservoir, 

Calif., April to July runoff.

– Truckee River at Farad, Calif., April to 

July runoff.

– Carson River at Fort Churchill, Nev., April to 

July runoff

– Runoff volume for each month from April through 

November as inflow to all seven major lakes and 

reservoirs upstream from Farad gaging station and 

intervening areas adjacent to the Truckee River 

between Lake Tahoe and Farad gaging station. 

Forecast is based on snowpack condition on April 

1 and median temperature and precipitation thereafter.

The following sections describe the data used by 

the operations model to route streamflow and to simulate operational practices in the Truckee River drainage 

network. Other sources of data can be used, so long as 

the model input requirements listed above are met. A 

more detailed description of the data used for simulations by the operations model is provided by a separate 

report titled, “Hydrologic Data Used in the River and 

Reservoir Operations Model, 1933–97, Truckee River 

Basin, California and Nevada” (Berris and others, 

2001).

Streamflow

Streamflow data are required as input to the 

USGS Truckee River Basin operations model at 

upstream model boundaries and at boundaries representing locations of tributary inflow upstream from the 

Vista gaging station. Upstream from the Farad gaging 

station, inflows are provided at model boundaries by 

three methods: (1) observed flow data from USGS 

gaging stations, (2) water balance computations, and 

(3) results from Precipitation-Runoff Modeling System 

(PRMS) simulations (Leavesley and others, 1983). 

Flow data measured at single gaging stations, when 

available, are used as direct input to channel reaches of 

the Little Truckee River upstream from Stampede Reservoir (reach 185), Sagehen Creek upstream from 

Stampede Reservoir (reach 198), and the Truckee 

River upstream from the Farad gaging station (reach 

230). Where inflow data from single gaging stations are 

not available for direct input to the model, then net 

inflows are provided to model boundaries by water balance computations using data from two or more gaging 

stations. For Lake Tahoe, net inflows, which include 

streamflow gains, precipitation gains, and evaporation 

losses, are determined by water balance computations 

because accurate precipitation gains and evaporation 

losses are not available for model simulations. Water 

balance computations are also used to determine net 

inflows for the Truckee River between the lake and the 

town of Truckee (reaches 110–140) and Donner Creek 

between Donner Lake and the Truckee River (reach 

149) during periods when reliable gaging station data 

are available (pl. 1). When and where reliable flow data

from gaging stations are not available for direct input to 

model boundaries or for water-balance computations of 

net inflows, then results from PRMS simulations are 

provided as inflows. PRMS, a physically based, distributed-parameter watershed model, provides simulated 

daily inflows from 16 headwater subbasins to these 

model boundaries (Jeton, 2000). 

Downstream from the Farad gaging station, 

inflows to the Truckee River from previously diverted 

water for agricultural and M&I use are simulated (see 

the later sections “Truckee Meadows Diversions” and 

7Donner, Martis Creek, and Independence Lakes, and 

Prosser, Stampede, and Boca Reservoirs.
Data for Simulation of Streamflow and Operations 25 Lake TahoeMartis Creek Lake

Prosser Creek

Reservoir

Boca

Reservoir

StampedeReservoir

Donner

Lake

Independence

Lake

Pyramid

Lake

Lahon

Reserv

169

150140130120 110

160

149

260250240

230

220210180170

280

290

270

300 310 320 330 340 350 360 370 380 390 400 410 420 430 440 450 460 

61

62

63 64 

580

49

187

188

189

198

185

194

199

195 208

178 209

145

168

168

100

Sagehen

Creek

Little Truckee Ditch

Little Truckee River

Independence

Creek

Steamboat Ditch

Coldron Ditch Katz Ditch

Dog Creek

Highland Ditch

North Truckee Drain

Truckee Ca

Carson River

Truckee River

Last Chance Ditch

Cochran Ditch

Eastman Ditch

Pioneer Ditch

Murphy Ditch

Groton Ditch

Steamboat Creek

Lake Ditch Orr Ditch

North Truckee Ditch

Sessions Ditch

Glendale Water Treatment Plant

Glendale Ditch

Noce Ditch

Sheep Ranch Ditch

McCarran Ditch

Hill Ditch

Washburn Ditch

Hunter Creek 

Hunter Creek Water

Treatment Plant Spill

Idlewild Water

Treatment Plant Highland Water

Treatment Plant Spill

Chalk Bluff Water Treatment Plant

Truckee Meadows Water Reclamation Facility

Derby

Diversion

Dam

Donner

Creek

Martis

Creek

Prosser

Creek

Truckee River

Truckee River

at Vista, Nev.

10350000 Truckee River at

Farad, Calif.

10346000

110

EXPLANATION

Reservoir reach and numRiver-reach number and U.S. Geological Survey s gaging station and ide numberGaged river outflow or in

 indicates direction of flo inflows not shown)

DIRECTION OF FLOW

Figure 3. Schematic diagram showing the river and reservoir reaches, outflo

ws, and inflows for the 

U.S. 

Geological 

Survey Truckee 

Rive
26 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

“Lower Truckee River Diversions”). The flow returned 

to the river from previously diverted water for agricultural uses could only be crudely estimated because 

ungaged returns from a given ditch could not be related 

to nearby gaged returns from other ditches. Agricultural irrigation return flows were estimated by applying simple return coefficients to diverted flows (Jeff 

Boyer, U.S. District Court Water Master, oral commun., 1993). M&I returns to the Truckee River were 

easier to estimate because they are measured at the 

Truckee Meadows Water Reclamation Facility. Simple 

return coefficients were determined for each month by 

comparing measured M&I diversions to measured 

M&I returns. M&I return flows were estimated by 

applying these return coefficients to flows diverted for 

M&I uses.

Time series containing estimates of tributary 

inflows or channel seepage losses for the reach 

between the Farad and Vista gaging stations also were 

estimated. Except for inflows from Dog Creek and 

Hunter Creek upstream from Reno, neither sufficient 

streamflow records from gaging stations nor detailed 

PRMS output were available to fulfill the need for 

gain/loss information for this reach of the Truckee 

River. Flow data measured at gaging stations, when 

available, or output from PRMS models provided daily 

inflows from Hunter Creek and Dog Creek. Except for 

inflows from these two basins, gains and losses for this 

reach of the river come from (1) water balance computation of net inflows (1981–92) or (2) regression analysis (1933–80, 1993–97). Truckee Meadows ungaged 

gains and losses (TMUGL) include all ground water 

inflows, tributary inflows, channel losses, and other 

gains except inflows from Dog and Hunter Creeks. 

TMUGL is computed as:

TMUGL =

Vista flow − (Farad + Dog Creek + Hunter Creek 

flows) + net agricultural and M&I diversions.

The daily values of TMUGL, which can contain 

both positive and negative values, are input upstream 

from inflows from the Truckee Meadows Water Reclamation Facility so that if the river “dries up” as a result 

of TMUGL, at least the treated sewage effluent flow 

volume will be present at the reach boundary representing the Vista gaging station.

Downstream from the Vista gaging station, all of 

the tributaries are ungaged and ephemeral. Tributary 

inflows for the Truckee River downstream from Vista 

and for the Truckee Canal do not normally supply large 

seasonal or annual volumes of water and therefore are 

not provided to the operations model.

Evapotranspiration

Time series of streamflow losses due to ET from 

phreatophytes were estimated (Berris, 1996). The time 

series were applied to the Truckee River downstream 

from the Vista gaging station. Upstream from Vista, 

streamflow losses were accounted for within the methods described above that provided inflows to and losses 

from the Truckee River. For the Truckee Canal, 

streamflow losses were accounted for by empirical 

methods and applied within the model code of the 

SPECL Block (Alan Olson, Bureau of Reclamation, 

written commun., 1996).

Climate

The operations model requires meteorologic data 

as precipitation and evaporation time series for simulation of reservoir and streamflow gains and losses. 

These time series were applied to lakes and reservoirs, 

except for Lake Tahoe, and to the Truckee River downstream from the Vista gaging station. Net inflows computed for Lake Tahoe include gains and losses from 

precipitation and evaporation. Upstream from Vista, 

gains to streamflow from precipitation and losses to 

streamflow from evaporation were accounted for 

within the methods described in the section above on 

streamflow data, that provided inflows to and losses 

from the Truckee River. For the Truckee Canal and 

Lahontan Reservoir, such gains and losses are 

accounted for by empirical methods and applied within 

the model code of the SPECL Block (Alan Olson, 

Bureau of Reclamation, written commun., 1996). A 

succeeding section, “Truckee River Diversions to 

Newlands Project,” further describes the use of computed gains and losses. 

Precipitation data applied to designated lake and 

reservoir reaches and channel reaches downstream 

from Vista were based on estimates or observed measurements obtained from National Weather Service climate stations, located in California, near Donner 

Memorial State Park (near Donner Lake), Truckee, 

Sagehen Creek, Boca Reservoir, and in Nevada, near 

Reno and Wadsworth. Estimates of daily precipitation 

data were necessary to extend the daily precipitation 

records at some of the above climate stations back to 
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 27

1933. Estimates were made by using a regional time 

series of daily precipitation data and computing the 

local time series of the appropriate climate stations 

listed above using statistical correlative methods (M.D. 

Dettinger, U.S. Geological Survey, written commun.,

1997, and Dettinger and Cayan, 1996). Average 

monthly evaporation rates for lake and reservoir 

reaches and channel reaches were estimated (Roderick 

L. Hall, Sierra Hydrotech, written commun., 1994; 

P.H. McGauhey and others, 1963; and S.W. Hostetler, 

U.S. Geological Survey, oral commun., 1994). 

Municipal and Industrial Demands

The operations model requires a time series of

M&I surface-water demand for the Truckee Meadows.

M&I demand is defined as the volume of water needed 

for the supply of a city, town or similar population

groups for the purposes of commerce, trade, or industry. This time series contains estimated M&I demand 

from surface-water sources in the Truckee Meadows

based on observed M&I demand data obtained from 

Sierra Pacific Power Company for the index period of

January 1995 through December 1995 (Richard D. 

Moser, Sierra Pacific Power Company, written commun., 1995). These estimates assume there is no variation of daily M&I demand from year-to-year. For 

model simulations, a growth coefficient based on the 

index period can be applied to the time series to simulate the increases or decreases in M&I demand resulting from population growth or decline. Thus, this time 

series can be considered an index time series that can 

be adjusted by the model user. This time series is used

to simulate M&I demand for water from channel 

reaches of the Truckee River between the Farad and 

Vista gaging stations in the operations model.

Lake Level and Streamflow Forecasts

Lake level and streamflow forecasts are often 

used to guide decisions in the model for reservoir and

river operations. Forecasts of lake levels at Lake Tahoe 

and flows at the gaging station Little Truckee River 

above Boca Reservoir, near Truckee, Calif., the Farad

gaging station, and the gaging station Carson River

near Fort Churchill, Nev., were provided by the Natural Resources Conservation Service (NRCS) (Rebecca

Wray, Natural Resources Conservation Service, written commun., 1995). Forecasts at these locations were 

computed using the Extended Streamflow Prediction

package (ESP) (Day, 1985) and the PRMS system 

(Leavesley and others, 1983) for those parts of the simulation period prior to the availability of NRCS forecasts. Other forecasts at locations and for periods not 

afforded by the NRCS also were computed using 

ESP/PRMS. All forecasts are for flows that would 

occur without regulation from upstream reservoirs.

DESCRIPTION AND SIMULATION OF 

TRUCKEE RIVER BASIN OPERATIONS

The constructed model simulates three major 

options regarding Truckee River Basin operational 

practices. The first option characterizes current (1998) 

operational practices and incorporates them into the 

model code of the SPCL block. The second option 

combines existing and proposed (draft TROA, WQSA) 

operations. The second option contains all of the constraints from the first option, but simulates additional

proposed operations. The third option simulates 

WQSA without draft TROA and is not described separately in this report.

The logic in the daily operations model represents 

the Truckee River operational practices that are governed by the water rights, court decrees, agreements, 

regulations, and informal conventions. Policies and 

rules within these legal documents can, therefore, be 

considered as quantitative and qualitative data that

guided the development of the model code. Successful

simulation of Truckee River Basin operations was 

achieved by representing these policies and rules in the 

code so that simulated flows and volumes conform to 

those legal constraints. 

The model simulates reservoir and river operations as governed by both physical processes and legal

constraints. Initial volume and flow conditions are 

derived from user-specified initial conditions. The

general logic in the operations model used to characterize current and proposed rules and policies governing 

Truckee River operations is shown as a flowchart on 

figure 4. Boxes on figure 4 represent one or more operational subblocks in the SPECL block of the model. 

The following discussion provides a generalized overview of the model subblocks and terms as shown in the 

flowchart. The subblocks are grouped in general classifications, and each classification is defined and discussed. To simplify this overview, the model subblocks 

are only generally referenced, and therefore the discussion of the general classifications in this section does 
28 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

not follow the same order as the boxes in the flowchart

(fig. 4). The subblocks, shown in bold italics, are discussed in more detail in subsequent sections, as will 

undefined terms introduced in the following overview.

For each time interval, miscellaneous constants 

and flags are assigned in the SPECL subblock called 

initial assignments and computations. Initial assignments and computations are made prior to simulations 

of releases, diversions, and exchanges. They include 

miscellaneous constants such as reservoir outlet 

capacities based on current reservoir stage; irrigation 

demands transferred to other uses, such as M&I demand or water-quality demand; minimum, enhanced, 

and preferred flow targets; recreation pool levels; 

Floriston rates targets; and M&I credit water base 

amounts. 

Many of these assignments are provided as 

default values, but because they may be revised by the 

modeler, they are called user options. Flags are integer 

values that direct a model run to simulate designated 

parts of model code. Flags may be user-option flags or 

computed flags. User-option flags may be revised by 

the modeler. Computed flags are assigned by the model 

code during a simulation. 

Flood-control criteria, simulated in the subblock 

flood-control criteria, determine when and how much 

water must be released from reservoirs to maintain 

reservoir flood-control space and thus minimize potential downstream flood damages. Flood-control criteria 

govern operations for all major reservoirs in the study 

area except for Lake Tahoe, where flood-control operations have not been formalized. Flood-control operations are different for each reservoir, and may include 

storage of water to avoid downstream flooding; precautionary drawdowns to avoid spills by decreasing 

reservoir storage to a lower threshold for the winter, 

called the wintertime cap; maintenance of the wintertime cap; spring filling rules; and maintenance of maximum reservoir volume during the summer. Floodcontrol operations are simulated by adjustment of 

reservoir releases. Uncontrolled spills, as the name 

suggests, cannot be managed but are computed within 

this subblock because they are closely related to floodcontrol criteria. Uncontrolled spills and flood-control 

operations have priority over other operations and are, 

therefore, simulated before other operations. Although 

operations based on flood-control criteria are not tied to 

specific water categories, water categories are assigned 

to releases determined for flood-control operations 

during simulations.

Storage priorities of reservoirs under current 

operations, simulated in the subblock reservoir storage 

priorities and pass-through requirements, dictate 

when and how much water of a specific water category 

can be stored in reservoirs. The principal water category that a reservoir was built or authorized to provide 

storage for is often called project water. Depending on 

reservoir priorities, current reservoir storage, and legal 

constraints, a reservoir may store project water by 

retaining all or part of reservoir inflow. If a reservoir 

does 

not currently have priority to store any project water, 

then that reservoir must “pass through” all inflows to 

a downstream reach for a higher-priority use, such as 

maintenance of Floriston rates or diversion to the 

Truckee Canal. Thus, by adjustment of reservoir 

releases in model simulations, a reservoir may store 

inflows or release stored water. Pass-through water 

retains the same category, but water may be stored 

under different categories depending on current 

reservoir storage and legal constraints. Some storage 

operations are allowed that facilitate coordination 

of reservoir releases to increase operational efficiency 

or are made by contractual agreement. These storage 

operations include contract storage in Stampede 

and Boca Reservoirs and storage of PCPOSW 

(Power Company privately owned stores water) in 

Boca Reservoir.

Just as simulated flood-control criteria determine 

when and how much water must be released from reservoirs, numerous simulated demands for water also 

dictate releases from reservoir storage. These demands 

are satisfied by adjustment of simulated reservoir 

releases and are typically prioritized on the basis of 

various rules, policies, and conventions. Computations 

that specify these release adjustments are made within 

several subblocks that simulate maintenance of Floriston rates and instream flows, and satisfaction of a 

number of demands including Power Company M&I, 

Newlands Project irrigation and wetlands supply, 

Pyramid Lake fishes, California M&I, and waterquality demands. Releases may consist of either 

“tagged” or “untagged” waters. Tagged releases must 

consist of specific water categories whereas untagged 

releases may consist of any category in the reservoir. 

The assignment of various categories to untagged 

releases is discussed in a subsequent section, “Merge 

Reservoir Releases for Multiple Objectives.” When 

categories are assigned to the untagged water for a 

given time interval, they become tagged releases for 
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 29

BEGIN:

New computational

time step

Initial assignments

and computations

Flood control criteria

releases and

uncontrolled spills

Floriston Rates

demands and

releases

Sierra Valley

diversions

Power company M&I

demands, releases,

and diversions

Truckee Meadows

diversions

Lower Truckee River

diversions

Truckee River

diversions to

Newlands Project

Pyramid Lake fish

demands and

releases

Water-quality

demands and

releases

TROA California M&I

demands and

releases

Reservoir storage

priorities under

current operations

Minimum instream

flow demands and

releases

Merge reservoir

releases for multiple

objectives

Exchanges under

current operations

TROA enhanced

minimum instream

flow demands and

releases

TROA credit water

storage

TROA mandatory

exchanges

TROA voluntary

exchanges

Assign inflow/outflow

values for input to

flow-routing

Flow-routing

END:

Current

computational

time step

Figure 4. Generalized flowchart of U.S. Geological Survey Truckee River Basin operations model
30 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

just that time interval. Releases specified in this overview are tagged releases except for those necessary to 

maintain current minimum flows and those based on 

flood-control criteria. Although maintenance of current 

minimum flows may require reservoir releases, usually 

no specific water categories are dedicated for their 

maintenance. As with any release, releases to meet 

demands are constrained by the capacity or hydraulic 

rating of the outlet works of each dam for a given storage level. It is assumed that all outlet gates in the penstock and spillway are open when determining the 

maximum release from each reservoir.

The term “river diversions” is used to reference 

simulated river operations that divert water from a 

channel reach to a specific off-river point of use. These 

diversions are usually outflow boundaries, and, except 

for return flows, water diverted from a channel reach is 

assumed to be consumptively used and is lost from the 

simulation. However, water diverted to the Truckee 

Canal is routed to Lahontan Reservoir along designated 

reaches. M&I and agricultural demands govern the 

volume of water diverted from each of the channel 

reaches. For the three simulation options described 

previously, diversions of specific water categories are 

determined by subblocks governing diversions in four 

segments of the flow-routing model: (1) diversions 

from the Little Truckee River to Little Truckee Ditch 

for agricultural demands in California outside of the 

Truckee River Basin, determined in the subblock 

Sierra Valley diversions; (2) diversions from the 

Truckee River between the Farad and Vista gaging 

stations to various ditches and intakes for M&I and 

agricultural demands in the Truckee Meadows, determined in the subblock Truckee Meadows diversions; 

(3) diversions from the Truckee River downstream 

from the Vista gaging station, except for the Truckee 

Canal, to various ditches for agricultural demands, 

determined in the subblock lower Truckee River diversions; and (4) diversion from the Truckee River to the 

Truckee Canal for project demands (agricultural and 

wetlands) of both the Truckee and Carson Divisions of 

the Newlands Project, determined in the subblock 

OCAP. Additionally, under the draft TROA simulation 

option, diversions from the Truckee River near the 

town of Truckee, Calif., are simulated for California 

M&I uses in the subblock California M&I demands. 

Diversions are influenced by various parameter assignments in the initial assignments and computations

subblock. For example, the diversion from the Little 

Truckee River to the Little Truckee Ditch is influenced 

by natural flow at the Farad gaging station, calculated 

as outlined by the Sierra Valley Decree in the initial 

assignments and computations subblock. Diversions 

also exert influence on other simulated operations. For 

example, the forecasted diversion of water from the 

Truckee River to the Truckee Canal in the OCAP subblock influences reservoir releases for Pyramid Lake 

fish determined in the subblock that satisfies cui-ui 

spawning demands. Water may also be diverted 

directly from Lake Tahoe and Donner Lake for local 

M&I use. 

Proposed reservoir releases that satisfy water 

right demands and other operational requirements are 

compared and evaluated to determine a merged release 

value for each reservoir in the subblock merge. The 

merge subblock assigns water categories for those proposed releases that do not require a specific category 

because, for accounting, all releases must be assigned 

to water categories. These untagged releases come 

from the subblocks that compute releases necessary to 

meet flood-control criteria and releases to make minimum flows. If both untagged and tagged waters must 

be released, then the untagged waters will be satisfied 

by the volume of tagged water released, and will 

assume the categories of the tagged-water demands up 

to a maximum of the proposed tagged releases. If 

untagged releases are greater than the demand for 

tagged releases, then categories are assigned, by a priority scheme, to that part of the untagged release that is 

greater than the proposed tagged releases. For example, 

suppose flood-control operations require an untagged 

release of 100 ft3/s from a reservoir. Water categories 

must be assigned to the entire untagged release. The 

untagged release may assume up to 100 ft3

/s of various 

water categories from tagged releases from that reservoir. Thus, if tagged releases of 100 ft3/s are 

proposed, then the entire untagged release will be 

satisfied by the 100 ft3/s tagged releases and the 

untagged release may assume the categories of the 

tagged releases. However, if the tagged releases are 

only 60 ft3/s, then only 60 ft3

/s of the 100 ft3/s 

untagged release will assume those water categories 

from the tagged releases, and then categories, if present 

in reservoir storage, must be assigned to the remaining 

untagged release of 40 ft3/s. 

A commonly used water-management transaction 

known as water exchange allows reservoir operators to 

meet multiple-use goals by moving stored water from 

one reservoir to another. Exchanges always involve 

specific quantities of specific water categories. There 
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 31

are three types of exchanges: (1) nonphysical exchange 

of a volume of water in one or more reservoirs for water 

in one or more other reservoirs, which, for this report, 

will be referred to as a paper exchange; (2) release of 

water from one reservoir for storage in a downstream 

reservoir, often called re-storage; and (3) release of 

one or more categories of water from one or more reservoirs in lieu of a release of water of yet another category from one or more other reservoirs, often called an 

in-lieu-of exchange. Exchanges always occur after all 

demands and constraints are considered to arrive at a 

proposed release. Exchanges are commonly meant to 

modify proposed releases of individual reservoirs, but 

not the total release from all reservoirs. 

Related to an exchange, the term transfer is used 

in this report to describe another mechanism to establish or accumulate proposed water categories. 

Although exchanges also may be used to establish or 

accumulate proposed water categories, transfers 

involve only one reservoir and the gain of a water category volume results from the conversion, or loss, of 

another category volume. Unlike exchanges, with 

transfers, the total releases from reservoirs may be 

modified. For example, a proposed reservoir operation 

called credit storage involves the transfer of the water 

category pooled water to a new credit water category. 

The volume of pooled water is transferred to a new 

credit water category retained in storage as a result of 

the reduction of the pooled water release. 

Simulation of current operations and, to a greater 

extent, proposed operations use exchanges and transfers of water categories between or within reservoirs as 

a method to attain multi-purpose storage and release 

objectives. Exchanges that are currently practiced are 

limited, but include a Tahoe–Prosser Exchange and a 

Donner–Boca Exchange. Both exchanges are simulated in the subblock current exchanges. Listed below 

are exchanges and transfers that are a part of proposed 

operations and the operations model subblocks in 

which they are simulated.

• Exchanges to meet draft TROA enhanced and 

preferred instream flows—simulated in the 

subblocks enhanced minimum instream flows

and preferred instream flows, respectively.

• Transfers to establish and store proposed water 

categories—simulated in the subblocks California M&I creation and credit storage.

• Several miscellaneous exchanges and transfers 

that involve storage rules of proposed water category volumes in specific reservoirs—simulated 

in the subblock TROA mandatory exchanges.

• Voluntary exchanges that involve specific objectives, such as exchanges of water categories for 

more efficient use of reservoir spills and drawdowns, maintenance of recreational pools, 

and optimal locations (in terms of security and 

access) for storage—simulated in the subblocks 

enhanced storage security, efficient use of 

releases, and maintenance of recreational pools. 

Simulated transfers are specified by criteria in 

draft TROA, but exchanges may be mandatory or voluntary. Mandatory exchanges are specified for certain 

water categories and purposes in draft TROA. Voluntary exchanges would be requested by interested parties. The types of water exchanges and water categories 

involved with voluntary exchanges are discussed in 

more detail later in the text.

For simulation of proposed operations, exchanges 

and transfers are important methods to modify simulated reservoir releases. To simulate proposed minimum and preferred instream flows downstream from a 

reservoir, for example, proposed water categories 

might be exchanged between two reservoirs, resulting 

in reduced releases from one reservoir and increased 

releases from the reservoir upstream from the instream 

flow requirement. Another example involves simulated 

storage of proposed water categories by a transfer. 

Establishment of Power Company M&I credit water, 

for example, involves storage of the consumptive use

portion of former agricultural water rights adjudicated 

by the Orr Ditch Decree (United States of America v. 

Orr Ditch Water Company, Equity No. A-3 (D. Nev. 

1944)) and acquired by Power Company for M&I use. 

Storage of Power Company M&I credit water may only 

be implemented to the extent that a reservoir would be 

releasing or passing through water to satisfy Orr Ditch 

Decree rights and, thus, Floriston rates. Therefore, 

water that would be released to maintain Floriston 

rates would be held in reservoir storage and assigned 

(transferred to) the category of Power Company M&I 

credit water.

The preceding discussion provided a general 

overview of the simulation of many current and proposed types of operations that move volumes of water 

from one reach to another, from one water category to 
32 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

another, or out of a reach during a time interval. The 

result of these operations is water volumes diverted, 

exchanged, or released from channels and reservoirs. 

These volume and flow quantities are used by the 

RCHRES block of HSPF to route flows, move water 

from reaches through various outlets, and exchange 

water categories from one reservoir to another.

Description and Simulation of 

Current Operations

Current reservoir and river operations are implemented primarily by adjusting reservoir releases, 

exchanging water categories between reservoirs, and 

diverting specific water categories from a channel. 

Adjustment of reservoir releases allows the reservoir 

operator to pass through inflows to downstream 

reaches, store inflows, and release water from reservoir 

storage for a variety of objectives. Exchanging water 

categories between reservoirs enables water managers 

to meet multiple-use goals. Finally, river diversions to 

meet irrigation and M&I demands are based on water 

rights. The following sections describe currently designated water categories, currently practiced river and 

reservoir operations, and losses and gains to reaches.

Current Water Categories

The following water categories and their definitions are used in the USGS Truckee River Basin operations model to simulate current reservoir and river 

operations.

• fish water—Waters stored in or released from 

Stampede Reservoir, uncommitted water released 

from Prosser Creek Reservoir, or other waters 

released to the Truckee River for the benefit of 

threatened or endangered fishes of Pyramid Lake.

• natural water—Water that originates from 

flow in Truckee River tributary subbasins not 

regulated by a reservoir or from flow that is 

passed through a reservoir without detention, 

except Lake Tahoe.

• pooled water—Water stored in Lake Tahoe and 

Boca Reservoir pursuant to the Orr Ditch Decree 

and the Truckee River Agreement that is dedicated to supporting Floriston rates. Also included 

in this designation are adverse- and non-adverseto-canal waters stored in the reservoir. Adverseto-canal water, historically referred to as supplemental storage water, refers to the first 25,000 

acre-ft of pooled water stored (or, if a lesser 

quantity is stored, then such lesser quantity) in 

Boca Reservoir in a given water year. Nonadverse-to-canal water, historically referred to 

as additional supplemental storage water, 

refers to pooled water stored in addition to 

adverse-to-canal water up to the capacity of Boca 

Reservoir. Non-adverse-to-canal water cannot be 

stored adverse to Truckee Canal diversions.

• privately owned stored water (POSW)—Water 

stored under the water rights of Power Company 

in Independence Lake and the water rights of 

Power Company and TCID in Donner Lake.

• Tahoe–Prosser Exchange water (TPEW)—

Water stored in Prosser Creek Reservoir that is 

established in accordance with the Tahoe–Prosser 

Exchange Agreement and intended to be released 

for the purpose of maintaining Floriston rates. 

• uncommitted water—Water stored in Prosser 

Creek Reservoir that is dedicated to the purposes 

of the Tahoe–Prosser Exchange Agreement for 

the establishment of Tahoe–Prosser Exchange 

water. Uncommitted water can be used for the 

benefit of threatened and endangered fishes of 

Pyramid Lake.

Current Reservoir Operations

Current reservoir operations are governed by 

rules in legal decrees and agreements. These reservoir 

operations primarily involve the adjustment of reservoir releases, but also include exchanges of water 

between reservoirs in the Truckee River Basin. This 

section describes currently-practiced reservoir operations and discusses how each operation is implemented 

in the model.

Flood-Control Criteria

Flood-control criteria are rules that specify 

(1) mandatory reservation of flood-control space in 

reservoirs and (2) maximum downstream river flows. 

Two types of spills are closely related to operations for 

flood-control criteria. First, an uncontrolled spill can 

occur when reservoir levels rise and outflows cannot 

be regulated by reservoir outlet structures. During 

uncontrolled spills, additional reservoir storage 

(termed surcharge) may actually exceed design storage 

values when inflows exceed the hydraulic capacity of 
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 33

the dam spillway. The second type, precautionary 

drawdown releases or controlled (planned) spills, 

occur when water is released through reservoir outlet 

structures only to lower the reservoir level and maintain flood-control space in the reservoir. 

Truckee River Basin reservoirs are operated 

for flood-control criteria based on various regulations 

and procedures specified in several documents from 

different agencies. Martis Creek Lake and Prosser, 

Stampede, and Boca Reservoirs are operated in accordance with USCOE flood-control criteria (U.S. Army 

Corps of Engineers, 1985). Lake Tahoe has no USCOE 

flood-control criteria, but is managed according to the 

Truckee River Agreement. Donner and Independence 

Lakes are operated to comply with California licensing 

requirements and dam safety criteria. Flood-control 

criteria for Lahontan Reservoir is specified for emergency and general release procedures (Dave Overvold, 

Bureau of Reclamation, written commun., 1996, 1997).

Flood-control criteria operate seasonally: fall, 

winter, spring, and summer. The fall precautionary 

drawdown period requires that reservoir levels be 

lowered to ensure sufficient flood-control space during 

the winter and spring. The drawdown period typically 

begins in late summer and ends by about November 1. 

During the winter, the reservoirs maintain flood-storage space at a constant reservoir elevation of wintertime cap. This period is typically November to late 

March. The spring filling season, from about April to 

June, is the period when the reservoirs are filled to 

maximum storage capacity with snowmelt runoff. 

During the summer months, from June to August, 

reservoirs are managed to meet downstream demands.

The following sections describe the flood-control 

criteria for each reservoir under current operations and 

as simulated in the operations model in the subblock 

flood-control criteria. General assumptions for floodcontrol criteria for all reservoirs in the model are as follows: the maximum release is based on the outlet 

capacity for each reservoir with all outlet gates open 

except for Lake Tahoe; when the reservoir elevation is 

less than the spillway crest, the outlet capacity is the 

outlet discharge rating curve; when the reservoir elevation is greater than the spillway crest, the outlet capacity is both the outlet and the spillway rating curves; and 

when the simulated flow is larger than 6,000 ft3

/s at 

Truckee River at Reno (reach 350), Prosser, Stampede, 

and Boca Reservoirs are simulated according to floodcontrol criteria to minimize releases and, therefore, to 

maximize storage below their respective reservoir 

spillway elevations.

Lake Tahoe

The portion of Lake Tahoe controlled by Tahoe 

Dam provides 744,600 acre-ft of storage between the 

natural rim elevation of 6,223.0 ft and the maximum 

storage elevation of 6,229.1 ft (U.S. Geological Survey, 1996, p. 336). The goal of Lake Tahoe flood operations is to not allow the lake elevation to exceed 

6,229.1, as specified in the Truckee River Agreement 

of 1935. Estimates of the forecasted rise of the lake are 

made on March 1 and April 1 of each year. When the 

current lake elevation is less than 6,228.0 ft, but the 

estimated rise is expected to exceed 6,230.0, the outflow is set to the maximum rate possible to remove 

that amount of water forecasted to be in excess of 

6,230.0 ft. When the current lake elevation exceeds 

6,228.0, the outflow is set to the maximum rate possible to remove that amount of water forecasted to be in 

excess of 6,229.1 ft (the maximum storage elevation). 

At low lake levels, maximum outflow rates are hydraulically controlled by the natural rim of the lake. At 

high lake levels, the dam is the dominant control for 

outflows. The FWM attempts to keep Lake Tahoe 

releases to the Truckee River to less than 2,600 ft3/s 

to avoid potential damage to a downstream sewage 

pipeline and other property damage. There is no emergency spillway, nor are there fall precautionary drawdowns or spring filling seasons defined for the lake.

The USGS Truckee River Basin operations 

model simulates operations resulting from high lake 

levels for Lake Tahoe as follows. In the subblock 

flood-control criteria, if the simulated Lake Tahoe elevation is less than 6,227.8 ft, there is no flood control 

release. When the simulated lake elevation is greater 

than 6,227.8 ft, the model forecasts probable maximum 

elevation of the lake for the year. If the forecasted elevation is less than 6,228.5 ft, then flood control release 

is set to zero. If the forecasted elevation is greater than 

6,228.5 ft, then flood control releases are determined 

for two cases: If Truckee River flow at Reno (reach 

350) is greater than 6,000 ft3

/s, the lake release is set to 

the inflow up to a maximum of 2,600 ft3/s; otherwise, 

the forecasted volume in excess of 6,228.5 ft is then 

released uniformly as a precautionary drawdown over 

the next 30 days to achieve an elevation of 6,228.5 ft 

at the end of the 30-day period. When the lake elevation 
34 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

is higher than 6,229.1 ft, releases are considered, in the 

operations model, to be uncontrolled spills from the 

lake and outflows are compared to the maximum of 

2,600 ft3

/s.

Donner Lake 

Donner Lake, operated by the Power Company, 

can provide a maximum effective flood control space 

of about 6,000 acre-ft (Richard D. Moser, Sierra 

Pacific Power Company, oral commun., 1999) due to 

outlet channel constraints just upstream from Donner 

Lake Dam. Releases to avoid potential problems 

caused by high water levels are established by California Division of Safety of Dams regulations (Richard D. 

Moser, Sierra Pacific Power Company, oral commun., 

1995). Within these regulations, the lake is operated 

using hydrologic judgement, information about current 

lake elevation, forecasted runoff conditions, and historical lake inflow patterns (Richard D. Moser, Sierra 

Pacific Power Company, oral commun., 1995). Hydrologic judgement is defined as using available or forecasted hydrological and meteorological data to make 

an operational decision. Uncontrolled spills above a 

lake elevation of 5,935.8 ft will equal the lake inflows. 

The fall precautionary drawdown season is typically 

defined as September 1 to November 15. During this 

period, the lake elevation is reduced to 5,926.9 ft to 

provide flood-control space. At that elevation, the 

upper two gates in the dam are held in the open position 

from November 16 to about April 15. However, partial 

filling of the lake may be allowed earlier if forecasts 

indicate below-average runoff conditions. 

The Donner Lake springtime filling season 

occurs from about April 16 to June 15 when the lake 

can be filled to a maximum allowable elevation of 

5,935.8 ft, using a flexible schedule based on runoff 

projections. When the lake elevation is less than the 

spillway crest, the outlet capacity is the outlet discharge rating curve (Richard D. Moser, Sierra Pacific 

Power Company, written commun., 1995). When the 

lake elevation is greater than the spillway crest, the 

outlet capacity is the spillway rating curve (Richard D. 

Moser, Sierra Pacific Power Company, written commun., 1995). The emergency spillway becomes effective at an elevation of 5,936.8 ft. 

The preceding Donner Lake flood-control criteria 

were implemented in the code as follows. Lake releases 

are simulated on the basis of the flood-control criteria 

from uncontrolled spills and precautionary drawdowns. 

The flood-control criteria can be separated into five 

conditions or periods: uncontrolled spills, fall, winter, 

spring, and summer. To simulate uncontrolled spills 

when the lake elevation is greater than 5,935.8 ft, the 

releases are set equal to the inflow times 1.5., a factor 

that approximates the hydrologic judgement typically 

used for uncontrolled spill operations. During the fall 

precautionary drawdown season, September 15 to 

November 15, lake elevation is lowered to and maintained at 5,926.9 ft. During this period, any water 

above this elevation is calculated daily and parcelled 

into daily volumes for prorated release from the current 

date until November 15. Wintertime reservoir capacity 

is specified in the code from November 16 to May 1 on 

the basis of a qualitative “runoff index,” which designates an upcoming runoff season as wet, average, or 

dry according to forecasts (see the section “Runoff 

Index,” under the section “Forecasts Affecting Operational Decisions”). For example, under conditions forecast as dry, as determined by the runoff index, the 

wintertime reservoir capacity is increased beginning 

February 15, earlier than under normal or wet forecast 

conditions. When reservoir storage exceeds the wintertime cap, the amount exceeding the wintertime cap 

is released. Springtime reservoir capacity is specified 

in the code from May 2 to June 15 based on the runoff 

index and storage curves provided by Richard D. 

Moser (Sierra Pacific Power Company, written commun., 1995). The allowable reservoir storage is calculated every 15 days and releases are simulated on the 

basis of the amount of storage above the calculated 

springtime reservoir storage. In the summer, from June 

16 to September 14, storage above 5,935.8 ft is 

released. 

Martis Creek Lake

Martis Creek Lake, operated by the USCOE, 

can provide 20,000 acre-ft of flood-control space. 

However, the full capacity of Martis Creek Lake is 

rarely used and never for extended storage. USCOE 

regulations state that outlet releases are limited to 100 

ft3/s during periods of normal inflows (U.S. Army 

Corps of Engineers, 1985, p. VII-3). When forecasts 

indicate the flow at Truckee River at Reno will exceed 

14,000 ft3

/s, Martis Creek Lake outflow gates are 

closed. When Truckee River at Reno flow is between 

6,000 ft3/s and 14,000 ft3

/s, Martis Creek Lake outflow 
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 35

is limited to the inflow. There is no specified fall precautionary drawdown season or spring filling season 

defined for Martis Creek Lake.

The Martis Creek Lake flood-control criteria 

were implemented in the code as follows. In the subblock flood-control criteria, when the simulated Martis Creek Lake elevation is greater than 5,838.0 ft and 

the Truckee River flow at Reno (reach 350) is greater 

than 6,000 ft3/s, the uncontrolled spill is set equal to the 

inflow. Flood control releases for Martis Creek Lake 

are simulated depending on Truckee River at Reno 

flow and reservoir levels under the following conditions. When flow at Truckee River at Reno exceeds 

14,000 ft3

/s, Martis Creek Lake outflow is set to zero. 

When Truckee River at Reno flow is between 6,000 

ft3/s and 14,000 ft3

/s, Martis Creek Lake precautionary 

drawdown releases are limited to reservoir inflow. 

When Martis Creek Lake level is less than 5,782 ft, 

precautionary drawdowns are set equal to inflows. 

Outlet releases are limited to a maximum of 100 ft3

/s 

during non-flood periods.

Prosser Creek Reservoir

Prosser Creek Reservoir is operated by BOR 

and can provide 20,000 acre-ft of flood-control space 

when the wintertime cap is in place. When the reservoir 

level exceeds 5,741.2 ft, the discharge rating curve 

(U.S. Army Corps of Engineers, 1985, Chart A-4-2) 

dictates releases for the reservoir spillway. The fall 

precautionary drawdown season is defined as October 

1 to October 31 (U.S. Army Corps of Engineers, 1985). 

However in practice, reservoir precautionary drawdowns can begin as early as September 1. This early 

drawdown date allows basin managers more flexibility 

in attaining multiple uses with reservoir releases to create flood-control space. During this period, the reservoir’s elevation is reduced to 5,703.7 ft and held at or 

below this level from November 1 to April 9. The 

spring filling season lasts from April 10 to May 20, 

based on runoff conditions, but filling can be delayed to 

as late as July 4 in wet years. If forecasted runoff is 

higher than certain volumes specified by the USCOE 

Flood-Control Diagram (U.S. Army Corps of Engineers, 1985, Chart A-8-1), then additional reservoir 

flood space must be maintained to accommodate the 

increased flood threat. 

The guidelines and rules for Prosser Creek Reservoir flood-control criteria were implemented in the 

code as follows. In the subblock flood-control criteria, 

uncontrolled spills and precautionary drawdowns are 

simulated. When the simulated reservoir elevation is 

greater than 5,741.2 ft, uncontrolled spills are set equal 

to the hydraulic rating of the river outlet structure and 

spillway combined. During the fall precautionary 

drawdown season, the storage volume simulated above 

reservoir elevation of 5,703.7 ft is calculated daily 

beginning September 3 and precautionary drawdowns 

releases are parcelled into equal daily volumes for prorated release from the current date to October 31. When 

reservoir storage exceeds the 5,703.7 ft wintertime cap, 

that excess water is released as precautionary drawdowns. Allowable storage during the springtime filling 

season from April 10 to July 4 is based on the USCOE 

Flood-Control Diagram (U.S. Army Corps of Engineers, 1985, Chart A-8-1). Simulations of daily 

releases of precautionary drawdowns are based on 

the amount of allowable reservoir storage shown by 

this diagram.

Independence Lake

Independence Lake, operated by the Power Company, can provide a maximum effective flood control 

space of 3,000 acre-ft during periods when the wintertime cap is in place. Releases to avoid potential problems caused by high water levels are established by 

California Division of Safety of Dams regulations. 

Within these flood-control criteria, the lake is operated 

using hydrologic judgement and information about current lake elevation, forecasted runoff, and historical 

lake inflow patterns (Richard D. Moser, Sierra Pacific 

Power Company, oral commun., 1995). When the lake 

levels exceed 6,949.3 ft (17,500 acre-ft), uncontrolled 

spills begin, which are governed by the spillway rating 

(Richard D. Moser, Sierra Pacific Power Company, 

written commun, 1995) to avoid endangering the dam 

structure. The fall precautionary drawdown season is 

defined as August 15 to November 1. During this 

period, the lake elevation is reduced to the elevation of 

the flashboards in the two bays of the emergency spillway (6,944.7 ft) (Richard D. Moser, Sierra Pacific 

Power Company, oral commun., 1999). This flood 

space allows for additional storage during high runoff 

periods in the winter. Independence Lake is typically 

held below 6,946.3 ft from November 2 to May 15. The 

springtime filling season begins May 15 and continues 

until about July 15 when the lake is filled to a maximum stage of 6,949.3 ft or storage of 17,500 acre-ft. 

The Power Company uses flexible schedules to fill the 
36 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

lake, based on runoff projections and consideration of 

temperature and remaining snowpack with reservoir 

filling at the end of the runoff period. 

The guidelines and rules for Independence Lake 

flood-control criteria were implemented in the code as 

follows. In the subblock flood-control criteria, uncontrolled spills and precautionary drawdowns are simulated. When the simulated lake elevation is greater than 

6,949.3 ft, the uncontrolled spills are set equal to the 

inflow times 1.5, a factor used as an approximation of 

the hydrologic judgement typically used for uncontrolled spill operations. During the fall precautionary 

drawdown season, the simulated volume above lake 

elevation of 6,944.7 ft is calculated on August 15 and 

October 17 and precautionary drawdowns are parceled 

into equal daily volumes for prorated releases from the 

current date to November 1. Wintertime (November 2 

to June 1) storage limit is based on the runoff index. 

For example, if the index forecasts below-average runoff conditions, the wintertime cap limit capacity is 

increased beginning February 1. When reservoir storage exceeds the current wintertime cap, the excess is 

released. The lake storage limit during filling season 

(June 2 to July 15) is based on the runoff index and 

storage curves provided by R. Moser (Sierra Pacific 

Power Company, written commun., 1995). The allowable reservoir storage is calculated every 7 days and 

precautionary drawdowns are based on the amount of 

storage in excess of the allowable reservoir storage 

limit. From July 16 to August 14, when reservoir levels 

exceed 6,948.5 ft, the excess greater than that amount 

above 6,948.5 ft is released.

Stampede and Boca Reservoirs

Stampede and Boca Reservoirs, operated by the BOR 

and WCWCD, respectively, provide a combined total 

of 30,000 acre-ft of flood-control space. These two 

reservoirs are operated in tandem for flood control. 

The fall precautionary drawdown season is defined 

as October 1 to October 31. During this period, the 

Stampede and Boca Reservoir elevations are reduced 

to the wintertime storage limits of elevation of 5,942.1 

ft and 5,596.4 ft, respectively. These elevations are 

held through the winter from November 1 to April 9. 

Springtime filling season for the reservoirs is from 

April 10 to July 4. Springtime filling criteria are constrained by the USCOE Flood-Control Diagram (U.S. 

Army Corps of Engineers, 1985, Chart A-8-2). Also, 

when Boca Reservoir levels exceed 5,605.0 ft, uncontrolled spills are governed by the Emergency Spillway 

Release Diagram (U.S. Army Corps of Engineers, 

1985, Chart A-9).

The guidelines and rules for Stampede Reservoir 

flood-control criteria were implemented in the code as 

follows. When the simulated reservoir elevation is 

greater than 5,948.7 ft, uncontrolled spills are simulated as the maximum capacity of the river outlet 

structure and spillway. During fall precautionary 

drawdown season, the storage volume simulated above 

the reservoir elevation of 5,942.1 ft is calculated daily 

and releases are parcelled into equal daily amounts 

from October 1 until October 31. A wintertime cap of 

5,942.1 ft is specified from November 1 to April 9. 

When reservoir storage exceeds the wintertime cap, the 

excess water is released as precautionary drawdowns. 

Releases due to precautionary drawdowns during the 

springtime filling season are made in accordance with 

the USCOE Flood-Control Diagram (U.S. Army Corps 

of Engineers, 1985, Chart A-8-2). 

The guidelines and rules for Boca Reservoir 

flood-control criteria were implemented in the code as 

follows. In the subblock flood-control criteria, when 

the reservoir elevation is greater than 5,600.0 ft, the 

uncontrolled spills are simulated as the volume of 

water above 5,600.0 ft and are constrained by the 

hydraulics of the outlet works and spillway. During 

the fall precautionary drawdown season, any storage 

greater than the reservoir elevation of 5,596.4 ft is calculated daily and released as precautionary drawdowns 

in equal daily amounts from October 1 until October 

31. A wintertime cap of 5,596.4 ft is maintained from 

November 1 to April 9. When reservoir storage 

exceeds the wintertime cap, the excess water is 

released. Releases for precautionary drawdowns 

during the springtime filling season are made in accordance with the USCOE Flood-Control Diagram (U.S. 

Army Corps of Engineers, 1985, Chart A-8-2).

Lahontan Reservoir

Lahontan Reservoir, operated by TCID, provides 

317,700 acre-ft of storage between 4,060.0 ft and 

4,163.67 ft, the maximum reservoir elevation with 

flashboards on the spillway crest (U.S. Geological 

Survey, 1996, p. 184). The current average height of 

the flashboards is 18 inches, which creates a reservoir 

storage volume of 316,900 acre-ft. Operating criteria 

do not allow the reservoir water surface to rise on the 

flashboards until the peak spring runoff has passed 
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 37

(Alan Olson, Bureau of Reclamation, written commun., 1999). Lahontan Reservoir flood operations are 

designed to prevent the reservoir elevation from 

exceeding a monthly maximum as specified in BOR 

regulations “General Filling Schedule and Release 

Procedures” for the reservoir (Alan Olson, Bureau of 

Reclamation, written commun., 1996). Estimates of the 

rise of the reservoir are forecasted on April 1 of each 

year. When the forecasted rise exceeds the maximum 

allowable storage limits, water is released to satisfy 

precautionary drawdown criteria. Outflow rates are 

confined by the maximum capacity of the reservoir 

power plant and river outlet works to about 2,500 ft3

/s. 

Any large releases or uncontrolled spills over the spillway greater than 2,000 ft3

/s can create localized flooding downstream from the reservoir. This condition is 

avoided whenever possible. Spring filling elevations 

defined for the reservoir are based on the optimal storage targets set forth for each month in OCAP. 

The criteria upon which flood-control releases 

due to pre-cautionary drawdowns are simulated within 

the USGS Truckee River Basin operations model in the 

subblock flood-control criteria as follows. Precautionary drawdown releases for Lahontan Reservoir are 

defined as those releases over and above the normal 

releases to meet project demand. If the daily stage of 

Lahontan Reservoir is less than 4,156.0 ft, then the 

flood-control release is set equal to 0. If the daily stage 

of Lahontan Reservoir is greater than 4,156.0 ft but less 

than 4,163.0 ft, a forecasted reservoir volume is computed, based either on NRCS forecasts of April–July 

runoff volume for the Carson River near Fort Churchill 

(used in code computations for the period JanuaryMay) or daily inflow times 21 days (used in code computations for the period June-December). The forecasted volume provides an estimate of inflow in the 

next three weeks to approximate the judgement used 

for reservoir operations. Projected releases to meet 

project demand and projected reservoir losses are not 

considered in this calculation. If the daily stage of 

Lahontan Reservoir is between 4,163.0 ft and 4,164.0 

ft, then the precautionary drawdown release is set to 

3,000 ft3/s. If the daily stage of Lahontan Reservoir is 

greater than 4,164.0 ft, then the precautionary drawdown release is set to 4,000 ft3

/s. If the forecasted reservoir volume is greater than 316,900 acre-ft (4,163.60 

ft), then the precautionary drawdown release is set 

equal to inflows (up to 3,000 ft3

/s) until that volume 

forecasted to be above 316,900 acre-ft has been evacuated from storage.

Also, if precautionary drawdown releases have 

not been set by the logic above, when the Lahontan 

Reservoir volume is greater than the monthly maximum water surface-water elevation as specified in 

Lahontan General Filling Schedule and Release Procedures, the net inflows to the reservoir are released up to 

a maximum of 2,000 ft3

/s. This monthly maximum 

water surface elevation ranges from 4,157.84 ft to 

4,163.67 ft.

Reservoir Storage Priorities and Pass-Throughs

A storage priority system for Truckee River reservoirs determines if a reservoir may or may not store 

water. This priority system is based on water storage 

rights. If a reservoir does not have the right to store at a 

given time, all inflows must be passed through that 

“junior” reservoir to satisfy “senior” priorities downstream. Pass-through releases are assigned to the natural water category. When a reservoir has the right and 

storage space to store water, it will retain all or part of 

the reservoir inflows. Floriston rates and Newlands 

Project demand for Truckee River water are parts of the 

storage priority system and influence reservoir storage.

Storage Priorities

Storage operations are based on decreed storage 

rights that necessitate a priority order for storing water 

in each reservoir. The following is a priority listing of 

target streamflows (Floriston rates) and annual reservoir storage amounts and categories that governs current reservoir storage operations (Alan Olson, Bureau 

of Reclamation, written commun., 1995). The first item 

listed has a senior right to store water, and the last item 

on the list cannot store water until all nine storage or 

streamflow demands above it have been satisfied. 

When storage and streamflow demands of senior 

priorities are concurrently being satisfied or forecast to 

be satisfied, reservoirs of various storage rights may 

store water simultaneously as long as senior priorities 

continue to be met. Notable examples of this concept 

follow the list.

1. Donner Lake —9,500 acre-ft storage split equally 

as PCPOSW and Truckee–Carson Irrigation District (TCIDPOSW). However, Donner Lake, can 

provide a maximum effective flood-control space 

of about 6,000 acre-ft (Richard D. Moser, Sierra 

Pacific Power Company, oral commun., 1999).
38 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

2. Independence Lake— initial 3,000 acre-ft storage 

as PCPOSW (up to full lake capacity, whichever 

is less) with winter drawdown of about 3,000 

acre-ft that is needed to fill in a typical year.

3. Floriston rates —target streamflows that 

satisfy Orr Ditch Decree (United States of 

America v. Orr Ditch Water Company, Equity 

No. A-3 (D. Nev. 1944)) diversion rights from 

the Truckee River except for the Truckee Canal 

diversion right. 

4. Lake Tahoe— storage as pooled water (up to 

full reservoir 6,229.1 ft elevation).

5. Boca Reservoir— initial 25,000 acre-ft storage 

as adverse-to-canal water (up to full reservoir 

capacity, whichever is less). 

6. Newlands Project — diversion to Truckee Canal 

pursuant to the Orr Ditch Decree and OCAP 

rights on the Newlands Project.

7. Boca Reservoir— additional 15,850 acre-ft 

storage as non-adverse-to-canal water (up to 

full reservoir capacity).

8. Independence Lake — additional 14,500 acre-ft 

storage as PCPOSW (up to full lake capacity).

9. Stampede Reservoir — 126,000 acre-ft storage 

as fish water (up to full reservoir capacity).

10. Prosser Creek Reservoir— 30,000 acre-ft 

storage as uncommitted water (up to full 

reservoir capacity).

The Truckee River system typically is operated 

according to the list above. For example, if Floriston 

rates are not met, then Boca Reservoir is not allowed to 

store additional water. However, when Boca is storing 

the entire flow of the Little Truckee River above Boca 

(satisfying its demands), Prosser Creek Reservoir is 

allowed to store reservoir inflows so long as senior priorities (such as Floriston rates) are being met. Two 

exceptions to the list occur in wet years. The first 

exception allows Boca water to be temporarily stored 

in Stampede Reservoir. That stored water is then 

released to Boca based on instream flow and Stampede 

power generation demands. The second exception 

allows Prosser Creek Reservoir to be filled prior to the 

filling of senior rights if, according to forecasts, all reservoir storage and target streamflows will be satisfied 

in wet years and that water is not needed to meet Floriston rates or diversion to the Truckee Canal. Independence Lake is generally filled concurrently with Boca 

Reservoir, based on runoff projections. Any water 

stored in the lake in excess of the legal storage rights 

would be released for re-storage in Boca at a later time. 

The USGS Truckee River Basin operations model 

simulates reservoir storage in the subblock reservoir 

storage priorities and pass-through requirements as 

follows. First, a simple forecast of the Little Truckee 

River inflow at the mouth is made and the forecast is 

used to determine whether exceptions to storage priorities can be made as described above. The forecasted 

inflow volume is calculated by multiplying the NRCS 

inflow forecast for Little Truckee River above Boca 

Reservoir by a drainage area ratio. On the first day of 

every month from January though May and again on 

May 31, the forecasted inflow to Boca is added to the 

simulated Boca storage. If the forecasted Boca Reservoir storage is greater than the reservoir capacity, then 

all reservoirs are filled concurrently after target 

streamflows are met. Otherwise, if the forecasted Boca 

storage is less than the reservoir capacity, the reservoirs are filled according to the storage priorities. In 

the latter situation, when Boca is storing the entire 

flow of the Little Truckee River above Boca (satisfying its demands), reservoirs with a junior right, such as 

Prosser Creek Reservoir, are not allowed to store reservoir inflows.

Next, using the same list of storage priorities as 

above, daily pass-through releases are specified on 

the basis of three periods and forecasted Boca Reservoir storage. The first period is during the non-filling 

season—January 1 to April 10 and July 16 to December 31—when inflows are assumed to be relatively 

small and all reservoirs are filled concurrently after 

target streamflows, such as meeting Floriston rates and 

Newlands Project demands, are met. The second period 

is during a normal-to-dry year when Boca is not forecasted to have excess water during filling season of 

April 11 to July 15. During this period, the reservoirs 

are filled according to the list of storage priorities. The 

third period is during a wet year when Boca is forecasted to have excess water during filling season of 

April 11 to July 15. During this period Prosser Creek 

Reservoir is filled concurrently with the other reservoirs. During all three periods, any pass-through 

releases are assigned the natural water category.

Assumptions in the reservoir storage priorities

subblock include the following items.
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 39

• The model simulates the storage of water categories as specified in the list of storage priorities for 

each reservoir.

• The model does not simulate the temporary storage of Boca Reservoir water in Stampede Reservoir for Stampede Reservoir optimal power 

generation.

Reservoir Pass-Throughs and Releases to 

Meet Newlands Project Demands

Storage priorities of some reservoirs upstream 

from Farad are influenced by demand for Truckee 

River water from the Newlands Project. According to 

the Truckee River Agreement of 1935, when the Newlands Project demand is not satisfied, a supplemental 

reservoir may not store water once the supplemental 

storage water impounded within a given year exceeds 

25,000 acre-ft. The supplemental reservoir referred to 

in the Truckee River Agreement is Boca Reservoir, 

and, as discussed previously in the section “Current 

Water Categories,” the first 25,000 acre-ft of supplemental storage water stored in the reservoir is typically 

referred to as adverse-to-canal water, because it can be 

stored adverse to Truckee Canal diversions. Truckee 

Canal diversions are determined by the Newlands 

Project demand in accordance with Operating Criteria and Procedures (OCAP) for Truckee River water 

and are discussed in a later section, “Truckee River 

Diversions to Newlands Project.” Additional supplementary storage water in excess of the first 25,000 

acre-ft stored in the reservoir is referred to as nonadverse-to-canal water because it cannot be stored 

adverse to Truckee Canal diversions. These two water 

categories are both types of pooled water because they 

are typically released to satisfy Floriston rates. Additionally, Independence Lake, with the exception of the 

first 3,000 acre-ft of annual storage, Stampede Reservoir, and Prosser Creek Reservoir may not store 

project water when Truckee Canal diversions to meet 

Newlands Project Demands have not been satisfied 

(John Simons, Bureau of Reclamation, written commun., 1991). 

Inflows must “pass through” a given reservoir 

when Newlands Project Demands for Truckee River 

water are not met. Reservoir pass throughs have the 

same specific category as reservoir inflows, and 

because the water is passed through to satisfy a specific 

demand, the pass-through is “tagged” to the inflow category natural water. The order of reservoir passthroughs to satisfy Newlands Project demands is 

shown below. It is based on storage priorities and goes 

from lowest priority to highest, but the order is 

reversed. (John Simons, Bureau of Reclamation, written commun., 1991). For instance, Prosser Creek Reservoir, the first listed item, has a low priority for 

storage and therefore water must pass through if Newlands Project demands are not satisfied.

1. Pass-through of natural water inflow from Prosser 

Creek Reservoir; 

2. Pass-through of natural water inflow from Stampede Reservoir;

3. Pass-through of natural water inflow from Independence Lake after the first 3,000 acre-ft of 

PCPOSW has been stored;

4. Pass-through of natural water inflow from Boca 

Reservoir after the first 25,000 acre-ft of adverseto-canal water has been stored.

Newlands Project demands for Truckee River 

water are satisfied when the Lahontan Reservoir 

monthly storage objective is achieved and the Truckee 

Division demands are being served as defined by 

OCAP or, if the objective is not achieved and demands 

have not been met, when the Truckee Canal capacity of 

about 900 ft3

/s is reached. See the section “Truckee 

River Diversions to Newlands Project” for further discussion of Newlands Project demands.

In addition to pass-throughs of inflow from 

Prosser, Stampede, and Boca Reservoirs and Independence Lake, TCID may release its portion of privately 

owned stored water (POSW) from Donner Lake to satisfy Newlands Project demands if diversions to the 

Truckee Canal allowable under OCAP and the Orr 

Ditch Decree cannot meet the demand. Usually, the 

release of the category TCID privately owned stored 

water (TCIDPOSW) from Donner Lake is during the 

fall precautionary drawdown season between September and November.

The USGS Truckee River Basin operations 

model simulates reservoir pass-throughs to satisfy 

Newlands Project demands in the subblock reservoir 

storage priorities and pass-through requirements. 

(Note that a following section, “Floriston Rates,”

describes reservoir pass-throughs for the maintenance 

of Floriston rates.) The diversion rights and the status 

of pooled water flows diverted to the Truckee Canal in 

reference to these rights are defined in the subblock 
40 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

OCAP. Pooled water from the Truckee River is 

diverted from reach 450 (upstream from Derby Dam) 

to the Truckee Canal, reach 61 (plate 1). If flow 

diverted to the canal is less than the diversion right, 

then the model determines the deficit, which corresponds to that additional flow of water needed to meet 

the diversion right. An excess is computed if pooled 

water at Derby Dam (reach 450, pl. 1) is more than the 

sum of canal diversion rights and Truckee River senior 

downstream water rights, the latter of which must be 

satisfied before water is diverted to the canal (see later 

section “Lower Truckee River Diversions”). The 

excess corresponds to the water not needed to meet 

Newlands Project demands and water rights downstream. 

For simulation of operations, the order listed 

below is used to simulate pass-throughs and releases 

from storage for meeting the Truckee Canal diversion 

rights. Note that Independence Lake is not simulated to 

provide pass-throughs for meeting the Truckee Canal 

demand because it is only rarely used in current practice (Jeff Boyer, U.S. District Court Water Master, oral 

commun., 1997). 

1. Pass-through of natural water inflow from 

Prosser Creek Reservoir; 

2. Pass-through of natural water inflow from 

Stampede Reservoir;

3. Pass-through of natural water inflow from Boca 

Reservoir after the first 25,000 acre-ft of adverseto-canal water has been stored;

4. Release of TCID water from Donner Lake (from 

September 1 to November 15).

The subblock reservoir storage priorities and 

pass-through requirements uses the deficit or excess 

value determined previously to appropriately adjust 

simulated pass-throughs and releases from the previous 

time interval. If the Newlands Project demand cannot 

be met by natural water from unregulated tributary 

basins and reservoir pass-throughs and releases, then 

that quantity of natural water needed to meet the 

demand cannot be stored in Prosser Creek, Stampede, 

and Boca Reservoirs. Natural water inflow to Martis 

Creek Lake is usually not stored except for floodcontrol operations. For simulations, natural water 

inflow needed to meet Newlands Project demands is 

passed through Prosser Creek Reservoir first. If the 

diversion right cannot be met after inflow has passed 

through Prosser Creek, then Stampede cannot store natural water inflow and must pass through its inflow. 

However, unlike Prosser Creek and Boca passthroughs, simulated Stampede pass-throughs do not 

necessarily reduce the deficit because Stampede passthroughs may be stored in Boca. For Boca, if the first 

25,000 acre-ft of water has been stored adverse-tocanal in a given year, additional natural water inflow 

cannot be stored, and all or part of this inflow must pass 

through until the Truckee Canal diversion right has 

been met. Lastly, if pass-through from Prosser Creek, 

Stampede, and Boca Reservoirs cannot meet the canal 

diversion right, TCIDPOSW water will be released 

from Donner Lake if the date is between September 1 

and November 15. This period is just after the recreation season and generally coincides with a period of 

precautionary drawdowns to maintain flood-control 

space in the lake.

If the flow of pooled water at Derby Dam exceeds Newlands Project demands and senior downstream water rights, the releases and pass-throughs of 

inflow are reduced accordingly in the opposite order 

of that specified above insofar as flood-control criteria 

will allow.

For simulations, only pooled water is diverted to 

the Truckee Canal for the Newlands Project. Therefore, 

the natural water that passes through the reservoirs and 

TCIDPOSW water released from Donner Lake are converted to pooled water just upstream from Derby Dam.

For simulations, it is assumed that reservoir passthroughs and releases are made according to an established priority. Simulations of pass-throughs for Newlands Project demands do not attempt to coordinate 

with pass-throughs from other reservoirs to benefit 

other uses.

Reservoir Demands

Under existing operations, several demands are 

described in legal decrees that are satisfied using reservoir releases and river diversions: Floriston rates, 

instream flows, Pyramid Lake fish, and POSW 

demands to satisfy M&I and irrigation water rights.

Floriston Rates

Floriston rates, described in the previous section 

“Chronology and Background of Decrees, Agreements, 

and Laws Affecting Operation,” are minimum-flow 

criteria for the Truckee River at the California-Nevada 

boundary and constitute the chief operational objective 
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 41

for the river (table 2). When flow rates measured at the 

USGS gaging station near Farad, Calif., meet Floriston 

rates, all agricultural, M&I, and hydropower water 

rights under the Orr Ditch Decree are assumed to be 

satisfied, except for Newlands Project demands. 

According to the Truckee River Agreement of 

1935, when Floriston rates are not met by the natural 

flow of the river, pooled water stored in Lake Tahoe 

and Boca Reservoir may be released to eliminate any 

deficit. The agreement specified priorities of reservoir 

release to attain Floriston rates when natural water in 

the river, alone, cannot maintain the rates. The major 

use of pooled water in Lake Tahoe is for maintenance 

of Floriston rates. Pooled water stored in the Boca Reservoir is also released for Floriston rates. The timing of 

the Boca pooled water release depends on when the 

water was stored and if it was stored adversely to 

Truckee Canal diversion rights. Additionally, between 

April 1 and October 31 of any given year, the reservoir 

used for Floriston rates depends on the water-surface 

elevation of Lake Tahoe (table 2). If the water-surface 

elevation is greater than 6,225.5 ft, then releases of 

Tahoe pooled water are minimized while releases of 

pooled water from Boca are maximized. If Boca 

releases of pooled water are insufficient to maintain 

Floriston rates, then additional pooled water will be 

released from the lake. If the water-surface elevation 

of the lake is less than or equal to 6,225.5 ft between 

April 1 and October 31, then releases of pooled water 

from the lake are used to maintain Floriston rates. If 

the pooled water release from the lake is insufficient 

to maintain rates, then pooled water from Boca will 

be released. 

Prosser Creek Reservoir, completed in 1962, 

provides another storage source from which to achieve 

Floriston rates. Uncommitted water is the project water 

stored in the reservoir. In accordance with the Tahoe–

Prosser Exchange Agreement of 1959, Prosser uncommitted water may be exchanged to a water category 

called Tahoe–Prosser Exchange water (TPEW) if 

releases of pooled water are made from Lake Tahoe to 

meet minimum instream flows rather than to meet Floriston rates. TPEW stored in Prosser Creek Reservoir 

through the Tahoe–Prosser Exchange Agreement can 

later be used as though it were Lake Tahoe pooledwater storage to maintain Floriston rates.

The Truckee River Agreement and other legal 

decrees and informal conventions or arrangements 

specify the order of reservoir releases to maintain 

Floriston rates assigned to the four water categories: 

(1) pooled water in Lake Tahoe, (2) adverse-to-canal 

water in Boca Reservoir, (3) non-adverse-to-canal 

water in Boca Reservoir, and (4) TPEW in Prosser 

Creek Reservoir. The adverse-to-canal and nonadverse-to-canal water categories in Boca are both 

pooled water, but are differentiated by whether the 

pooled water was or was not stored adverse to Truckee 

Canal diversion rights. Adverse-to-canal water is the 

first 25,000 acre-ft of pooled water stored in Boca and 

has a higher storage priority than water diverted to the 

Truckee Canal. Non-adverse-to-canal water is the additional storage of pooled water and has a lower storage 

priority than water diverted to the canal. In current 

practice, reservoir releases to maintain Floriston rates 

are not necessarily made sequentially (one at a time), 

but are commonly blended from more than one reservoir to satisfy other operational objectives. Recreational objectives are also considered in current 

operational practices when assigning orders to reservoir releases for Floriston rates. Recreational objectives include maintaining minimum storage levels that 

enhance activities such as boating and fishing. 

Although Donner Lake is the only reservoir that has a 

legal recreational pool, Prosser Creek and Boca Reservoirs may be operated to provide recreational pools.

The USGS Truckee River Basin operations 

model simulates the maintenance of Floriston rates as 

follows. First, in the subblock initial assignments and 

computations, the status of flow at the Farad gaging 

station (reach 240) is defined in reference to Floriston 

rates. The categories natural water flow and pooled 

water flow are added, and that sum, hereafter in this 

discussion called pooled water, is compared with target 

rates as defined in table 2. If the summed pooled water 

flow is less than the target rates, then the deficit is 

determined to be that additional flow of water needed 

to maintain the rates. Likewise, if the summed pooled 

water flow is more than the target rates, the excess is 

determined to be that amount of pooled water not 

needed to maintain the rates.

The following list is the order of water categories 

and sources used to maintain Floriston rates. A more 

detailed description follows the list.

1. Natural water inflows from unregulated tributary 

subbasins (sidewater).

2. Pass-through of natural water inflow from 

Prosser Creek Reservoir.
42 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

3. Pass-through of natural water inflow from 

Stampede Reservoir.

4. Pass-through of natural water inflow from 

Boca Reservoir.

5. Release of pooled water from Lake Tahoe if: 

a. Flow just downstream from the lake does 

not meet the minimum instream flow target.

b. The date is between April 1 and October 31 

and if the water surface elevation is between 

6,223.0 (outlet rim) and 6,225.5 ft, or 

c. The date is between November 1 and 

March 31.

6. Release of Tahoe–Prosser Exchange water 

from Prosser Creek Reservoir if:

a. The date is between April 1 and September 3 

(recreation season) and if total reservoir 

water volume is greater than or equal to 

19,000 acre-ft (recreation volume threshold), 

or

b. The date is between September 4 and 

March 31.

7. Release of adverse-to-canal water from 

Boca Reservoir.

8. Release of non-adverse-to-canal water from 

Boca Reservoir.

9. Release of Tahoe–Prosser Exchange water from 

Prosser Creek if the date is between April 1 and 

September 3 and if total reservoir water volume 

is less than 19,000 acre-ft.

10. Release of pooled water from Lake Tahoe if the 

date is between April 1 and October 31 and if the 

water surface elevation is greater than 6,225.5 ft.

The subblock maintenance of Floriston rates, 

uses the deficit and excess determined previously to 

appropriately adjust releases from the previous time 

interval to maintain rates for the current interval. If 

sidewater, reservoir pass-throughs of natural water, and 

reservoir releases from the previous time interval cannot maintain rates for the current time interval, then a 

deficit exists, and that quantity of natural water inflow 

to Prosser Creek, Stampede, and Boca Reservoirs 

needed to eliminate the deficit cannot be stored, and 

thus must pass through that reservoir. Natural water 

inflows to Martis Creek Lake are usually released, 

except when they are stored for flood-control operations. As previously discussed in the section “Storage 

Priorities,” only up to 3,000 acre-ft of Independence 

Lake inflow may be stored adverse to Floriston rates. 

However, for simulations it is assumed that the lake is 

not operated to provide pass-throughs for meeting Floriston rates because it is only rarely used in current 

practice. Donner Lake inflow, however, may be stored 

adverse to Floriston rates. Inflow to Lake Tahoe is considered pooled water for model simulations and, as discussed earlier, will be released as necessary to maintain 

Floriston rates. For simulations, natural water inflows 

needed to make rates are passed through Prosser Creek 

Reservoir first, Stampede Reservoir second, and Boca 

Reservoir third. The order is assumed on the basis of 

storage priorities specified by reservoir storage rights 

(Jeff Boyer, U.S. District Court Water Master, oral 

commun., 1994).

If Floriston rates cannot be met after inflows have 

passed through Prosser Creek, Stampede, and Boca 

Reservoirs, then releases of stored water must be made 

from Lake Tahoe, Prosser, or Boca. The first choice for 

release is pooled water from Lake Tahoe if (1) additional releases are also needed to maintain minimumflow targets just downstream from the lake, (2) if date 

is between April 1 and October 31 and if the water-surface elevation is between 6,223.0 ft (the rim) and 

6,225.5 ft, or (3) the date is between November 1 and 

March 31. Minimum-flow targets just downstream 

from Tahoe are specified as 50 ft3

/s between October 1 

and March 31, and 70 ft3

/s for the remainder of the 

year, as described in the subsequent section “Minimum 

Instream Flows.”

If pooled water releases from Lake Tahoe are 

not adequate to maintain Floriston rates, then Tahoe–

Prosser Exchange water (TPEW) from Prosser Creek 

Reservoir is the next priority for release, depending on 

recreational objectives. For simulations, the recreational season is defined between the dates April 1 and 

September 3. If the date is outside of the recreational 

season or if the date is within the recreational season 

and water volume in Prosser is greater than the recreational volume threshold (19,000 acre-ft), then TPEW 

is considered for release to maintain Floriston rates 

(Jeff Boyer, U.S. District Court Water Master, oral 

commun., 1994).
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 43

If pooled water releases from Lake Tahoe and 

TPEW from Prosser are not adequate to maintain Floriston rates, then pooled water releases from Boca, as 

adverse-to-canal water and non-adverse-to-canal water 

(in that order) are the next priorities for release.

After Boca Reservoir, the next priority for release 

is from TPEW from Prosser Creek Reservoir (1) if the 

volume of the reservoir is less than the recreational 

threshold of 19,000 acre-ft and (2) if the date is within 

the reservoir recreational season. 

Finally, if all appropriate water categories are not 

available to maintain Floriston rates under the conditions stated above, pooled water is released from Lake 

Tahoe if the water-surface elevation of the lake is 

above 6,225.5 ft and if the date is between April 1 and 

October 31. When natural water flows in the Truckee 

River are low and volumes of the appropriate water categories in the lake and Prosser and Boca Reservoirs are 

inadequate to maintain rates during drought periods, 

rates of pooled water and natural water flow at the 

Farad gaging station may be less than Floriston rates.

If Floriston rates are exceeded, then releases and 

pass-throughs of inflow are reduced accordingly in the 

opposite order specified above. Rates of pooled water 

and natural water flow at the Farad gaging station commonly exceed Floriston rates during periods of high 

water, such as during the spring snowmelt season or 

during large storm events in the winter and spring. 

During these conditions, even though reservoir releases 

may be reduced to zero, inflows to the Truckee River 

from sidewater or natural water inflows passed through 

reservoirs in accordance with flood-control criteria, 

may be large enough to exceed the rates. However, 

the goal of the subblock maintenance of Floriston 

rates is to maintain pooled water and natural water 

flows at the Farad gaging station as close as possible 

to Floriston rates.

Several assumptions were used in the model code 

development for simulation of Floriston rates.

• Similar to the simulation of reservoir passthroughs for Newlands Project demands, Independence Lake is not simulated to provide passthroughs specifically for the maintenance of Floriston rates. In current practice, it is not commonly operated to meet rates.

• No volume objective for recreation is considered 

for Boca Reservoir when computing releases for 

Floriston rates. However, elsewhere in the model 

code, as described in the related draft TROA section “Voluntary Exchanges,” recreational threshold volumes of Boca are considered.

• Reservoir releases are simulated by rank order. 

Simulations of releases for Floriston rates do not 

attempt to combine reservoir releases from more 

than one reservoir to optimize other objectives. 

However, in the code simulating draft TROA and 

WQSA operations as described later in this 

report, water categories are exchanged and 

releases amongst reservoirs are blended to meet 

multiple objectives such as storage of credit 

waters, attaining enhanced and preferred flows, 

maintaining reservoir recreational volumes, and 

storage of water categories for enhanced storage 

security in preferred reservoirs. Such exchanges 

may result in releases for Floriston rates from 

more than one reservoir.

• The specified order of reservoir pass-through of 

inflows for Prosser Creek, Stampede, and Boca 

Reservoirs is based on reservoir storage priorities. 

It was assumed that pass-through of inflows 

would be in the opposite order of storage priorities.

• The specified orders of reservoir releases for Lake 

Tahoe, and Boca and Prosser Creek Reservoirs 

were partially assumed because Prosser was completed more than 25 years after the Truckee River 

Agreement specified orders of release for Lake 

Tahoe and the supplemental reservoir, Boca. 

Additionally, in the simulation of adverse- and 

non-adverse-to-canal releases from Boca, dates 

of storage of these waters, as described in the 

Truckee River Agreement were not considered. 

Instead, adverse-to-canal water was assumed to 

be released prior to non-adverse-to-canal water.

• Net inflow to Lake Tahoe is considered pooled 

water rather than natural water for model simulations. Therefore, pass-throughs for maintenance 

of Floriston rates are not simulated for Tahoe.

Minimum Instream Flows

Several reservoirs in the Truckee River Basin are 

operated to provide releases necessary to maintain minimum instream flows just downstream from the reservoirs. The following list describes minimum instream 

flows for each reservoir.
44 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

Lake Tahoe

The Tahoe–Prosser Exchange Agreement of 

1959 requires releases from Lake Tahoe 

pooled water storage to maintain minimum 

instream flows just downstream from the lake 

during periods when a release from storage 

would otherwise not be required to maintain 

such flows. The agreement requires a minimum instream flow below the lake of 50 ft3

/s 

between October 1 and March 31 and a flow 

of 70 ft3

/s for the remainder of the year if that 

same amount of water can be exchanged to 

Tahoe–Prosser Exchange water (TPEW) in 

Prosser Creek Reservoir from storage of 

Prosser inflow that would otherwise pass 

through the reservoir or from previously 

stored uncommitted water. Uncommitted 

water in Prosser is water already in storage, 

but TPEW is only created by the Tahoe–

Prosser Exchange. Thus, the availability of 

uncommitted water for exchange in Prosser 

may limit Lake Tahoe releases to maintain 

instream flows.

Donner Lake

Releases are made to maintain a minimum 

instream flow downstream from the lake of 

2 ft3

/s when the flow immediately below the 

confluence with Cold Creek is 5 ft3/s or more. 

Otherwise, the minimum instream flow is 

3 ft3

/s. Between November 15 and April 15, 

the upper two gates of the dam must be held 

open and, as a result, instream flows are governed by inflows to the lake. According to the 

Donner Lake Indenture of 1943, water cannot 

be released from the lake if the water surface 

elevation is lower than 5,932.0 ft and the date 

is between June 1 and August 31.

Martis Creek Lake

No minimum instream flow requirements exist 

downstream from Martis Creek Lake.

Prosser Creek Reservoir

Releases are made to maintain a minimum 

instream flow downstream from Prosser of 

5 ft3/s or inflow to the reservoir, whichever is 

less.

Independence Lake

Releases are made to maintain a minimum 

instream flow downstream from the lake of 

2 ft3

/s.

Stampede Reservoir 

Releases are made to maintain a minimum 

instream flow downstream from Stampede of 

30 ft3/s. These releases may be re-stored in 

Boca if allowed in conformance to storage 

rules.

Boca Reservoir 

No minimum instream flow requirements exist 

downstream from Boca Reservoir.

The USGS Truckee River Basin operations 

model simulates reservoir releases to maintain minimum instream flows in four subblocks. The subblock 

initial assignments and computations assigns proposed releases from each reservoir to maintain instream 

minimum flows. The subblock reservoir releases to 

meet minimum flows modifies the proposed releases 

by applying various rules and constraints for all reservoirs required to release for minimum flows except 

Lake Tahoe. The subblock merge then compares proposed untagged releases for minimum flows to other 

proposed releases that are tagged, such as tagged 

releases of pooled water to meet Floriston rates. As 

previously discussed in the section “Description and 

Simulation of Truckee River Basin Operations,” the 

merge subblock assigns water categories for those 

proposed untagged releases for minimum flows. For 

Lake Tahoe, pooled water releases for minimum flows 

are simulated by the Tahoe–Prosser Exchange logic in 

the subblock current exchanges. 

Proposed releases from Donner Lake to maintain 

minimum flows are set to 3 ft3/s in the subblock initial 

assignments and computations. Although required 

releases may be reduced from 3 ft3/s to 2 ft3/s depending on Donner Creek flow downstream from Cold 

Creek, for model simulations, flow data are not available to determine such a reduction. Model code in the 

subblock reservoir releases to meet minimum flows

limits the proposed release to the outlet capacity of the 

dam for the current water surface elevation, and if the 

current water surface elevation of the lake is less than 

5,932.0 ft between June 1 and August 31, reduces the 

proposed release to zero. Model code in the subblock 
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 45

merge compares the proposed release to other tagged 

releases for assignment of water categories to the 

release. 

Proposed releases to maintain minimum flows

from Prosser Creek Reservoir, Independence Lake, 

and Stampede Reservoir are set to 5, 2, and 30 ft

3/s, 

respectively, in the subblock initial assignments and

computations. For these reservoirs, model code in the

subblock reservoir releases to meet minimum flows

limitsthe proposed releasesto the outlet capacity of the

dams for the current water surface elevation and, for

Prosser, the inflow to the reservoir. As for Donner 

Lake, model code in the subblock merge compares the 

proposed releases to other tagged releases for assignment of water categories to the releases.

Proposed pooled water releases from Lake Tahoe 

to maintain minimum flows are set to 50 ft

3

/s between 

October 1 and March 31 and 70 ft

3

/s for the remainder 

of the year. In the model code thatsimulatesthe Tahoe–

Prosser Exchange in the subblock current exchanges, 

the proposed minimum-flow release from the lake is 

limited to the storage of Prosser Creek Reservoir 

inflow that would otherwise pass through the reservoir

or from previously stored uncommitted water available 

for exchange to Tahoe–Prosser Exchange water in the 

reservoir (see subsequent section, “Tahoe–Prosser

Exchange”). Use of the subblock merge is not necessary because releases for minimum flows from Lake 

Tahoe are tagged as pooled water. A user option may 

allow the minimum flow to be set equal to the flow

needed for rafting activities, about 200 ft

3/s.

Pyramid Lake Fish

Because cui-ui and Lahontan cutthroat trout in 

Pyramid Lake are listed as endangered and threatened

species, respectively, under the ESA, the Department

of the Interior is responsible for the recovery of these 

species. Several plans to accomplish the recovery of

these species have been developed (Strekal and others,

1992; Buchanan and Strekal, 1988) and management

activities and species response to environmental conditions have been documented (Heki, 1994, and Heki and

Cowan, 1994). These plans include goals of providing 

optimal spawning habitat and providing upstream 

storage of water for later release during times when

fish spawn.

An important objective for fish recovery is to

provide spawning habitat. Cui-ui spawn in the lower

Truckee River, typically between March and July 

depending on river flow and accessto the river. Spawning and development of eggs and larvae are affected 

by water depth, velocity, temperature, and quality. 

Spawning and rearing factors are largely functions of

the lower Truckee River flow during certain times of

the year, which is affected by reservoir storage and 

releases, diversions, and natural and return flows to the

river downstream from reservoirs. Biologists have

developed procedures to promote spawning and 

recruitment by regulating the flow of the lower Truckee 

River (Strekal and others, 1992, Buchanan and Strekal,

1988). These procedures establish flow regimes and

cui-ui flow targets at Truckee River near Nixon (hereafter referred to as the Nixon gaging station) based on 

water availability and management options. Although 

flows are currently managed to encourage cottonwood

growth for shade along the lower Truckee River, no 

formal criteria have been established that could be

incorporated into the model code. In addition, no flow

management strategy has been developed yet for 

Lahontan cutthroat trout. 

Flow regimes can be defined according to the 

level or timing of spawning activity for a given spring

runoff season. Flow regimes have been separated into 

four groups: (1) full spawning with early (mid-June)

completion, sometimes referred to as a “fish run,”

(2) reduced spawning to allow for human collection of

eggs, (3) no spawning, or (4) full spawning with late 

(mid-July) completion. Flow regimes are based on the 

forecasted Pyramid Lake level, “attraction flows” at

Pyramid Lake, water volume available for spawning, 

and the time of the year. Attraction flows are defined by 

the average Truckee River discharge into Pyramid 

Lake from January to April of a spawning season 

which, if sufficient, may serve as a stimulus to initiate 

a spawning run (Buchanan and Strekal, 1988, p. C-2). 

Cui-ui flow targets are set on the basis of the flow 

regime (table 4) and maximum flows(up to 2,500 ft

3

/s) 

during a spawning season at the Nixon gaging station.

As flow targets vary, changes in flow are smoothed or 

“ramped” gradually, such that large changes between 

daily flows are minimized.

A related objective for fish recovery is to provide 

storage of water in Truckee River Basin reservoirs for 

spawning. The judgement Carson-Truckee Water Conservancy District v. Watt, 1982 requires all project 

water in Stampede Reservoir to be for the benefit of 

Pyramid Lake fishes. Uncommitted water stored in 

Prosser Creek Reservoir in excess of storage under the 
46 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

Tahoe–Prosser Exchange Agreement also has been 

reserved (Bureau of Reclamation, 1959) to provide 

water for release to Pyramid Lake forspawning habitat.

Current Pyramid Lake fish operations are used to

manage the water available for spawning flows at

Nixon gaging station, based on the (1) determination of

flow regimes and cui-ui flow targets, (2) demand forecast and inflow forecasts, and reservoir storage rights, 

and (3) fish water available in Stampede and Prosser

Creek Reservoirs.

Large releases from Boca Reservoir are sometimes necessary to satisfy Pyramid Lake fish flow 

targets. Hydraulic constraints of the outlet structure at

Boca require commitment of additional stored waters

used to maintain Boca stages sufficient to attain these 

large releases. This temporarily stored water in Boca

is called Boca pressure water. Boca pressure water 

is delivered to Boca Reservoir from Stampede Reservoir during full spawning regimes from about April 1

to May 30 (Garry Stone, U.S. District Court Water

Master, oral commun., 1996). The Boca stage necessary for Boca pressure water is about 5,560.6 ft. 

(9,000 acre-ft), which is the hydraulic head necessary 

to release 1,000 ft

3/s, or about 2,000 acre-ft/d, through 

the outlet works. Fish water from Stampede Reservoir 

is used to maintain Boca pressure water targets (Chester Buchanan, U.S. Fish and Wildlife Service, written

commun, 1997) and instream flows.

The USGS Truckee River Basin operations

model simulates Pyramid Lake fish operations in

the subblock as follows: (1) initial numerical assignments and computations are made, (2) the amount of

water available for fish operations is computed, (3) the

flow regime and cui-ui flow targets are determined, 

(4) releases of stored fish water from Truckee River

Basin reservoirs are determined to maintain cui-ui flow 

targets, and (5) releases from Stampede Reservoir are 

determined to maintain Boca pressure water.

First, cui-ui flow targets are set equal to targets 

described by the recovery plans (Strekal and others, 

1992; Buchanan and Strekal, 1988). Other assignments 

that are used in simulations of Pyramid Lake fish operations include the following items: (1) “attraction

flow” accumulator at reach 540 (near Nixon) is reset to 

zero on January 1, and (2) maximum flow accumulator 

at reach 540 is reset to zero on January 1. The maximum flow accumulator is limited to 2,500 ft

3

/s. These 

items are discussed below in the text.

After initial numerical assignments and computations are made, the amount of water available

for Pyramid Lake fish operations is computed in the 

subblock Pyramid Lake fish operations. This amount

includes existing storage of fish waters in reservoirs

plus forecasted inflow to the Truckee River Basin 

minus forecasted demands for serving Orr Ditch rights 

and Newlands Project demands, minus forecasted

senior rights in upstream reservoirs for reservoir 

storage minus allowance for 10,000 acre-ft in Prosser 

Creek Reservoir and 50,000 acre-ft in Stampede 

Reservoir (Alan Olson, Bureau of Reclamation, oral

commun., 1996).

Next, the flow regime and cui-ui flow targets

are determined. Flow regimes are determined on 

January 1, March 1, April 1, May 1, and August 1 on 

the basis of the Pyramid Lake level, attraction flow 

accumulator at Nixon, water volume available for 

spawning, and the month. As discussed previously, 

theoretical flow regimes have been separated into four

groups: (1) full spawning with early (mid-June) completion, (2) reduced spawning to allow for human collection of eggs, (3) no spawning, and (4) full spawning

run with later completion. Flow regime 4 was not simulated because it was not likely to occur in actual operations (Chester Buchanan, USFWS, oral commun.,

1997). On the basis of the cui-ui flow regime, the cuiui flow target (table 4) is specified as a flow at Nixon 

gaging station (reach 540). The targets vary according 

to date, flow regime, total attraction flow, and maximum flow at reach 540 since January 1. Ramping 

between cui-ui flow targets is simulated by varying 

flow targets gradually in the model by about 95 ft3

/s 

per day.

Next, the model determines releases from Truckee River Basin reservoirs for the maintenance of 

cui-ui flow targets at Nixon gaging station. The amount 

of water available for Pyramid Lake fish operations 

is compared to the cui-ui flow target at reach 540. If 

the available flow is less than the target, then a deficit 

is determined as that additional flow of water needed 

to achieve the target. Likewise, if the available flow 

is greater than the target, an excess is determined as 

the amount of available cui-ui flow not needed to maintain targets.

The following are the current water categories 

and sources used to maintain cui-ui flow targets (Chester Buchanan, U.S. Fish and Wildlife Service, written 

commun, 1997). 
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 47

1. Boca Reservoir fish water (from Stampede

Reservoir). The delivery of Pyramid Lake fish 

water from Stampede through Boca is described 

later in this section.

2. Prosser Creek Reservoir uncommitted water.

The subblock Pyramid Lake fish operations uses 

the simulated deficit or excess computation to adjust

releases every third day to allow for travel time to reach

540 from upstream reservoirs. If the cui-ui flow target

is not being met by available cui-ui flow, then additional releases of stored fish water must be made from 

Truckee River Basin reservoirs in the order specified 

above. If existing cui-ui flow targets are exceeded, then

reservoir releases are reduced accordingly in the opposite order specified above. 

The following discussion describes how the 

operations model simulates the maintenance of Boca 

pressure water volume for current operations. Boca

pressure water is delivered to Boca Reservoir from

Stampede Reservoir in the model during flow regime 1

from March 1 to June 5. The status of existing fish 

water storage and total stage in Boca is compared to 

the Boca pressure water targets of 2,000 acre-ft and 

5,560.6 feet, respectively. If either the simulated Boca 

fish water storage or elevation is less than the target, 

then the deficit is determined as that additional volume 

of water needed for storage in Boca to maintain the

volume of Boca pressure water targets. Fish water 

released from Stampede is used to maintain Boca 

pressure water targets.

The following assumptions were used in the

model code to simulate the Pyramid Lake fish operations.

• A tolerance of 10 ft

3/s is used to determine when

Pyramid Lake fish releases from upstream reservoirs Boca or Prosser are necessary. If Nixon 

flows are within 10 ft

3/s of the targets, no additional releases are made. This tolerance may be 

modified by the user.

• Operations to promote the growth of cottonwood 

trees along the lower Truckee River corridor were

not included because the hydrograph recession

guidelines provided by the U.S. Fish and Wildlife 

Service (Lisa Heki, written commun., 1997) fell

Table 4. Fish flow targets to optimize spawning success by regulation of flows at 

Truckee River near Nixon, Nevada (from Strekal and others, 1992, and Buchanan 

and Strekal, 1988)

[Symbol: >, greater than]

Fish flow targets at the Truckee River near Nixon gaging station

(cubic feet per second)

Flow regime 1 Flow regime 2 Flow regime 3 Flow regime 4

January 90 50 0 90

February 120 50 0 120

March 190 50 0 190

April 1570

1 Transition between fish flow targets are changed or “ramped” such that daily change in flows 

are 95 cubic feet per second.

50 0 1570

May 1, 2>1,000

2 Fish flow target equals maximum simulated daily streamflow at reach 540 but does not exceed 

2,500 cubic feet per second.

150 0 1,2>1,000

June 350

3 Fish flow targets are ramped down to 50 cubic feet per second by June 30.

0 0 1,2>1,000

July 0 0 0 450

4 Fish flow targets are ramped down to 50 cubic feet per second by July 31.

August 0 0 0 0

September 0 0 0 0

October 0 0 0 0

November 0 0 0 0

December 0 0 0 0
48 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

within the cui-ui spawning flow recession and 

thus would be superseded by them.

Privately Owned Stored Water

Privately owned stored water (POSW) is 

defined as water owned by the Power Company 

(PCPOSW) or TCID (TCIDPOSW). PCPOSW water 

is established and typically stored in Donner and Independence Lakes. However, under certain conditions 

PCPOSW may also be stored in Stampede and Boca 

Reservoirs. TCIDPOSW is established and stored in 

Donner Lake. Hereafter, reservoir and river operations 

regarding PCPOSW and other water rights owned by 

the Power Company will be called “Power Company 

operations” and those operations regarding TCIDPOSW in Donner Lake will be called “Truckee–Carson 

Irrigation District operations.”

Current Power Company operations use guidelines based on decrees and rulings, inflow forecasts, 

current runoff conditions, and reservoir storage to 

determine a strategy for satisfying M&I demands 

(Richard D. Moser, Sierra Pacific Power Company, 

written commun., 1995). Power Company water 

supplies consist of ground-water and surface-water 

resources. Power Company ground-water supplies are 

pumped from wells throughout the Truckee Meadows. 

Use of the ground-water supplies is spatially and temporally distributed in a given year. The monthly distribution of ground-water pumpage for 1995 has been 

provided by the Power Company (Richard D. Moser, 

Sierra Pacific Power Company, written commun., 

1995). The maximum annual ground-water pumpage 

for M&I is based on forecasted and actual runoff conditions (Richard D. Moser, Sierra Pacific Power Company, oral commun., 1995). Power Company surfacewater supplies can be separated into two groups: Power 

Company water originating from reservoir storage of 

POSW and Power Company water originating from 

river sources.

Power Company water originating from reservoir 

storage rights currently includes PCPOSW in Donner 

and Independence Lakes, and recent agreements have 

allowed the Power Company to store additional 

PCPOSW in Boca and Stampede Reservoirs for power 

generation and M&I supplies during droughts. In the 

Truckee River Agreement, the Power Company is 

allowed to consistently store up to 800 acre-ft of 

PCPOSW in Boca Reservoir (called Boca pondage). 

This volume of water allows the Power Company to 

store PCPOSW in Boca for use in regulating flow for 

power generation and meeting Floriston rates. The 

Interim Storage Agreement (Bureau of Reclamation, 

1994) allows the Power Company to store PCPOSW 

(called contract storage) in Stampede and Boca Reservoirs. The agreement is intended to provide additional storage capacity for SPPC to meet domestic, 

municipal, and industrial demands in Truckee Meadows during drought years. Also, the agreement stipulates that any PCPOSW stored above 5,000 acre-ft in 

Stampede and Boca Reservoirs above the Boca pondage be exchanged to fish water on September 1. 

PCPOSW released from Independence and Donner 

Lakes (see the section “Donner–Boca Exchange,”

under “Current Operational Exchanges”) and Stampede Reservoir during summer and fall precautionary 

releases and to meet enhanced flows from Stampede 

are used to fill the contract storage. When TROA 

is finalized, the Interim Storage Agreement will 

be nullified. 

Independence Lake is informally operated with 

consideration of minimum pool of 7,500 acre-ft for 

Lahontan cutthroat trout access to spawning habitat 

upstream from the lake (Richard D. Moser, Sierra 

Pacific Power Company, written commun., 1995).

The Power Company’s water supply originating 

from river sources is defined by the Truckee River 

Agreement of 1935 and Orr Ditch Decree (United 

States of America v. Orr Ditch Water Company, Equity 

No. A-3 (D. Nev. 1944)). These documents provide 

rules and priorities for the allocation of Truckee River 

water to Truckee Meadows water-rights downstream 

from the Farad gaging station (see section “Truckee 

Meadows Diversions.” The Truckee River Agreement 

specifies that the Power Company shall have the right 

to the first 40 ft3

/s of pooled water in the Truckee River 

at Farad (Truckee River Agreement, p. 7). Additionally, the Power Company has been purchasing agricultural water rights defined by the Orr Ditch Decree and 

converting them to M&I water rights. Current (1991) 

converted water rights are defined in a FWM table 

“Truckee Meadows Priorities” (Jeff Boyer, U.S. District Court Water Master, written commun., 1994). The 

Truckee River Agreement of 1935 also specifies that 

the Power Company has the right to the first 13.6 ft3

/s 

of water in Hunter Creek, which is also used as a M&I 

water right. 

Determination of Power Company demands is 

based on historical patterns of M&I water use and population (Richard D. Moser, Sierra Pacific Power Com-
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 49

pany, oral commun., 1995). The Power Company 

historically has diverted water to five treatment plants 

—Glendale, Chalk Bluff, Highland, Hunter, and 

Idlewild. As of 1995, diversions are only being made to 

the Glendale and Chalk Bluff plants; Highland, Hunter 

and Idlewild have been retired. Meeting the demands is 

based on available surface- and ground-water supplies 

and availability and limits of surface-water treatment 

capacity. Ground-water use is maximized in a drought 

in order to conserve surface-water supplies (Richard D. 

Moser, Sierra Pacific Power Company, oral commun., 

1999). Surface-water supplies stored in a reservoir may 

be carried over from one year to the next. 

The USGS Truckee River Basin operations 

model simulates Power Company operations by first 

making numerical assignments and computations are 

made to determine Power Company M&I demands 

and location of M&I diversions. Logic in the subblock 

Power Company operations is used to determine: 

(1) PCPOSW originating from reservoir storage and 

water originating from the Orr Ditch Decree, (2) M&I 

diversions amounts, (3) Boca Reservoir storage of 

PCPOSW, and (4) reservoir storage of PCPOSW 

according to the Interim Storage Agreement.

First, in the subblock initial assignments and 

computations, three options were developed to determine the Power Company M&I demands. The first 

option uses the rate of population growth from 1995 to 

determine the M&I demand. A user-defined variable 

incrementally changes the 1995 M&I demand prior to 

and subsequent to 1995, assuming a constant relation 

between population and M&I demand. This demand 

changes every year, based on the assumption of constant percentage growth of population. The second 

option uses historical M&I demands from the Power 

Company for 1977–97. The third option uses a constant 

M&I demand pattern (currently set at the 1995 demand 

pattern) from the Power Company for all years of a 

simulation run. In all three options, the model diverts 

M&I water to two treatment plants—Chalk Bluff and 

Glendale plants—using a fixed monthly distribution to 

the plants based on historic diversions for 1995–97.

Other computations include the following items.

• Determination of the maximum annual groundwater pumpage for M&I is based on whether the 

forecasted runoff index designation is computed 

to be normal, wet, or dry (see the section “Runoff 

Index,” under the section “Forecasts Affecting 

Operational Decisions”). Once the annual amount 

is determined, monthly supplies from ground 

water are computed on the basis of historical 

pumpage data for normal, wet, or dry years in the 

Truckee Meadows area (Richard D. Moser, Sierra 

Pacific Power Company, written commun, 1995). 

• A tolerance of 5.0 ft3

/s is used to determine when 

the PCPOSW releases are necessary. If releases 

are within 5.0 ft3

/s of targets, no additional 

releases are made. 

Next, M&I sources are determined in the subblock Power Company operations. First, all groundwater and surface-water M&I supplies are summed. 

This sum includes M&I surface-water supplies originating from river rights (as determined in the section 

“Truckee Meadows Diversions”), Hunter Creek M&I 

supplies, current PCPOSW releases from Truckee 

River Basin reservoirs, and ground-water M&I supplies. If the supplies are less than the demands, then the 

deficit is determined as that additional flow of water 

needed to satisfy M&I demands. Likewise, if the supplies are more than the demands, the excess is determined to be that water not needed to maintain M&I 

demands.

The following list identifies the surface-water 

sources used to satisfy M&I demands in the Truckee 

Meadows. Specific ground-water sources are not simulated by the model. 

• First 40 ft3/s of Truckee River pooled water and 

first 13.6 ft3/s of Hunter Creek streamflow per 

Truckee River Agreement.

• Available Orr Ditch Decree (United States of 

America v. Orr Ditch Water Company, Equity 

No. A-3 (D. Nev. 1944)) agricultural rights flowing in the Truckee River converted to M&I rights 

(see section “Truckee Meadows Diversions”).

• Release of PCPOSW from Boca Reservoir. 

PCPOSW in Boca originates from Stampede 

Reservoir or Independence Lake.

• Release of PCPOSW from Donner Lake if the 

date is between April 1 and August 31 and if the 

lake elevation is above 5,932.0 ft (recreational 

pool) per Donner Lake Indenture (see section 

“Maintenance of Recreational Pools”) or if the 

date is between September 1 and March 31.
50 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

The subblock Power Company operations uses 

the deficit or excess determined previously to adjust 

simulated releases computed for the previous time 

interval. If M&I demands cannot be met by current 

streamflow, then releases of stored PCPOSW water 

must be made from Truckee River Basin reservoirs. 

The first choice for release is Boca Reservoir PCPOSW 

if the date is between April 1 and August 31. If 

PCPOSW releases from Boca cannot be made or are 

not adequate to satisfy M&I demands, then PCPOSW 

from Donner Lake is next for release. The filling of 

M&I water supplies in Boca Reservoir from Stampede 

Reservoir and Independence Lake is described below. 

If M&I supplies exceed demand, then reservoir 

releases are reduced accordingly in the opposite order 

specified above. The M&I diversions are then simulated at the appropriate quantity and location. 

The USGS Truckee River Basin operations 

model simulates the maintenance of Boca Reservoir 

PCPOSW, which facilitates Power Company access 

to their water. In this subblock the volume of Boca 

PCPOSW storage is compared to 800 acre-ft. If the 

current Boca PCPOSW storage is less than 800 acre-ft, 

then the deficit is determined to be the additional storage of water needed to attain the 800-acre-ft requirement. The categories and sources used to maintain 

Boca PCPOSW storage are PCPOSW in Stampede 

Reservoir and PCPOSW in Independence Lake if Independence Lake storage is greater than 7,500 acre-ft. 

The subblock Boca re-regulation uses the 

demand deficit determined previously to adjust 

releases simulated for the previous time interval. If 

Boca Reservoir PCPOSW has a deficit, then releases of 

stored M&I water must be made from Little Truckee 

River Basin reservoirs upstream from Boca. The first 

choice for release is PCPOSW in Stampede Reservoir. 

If PCPOSW releases from Stampede are not adequate 

to achieve Boca PCPOSW storage, then PCPOSW 

from Independence Lake above the storage of 

7,500 acre-ft is the next priority for release. 

The following discussion describes how the 

model simulates reservoir storage according to the 

Interim Storage Agreement. The model allows the 

Power Company to store Interim Storage Agreement 

PCPOSW in Stampede Reservoir only under current 

operating rules. To store PCPOSW in Stampede 

according to the interim storage agreement, PCPOSW 

may be released from Independence Lake and re-stored 

in Stampede during three periods. First, during the 

summer period, July 16 to August 17, Independence 

Lake waters may be released for the Interim Storage 

Agreement if (1) lake storage is above a storage of 

7,500 acre-ft, (2) lake releases are less than 30 ft3

/s, and 

(3) Stampede levels are below reservoir storage limit of 

226,500 acre-ft. Second, during the precautionary 

drawdown period, August 18 to November 1, lake 

releases are increased to lower the lake to wintertime 

cap. For both periods, these releases can be stored in 

Stampede Reservoir as PCPOSW as long as Stampede 

storage is below the flood-control criteria storage limit 

for that period. On September 1, any PCPOSW stored 

in Stampede greater than 5,000 acre-ft is exchanged to 

fish water. Fish credit water is not simulated as a separate water category under current conditions in the 

operations model.

Truckee-Carson Irrigation District operations 

using TCIDPOSW from Donner Lake are described in 

the sections “Truckee River Diversions to Newlands 

Project,” “Reservoir Pass-Throughs and Releases to 

Meet Newlands Project Demand,” and “Merge Reservoir Releases for Multiple Objectives.”

Current Operational Exchanges

Exchanges under current operations are in-lieu-of 

exchanges. In this type of exchange, water is released 

from one reservoir in exchange for storage of an equal 

volume of water in another reservoir. Three common 

exchanges are currently practiced and simulated by the 

operations model: the Tahoe–Prosser Exchange, the 

Donner–Boca Exchange, and the Boca–Stampede 

Exchange.

Tahoe–Prosser Exchange

The Tahoe–Prosser Exchange Agreement of 1959 

specifies the operation of Lake Tahoe and Prosser 

Creek Reservoir in order to meet multiple uses (Bureau 

of Reclamation, 1959). This agreement requires 

releases from Lake Tahoe to maintain minimum 

instream flow in the Truckee River downstream from 

the lake during periods when water would otherwise be 

stored and accumulated for later release. The required 

minimum flows downstream from the lake are 50 ft3

/s 

between October 1 and March 31 and 70 ft3

/s for the 

remainder of the year. In exchange for the minimumflow releases, an equivalent volume of water must be 

stored concurrently in Prosser Creek Reservoir in order 

to compensate for the release from the lake when not 

required for Floriston rates. Prosser water from the category uncommitted water or Prosser releases of natural 
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 51

water are used for the exchange. As pooled water is 

released from the lake solely to meet minimum 

instream flows, an equivalent volume of natural water 

releases or uncommitted water are converted to 

Tahoe–Prosser Exchange water (TPEW) in Prosser 

Creek Reservoir. TPEW stored in Prosser through this 

exchange can then used to maintain Floriston rates as 

though it were pooled water stored in Lake Tahoe.

The operations model simulates the Tahoe–

Prosser Exchange in the subblock current exchanges. 

The model code in that subblock uses the minimumflow requirement for the Lake Tahoe outlet of either 

50 ft3/s or 70 ft3/s, assigned in the subblock initial 

assignments and computations, to simulate the 

Tahoe–Prosser Exchange. After the assignment of minimum flows downstream from Tahoe, the following 

computations are determined: (1) the additional release 

needed to maintain the minimum flows from Tahoe, 

(2) the volume of uncommitted water available for 

exchange in Prosser, (3) the volume of Prosser releases 

available as natural water, and (4) if Prosser has storage 

space available. To determine the minimum-flow 

release from Lake Tahoe, the minimum-flow requirement is compared to the Tahoe release currently simulated. If the Tahoe release exceeds the minimum-flow 

requirement, no exchange is necessary. However, if the 

Tahoe release is less than the minimum-flow requirement, the difference is the additional release needed 

solely to maintain the minimum-flow requirement. 

This minimum-flow release, limited to the volume of 

pooled water available in Lake Tahoe and the outlet 

capacity of the lake, is used for the Tahoe–Prosser 

Exchange. The volume of uncommitted water available 

for exchange in Prosser Creek Reservoir is simply the 

volume of that category in storage.

The proposed minimum-flow release from Lake 

Tahoe is limited to (1) Prosser Creek Reservoir releases 

available as natural water and (2) the uncommitted 

water available for exchange to TPEW in Prosser. 

The volume of uncommitted water or releases available 

as natural water for exchange to TPEW in Prosser is 

equivalent to the additional minimum-flow release 

needed from Tahoe. No releases solely for minimum 

flows downstream from Tahoe are made once the 

supply of uncommitted water or releases are depleted 

in Prosser. 

For simulation of the Tahoe–Prosser Exchange, 

a tolerance of 0.5 ft3/s is used to determine when minimum-flow releases from the lake are necessary. If 

releases from Tahoe are within 0.5 ft3/s of minimumflow requirements, no additional releases are made.

Donner–Boca Exchange

The Donner–Boca Exchange is an informal 

agreement that specifies the operation of Donner Lake 

and Boca Reservoir in order to meet multiple uses 

(Richard D. Moser, Sierra Pacific Power Company, 

oral commun., 1995; Jeff Boyer, U.S. District Court 

Water Master, oral commun., 1996). This agreement 

specifies that Donner Power Company privately owned 

stored water (PCPOSW) required for precautionary 

drawdown may be released for maintenance of Floriston rates in exchange for reduction of an equivalent 

volume of pooled water release from Boca and conversion of that retained water to PCPOSW. Thus, depending on the volumes of water exchanged, all or some 

releases for maintenance of Floriston rates will be 

made from Donner instead of Boca. In effect, this 

exchange allows the releases required from Donner to 

meet three objectives instead of one: (1) fall precautionary drawdown for creation of flood-control space, 

(2) maintenance of Floriston rates, and (3) PCPOSW 

from Donner Lake is stored in Boca Reservoir instead 

of being released and not used downstream.

The operations model simulates the Donner–

Boca Exchange in the subblock current exchanges. 

For an exchange to take place, the model code in that 

subblock requires that the date is between August 15 

and November 15 of any given year, Boca Reservoir is 

not making required precautionary drawdown releases 

(see section “Flood-Control Criteria”), Donner Lake is 

making required precautionary drawdown releases, 

and Boca is releasing pooled water for maintenance of 

Floriston rates. To determine the volume of water to be 

exchanged, the simulated releases of PCPOSW from 

Donner are compared with pooled water releases, 

either as adverse- or non-adverse-to-canal water, from 

Boca. If the pooled water release from Boca is more 

than the PCPOSW release from Donner, then the 

exchange volume is limited to the amount of the 

PCPOSW release. Likewise, if the pooled water release 

is less than the PCPOSW release, then the exchange 

volume will be equivalent to the pooled water release 

from Boca.
52 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

After the exchange volume has been determined 

for Donner, that volume of PCPOSW is exchanged to 

natural water and released. For Boca, the exchange of 

pooled water to PCPOSW is more complex because 

pooled water consists of adverse- and non-adverse-tocanal waters. Adverse-to-canal water is exchanged to 

PCPOSW before non-adverse-to-canal water is 

exchanged. The releases of adverse- and non-adverseto-canal waters from the reservoir are reduced by the 

same volumes that were exchanged.

The following assumptions were used in the 

model code to simulate the Donner–Boca Exchange.

• This exchange is not formally specified and 

described in a legal agreement. Thus, the conditions necessary to initiate this exchange and the 

categories involved in this exchange may 

change in response to changing needs of the 

parties involved.

• The exchange will be simulated if no required 

precautionary drawdown releases from Boca are 

currently simulated, even if Boca Reservoir is 

above the wintertime cap level. An exchange of 

PCPOSW from Donner Lake to Boca under this 

condition would provide more storage security 

for PCPOSW than if this exchange is not simulated and release of PCPOSW from Donner is 

required for precautionary drawdown.

• The exchange will be simulated only when the 

precautionary drawdown release of PCPOSW 

water from Donner Lake is above 5 ft3/s and the 

release of pooled water from Boca Reservoir is 

above 5 ft3/s. These threshold flows may be 

changed by the user.

Boca–Stampede Exchanges

It will often be desirable to exchange water stored 

in Boca Reservoir to Stampede Reservoir. Stampede is 

the largest reservoir in the Little Truckee River Basin 

(storage 226,500 acre-ft), and provides greater flexibility in storing water. Water is less likely to be released 

from this reservoir for flood-control criteria. Water 

released from Stampede is not generally constrained by 

outlet hydraulics and may be re-stored in Boca Reservoir. Stampede’s large storage capacity and flexibility 

in operations mean that it will normally possess more 

secure storage than other reservoirs. Also, because 

Stampede has a junior storage right to other reservoirs 

in the Truckee River Basin, it will be the last to fill. 

The USGS Truckee River Basin operations 

model simulates Boca–Stampede Exchange operations 

in the subblock enhanced storage security. The 

exchanges from Boca to Stampede are either paper 

exchanges, in which equal volumes are traded between 

the two reservoirs with no physical movement of water 

involved, or re-storage exchanges, in which water is 

released for storage in a downstream reservoir. There 

are three likely conditions under which these 

exchanges are simulated. 

1. When the storage of pooled water in Boca Reservoir is less than 5,000 acre-ft, then exchange nonadverse-to-canal water in Stampede Reservoir 

with fish water in Boca. This condition is simulated when Boca is using pooled waters for Floriston rates and Stampede pooled water is needed 

in Boca. The following exchanges are possible 

when Boca pooled water storage is less than 

5,000 acre-ft.: (1) paper-exchange fish water in 

Boca with non-adverse-to-canal water in Stampede Reservoir, and (2) exchange (by re-storage) 

non-adverse-to-canal water in Stampede to Boca.

2. When any non-adverse-to-canal (pooled) water is 

remaining in Stampede Reservoir on April 1, then 

exchange that non-adverse-to-canal water in 

Stampede to Boca Reservoir. Pooled water may 

reside in Stampede as a result of previous 

exchanges, such as those made to facilitate the 

timely release of fish water for spawning. The 

fish water in Boca may be spilled and lost during 

springtime filling of Boca. Thus, it would benefit 

Pyramid Lake fishes if any fish water in Boca 

could be exchanged to Stampede. When the date 

is April 1 and non-adverse-to-canal water is 

present in Stampede, a paper-exchange of fish 

water in Boca Reservoir with non-adverse-tocanal water in Stampede is simulated. 

3. As discussed in the section “Pyramid Lake Fish,”

simulated fish water is released from Stampede 

Reservoir for storage in Boca Reservoir as Boca 

pressure water. To maintain the Boca pressure 

water storage, when fish water storage in Boca 

falls below 2,000 acre-ft during a flow regime 1 

from March 1 to June 5, then a paper exchange 

of fish waters in Stampede is made with nonadverse-to-canal or adverse-to-canal pooled 

water in Boca. In this exchange for enhanced 

storage, a paper exchange is simulated between 
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 53

Stampede fish water and one of the two categories of pooled water in Boca: (1) paper-exchange 

non-adverse-to-canal water in Boca with fish 

water in Stampede, and (2) paper-exchange 

adverse-to-canal water in Boca with fish water 

in Stampede.

Merge Reservoir Releases for Multiple Objectives

Water released from a given reservoir may serve 

several objectives under current operations. As previously discussed, releases may consist of tagged waters 

of specific water categories, or may consist of untagged 

waters of any water category. Typically, releases made 

to satisfy specific downstream demands are tagged to 

specific water categories. Such releases in current 

operations are made to maintain or satisfy Floriston 

rates, Power Company M&I demands, Newlands 

irrigation, and Pyramid Lake fish flows. Untagged 

releases result from spills (including both uncontrolled 

spills over reservoir spillways and precautionary drawdowns based on flood-control criteria) or maintenance 

of minimum flows.

Releases of untagged and tagged waters from a 

given reservoir form what may be called a “merged 

reservoir release” because the untagged release may 

assume the categories of the tagged-water release. 

Thus, more than one objective may be satisfied. For 

example, minimum instream flows downstream from 

Lake Tahoe may be satisfied if releases made for 

Floriston rates exceed the minimum-flow requirement. 

If the demand for untagged releases is greater than 

proposed tagged releases, then water categories must 

be assigned to that part of the untagged releases that is 

greater than the proposed tagged releases by a rankorder scheme. The Interim Storage Contract of 1994 

(Bureau of Reclamation, 1994) addresses the rank 

order of water categories for mandatory untagged 

releases based on flood-control criteria from Stampede 

and Boca Reservoirs. These categories are used when 

uncontrolled spills and precautionary drawdowns from 

these reservoirs exceed tagged releases. The following 

list provides the order of water categories for release 

from storage in Stampede during these conditions. 

Note that project waters (fish water in Stampede and 

pooled water in Boca) are released last.

1. PCPOSW (Power Company privately owned 

stored water) in excess of 5,000 acre-ft when total 

combined storage of PCPOSW in both Stampede 

and Boca Reservoirs exceeds 5,000 acre-ft.

2. Fish credit water.8

3. Remainder of PCPOSW in both Stampede and 

Boca Reservoirs.

4. Fish water.

For Boca Reservoir, the following list provides 

the order of water categories for release from storage 

during these conditions.

1. PCPOSW in excess of 5,000 acre-ft when total 

combined storage of PCPOSW in both Stampede 

and Boca Reservoirs exceeds 5,000 acre-ft.

2. Fish credit water.

3. Fish water.

4. Remainder of PCPOSW in both Stampede and 

Boca Reservoirs.

5. Pooled water.

Untagged releases based on spills for the other 

Truckee River reservoirs and untagged releases for 

minimum flows at all reservoirs are not directly 

addressed in legal agreements and decrees.

The operations model simulates merged reservoir 

releases for multiple objectives in the subblock merge. 

First, for each reservoir, the proposed tagged releases 

are summed and then compared to the mandatory 

untagged releases representing flood-control releases 

or releases for downstream minimum flows. The larger 

of these two types of releases will be used as the newly 

proposed release. If the tagged release is greater than 

the mandatory untagged release, then the mandatory 

untagged release is satisfied by the water categories 

already proposed for release. Thus, additional untagged 

releases are not necessary. However, if the mandatory 

untagged release is greater than the tagged release, then 

the newly proposed release volume will be equivalent 

to the volume of the mandatory untagged release. The 

8

Fish credit water, under current operations as defined in 

the Interim Storage Agreement, is established by conversion on 

September 1 of that part of the combined storage of Power Company privately owned stored water in Stampede and Boca Reservoirs in excess of 5,000 acre-ft. Fish credit water is not simulated 

as a separate water category under current conditions in the operations model. Fish credit water is used for Pyramid Lake fish species similarly to fish water, but during spill situations, fish credit 

water will spill before fish water, as listed above. Fish credit water 

is further defined for draft TROA operations in the subsequent 

section “Proposed Water Categories.”
54 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

release is composed of categories used in the tagged 

releases up to the total volume of that tagged release. 

The difference between the untagged and tagged 

releases represents that volume of the mandatory 

untagged releases that must be assigned to water categories. Table 5 lists tagged and mandatory untagged 

releases for current operations from each reservoir as 

simulated in the model. 

For each reservoir, if it is determined that 

untagged releases exceed tagged releases, then that volume of untagged releases that exceeds tagged releases 

must be assigned to water categories according to a 

rank order (table 6). Each water category is assigned to 

the remaining untagged volume on the basis of rank 

order and the volume of the category available. In table

6, high rank (1 is highest) refers to the simulated release

order. If the volume of a water category of higher rank 

is insufficient to fill the remaining untagged volume, 

then a water category of a lower rank is used and this 

process is repeated until the remaining untagged volume is fully tagged with categories. For Prosser Creek 

and Stampede Reservoirs, the order of water categories 

changes for different types of releases as shown in 

table 6.

The following assumptions were used in the 

model code development for simulation of the merged 

releases from reservoirs.

• Except for those water categories specifically 

assigned in the Interim Storage Agreement 

(Bureau of Reclamation, 1994) for Stampede and 

Boca Reservoirs, the rank order of water categories for untagged releases is assumed. These rank 

orders may be modified by the model user.

• Natural water is assumed to be the inflow category for all reservoirs except Lake Tahoe, where 

pooled water is the inflow category. Thus, if a reservoir cannot store and must pass through all 

inflow, the water category passed through is natural water. Natural water can be applied toward 

Floriston rates, Truckee Canal demand, and Pyramid Lake fish demand.

• For each reservoir, there is only a stepwise determination of water categories for untagged 

releases as defined by the rank orders shown in 

table 6. Except for some blending of Power Company and TCID releases from Donner Lake, there 

is no blending of water categories for untagged 

releases in the subblock merge.

• Fish credit water is not simulated for current operations. If PCPOSW in the reservoirs exceeds 

5,000 acre-ft on September 1, that excess will 

transfer to fish water instead of fish credit water 

as stated in the Interim Storage Agreement. The 

rank order of water categories used for simulations and shown in table 6 does not consider

whether the volume of PCPOSW is greater than 

or less than 5,000 acre-ft.

• All Martis Creek Lake releases are simulated in 

the subblock flood-control criteria, as this reservoir is operated for flood control. See the previous section, “Flood Control-Criteria,” for a 

description of Martis Creek Lake operations. 

Storage in and releases from this reservoir consist 

only of natural water under current operations.

Current River Operations

In the Nevada part of the Truckee River Basin, 

water rights are based on the doctrine of prior appropriation, which is often stated as “first in time, first in 

right.” This doctrine states that the first person to put a 

quantity of water to beneficial use has a higher priority, 

or right, to the water than a subsequent water user. A 

water user is assigned a priority date (date of establishment of a water right) that is significant in relation 

to the dates assigned to other users of the same source 

of water. The priority date is important when the quantity of available water is insufficient to satisfy entitlements of all active water rights. Under drought 

conditions, users with later appropriative dates may not 

receive full entitlement or the amount normally 

diverted. Almost all of the major diversions from the 

Truckee River lie in the Nevada part of the basin and 

are governed by the prior appropriations doctrine. 

These major diversions include the Truckee Meadows 

diversions, lower Truckee River diversions, and Truckee River diversions to the Newlands Project.

In the California part of the Truckee River Basin, 

water rights are based on riparian water rights doctrine. 

The riparian doctrine states that all persons who own 

the land adjacent to a stream have an equal right to 

make reasonable use of the natural streamflow. Riparian users share the streamflow among themselves, and 

the concept of priority of use is not applicable. Under 

drought conditions users share shortages. Few major 

Truckee River diversions in the California part of the 

basin exist, but those few are operated according to 

individual decrees, such as the Sierra Valley Decree.
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 55

Current river operations can be defined as net 

diversions from the Truckee River in Nevada and California to satisfy the exercise of agricultural and M&I 

water rights. Most diversions made to meet agricultural 

demands occur during the irrigation season. The irrigation season usually is within the period from April 

through October of any given year. In practice, the 

beginning and end of the irrigation season are determined by the amount of recent precipitation, the type of 

crop grown, or the amount of water available in the 

river. Current river operations to meet agricultural 

demands are described in the next four sections. River 

operations to meet M&I demands under current operating conditions are described in a previous section, 

“Privately Owned Stored Water.”

Sierra Valley Diversion

The Sierra Valley Settlement Agreement of 1993 is the 

basis of operations for diversion of water out of the 

Little Truckee River to the Feather River Basin in 

California. The Sierra Valley Ditch diversion is determined using the 1991 Truckee Meadows priority table 

(Jeff Boyer, U.S. District Court Water Master, written 

commun., 1994) and the unregulated natural flow 

at Farad. According to the priority table, Sierra Valley 

has a priority date of 1870 and has a right to divert 

water when the unregulated flow is greater than 

196 ft3/s at Farad. The unregulated flow at Farad is 

computed using an equation, defined in the Sierra Valley Settlement Agreement of 1993, that relates measured flow at Farad, changes in storage in Truckee 

River reservoirs, Sierra Valley diversions, and evaporation in Truckee River reservoirs. This unregulated 

flow is computed using a 3-day running average. Also, 

Table 5. Tagged and untagged releases from reservoirs for current operations

Reservoir Tagged releases Untagged releases

Lake Tahoe Floriston rates: pooled water Releases due to high lake-level conditions

Minimum instream flow releases

Donner Lake Power Company M&I demand: PCPOSW

TCID demand for Newlands irrigation: TCIDPOSW

Pass-through of natural water based on storage 

priorities: natural water

Releases due to high lake-level conditions

Minimum instream flow releases

Prosser Creek Reservoir Floriston rates: pooled water (Tahoe–Prosser 

Exchange water) and natural water

Pyramid Lake fish releases: uncommitted water

Pass-through of natural water based on storage priorities

Flood-control releases including uncontrolled 

spills and precautionary drawdowns

Minimum instream flow releases

Independence Lake Power Company M&I demand: PCPOSW

Pass-through of natural water based on storage priorities

Releases due to high lake-level conditions

Minimum instream flow releases

Stampede Reservoir Pass-through of natural water based on storage priorities

Pyramid Lake fish releases: fish water

Power Company M&I demand: PCPOSW

Flood-control releases including uncontrolled 

spills and precautionary drawdowns

Minimum instream flow releases

Boca Reservoir Floriston rates: pooled water (adverse-to-canal and 

non-adverse-to-canal waters) and natural water

Pass-through of natural water based on storage priorities

Pyramid Lake fish releases: fish water

Power Company M&I demand: PCPOSW

Flood-control releases including uncontrolled 

spills and precautionary drawdowns

Lahontan Reservoir Carson Division demand for Newlands irrigation: 

pooled water

Flood-control releases including 

precautionary drawdowns
56 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

minimum-flow requirements of the Little Truckee 

River below the Sierra Valley diversion are considered. These minimum-flow requirements are 5 ft3

/s 

from March 15 to June 15, 3 ft3/s from June 16 to 

September 30, and zero the remainder of the year, 

as stated in the Sierra Valley Settlement Agreement 

of 1993.

The USGS Truckee River Basin operations model 

simulates Sierra Valley diversions in the subblock 

Sierra Valley diversions. The model computes the 

unregulated flow at Farad using the Sierra Valley 

Settlement Agreement equation with a 3-day running 

average of the daily flow. Using the Truckee Meadows 

priority table, the model simulates Sierra Valley ditch 

diversions during the irrigation season when the 

unregulated flow at Truckee River at Farad is greater 

than 196 ft3

/s. Diversions are limited to ditch capacity 

of 60 ft3

/s and to total flow physically available in the 

Little Truckee River (reach 185) above the diversion. 

Additionally, ditch diversions must leave adequate 

flow in the river to satisfy downstream minimum-flow 

requirements of 3 ft3/s or 5 ft3/s. Diversions are 

stopped when the allowable annual diversion volume 

of 14,266 acre-ft is reached.

Truckee Meadows Diversions 

Several diversions from the Truckee River are 

made for agricultural and M&I use in the Truckee 

Meadows between the USGS gaging station Truckee 

River at Farad, Calif., and the USGS gaging station 

Table 6. Rank order of water categories assigned to untagged releases, by

reservoir, under current operations

Reservoir Water Categories Assigned to Untagged Release

Lake Tahoe 1. Pooled water.

Donner Lake 1. Natural water.

2. PCPOSW and TCIDPOSW.

Prosser Creek Reservoir FOR FLOOD-CONTROL RELEASE:

1. Natural water.

2. Uncommitted water.

3. Tahoe–Prosser Exchange water.

FOR MINIMUM FLOW RELEASE

1. Natural water.

Independence Lake 1. Natural water.

2. PCPOSW.

Stampede Reservoir FOR FLOOD-CONTROL RELEASE:

1. Natural water.

If controlled spill (precautionary drawdown):

2. Fish water.

3. PCPOSW.

If uncontrolled spills:

2. PCPOSW.

3. Fish water.

FOR MINIMUM FLOW RELEASE:

1. Natural water.

2. Fish water.

Boca Reservoir 1. Natural water.

2. Fish water.

3. PCPOSW.

4. Adverse-to-canal water pooled water.

5. Non-adverse-to-canal water pooled water.

Lahontan Reservoir 1. Pooled water.
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 57

Truckee River at Vista, Nev. The Orr Ditch Decree 

(United States of America v. Orr Ditch Water Company, Equity No. A-3 (D. Nev. 1944)) provides rules 

and priorities for the allocation of Truckee River water 

to water-right holders downstream from the Farad 

gaging station. The Decree established both agricultural and M&I water rights. Since the court decision, 

many agricultural rights have been converted to M&I 

rights for use by the Power Company. Additionally, the 

Truckee River Agreement recognizes the Power Company’s right to a continuous flow of 40 ft3/s for M&I 

use in the Truckee Meadows. As of 1991, agricultural 

and M&I water rights are implemented by the Federal 

Water Master (FWM) through the use of the Truckee 

Meadows priority table (Jeff Boyer, U.S. District Court 

Water Master, written commun., 1994). Water rights 

are determined according to a fixed schedule of allotments based on priority date. The schedule lists the 

name of the ditch, water user, priority date, quantity of 

water available for each right, and estimated transit 

loss. Transit losses, also called conveyance losses, 

include seepage, evaporation, and phreatophyte use 

between the headgates at the river and the point of 

delivery.

Diversions from the river to a ditch are determined by considering (1) the water-right duties of 

each ditch as specified in the Orr Ditch Decree, (2) the 

irrigated acreage served by each ditch, and (3) an efficiency factor, which includes transit losses specified in 

the Orr Ditch Decree, for each ditch (Jeff Boyer, U.S. 

District Court Water Master, written commun., 1994). 

The water-right duty is defined as the volume of water 

decreed to be applied to each acre of irrigated land, in 

units of acre-ft per acre. The efficiency factor of a ditch 

diversion is a fraction (between 0 and 1) computed as 

the volume of water delivered to water-rights holders at 

the lateral farm headgates, divided by total diversion 

from the Truckee River. This measure is estimated, 

but includes updated information for each ditch diversion regarding transit losses specified by the Orr Ditch 

Decree (Jeff Boyer, U.S. District Court Water Master, 

written commun., 1994). 

The USGS Truckee River Basin operations 

model simulates Truckee River diversions in the Truckee Meadows by determining agricultural and M&I 

rights in the subblock initial assignments and computations and simulating diversions in the subblock Truckee Meadows diversions.

First, default numerical values are assigned to 

ditch duties, irrigated acreage, and efficiency for each 

agricultural and M&I right in the Truckee Meadows. 

These values are specified by the Truckee Meadows 

priority table, as described in the previous section, 

“Privately Owned Stored Water” (Jeff Boyer, U.S. 

District Court Water Master, written commun., 1994). 

All values assigned to duties, irrigated acreage, and 

efficiency may be modified by the user. Numerical values are not assigned to ditches that are considered permanently abandoned. If the ditch is not currently 

(1998) used, but is structurally intact for possible irrigation in the future, irrigated acreage is assigned a 

value of zero, but ditch duties remain as those specified 

in the Orr Ditch Decree. The maximum cumulative 

annual diversion, in acre-feet, for each ditch is computed by dividing the duty by the efficiency and then 

multiplying that result by the irrigated acreage. The 

irrigated acreage is those lands with decreed rights currently being irrigated. Rights, stated in terms of flow 

per day, are determined by dividing maximum cumulative annual diversion by the length of the irrigation season. Additionally, ditch diversion accumulators are 

reset to zero for each ditch at the beginning of the irrigation season, and all ditch diversions are set to zero 

outside of the irrigation season.

After initial numerical assignments and computations are made, based on the M&I rights as 

described above, M&I diversions are determined as 

in the previous section, “Privately Owned Stored 

Water.” Based on the agricultural rights as described 

above, diversions of Truckee River water for agricultural use are determined and simulated in the subblock 

Truckee Meadows diversions. To simplify the complexity of managing many individual water-right priority dates, several water-right priority dates were 

grouped together. The conditional logic compares the 

natural and pooled water flow at Farad to the total 

amount of agricultural and M&I rights that could be 

satisfied. Senior demands will be satisfied before junior 

demands. If the combined natural and pooled water 

flow at Farad is less than the total amount of demands, 

some junior priority-date groups will not be satisfied. 

Water to meet the agricultural rights allowable under 

simulated flow conditions is diverted from the mainstem to the appropriate ditch. Once the accumulated 

daily ditch diversions during an irrigation season has 

reached the maximum cumulative annual diversion for 

that ditch, the diversion is set to zero until the next irrigation season. 
58 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

In the Truckee Meadows, inflows to the Truckee 

River can include tributaries, ground-water gains, agricultural diversion returns, and M&I diversion returns. 

Time series containing estimates of tributary inflows or 

channel seepage losses, which could include groundwater gains or losses for the reach between Farad and 

Vista gaging stations, are described in the section 

“Data for Simulation of Streamflow and Operations.”

M&I and agricultural returns are determined by using 

observed or estimated values for use and returns in the 

Truckee Meadows and computing a monthly distribution (expressed as a percentage of annual return) of 

agricultural and M&I returns. 

Two important assumptions are made in this subblock. First, the default length of the irrigation season 

is 200 days. This variable may be changed by the user. 

Second, the beginning date of the irrigation season is 

determined every spring as either April 1 or April 15, 

based on the runoff index as described the section 

“Runoff Index,” under the section “Forecasts Affecting 

Operational Decisions.”

Lower Truckee River Diversions

The USGS gaging station Truckee River at Vista, 

Nev., designates a boundary between the upstream agricultural and urban lands of the Truckee Meadows and 

downstream agricultural and undeveloped range lands. 

Except for a diversion to the Newlands Project via the 

Truckee Canal that can carry up to about 900 ft3

/s (discussed in the subsequent section “Truckee River Diversions to Newlands Project”), virtually all diversions 

downstream from the Vista gaging station are to 

ditches that usually carry less than 40 ft3/s for irrigation 

of crops. 

The Truckee River Agreement of 1935 and the 

Orr Ditch Decree of 1944 provide rules and priorities 

for the allocation of Truckee River water to water-right 

holders downstream from the Vista gaging station. 

According to the Truckee River Agreement, 31 percent 

of all “diverted flow” between the Iceland gaging 

station and Derby Dam is allocated to the Truckee and 

Carson Divisions of the Newlands Project and to the 

Power Company’s highest-priority rights for Truckee 

River water to satisfy M&I demands. The other 69 percent is allocated to other agricultural and M&I 

demands. The Iceland gage is not currently operational 

and the USGS Farad gaging station (pl. 1) is used as a 

surrogate. The term diverted flow is considered to be 

that water used to meet Floriston rates and diverted 

from the Truckee River to ditches, the Truckee Canal, 

and municipal water intakes to meet agricultural and 

M&I demands, and Truckee River flow downstream 

from Derby Dam in excess of those irrigation rights 

downstream from Derby Dam. The “31-percent rule” is 

rarely practiced in the computation of allowable diversions to the Newlands Project, and therefore is not simulated in the operations model (Jeff Boyer, U.S. 

District Court Water Master, oral commun., 1996).

The Orr Ditch Decree, in part, adjudicates the 

appropriative surface-water rights on the Truckee 

River downstream from the Vista gaging station. These 

major water rights include diversions to Indian Ditch 

downstream from the Nixon gaging station (Claim 

Nos. 1 and 2), and diversions at Derby Dam to the 

Truckee Canal for the Newlands Project (Claim No. 3, 

which, in practice, is replaced by Adjusted OCAP). 

Additionally, for points of diversion downstream from 

the Vista gaging station, water rights are determined 

according to a fixed schedule of allotments based on 

priority date. The schedule lists the name of the water 

user, name of the ditch, quantity of water available for 

each right, and estimated transit loss.

As discussed in the previous section “Truckee 

Meadows Diversions,” diversions from the Truckee 

River for each ditch are determined by considering

(1) the water-right duties of each ditch as specified in 

the Orr Ditch Decree, (2) the irrigated acreage served 

by each ditch, and (3) an efficiency factor, which 

includes transit losses specified in the Orr Ditch 

Decree (U.S. District Court Water Master, written 

commun., 1995).

Under current operational practices, except for 

diversions to the Newlands Project, water rights along 

the Truckee River downstream from the Vista gaging 

station are usually satisfied, and therefore coordination 

of diversions with regard to the priority date of each 

water right is rarely practiced (Jeff Boyer, U.S. District 

Court Water Master, oral commun., 1996). This is 

because inflows from TMWRF, Steamboat Creek, and 

North Truckee Drain upstream from Vista, and groundwater inflows downstream from Derby Dam, usually 

provide ample water for irrigation demands. However, 

during dry years when the available flow rate is insufficient to satisfy all irrigation demands concurrently, 

attempts have been made to regulate diversions on a 

rotational basis to minimize shortages to individual 

water rights. Only during extreme shortages will diversions need to be coordinated by a schedule based on 

water-right priority dates.
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 59

The following discussion describes how the 

USGS Truckee River Basin operations model simulates Truckee River diversions downstream from the 

Vista gaging station. The discussion does not include 

diversions to the Newlands Project via the Truckee 

Canal, which is described in the subsequent section 

“Truckee River Diversions to Newlands Project.” To 

simulate diversions from the Truckee River downstream from the Vista gaging station, (1) initial numerical assignments and computations are made, and (2) 

daily irrigation demands, diversions, and returns are 

determined. These topics will be further described 

below.

In the subblock initial assignments and computations, default numerical values are assigned to ditch 

duties, irrigated acreage, and efficiency for each ditch 

downstream from the Vista gaging station (U.S. District Court Water Master, written commun., 1995). All 

values assigned to duties, irrigated acreage, and efficiency may be modified by the user. Numerical values 

are not assigned to ditches that are considered permanently abandoned. If the ditch is not currently (1998) 

used, but is structurally intact for possible irrigation in 

the future, irrigated acreage and efficiency are assigned 

values of zero, but ditch duties remain as those specified in the Orr Ditch Decree.

From these assignments, the maximum annual 

diversion volume for each ditch is computed in acrefeet. The maximum annual diversion volume is used to 

compute the daily diversion right, or demand, for each 

ditch as described later in the subsection “Daily Diversion Right.” For a given ditch, when the accumulated 

daily ditch diversion during an irrigation season reach 

the maximum allowable volume for the year, the diversion is “turned off” until the next irrigation season the 

following year. Other assignments in this subblock 

include the following items.

• Constant ground-water inflows are assigned to 

each reach of the Truckee River between Derby 

Dam and Marble Bluff Dam. The default values 

of ground-water inflows are based on USGS 

seepage runs, but may be modified by the user. 

The seepage runs were serial, nearly concurrent 

streamflow measurements along the length of the 

river and some irrigation ditches to determine 

where flow is gained from or lost to ground water 

(Berris, 1996). 

• Returns from water diverted to irrigation ditches, 

provide inflows to the river between the Vista 

gaging station and Marble Bluff Dam. The returns 

are assigned default values based on FWM estimates, but may be modified by the user (U.S. District Court Water Master, written commun., 

1995). These values are fractional factors that are 

applied to each ditch diversion.

• Ditch diversion accumulators are reset to zero for 

each ditch at the beginning of the irrigation season. Each accumulator accounts for total diversion volume to date by summing simulated daily 

ditch diversions.

• All ditch diversions and returns are set to zero 

outside of the irrigation season.

After initial numerical assignments and computations are made, daily irrigation demands, diversions, 

and returns are determined in the subblock lower Truckee River diversions. The Truckee River downstream 

from the Vista gaging station was divided into three 

segments for simulation of irrigation diversions: segment 1 from the Vista gaging station to Derby Dam 

(reaches 400 through 450), segment 2 from Derby Dam 

to Wadsworth, Nev. (reaches 460 through 490), and 

segment 3 from Wadsworth to Marble Bluff Dam 

(reaches 500 through 570). Simulation of daily irrigation demands, diversions, and returns involves five 

computations: (1) daily diversion right, or demand, for 

each ditch, (2) the “effective” demand for each ditch 

within a segment, (3) the total effective demand of all 

diversions within a segment, (4) daily diversions from 

the river to each ditch, and (5) daily returns to the river 

from each ditch. The term “effective” demand refers to 

the net demand from each ditch for water at the 

upstream end of the given segment, after considering 

inflows to and outflows from the river within that segment. The total effective demand may be more or less 

than the summed demands for all ditches in the segment, depending on inflow and outflow locations and 

volumes. When the total effective demand is greater 

than the simulated flow at the upstream end of a given 

segment, it is used to determine a factor for adjusting 

daily diversion rights of ditches within that segment.

1. Daily Diversion Right—The first computation is 

to determine the daily diversion right for each 

ditch. The daily diversion right is simply the maximum annual diversion volume (discussed earlier 

under initial assignments and computations) 

divided by the number of irrigation days and con-
60 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

verted to units of flow, cubic feet per second. This 

flow-rate value represents the average daily 

diversion demand for each ditch from the river at 

the location of the given ditch. Once the maximum annual diversion volume has been met, the 

daily diversion right becomes zero. 

2. Effective Demand—The second computation is 

the effective demand for each ditch. If a daily 

diversion right exists, it is then adjusted by subtracting inflows from ground water and precipitation, and adding outflows to evaporation and 

phreatophyte ET from the reach in which the 

ditch lies. Irrigation return flows from upstream 

ditches are also considered as inflows to a reach 

for this computation. This adjusted daily diversion right is called the effective ditch demand and 

characterizes the specific ditch’s demand for 

water at the upstream end of each segment. For 

example, if Gregory Ditch, a diversion in reach 

470 of segment 2 downstream from Derby Dam, 

has a daily diversion right of 3.3 ft3

/s, but evaporation and phreatophyte ET remove 0.2 ft3/s from 

that reach, the effective Gregory Ditch demand 

will be 3.5 ft3

/s at Derby Dam, the upstream end 

of segment 2. 

3. Total Effective Demand—The third computation 

is to determine the total effective demand by 

totalling the effective demand for all ditches 

within a segment. 

4. Daily Ditch Diversions—The fourth computation 

is to determine daily ditch diversions from the 

river to each ditch. The total effective demand is 

first compared to the simulated flow at the 

upstream end of the segment. If the total effective 

demand for a segment is less than the simulated 

flow, then each ditch within that segment may 

divert its entire daily diversion right. However, if 

the total effective demand is greater than the simulated flow, the entire daily diversion right for 

each ditch in the segment cannot be satisfied and 

a more complex approach is used to determine the 

diversions in a given segment. In those cases 

where water supply is insufficient, an adjustment 

factor is then determined. The adjustment factor 

represents the fraction of the total effective 

demand that can be satisfied by simulated flow at 

the upstream end of the segment, and is applied to 

the daily diversion right of each ditch in that segment. Under conditions when full entitlement is 

not possible, four steps are necessary to determine daily ditch diversions. These four steps 

adjust the daily diversion right of each ditch by 

(1) the adjustment factor just described above, 

(2) inflows from ground-water and precipitation 

to the reach in which the ditch lies, (3) outflows 

from the reach to evaporation and phreatophyte 

ET, and (4) return flows from upstream ditches. 

5. Irrigation Return Flows—The fifth computation 

is to determine return flows of diverted water 

from each ditch back to the river. Return flows to 

the Truckee River are simulated by applying the 

fractional factor described previously and determined in the subblock initial assignments and 

computations to each daily ditch diversion. 

Return flows from upstream ditches are also considered as inflows to a reach for the computation 

of effective demand for each ditch.

An additional objective of the simulation of lower 

Truckee River diversions is to provide the total effective demand of all diversions in segments 2 and 3 

downstream from Derby Dam to Marble Bluff Dam. 

Water rights of the diversions downstream from Derby 

Dam are more senior than the Truckee River water 

rights of the Newlands Project. Thus, allowable simulated diversions to the Newlands Project depend upon 

the total effective demand needed to satisfy water-right 

holders on the Truckee River downstream from Derby 

Dam. Truckee River water can only be diverted to the 

Truckee Canal after the senior water rights downstream 

from Derby Dam are satisfied.

Several assumptions were used in the model code 

to simulate Truckee River diversions downstream from 

the Vista gaging station.

• The default length of the irrigation season is 200 

days and begins on April 1 or April 15, based on 

NRCS runoff forecasts at Farad (Rebecca Wray, 

written commun., 1995). The earlier date is used 

if below-average to average runoff volume is 

forecasted, and the later date is used if normal or 

above-average runoff volume is forecasted. The 

length or begin date may be modified by the 

model user. 

• The model simulates diversions to ditches as continuous or average amounts for each day throughout the irrigation season, so long as Truckee River 
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 61

water is available. It is recognized that actual irrigation practices utilize water in a more cyclic 

manner. For example, in actual practice, fields 

might only be irrigated once every week or so 

with a larger daily diversion than the constant 

diversion simulated by the model. It is assumed 

that, in practice, the total volume diverted by any 

given ditch over a period of several days would be 

the same volume as that produced by the average 

daily diversion simulated by the model. This also 

means that given ample supplies of water, the 

model will divert the full legal amount every year, 

whether or not the water is needed (in actual 

operations, recent rains and different crop types 

may reduce the amount of water required by an 

irrigator).

• Diversions are not coordinated with regard to 

the priority date of each water right. Such coordination is rarely practiced because river flows 

usually provide ample water to meet irrigation 

demands.

• All ditches in a given segment are coordinated, 

but each of the three segments is autonomous. 

Thus, if flow at the upstream end of a given segment cannot satisfy the total effective demand, 

all ditches in that segment share the deficit. An 

exception to this assumption is when significant 

inflows contribute water to reaches toward the 

downstream end of the segment.

• Estimates of ground-water inflows are only 

used along the Truckee River downstream 

from Derby Dam and are based on seepage runs 

(Berris, 1996).

• The 31-percent rule is not simulated because 

it is rarely practiced in the computation of allowable diversions to the Newlands Project (Jeff 

Boyer, U.S. District Court Water Master, oral 

commun., 1996). 

• Returns to the river from ditch diversions are 

based on simple fractional factors applied to daily 

ditch diversions. Information on (1) hydraulic 

characteristics of some irrigation systems, (2) 

water rights, and (3) historical and present patterns of water use, returns, and spills obtained 

from the FWM were helpful to estimate returns to 

the Truckee River (U.S. District Court Water 

Master, written commun., 1995). The methods of 

estimating return flows are crude, but are more 

accurate than if return flows from diversions were 

ignored. As better information becomes available, the fractional factors may be modified by 

the user.

Truckee River Diversions to Newlands Project

Diversion of Truckee River water at Derby Dam 

to the Newlands Project via the Truckee Canal provides 

water for irrigation to about 3,500 acres, called the 

Truckee Division, along the Truckee Canal near Fernley, Nev., and about 56,500 acres, called the Carson 

Division, downstream from Lahontan Reservoir near 

Fallon, Nev. (Al Olson, Bureau of Reclamation, oral 

commun., 1997). The 32.5 mile-long Truckee Canal 

has a capacity of about 900 ft3/s and terminates at the 

reservoir. The interbasin diversion from the Truckee 

River to Lahontan Reservoir is used to supplement 

inflow from the Carson River for use by the Carson 

Division of the Newlands Project. For current river 

operations, only water from the categories pooled 

water (which includes natural water inflow to the river 

upstream from Derby Dam) and TCID water may be 

diverted to the Newlands Project.

Operating Criteria and Procedures (OCAP) were 

first introduced in 1967 with the objective to maximize 

the use of Carson River water for the Newlands Project 

and minimize the diversion of Truckee River water via 

the Truckee Canal. A more stringent OCAP was 

approved in 1973, and in 1988 the OCAP that was used 

from 1988 to 1997 was approved (Bureau of Reclamation, 1988). A revised OCAP called Adjusted OCAP, 

was implemented in December, 1997 (Bureau of Reclamation, 1997). Hereafter, OCAP in this report will 

describe the Adjusted OCAP approved in 1997, unless 

otherwise indicated. 

The OCAP establishes criteria for diversions of 

pooled water from the Truckee River to the Truckee 

Canal to provide irrigation water to the Newlands 

Project. The OCAP are consistent with the fulfillment 

of the Federal Trust responsibility to the Pyramid Lake 

Indian Reservation, meeting the requirements of the 

Endangered Species Act (ESA), and complying with 

the Orr Ditch Decree of 1944. Thus, waters dedicated 

to threatened and endangered Pyramid Lake fish and to 

more senior water rights on the Truckee River downstream from Derby Dam are not diverted to the Truckee 

Canal. Diversions from the Truckee River to the Truckee Canal are based on end-of-month storage objec-
62 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

tives for Lahontan Reservoir, projected water demands 

from the Truckee Division, and estimated Truckee 

Canal losses between Derby Dam and the reservoir. 

The Lahontan Reservoir storage objectives are 

shown in table 3 for the months June through December. For those months, pooled water may be diverted 

from the Truckee River to Lahontan when the reservoir 

volume is forecast to be less than the lower storage 

objective. Diversions are discontinued when the reservoir volume is forecast to equal or exceed the upper 

storage objective. The end-of-month Lahontan storage 

objectives for the months January through June 

are variable, with a goal of achieving a storage of 

190,000 acre-ft at the end of June. The Lahontan storage objectives for those months are influenced by 

(1) forecasted Carson River flow volume at the USGS 

gaging station Carson River at Fort Churchill, Nev.,

from the end of the current month through May or June, 

(2) Lahontan Reservoir losses from the end of the current month through May or June, and (3) forecasted 

Carson Division demand for irrigation water from the 

end of the current month through May or June. Two 

storage objectives are computed, based on the above 

items 1 through 3 for May and June. The minimum 

storage objective is then selected as the final storage 

objective for the current month.

After the end-of-month Lahontan Reservoir 

storage objective has been determined, the diversion of 

Truckee River water to the Truckee Canal can be determined. The diversion to the Truckee Canal is based on 

(1) the end-of-month storage objective for the reservoir, (2) the Truckee Division demand for the current 

month, (3) Truckee Canal conveyance losses for the 

current month, (4) the Carson Division demand for the 

current month, (5) reservoir seepage and evaporation 

losses for the current month, (6) reservoir storage at 

the beginning of the current month, and (7) forecasted 

Carson River flow volume at the USGS gaging station 

Carson River at Fort Churchill, Nev., for the current 

month.

Other aspects of OCAP include (1) calculation 

of the maximum allowable diversion (MAD) for each 

year, (2) establishment of efficiency targets, and (3) 

storage of credit water in Stampede Reservoir. The 

MAD is calculated annually as the maximum volume 

of water permitted to be diverted to the Newlands 

Project to satisfy the exercise of Newlands Project 

water rights. Efficiency targets and incentives were 

established as conservation measures to attain and 

improve project efficiency. Newlands Project efficiency is computed as the total amount of water delivered to water-rights holders at the farm headgates, 

divided by total delivery of water for use in the Truckee 

and Carson Divisions of the Newlands Project. Low 

efficiencies mean that conveyance/transit losses, such 

as seepage, evaporation, or other operational losses 

prior to delivery of water to headgates, are large. If the 

actual efficiency exceeds or falls short of the efficiency 

targets, incentive water credits or disincentive water 

debits, respectively, are applied to the Lahontan Reservoir storage level for determining Truckee River diversions. The Newlands Project may temporarily store 

credit water in Stampede in lieu of diversion to Lahontan to avoid spills and exceeding Lahontan storage targets. The credit water retained in Stampede may be 

released later in that year for diversion to Lahontan or, 

if not needed to meet Lahontan storage targets, may be 

retained for later release to Pyramid Lake.

The operations model simulates diversions to the 

Newlands Project in the subblock OCAP. To simulate 

diversions to the Truckee Canal, the model (1) assigns 

numerical values to constants and variables, (2) determines Lahontan Reservoir monthly storage objectives, 

(3) computes Lahontan Reservoir demands from the 

Truckee River, and (4) determines and simulates proposed Truckee River diversions. The first step, numerical assignments of constants and variables, represents 

important components for further computations. 

Assignments are made to specify values for the following items.

• Carson Division demand—Annual and monthly 

values that represent demands for irrigation water 

downstream from Lahontan Reservoir. Default 

values are provided (Al Olson, Bureau of Reclamation, written commun., 1996) or may be specified by the model user.

• Truckee Division demand—Monthly values that 

represent demands for irrigation water from the 

Truckee Canal for lands adjacent to the canal near 

Fernley, Nev. Two options of default values are 

provided (Al Olson, Bureau of Reclamation, written commun., 1996). Additionally, values may be 

specified by the model user.

• Truckee River downstream water rights—

Monthly demands for irrigation water from the 

Truckee River downstream from Derby Dam. 

These water rights are senior to water rights in the 

Newlands Project, and thus must be met before 
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 63

diversions can be made to the Newlands Project. 

Demands for irrigation water are computed in the 

subblock lower Truckee River diversions. These 

demands are based on water rights specified by 

the Orr Ditch Decree of 1944 and acreages currently irrigated (Jeff Boyer, U. S. District Court 

Water Master, written commun., 1995). (See the 

section “Lower Truckee River Diversions” for a 

more detailed description of the simulation of 

demands for irrigation water downstream from 

Derby Dam.) This is one of two options that 

describe senior water rights demands downstream 

from Derby Dam. The second option provides 

default values of irrigation demands that correspond to Orr Ditch Decree Claim 1 and other 

irrigation rights downstream from Derby Dam 

(Stetson Engineers Inc. and G.T. Orlob & Associates, written commun., 1996). Values of irrigation demands may also be specified by the 

model user.

• Lahontan Reservoir storage targets—Monthly 

upper and lower storage targets for the months 

June through December for the 1988 OCAP. 

Default values are provided as specified in the 

1988 OCAP (table 3) (Bureau of Reclamation, 

1988). A second option provides other default 

values for Lahontan Reservoir storage targets as 

specified in Adjusted OCAP (table 3) (Bureau of 

Reclamation, 1997). Values may also be specified by the model user.

• Lahontan Reservoir losses—Monthly reservoir 

losses that include seepage and evaporation. 

Default values are provided (Al Olson, Bureau of 

Reclamation, written commun., 1996).

• Truckee Canal conveyance losses—Daily conveyance losses along the entire canal. Estimated 

by regression equations provided by the BOR 

(Alan Olson, Bureau of Reclamation, written 

commun., 1996).

After numerical values are assigned to the variables described above, Lahontan Reservoir storage 

objectives are determined on the first day of each 

month. The following discussion describes the determination of storage objectives for the Adjusted OCAP, 

but, except for the presence of lower and upper storage 

objectives and the goal of obtaining higher storage 

objectives than Adjusted OCAP objectives, the 

determination is similar for the 1988 OCAP (Bureau 

of Reclamation, 1997). For the months July through 

December, storage objectives for Lahontan Reservoir 

specified in the Adjusted OCAP are used for simulations (table 3). However, for the months January 

through June, the model code computes the end-ofmonth storage objectives with a goal of achieving a 

storage of 190,000 acre-ft by the end of June. Within 

that period, for the months January through April, 

the storage objective is computed twice; the first 

computation determines the current monthly storage 

objective for the period from the end of the current 

month through May, and the second computation determines the current monthly storage objective for the 

period from the end of the current month through June. 

When the simulation date is in May, only one storage 

objective is computed for the period from the end of 

May through June. For June simulations, the storage 

objective is simply 190,000 acre-ft. 

The computation of the monthly storage objective 

for the months January through May requires an estimate of forecasted inflows to and outflows from 

Lahontan Reservoir. Forecasted Carson River inflows 

to Lahontan required for the computation are provided 

by the NRCS in their April through July runoff forecast 

for the USGS streamflow station Carson River at Fort 

Churchill, Nev. (Rebecca Wray, Natural Resources 

Conservation Service, written commun., 1995). Appropriate coefficients are provided to adjust the forecasted 

inflow to represent the periods form the end of the 

current month through May or June (Bureau of Reclamation, 1988). Forecasted outflows from Lahontan 

provided by BOR include forecasted reservoir seepage 

and evaporation and forecasted Carson Division 

demands (Alan Olson, Bureau of Reclamation, written 

commun., 1996). Forecasted reservoir seepage and 

evaporation represent the period from the end of the 

current month through May or June. Forecasted Carson 

Division demands are annual values adjusted by a coefficient provided to represent the period from the end of 

the current month through May or June. Inflows to 

Lahontan from the Truckee Canal are not considered in 

this computation. The final monthly storage objective 

is the minimum of the May and June computations if 

the month is between January and April, the June computation if the month is May, and 190,000 acre-ft if the 

month is June.

After Lahontan Reservoir storage objectives have 

been determined, Lahontan demands for Truckee River 

water are computed. The demands for Truckee River 
64 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

water are for the remainder of the current month and 

can be updated about once every five days, but this frequency can be modified by the user. The results of the 

computations indicate how much water is needed from 

the Truckee Canal to fulfill Lahontan storage objectives. In addition to requiring the current month storage 

objective, the computation requires current Lahontan 

storage and estimates of Carson River inflow, Carson 

Division demands, and reservoir seepage and losses 

from the current date to the end of the current month. If 

the monthly storage objective can be met at the end of 

the current month without importation of water from 

the Truckee River, then proposed diversions from the 

Truckee River for the remainder of the month are 

assigned to be zero. Otherwise, proposed diversions 

from the Truckee are computed as the difference 

between the storage objective and the forecasted reservoir storage at the end of the month without Truckee 

River inflow. 

In addition to providing water to the Carson Division via Lahontan Reservoir, the proposed diversion 

from the Truckee River must also provide irrigation 

water to the Truckee Division and provide enough 

water to compensate for conveyance losses along the 

Truckee Canal. Therefore, the computation of the proposed diversion requires a forecast of Truckee Division 

demands for the remainder of the month (Alan Olson, 

Bureau of Reclamation, written commun., 1996). The 

proposed diversion is then converted to daily flow and 

daily Truckee Canal conveyance losses are added. 

Conveyance losses are simulated using regression 

equations that are based on flow in the canal and the 

current month (Alan Olson, Bureau of Reclamation, 

written commun., 1996). Lastly, after all demands for 

Truckee River water are totalled, the daily proposed 

diversion is compared to the 900-ft3/s capacity of the 

Truckee Canal and the lesser of the two values is set as 

the desired diversion amount.

The proposed diversion computed above is a 

“sustained” diversion because that diversion will 

attempt to satisfy, using a constant diversion amount, 

the Lahontan Reservoir storage objective at the end of 

the current month. An alternative option in the model 

computes an “opportunistic” diversion that proposes to 

divert the maximum flow of water available from the 

Truckee River while still considering the capacity of 

the Truckee Canal. If the Lahontan storage objective is 

met before the end of the current month, the diversion 

to the reservoir is reduced to zero. This second model 

option still simulates a diversion to the Truckee Canal 

to provide irrigation water to the Truckee Division.

After the proposed diversion is computed, the 

diversion may be further limited by the availability of 

pooled water in the Truckee River and senior Truckee 

River water rights downstream from Derby Dam. For 

simulations, only water from the category pooled water 

may be diverted to the Newlands Project. Therefore, if 

TCID water is released from Donner Lake, it is converted to pooled water just upstream from Derby Dam 

for proper simulation of diversions.

An additional computation in the model code in 

the subblock OCAP is a forecast of Truckee Canal 

demand from the Truckee River for the periods March 

through June and April through June. These forecast 

diversion demands are made on the first day of March 

and April and are provided to the subblock Pyramid 

Lake fish operations to determine necessary releases 

from Truckee River reservoirs for Pyramid Lake fish 

spawning runs. This computation uses the Lahontan 

storage target of 190,000 acre-ft for June. The forecast 

then determines how much additional Truckee River 

water is necessary to make the June storage target, 

starting from the current storage. Similar to the forecasts described above, a water balance is determined to 

compute forecasted Truckee Canal demand from the 

current date though June. The water balance uses current Lahontan Reservoir storage, inflow from the Carson River to the reservoir, and several outflows from 

the reservoir and the Truckee Canal. Outflows include 

the Carson Division demand and seepage and evaporation losses from Lahontan Reservoir, the Truckee Division demand, and Truckee Canal losses from the 

Truckee Canal (Alan Olson, Bureau of Reclamation, 

written commun., 1996). 

Several assumptions were used in the model 

code development to simulate diversions to the 

Newlands Project.

• For simulation of the 1988 OCAP, July through 

December diversions to the Truckee Canal are 

based only on the lower storage objective of 

Lahontan Reservoir. The upper storage objective 

is not used to decide when diversions are reduced 

to zero.

• Computations of the forecasted end-of-month 

Lahontan Reservoir storage are made periodically 

throughout each month. Estimates of Carson 

Division demand and the reservoir seepage and 
DESCRIPTION AND SIMULATION OF TRUCKEE RIVER BASIN OPERATIONS 65

losses for the remainder of the month are prorated 

on a daily basis from the monthly values provided. Estimates of Carson River inflows for the 

remainder of the month are attained by subtracting simulated flow volumes since the beginning 

of the current month from the monthly forecast 

provided.

• Operations based on judgement, in contrast to 

documented rules and policies, are not simulated, 

nor are aspects of OCAP outside of the geographical scope of the operations model. Therefore, 

Newlands Project maximum allowable diversion 

(MAD), efficiency targets, incentives, and disincentives are not considered for the simulation of 

Truckee River diversions. These aspects of 

OCAP are dictated by unpredictable human and 

climatic factors in the Carson Division downstream from Lahontan Reservoir and the Truckee 

Division adjacent to the Truckee Canal. Also, 

individual actions taken by the Federal Water 

Master or BOR to reduce diversions to the Truckee Canal are not simulated. As a result, storage 

of credit water in Stampede Reservoir based on 

these types of decisions is not simulated. 

• The Truckee Canal capacity is assumed to be 

900 ft3/s. It may be modified by the user.

• Truckee Canal conveyance losses are assumed to 

be uniform along the 32.5-mile length of the 

canal. Losses for each canal reach were determined by the proportion of the length of that 

reach to the length of the entire canal.

• Inherent error exists in forecasted values. Therefore, simulated operations based on forecasts may 

not be as accurate as they would be with perfect 

foresight.

• A minimum flow of 5.0 ft3/s is simulated for the 

terminal reach of the Truckee Canal when Truckee Division demand for Truckee River water is 

positive but Lahontan Reservoir demand for 

Truckee River water is zero. This assumption 

assures that Truckee Division demands are satisfied.

• Truckee Division demands are opportunistically 

satisfied regardless of Lahontan Reservoir 

demands for Truckee River water.

• Diversions from the Truckee Canal to satisfy 

Truckee Division demands are apportioned along 

the reaches of the canal based on measured flows 

from 10 diversions along the Truckee Canal for 

water year 1993. The measured flow from each 

diversion was compared to the total measured 

flow from the 10 diversions to determine a proportion coefficient for each diversion. The appropriate coefficient is then applied to the monthly 

Truckee Division demand to estimate the 

monthly diversion from each reach.

• Diversions to satisfy animal demands (stockwater) along the Truckee Canal are not simulated. 

However, an option is available to specify stockwater demands along the canal.

• Categories are converted to pooled water at the 

downstream end of several reaches for use by Orr 

Ditch Decree water rights, including the Newlands Project. The following are water category 

changes for Truckee River reaches.

– For reach 240, just downstream from the Farad 

gaging station, the category natural water converts to pooled water.

– For reach 360, just downstream from the Glendale Water Treatment Plant, the most downstream Truckee Meadows M&I water intake 

on the Truckee River, natural water converts to 

pooled water and PCPOSW and Power Company M&I credit water convert to pooled 

water. Power Company M&I credit water is a 

water category only used in draft TROA operations. It is defined for draft TROA operations 

in the subsequent section “Proposed Water 

Categories.”

– For reach 390, just downstream from Truckee 

River confluences with Steamboat Creek and 

North Truckee Drain, natural water converts to 

pooled water.

– For reach 440, at the USGS gaging station 

Truckee River below Tracy, Nev., natural water 

and TCIDPOSW convert to pooled water.

Losses and Gains to Reaches

Losses and gains due to evaporation, precipitation, and inflows modify the volumes of reservoir and 

river reaches. Adjustments of reservoir and river storage accounts of water categories from evaporation, precipitation, and inflows are not directly addressed under 

current operations (Jeff Boyer, U.S. District Court 
66 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

Water Master, oral commun., 1998). For reservoirs, 

evaporation, precipitation, and inflows are not considered separately; rather, “net inflow” is computed as the 

change in reservoir volume plus measured outflows for 

each day. When daily net inflow is positive, the inflow 

of a given reservoir exceeds losses, and conversely, 

when daily net inflow is negative, losses from evaporation and seepage exceed the daily inflow. 

Under current operations, inflow to reservoirs, 

including tributary inflow and precipitation, is assigned 

to pooled water for Lake Tahoe and to natural water 

for the other lakes and reservoirs. However, when 

evaporation exceeds inflows, net inflow is negative 

and reservoir storage will decrease. Although not 

directly addressed in legal decrees and agreements, 

storage accounts of water categories must be adjusted 

for the reduction in storage in current operational practices. The accounts of water categories listed below 

for the seven major reservoirs upstream from the Farad 

gaging station are considered a reasonable approximation of those used in current practice to reduce reservoir 

storage.

Lake Tahoe

Reduction in reservoir storage is allocated 

entirely to pooled water.

Donner Lake

Reduction in reservoir storage is allocated first 

to daily Donner Lake inflow and second equally 

to Power Company privately owned stored water 

(PCPOSW) and TCID privately owned stored 

water (TCIDPOSW).

Martis Creek Lake

Reduction in reservoir storage is assigned to 

natural water.

Prosser Creek Reservoir

Reduction in reservoir storage is allocated first 

to natural water inflow and uncommitted water 

in proportion to their volumes, and second to 

Tahoe–Prosser Exchange water. 

Independence Lake

Reduction in reservoir storage is allocated 

first to Independence Lake inflow and second 

to PCPOSW.

Stampede Reservoir

Reduction in reservoir storage is allocated to 

all water categories in storage in proportion to 

their volumes.

Boca Reservoir

Reduction in reservoir storage is allocated to 

all water categories in storage in proportion to 

their volumes.

The following discussion describes how the 

operations model simulates evaporation, precipitation, 

and inflow losses and gains from reservoir and river 

reaches. First, the methods to simulate gains and losses 

will be described, and then the selection of water-category accounts for gains and losses.

Depending on the external time series input to 

reservoir and river reaches, either net inflow or separate evaporation and precipitation fluxes may be simulated (see previous section “Data for Simulation of 

Streamflow and Operations”). Unlike most operations, 

which are simulated in the SPECL block, tributary 

inflow, evaporation and precipitation fluxes, or net 

inflow to and from reservoir and river reaches is simulated in the RCHRES block of HSPF.

For Truckee River reservoirs except Lake Tahoe, 

Pyramid Lake, and river reaches downstream from 

Vista, external time series of evaporation and precipitation rates are input to the simulation model. Additionally, inflows are input to the model at reservoir reaches 

representing upstream model boundaries (Truckee 

River reservoirs except Lake Tahoe and Pyramid 

Lake). The inflows were determined by PRMS 

simulations as described in the previous section, 

“Data for Simulation of Streamflow and Operations.”

To simulate evaporation and precipitation volume 

fluxes to each reservoir and river reach, the time 

series of rates are applied to the daily simulated 

surface area of reservoir and river reaches (see 

previous section, “Description of Hydrological 

Simulation Program–FORTRAN”). 

For Lake Tahoe and river reaches upstream from 

Vista, external time series of net inflows are input to the 

simulation model. Evaporation and precipitation are 

included in net inflow, and therefore are not considered 

separately as described just above. Daily net inflow to 

Tahoe was calculated by continuity; daily net inflow 

equals the change in storage plus outflow. External 

time series of daily net inflows to river reaches 

upstream from Vista were provided by two methods as 

described in the previous section, “Data for Simulation 

of Streamflow and Operations.” Upstream from Farad, 

daily net inflows to river reaches were determined by 

model simulations using PRMS. Between Farad and 

Vista, daily net inflows were determined using water 
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 67

balance computations or regression analysis. When 

daily net inflow is positive, the inflow to Tahoe or to 

the river reaches upstream from Vista exceeds losses, 

and conversely, when daily net inflow is negative, 

losses from evaporation exceed the daily inflow. For 

Lahontan Reservoir, losses are simulated as described 

in the previous section, “Truckee River Diversions to 

Newlands Project.”

Storage accounts of water categories must be 

adjusted for changes in storage resulting from losses 

and gains to reaches. Reservoir inflows for simulation 

of current operations, including tributary inflow and 

precipitation, are assigned to pooled water for Lake 

Tahoe and to natural water for the other lakes and reservoirs. For river reaches, inflow, including tributary 

inflow and precipitation, is assigned to natural water 

upstream from the Farad gaging station. Downstream 

from Farad, all inflows from tributaries and precipitation are assigned to pooled water. 

Simulated losses from river reaches from evaporation and ET from phreatophytes are assigned to 

pooled water downstream from the Vista gaging station 

(Berris, 1996). Upstream from the Vista gaging station, 

losses from river reaches are implicit in the described 

methods used to determine net inflows from tributaries. 

Because the net inflows to river reaches upstream from 

Farad are positive, losses are not assigned to water 

categories upstream from Farad. However, losses may 

exist between Farad and Vista. These losses are 

assigned to pooled water.

Simulated reservoir losses, except for Pyramid 

Lake, from evaporation or negative net inflows are 

allocated to categories as described in the list above by 

rank order. If more than one category shares the same 

rank, then evaporation is assigned to those categories in 

proportion to the volumes of those categories. For Pyramid Lake, evaporation will be allocated to pooled 

water.

Assumptions were made in developing the code 

to simulate losses and gains from evaporation and precipitation and some of the more notable assumptions 

follow.

• Depending on the external time series data, tributary inflows, evaporation, and precipitation, 

rather than net inflows, may each be input to the 

simulation model for all reservoir reaches except 

Lake Tahoe (see previous section, “Data for Simulation of Streamflow and Operations”). This 

assumption may create small differences, when 

loss and gain volumes are assigned to water categories, when compared to the assignment of 

losses and gains to water categories using just net 

inflow as input to the simulation model for those 

reaches.

• Evaporation is only assigned to natural water for 

Martis Creek Lake simulation.

Description and Simulation of Operations

Under Draft Truckee River Operating 

Agreement and Water Quality Settlement

Agreement

Draft TROA (Bureau of Reclamation and others, 

1998), still being negotiated as of 1998, and the 

WQSA, signed in 1996, are designed to make more 

effective and efficient use of water categories in reservoir operations to achieve multiple objectives, including:

1. Increasing the drought water supply for M&I uses 

in the Truckee River Basin in California and the 

Truckee Meadows.

2. Increasing the water supply and improving water 

management for maintenance of cui-ui flow targets for endangered and threatened Pyramid Lake 

fish.

3. Enhancing instream flow for fish and water quality.

4. Maintaining reservoir storage levels for recreational uses.

5. Satisfying the exercise of Orr Ditch Decree 

water rights.

6. Satisfying dam safety and flood-control 

requirements.

The objectives may be achieved by revising many 

of the current operations regarding water storage and 

release practices. Such changes to current operations 

will add the flexibility to practice different operations 

that are more effective for different circumstances. 

However, operations under draft TROA and WQSA are 

designed to not conflict with Orr Ditch Decree water 

rights or interfere with flood-control criteria. The fol-
68 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

lowing example illustrates how a proposed reservoir 

operation, the in-lieu-of exchange, can be used to 

achieve multiple objectives.

In-lieu-of exchanges involve the release of one or 

more water categories from one or more reservoirs inlieu of a release of water of yet another category from 

one or more other reservoirs. This type of exchange is 

illustrated for Boca Reservoir and Lake Tahoe as follows. Suppose pooled water in Boca is currently being 

released at a rate of 60 ft3

/s to satisfy Floriston rates. 

However, an enhanced draft TROA minimum-flow 

requirement downstream from Lake Tahoe requires a 

release of 75 ft3

/s, or an additional release of 25 ft3/s 

greater than the current release of 50 ft3/s downstream 

from the lake, which is only enough to meet current 

minimum-flow requirements. If a proposed credit 

water category is available to increase the release from 

Tahoe and if the release from Boca pooled water can be 

reduced by an equivalent amount, an in-lieu-of 

exchange may be made to satisfy both the enhanced 

flow requirement and the Floriston rate requirement. 

This example uses fish credit water to increase 

the release from Lake Tahoe, but one or more other 

proposed credit water categories in Tahoe may be used 

for this exchange. Thus, 25 ft3

/s of the 60 ft3/s pooled 

water release from Boca Reservoir may be substituted 

by a release using fish credit water from Tahoe. First, 

the pooled water release from Boca of 60 ft3

/s is 

reduced to 35 ft3/s. That volume of pooled water not 

released from Boca and now held in storage is 

exchanged to fish credit water. At the same time, an 

equivalent volume of fish credit water in Tahoe is 

exchanged to pooled water and then immediately 

released to be counted toward Floriston rates. Thus, a 

transaction occurred in which part of a pooled water 

release from Boca was substituted by a release from 

Tahoe of pooled water (exchanged from fish credit 

water). The following four objectives were achieved by 

this in-lieu-of exchange.

1. Floriston rates were maintained even though 

the pooled water releases originated from 

different reservoirs.

2. The enhanced draft TROA minimum-flow 

requirement was achieved downstream from 

Lake Tahoe.

3. Boca Reservoir water-surface elevation was 

sustained for recreational uses.

4. Fish credit water was moved from Lake Tahoe 

to Boca Reservoir. Fish credit water in Boca 

can then be exchanged upstream into Stampede 

Reservoir, which is considered to be the safest 

reservoir for long-term storage of credit water 

and more accessible than Lake Tahoe. 

Draft TROA and WQSA are separate agreements 

that can be implemented separately or together. 

Although the two agreements contain separate objectives, they do contain many common elements. For this 

report, it will be assumed that when draft TROA is 

implemented, WQSA will be implemented also. 

WQSA will utilize procedures and opportunities primarily provided by draft TROA, and will not provide 

additional procedures. However, WQSA by itself does 

not provide as many opportunities to achieve waterquality benefits as does draft TROA. Additionally, 

WQSA by itself does not provide opportunities to 

achieve benefits other than water-quality benefits, as 

does draft TROA. Although draft TROA and WQSA 

will only be discussed together hereafter in this report, 

the USGS Truckee River operations model provides 

three options for simulation: (1) current operations, 

(2) current operations combined with draft TROA and 

WQSA operations, and (3) current operations, combined with WQSA operations, but without draft TROA 

operations.

Two key elements of draft TROA and WQSA that 

enable changes to current operations include (1) reduction of reservoir releases used to maintain flows for 

Floriston rates and simultaneous retention of that water 

as credit water in storage, and (2) exchange of water 

stored in or released from Truckee River reservoirs 

with water stored in other Truckee River reservoirs. 

The first element involves reducing the required flow at 

the Farad gaging station by parties entitled to otherwise 

divert Truckee River water from Floriston rates 

releases. The consumptive use portion of such water 

would be retained as credit storage in reservoirs and 

would be converted to new credit water categories for 

accounting purposes. Additionally, this first element 

involves reducing the required flow at the Farad gaging 

station when Truckee River flows downstream from 

Derby Dam, that were released for Floriston rates, are 

not needed to satisfy Orr Ditch Decree rights or instream flow targets. For this method of credit storage, 

the entire volume of water not needed to satisfy Orr 

Ditch Decree rights is retained and converted to a credit 

water category. Credit storage, as described above, 
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 69

does not reduce Floriston rates. Instead, the rates would 

be a standard from which flow reductions and subsequent water storage can be determined. The newly designated water categories would be available only to 

satisfy those objectives for which they were retained in 

storage. These water categories, newly designated for 

draft TROA and WQSA, will be defined in the subsequent section “Proposed Water Categories.”

The second element involves the use of water 

exchanges between reservoirs to coordinate releases 

and achieve multiple objectives. Many exchanges are 

specifically referred to in draft TROA as mandatory 

exchanges. These exchanges must occur when specified conditions exist. Voluntary exchanges are subject 

to agreement between affected parties. Many voluntary 

exchanges are explicitly referred to in draft TROA, but 

additional voluntary exchanges, not specifically enumerated in the draft TROA, also are allowed if the 

affected parties agree. 

Proposed Water Categories

A major difference between current and draft 

TROA operations is the creation, use, and exchange of 

credit waters under draft TROA. The following credit 

water categories are identified in draft TROA (with 

base amounts or storage limits where applicable).

• California M&I credit water (CMICW) —

Water stored for M&I uses in California. Up to 

8,000 acre-ft of CMICW could be accumulated 

with a maximum of 3,000 acre-ft in Truckee 

River reservoirs other than Lake Tahoe. 

• Fernley credit water—Water stored and used 

by the town of Fernley for M&I purposes.

• Fish credit water—Water stored and used for the 

benefit of Pyramid Lake fish. This credit water is 

established, stored, and managed differently than 

fish water under current operations. There is no 

storage limit of fish credit water.

• Joint Program fish credit water (JPFCW) —

A part of fish credit water stored and used by 

California for recreational pool and instream flow 

purposes. The total amount of JPFCW in storage 

at any time shall not exceed 20,000 acre-ft.

• Newlands Project credit water—Water stored 

and used to satisfy OCAP demands.

• Other credit water—Water stored and used 

for beneficial uses that are not defined in draft 

TROA at this time.

• Power Company emergency drought supply 

(PCEDS)—Water stored in Stampede Reservoir 

to provide water under severe drought conditions for Truckee Meadows M&I purposes. 

The maximum amount for PCEDS is 7,500 acreft as defined in draft TROA.

• Firm Power Company M&I credit water (firm 

PCMICW)—Water stored in Stampede Reservoir 

and used to provide water under drought conditions to Truckee Meadows for M&I purposes. 

The base amount for firm PCMICW is defined 

below in the definition for nonfirm PCMICW.

• Nonfirm Power Company M&I credit water

(nonfirm PCMICW) —Any water other than 

firm PCMICW and PCPOSW stored in a Truckee 

River reservoir and used for Truckee Meadows 

M&I purposes. The amount of firm and nonfirm 

PCMICW stored would be based on M&I 

demand in Truckee Meadows and California 

depletions (diverted water not returned to the 

Truckee River) in the Truckee River Basin in California. The amount of nonfirm PCMICW to be 

carried over from one year to the next is based on 

the existence of a drought situation as defined in 

the section “Forecasts Affecting Operational 

Decisions.” As annual M&I demand in the Truckee Meadows for Truckee River water increases 

from 80,000 acre-ft/yr to 119,000 acre-ft, and as 

California’s M&I depletion of Truckee River 

basin water increases from 3,000 to 16,000 acreft per year, the nondrought-situation carryover 

limit for storing firm PCMICW would increase 

from 2,000 to 12,000 acre-ft and the nondroughtsituation carryover limit for nonfirm PCMICW 

would increase from 4,000 to 20,000 acre-ft as 

described by the Preliminary Settlement Agreement (PSA) (California Department of Natural 

Water Resources, 1991, p.126). During the nondrought situation an adjustment, as a percent 

determined in the PSA, is made in the computation for the carryover storage of nonfirm 

PCMICW, whereas during a drought situation, 

no adjustment is made.

• Water-quality credit water (WQCW)—Water 

acquired and dedicated to augment instream 
70 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

flows in the Truckee River from the Truckee 

Meadows to Pyramid Lake to enhance water 

quality and preserve wildlife and fish habitat 

along the lower Truckee River downstream 

from Derby Dam, pursuant to the Truckee River 

Water Quality Agreement. There is no storage 

limit for WQCW. 

Proposed Reservoir Operations

Under draft TROA and WQSA, several reservoir 

operations use proposed water categories for storage, 

exchanges, and demands. These operations are discussed in the following sections. 

Storage of Proposed Water Categories

Under draft TROA and WQSA, credit water 

categories can be established and accumulated within 

several Truckee Basin reservoirs. Draft TROA allows 

flexibility for storage and accumulation of these new 

water categories; several categories of water may be 

stored in the same reservoir and each category may be 

stored in several reservoirs. Currently (1998), there are 

several “new” categories of credit water still under 

negotiation. As a result of conceptual uncertainties 

associated with these “new” water categories and time 

constraints for documentation of this model, the proposed water categories referred to as Fernley credit 

water, Newlands Project credit water, and other credit 

water were not coded and simulated in the USGS Truckee River Basin operations model and, therefore, are 

not described further in this report.

California Municipal and Industrial Credit Water 

Under draft TROA, California can store a part of 

its unused surface-water allocation in Truckee River 

reservoirs for M&I purposes. California M&I credit 

water (CMICW) would be created in Lake Tahoe by 

exchange of a direct diversion appropriative right of 

natural water originating downstream from Tahoe in 

lieu of a release from Tahoe to satisfy that diversion 

amount. Once in Lake Tahoe, it could be exchanged to 

other Truckee River reservoirs. Up to 8,000 acre-ft 

could be accumulated, with a maximum of 3,000 acreft in Truckee River reservoirs other than Lake Tahoe. 

That part of California’s surface-water allocation not 

diverted (either directly for agricultural or M&I use or 

accumulated as CMICW storage) can be used to create 

Joint Program fish credit water (JPFCW), which could 

be used to maintain instream flows or recreational pool 

levels in California. Generally, storage, release, and 

exchange of CMICW storage would have a priority 

junior only to that of project water. 

The following discussion describes how the operations model simulates storage of CMICW. Simulation 

of CMICW and JPFCW is difficult because, in actual 

operations, management criteria not yet established 

will be used in a planning and scheduling process that 

determines what part of California’s surface-water 

allocation will be used for direct diversion (for M&I or 

agricultural use), for storage as CMICW, or for storage 

as JPFCW. Because the scheduling procedure to be 

used by California could not be fully characterized in 

the model code, the simplifying assumptions that follow were developed. In the operations model, California’s surface-water allocation is first used to satisfy 

direct diversion demands for agricultural and M&I use. 

That part of the surface-water allocation not used can 

then be used to satisfy storage needs for CMICW. After 

direct diversion and storage of CMICW, any of California’s unused surface-water allocation will be available to create JPFCW.

The first step in simulating the storage of 

CMICW is to assign numerical values to the following 

variables in the initial numerical assignments and 

computations subblock.

• Annual volumes are established for California 

surface-water allocation (10,000 acre-ft) and total 

allocation (32,000 acre-ft). Total allocation 

includes both surface- and ground-water allocations.

• Variables are initialized that accumulate annual 

CMICW storage and JPFCW storage.

• Base demands are set for California M&I ground 

and surface water and for surface-water irrigation. The default base level demands are 1992 

values obtained from John Sarna (California 

Division of Water Resources, oral commun., 

1997).

• Annual growth-rate factors are set for M&I 

surface-water use, M&I ground-water use, 

and surface-water irrigation.

• A CMICW storage factor, used to determine the 

target amount of credit water storage desired in 

any year, is set by the user. The factor is computed as ratio of the desired amount of credit 

water in storage divided by the current direct 

diversion demand for surface water. For example, 
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 71

if the direct diversion demand for surface water in 

a given year is expected to be 5,000 acre-ft, California may elect to keep only three-fourths of 

that amount in storage as credit water storage for 

insurance purposes in case of drier-than-expected 

conditions. So, the CMICW storage factor in 

this instance would be 0.75 and would be in 

effect for the entire simulation. In this example, 

CMICW would only be created if current storage 

of CMICW was less than the target storage of 

3,750 acre-ft (0.75 x 5,000 = 3,750), even though 

up to 8,000 acre-ft of CMICW can be stored 

under draft TROA rules. 

After initial numerical assignments and computations are made, storage of CMICW up to the target 

amount is simulated in the subblock California M&I 

creation. If the demand (base demand adjusted by the 

growth-rate factor) for direct diversion of surface water 

in a year is less than California’s surface-water allocation (10,000 acre-ft), then the balance is available for 

storage in Lake Tahoe as CMICW if the following conditions are met.

• Lake Tahoe releases must be greater than minimum or enhanced reservoir release requirements.

• Floriston rates are satisfied.

• Total CMICW currently simulated in storage 

must be less than 8000 acre-ft. 

• Total CMICW currently simulated in storage is 

less than the target CMICW storage.

• The proposed amount of water to be stored as 

CMICW must be available as additional pooled 

water in Lake Tahoe. Also, the hydraulic capacity 

of the outlet at the lake must be sufficient to allow 

the release, in addition to what is already being 

released, of that amount of water proposed for 

storage as CMICW, just as would be required if 

California were to exercise its direct diversion 

right downstream. 

If all of these conditions are met, then an amount 

up to the target amount of CMICW is created by transfer of pooled water in Lake Tahoe to CMICW. The target storage amount is further adjusted by the amount of 

CMICW already in storage. In other words, a final target storage is computed by subtracting any existing 

CMICW already in storage from the target storage. 

Any of California’s remaining surface-water allocation 

not targeted for storage or already planned for direct 

diversion will then be available for storage as JPFCW. 

The amount of water available for JPFCW will be the 

surface-water allocation minus California’s planned 

direct diversion minus the target storage for CMICW. 

Using the example in the last bullet under initial computations above, if California demand for direct diversion of surface water is 5,000 acre-ft and the storage 

factor is 0.75, then 1,250 acre-ft would be available for 

the creation of JPFCW that year (10,000 − 5,000 − 

3,750 = 1,250), assuming no existing storage of 

CMICW at the time. See the following section, “Power 

Company Municipal and Industrial Credit Water, Fish 

Credit Water, Water-Quality Credit Water, and Joint 

Program Fish Credit Water,” for a discussion of the 

establishment and storage of JPFCW. 

Various assumptions were used in this subblock.

• California M&I diversions are assumed to be constant for every day of the year from January 1st 

through December 31st. Irrigation diversions are 

assumed to be constant for every day of the irrigation season (length of beginning and ending 

dates for the irrigation season may vary). As with 

irrigation water, no more than 25 percent of the 

surface water available for CMICW can be used 

in any one month for creation of CMICW.

• The entire surface-water allocation each year is 

used for direct diversion (for agricultural and 

M&I use), CMICW storage, or JPFCW storage. 

The ground-water use is thus limited to 22,000 

acre-ft per year (32,000 − 10,000 = 22,000), even 

though more ground water could be used in practice if the surface-water allocation is not used. 

The demand for ground water is accounted for in 

this program because it must be known to determine California depletions and is used, ultimately, in the computation of allowable Power 

Company M&I credit water storage (see the 

section “Proposed Water Categories”).

• The operations model does not allow exchanges 

for storage of up to 3,000 acre-ft of CMICW in 

other Truckee River reservoirs, even though draft 

TROA permits such exchanges. Currently, the 

only fresh-water intake (point of demand) for 

California M&I use is at the town of Truckee, 

Calif. Lake Tahoe is the only storage facility 

upstream from Truckee that could be operated to 

meet California M&I demands. CMICW supplies 
72 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

exchanged to other Truckee River reservoirs 

could not be called upon unless (1) new treatment 

facilities were constructed downstream from one 

or more of these reservoirs, or (2) a voluntary 

exchange of that CMICW into Lake Tahoe was 

made. For these reasons, the ability to exchange 

up to 3,000 acre-ft of CMICW from Lake Tahoe 

to other reservoirs was not included in the operations model. 

Power Company Municipal and Industrial Credit 

Water, Fish Credit Water, Water-Quality Credit 

Water, and Joint Program Fish Credit Water

Draft TROA provides procedures for accumulation and storage of Power Company M&I credit 

water (PCMICW), fish credit water, water-quality 

credit water (WQCW), and Joint Program fish 

credit water (JPFCW) in addition to storage of other 

water categories. The following discussion will first 

describe how these credit waters will be accumulated 

under draft TROA and then describe accumulation as 

simulated in the operations model.

As previously discussed, PCMICW can be used 

as M&I drought supply by the Power Company. It can 

be accumulated by (1) creating and accumulating the 

consumptive use portion of former agricultural diversion rights (specified in the Orr Ditch Decree) acquired 

by the Power Company that would have been released 

to maintain Floriston rates, (2) re-storage of PCPOSW 

released from Independence Lake to a designated reservoir, or (3) implementing a number of mandatory 

and voluntary exchanges and transfers. Only the first 

method will be described in this section. For that 

method, PCMICW will be accumulated by a reduction 

of releases used to maintain Floriston rates corresponding to the daily consumptive use portion of the former 

agricultural diversion right. The term former agricultural diversion right means a water right from the 

Truckee River or its tributaries, originally used for 

irrigation in accordance with the Orr Ditch Decree, 

that has been purchased or otherwise acquired for uses 

other than agricultural. The second and third methods 

of accumulating PCMICW are addressed in the sections “Mandatory Exchanges and Transfers” and 

“Voluntary Exchanges,” respectively.

PCMICW will be classified as either “firm”

or “nonfirm.” Firm Power Company M&I credit 

water (firm PCMICW) can only be stored in Stampede Reservoir. It is a relatively secure water category 

because it is given a high priority for storage and would 

be one of the last waters to evaporate or to be released 

or spilled during flood-control operations. Firm 

PCMICW also has the first right to credit store in 

Stampede from July 1 to December 31 of any year if 

the volume of firm PCMICW in the reservoir is below 

its base amount and if a nondrought situation is determined (see previous section “Proposed Water Categories” and a later section “Drought Situation” for 

discussions on firm PCMICW base amounts and nondrought situations, respectively). Nonfirm Power 

Company M&I credit water (nonfirm PCMICW)

will be less secure than firm PCMICW because it has a 

lower priority for storage and will evaporate or be 

released or spilled during flood-control operations 

before firm PCMICW. Nonfirm PCMICW can be 

stored in all Truckee River reservoirs. PCMICW created by release reductions can be added to reservoir 

storage even if that storage means downstream waterquality targets9

 will not be achieved.

Fish credit water is water other than fish water 

that can be stored and used directly for the benefit of 

Pyramid Lake fish. Fish credit water can be accumulated by (1) retaining in storage that portion of pooled 

water not needed to immediately satisfy Orr Ditch 

Decree water rights and that would have flowed to 

Pyramid Lake, and (2) implementing a number of 

mandatory and voluntary exchanges and transfers. 

Only the first method will be described further in this 

section. For that method, pooled water not needed to 

meet Orr Ditch Decree demands and retained as fish 

credit water would have flowed to Pyramid Lake as 

excess to Orr Ditch demands. The second method of 

accumulating fish credit water, implementing exchanges and transfers, is addressed in the sections of 

this report, “Mandatory Exchanges and Transfers” and 

“Voluntary Exchanges.” Unlike accumulation of 

PCMICW corresponding to acquired water rights, 

there is no limit to the accumulation of fish credit 

water. The priority for storage of fish credit water is 

less than that of pooled water, firm PCMICW, and fish 

water. Therefore, it will be spilled before these other 

9

Water-quality targets consist of target instream flows in the 

Truckee River at Sparks or downstream from Derby Dam (reaches 

370 and 450, respectively) to resolve water-quality problems and 

to improve fish and wildlife habitat. Water-quality targets will be 

discussed later in the section “Water-Quality Targets and Related 

Instream Flow Transfers.”
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 73

categories. Unlike PCMICW, fish credit water cannot 

be accumulated if such storage results in water-quality 

targets not being achieved.

The first 7,500 acre-ft of PCMICW transferred to 

fish credit water in Stampede Reservoir will be 

reserved as a drought water supply for Truckee Meadows M&I uses. This water, called Power Company 

emergency drought supply (PCEDS) in the operations model, can only be used for M&I purposes after 

nonfirm and firm PCMICW and Power Company 

POSW (PCPOSW) supplies have been exhausted and 

5,000 acre-ft has been pumped from the dead storage 

pool of Independence Lake. PCEDS water will have 

the highest-storage priority and, therefore, will not be 

subject to spill and will not be subject to evaporation 

unless it is the last water category in Stampede Reservoir. A more detailed discussion on the creation of 

PCEDS is presented in a subsequent section, “Other 

Exchanges and Transfers.”

As previously discussed, a part of California’s 

surface-water allocation not scheduled for diversion 

directly from the Truckee River or stored as California 

M&I credit water may be reserved as Joint Program 

fish credit water (JPFCW) for use in providing minimum instream flows and reservoir recreation pools in 

Truckee River reservoirs in California. Provided that 

storage of PCEDS water in Stampede Reservoir is at its 

7,500 acre-foot limit, half of the fish credit water accumulated and stored each year will be considered to be 

JPFCW, up to the annual allocation limit and subject to 

a 20,000 acre-ft maximum at any time. The priority for 

storage and spill is that of fish credit water. Once 

released for instream flows, JPFCW will ultimately 

flow to Pyramid Lake, but it can be temporarily restored in a downstream reservoir.

As previously discussed in the section “Proposed 

Water Categories,” water-quality credit water

(WQCW) is dedicated to augment instream flows in the 

Truckee River from the Truckee Meadows to Pyramid 

Lake for the enhancement of water quality and to preserve wildlife and fish habitat along the lower Truckee 

River downstream from Derby Dam. The WQSA provides for acquisition of Orr Ditch Decree water rights 

for the creation of WQCW. The accumulation of 

WQCW will correspond to the consumptive use portion of acquired water rights. Additional accumulation 

of WQCW of up to 6,700 acre-ft per year will correspond to those Orr Ditch water rights irrigated by sewage effluent from Truckee Meadows ground-water 

sources rather than irrigated from pooled water from 

the Truckee River. 

WQCW can be accumulated or created by three 

methods under draft TROA in conjunction with 

WQSA. The first method involves reducing releases 

corresponding to the consumptive use portion of Orr 

Ditch Decree water rights acquired under WQSA that 

would otherwise have been released to maintain Floriston rates, and converting the retained pooled water 

WQCW. The second method involves the accumulation of WQCW during a fish run corresponding to the 

consumptive use portion of acquired Orr Ditch Decree 

water rights flowing directly to Pyramid Lake. This 

water was not released to maintain Floriston rates and, 

in effect, augments fish water releases during the fish 

run. As a result, the excess water flowing to Pyramid 

Lake corresponds to a volume of fish water not 

released from reservoirs during periods when cui-ui 

flow targets are in effect (fish runs). It is this stored 

volume of fish water that may be converted to WQCW 

in accordance with the daily water rights acquired 

under WQSA. A discussion on cui-ui flow targets is 

given in the previous section, “Pyramid Lake Fish.”

The third method involves the instream creation of 

WQCW within the Truckee River by transferring to 

WQCW that part of pooled water obligated to Orr 

Ditch Decree water rights acquired by WQSA. 

Instream creation of WQCW is different from the previous two methods in that it involves creation of 

WQCW as a flow within the river rather than as storage 

within a reservoir. The instream flow conversions are 

limited to those times when Truckee River flow is less 

than the specified water-quality target. 

The first and second methods of accumulation of 

WQCW will be described further in this section. The 

third method of WQCW accumulation, instream creation of WQCW is addressed in a subsequent section, 

“Water-Quality Targets and Related Instream Flow 

Transfers.” The priority for storage of WQCW is junior 

to the priority of all water categories designated under 

current operations, Power Company M&I credit waters 

(PCMICW), fish credit water, California M&I credit 

water (CMICW), Joint Program fish credit water 

(JPFCW), and Power Company emergency drought 

supply (PCEDS). Accordingly, WQCW will be spilled 

before these other categories. 

The following discussion describes how the 

model simulates the creation of the draft TROA 

categories Power Company M&I credit water 
74 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

(PCMICW), fish credit water including Joint Program 

fish credit water (JPFCW), and water-quality credit 

water (WQCW). The initial assignments and computations subblock determines the volume of Orr Ditch 

Decree water rights acquired for PCMICW and 

WQCW. The credit storage subblock computes accumulations of PCMICW, WQCW, and fish credit water 

and JPFCW by reduction of releases for Floriston rates. 

WQCW also may be accumulated by a second method 

in the credit storage subblock, in which fish and fish 

credit waters retained during fish runs are exchanged to 

WQCW. A third method for creation of WQCW 

involves the instream conversion of pooled water to 

WQCW in the Truckee River and is described in the 

section “Water-Quality Targets and Related Instream 

Flow Transfers.” The primary objective of instream 

creation of WQCW is similar to the objective of releasing WQCW: to satisfy water-quality targets at Sparks 

and downstream from Derby Dam. Therefore, the 

instream creation of WQCW is simulated with reservoir releases of water-quality water in the subblock 

water-quality credit water operations. Lastly, credit 

waters accumulated by exchanges between reservoirs 

or by re-storage is typically an auxiliary benefit from 

many operations that are discussed in numerous sections regarding draft TROA operations. Such operations that serve other objectives in addition to their 

primary objective can be called “multi-purpose” operations and illustrate the flexibility available under draft 

TROA. Consequently, these multi-purpose operations 

are discussed elsewhere in this report. Additionally, 

creation of firm and nonfirm PCMICW and creation of 

Power Company emergency drought supply (PCEDS) 

will be described in a subsequent section, “Other 

Exchanges and Transfers.”

The initial assignments and computations subblock provides default values of former irrigated acreages to determine water rights acquired for PCMICW 

and WQCW waters. The default values may be modified by the user. Acquired water rights are determined 

by applying consumptive use duties, rather than irrigation ditch duties, to the former irrigated acreages. 

Consumptive use duties, referring to water actually 

consumed for irrigation that does not return to the river, 

are assumed to be 2.5 acre-ft per acre. These duties are 

less than irrigation ditch duties because ditch efficiencies and return flows are not considered. 

Additional water rights for creation of WQCW, 

up to 6,700 acre-ft per year, are obtained from irrigation of Orr Ditch water rights using sewage effluent 

originating from Truckee Meadows ground water 

sources rather than pooled water from the Truckee 

River. Thus, irrigators use sewage effluent instead of 

pooled water. As a result, that pooled water may be 

retained in storage for conversion to WQCW. The volume of sewage effluent used for irrigation is set by the 

user in the subblock initial assignments and computations. This volume is then added to the acquired water 

rights for creation of WQCW.

From the above assignments and computations, 

the annual water rights acquired for PCMICW and 

WQCW are used to compute the daily water rights for 

each purpose. Because the Power Company may 

directly divert acquired agricultural water rights from 

the Truckee River for M&I uses, the daily water right 

for credit storage is limited to the consumptive use portion of acquired rights not diverted (a discussion of 

Power Company M&I demands for Truckee River 

water was given in the previous section “Privately 

Owned Stored Water”). The daily water rights constitute the maximum daily volume of PCMICW and 

WQCW that may be created. The creation of each 

water category during a given month may not exceed 

25 percent of its annual water right allocation. It is 

assumed that former agricultural diversion rights can 

only be used to create draft TROA water categories 

during the irrigation season because these rights are 

based on agricultural uses during this period.

Creation of fish credit and Joint Program fish 

credit waters (JPFCW) are not based on model code in 

the initial assignments and computations subblock. 

Instead, creation of fish credit water, from which 

JPFCW and Power Company emergency drought supply (PCEDS) waters are created, is based on retaining 

pooled water releases for the maintenance of Floriston 

rates if that release is not needed to satisfy Orr Ditch 

Decree rights and, as a result, flows to Pyramid Lake. 

Therefore, a determination is made in the subblock 

credit storage whether or not pooled water releases for 

Floriston rates can be retained for creation and storage 

of these waters.

After initial assignments and computations are 

made, the subblock credit storage simulates the creation and storage of credit water by (1) reducing the 

portion of releases for Floriston rates not required to 

satisfy the exercise of water rights and converting the 

retained water to Power Company M&I credit, fish 

credit, or water-quality credit waters, or (2) converting 

retained fish and fish credit waters to WQCW during 

fish runs. Reduction of releases to maintain Floriston 
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 75

rates are made in accordance with (1) excess Power 

Company water rights not diverted for M&I uses that 

could convert to PCMICW and water rights acquired 

for WQCW, (2) the flow of pooled water to Pyramid 

Lake for fish-credit water, and (3) the allowable reduction of releases of pooled water for Floriston rates. 

Note that reservoir pass-throughs of natural water for 

Floriston rates and Truckee Canal diversion rights, as 

discussed in the sections “Floriston Rates” and “Reservoir Pass-Throughs to meet Newlands Project 

Demands,” may also be reduced and the natural water 

retained will be used for creation and storage of 

PCMICW, fish credit water, and WQCW. Hereafter, to 

simplify the text, reduction of these reservoir passthroughs will be implicitly included within the discussion of reduction of Floriston rates releases for creation 

and storage of credit waters. 

Priorities and constraints further influence the 

manner in which the credit waters are created and accumulated. PCMICW and fish credit water have equal 

priority for creation and storage, whereas WQCW has 

a lesser priority. However, the Power Company will 

have the first right to store firm PCMICW in Stampede 

Reservoir from July 1 through the following December 

31 of any year if the volume of firm PCMICW in 

Stampede is below the base amount and if it is determined that a drought situation does not exist. (See the 

subsequent section “Forecasts Affecting Operational 

Decisions” for a description of a drought situation.) 

Note that for simulations, nonfirm PCMICW will be 

first established under the conditions described above. 

Firm PCMICW will then be established from nonfirm 

PCMICW up to the base amount by simulating a 

transfer as described in the subsequent section “Other 

Exchanges and Transfers.” Fish credit water and 

WQCW may not be added to storage by reduction of 

releases if that storage results in water-quality targets 

not being met in the Truckee River at Sparks or 

downstream from Derby Dam (reaches 370 and 450, 

respectively). 

The following is an overview of the conditional 

logic upon which storage of PCMICW, fish credit 

water, WQCW, and JPFCW by reduction of releases 

for Floriston rates is based.

1. Determine credit storage rights. Credit storage 

rights are the volume of credit waters that can be 

accumulated in appropriate reservoirs based on 

appropriate adjustments to former diversion 

rights or to unused pooled water flowing to 

Pyramid Lake (reach 580).

Adjust former diversion rights acquired for 

PCMICW as determined in the subblock initial 

assignments and computations. Daily credit 

storage rights for PCMICW are based on acquired 

rights (estimated consumptive use portion of 

diversion right) not currently needed for Truckee 

Meadows water demand as determined in the subblock Power Company operations. Credit storage rights are reduced to zero if accumulated 

creation for the year exceeds the acquired water 

rights or if releases of PCPOSW or PCMICW are 

made to satisfy Truckee Meadows water demand.

Determine credit storage rights of fish credit 

water based on pooled water downstream from 

Derby Dam (reach 450) that flows to Pyramid 

Lake and storage of fish credit and Joint Program 

fish credit water from the previous time step. 

Credit storage rights for fish credit water are 

reduced to zero during fish runs.

Adjustments to daily credit storage rights for 

WQCW are limited by the accumulated amount 

each year. If accumulated WQCW equals or 

exceeds the acquired rights, storage rights are 

reduced to zero. Further, credit storage rights are 

reduced to zero when attainment of water-quality 

targets along the Truckee River depends on 

releases or instream creation of WQCW or if 

water-quality targets cannot be attained.

2. Determine maximum reduction of releases for 

Floriston rates for each reservoir. The maximum 

reduction is based on the difference between 

the currently calculated release value and the 

required minimum release for each appropriate 

reservoir. Required minimum releases, or 

“release floors,” are of two types: overall and 

category. “Overall release floors” are based on 

releases that do not require specific category 

releases, such as releases for minimum-flow targets or releases for required spills or precautionary drawdowns. “Category release floors” are 

based on specific categories that are involved 

in higher-priority operations and exchanges than 

those currently considered, such as the Tahoe–

Prosser Exchange, as discussed in the section 

“Tahoe–Prosser Exchange” under “Current 
76 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

Operational Exchanges.”

The allowable reduction in release is determined 

for the following reservoirs and water categories.

• Lake Tahoe—pooled water.

• Donner Lake—not applicable (no credit 

waters are created in this reservoir by the 

operations model).

• Martis Creek Lake—not applicable (current 

version of operations model does not simulate creation of credit waters in this reservoir, 

although draft TROA specifies creation of 

fish credit water during flood-control operations).

• Prosser Creek Reservoir—Tahoe–Prosser 

Exchange water and natural water.

• Independence Lake—not applicable (no 

credit waters created in this reservoir by the 

operations model).

• Stampede Reservoir—natural water.

• Boca Reservoir—adverse-to-canal, nonadverse-to-canal, and natural waters.

3. Determine preliminary volume of credit water 

that can be created by reduced reservoir releases. 

Total credit storage rights (PCMICW storage 

rights plus fish credit water storage rights plus 

WQCW storage rights from item 1 above) are 

compared with total allowable reduction of reservoir releases (item 2) from all appropriate reservoirs listed above. The minimum value is 

considered as a preliminary measure of the total 

volume of credit water that can be created in all 

appropriate reservoirs. 

4. Determine maximum amount of credit waters that 

can be created while accounting for water-quality 

flow targets at Sparks and downstream from 

Derby Dam. The flow targets are currently set 

to 300 ft3/s and 135 ft3/s, respectively, during 

June–September and 50 ft3

/s at both sites for the 

remainder of the year. This computation involves 

computing the difference between simulated flow 

at Sparks and below Derby Dam at the beginning 

of the time step and the value of the respective 

water-quality targets. This computation ensures 

that the creation of fish credit water and WQCW 

will not reduce simulated flows below waterquality targets.

5. Determine the volumes for PCMICW, WQCW, 

and fish credit water that can be created and 

stored using the maximum amount of credit water 

that can be created (item 4). This determination 

imposes a complex set of constraints and limitations for the credit waters, including priorities for 

creation, storage, and adherence to water-quality 

targets. As previously discussed, PCMICW and 

fish credit water typically have equal priority of 

creation and storage, whereas WQCW has a 

lesser priority. However, firm PCIMICW may 

have the highest priority for credit storage in 

Stampede Reservoir between July 1 and December 1 if the storage of firm PCIMICW is below its 

base amount and if there is no drought situation. 

Additionally, creation of fish credit water and 

WQCW must not result in the failure to achieve 

water-quality targets. Creation of PCMICW, 

however, is not limited by this constraint. 

For simulations, the creation and storage of each 

type of credit water is based on a comparison of 

the overall maximum volume available for credit 

water creation (item 4) and the total daily credit 

storage right determined for each type of credit 

water (item 1). The outcomes of the comparisons 

determine the volume of each type of credit water 

that can be created for all appropriate reservoirs. 

The reservoir for which each credit water is created is determined after this step. The outcomes 

of the comparisons are outlined in detail below.

• If the maximum volume available for credit 

water creation equals or exceeds the total 

storage right of all credit waters considered, 

then the creation of each type of credit water 

will correspond to the daily credit storage 

right for that type of water determined in 

item 1 above.

• If the maximum volume available for credit 

water creation is less than the total storage 

right of all credit waters considered, then two 

outcomes are possible.

If the maximum volume available for credit 

water creation is less than the total storage 

right of PCMICW, fish credit water, and 
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 77

WQCW, but exceeds the storage right of 

PCMICW plus fish credit water, then creation of PCMICW and fish credit waters will 

correspond to the daily credit storage rights 

for those waters as determined in item 1 

above. Because of its lesser priority for creation and storage, creation of WQCW will 

be restricted to the difference between maximum volume available for credit water creation and the storage right of PCMICW plus 

fish credit water just determined.

If the maximum volume available for credit 

water creation is less than the storage right of 

PCMICW plus fish credit water, then 

WQCW cannot be created because of its 

lower priority for creation. Because 

PCMICW and fish credit waters have an 

equal priority for creation, the model computes a proportional coefficient relating maximum volume available for credit water 

creation to the storage right of PCMICW plus 

fish credit water. The proportional coefficient 

is applied only to the daily credit storage right 

for fish credit water. The coefficient is not 

used for the creation of PCMICW because 

the creation of this water category is not 

restricted by the attainment and maintenance of water-quality targets. Therefore, 

PCMICW is computed simply as the difference between the total volume of credit water 

creation unrestricted by water-quality targets 

(item 3 above) and the volume of fish credit 

water to be created.

6. Determine the total reduction in releases for Floriston rates corresponding to the volume of credit 

waters to be created and accumulated in reservoirs. The total reduction of releases for Floriston 

rates is simply the summation of the volumes of 

credit water creation determined in item 5 and 

corresponds to the maximum volume of credit 

water that can be created while accounting for 

water-quality flow targets described in item 4. 

The subblock credit storage uses the total reduction in releases for Floriston rates to appropriately 

adjust reservoir releases to retain pooled and natural waters for transfer to credit waters.

The adjustment of releases from each reservoir 

and the volume of retained pooled and natural 

water to be converted to PCMICW, fish credit 

water, and WQCW in each reservoir is outlined in 

item 7.

7. Prioritize the reservoirs and stored water categories used for credit water creation and storage. 

The following list describes the order of reservoirs for the simulation of reducing releases for 

Floriston rates and converting the category of the 

retained water to credit waters. The list is based 

on the rank-order list of reducing releases when 

Floriston rates are exceeded, as described in the 

section “Floriston Rates.”

• Lake Tahoe pooled water if the date is 

between April 1 and October 31 and if the 

water surface elevation is greater than 

6,225.5 ft.

• Prosser Creek Reservoir Tahoe–Prosser 

Exchange water if the date is between April 1 

and September 3 and if storage is less than 

19,000 acre-ft (desired recreation volume 

threshold).

• Boca Reservoir non-adverse-to-canal water.

• Boca Reservoir adverse-to-canal water.

• Prosser Creek Reservoir Tahoe–Prosser 

Exchange water if the date is between April 1 

and September 3 and if storage is greater than 

19,000 acre-ft or if the date is between September 4 and March 31.

• Lake Tahoe pooled water if the date is 

between April 1 and October 31 and if the 

water surface is between 6,223.0 ft (outlet 

rim) and 6,225.5 ft or if the date is between 

November 1 and March 31.

• Stampede Reservoir natural water.

• Boca Reservoir natural water.

• Prosser Creek Reservoir natural water.

8. Determine the reduction of releases for each 

appropriate reservoir. For each reservoir listed 

above in item 7, the total reduction in releases for 

Floriston rates determined in item 6 is compared 

to the maximum reduction in releases for that reservoir (item 2). The minimum value of the comparison is then used to reduce the release for each 

reservoir.
78 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

9. Determine the volume of retained water to be 

transferred to each type of credit water at each 

reservoir. The total reduction in releases for Floriston rates (item 6) represents the volume of 

releases to be reduced and subsequently credit 

stored. It will be used to govern credit water creation in each reservoir. 

If the maximum reduction in release for Floriston 

rates at a given reservoir (determined in item 2) 

equals or exceeds the total reduction in releases 

for Floriston rates for all appropriate reservoirs 

(item 6), then the volume of retained water used 

for transfer to each type of credit water corresponds to the volume that can be created and 

accumulated of that type of credit water for all 

appropriate reservoirs, as described in item 5.

If the maximum reduction in release for Floriston 

rates at a given reservoir is less than the total 

reduction in releases for Floriston rates for all 

appropriate reservoirs, then the volume of 

retained water transferred to each type of credit 

water is proportionally reduced from the volume 

of each type of credit water that can be created 

and accumulated for all appropriate reservoirs.

10. Transfer retained water to appropriate credit 

water categories as determined in item 9.

11. Decrement the total reduction in releases for Floriston rates corresponding to the volume of credit 

waters to be created and accumulated in reservoirs (item 6) according to the volume of retained 

water to be transferred to credit waters (item 8).

Decrement the volume of each type of credit 

water that is available for creation (item 5) 

according to the volume of retained water transferred to each type of credit water (item 9).

12. Determine the creation of Joint Program fish 

credit water (JPFCW), which is based on the 

unused portion of California’s surface-water allocation each year (see discussion in the section 

“California Municipal and Industrial Credit 

Water.”) If California does not use the direct 

diversion rights of its surface-water allocation or 

credit store the unused portion of that direct 

diversion right, then the unused annual allocation 

amount is available for creation of JPFCW. 

JPFCW is created concurrently with fish credit 

water. Half of the created fish credit water is 

transferred to JPFCW. 

Creation of Power Company emergency drought 

supply (PCEDS) is discussed in the section 

“Other Exchanges and Transfers,” and is simulated in the subblock TROA mandatory 

exchanges.

13. Accumulate credit waters as they are created and 

stored each calendar year. The PCMICW and 

WQCW accumulated each year will be compared 

with credit storage rights on the following day 

(item 1).

In addition to the creation of credit waters by 

reduction of releases for Floriston rates, WQCW may 

be created during periods when cui-ui flow targets are 

in effect (fish runs) (see section “Pyramid Lake Fish”). 

This is accomplished by converting retained fish and 

fish credit waters already in storage to WQCW in 

exchange for unused pooled water flowing to Pyramid 

Lake during a fish run. The unused pooled water flowing past upstream diversions to Pyramid Lake used for 

this exchange results from reduced consumptive use 

associated with former agricultural water rights 

acquired in accordance with the provisions of WQSA. 

This unused pooled water augments, in effect, fish 

water and fish credit water releases during a fish run.

The following list is an overview of the conditional logic upon which the storage of WQCW by 

retention of fish and fish credit waters during a fish run 

is based.

1. Determine credit storage rights of WQCW. 

Adjust former diversion rights acquired for 

WQCW as determined in the subblock initial 

assignments and computations. Daily credit 

storage rights exist if (1) WQCW volume established for the current year is less than the consumptive use portion of former agricultural rights 

acquired, (2) the simulation period is within a fish 

run of fish regime 1 (see section “Pyramid Lake 

Fish”), and (3) unused pooled water corresponding to the consumptive use portion of daily water 

rights acquired by WQSA is flowing to Pyramid 

Lake (reach 580). If any of these conditions is not 

true, WQCW will not be accumulated. Note that 

during fish runs, the daily water rights acquired 

by WQSA will flow past diversions, including the 
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 79

Truckee Canal, to Pyramid Lake. Additional 

adjustments limit the accumulation of WQCW.

• WQCW will not be accumulated when attainment of water-quality targets along the Truckee River depends on current releases or 

instream creation of WQCW.

• WQCW accumulation will be limited to the 

consumptive use portion of acquired water 

rights flowing to Pyramid Lake.

• WQCW accumulation will be further limited 

to the cui-ui flow targets determined for fish 

regime 1. 

2. Prioritize the reservoirs and stored water categories used for creation of WQCW during a fish run. 

The following list is the order in which reservoirs 

and water categories are evaluated for storage of 

WQCW and is loosely based on the priority list 

of reservoir releases for fish runs (see section 

“Pyramid Lake Fish”). 

• Stampede Reservoir—fish credit water.

• Prosser Creek Reservoir—fish credit water.

• Boca Reservoir—fish credit water.

• Lake Tahoe—fish credit water.

• Stampede Reservoir—fish water.

• Prosser Creek Reservoir—uncommitted 

water.

• Boca Reservoir—fish water.

3. Determine the volume of WQCW to be created in 

each reservoir that potentially can release fish and 

fish credit water for cui-ui flow targets. However, 

a given reservoir cannot credit store if it is releasing for flood control as mandated by flood-control criteria (see previous section, “Flood-Control 

Criteria”). 

If the reservoir is allowed to credit store, the volume of credit storage is computed on the basis of 

the daily credit storage right (item 1 above) and 

the volume of water from appropriate water categories that could potentially be released for the 

fish run. The potential release of that water category is limited by the volume available in storage 

and the hydraulic constraints of the outlet. 

4. Transfer that volume of retained fish or fish credit 

water to WQCW in accordance with item 3.

5. Decrement the daily credit storage right, determined in item 1, by the volume of fish and fish 

credit water transferred to WQCW.

6. Add the newly created credit water to the annual 

accumulated WQCW. The annual accumulated 

WQCW will be compared with credit storage 

rights on the following day (item 1).

Several assumptions were made in developing the 

code to simulate the creation, accumulation, and storage of all kinds of credit waters. Some of the more 

notable assumptions follow.

• Credit waters can only be created during the irrigation season if their creation is based on former 

diversion rights specified in the Orr Ditch Decree. 

This assumption is specific to PCMICW and 

WQCW. The volume of these waters created in 

any given month within the irrigation season may 

not exceed 25 percent of their annual water right.

• PCMICW accumulation is simulated as nonfirm 

PCMICW from which firm PCMICW will later 

be created by transfer in accordance to the base 

amount required for firm PCMICW (see subsequent section, “Other Exchanges and Transfers”).

• Simulations of credit water creation and storage 

do not attempt to combine reductions of releases 

from more than one reservoir concurrently to 

optimize other objectives. However, elsewhere in 

the model code, water categories and releases are 

exchanged between reservoirs to satisfy other 

objectives. 

• Credit water creation and storage are not simulated for Martis Creek, Donner, and Independence Lakes.

• The priority order of reservoirs for reducing 

releases for Floriston rates and subsequent creation of credit waters is based on priorities for 

reducing releases when Floriston rates are 

exceeded. The priority list may be rearranged by 

the model user.

• The priority order of reservoirs for creation and 

storage of WQCW during fish runs is assumed 

and is loosely based on the priority list of reser-
80 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

voir releases for fish runs. The priority list may be 

rearranged by the model user.

• Reservoir releases of fish or fish credit water during a fish run are not required for creation of 

WQCW during a fish run. The only requirement 

is to demonstrate that reservoirs would have had 

to release fish or fish credit water if pooled water 

did not augment flow to Pyramid Lake.

Reservoir Releases to Meet Downstream Demands 

Under draft TROA, reservoir releases and diversions to satisfy demands may differ from those specified under current operations. These differences may 

be as simple as updated specifications for release procedures to maintain Floriston rates. However, most of 

the changes will be more extensive. First, additional 

proposed demands (California M&I, water-quality 

targets, and local M&I water use from Lake Tahoe 

and Donner and Independence Lakes) will need to be 

simulated under draft TROA conditions. Second, in 

addition to the current categories used to satisfy current 

demands, TROA will provide categories that could be 

used to meet both current demands (for example, 

PCMICW for Power Company Operations demands 

and fish credit water for Pyramid Lake fish demands) 

and new demands under draft TROA (for example, 

CMICW for California M&I demands and WQCW for 

water quality demands). Also, reservoir releases to satisfy these demands, along with storage or exchange of 

credit waters, can be managed to achieve multiple 

objectives under draft TROA. These demands are 

described further in the sections that follow.

In addition to describing proposed release procedures for maintenance of Floriston rates, four types 

of credit waters used in these releases are discussed in 

this section: (1) Power Company M&I credit water, 

(2) fish credit water, (3) California M&I credit water, 

and (4) water-quality credit water. A separate reservoir 

demand specified in the draft TROA is diversion of 

water from Lake Tahoe, and Donner and Independence 

Lakes for M&I use in California. Operations to satisfy 

demands for JPFCW are described in the sections dealing with mandatory and voluntary exchanges.

Floriston Rates

Release procedures for maintaining Floriston 

rates will be modified for Tahoe–Prosser Exchange 

water (TPEW) under draft TROA. TPEW will continue 

to be released to maintain Floriston rates, but in accordance with new rules linked to volumes and water-surface elevations of Prosser Creek Reservoir, Boca 

Reservoir, and Lake Tahoe. TPEW released to maintain Floriston rates will not produce flows at Farad, 

exclusive of all categories except natural water and 

pooled water (including TPEW), in excess of Floriston 

rates unless additional releases of TPEW from Prosser 

Creek Reservoir are necessary to assure that active 

storage does not exceed the flood-control criteria of 

8,640 acre-ft on November 1. Additionally under draft 

TROA, TPEW will be released for Floriston rates 

according to the following criteria.

1. TPEW will be released from Prosser Creek Reservoir to assure that its storage in that reservoir 

shall not be greater than 7,500 acre-ft if (a) Boca 

Reservoir storage will be less than 32,900 acre-ft, 

and if (b) Lake Tahoe water-surface elevation 

will be lower than 6,227.5 feet on November 1.

2. All TPEW in Prosser Creek Reservoir will be 

released before the date Boca Reservoir storage is 

scheduled to be less than 20,000 acre-ft.

3. TPEW will be released from Prosser Creek Reservoir in accordance with flood-control criteria to 

assure that the volume of TPEW in storage will be 

no greater than 8,640 acre-ft of active storage on 

November 1.

The USGS Truckee River Basin operations 

model simulates the maintenance of Floriston rates 

using a rank-order procedure based on rules described 

previously for current operations (see section “Floriston Rates” under “Current Reservoir Operations”) and 

additional criteria specified in draft TROA and 

described above. As previously discussed, the status of 

flow at the Farad gaging station (reach 240) is defined 

in reference to Floriston rates in the subblock initial 

assignments and computations. The water categories 

natural water flow and pooled water flow (including 

releases of TPEW from Prosser Creek Reservoir) are 

added and that sum is compared with target Floriston 

rates as defined in table 2. The subblock maintenance 

of Floriston rates uses the computed deficit or excess 

to determine reservoir releases and pass-throughs of 

natural water for maintenance of Floriston rates.

The following list describes the order of water 

categories and sources used to maintain Floriston rates. 

If a deficit is determined, additional reservoir releases 

or pass-throughs of natural water will be simulated in 
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 81

the order described below. If Floriston rates are 

exceeded, then releases and pass-throughs of inflow are 

reduced in the opposite order. Most of these sources 

also are used for the simulation of current operations 

and were described previously. Those sources under 

draft TROA that differ from current operations are 

marked with an asterisk (*).

1. Natural water inflows from unregulated tributary 

subbasins (sidewater) and pass-through of natural 

water inflow to reservoirs that is not stored or 

evaporated.

2. Pass-through of natural water inflow from Prosser 

Creek Reservoir.

3. Pass-through of natural water inflow from Stampede Reservoir.

4. Pass-through of natural water inflow from Boca 

Reservoir.

5. Release of pooled water from Lake Tahoe if, in 

addition to maintaining Floriston rates, additional 

releases are also needed to maintain minimumflow targets just downstream from the lake (see 

previous section, “Minimum Instream Flows,”

for a description of minimum-flow targets under 

current operations).

*6. Release of TPEW from Prosser Creek Reservoir 

if:

a. The date is between June 1 and November 1, 

Boca Reservoir storage volume is less than 

32,900 acre-ft, Lake Tahoe water-surface 

elevation is less than 6,227.5 ft, and storage 

of TPEW in Prosser Creek Reservoir is 

greater than 7,500 acre-ft. If the date is 

between June 1 and September 3 (part of the 

recreation season), TPEW is released from 

Prosser Creek Reservoir only if that reservoir’s water volume is greater than or equal 

to 19,000 acre-ft (recreation volume threshold). After September 3, this constraint is 

not simulated. June 1 is used as the start 

date for this release because it is assumed 

that there will be ample time between June 1 

and November 1 to release TPEW to assure 

that its storage in Prosser Creek Reservoir 

will be no greater than 7,500 acre-ft by 

November 1 if the other criteria apply. 

b. At any time the Boca Reservoir storage is 

less than 20,000 acre-ft.

c. The date is between September 4 and 

November 1 and TPEW in storage in 

Prosser Creek Reservoir is greater than 

8,640 acre-ft.

7. Release of pooled water from Lake Tahoe if:

a. The date is between April 1 and October 31 

and if the water surface elevation is between 

6,223.0 (outlet rim) and 6,225.5 ft.

b. The date is between November 1 and 

March 31.

8. Release of Tahoe–Prosser Exchange water from 

Prosser Creek Reservoir if:

a. The date is between April 1 and September 

3 (recreation season) and if total reservoir 

water volume is greater than or equal to 

19,000 acre-ft (recreation volume threshold), or

b. The date is between September 4 and 

March 31.

9. Release of adverse-to-canal water from Boca 

Reservoir.

10. Release of non-adverse-to-canal water from Boca 

Reservoir.

11. Release of Tahoe–Prosser Exchange water from 

Prosser Creek Reservoir if the date is between 

April 1 and September 3 and if total reservoir 

water volume is less than 19,000 acre-ft.

12. Release of pooled water from Lake Tahoe if the 

date is between April 1 and October 31 and if the 

water surface elevation is greater than 6,225.5 ft.

The following assumptions are used in the model 

code development for simulation of maintenance of 

Floriston rates under draft TROA, in addition to those 

assumptions listed in the discussion of Floriston rates 

in the section “Current Reservoir Operations.”

• Reservoir releases and pass-throughs are not 

“scheduled” in advance for smoothing of reservoir releases over weekly/monthly periods. Methods to schedule reservoir operations in the 

Truckee River Basin are undocumented. Releases 

and pass-throughs for maintenance of Floriston 
82 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

rates are determined on a daily basis contingent 

upon the criteria specified above. 

• TPEW is stored only in Prosser Creek Reservoir 

for simulations. In actual operations under draft 

TROA, it may occasionally be exchanged to 

another reservoir.

Power Company Municipal and Industrial Credit Water

Under draft TROA, the Power Company will 

have the right to store and release PCMICW in all 

Truckee River Basin reservoirs. This will provide additional waters to satisfy Power Company M&I demands 

and increase the M&I drought supply. Draft TROA 

does not state that Boca pondage will be available for 

storage of PCPOSW. 

The USGS Truckee River Basin operations 

model simulates proposed operations of Power Company M&I credit water as follows. PCMICW categories may be used in addition to the current water 

categories for releases to satisfy M&I demands. As previously described under current operations, the model 

simulates Power Company operations M&I demands 

and the location of M&I diversions. Logic in the Power 

Company operations subblock is then used to determine (1) PCPOSW supplies available from reservoir 

storage or other Orr Ditch Decree rights, and (2) M&I 

diversion demands. The simulation of releases to meet 

M&I demands under draft TROA using PCMICW is 

similar to the simulation of PCPOSW releases as discussed in the section “Privately Owned Stored Water.”

The logic for the draft TROA and current operations is 

the same except that the allowable M&I reservoir 

releases of firm and nonfirm PCMICW for draft TROA 

are based on (1) drought situation, as defined in the section “Drought Situations,” and (2) PCPOSW stored in 

Donner and Independence Lakes. The re-regulation of 

Power Company water within Boca Reservoir is discussed later in this section.

The following sources are used to satisfy Power 

Company M&I demands under draft TROA. Most are 

also used in current operations and were described in 

the section “Privately Owned Stored Water.” Those 

sources under draft TROA that differ from current 

sources are marked with an asterisk (*). Current 

sources previously presented are listed here again for 

reader convenience.

1. First 40 ft3/s of Truckee River and first 13.6 ft3/s 

of Hunter Creek streamflow per Truckee River 

Agreement.

2. Available Orr Ditch Decree (United States of 

America v. Orr Ditch Water Company, Equity No. 

A-3 (D. Nev. 1944)) agricultural rights converted 

to M&I rights flowing in the Truckee River.

3. Release of PCPOSW from Boca Reservoir.

4. Release of PCPOSW from Donner Lake if the 

date is between April 1 and August 31 and if the 

water surface elevation is above 5,932.0 ft recreational pool per Donner Lake Indenture (see section “Maintenance of Recreational Pools”).

5. Release of PCPOSW from Donner Lake if the 

date is between September 1 and March 31.

*6. During a drought situation (defined later in the 

section “Drought Situations,” under the section 

“Forecasts Affecting Operational Decisions”), 

the following reservoir releases are used in the 

order shown below:

a. Nonfirm PCMICW in Lake Tahoe.

b. Nonfirm PCMICW in Prosser Creek 

Reservoir.

c. Nonfirm PCMICW in Boca Reservoir.

The following list shows the order of the sources 

used in the model to re-regulate Power Company 

waters by storing them in Boca Reservoir under draft 

TROA operations. Some of these sources also are used 

in simulation of current operations and were described 

in the section “Privately Owned Stored Water.” Those 

sources under draft TROA that differ from current 

sources are marked with an asterisk (*). Regardless of 

whether or not a drought situation exists, sources 1 and 

2 are available.

1. PCPOSW in Stampede Reservoir.

2. PCPOSW in Independence Lake if lake storage is 

above 7,500 acre-ft. 

*3. PCPOSW in Independence Lake if lake storage is 

above 7,500 acre-ft if under drought situation as 

defined in the section “Drought Situation.”

*4. Nonfirm PCMICW in Stampede Reservoir if 

under drought situation.
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 83

*5. Firm PCMICW in Stampede Reservoir if under 

drought situation.

*6. Remainder of PCPOSW in Independence Lake 

above outlet (6,921.0 ft) if under drought situation.

*7. 7,500 acre-ft of PCEDS credit water in Stampede 

Reservoir if under drought situation.

Several assumptions were used in the model code 

development for simulation of releases of PCMICW 

that are different from current operations.

• Under draft TROA, the order of water categories 

allows for the pumping of 5,000 acre-ft of water 

in Independence Lake below the outlet elevation 

of 6,921.0 ft prior to using the 7,500 acre-ft of 

PCEDS water in Stampede Reservoir. This scenario is not simulated by the operations model 

due to model limitations.

• As described in procedures in draft TROA, and 

subject to compliance with the National Environmental Policy Act, the California Environmental 

Quality Act, and administrative/regulatory 

review, the order of water categories used by the 

Power Company allows for the pumping of Lake 

Tahoe below the natural rim after using the 7,500 

acre-ft of PCEDS in Stampede Reservoir. This 

scenario, also, is not simulated by the operations 

model due to model limitations.

Fish Credit Water

In addition to releases of fish water and uncommitted water, some of the demands for Pyramid Lake 

fish will be met by the release of fish credit waters 

under draft TROA operations.

The USGS Truckee River Basin operations 

model simulates release of fish credit water in the subblock Pyramid Lake fish operations as follows. Fish 

credit water may be used in addition to current water 

categories for releases to satisfy fish demands and for 

storage to satisfy Boca pressure water storage. As previously described under current conditions, determination of releases needed to satisfy the needs of Pyramid 

Lake fish requires the model to compute the amount of 

water available for fish operations, the flow regime, 

and cui-ui flow targets. Additionally, the model determines the need for Boca Reservoir storage of fish water 

or fish credit water according to Boca pressure water.

The logic for draft TROA and current operations 

to satisfy Pyramid Lake fish demands is the same 

except for the release of fish credit water. The list 

below shows the sources of reservoir releases used in 

the model under draft TROA. Most of these sources 

also are used in current operations and were described 

in the section “Pyramid Lake Fish.” Those sources 

under draft TROA that differ from current sources are 

marked with an asterisk (*). Current sources are listed 

again here for reader convenience. The term prescribed 

threshold volume refers to reservoir volumes specified to constrain selected reservoir operations for the 

purposes of maintaining the security of water categories. The term preferred flow targets is described in 

the section “Preferred Instream Flows.”

*1. Fish credit water in Lake Tahoe, if storage is 

above the Lake Tahoe prescribed threshold volume. Use Tahoe releases up to preferred flow target.

*2. Fish credit water in Boca Reservoir, if storage is 

above the Boca Reservoir prescribed threshold 

volume.

*3. Fish credit water in Prosser Creek Reservoir, if 

storage is above the Prosser Creek Reservoir prescribed threshold volume. Use Prosser Creek 

Reservoir releases up to preferred flow target.

*4. Remaining fish credit water in Lake Tahoe.

*5. Remaining fish credit water in Boca Reservoir.

*6. Remaining fish credit water in Prosser Creek Reservoir.

7. Fish water in Boca Reservoir (from Stampede 

Reservoir).

8. Uncommitted water in Prosser Creek Reservoir.

The following two sources of Stampede Reservoir releases are used in the model to satisfy Boca 

pressure storage in draft TROA simulations. Source 2 

also is used for current operations and described in the 

section “Pyramid Lake Fish.” The source marked with 

an asterisk (*) is different from current sources.

*1. Fish credit water in Stampede Reservoir.

2. Fish water in Stampede Reservoir.
84 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

California Municipal and Industrial Credit Water

Currently, there are no operations implemented to 

satisfy California M&I demands. Under draft TROA 

operations, CMICW will be used to meet California 

M&I demands. Current California M&I demands are 

not published, but are expected to increase as population growth continues in the Truckee, Calif. area. Most 

of California M&I credit water will be diverted at Truckee. As specified in draft TROA, for California to make 

direct diversions, flow at Truckee River at Farad must 

be greater than the rights senior to the CMICW. These 

rights are the sum of claims 1 and 2 of the Orr Ditch 

Decree (United States of America v. Orr Ditch Water 

Company, Equity No. A-3 (D. Nev. 1944)) plus 40 ft3

/s. 

The Truckee River Agreement of 1935 specifies that 

the Power Company shall have the right to the first 40 

ft3

/s of pooled water in the Truckee River at Farad.

The USGS Truckee River Basin operations 

model simulates releases of California M&I credit 

water as follows. To simulate releases for California 

M&I operations from the Truckee River, (1) initial 

numerical assignments and computations are made, 

and (2) releases to meet California M&I demands 

are determined.

California M&I demands are specified on the 

subblock initial assignments and computations. These 

demands require the user to specify:

• Growth rates for California M&I surface-water 

and ground-water use,

• Growth rate for California agriculture surface 

water,

• Consumptive use factors for water used to satisfy 

California agricultural and M&I demands,

• Decimal fraction of current annual California surface-water M&I usage that will be held in storage,

• California annual surface-water allocation and 

total allocation, and 

• Base-year levels for California M&I surfacewater and ground-water diversions and agricultural surface-water use.

Other assignments in this subblock include the 

following.

• A tolerance of 0.1 ft3

/s is assigned to determine 

when CMICW releases are necessary. If releases 

for CMICW are within 0.1 ft3

/s of the demand, no 

additional releases are made. This tolerance may 

be modified by the user.

• The total flow of rights senior to the CMICW is 

calculated as the sum of Indian Ditch diversion 

plus the Power Company right of 40 ft3

/s.

After initial numerical assignments and computations are made, releases to meet California M&I 

demands are determined in the subblock California 

M&I demands. First, the natural water flow at Truckee, Calif. (reach 150) is determined. Second, the status 

of river flow at this site is compared to the California 

M&I demands. If the river flow is less than the demand, 

then the deficit is determined as that additional flow of 

water needed to achieve the California M&I demands. 

Likewise, if the river flow is more than the demand, the 

excess is determined. M&I credit water, if available, is 

released from Lake Tahoe if a demand is not achieved. 

No action is taken if streamflow is in excess of California M&I demand. 

Several assumptions were used in this subblock.

• No CMICW is stored in reservoirs other than 

Lake Tahoe because the M&I intakes are located 

at Truckee, Calif. as described in the section 

“California M&I Credit Water” under “Storage 

of Proposed Water Categories.”

• Daily surface-water diversions equal the sum of 

agricultural and M&I diversions during irrigation 

season. Outside of the irrigation season, when 

irrigation demands are zero, the daily diversion 

equals the M&I diversion.

• Because the exact value for current California 

M&I demands are not published, the default M&I 

demand used in the model should be considered 

an estimate.

• Claims 1 and 2 of the Orr Ditch Decree are 

assumed in the model to be the simulated diversion for Indian Ditch as described in the section 

“Lower Truckee River Diversions,” based on current operation practices. This simulated diversion 

is based on 1991 converted water rights defined in 

a FWM table “Truckee Meadows Priorities” (Jeff 

Boyer, U.S. District Court Water Master, written 

commun., 1994). Also, Indian Ditch diversions 

are only simulated during the irrigation season. 

Claims 1 and 2, as defined in the Orr Ditch 

Decree, are more than this simulated diversion.
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 85

Diversion of Water in Lake Tahoe and 

Donner and Independence Lakes for 

Municipal and Industrial Use in California

This section addresses operations that divert 

waters directly from Lake Tahoe and Independence and 

Donner Lakes. These diversions differ from those 

diversions described in the sections “Truckee Meadows Diversions,” “Privately Owned Stored Water,”

“Power Company M&I Credit Water,” and “California 

M&I Credit Water.” Under draft TROA, the combined 

maximum interstate allocations for the Lake Tahoe 

Basin total 34,000 acre-ft, of which 11,000 acre-ft is for 

Nevada users and 23,000 acre-ft is for use in California. This allocation can be derived from ground-water 

or surface-water sources. The allocation is principally 

for M&I use, but also can be used for snowmaking. For 

Donner Lake, the maximum annual allotment specified 

in the draft TROA for M&I water use is 990 acre-ft, and 

for Independence Lake it is 50 acre-ft. General guidelines for monthly M&I diversions from Donner and 

Independence Lakes were obtained (Richard D. Moser, 

Sierra Pacific Power Company, oral commun., 1997). 

For 1994, annual diversions from Lake Tahoe for 

California were about 16,900 acre-ft (John Sarna, California Department of Natural Resources, written 

commun., 1998) and for Nevada were about 10,000 

acre-ft (Thomas R. Scott, Bureau of Reclamation, 

oral commun., 1998).

The following discussion describes how the operations model simulates diversions from Lake Tahoe 

and Donner and Independence Lakes for M&I use. 

First, both the maximum and annual M&I use in acrefeet is specified for all three lakes in the initial numerical assignments and computations subblock. For 

Lake Tahoe and Donner and Independence Lakes, the 

maximum annual allotment specified for M&I water 

use is 26,900 acre-ft (John Sarna, California Department of Natural Resources, written commun., 1998), 

990 acre-ft, and 50 acre-ft, respectively, and the current 

annual usage is 26,900, 495, and 0 acre-ft, respectively. 

The volumes may be changed by the user. After these 

initial assignments, diversions are determined in the 

code in the subblock California M&I demands using 

the following logic.

• Lake Tahoe and Donner Lake—Because residents use water from Lake Tahoe and Donner 

Lake year-round, it was assumed that M&I uses 

takes place from January 1 to December 31. 

Observed values for M&I use in the Truckee 

Meadows (Richard D. Moser, Sierra Pacific 

Power Company, oral commun. 1995), were used 

to determine a monthly distribution (expressed as 

a percentage of annual use). This monthly percentage distribution was multiplied times the 

annual allotment to compute, a constant daily 

M&I diversion for each month for Lake Tahoe 

and Donner Lake.

• Independence Lake—The model default is that no 

water be simulated for diversion from Independence Lake. If changed by the user, M&I diversions from the lake will take place during the 

summer, between June 1 and August 30. The 

annual M&I use would be simulated by dividing 

the specified annual allotment over the 3-month 

period.

• The operation model is designed to divert pooled 

water from Lake Tahoe and natural water from 

Donner and Independence Lakes for M&I water 

use in California.

Water-Quality Targets and 

Related Instream Flow Transfers

Releases and instream flow transfers can be 

made in accordance with the WQSA to achieve target 

instream flows in the Truckee River from Reno to Pyramid Lake. The objective of these water-quality targets 

is to provide streamflows adequate to resolve some of 

the water quality problems in the Truckee River in 

Nevada and, simultaneously, to improve fish and wildlife habitat along the Truckee River.

Water-quality flow targets have been specified 

for Truckee River at Sparks and Truckee River below 

Derby Dam. The flow targets are currently set to 

300 ft3

/s and 135 ft3/s, respectively, during June–September, and 50 ft3

/s at both sites for the remainder of 

the year (Chester Buchanan, U.S. Fish and Wildlife 

Service, oral commun, 1999). Releases to augment 

other water categories in the river to meet the waterquality targets are made using WQCW created as 

described in the previous section “Storage of Proposed 

Water Categories.” It is anticipated that most WQCW 

will be created in Lake Tahoe and Stampede, Boca, and 

Prosser Creek Reservoirs. Releases of WQCW from 

these reservoirs will be used to satisfy flow targets at 

Sparks and below Derby Dam. It is anticipated that 

Boca will be used for temporary storage of WQCW for 

quick release to the mainstem Truckee River, similar to 
86 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

current operations for Boca pressure water conditions. 

The schedule and amount of WQCW that would be 

temporarily stored in Boca are not currently specified.

The USGS Truckee River Basin operations 

model simulates releases for water-quality targets as 

follows. All WQCW releases and flow transfers may 

be turned off or on at the option of the user. Simulation 

of releases to meet water-quality target requires that 

(1) initial numerical assignments and computations are 

made, (2) reservoir releases to meet water-quality targets are determined, and (3) Stampede Reservoir 

WQCW releases to Boca Reservoir be determined. 

First, water-quality flow targets at Sparks (reach 

380) and below Derby Dam (reach 460) are specified 

each month in the initial assignments and computations subblock. These targets may be changed by the 

user. Water rights in the Orr Ditch Decree, including 

the Truckee Division of the Newlands Project, that 

have been acquired for uses specified in WQSA are 

specified in this subblock. These acquired water rights 

may be modified by the user. Additionally, a tolerance 

of 0.1 ft3

/s is assigned to determine when WQCW 

releases are necessary. If releases of WQCW bring the 

total streamflow at Sparks and below Derby Dam to 

within 0.1 ft3/s of targets, no additional releases are 

made. This tolerance may be modified by the user.

After initial numerical assignments are made, reservoir releases to meet water-quality targets are determined in the subblock water-quality credit water 

operations. The first step is to determine the total river 

flow simulated at Sparks and below Derby Dam. The 

streamflow at these sites is compared to the specified 

water-quality flow targets. If the river flows are less 

than a target, the deficit is determined as that additional 

flow of water needed to achieve water-quality targets. 

Likewise, if the simulated river flows at these locations 

are more than the targets, an excess is determined, upon 

which reductions in releases of WQCW are based.

The following reservoir sources of WQCW are 

used in the model to achieve water-quality targets.

1. Lake Tahoe, if the volume is greater than the 

lake’s prescribed threshold volume.

2. Prosser Creek Reservoir, if the volume is greater 

than the reservoir’s prescribed threshold volume.

3. Boca Reservoir, if the volume is greater than the 

reservoir’s prescribed threshold volume.

4. Prosser Creek Reservoir, if the volume is greater 

than the reservoir’s recreational level. The recreational level is described in the section “Maintenance of Recreational Pools.”

5. Remainder of WQCW from Lake Tahoe.

6. Remainder of WQCW from Prosser Creek 

Reservoir.

7. Remainder of WQCW from Boca Reservoir.

The subblock water-quality credit water operations uses the deficit and excess values determined previously to appropriately adjust releases every third day. 

If the water-quality targets cannot be met by existing 

surface-water supplies and by reservoir releases from 

the previous time interval, then additional releases of 

stored WQCW must be made from Truckee River 

Basin reservoirs in the order specified above. Likewise, 

if existing water-quality targets are exceeded, then reservoir releases are reduced accordingly in the opposite 

order specified above. 

Next, the model determines Stampede Reservoir 

WQCW releases to Boca Reservoir. The objective of 

these releases is to provide ample supply of WQCW to 

Boca Reservoir for releases directly to the Truckee 

River to satisfy water-quality targets. The storage of 

WQCW in Boca is compared to the total volume of 

WQCW reservoir releases for that day. If the WQCW 

storage in Boca is less than the total volume of WQCW 

reservoir releases, then WQCW from Stampede is 

delivered to Boca to meet WQCW releases from Boca 

for the next day.

The following assumptions were used in this subblock.

• Storage of WQCW is not simulated for Donner 

and Independence Lakes. 

• Water-quality targets may be met by flows provided for other uses. For example, if water to 

meet Floriston rates demand satisfies water-quality targets, then no additional release of WQCW 

from reservoirs is necessary.

• The locations and magnitudes of water-quality 

targets have changed since the signing of WQSA 

and are subject to revision based on further negotiations with interested parties. 

Similar to the release of WQCW from reservoir 

storage to achieve and maintain water-quality targets in 

the Truckee River, WQCW may be created as instream 

flow to also achieve and maintain water-quality targets. 
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 87

This method involves the instream flow transfer of 

that part of pooled water obligated to Orr Ditch Decree 

rights acquired by WQSA to WQCW. Instream flow 

transfers are limited to those times when Truckee River 

flows are less than specified water-quality targets. 

Instream creation of WQCW is a river operation that 

involves creation of that category as flow within the 

river, rather than as storage within a reservoir.

The following discussion describes the simulation of instream flow transfers to create WQCW. Similar to the creation of credit water as storage in 

reservoirs, the initial assignments and computations

subblock determines the volume of Orr Ditch Decree 

rights acquired for the conversion to WQCW as either 

flow or storage. The quantity of WQCW created by 

instream flow transfers is then simulated in the subblock water-quality credit water operations. 

As described in the section “Power Company 

M&I Credit Water, Fish Credit Water, Water-Quality 

Credit Water, and Joint Program Fish Credit Water,”

the Orr Ditch Decree water rights acquired for the creation of WQCW are determined in the subblock initial 

assignments and computations. Similar to the creation 

of WQCW water in storage, the instream transfer of 

pooled water to WQCW as flow is limited to the consumptive use portion of former agricultural water 

rights or effluent volume originating from Truckee 

Meadows ground water and reused for irrigation. However, unlike creation of WQCW as reservoir storage, 

creation of WQCW as flow is strictly for the immediate 

maintenance of downstream water-quality targets 

rather than for future satisfaction of that demand.

Instream transfers of pooled water to WQCW 

may be simulated concurrently with reservoir releases 

of WQCW in the subblock water-quality credit water 

operations. The instream exchanges are simulated 

between reach 250 and reach 260, just downstream 

from the Farad gaging station and just upstream from 

Truckee Meadows M&I and agricultural diversions 

and the California-Nevada State boundary. Additionally, creation of WQCW by instream transfers is 

restricted to the period between June and September, 

when streamflow is more likely to be less than waterquality targets. After September, if water-quality targets cannot be maintained, WQCW will be released 

from reservoirs if it is available. The following overview describes the conditional logic that simulates creation of instream WQCW.

1. Determine the volume available for WQCW creation which is based on acquired rights determined in the initial assignments and 

computations subblock. If the accumulated creation of WQCW, as storage and flow, equals or 

exceeds the acquired rights, additional credit 

water cannot be created. Additionally, if Floriston 

rates cannot be maintained, then the volume of 

acquired water rights available for credit water 

creation is reduced on the basis of the pooled 

water flow available for transfer.

2. Determine the volume of the instream flow 

transfer from pooled water to WQCW. As for 

the release of WQCW described previously, a 

deficit or excess is determined, depending on a 

comparison of the river flow at Sparks and below 

Derby Dam and the established water-quality 

targets. The volume of the transfer is determined 

by adjusting the transfer from the previous time 

step corresponding to the deficit or excess. Thus, 

for a deficit, more water will be transferred to 

WQCW and for an excess, less water will be 

transferred in accordance to the volume of 

acquired rights and the pooled water in reach 

250 available for exchange.

3. Transfer pooled water flow to WQCW flow.

4. Accumulate the WQCW as it is created each 

calendar year. The cumulative total also includes 

water-quality water created in reservoir storage. 

The annual accumulated WQCW will be compared with acquired water rights on the following 

day to determine if more credit water may be 

created.

Two assumptions were made in developing the 

code to simulate the instream creation of water-quality 

water. 

• WQCW is created by instream flow transfers 

prior to being released from reservoirs. It is 

assumed that stored water-quality water can be 

saved to achieve water-quality flow targets later 

in the year.

• WQCW is created just downstream from the 

Farad gage because the acquired water rights are 

Orr Ditch Decree rights, and therefore are associated with Floriston rates.
88 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

Mandatory Exchanges and Transfers

Under draft TROA, mandatory exchanges are 

used for moving water categories (physically or administratively) among reservoirs. Transfers, as defined for 

this report, are used to create storage of one category by 

eliminating an equal volume of another category in the 

same reservoir. Mandatory exchanges and transfers 

simulated in the Truckee River Basin operations model 

are used to (1) achieve enhanced minimum instream 

flows as described below in the section “Enhanced 

Minimum Instream Flows,” and (2) favor the storage of 

selected new credit water categories depending on specific conditions, such as current reservoir storage and 

the presence of drought situations as described in a 

later section, “Other Exchanges and Transfers.”

Enhanced Minimum Instream Flows

Currently, several reservoirs in the Truckee River 

Basin are operated to provide releases necessary to 

maintain instream flows just downstream from reservoirs. However, draft TROA provides for greater minimum instream flows than previously described in 

current operations. The greater flows, termed 

enhanced minimum instream flows, would be 

achieved using draft TROA credit water categories, 

PCPOSW, uncommitted water, and fish water. Additional releases of these water categories requires that 

they be either re-stored in another reservoir or 

exchanged with water categories in other reservoirs 

(in-lieu-of exchanges). Additionally, the use of such 

waters for enhanced minimum instream flows may 

depend on the security of the new storage location, the 

current availability and location of reservoir storage 

before re-storage or exchange, type of season (normal 

season or dry season), and the current status of streamflow with respect to enhanced flow targets at given 

locations. California, at its discretion, could use 

JPFCW to enhance minimum instream flows without 

re-storage or exchange with water in another reservoir.

Releases of all water categories except JPFCW to 

enhance instream flows require that the storage level in 

those Truckee River reservoirs selected for release, restorage, or exchange be within prescribed constraints. 

These constraints, called threshold volumes, were 

selected to ensure security of re-stored or exchanged 

water from the threat of reservoir spill when reservoir 

levels are high or the threat of limited outlet capacity, 

recreation potential, or water category availability 

when reservoir levels are low.

Enhanced minimum-flow targets would be set to 

one of two levels, depending on whether the current 

season is defined as a normal season or a dry season. 

The designation of a season as normal or dry would be 

dependent upon the magnitude of pooled water stored 

in Lake Tahoe and the current April-through-July forecast of Truckee River Basin natural flow in the river at 

the California–Nevada State boundary (see subsequent 

section “Determination of Normal and Dry Season”). 

Note that wetter-than- average conditions would place 

enhanced minimum-flow targets at those defined for a 

“normal season.” These seasons were established as a 

method to integrate forecasting and current quantity of 

flow into the determination of enhanced minimumflow targets. This method assures that water rights will 

not be impaired while improving the prospects of 

enhancing minimum instream flow. 

Several reservoirs in the Truckee River Basin 

would be operated to provide releases necessary to 

maintain enhanced instream flows just downstream 

from the reservoirs. The following list describes the 

flow targets for each reservoir as specified in the draft 

TROA (Bureau of Reclamation and others, 1998):

• Lake Tahoe—Enhanced minimum-flow target for 

a normal season is 75 ft3/s. Draft TROA credit 

water categories will be released to supplement 

the existing minimum-flow targets to the extent 

that the draft TROA credit water categories can be 

exchanged to another reservoir. During a dry season, if pooled water is not sufficient to maintain 

the existing minimum-flow targets, then draft 

TROA water categories will be combined with 

the existing pooled water release for a total of 

37.5 ft3

/s to the extent that the draft TROA credit 

water categories can be exchanged to another reservoir. No draft TROA credit water categories 

will be released if pooled water release is greater 

than 37.5 ft3

/s but less than the existing minimum-flow targets.

• Donner Lake—Enhanced minimum-flow target 

for a normal season is 8 ft3

/s and 4 ft3/s during a 

dry season. PCPOSW and TCIDPOSW will each 

contribute up to one-half the total toward the 

release to supplement the existing minimum-flow 

targets of 2-3 ft3/s, provided these categories 

can be exchanged to another reservoir.

• Martis Creek Lake—Enhanced minimum-flow 

releases from Martis Creek Lake are not required.
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 89

• Prosser Creek Reservoir—Enhanced minimumflow target for a normal season is 16 ft3/s. 

Uncommitted water will supplement the existing 

minimum-flow target of 5 ft3

/s up to an intermediate enhanced target of 10 ft3/s, provided that 

either (1) it be exchanged to another reservoir, or 

(2) the release of Stampede Reservoir fish water 

be reduced by an equal amount. Draft TROA 

water categories will then be released as necessary to increase the enhanced minimum-flow 

release to 16 ft3

/s if the draft TROA categories 

can be exchanged to another reservoir. During a 

dry season, the enhanced minimum-flow target is 

8 ft3/s at Prosser Creek Reservoir. Uncommitted 

water will supplement the existing minimumflow target of 5 ft3

/s, provided (1) it can be 

exchanged to another reservoir, or (2) the release 

of Stampede Reservoir fish water can be reduced 

by an equal amount. If necessary, draft TROA 

credit water categories will be released to attain 

the 8 ft3/s enhanced target if these categories can 

be exchanged to another reservoir.

• Independence Lake—Enhanced minimum-flow 

targets range from 2 to 8 ft3

/s during the normal 

season and from 2 to 4 ft3/s during the dry season 

(table 7). PCPOSW water will supplement the 

existing minimum-flow target of 2 ft3

/s when 

the enhanced flow target is greater than 2 ft3/s. 

Although it is not necessary to exchange releases 

for the enhanced flow target to another reservoir, 

such releases may be re-stored in downstream 

reservoirs.

• Stampede Reservoir—Enhanced minimum-flow 

target for a normal season is 45 ft3/s. All water 

categories in storage except firm PCMICW, 

PCEDS, and TPEW will be released to supplement the existing flow target of 30 ft3/s if these 

categories can be exchanged to another reservoir 

or re-stored in Boca Reservoir. However, as discussed for Prosser Creek Reservoir, the existing 

flow target for Stampede Reservoir may be 

reduced by up to 5 ft3/s to provide enhanced minimum flows downstream from Prosser Creek Reservoir. During a dry season, if fish water is not 

sufficient to maintain the existing flow target of 

30 ft3/s, then the water categories, as discussed 

above, will be released to enhance the existing 

fish water release to 22.5 ft3/s to the extent that 

the waters can be exchanged to another reservoir 

or re-stored in Boca Reservoir. No draft TROA 

credit water categories will be released if the 

existing release is greater than 22.5 ft3

/s but less 

than the existing 30 ft3

/s minimum-flow target.

• Boca Reservoir—Enhanced minimum-flow 

releases from Boca Reservoir are not required.

Releases for maintenance of enhanced minimum 

instream flows are simulated in the USGS Truckee 

River Basin operations model as follows. Model code 

in the subblock initial assignments and computations

determines initial values of proposed releases to meet 

enhanced minimum flows. The assignments specified 

for Lake Tahoe, Donner and Independence Lakes, and 

Prosser and Stampede Reservoirs are based on whether 

it is a normal or dry season. Assignments of enhanced 

minimum flows for Independence Lake are based also 

on the current month and reservoir storage. 

The proposed reservoir releases for maintenance 

of enhanced minimum flows are modified in the subblock enhanced minimum instream flows, based on 

various rules and constraints for those reservoirs 

required to release for enhanced minimum flows. In 

this subblock, enhanced minimum instream flows are 

based on whether (1) water categories involved in the 

releases can be re-stored in another reservoir, (2) the 

water categories can be exchanged with other water 

categories in another reservoir, or (3) specified water 

categories are available, such as JPFCW, that do not 

require re-storage or exchange into other reservoirs. 

The following discussion describes how the model 

code in the subblock enhanced minimum instream 

flows modifies the initial numerical values of required 

reservoir releases to maintain enhanced minimum 

flows. 

First, the status of reservoir releases is compared 

to enhanced minimum-flow targets for those reservoirs 

required to maintain enhanced minimum flows. The 

releases from these reservoirs correspond to flows just 

downstream from the reservoir outlets. If a given 

release is less than the target, then the deficit is determined as that additional flow of water needed to 

achieve the flow target. Likewise, if a given release is 

greater than the target, the excess is determined to eliminate unnecessary releases.

Second, for each reservoir with a release less than 

the enhanced flow target (release deficit), the model 

determines the potential for additional releases. The 

availability of additional releases is based on the vol-
90 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

ume of specific water categories available for release in 

accordance to the criteria described previously, as 

specified in draft TROA (Bureau of Reclamation and 

others, 1998), and hydraulic constraints of the reservoir 

outlet. Additional releases of specific water categories 

are based on the proportion of a given category volume 

to the total volume of water categories available for 

additional release. Mandatory exchange criteria for 

Donner Lake require minimum threshold volumes, and 

as a result, enhanced instream flow releases may be 

restricted from the lake if volumes are less than the 

minimum threshold volumes. For each reservoir, the 

model checks the following water categories for contribution to enhanced releases.

• Lake Tahoe—WQCW, fish credit water, and 

nonfirm PCMICW.

• Donner Lake—PCPOSW (for simulations, 

TCIDPOSW is not used to achieve enhanced 

instream flow targets).

• Martis Creek Lake—not applicable.

• Prosser Creek Reservoir—uncommitted, 

WQCW, nonfirm PCMICW, and fish credit 

water.

• Independence Lake—PCPOSW.

• Stampede Reservoir—fish water, PCPOSW, 

pooled water, WQCW, nonfirm PCMICW, 

and fish credit water.

• Boca Reservoir—not applicable.

Third, for each reservoir with a release greater 

than the enhanced flow target (release excess), the 

model determines the amount that releases from given 

water categories may be decreased. For in-lieu-of 

exchanges, the water categories in reservoirs with 

release excesses can be exchanged with water categories in those reservoirs with release deficits. The 

amount of reduction in releases of a given water category is based on the difference between the currently 

simulated release and the required minimum release 

(release floor). As previously discussed, release floors 

are of two types: overall and category. Overall release 

floors are based on releases that do not require specific 

category releases, such as releases for existing minimum-flow targets and releases for uncontrolled spills 

or precautionary drawdowns. Category release floors 

are based on specific categories that are involved in 

previously simulated exchanges, such as the Tahoe–

Prosser Exchange, as discussed in the section “Tahoe–

Prosser Exchange.” In addition to the consideration of 

release floors, the reduction of releases is based on the 

proportion of each water category released to the total 

release of water categories available for reduction and 

whether the reservoir volume is greater than its maximum threshold volume. Finally, mandatory exchange 

criteria for Lake Tahoe and Prosser, Stampede, and 

Boca Reservoirs require maximum threshold volumes, 

and as a result, reduction of releases will be restricted 

in these reservoirs if volumes are greater than the maximum threshold volumes. Designated minimum threshold volumes for Lake Tahoe will restrict reduction of 

releases if the storage volume is less than a given minimum threshold volume. For each reservoir where a 

release excess is computed, the following water categories are checked to determine if releases can be 

reduced.

• Lake Tahoe—fish credit water, nonfirm 

PCMICW, WQCW, and pooled water.

Table 7. Independence Lake enhanced minimum flow targets

[Abbreviation: ft3/s, cubic feet per second]

Storage (acre-feet)

and season type

January

(ft3/s)

February–March

(ft3/s)

April–July

(ft3/s)

August–September

(ft3/s)

October–December

(ft3/s)

Less than or equal to 7,500:

Normal and dry season 2 2 2 2 2

Greater than 7,500 and less than or equal to 12,500:

Normal and dry season 3.5 2 4 2 3.5

Greater than 12,500:

Normal season 7 4 8 4 7

Dry season 3.5 2 4 2 3.5
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 91

• Donner Lake—not applicable. (For simulations, 

no credit waters are exchanged into this reservoir, 

and as a consequence, reservoir releases are not 

reduced for in-lieu-of exchanges).

• Martis Creek Lake—not applicable.

• Prosser Creek Reservoir—fish credit water, 

nonfirm PCMICW, WQCW, uncommitted 

water, Tahoe–Prosser Exchange water, and 

natural water.

• Independence Lake—not applicable (For simulations, no credit waters are exchanged into this reservoir and, as a consequence, reservoir releases 

are not reduced for in-lieu-of exchanges.)

• Stampede Reservoir—not applicable (Credit 

water categories are first exchanged into Boca 

Reservoir and subsequently exchanged into 

Stampede Reservoir in other types of exchanges. 

See the later section “Voluntary Exchanges.”)

• Boca Reservoir—fish credit water, WQCW, nonfirm PCMICW, PCPOSW, fish water, adverseto-canal pooled water, non-adverse-to-canal 

pooled water, and natural water.

Fourth, determine release increases for those reservoirs that require and are capable of such releases for 

the enhanced instream flow targets. As discussed 

above, the enhanced releases may be restricted depending on the minimum and maximum threshold volumes 

of given reservoirs. Three methods are used to determine enhanced releases: (1) re-storage of water categories in another reservoir, (2) in-lieu-of exchange of 

water categories to another reservoir, and (3) release of 

specific water categories when available, such as 

JPFCW, without re-storage or exchange. For the inlieu-of exchange method (item 2), potential release 

increases of water categories from reservoirs must be 

compared with potential release reductions of water 

categories from different reservoirs. The other two 

methods do not require such a comparison. At a given 

reservoir, if enhanced instream flows cannot be met by 

re-storage or exchange in another reservoir, then 

JPFCW is released.

The operations model simulates reservoir releases 

for enhanced minimum-flow targets by the three methods listed above according to the following list. The list 

is based on a rank order of probable releases for 

enhanced instream flow (Lake Tahoe, Stampede Reservoir, Prosser Creek Reservoir, Independence Lake, and 

Donner Lake). Unless indicated, water categories 

involved in release increases and decreases are those 

previously discussed in this section. 

Lake Tahoe 

In-lieu-of exchanges:

• Lake Tahoe release increase concurrent with 

Prosser Creek Reservoir release decrease. 

Water categories listed above for Lake Tahoe 

enhanced releases are exchanged with categories used to reduce Prosser Creek Reservoir releases.

• Lake Tahoe release increase concurrent with 

Boca Reservoir release decrease. Water categories listed above for Lake Tahoe enhanced 

releases are exchanged with categories used 

to reduce Boca Reservoir releases.

Release with no exchange or re-storage:

• Lake Tahoe release increase of JPFCW.

Stampede Reservoir

Re-storage:

• Stampede Reservoir release increase with 

Boca Reservoir re-storage of water categories 

listed above for enhanced releases

In-lieu-of exchanges:

• Stampede Reservoir and corresponding Boca 

Reservoir release increases concurrent with 

Lake Tahoe release decrease. Water categories listed above for Stampede enhanced 

releases are exchanged with categories used 

to reduce Lake Tahoe releases. The increased 

release from Stampede is passed through 

Boca to meet the same demands downstream 

on the Truckee River as would have been satisfied by releases from Lake Tahoe prior to an 

exchange.

• Stampede Reservoir and corresponding Boca 

Reservoir release increases concurrent with 

Prosser Creek Reservoir release decrease. 

Water categories listed above for Stampede 

Reservoir enhanced releases are exchanged 

with categories used to reduce Prosser Creek 

Reservoir releases. As described above, the 

increased release from Stampede is passed 
92 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

through Boca to meet the same demands 

downstream on the Truckee River as would 

have been satisfied by releases from Prosser 

prior to an exchange.

Release with no exchange or re-storage:

• Stampede Reservoir release increase of 

JPFCW.

Prosser Creek Reservoir

In-lieu-of exchanges:

• Prosser Creek Reservoir release increase of 

uncommitted water concurrent with Lake 

Tahoe release decrease. The uncommitted 

water from Prosser Creek Reservoir is 

exchanged with water categories used to 

reduce Tahoe releases.

• Prosser Creek Reservoir release increase of 

uncommitted water concurrent with Boca 

Reservoir release decrease. The uncommitted 

water from Prosser Creek Reservoir is 

exchanged with water categories used to 

reduce Boca releases.

• Prosser Creek Reservoir release increase of 

uncommitted water concurrent with Stampede Reservoir release decrease of fish water. 

There is no exchange of water categories 

between the two reservoirs because uncommitted water is commonly used for similar 

objectives as fish water, such as cui-ui fish 

runs. However, there is an exchange of 

release quantities between the two reservoirs.

• Prosser Creek Reservoir release increase of 

appropriate categories other than uncommitted water concurrent with Lake Tahoe release 

decrease. Water categories, other than 

uncommitted water, listed above for Prosser 

Creek Reservoir enhanced releases are 

exchanged with categories used to reduce 

Tahoe releases.

• Prosser Creek Reservoir release increase of 

appropriate categories other than uncommitted water concurrent with Boca Reservoir 

release decrease. Water categories, other than 

uncommitted water, listed above for Prosser 

Creek Reservoir enhanced releases are 

exchanged with categories used to reduce 

Boca releases.

Release with no exchange or re-storage:

• Prosser Creek Reservoir release increase of 

JPFCW.

Independence Lake

Re-storage:

• Independence Lake release increase of 

PCPOSW with Stampede Reservoir or Boca 

Reservoir re-storage.

Donner Lake

In-lieu-of exchanges:

• Donner Lake release increase concurrent 

with Lake Tahoe release decrease. Water 

categories listed above for Donner Lake 

enhanced releases are exchanged with categories used to reduce Tahoe releases.

• Donner Lake release increase concurrent 

with Prosser Creek Reservoir release 

decrease. Water categories listed above 

for Donner Lake enhanced releases are 

exchanged with categories used to reduce 

Prosser Creek Reservoir releases.

• Donner Lake release increase concurrent 

with Boca Reservoir release decrease. Water 

categories listed above for Donner Lake 

enhanced releases are exchanged with categories used to reduce reservoir releases.

Several assumptions were made in this subblock.

• Because of the large number of categories available for releases from reservoirs for enhanced 

minimum-flow targets, a large number of exchanges are possible. The USGS Truckee River 

Basin operations model simulates only the most 

likely water categories and exchanges that would 

be used to attain or maintain enhanced instream 

flows.

• Additional releases from Prosser Creek Reservoir 

to prevent the formation of ice that could reduce 

instream flows in Prosser Creek are specified in 

draft TROA. These releases are not simulated in 

the operations model.
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 93

• If simulated releases from Donner Lake are not 

adequate for maintenance of enhanced minimumflow targets, only PCPOSW is simulated to provide all water necessary toward maintenance of 

enhanced minimum-flow targets, provided it can 

be exchanged to another reservoir. Although 

stored in Donner Lake, TCIDPOSW is not simulated to contribute toward enhanced minimumflow targets. 

• If simulated releases from Independence Lake are 

not adequate for maintenance of enhanced minimum-flow targets, only PCPOSW in the lake is 

simulated to provide water for enhanced minimum-flow targets.

• Instream flows in reaches of the Truckee River 

between hydropower diversion and return points 

are specified in draft TROA. Except for the 

Truckee River downstream from Lake Tahoe, 

enhanced flow targets along the mainstem Truckee River are not simulated.

• If available, JPFCW will be released from a given 

reservoir if enhanced minimum-flow targets cannot be met by releases that require exchange or restorage in another reservoir.

• Maximum and minimum reservoir threshold volumes are simulated as constant daily values 

throughout a month rather than as interpolated 

values between end-of-month values specified in 

draft TROA. The reservoir levels used for comparison with the threshold volumes are the current 

day’s simulated volume, not a forecasted volume. 

Neither forecasted volumes nor seasonal foresight10 were used in determining the exchanges 

for maintenance of enhanced minimum-flow targets (see section “Model Limitations, Assumptions, and Suggested Improvements” for a 

discussion on the subject of foresight).

• Reservoirs not located on the Little Truckee River 

are not simulated to exchange directly into Stampede Reservoir. Such exchanges are first made 

directly into Boca Reservoir for later exchange 

into Stampede (see subsequent section “Voluntary Exchanges”).

• Water categories may change during a simulated 

exchange into another reservoir. The following 

list illustrates those water category changes for 

exchanges to meet enhanced minimum-flow targets.

1. Uncommitted water changes to fish credit 

water when exchanged from Prosser Creek 

Reservoir to storage in another reservoir.

2. PCPOSW changes to nonfirm PCMICW 

when an exchange is simulated from Donner 

Lake to storage in another reservoir.

Other Exchanges and Transfers

Other mandatory exchanges and transfers 

specified in draft TROA (Bureau of Reclamation 

and others, 1998) are based on category storage 

limits, drought situation, time of the year, or some 

combination of these criteria. These other exchanges 

and transfers are used to maintain base amounts of 

firm PCMICW, nonfirm PCMICW, and PCEDS and to 

transfer (1) PCPOSW to PCMICW and (2) PCMICW 

to fish credit water on specific dates. Base amounts of 

PCMICW are described in the section “Proposed 

Water Categories.”

The following is a list of these other mandatory 

exchanges and transfers, which are simulated in the 

USGS Truckee River Basin operations model in the 

subblock TROA mandatory exchanges. Note that the 

term drought situation has a specific meaning in draft 

TROA and its determination is prerequisite to many 

operations including some of the operations listed 

below. It is described in the section “Drought Situations.” Following the list is a detailed explanation of 

each of the mandatory exchanges or transfers. 

1. Create firm PCMICW in Stampede Reservoir 

when firm PCMICW storage falls below its base 

amount by transfer of nonfirm PCMICW in Stampede to firm PCMICW storage. 

2. Create PCEDS in Stampede Reservoir when 

PCEDS storage falls below its base amount during a nondrought situation by transfer of fish 

credit water in Stampede to PCEDS or re-storage 

exchange of Independence Lake PCPOSW to 

Stampede PCEDS, when requested by the Power 

Company.

3. Move nonfirm PCMICW to Stampede Reservoir 

from other reservoirs when the volume of non10Seasonal foresight utilizes forecasts of both inflow and 

reservoir management to construct an operational forecast.
94 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

firm PCMICW in Stampede falls below its base 

amount during a drought situation between July 1 

to April 1 by paper exchange of nonfirm 

PCMICW in Lake Tahoe, Prosser Creek Reservoir, and Boca Reservoir with fish and fish credit 

water storage in Stampede.

4. Move nonfirm PCMICW to Stampede Reservoir 

from other reservoirs to attain an additional 6,000 

acre-ft of storage of nonfirm PCMICW (based on 

the consumptive use portion of former agricultural rights) in Stampede, during a drought situation between the dates of April 15 and July 1 

(base amounts are not considered for this 

exchange). This move will be achieved by paper 

exchange of nonfirm PCMICW in Lake Tahoe 

and Boca and Prosser Reservoirs with fish water 

or fish credit water storage in Stampede.

5. Create firm PCMICW in Stampede Reservoir 

when the volume of firm PCMICW in Stampede 

falls below its base amount during a nondrought 

situation between July 1 to December 31. Firm 

PCMICW will be created by paper exchange of 

PCMICW in Lake Tahoe and Prosser and Boca 

Reservoirs with fish or fish credit water storage 

in Stampede.

6. Create fish credit water in Prosser Creek Reservoir, Lake Tahoe, and Boca and Stampede Reservoirs when the storage volume of nonfirm 

PCMICW is above the base amount on April 1 

during a nondrought situation. Fish credit water 

will be created by transfer of nonfirm PCMICW 

in Prosser, Tahoe, Boca, and Stampede to fish 

credit water. During a drought situation, this 

transfer will not occur.

7. Create PCMICW in Stampede Reservoir or Boca 

Reservoir by transfer of PCPOSW to PCMICW 

on January 1.

Firm PCMICW in Stampede Reservoir when firm 

PCMICW storage falls below its base amount

The operations model simulates the transfer of 

nonfirm to firm PCMICW in item 1 by first comparing 

the amount of firm PCMICW to the base amount for 

that category. If the storage of firm PCMICW in Stampede Reservoir falls below its base amount and nonfirm 

PCMICW exists in the reservoir, then transfer the 

amount of nonfirm PCMICW to firm PCMICW in the 

reservoir up to the base amount for firm PCMICW. In 

draft TROA, this transfer is not specified. For model 

simulations, this transfer maintains the base amount of 

firm PCMICW in Stampede. Any remaining amount of 

PCMICW simulated in Stampede is stored as nonfirm 

PCMICW. 

PCEDS in Stampede Reservoir when PCEDS 

storage falls below its base amount during a 

nondrought situation

The operations model simulates exchanges for 

creation of PCEDS in item 2 by first comparing the 

amount of PCEDS in Stampede Reservoir to the base 

amount (7,500 acre-ft) for that category, and then 

determining PCEDS category transfers. When the storage of PCEDS falls below its base during a nondrought 

situation, the volume necessary to achieve the base 

amount is exchanged from available sources. The simulation is based on the date and conditions in the following order listed below:

• Transfer fish credit water in Stampede Reservoir 

to PCEDS water in Stampede.

• Re-storage exchange by release of PCPOSW in 

Independence Lake to Stampede Reservoir if the 

lake storage is above the recreational pool level 

(see section “Maintenance of Recreational 

Pools”) and Independence releases are below the 

preferred flow target releases (see section “Preferred Instream Flows”). Exchange PCPOSW in 

Stampede Reservoir to PCEDS in the reservoir.

• Transfer PCPOSW in Stampede Reservoir to 

PCEDS water in the reservoir.

The assumptions used in subblock TROA mandatory exchanges are as follows:

• For simulations, only the transfers and re-storage 

exchanges between waters in Stampede Reservoir 

listed above are used to create PCEDS water in 

Stampede, even though other exchanges are possible between waters in Boca and Stampede Reservoirs.

• The draft TROA states that the first 7,500 acre-ft 

of Power Company’s credit water in Stampede 

Reservoir transferred to fish credit water shall 

become the PCEDS. PCEDS is created in the 

model from fish credit water as described above. 

It is assumed that once initially created, PCEDS 

will only be used during extreme droughts, and 
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 95

therefore additional PCEDS creation will be 

infrequent. 

Nonfirm PCMICW to Stampede Reservoir from other 

reservoirs when the volume of nonfirm PCMICW in 

Stampede Reservoir falls below its base amount during 

a drought situation between July 1 and April 1

The operations model simulates the paper 

exchange to accumulate additional nonfirm PCMICW 

in Stampede Reservoir in item 3 by first comparing the 

amount of nonfirm PCMICW to the base amount for 

that category. If a drought situation exists, and the current date is between July 1 and April 1, and if the storage of nonfirm PCMICW in the reservoir falls below 

its base amount, then paper exchanges are simulated to 

bring nonfirm PCMICW storage up to the base amount 

in the order below.

• Paper-exchange nonfirm PCMICW in Lake 

Tahoe and Prosser and Boca Reservoirs with fish 

credit water in Stampede Reservoir.

• Paper-exchange nonfirm PCMICW in Lake 

Tahoe and Prosser and Boca Reservoirs with fish 

water in Stampede Reservoir.

The draft TROA states that the Power Company 

can exchange or displace fish credit water or fish water 

in Stampede Reservoir from July 1 to the following 

April 1 to the extent necessary to enable the Power 

Company to store the base amounts of firm and nonfirm M&I credit water. It is assumed that nonfirm

PCMICW storage up to the base amount is simulated in 

the model as described in item 3. Firm PCMICW storage up to the base amount is simulated using the transfer described in item 1. For a further discussion on 

displacement, see the section “Merge Reservoir 

Releases for Multiple Objectives.”

Note that if firm PCMICW volume is less than its 

base amount in Stampede Reservoir during a drought 

situation between July 1 and April 1, these paper 

exchanges provide a mechanism to accumulate additional nonfirm PCMICW from which firm PCMICW 

can be credited as described in item 1 above.

Nonfirm PCMICW to Stampede Reservoir from other 

reservoirs to attain an additional 6,000 acre-ft of 

storage of nonfirm PCMICW in Stampede Reservoir 

during a drought situation between the dates of April 

15 and July 1

The operations model simulates the paper 

exchange to accumulate nonfirm PCMICW in Stampede Reservoir as described in item 4 by first comparing the amount of nonfirm PCMICW stored in the 

reservoir since April 15 to 6,000 acre-ft (as stipulated 

in the draft TROA (Bureau of Reclamation and others, 

1998) and determining the presence or absence of a 

drought situation. If in a drought situation, between 

April 15 and July 1, and if storage of nonfirm 

PCMICW in the reservoir since April 15 is less than 

6,000 acre-ft, then the paper exchanges below are simulated.

• Paper-exchange nonfirm PCMICW in Prosser 

Creek Reservoir, Lake Tahoe, and Boca Reservoir with fish credit water in Stampede Reservoir.

• Paper-exchange nonfirm PCMICW in Prosser 

Creek Reservoir, Lake Tahoe, and Boca Reservoir with fish water in Stampede Reservoir.

Firm PCMICW in Stampede Reservoir when the 

volume of firm PCMICW in Stampede Reservoir falls 

below its base amount during a nondrought situation 

between July 1 and December 31

The paper exchange to accumulate firm 

PCMICW as described in item 5 by first comparing the 

amount of firm PCMICW in Stampede Reservoir to its 

base amount and determining the presence or absence 

of a drought situation. If a nondrought situation exists, 

and the current date is between July 1 and December 

31, and if the storage of firm PCMICW in the reservoir 

falls below its base amount, then paper exchanges are 

simulated to increase nonfirm PCMICW storage in the 

reservoir using the operations below.

• Paper-exchange nonfirm PCMICW in Lake 

Tahoe and Prosser and Boca Reservoirs with fish 

credit water in Stampede Reservoir.

• Paper-exchange nonfirm PCMICW in Lake 

Tahoe and Prosser and Boca Reservoirs with fish 

water in Stampede Reservoir.

The draft TROA states that the Power Company 

shall have the first right to store firm M&I credit water 

in Stampede Reservoir from the previous July 1 

through December 31 up to the base amount of firm 

M&I credit water. For the model, it is assumed that 

nonfirm PCMICW storage is simulated by paper 

exchanges in the model as just described, and firm 

PCMICW storage up to the base amount is simulated 
96 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

using the transfer described in item 1. As stated in the 

section “Storage of Proposed Water Categories,” nonfirm PCMICW will be accumulated by a reduction of 

releases used to maintain Floriston rates corresponding 

to the daily consumptive use of the former agricultural 

diversion rights. That accumulation of credit water is 

different than the paper exchanges described in item 5.

Fish credit water in Prosser Creek Reservoir, Lake 

Tahoe, and Boca and Stampede Reservoirs when the 

storage volume of nonfirm PCMICW is above the base 

amount on April 1 during a nondrought situation.

The operations model simulates the transfer of 

nonfirm PCMICW to fish credit water in item 6 by first 

comparing the amount of nonfirm PCMICW to the 

base amount for that category and determining the 

presence or absence of a drought situation. When not in 

a drought situation and if the April 1 storage of nonfirm 

PCMICW in reservoirs is greater than the base amount, 

the excess nonfirm PCMICW is transferred to fish 

credit water. Those transfers simulated by the operations model include the transfer of nonfirm PCMICW 

in Prosser Creek Reservoir, Lake Tahoe, Boca Reservoir, and Stampede Reservoir in that rank order to fish 

credit water in those same reservoirs.

PCMICW in Stampede or Boca Reservoirs by transfer 

of PCPOSW to PCMICW on January 1

The operations model simulates the transfer of 

PCPOSW and PCMICW as described in item 7. Under 

draft TROA, PCPOSW in reservoirs other than Donner 

and Independence Lakes shall retain its classification 

as PCPOSW until December 31, after which time it 

transfers to PCMICW. If PCPOSW is being stored in 

Stampede or Boca Reservoirs on January 1, then a 

transfer of PCPOSW to nonfirm PCMICW is made 

in the following reservoirs:

• Transfer PCPOSW to nonfirm PCMICW in 

Stampede Reservoir.

• Transfer PCPOSW in excess of 800 acre-ft 

(Boca Reservoir PCPOSW level) to nonfirm 

PCMICW in Boca.

The assumptions used in this section are as 

follows:

• Storage of PCPOSW is not simulated in 

Lake Tahoe and Prosser Creek Reservoir. 

• Under current operations, as described in the 

previous section, “Privately Owned Stored 

Water,” the Power Company stores PCPOSW 

in Boca Reservoir in accordance with rules in 

the Truckee River Agreement, and may store 

additional PCPOSW in Boca and Stampede Reservoirs as described in the Interim Storage Agreement. Under draft TROA, storage of PCPOSW in 

Boca and Stampede Reservoirs as defined by the 

Interim Storage Agreement will be superseded by 

credit water operations. The operations model 

code reflects these differences between current 

and draft TROA reservoir management.

The assumptions used in this section, “Other 

Exchanges and Transfers,” are as follows.

• Forecasting reservoir levels could provide a more 

realistic estimate of the probability of losing certain water categories to reservoir spills. Current 

reservoir levels are used in the model for the 

exchanges listed in this section.

• Storage of nonfirm PCMICW is not simulated for 

Independence and Donner Lakes in the model. 

Voluntary Exchanges

Under the draft TROA and WQSA operations, 

exchanges are used for moving water of various categories among the reservoirs. Many of these exchanges 

would be voluntary and the criteria that might trigger 

these exchanges are not specified in the draft TROA. 

Voluntary exchanges would be requested by the interested parties and the terms and conditions would be 

agreed to by the parties. Voluntary exchanges would 

not interfere with the storage or release of current 

waters associated with any reservoir. Also, no voluntary exchanges would interfere with the achievement of 

minimum instream flows or the mandatory exchanges 

described in the section “Mandatory Exchanges and 

Transfers.” Voluntary exchanges allow scheduled 

releases to meet several objectives instead of one, such 

as (1) preferred instream flows, (2) enhanced storage 

security, (3) efficient use of releases for precautionary 

drawdowns, and (4) maintenance of recreational pools. 

The following sections describe these exchanges and 

how the USGS Truckee River operations model simulates them.
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 97

Preferred Instream Flows

Under draft TROA, guidelines for preferred 

instream flows further increase flow targets described 

in the previous sections “Instream Flows and Enhanced 

Minimum Instream Flows.” Preferred instream flow 

targets (hereafter referred to as preferred flows) vary 

by season and location, and Truckee River system 

operators would attempt to achieve these targets only 

when practicable through exchanges and scheduling of 

releases consistent with water rights. The preferred 

flow targets would help to better serve fish and recreational interests. Draft TROA would provide opportunities for using credit and POSW waters to increase the 

flow rates beyond mandatory enhanced minimum 

instream flows (see previous discussion in the section 

“Enhanced Minimum Instream Flows”) to the rates 

prescribed for voluntary preferred flows. These water 

categories could be used to increase instream flows 

only if they could be re-stored in another reservoir or 

exchanged for water in another reservoir. As was the 

case for enhanced minimum instream flows, 

exchanges made to attain the higher targets for preferred flows depend on the water category’s security in 

storage when re-stored or exchanged, its availability 

and location in reservoir storage before re-storage or 

exchange, and the current status of streamflow with 

respect to preferred flow targets at specific locations. 

Similar to enhanced minimum instream flows, California, at its discretion, could use Joint Program fish credit 

water (JPFCW) to achieve preferred flows without restorage or exchange into another reservoir.

As with other mandatory exchanges, the current 

storage within reservoirs targeted for re-storage or 

exchange to facilitate preferred flows needs to be 

within prescribed thresholds. These threshold volumes were developed to ensure security of re-stored or 

exchanged water with regard to the threat of reservoir 

spill when reservoir levels are high or the threat of limited outlet capacity or recreation potential when reservoir levels are low. Unlike enhanced instream flow 

guidelines, normal and dry seasons are not used to 

determine preferred flow targets. 

Several reservoirs in the Truckee River Basin 

would be operated to provide releases necessary for the 

maintenance of preferred flows, which are not specified by draft TROA. Rather, draft TROA indicates that 

the State of California will submit operating guidelines, 

called “California Guidelines,” that will address preferred flows below reservoirs. It is anticipated that the 

guidelines will address many concerns, and thus provide a degree of flexibility for the determination of preferred flow targets and the methods to achieve them. 

However, for purposes of model simulations, table 8

specifies assumed preferred flows below each reservoir 

(Roderick L. Hall, Sierra Hydrotech, written commun., 

p. 4, August 23, 1996).

The USGS Truckee River Basin operations 

model simulates preferred flow exchange operations as 

follows. Like the simulation of reservoir releases for 

maintenance of enhanced minimum instream flow targets, reservoir releases for maintenance of preferred 

flows are simulated in two subblocks of the operations 

model. The subblock initial assignments and computations assigns proposed releases for each reservoir for 

maintenance of preferred flows. The subblock preferred instream flows modifies the proposed releases 

by applying various rules and constraints required for 

reservoir releases and exchanges for preferred flows.

In the subblock initial numerical assignments 

and computations, the following are specified.

Table 8. Assumed preferred instream flow targets downstream of reservoirs

[Abbreviation: ft3/s, cubic feet per second]

Location January

(ft3/s)

February–March

(ft3/s)

April–July

(ft3/s)

August–September

(ft3/s)

October–December

(ft3/s)

Lake Tahoe 250 150 300 150 2,502

Donner Lake 50 20 50 10 50

Martis Creek Lake 1

1 Maintenance of preferred instream flows downstream from Martis Creek Lake is not required.

—— — — —

Prosser Creek Reservoir 50 35 75 30 50

Independence Lake 20 10 20 10 20

Stampede Reservoir 125 100 125 100 125

Boca Reservoir 2

2 Maintenance of preferred instream flows downstream from Boca Reservoir is not required.

—— — — —
98 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

• The user specifies whether releases and 

exchanges to maintain preferred flow targets 

downstream from reservoirs will be simulated or 

not. If so, the user also specifies, on a reservoirby-reservoir basis, whether releases and 

exchanges to maintain preferred flow targets 

downstream from each reservoir will be simulated or not. 

• Preferred flow objectives are specified for Donner and Independence Lakes, Stampede and 

Prosser Reservoirs, and Lake Tahoe based on the 

month (table 8). These values may be changed by 

the user. Boca Reservoir and Martis Creek Lake 

have no preferred flow targets.

• Once the option to simulate preferred flows has 

been selected, the user may choose one of three 

options for preferred flow targets:

1. Simulate preferred flows at the full target levels (table 8), even if only for a short period of 

time, until available credit and POSW waters 

are depleted.

2. Reduce the target flow rates to extend the 

flow increase over enhanced minimum 

instream flows through the summer, based on 

the current storage of JPFCW in a reservoir.

3. Reduce the target flow rates to extend the 

flow increase over enhanced minimum 

instream flows as described in item 2. However, the target flow rates will be based on the 

current storage of nonfirm Power Company 

M&I credit water (nonfirm PCMICW), 

fish credit water, water-quality credit water 

(WQCW), and Power Company POSW 

(PCPOSW) in addition to JPFCW in a 

reservoir.

If option 2 or 3 is selected, rather than maintaining full-target flows for a short period (table 8), the 

computations associated with these options would simulate maintenance of a lower target flow throughout the 

summer when reservoir storage of water categories 

would otherwise be insufficient. Thus, these two 

options will simulate reservoir releases designed to 

extend a lower rate of preferred flows over longer periods of time.

The reservoir releases for achievement of full or 

reduced preferred flow targets in the initial numerical 

assignments and computations subblock are modified 

in the subblock preferred instream flows. Hereafter, 

for clarity of discussion, “full” or “reduced” preferred 

flow targets will be referred to simply as “preferred”

flow targets. This subblock modifies the proposed 

releases by applying various rules and constraints for 

all reservoirs required to release for preferred flows. 

In this subblock, reservoir releases to maintain preferred flow targets are based on whether (1) water 

categories involved in the releases can be re-stored in 

another reservoir, (2) water categories can be 

exchanged with other water categories in another reservoir, or (3) JPFCW, which does not require re-storage 

or exchange into other reservoirs, is available.

First, the status of reservoir releases is compared 

to preferred flow targets downstream from the reservoirs. If a given release is less than the target, then the 

deficit is determined as that additional flow needed to 

achieve the preferred flow target. Likewise, if a given 

release is greater than the target, the excess is determined so that releases may be reduced to target rates, if 

possible.

Second, when the reservoir release is less than the 

preferred flow target, the availability of water categories for additional releases is determined while considering the hydraulic constraints of the reservoir outlet. 

Additional releases of waters are based on the proportion of a given category volume to the total volume of 

water categories available for additional release. As 

discussed above, minimum threshold volumes are 

required for Donner Lake for security of exchanged 

waters or for maintenance of recreational pool levels, 

and as a result, releases for preferred flows may be 

restricted from the lake. For each reservoir the availability of the following water categories is checked for 

preferred flow releases:

• Lake Tahoe—WQCW, fish credit water, and nonfirm PCMICW.

• Donner Lake—PCPOSW. For simulations, 

TCIDPOSW is not used to achieve enhanced 

instream flow targets.

• Martis Creek Lake—not applicable.

• Prosser Creek Reservoir—WQCW, fish credit 

water, and nonfirm PCMICW.

• Independence Lake—PCPOSW.

• Stampede Reservoir—WQCW, fish credit water, 

and nonfirm PCMICW.

• Boca Reservoir—not applicable.
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 99

Third, for each reservoir with a release excess, a 

determination is made regarding the amount releases 

from given water categories may be decreased. Water 

categories in reservoirs with release excesses can be 

exchanged with water categories in those reservoirs 

with release deficits (an in-lieu-of exchange), similar to 

exchanges involved in enhanced flow targets. Reduction of a given water category release is also limited by 

overall and category release floors, which may be the 

current enhanced flow target. Additionally, the reduction of releases for each water category is based on the 

proportion of that water category released, to the total 

release of all water categories available for reduction. 

Lastly, maximum threshold volumes must be considered for Lake Tahoe and Prosser, Stampede, and Boca 

Reservoirs, and a minimum threshold volume must be 

considered for Lake Tahoe for security of exchanged 

waters, and as a result, the reduction of releases may be 

restricted in these reservoirs. For each reservoir the following water categories are checked for reduced 

releases.

• Lake Tahoe—WQCW, fish credit water, nonfirm 

PCMICW, and pooled water.

• Donner Lake—Not applicable (no credit waters 

are stored in this reservoir).

• Martis Creek Lake—not applicable.

• Prosser Creek Reservoir—WQCW, fish credit 

water, nonfirm PCMICW, uncommitted water, 

natural water, and Tahoe–Prosser Exchange 

water.

• Independence Lake—not applicable (no credit 

waters are stored in this reservoir).

• Stampede Reservoir—not applicable. Water categories are first exchanged into Boca Reservoir 

and subsequently exchanged into Stampede Reservoir in other types of exchanges (see the later 

section “Voluntary Exchanges”).

• Boca Reservoir—fish credit water, WQCW, nonfirm PCMICW, PCPOSW, fish water, adverseto-canal pooled water, non-adverse-to-canal 

pooled water, and natural water.

Fourth, release increases are determined for reservoirs that require and are capable of such releases to 

achieve downstream preferred flow targets. Releases 

for preferred flows are determined by three methods: 

(1) re-storage of water categories in another reservoir, 

(2) exchange of water categories to another reservoir, 

and (3) release of JPFCW without re-storage or 

exchange in other reservoirs. For exchanges (item 2), 

potential release increases of water categories from reservoirs must be compared with potential release reductions of water categories from different reservoirs. The 

other two methods (items 1 and 3) do not require such 

comparisons. 

The operations model simulates reservoir releases 

for preferred flow targets by the following list, which is 

based on the likely rank order releases for preferred 

flow targets (Lake Tahoe, Stampede Reservoir, Prosser 

Creek Reservoir, Independence Lake, and Donner 

Lake). At a given reservoir, if preferred flows cannot be 

met by exchange or re-storage in another reservoir, 

then JPFCW is released, if available. Unless indicated, 

water categories involved in release increases and 

decreases are those previously discussed in this section.

Lake Tahoe 

In-lieu-of exchanges:

• Lake Tahoe release increase concurrent with 

Prosser Creek Reservoir release decrease. 

Water categories listed above for Lake Tahoe 

preferred flow release increases are 

exchanged with categories used to reduce 

Prosser Creek Reservoir releases.

•Lake Tahoe release increase concurrent with 

Boca Reservoir release decrease. Water categories listed above for Lake Tahoe preferred 

flow release increases are exchanged with 

categories used to reduce Boca Reservoir 

releases.

Release with no exchange or re-storage:

• Lake Tahoe release increase of JPFCW.

Stampede Reservoir

Re-storage:

• Stampede Reservoir release increase using 

water categories listed above for preferred 

releases, followed by re-storage in Boca Reservoir.

In-lieu-of exchanges:

• Stampede Reservoir (and corresponding 

Boca Reservoir) release increases concurrent 

with Lake Tahoe release decrease. Water cat-
100 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

egories listed above for Stampede preferred 

flow releases are exchanged with categories 

used to reduce Tahoe releases. The increased 

release from Stampede is passed through 

Boca to meet the same demands downstream 

on the Truckee River as would have been satisfied by releases from Tahoe prior to an 

exchange.

• Stampede Reservoir (and corresponding 

Boca Reservoir) release increases concurrent 

with Prosser Creek Reservoir release 

decrease. Water categories listed above for 

Stampede preferred flow releases are 

exchanged with categories used to reduce 

Prosser releases. As described above, the 

increased release from Stampede is passed 

through Boca to meet the same demands 

downstream on the Truckee River as would 

have been satisfied by releases from Prosser 

prior to an exchange.

Release with no exchange or re-storage:

• Stampede Reservoir release increase of 

JPFCW.

Prosser Creek Reservoir

In-lieu-of exchanges:

• Prosser Creek Reservoir release increase concurrent with Lake Tahoe release decrease. 

Water categories listed above for Prosser 

Creek Reservoir preferred flow releases are 

exchanged with categories used to reduce 

Lake Tahoe releases.

• Prosser Creek Reservoir release increase concurrent with Boca Reservoir release decrease. 

Water categories listed above for Prosser 

Creek Reservoir preferred flow releases are 

exchanged with categories used to reduce 

Boca releases.

Release with no exchange or re-storage:

• Prosser Creek Reservoir release increase of 

JPFCW.

Independence Lake

Re-storage:

• Independence Lake release increase of 

PCPOSW with Stampede Reservoir re-storage.

Donner Lake

In-lieu-of exchanges:

• Donner Lake release increase concurrent 

with Lake Tahoe release decrease. Water categories listed above for Donner Lake preferred flow releases are exchanged with 

categories used to reduce Lake Tahoe 

releases.

• Donner Lake release increase concurrent 

with Prosser Creek Reservoir release 

decrease. Water categories listed above for 

Donner Lake preferred flow releases are 

exchanged with categories used to reduce 

Prosser Creek Reservoir releases.

• Donner Lake release increase concurrent 

with Boca Reservoir release decrease. Water 

categories listed above for Donner Lake preferred flow releases are exchanged with categories used to reduce Boca Reservoir 

releases.

Several assumptions were used in this subblock.

• Because of the large number of categories available for releases from reservoirs for preferred 

flow targets, a large number of voluntary 

exchanges are possible. The USGS Truckee River 

Basin operations model simulates only the most 

likely water categories and exchanges that would 

be used to attain or maintain preferred flow targets.

• Instream preferred flows are specified for several 

locations along the mainstem Truckee River in 

draft TROA. Except for the Truckee River downstream from Lake Tahoe, preferred flow targets 

along the mainstem Truckee River are not simulated. 

• Maximum and minimum reservoir threshold volumes are simulated as constant daily values 

throughout a month, rather than as interpolated 

values between end-of-month values specified in 

draft TROA. The reservoir levels used for comparison with the threshold volumes are the current 

day’s simulated volume, not a forecasted volume. 

Similar to exchanges involved to maintain 
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 101

enhanced flow targets, neither forecasted volumes nor seasonal foresight were used in determining the exchanges to maintain enhanced 

minimum-flow targets.

• Increases and reductions of reservoir releases by 

exchanges with another reservoir are determined 

by the proportion of each water category available in relation to the total volume of water categories available for the release increase or 

reduction, unless specified otherwise.

• Reservoirs not located on the Little Truckee 

River are not simulated to exchange directly 

into Stampede Reservoir. Such exchanges are 

first made directly into Boca Reservoir for later 

exchange into Stampede (see the section “Voluntary Exchanges”).

• Water categories may change during an exchange 

into another reservoir. The following list illustrates those water category changes for exchanges 

to meet preferred flow targets.

1. Uncommitted water changes to fish credit 

water when exchanged from Prosser Creek 

Reservoir to storage in another reservoir.

2. PCPOSW changes to nonfirm PCMICW 

when exchanged from Donner Lake to storage in another reservoir.

Enhanced Storage Security and Access

Voluntary exchanges for enhanced storage security have the objective of relocating a specific volume 

and category of water from one reservoir to another 

reservoir that is less likely to release water due to floodcontrol criteria, or in which release amounts will not 

be hydraulically constrained during periods of low 

reservoir volumes. These are all considered voluntary 

exchanges, which means the transaction must be 

agreed to by owners of all affected water categories.

The storage characteristics of reservoirs in the 

Truckee River Basin can vary depending on the time of 

year, inflow, reservoir storage, recreational pools, and 

releases for downstream flows. Because of the many 

variables and implications to consider, draft TROA 

contains no criteria for voluntary exchanges to enhance 

the security of or access to credit water. 

It will often be desirable to exchange water stored 

in Lake Tahoe and Prosser Creek Reservoir to Boca 

Reservoir. Although Tahoe is the largest reservoir in 

the system (usable storage 744,600 acre-ft), waters in 

storage may be lost or simply unavailable. First, the 

hydraulic capacity of the outlet diminishes as the water 

level approaches the natural rim (6,223.0 ft, Lake 

Tahoe datum). Second, as specified in the Truckee 

River Agreement, the goal of Tahoe flood operations 

is to spill water so as to maintain the lake’s water-surface at an elevation of 6,229.1 ft or less. In these two 

instances, the inability to access one’s water or the 

danger of spilling water at a time when it cannot be 

used occasionally makes Tahoe a less desirable storage 

location.

Prosser Creek Reservoir has a limited storage 

(29,800 acre-ft) capacity in the spring. Later in the 

year, the fall precautionary drawdown may require that 

water be spilled to achieve a storage volume of about 

9,800 acre-ft, in accordance with flood-control criteria. 

Because of the potential for spills, Prosser may also be 

a less desirable storage location.

Boca Reservoir is a better choice for storage 

because more storage (41,100 acre-ft) is available than 

in Prosser Creek Reservoir. Also, an exchange to Boca 

is needed to move a block of water to an even safer 

location, Stampede Reservoir. 

Stampede Reservoir is the largest reservoir in 

the Little Truckee River Basin (total capacity of 

226,500 acre-ft), and provides much flexibility in 

storing water. Water is less likely to be released from 

this reservoir because of flood-control criteria. Waters 

released from Stampede are not generally constrained 

by outlet hydraulics and may be re-stored in Boca Reservoir. Stampede’s large storage capacity and flexibility in operations means that it will normally possess 

more secure storage characteristics and provide better 

accessibility than other reservoirs. Also, because Stampede has a junior storage right to other reservoirs in the 

Truckee River Basin, it will be the last to fill, and thus 

is less likely to spill. 

The USGS Truckee River Basin operations 

model simulates enhanced storage security exchange 

operations in the subblock enhanced storage security 

using, a simplistic approach that allows exchanges into 

only two reservoirs, Boca and Stampede. Simulated 

exchanges from Lake Tahoe or Prosser Creek Reservoir to Boca for the purpose of enhanced security are 

in-lieu-of exchanges. In this type of exchange, water is 

released from one reservoir in exchange for storage of 

an equal volume in another reservoir. Most of the simulated exchanges from Boca to Stampede are paper 

exchanges in which equal volumes are traded between 
102 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

the two reservoirs with no physical movement of water 

involved. Also, exchanges for enhanced storage security in the model may be turned off or on (all or none) 

at the option of the user.

Exchanges from Lake Tahoe or Prosser Creek 

Reservoir to Boca Reservoir

In the operations model, in-lieu-of exchanges are 

simulated from Lake Tahoe or Prosser Creek Reservoir 

to Boca Reservoir. The first step in simulating 

exchanges from Tahoe or Prosser to Boca would be to 

determine how much, if any, additional release from 

Tahoe can be made using the categories WQCW, nonfirm PCMICW, and fish credit water. Similarly, it must 

be determined if additional releases from Prosser can 

be made using the categories WQCW, nonfirm 

PCMICW, and fish credit water. In this first step, the 

previously determined releases and hydraulic capacity 

of the outlets are considered. The second step is to 

determine the amount that Boca may reduce its releases 

of the categories fish credit water, WQCW, nonfirm 

PCMICW, PCPOSW, fish water, adverse-to-canal 

water, non-adverse-to-canal water and natural water. 

The amount of reduction in releases of a given water 

category is based on the difference between the currently simulated release and the overall and category 

release floors (described in the section “Enhanced Minimum Instream Flows”). In addition to the consideration of release floors, the reduction of releases is based 

on the proportion of each water category released to the 

total release of water categories available for reduction. 

Finally, potential release increases from Prosser and 

Tahoe are compared to potential Boca release reductions using the exchange water categories listed above, 

if available, and the following list.

1. Prosser–Boca Exchange—If Prosser Creek 

Reservoir is above its prescribed threshold 

volume, increase releases from Prosser and 

reduce releases from Boca Reservoir. The prescribed threshold volumes are described in the 

section “Storage of Proposed Water Categories.”

2. Tahoe–Boca Exchange—If Lake Tahoe is 

above its prescribed threshold volume, increase 

releases from Tahoe and reduce releases from 

Boca Reservoir categories.

3. Prosser–Boca Exchange—Increase releases 

from Prosser Creek Reservoir and reduce releases 

from Boca Reservoir, regardless of water levels 

in Prosser.

4. Tahoe–Boca Exchange—Increase releases 

from Lake Tahoe and reduce releases from Boca 

Reservoir, regardless of water levels in Tahoe.

Exchanges from Boca Reservoir to Stampede Reservoir

To enhance storage security, water is moved from 

Boca Reservoir to Stampede Reservoir mostly by paper 

exchanges. There are four likely conditions under 

which these exchanges are simulated and each condition, as coded in the model, is described below.

1. When the storage of pooled water in Boca Reservoir is less than 5,000 acre-ft, then exchange 

non-adverse-to-canal water in Stampede Reservoir to Boca. This condition is simulated when 

Boca is using pooled waters for Floriston rates 

and pooled water in Stampede is needed in Boca. 

Non-adverse-to-canal water can be stored in 

Stampede using exchanges as described in conditions (2) and (3) of Boca–Stampede Exchanges 

and in the sections “Enhanced Minimum Flows”

and “Preferred Instream Flows.” The following 

list shows the rank order of exchanges possible 

when Boca Reservoir pooled water storage is less 

than 5,000 acre-ft. The sources marked with an 

asterisk (*) are different from current sources.

• Paper-exchange fish water in Boca Reservoir 

with non-adverse-to-canal water in Stampede 

Reservoir.

• *Paper-exchange fish credit water in Boca 

Reservoir with non-adverse-to-canal water in 

Stampede Reservoir.

• *Paper-exchange JPFCW in Boca Reservoir 

with non-adverse-to-canal water in Stampede 

Reservoir. 

• *Paper-exchange nonfirm PCMICW in Boca 

Reservoir with non-adverse-to-canal water in 

Stampede Reservoir. 

• *Paper-exchange WQCW in Boca Reservoir 

with non-adverse-to-canal water in Stampede 

Reservoir. 

• Exchange (by re-storage) non-adverse-tocanal water in Stampede Reservoir to Boca 

Reservoir.
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 103

2. When any non-adverse-to-canal (pooled) water is 

remaining in Stampede Reservoir on April 1, then 

exchange that non-adverse-to-canal water to 

Boca Reservoir. Pooled water may reside in 

Stampede as a result of previous exchanges, such 

as those made to facilitate the timely release of 

fish water for spawning. These pooled waters 

should be removed from Stampede to allow for 

spring time filling of the reservoir with fish 

waters. The following list shows the rank order of 

the exchanges when the date is April 1 and nonadverse-to-canal water is remaining in Stampede. 

The sources marked with an asterisk (*) are different from current sources.

• Paper-exchange fish water in Boca Reservoir 

with non-adverse-to-canal water in Stampede 

Reservoir. 

• *Paper-exchange fish credit water in Boca 

Reservoir with non-adverse-to-canal water in 

Stampede Reservoir. 

• *Paper-exchange JPFCW in Boca Reservoir 

with non-adverse-to-canal water in Stampede 

Reservoir. 

• *Paper-exchange nonfirm PCMICW in Boca 

Reservoir with non-adverse-to-canal water in 

Stampede Reservoir. 

• *Paper-exchange WQCW in Boca Reservoir 

with non-adverse-to-canal water in Stampede 

Reservoir. 

3. In the previous sections, “Pyramid Lake Fish”

and “Fish Credit Water,” simulated fish and fish 

credit waters are released from Stampede Reservoir for storage in Boca Reservoir as Boca pressure water in order to gain more timely access to 

these water categories when needed. To maintain 

the Boca pressure water storage when fish water 

and fish credit water storage in Boca falls below 

2,000 acre-ft during a fish regime 1 from March 1 

to June 5, fish water in Stampede is exchanged to 

Boca. In this exchange for enhanced storage security, paper exchanges are simulated between 

Stampede fish water and fish credit water and 

four categories of Boca waters. The following list 

shows the ranked order of the exchanges simulated under these conditions. Again, the sources 

marked with an asterisk (*) are different from current sources.

• *Paper-exchange non-adverse-to-canal water 

in Boca Reservoir with fish credit water in 

Stampede Reservoir. 

• *Paper-exchange adverse-to-canal water in 

Boca Reservoir with fish credit water in 

Stampede Reservoir. 

• *Paper-exchange JPFCW in Boca Reservoir 

with fish credit water in Stampede Reservoir. 

• *Paper-exchange nonfirm PCMICW in Boca 

Reservoir with fish credit water in Stampede 

Reservoir. 

• Paper-exchange non-adverse-to-canal water 

in Boca Reservoir with fish water in Stampede Reservoir. 

• Paper-exchange adverse-to-canal water in 

Boca Reservoir with fish water in Stampede 

Reservoir. 

• *Paper-exchange JPFCW in Boca Reservoir 

with fish water in Stampede Reservoir. 

• *Paper-exchange nonfirm PCMICW in Boca 

Reservoir with fish water in Stampede Reservoir. 

4. As described in the previous section “WaterQuality Targets and Related Instream Flow 

Transfers,” Boca Reservoir will be used for 

temporary storage of WQCW for quick release to 

the Truckee River. This type of re-regulation will 

facilitate timely access to WQCW when needed. 

To maintain this temporary storage of WQCW, 

when the WQCW in Boca falls below 300 acre-ft 

between June 1 and September 30, and Stampede 

Reservoir WQCW releases, as determined in the 

previous section, are not enough to create 300 

acre-ft of WQCW storage in Boca, then WQCW 

is exchanged in Stampede to Boca. In this 

enhanced storage-security exchange, paper 

exchanges are simulated between Stampede 

WQCW and five categories of Boca waters as follows in ranked order.

• Paper-exchange non-adverse-to-canal water 

in Boca Reservoir with WQCW in Stampede 

Reservoir. 

• Paper-exchange fish water in Boca Reservoir 

with WQCW in Stampede Reservoir. 
104 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

• Paper-exchange fish credit water in Boca 

Reservoir with WQCW in Stampede Reservoir. 

• Paper-exchange JPFCW in Boca Reservoir 

with WQCW in Stampede Reservoir. 

• Paper-exchange nonfirm PCMICW in Boca 

Reservoir with WQCW in Stampede Reservoir. 

This subblock includes the following assumptions.

• Although a large number of categories and voluntary exchanges are possible, the operations model 

only simulates the most likely exchanges for 

enhanced security. Exchanges for this purpose are 

only simulated from Lake Tahoe and Prosser 

Creek Reservoir to Boca Reservoir, and from 

Boca Reservoir to Stampede Reservoir. Donner 

and Independence Lakes are not included in these 

exchanges for enhanced storage. Additional 

exchanges, and the order in which the exchanges 

are considered, can be implemented by modifying 

the code in the operations model, but only by 

experienced programmers.

• Exchanges as described in the section “Current 

Operational Exchanges,” such as the Tahoe–

Prosser and Donner–Boca Exchanges, will occur 

prior to the exchanges described in this section. 

• An exchange for enhanced security is not simulated if the reservoir receiving the water is above 

the maximum prescribed threshold volume. 

Water will not be exchanged out of Prosser Creek 

Reservoir if the uncommitted water volume falls 

below 9,800 acre-ft. This constraint on exchanges 

is assumed to allow enough uncommitted water in 

Prosser for the Tahoe–Prosser Exchange (Thomas R. Scott, Bureau of Reclamation, oral commun., 1997). The reservoir levels used for 

comparison with the prescribed threshold volumes in the conditional logic for enhanced storage security are the current day’s simulated 

volume, not a forecasted volume. Neither forecasted volumes nor foresight was used in determining the exchanges for enhanced security. 

• JPFCW is not considered in exchanges of credit 

waters from Lake Tahoe or Prosser Creek Reservoir to Boca Reservoir because there are no 

guidelines to determine what reservoir is strategically superior for storage of JPFCW.

• In the operations for enhanced storage security, 

pooled water can be exchanged into Stampede 

Reservoir. The only pooled water stored in Stampede in the model is non-adverse-to-canal water. 

This assumption was necessary to minimize the 

number of pooled water categories in Stampede.

Efficient Use of Releases for Precautionary Drawdowns

Under flood-control criteria, it is sometimes necessary to release water from a reservoir as a precautionary drawdown. Voluntary exchanges under draft 

TROA will allow precautionary drawdown releases to 

meet several objectives. In addition to the Donner–

Boca Exchange described in the section “Current Operational Exchanges,” the three most likely exchanges for 

efficient use of releases for precautionary drawdowns 

to be practiced are a Donner–Tahoe Exchange, a 

Prosser–Tahoe Exchange, and a Prosser–Boca 

Exchange. These three exchanges would be informal 

agreements that specify that waters required to be 

released for flood control due to precautionary drawdown may be exchanged to pooled water for maintenance of Floriston rates.

In these in-lieu-of exchanges, water released 

from one reservoir for precautionary drawdown is 

exchanged to pooled water for maintenance of Floriston rates. In exchange, an equivalent volume of pooled 

water that was being released from the reservoir contributing to Floriston rates will be reduced. The volume 

stored as a result of the reduction in releases is then 

exchanged to the category that had to be released for 

precautionary drawdown. Thus, depending on the volumes of water exchanged, all or some releases of 

pooled water for maintenance of Floriston rates will be 

made from other reservoirs. In effect, these exchanges 

allow the releases required from precautionary drawdowns to meet three objectives instead of one: (1) precautionary drawdown to the wintertime cap for 

creation of flood-control space, (2) maintenance of 

Floriston rates, and (3) storage of nonpooled waters in 

other reservoirs for later use rather than release downstream. 

The USGS Truckee River Basin operations 

model simulates exchanges for efficient use of water 

associated with precautionary drawdowns in the subblock efficient use of releases. The three in-lieu-of 

exchanges are similar to the Donner–Boca Exchange, 
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 105

described in the section “Current Operational Exchanges.” These exchanges are simulated during precautionary drawdown periods for Donner Lake and 

Prosser Creek Reservoir. The following list describes 

the exchanges coded in the operations model. 

• Donner–Tahoe Exchange—From August 15 to 

November 15, exchange PCPOSW released as 

precautionary drawdown from Donner Lake with 

pooled water in Lake Tahoe being released. The 

PCPOSW exchanged into Tahoe becomes nonfirm PCMICW.

• Prosser–Tahoe Exchange—From October 1 to 

31, exchange uncommitted water released as precautionary drawdown from Prosser Creek Reservoir with pooled water in Lake Tahoe being 

released. The uncommitted water exchanged into 

Tahoe becomes fish credit water. 

• Prosser–Boca Exchange—From October 1 to 31, 

exchange uncommitted water released as precautionary drawdown from Prosser Creek Reservoir 

with adverse-to-canal water in Boca Reservoir 

being released. The uncommitted water 

exchanged into Boca becomes fish credit water.

Assumptions in this subblock include the following items.

• An exchange made to efficiently use precautionary drawdowns for release will not be simulated 

if the receiving reservoir is above the prescribed 

threshold volume.

• A tolerance of 3.0 ft3

/s of reservoir releases due to 

precautionary drawdown is used to determine 

when these exchanges can be simulated. If 

releases are less than 3.0 ft3/s, no exchange will 

be simulated. This tolerance may be modified by 

the user.

• Under draft TROA, the exchanges described in 

this section for efficient use of releases for precautionary drawdowns are simulated whenever 

possible. The user does not have the option to prevent these exchanges from being simulated.

• There is a difference between the Prosser–Boca 

Exchanges described in this section and in the 

section “Enhanced Storage Security and Access.”

The exchange described in this section can only 

be simulated between October 1 and April 9 during precautionary drawdowns and between 

uncommitted water and adverse-to-canal water. 

The exchanges described in the other section can 

be simulated anytime between several categories, 

but exchanges are not simulated with uncommitted water.

• Although a large number of categories and voluntary exchanges are possible for the efficient use of 

releases for precautionary drawdowns, the operations model only simulates the listed exchanges. 

• Draft TROA credit water categories were not considered for the efficient use of releases for precautionary drawdowns exchanges. As described in 

the section “Merge Reservoir Releases for Multiple Objectives,” under “Proposed Reservoir 

Operations,” in most situations credit water categories will be displaced before current water categories. However, it has been assumed in the 

operations model that current water categories 

will provide a better opportunity for the water not 

to be displaced. 

Maintenance of Recreational Pools

One of the multiple-use benefits of reservoirs is to 

maintain storage levels that enhance boating, fishing, 

and other summer recreational uses. These storage levels that promote public use of the reservoirs are called 

recreational pools. Different types of reservoir 

releases or exchanges may cause reservoir levels to be 

above or below recreational pools. When possible, reservoir releases or exchanges can be operated to maintain a recreational pool. 

Under current operations, the only reservoir that 

has a legal recreational pool is Donner Lake (stage of 

5,932.0 ft or storage of 6,310 acre-ft), as defined in the 

Donner Lake Indenture of 1943. Prosser Creek Reservoir is informally operated by adjustment of reservoir 

releases with consideration of a recreational pool of 

19,000 acre-ft, as described in the section “Floriston 

Rates.” Independence Lake is informally operated with 

consideration of minimum pool volume of 10,000 acreft to benefit Lahontan cutthroat trout spawning 

upstream from the lake (Richard D. Moser, Sierra 

Pacific Power Company, written commun., 1995). No 

formal exchanges for maintenance of recreational 

pools are used in current operations.

Under draft TROA, California would recommend 

minimum recreational pools for reservoirs that would 

apply from about June through Labor Day. Water 

would be voluntarily exchanged among the reservoirs 
106 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

to achieve the objectives, but would not interfere with 

downstream demands, mandatory exchanges, or any 

current legal agreements or decrees. Also under draft 

TROA, JPFCW may be used in voluntary exchanges to 

meet recreational pool objectives. Minimum recreational pool levels for Truckee River Basin reservoirs 

have been defined as follows (Kathleen Egan, City of 

Truckee, written commun., 1997).

• Donner Lake—8,800 acre-ft.

• Prosser Creek Reservoir—19,000 acre-ft.

• Boca Reservoir—33,500 acre-ft.

• Stampede Reservoir—127,000 acre-ft.

• Independence Lake—10,000 acre-ft.

• Lake Tahoe and Martis Creek Lake—no defined 

recreational pool volumes.

The USGS Truckee River Basin operations 

model simulates maintenance of recreational pools in 

the subblock maintenance of recreational pools as follows. Operations considering recreational pools for 

Donner and Independence Lakes and Prosser Creek 

Reservoir are simulated in several subblocks and the 

user does not have the option to turn these operations 

on or off. Therefore, although recreational pool objectives are set for Donner Lake and Independence Lakes 

and Prosser and Boca Reservoirs, voluntary exchanges 

are only simulated to maintain Boca Reservoir recreational pool objectives. All draft TROA exchanges for 

enhancement of the recreational pool objectives for 

Boca may be turned off or on at the option of the user. 

The operations model does not simulate exchanges to 

meet recreational pool levels for Martis Creek Lake 

and Lake Tahoe. It is assumed that the high storage 

needed for recreational pools in Stampede could only 

be met in years in which runoff is above average. It 

would be difficult to implement the number and magnitude of the exchanges necessary to satisfy the recreational pool level in a dry year. 

Next, as in actual operations, the model can manage various types of releases to maintain recreational 

pools. These simulated releases for each reservoir are 

described in various subblocks of the model. The following list describes the operations in various subblocks where recreational pool maintenance is 

considered for Donner and Independence Lakes and 

Prosser and Boca Reservoirs. These releases are simulated under both current operations and draft TROA.

• Donner Lake—A recreational pool was first specified in the Donner Lake Indenture of 1943 to be 

held above 5,932.0 ft and below 5,935.8 ft for the 

months of June through August. In the operations 

model, there is no specific subblock to maintain 

recreational pools for the lake. However, in some 

subblocks that determine the releases from the 

lake, the recreational pool of 5,932 ft or 6,310 

acre-ft is considered. For example, in the section 

“Privately Owned Stored Water,” Donner Lake 

elevation is held above 5,932 ft for the period 

June 16 to September 1. (See also the other sections “Storage Priorities,” “Reservoir PassThroughs and Releases to Meet Newlands Project 

Demands,” and “Minimum Instream Flows.”)

• Independence Lake—Recreational pools of 

10,000 and 7,500 acre-ft have been coded for current operations and draft TROA, respectively. 

There is no specific subblock for maintenance of 

recreational pools for Independence Lake. However, in other subblocks that determine the 

releases from the lake, the recreational pool is 

considered. (See section “Privately Owned 

Stored Water” in the section “Current Reservoir 

Operations.”) For example, when Independence 

releases are needed to fill Boca Reservoir 

PCPOSW to 800 acre-ft, and if lake levels are 

below the recreational pool of 10,000 acre-ft, no 

releases will be made. The Independence Lake 

recreation pool of 7,500 acre-ft is also included in 

the section “Privately Owned Stored Water” in 

the section “Current Reservoir Operations,” and 

in sections “Power Company M&I Credit Water”

and “Mandatory Exchanges and Transfers” of the 

“Proposed Reservoir Operations” section.

• Prosser Creek Reservoir—There is no specific 

subblock for maintenance of recreational pool for 

Prosser Creek Reservoir. However, in two subblocks that determine the releases from the reservoir, the recreational pool is considered. For 

example Prosser recreational pool is considered 

in the section “Floriston Rates.” When Prosser 

releases are needed to satisfy Floriston rates 

demands, and if reservoir levels are below the 

minimum recreational pool of 19,000 acre-ft, no 

releases will be made unless there are no alternative sources. (See also the section “Water-Quality 

Targets and Related Instream Flow Transfers.”)
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 107

• Boca Reservoir—In the subblock maintenance 

of recreational pools, exchanges for recreational 

pools are simulated. In the operations model, 

exchanges from Lake Tahoe or Prosser Creek 

Reservoir to Boca for the purpose of maintenance 

of recreational pools are in-lieu-of exchanges. In 

these exchanges, releases from Boca are 

decreased with the objective of maintaining water 

levels for a recreational pool. The volume that 

would have been released from Boca will instead 

be released from Lake Tahoe or Prosser Creek 

Reservoir. Under the following conditions, inlieu-of exchanges are simulated. 

1. Date is between May 1 and August 30 (recreational season), and 

2. It is a normal season, as defined in the 

section “Normal and Dry Season,” and 

3. Boca Reservoir storage must be no more than 

4,000 acre-ft above the recreational pool of 

33,500 acre-ft. If the Boca storage is greater 

than 37,500 acre-ft, then no exchanges 

for recreational pools will occur. This 

4,000 acre-ft provides a volume range above 

the recreational pool level, but below the 

flood-control criteria volume, where the recreational pool exchanges are likely to occur.

The first step in simulating in-lieu-of exchanges 

from Lake Tahoe or Prosser Creek Reservoir to Boca 

Reservoir is to determine how much, if any, additional 

release from Tahoe can be made using the categories 

pooled water and JPFCW. Similarly, it must be determined if additional releases from Prosser can be made 

using the categories TPEW and JPFCW. The previously determined releases and hydraulic capacity of the 

outlet are also considered. The second step is to determine the amount that Boca Reservoir may reduce its 

releases of the categories adverse-to-canal and nonadverse-to-canal water, JPFCW, fish credit water, 

WQCW, nonfirm PCMICW, PCPOSW, and fish 

water. The amount of reduction in releases of a given 

water category is based on the difference between the 

currently simulated release and the overall and category release floors (described in the section “Enhanced 

Minimum Instream Flows”). In addition to the consideration of release floors, the reduction of releases is 

based on the proportion of each water category released 

to the total release of water categories available for 

reduction. Finally, potential release increases from 

Prosser Creek Reservoir and Lake Tahoe are compared 

to potential Boca Reservoir release reductions using 

the exchange water categories listed above, if available, and the following list.

1. Prosser–Boca Exchange—The increased release 

of water categories from Prosser Creek Reservoir 

are exchanged with a reduced release of water 

categories from Boca Reservoir.

2. Tahoe–Boca Exchange—The increased release 

of water categories from Lake Tahoe are 

exchanged with a reduced release of water categories from Boca Reservoir.

Assumptions in this subblock for maintenance of 

recreational pools in Boca Reservoir include the following items.

• Although other categories and voluntary 

exchanges are possible for maintaining recreational pools, the operations model simulates 

only the listed exchanges with the stated categories. 

• Forecasting reservoir levels could provide a more 

realistic probability of maintaining recreational 

pools from May 1 to August 30. However, only 

current reservoir levels are used in the model to 

determine exchanges for maintenance of recreational pools. 

• An exchange for maintenance of recreational 

pools is not simulated if the receiving reservoir 

(Boca Reservoir) is above the prescribed threshold volume.

Merge Reservoir Releases for Multiple Objectives

Similar to existing operations as described under 

this title in the section “Description and Simulation of 

Current Operations,” water released from a given reservoir under draft TROA may serve a variety of objectives. Releases may consist of specified (tagged) water 

categories or untagged waters that consist of any water 

category. Typically, releases made to satisfy specific 

downstream demands are tagged to specific water categories. Untagged releases result from spills (including 

both uncontrolled spills over reservoir spillways and 

precautionary drawdowns based on flood-control criteria) or maintenance of minimum flows.
108 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

A draft TROA article entitled “Operations”

addresses the order of water categories for mandatory 

untagged releases based on flood-control criteria from 

Truckee River reservoirs (Bureau of Reclamation and 

others, 1998). Under these proposed operations, the 

order of water categories assigned to untagged releases 

may change depending on whether or not a drought 

situation exists (see subsequent section “Drought Situation”). The categories of water described in the

Operations article are pooled water (including adverseand non-adverse-to-canal water), Tahoe–Prosser

Exchange water, fish water, privately owned stored 

water (POSW), uncommitted water, fish credit water, 

Joint Program fish credit water (JPFCW), firm Power 

Company M&I credit water (firm PCMICW), nonfirm 

Power Company M&I credit water (nonfirm 

PCMICW), California M&I credit water (CMICW), 

water-quality credit water (WQCW), Fernley credit 

water, Newlands Project credit water, irrigation credit 

water, and other credit water. 

The operations model simulates merged reservoir 

releases for multiple objectives in the subblock merge. 

As discussed earlier in the current operations section, if 

tagged releases are greater than untagged releases from 

a reservoir, then the mandatory untagged releases are 

satisfied by the water categories already proposed for 

release. However, if the untagged releases are greater 

than the tagged releases, then the difference between 

the untagged and tagged releases must be computed, 

and it is this difference that represents that volume of 

the mandatory untagged releases that must be assigned 

to water categories. Table 9 lists the rank-order scheme 

of water categories assigned to untagged releases for 

proposed operations from each reservoir. Note that 

table 9 lists water categories used for both current and

proposed operations. The categories of water utilized 

for merged reservoir releases in the model are natural 

water, pooled water, fish water, PCPOSW, TCIDPOSW, uncommitted water, fish credit water, Joint 

Program fish credit water (JPFCW), firm PCMICW, 

nonfirm PCMICW, CMICW, and WQCW. The water 

categories Fernley credit water, Newlands Project 

credit water, irrigation credit water, and other credit 

water are not simulated by the operations model, as 

discussed in the section “Storage of Proposed Water 

Categories.”

Under draft TROA and WQSA, the presence of a 

drought situation may change the order of water categories assigned to untagged releases. Additionally, the 

rank-order scheme of water category assignments to 

untagged releases may change for different types of 

releases (flood-control and minimum flow) as illustrated in table 9. 

Unlike current operations, under draft TROA and 

WQSA, inflow water categories may force releases of 

other water categories in reservoir storage when mandatory untagged releases are required, such as a precautionary drawdown or uncontrolled spill. These forced 

releases, called displacements, depend on the rankorder scheme of a reservoir (table 9). Thus, inflow of a 

given water category will displace water categories of

lower rank. Typically, draft TROA credit water categories are of lower rank than the unregulated inflow categories: pooled water for Lake Tahoe and natural water 

for other reservoirs. Exceptions are firm PCMICW and 

Power Company emergency drought supply (PCEDS) 

in Stampede Reservoir, which cannot be displaced. 

Except for Lake Tahoe, where pooled water inflow to 

the lake remains as pooled water when stored, natural 

water inflows will convert to the assigned project

waters of a given reservoir once stored. Thus, mandatory untagged releases serve to displace many draft 

TROA credit water categories by the creation of project 

waters. Regulated inflows released from upstream reservoirs may also displace water categories of lower 

rank during mandatory untagged releases. Thus, during 

a drought situation, reservoir inflow of nonfirm 

PCMICW released from Stampede may displace fish 

credit water and JPFCW in Boca Reservoir (table 9).

The following assumptions were used in the 

model code development for simulating the merged 

releases for proposed operations from reservoirs.

• Although draft TROA article “Operations”

addresses the order of water categories assigned 

to such untagged releases as spills and displacements, a slightly different rank order of water categories for untagged releases is assumed for 

simulations. The order, shown in table 9, may be

modified by the model user.

• Natural water is simulated as the unregulated 

inflow category for all reservoirs except Lake 

Tahoe. For Tahoe, pooled water is simulated as 

the inflow category. For Stampede and Boca Reservoirs, in addition to inflows of natural water 

from unregulated subbasins and pass-throughs 

from upstream reservoirs, inflow categories consist of other water categories released from 

upstream reservoirs.
DESCRIPTION AND SIMULATION OF OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER 109

:

Reservoir Water Categories Assigne

Stampede Reservoir FOR FLOOD-CONTROL RELEA

1. Water-quality credit water2. California M&I credit waterIf no drought situation exists:

3. Nonfirm Power Compan4. Fish credit water and Joi5. Power Company POSW6. Non-adverse-to-canal po7. Natural water8. Fish water

If drought situation exists:

3. Fish credit water and Joi4. Power Company POSW5. Non-adverse-to-canal po6. Natural water7. Fish water8. Confirm Power Compan

FOR MINIMUM INSTREAM FL

1. Natural water2. Fish water

Boca Reservoir FOR FLOOD-CONTROL RELEA

1. Water-quality credit water2. California M&I credit waterIf no drought situation exists:

3. Nonfirm Power Compan

credit water

4. Joint Program fish credit 

If drought situation exists:

3. Fish credit water and Joi4. Nonfirm Power Compan

5. Fish water6. Power Company POSW if v

than 800 acre-feet

7. Natural water8. Adverse-to-canal pooled wa9. Non-adverse-to-canal poole

10. Power Company POSW if v

800 acre-feet

Lahontan Reservoir FOR FLOOD-CONTROL RELEA

1. Pooled water

:Table 9. Rank order of water categories assigned to untagged releases under 

Truckee 

River Operating Agreement and

Water 

Quality Se

Reservoir Water Categories Assigned to Untagged Release

Lake Tahoe FOR FLOOD-CONTROL RELEASE:

1. Water-quality credit water2. California M&I credit waterIf no drought situation exists:

3. Nonfirm Power Company M&I credit water 

and fish credit water

4. Joint Program fish credit water

If drought situation exists:

3. Fish credit water and Joint Program fish credit water4. Nonfirm Power Company M&I credit water

5. Pooled water

FOR MINIMUM INSTREAM FLOW RELEASE:

1. Pooled water (see section “Tahoe–Prosser Exchange”)

Donner Lake FOR FLOOD-CONTROL AND MINIMUM 

INSTR

E

AM F

L

O

W

R

ELE

ASES:

1. Natural water.2. Power Company POSW and TCID POSW.

Prosser Creek Reservoir

FOR FLOOD-CONTROL RELEASE:

1. Water-quality credit water2. California M&I credit waterIf no drought situation exists:

3. Nonfirm Power Company M&I credit water 

and fish credit water

4. Joint Program fish credit water

If drought situation exists:

3. Fish credit water and Joint Program fish credit water4. Nonfirm Power Company M&I credit water

5. Natural water6. Uncommitted water7. Tahoe–Prosser Exchange water

FOR MINIMUM INSTREAM FLOW RELEASE:

1. Natural water2. Uncommitted water

Independence Lake FOR FLOOD-CONTROL RELEASE AND MINIMUM 

INSTREAM FLOW RELEASES:

1. Natural water2. Power Company POSW
110 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

• All Martis Creek Lake releases are simulated in 

the subblock flood-control criteria, because this 

reservoir is operated for flood control. See the 

previous section “Flood Control-Criteria,” for a 

description of Martis Creek Lake operations. 

Storage in and releases from this reservoir consist 

only of natural water for simulations under proposed operations.

Losses and Gains to Reaches

Under draft TROA and WQSA operations, evaporation, precipitation, and inflows create losses or 

gains to reaches that modify accounts of water categories. Draft TROA provides guidelines for the adjustment of reservoir storage accounts of water categories 

from daily net evaporation. Daily net evaporation is 

calculated as the evaporation rate minus the precipitation applied to the surface area of a reservoir for a given 

day. When precipitation and inflows exceed evaporation, usually from November or December through 

May or June, reservoir storage will increase, and that 

increase is considered as a positive reservoir inflow of 

pooled water for Lake Tahoe or natural water for the 

other lakes and reservoirs. When evaporation exceeds 

precipitation and inflows, reservoir storage will 

decrease, and that decrease is considered as a loss 

assigned to water categories based on a rank-order 

scheme described as follows.

Lake Tahoe

Part of the net evaporation will be assigned to 

water categories in storage other than pooled 

water. That part of net evaporation will be determined by applying to the net evaporation a proportion relating the increase in lake surface area 

attributed to the volume of only these categories 

to the total lake surface area. The remaining part 

of net evaporation is assigned to pooled water.

Donner Lake

Net evaporation will be allocated first to daily 

Donner Lake inflow, and then to categories in 

storage other than Power Company POSW 

(PCPOSW) and (TCIDPOSW). The net evaporation will be determined by applying to the 

remaining net evaporation a proportion relating 

the increase in lake surface area attributed to the 

volume of these categories to the total lake surface area. The remaining part of net evaporation 

is assigned to PCPOSW and TCIDPOSW waters.

Martis Creek Lake

Net evaporation will be allocated to all water categories in storage in proportion to the volumes of 

the water categories.

Prosser Creek Reservoir

Net evaporation will be first allocated to all water 

categories in storage except Tahoe–Prosser 

Exchange water and dead and inactive storage in 

proportion to the volumes of the water categories. 

Then the remaining part of net evaporation will 

be assigned first to Tahoe–Prosser Exchange 

water (TPEW) and second to dead and inactive 

storage.

Independence Lake

Net evaporation will be allocated first to daily 

Independence Lake inflow and then to categories 

in storage other than PCPOSW. The net evaporation will be determined by applying to the 

remaining net evaporation a proportion relating 

the increase in lake surface area attributed to the 

volume of these categories to the total lake surface area. The remaining part of net evaporation 

is assigned to PCPOSW water.

Stampede Reservoir

Net evaporation will be allocated first to all water 

categories in storage except Power Company 

emergency drought supply (PCEDS), firm 

PCMICW, TPEW, and dead and inactive storage 

in proportion to the volumes of the water categories, and then to the following categories by priority order: firm PCMICW, PCEDS, TPEW, and 

last to dead and inactive storage.

Boca Reservoir

Net evaporation will be allocated to all water categories in storage in proportion to their volumes.

Draft TROA also provides guidelines for the 

adjustment of storage accounts of water categories of 

river reaches. Flow in the Truckee River and its tributaries may increase or decrease as water moves through 

river reaches downstream. All increases in flow will be 

allocated to natural water. Decreases are called conveyance losses and will be proportionately allocated to the 

flow of all water categories except privately owned 

stored water

The following discussion describes the simulation of evaporation, precipitation, and inflow losses 

and gains from reservoir and river reaches in the USGS 
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 111

Truckee River Basin operations model: first, the methods to simulate gains and losses and then the selection 

of water-category accounts for gains and losses.

Depending on the external time series input for 

reservoir and river reaches, either net inflow or separate evaporation and precipitation fluxes may be simulated (see previous section, “Data for Simulation of 

Streamflow and Operations”). As described under this 

title in the section “Description and Simulation of Current Operations,” evaporation and precipitation fluxes 

or net inflow to and from reservoir and river reaches is 

simulated in the RCHRES block. 

For Truckee River reservoirs (except Lake 

Tahoe), for Pyramid Lake, and for river reaches downstream from Vista, external time series of evaporation 

and precipitation depths are input to the simulation 

model. For Lake Tahoe and river reaches upstream 

from Vista, external time series of net inflows are input 

to the simulation model. Although net evaporation may 

not be simulated for reservoir reaches as described in 

draft TROA, the simulation of net inflows or separate 

evaporation and precipitation fluxes results in the same 

objective as simulation of net evaporation: determination of net gains or losses to the given reservoir reach. 

For Lahontan Reservoir, losses are simulated as 

described in the previous section “Truckee River 

Diversions to Newlands Project.” For a more detailed 

discussion of the methods used to construct the external 

time series, see the previous sections “Data for Simulation of Streamflow” and “Operations and Losses and 

Gains to Reaches” under “Current Operations.”

Storage accounts of water categories must be 

adjusted for changes in storage resulting from losses 

and gains to reaches. As for simulation of current operations, inflow under draft TROA, including unregulated tributary inflow and precipitation, is assigned to 

pooled water for Lake Tahoe and to natural water for 

the other lakes and reservoirs. For river reaches, 

inflow, including unregulated tributary inflow and precipitation, is assigned to natural water from Lake Tahoe 

to the Farad gaging station (reaches 100 through 240). 

Downstream from the Farad gaging station (reaches 

250 through 580), all inflows from tributaries and precipitation are assigned to pooled water. 

Conveyance losses from river reaches are simulated using evaporation and ET from phreatophytes. 

Downstream from the Vista gaging station, these losses 

are assigned to pooled water (Berris, 1996), and 

upstream from the Vista gaging station, they are 

implicit in the methods used to determine net inflows 

from tributaries. Because the net inflows to reaches 

from Lake Tahoe to the Farad gaging station are positive, losses between Tahoe and Farad are not assigned 

to water categories. Losses between Farad and Vista 

are assigned first to pooled water, second to fish water, 

and last to WQCW.

Simulated reservoir losses from evaporation or 

negative net inflows are assigned to categories by rank 

order. If more than one category shares the same priority, then losses are assigned to those categories in proportion to their volumes. The following are the water 

category assignments to reservoir losses from evaporation or negative net inflows in the operations model.

Lake Tahoe

Net losses will be allocated to pooled water.

Donner Lake

Evaporation will be allocated first to Donner 

Lake inflows. The remaining part of evaporation 

will then be assigned equally to PCPOSW and 

TCIDPOSW.

Martis Creek Lake

All evaporation will be assigned to natural water.

Prosser Creek Reservoir

Evaporation is allocated first to all water 

categories in storage except Tahoe–Prosser 

Exchange water (TPEW) in proportion to the 

volumes of the water categories. After applying 

evaporation to the water categories as described 

above, the remaining part of evaporation is 

allocated to TPEW.

Independence Lake

Evaporation is allocated first to Independence 

Lake inflows. The remaining part of evaporation 

is allocated to PCPOSW.

Stampede Reservoir

Evaporation is allocated first to all water categories in storage except firm PCMICW and PCEDS 

in proportion to their volumes. The remaining 

part of evaporation is allocated first to firm 

PCMICW and second to PCEDS water.

Boca Reservoir

Evaporation will be allocated to all water categories in storage in proportion to their volumes.

Pyramid Lake

Evaporation will be allocated to pooled water.
112 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

Several assumptions were made in developing the 

code simulating losses and gains from evaporation and 

precipitation. Some of the more notable assumptions 

follow.

• Water categories other than natural water, 

PCPOSW, and TCIDPOSW are not assigned to 

evaporation for Donner Lake simulations. Water 

categories other than natural water and PCPOSW 

are not assigned to evaporation for Independence 

Lake simulation.

• Net losses for Lake Tahoe are not applied to the 

increased surface area attributed to the volumes 

of specified categories other than pooled water. 

For the lake, net losses will be applied only to 

pooled water. This assumption is not expected to 

create largely different results because increased 

surface areas attributed to the draft TROA categories typically will be small compared to the surface areas related to the volume of pooled water.

• Evaporation is assigned only to natural water for 

Martis Creek Lake simulation.

• For Prosser Creek and Stampede Reservoirs, volumes of dead and inactive storage are not simulated as water categories. Instead, evaporation is 

assigned to other categories in the order specified 

above.

• In the simulation model, Stampede Reservoir will 

not contain Tahoe–Prosser Exchange water. 

Therefore, evaporation is not assigned to Tahoe–

Prosser Exchange water.

Forecasts Affecting Operational Decisions

This section describes three runoff and reservoir 

storage forecasts used to guide the simulation of operations. Under draft TROA, two of the forecasts are a 

determination of (1) a normal or dry season, and (2) a 

drought situation, and the third is the “runoff index”. 

Although not specified in the draft TROA, the runoff 

index is used in the operations model for several logical 

decisions that require judgement or a need for qualitatively categorizing an upcoming runoff season.

Normal and Dry Season

In article nine of the draft TROA, Beneficial Uses of 

Water in California for Instream Flows and Recreation, (Bureau of Reclamation and others, 1998), proposed criteria are specified for the release of water 

from reservoirs to maintain instream flows for fish and 

biological resources. Instream flows and enhanced 

minimum instream flows for reservoirs are specified 

on the basis of whether the season is normal or dry, as 

determined by certain reservoir releases, storage and 

forecasted runoff. In general, the determination of normal or dry season depends upon the amount of pooled 

water stored in Lake Tahoe and the current forecast of 

Truckee River Basin natural flow in the Truckee River 

at the California–Nevada State line. The determination 

of a normal or dry season is made on each day from 

February through June using graphs from draft TROA 

shown in figures 5 and 6. A separate determination is

specified for days in July through January. Separate 

designations will be made for the Lake Tahoe Basin 

and for the Truckee River Basin.

The USGS Truckee River Basin operations 

model simulates determination of normal or dry season 

in the subblock initial numerical assignments and 

computations as follows. 

• For the months of February through June, the simulated current Lake Tahoe pooled water volume 

and the current NRCS forecast of April-July 

Truckee River Basin runoff at Farad are used to 

determine a normal or dry season on the basis of 

the graphs on figures 5 and 6, which are taken 

from the draft TROA.

• For the month of October, the designation is the 

same as that computed for September except if 

pooled water stored in Lake Tahoe is less than 

specified volumes. For Lake Tahoe, the season 

will be designated as a dry season if the volume 

of pooled water stored in Lake Tahoe is less than 

150,000 acre-ft. For Donner Lake, Prosser Creek 

Reservoir, Independence Reservoir, Stampede 

Reservoir, and Boca Reservoir, the season will be 

designated as a dry season if the volume of pooled 

water stored in Lake Tahoe is less than 50,000 

acre-ft.

• For the months of July through September, the 

designation is the same as that computed for June. 

For the months of November through January, the 

designation is the same as that computed for 

October.

The following assumption was used in the model 

code development for determination of normal and dry 

season.
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 113

Figure 5. Determination of normal or dry seasons for Lake Tahoe, February–June

10050

100

150

200

250

300

350

150 200 250 300 350 400 450

LAKE TAHOE POOLED WATER STORAGE, IN THOUSANDS OF ACRE-FEET

NATURAL RESOURCES CONSERVATION SERVICE

APRIL-TO-JULY RUNOFF FORECAST FOR TRUCKEE

RIVER AT FARAD, CALIFORNIA (10346000), IN

THOUSANDS OF ACRE-FEET

NATURAL RESOURCES CONSERVATION SERVICE

APRIL-TO-JULY RUNOFF FORECAST FOR TRUCKEE

RIVER AT FARAD, CALIFORNIA (10346000), IN

THOUSANDS OF ACRE-FEET

10050

100

150

200

250

300

350

150 200 250 300 350 400 450

LAKE TAHOE POOLED WATER STORAGE, IN THOUSANDS OF ACRE-FEET

Storage = 60,000 acre-feet

Storage = 425,000 acre-feet

Storage = 389,000 acre-feet

Storage = 430,000 acre-feet

Forecast = 300,000 acre-feet

Forecast = 180,000 acre-feet

Forecast = 140,000 acre-feet

Storage = 55,000 acre-feet

Forecast = 200,000 acre-feet

Storage = 80,000 acre-feet

Storage = 419,000 acre-feet

Storage = 378,000 acre-feet

Storage = 419,000 acre-feet

Forecast = 300,000 acre-feet

Forecast = 180,000 acre-feet

Forecast = 140,000 acre-feet

Storage = 60,000 acre-feet

Forecast = 200,000 acre-feet

Normal season

No change from season

determination made

previous day

Dry season

Normal season

No change from season

determination made

previous day

Dry season

FEBRUARY

MARCH
114 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

10050

100

150

200

250

300

350

150 200 250 300 350 400 450

LAKE TAHOE POOLED WATER STORAGE, IN THOUSANDS OF ACRE FEET

NATURAL RESOURCES CONSERVATION SERVICE

APRIL-TO-JULY RUNOFF FORECAST FOR TRUCKEE

RIVER AT FARAD, CALIFORNIA (10346000), IN

THOUSANDS OF ACRE-FEET

NATURAL RESOURCES CONSERVATION SERVICE

APRIL-TO-JULY RUNOFF FORECAST FOR TRUCKEE

RIVER AT FARAD, CALIFORNIA (10346000), IN

THOUSANDS OF ACRE-FEET

10050

100

150

200

250

300

350

150 200 250 300 350 400 450

LAKE TAHOE POOLED WATER STORAGE, IN THOUSANDS OF ACRE FEET

Storage = 110,000 acre-feet

Storage = 390,000 acre-feet

Storage = 360,000 acre-feet

Storage = 390,000 acre-feet

Forecast = 300,000 acre-feet

Forecast = 180,000 acre-feet

Forecast = 140,000 acre-feet

Storage = 80,000 acre-feet Forecast = 200,000 acre-feet

Storage = 160,000 acre-feet

Storage = 355,000 acre-feet

Storage = 328,000 acre-feet

Storage = 355,000 acre-feet

Forecast = 300,000 acre-feet

Forecast = 180,000 acre-feet

Forecast = 140,000 acre-feet

Storage = 110,000 acre-feet

Forecast = 200,000 acre-feet

Normal season

No change from season

determination made

previous day

Dry season

Normal season

No change from season

determination made

previous day

Dry season

APRIL

MAY

Figure 5. Determination of normal or dry seasons for Lake Tahoe, February–June—Continued
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 115

10050

100

150

200

250

300

350

150 200 250 300 350 400 450

LAKE TAHOE POOLED WATER STORAGE, IN THOUSANDS OF ACRE FEET

NATURAL RESOURCES CONSERVATION SERVICE

APRIL-TO-JULY RUNOFF FORECAST FOR TRUCKEE

RIVER AT FARAD, CALIFORNIA (10346000), IN

THOUSANDS OF ACRE-FEET

Storage = 165,000 acre-feet

Storage = 293,000 acre-feet

Storage = 273,000 acre-feet

Storage = 293,000 acre-feet

Forecast = 300,000 acre-feet

Forecast = 180,000 acre-feet

Forecast = 140,000 acre-feet

Storage = 155,000

acre-feet

Forecast = 200,000 acre-feet

Normal season

No change from season

determination made

previous day

Dry season

JUNE

Figure 5. Determination of normal or dry seasons for Lake Tahoe, February–June—Continued

• If the designation computed in the subblock falls 

in between the dry and normal year, (shown as 

“NO CHANGE” in figures 5 and 6), then no 

change in the normal or dry year designation will 

be computed.

Drought Situations

As used in the context of draft TROA, the term 

drought situation means a year in which it seems 

likely that there either will not be sufficient natural 

flow and pooled water in storage in Truckee River reservoirs to meet Floriston rates through October 31, or 

the projected level of Lake Tahoe pooled water on or 

before the following November 15 will be below 

6,223.5 ft, Lake Tahoe datum. This determination is 

based on the April 1 seasonal Truckee River runoff 

forecast assuming median precipitation after April 1. 

The occurrence of a drought situation affects other 

operations in the model, such as these.

1. The allocation of fish credit water and Power 

Company nonfirm M&I credit water spilled from 

Stampede Reservoir. In a drought situation, fish 

credit water is spilled before PCMICW. In nondrought situation years, PCMICW spills before 

fish credit water (see the section “Merge Reservoir Releases for Multiple Objectives,” under 

“Proposed Reservoir Operations”).

2. The transfer (conversion) of excess nonfirm 

M&I credit water to fish credit water. This conversion takes place in any year that is not projected to be in a drought situation (see the section 

“Other Exchanges and Transfers,” under “Proposed Reservoir Operations”).

3. The priority for storage and accumulation of 

Power Company M&I credit water and fish 

credit water (see the sections (1) “Other 

Exchanges and Transfers,” and (2) “Power 

Company M&I Credit Water, Fish Credit Water, 

Water-Quality Credit Water, and Joint Program 

Fish Credit Water,” under “Proposed Reservoir 

Operations”). 
116 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

200 250150

100

150

200

250

300

350

400 450 500300 350

LAKE TAHOE POOLED WATER STORAGE, IN THOUSANDS OF ACRE FEET

NATURAL RESOURCES CONSERVATION SERVICE

APRIL-TO-JULY RUNOFF FORECAST FOR TRUCKEE

RIVER AT FARAD, CALIFORNIA (10346000), IN

THOUSANDS OF ACRE-FEET

200 250150

100

150

200

250

300

350

400 450 500300 350

LAKE TAHOE POOLED WATER STORAGE, IN THOUSANDS OF ACRE FEET

NATURAL RESOURCES CONSERVATION SERVICE

APRIL-TO-JULY RUNOFF FORECAST FOR TRUCKEE

RIVER AT FARAD, CALIFORNIA (10346000), IN

THOUSANDS OF ACRE-FEET

Storage = 425,000 acre-feet

Storage = 390,000 acre-feet

Forecast = 300,000 acre-feet

Forecast = 180,000 acre-feet

Forecast = 140,000

acre-feet

Forecast = 200,000

acre-feet

FEBRUARY

MARCH

Storage = 419,000 acre-feet

Storage = 378,000 acre-feet

Forecast = 300,000 acre-feet

Forecast = 180,000 acre-feet

Forecast = 140,000

acre-feet

Forecast = 200,000

acre-feet

Normal season

No change from season

determination made

previous day

Dry season

Normal season

No change from season

determination made

previous day

Dry season

Figure 6. Determination of normal or dry seasons for Donner Lake, Prosser Creek Reservoir, Independence Lake, 

Stampede Reservoir, and Boca Reservoir, February–June
OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER QUALITY SETTLEMENT AGREEMENT 117

Figure 6. Determination of normal or dry seasons for Donner Lake, Prosser Creek Reservoir, Independence Lake, 

Stampede Reservoir, and Boca Reservoir, February–June—Continued

200 250150

100

150

200

250

300

350

400 450 500300 350

LAKE TAHOE POOLED WATER STORAGE, IN THOUSANDS OF ACRE FEET

NATURAL RESOURCES CONSERVATION SERVICE

APRIL-TO-JULY RUNOFF FORECAST FOR TRUCKEE

RIVER AT FARAD, CALIFORNIA (10346000), IN

THOUSANDS OF ACRE-FEET

200 250150

100

150

200

250

300

350

400 450 500300 350

LAKE TAHOE POOLED WATER STORAGE, IN THOUSANDS OF ACRE FEET

NATURAL RESOURCES CONSERVATION SERVICE

APRIL-TO-JULY RUNOFF FORECAST FOR TRUCKEE

RIVER AT FARAD, CALIFORNIA (10346000), IN

THOUSANDS OF ACRE-FEET

Storage = 390,000 acre-feet

Storage = 360,000 acre-feet

Forecast = 300,000 acre-feet

Forecast = 180,000 acre-feet

Forecast = 140,000 acre-feet

Forecast = 200,000

acre-feet

Storage = 355,000 acre-feet

Storage = 328,000 acre-feet

Forecast = 300,000 acre-feet

Forecast = 180,000 acre-feet

Forecast = 140,000 acre-feet

Forecast = 200,000 acre-feet

Normal season

No change from season

determination made

previous day

Dry season

Normal season

No change from season

determination made

previous day

Dry season

APRIL

MAY
118 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

Figure 6. Determination of normal or dry seasons for Donner Lake, Prosser Creek Reservoir, Independence Lake, 

Stampede Reservoir, and Boca Reservoir, February–June—Continued

200 250150

100

150

200

250

300

350

400 450 500300 350

LAKE TAHOE POOLED WATER STORAGE, IN THOUSANDS OF ACRE FEET

NATURAL RESOURCES CONSERVATION SERVICE

APRIL-TO-JULY RUNOFF FORCAST FOR TRUCKEE

RIVER AT FARAD, CALIFORNIA (10346000), IN

THOUSANDS OF ACRE-FEET

Storage = 293,000 acre-feet

Storage = 273,000 acre-feet

Forecast = 300,000 acre-feet

Forecast = 180,000 acre-feet

Forecast = 140,000 acre-feet

Forecast = 200,000 acre-feet

Normal season

No change from season

determination made

previous day

Dry season

JUNE

The operations model simulates the determination of a drought situation as follows. In general, the 

subblock initial assignments and computations determines a drought situation once each year on April 1st 

using forecasts of monthly runoff volumes for the next 

8 months (April through November) at major streams 

within the Lake Tahoe and Truckee River Basins. 

Using these monthly forecasts at various locations, the 

model simulates selected major operations using 1-

month computation intervals for the period April 

through November. At the end of each month’s operational computations, the model determines if a shortfall 

in Floriston rates has occurred or if Tahoe’s pooled 

water elevation has fallen below 6,223.5 ft. This simplified operational forecast code within the model 

seeks only to satisfy the first few storage or demand 

priorities for water:

1. Fill Donner Lake.

2. First 3,000 acre-ft of storage in Independence 

Lake.

3. Floriston rates (demand).

4. Lake Tahoe storage.

5. First 25,000 acre-ft of Boca adverse-to-canal 

storage rights.

In the initial assignments and computations subblock, the storages and category amounts used by the 

drought situation code are the simulated amounts from 

the main HSPF model as of March 31st each year. The 

user must indicate, with a user option flag, whether the 

runoff forecasted time series to be used are net inflows 

to reservoirs (include the effects of evaporation and 

precipitation) or inflows only. If the forecasted time 

series for input to the reservoir are inflows only, they 

will be adjusted for precipitation and evaporation. 

The following is an overview of the subblock 

simplified forecast procedure to determine drought 

situation, which computes (April 1 of every simulation 

year) whether or not a drought situation exists. This 

“condensed” version of operations described below is 

unique to this subblock and in no way reflects the complex interactions simulated in the other subblocks.
DESCRIPTION AND SIMULATION OF OPERATIONS UNDER DRAFT TRUCKEE RIVER OPERATING AGREEMENT AND WATER

1. Using forecasted runoff volumes for the month of 

April, the model checks whether the storage 

rights of Donner and Independence Lakes listed 

above have been satisfied.

2. Next, the model determines if Floriston rates can 

be met by sidewater and pass-through water 

from reservoirs. If not, pooled water (including 

Tahoe–Prosser Exchange water existing on April 

1st in Prosser Creek Reservoir) is released from 

the reservoirs in the order specified by the Truckee River Agreement (see discussion in the section “Floriston Rates”). If, on the other hand, 

Floriston rates can be satisfied, then storage of the 

first 25,000 acre-ft of water in Boca Reservoir is 

allowed to begin. 

3. At the end of the April calculations, if the water 

surface corresponding to pooled water in Lake 

Tahoe fell below 6,223.5 ft or if Floriston rates 

were not met, then a computed flag is switched 

from 0 (no drought situation) to 1 (drought situation exists). If the drought situation flag is set to 1 

at any time during the calculations, the remainder 

of the monthly steps in this computation are 

skipped and operations in the other model subblocks will consider the period to be in a drought 

situation. If no drought situation is indicated after 

the April computations, the subblock computations proceed to simulate operations for the 

month of May using expected (forecasted) runoff 

volumes for that month. 

4. The procedure is repeated using the forecasted 

runoff for each remaining month, May through 

November, and the end result of this subblock of 

code is a drought situation flag setting on April 1 

of either 0 or 1. This flag value is used in the daily 

computations of other subblocks until the following April 1, when a new flag value is computed 

once again.

Several assumptions were made in developing the 

code to determine the existence of a drought situation 

in the context of draft TROA. Some of the more notable 

assumptions follow.

• Because the purpose of this part of the code is to 

simulate Lake Tahoe water-surface elevation and 

the system’s ability to maintain Floriston rates 

with pooled water, sidewater, and pass-through 

water, it was not necessary to simulate any storage with a lower priority than Donner Lake and 

Independence Lakes (first 3,000 acre-ft), Lake 

Tahoe, and Boca Reservoir (first 25,000 acre-ft).

• No accumulation of storage attributable to the 

current year is assumed to have taken place in 

Independence Lake prior to April 1st of that year. 

Donner Lake’s winter operations leave the outflow gates open, so no accumulation of storage 

before April 1 also can be assumed.

• Only the first 25,000 acre-ft (adverse-to-canal) 

storage rights are simulated in Boca Reservoir. 

The non-adverse-to-canal water (next 15,000 

acre-ft) has a later storage priority than Truckee 

Canal diversions, and, for purposes of simplification, Truckee Canal operations were not simulated in this subblock.

• In this single-purpose subblock, developed 

only for forecasting, the only Tahoe–Prosser 

Exchange water in Prosser Creek Reservoir available for supporting Floriston rates is the simulated volume on April 1st. The Tahoe–Prosser 

Exchange is not simulated in this subblock of 

code. Because minimum flows from Tahoe are 

not simulated in this subblock, any water drafted 

from Tahoe is used for Floriston rates. So, instead 

of forecasting the release of minimum flows from 

Tahoe and exchanging pooled water into Prosser 

Creek Reservoir via the Tahoe–Prosser 

Exchange, this subblock just keeps that water in 

Tahoe. This will not affect the forecast on 

whether Floriston rates will be met, but could 

make the forecast level of Lake Tahoe greater 

than it should be by as much as a tenth of a foot.

• If the pooled water elevation in Lake Tahoe ever 

exceeds 6,227.5 ft, as computed within this subblock, it is assumed that enough water exists to 

satisfy Floriston rates for the remainder of the 

year without the elevation falling below 6,223.5 ft 

and the remainder of the drought situation subblock calculations are simply skipped and the 

drought situation flag is set to 0, indicating a 

nondrought situation for use in other operational 

subblocks.

Runoff Index

In the management of the Truckee River Basin 

reservoirs and rivers, many operational decisions are 

based on expected runoff volumes, which in turn are 

based on snowpack conditions and historic USGS 
120 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

streamflow records. A runoff index is computed in the 

USGS Truckee River Basin operations model, and is 

used as a component of hydrologic judgement needed 

to make certain operational decisions. These operations 

include springtime reservoir filling for Donner and 

Independence Lakes, establishing beginning date of 

irrigation season, and determining ground-water use in 

the Truckee Meadows as described in their respective 

sections. Based on the historic NRCS forecasted flow 

data (1922–97) for the Truckee River near Farad

streamflow station, the forecasted flows are split into 

three runoff groupings—wet, average, or dry years. 

Runoff groupings are defined using forecasted flow 

data and long-term mean runoff at Farad from historic 

USGS streamflow records. If the forecast is greater 

than the long term mean runoff plus one-half the standard deviation, the year is considered wet. If the forecast is less than the mean minus one-half the standard 

deviation, the year is considered dry. Otherwise, the 

year is considered average. This qualitative runoff 

index is used in both current and proposed reservoir 

operations.

COMPARISON OF SIMULATED AND 

OBSERVED OPERATIONS

The Truckee River Basin operations model was 

developed to provide water managers with a tool capable of simulating both hydrologic processes and 

river/reservoir operations using a daily, rather than 

monthly, computation interval. A daily model is 

needed to examine policies that can be affected by the 

dynamic nature of streamflow and river/reservoir operations that exist in the day-to-day management of water 

resources in the Truckee River Basin. Because the 

model is flexible, comprehensive, and documented, 

all interested parties can apply a common model to 

examine individual interests, allowing negotiations or 

the investigation of alternative management policies to 

proceed with the confidence that all parties can reproduce and verify the results. The model documented in 

this report is not intended for use in simulating historical streamflow. It was specifically designed to facilitate 

relative comparisons of the effects of alternative management practices or allocations on flows and storages 

within the system. Relative comparisons allow management to base decisions on whether a situation will 

improve or worsen under a proposed operating scenario. Exact water volumes attributable to changes 

in operations cannot be simulated, and results should 

not be considered to be anything other than reasonable 

estimates.

Traditional model development usually entails 

calibration and verification tasks to demonstrate the 

reliability of the model. Because observed streamflows 

are not meant to be reproduced by this model, a classic 

calibration comparing observed and simulated volumes 

or streamflows is problematic with this model and its 

current databases. However, the physically based flowrouting processes embedded in the operations model 

were evaluated in a previous report by Berris (1997). 

Currently (1998), TROA has not yet been signed 

and implemented and, therefore, no observed data

resulting from the proposed operations exist that could 

be used for comparison. Testing the simulation of current operations by the model also is difficult for a number of reasons explained in the paragraphs below. 

First, the complexity of actual historical and current river and reservoir operations in the Truckee River 

Basin has been compounded by unique, one-time 

agreements that deviated from “normal” operations. 

The operations model does not simulate any of these 

one-time agreements. Dated operations could have 

been coded to account for known deviations, but, 

because the reasoning behind these actions was 

not always documented and it was not known if 

such actions would ever be taken again, simulation 

of such one-time operations were not programmed 

into the model.

Second, there have been many times when 

nonroutine, minor operations have been executed in 

the Truckee River Basin. Although these operations 

were allowable, they were not documented in specific 

legal decrees or agreements. The USGS Truckee River 

Basin operations model does not simulate such nonroutine operations. 

Third, there is considerable flexibility in how the 

reservoirs can be managed to meet the objectives of 

major decrees and agreements. This human element of 

judgement allows basin managers to implement 

required operations differently every year and not 

exactly according to rules or stipulations explicitly 

documented in any one decree or agreement. The interactions between the reservoirs are very complex and 

are often undocumented and inconsistent. The operations model attempts to simulate these interactions with 

a simplified logic using the same method from year to 

year, but the logic cannot simulate all possible interac-
COMPARISON OF SIMULATED AND OBSERVED OPERATIONS 121

tions and variable human judgement. Thus, the course 

of action simulated by the operations model will be the 

same each year under equal conditions. 

Finally, there may be differences between the 

input data used in model simulations and the available 

data that guided the historic operations. For example, 

except for Lake Tahoe, reservoir inflows used in testing the operations model were taken from PRMS simulations (Jeton, 2000). Additionally, the use of PRMS 

models allows for the determination of inflow forecasts 

required by the operations model. Observed reservoir 

inflows for 1933–97 were not available due to limited 

data sets and varying dates of Truckee River reservoir 

construction. Forecasts of streamflow volume is 

another example of input data that may be different 

from that used historically by system managers.

The above factors affecting model input data and 

actual reservoir operations make side-by-side comparisons of observed and simulated data difficult, if not 

impossible, to reconcile. In view of these constraints, 

only limited testing of the USGS Truckee River Basin 

operations model by comparison with historical data 

can be accomplished. Simulations of Truckee River 

streamflow were made by applying historical and

synthesized channel and reservoir inflow time series 

to conditional logic in the HSPF SPECL block. The 

synthesized inflow time series determined from PRMS 

simulations were used when observed data were not 

available. Simulations for the water years 1989–97 

and 1933–97 were made for the Truckee River Basin. 

Because TROA has not yet been implemented, only 

current operations were simulated for comparison with 

observed streamflows in this test. 

The period 1989–97 was chosen to test the simulation of reservoir and river operations because it is the 

most representative of the current operating strategy 

that was coded in the model, all storage reservoirs were 

present, operations were relatively consistent over this 

period, and better documentation of all operations in 

the basin was available beginning at about that time. 

Because Truckee Canal diversions dictated by the 1988 

OCAP played a major role in determining river operations, that year was chosen to begin simulations. 

The period 1933–97 was chosen to test the 

simulation of streamflow volumes by evaluating the 

overall difference between observed and simulated 

streamflows over a long period. Although not all 

storage reservoirs and current operations were in place 

for this entire period, it is assumed that over a long 

period of time that encompasses several decades, the 

seasonal and annual effects of reservoir operations 

will be small compared to the longer term patterns 

of streamflow volumes.

There are many possible geographic locations and 

hydrologic characteristics (such as reservoir storage 

volume, flow duration, and so forth) for which comparisons could be made. Streamflow in the main channel 

is an easily measured and comparable response that 

integrates the many complex and interrelated operations in the basin. Because river and reservoir operations are reflected in downstream flows, and to simplify 

what could be lengthy and detailed comparisons, 

graphical comparisons of observed and simulated 

streamflow at three sites along the Truckee River are 

provided for the 1989–97 comparisons: Truckee River 

at Farad, Calif., Truckee River at Vista, Nev., and 

Truckee River near Nixon, Nev. (figs. 7–9). 

To simplify the graphs and facilitate visual comparison of simulated to observed flows, model outputs 

of daily mean flows were condensed to monthly means 

for these illustrations. A simple quantitative comparison of observed and simulated streamflow volumes for 

the 1933–97 period at the Farad gage, is discussed 

below to evaluate long-term differences between historical and simulated streamflow volumes rather than 

to evaluate differences between historical and simulated reservoir and river operations.

As can be seen from figures 7–9, the simulations

with the operations model reflect quite well the general 

timing and magnitude of observed monthly flows. 

For example, in January 1997, which contained high 

flows, model simulations adequately represent 

observed flows. Also, during the drought years of 

1990–91, model simulations characterized the low 

flows of the period.

Figures 7–9 show simulated monthly mean flows

at Farad, Vista, and Nixon during the spring of 1989 to 

be higher than actually observed. This probably is due 

to some combination of one-time operations and higher 

simulated storage levels in Lahontan Reservoir. Several one-time operations occurred from 1988–90 (Jeff 

Boyer, U.S. District Court Water Master, oral communication, 1998). For example, a special permit to store 

water in Prosser Creek Reservoir for fish and wildlife 

concerns was issued in March 1989. The water was 

kept in storage for the next year and flood-control 

releases from Prosser Creek Reservoir were not made 

during the normal precautionary drawdown period. 

Additionally, work on the release gates at Lake 

Tahoe’s outlet required some one-time operational 
122 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

decisions to protect water rights in Nevada. These onetime operations may have changed water categories in 

the river, resulting in slightly modified river operations 

in the Truckee Meadows and even greater differences 

related to OCAP diversions to the Truckee Canal at 

Derby Dam. These complex interactions were not simulated by the operations model. Finally, simulated storage levels in Lahontan Reservoir were higher than 

observed. As a result, less water was simulated for 

diversion to the Newlands Project via the Truckee 

Canal, allowing extra water to flow to Pyramid Lake. 

The simulated monthly mean flows at Farad, 

Vista, and Nixon during the spring of 1994 also are 

lower than observed. This probably is due to a one-time 

operation that provided spawning flows for cui-ui 

during the spring of the drought year of 1994. The 1994 

runoff season was considered the last year of the 

drought, which lasted from 1987 to 1994. Under “normal” operation, a fish run generally will not occur in 

dry years. However, a fish run (flow regime 1) was not 

simulated by the operations model because the simulated total fish water in storage in Truckee River Basin 

reservoirs and the forecasted inflows were lower than 

the conditional logic allows as necessary for a fish run. 

This one-time operation of a fish run was not simulated 

by the operations model. Lastly, for the winter of 1996, 

flows were overestimated in February and underestimated in the spring of 1996. This is due to simulated 

reservoir releases earlier than in actual operations.

A simple quantitative comparison of observed 

and simulated streamflow volumes for the period 

1933–97 at the Farad gaging station describes longterm differences for evaluation of simulated streamflow volumes. Percent bias of simulated versus 

observed streamflows is used as the statistical measure 

for the evaluation. For this 65-year period, long-term 

average streamflows, rather than mean monthly or 

daily, were used to reduce the effects of daily operaFigure 7. Observed and simulated monthly mean streamflows for the period October 1, 1988, 

through September 30, 1997, for Truckee River at Farad, Calif. (station 10346000)

Observed

Simulated

0

800

1,600

2,400

3,200

4,000

4,800

5,600

6,400

7,200

8,000

MONTHLY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

1989 1990 1991 1992 1993 1994 1995 1996 1997

CALENDAR YEAR
COMPARISON OF SIMULATED AND OBSERVED OPERATIONS 123

tions variations and other short-term variations while 

reflecting longer-term patterns of streamflow volumes. 

For the period 1933–97, the percent bias of simulated 

mean annual streamflow was -13 percent at the Farad 

gaging station. 

The period 1933–97 was split into two separate 

periods, 1933–80 and 1981–97, to further evaluate 

differences in observed and simulated streamflow 

volumes. The two periods allow for streamflow comparisons between modern and historical periods of 

different inflow data provided as input to the operations 

model and different reservoir configurations upstream 

from Farad. Operational variables, such as different 

effective dates of decrees and agreements, flexible 

adherence to decrees and agreements, and other 

unknown or minor operational variables may also 

influence simulation results, but they are difficult to 

identify and their influence on simulation results is difficult to specify.

For the periods 1933–80 and 1981–97, percent 

biases at the Farad gaging station were -18 percent 

and -2 percent, respectively. Differences between the 

inflow data used in model simulations and actual 

inflows between the outlet of Lake Tahoe and Farad 

are an important reason for the negative bias between 

simulated and observed flows. It is likely that errors 

from PRMS simulations of inflows, the use of synthetic 

meteorological data used as input for PRMS simulations of inflows, and different reservoir configurations 

contribute toward the negative bias at Farad prior 

to 1981.

Simulation errors from PRMS models contribute 

toward the percent bias at Farad. The PRMS models 

were calibrated only for the water years 1980–97 or 

1994–97 for most of the modeled subbasins in the 

Truckee River Basin between Lake Tahoe and the 

Farad gaging station. Percent bias from PRMS model 

simulations range from -7 to +7 percent for calibrated 

Figure 8. Observed and simulated monthly mean streamflows for the period October 1, 1988, 

through September 30, 1997, for Truckee River at Vista, Nev. (station 10350000)

Simulated

Observed

0

800

1,600

2,400

3,200

4,000

4,800

5,600

6,400

7,200

8,000

MONTHLY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND 

1989 1990 1991 1992 1993 1994 1995 1996 1997

CALENDAR YEAR
124 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

subbasin models upstream from Farad (Jeton, 2000). 

The PRMS models were calibrated to only 5 of 14 subbasins, which comprise only about 30 percent of the 

total drainage basin area between Lake Tahoe and 

Farad. Observed data from the other nine subbasins 

were not available for model calibration. Additionally, 

the accuracy of simulated streamflow data prior to the 

period of PRMS model calibrations, as described 

above, is uncertain. PRMS simulation accuracies could 

be improved by increased availability of observed 

streamflow data for model calibrations.

The meteorological data used as input to the 

PRMS models for simulation of inflows to the operations model also contribute toward the percent bias 

at Farad. For the water years 1981–97—the period of 

-2 percent bias—observed meteorological data were 

used for PRMS simulation of inflows. However, for the 

period 1933–80—the period of -18 percent bias—

synthetic meteorological data (Michael Dettinger, 

U.S. Geological Survey, written commun., 1998) were 

used to simulate most of the PRMS inflows.

Different reservoir configurations between Lake 

Tahoe and Farad also contribute toward the negative 

bias at Farad. The operations model simulates the operations of seven reservoirs upstream of Farad for the 

period 1933–97, but Prosser Creek Reservoir, Stampede Reservoir, and Martis Creek Lake were not constructed until 1962, 1970, and 1971, respectively (table 

1). The simulation of evaporation from these three reservoirs prior to their actual construction contributes 

toward simulated losses of water volumes resulting in 

negative simulation errors. The effects of bank storage 

and release from these reservoirs are not known, and it 

is uncertain how bank storage would affect simulation 

errors. Additionally, errors from the simulation of 

operations from these reservoirs prior to their construction are not known.

Figure 9. Observed and simulated monthly mean streamflows for the period October 1, 1988, 

through September 30, 1997, for Truckee River near Nixon, Nev. (station 10351700)

Observed

Simulated

0

800

1,600

2,400

3,200

4,000

4,800

5,600

6,400

7,200

8,000

MONTHLY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

1989 1990 1991 1992 1993 1994 1995 1996 1997

CALENDAR YEAR
MODEL LIMITATIONS, ASSUMPTIONS, AND SUGGESTED IMPROVEMENTS 125

MODEL LIMITATIONS, ASSUMPTIONS, 

AND SUGGESTED IMPROVEMENTS

Simulation of the hydrologic and physical processes in the channel and reservoir network of the 

Truckee River Basin using HSPF is, by itself, a rigorous and data-intensive undertaking. That task is made 

even more difficult by the need to simulate the complex 

operations (both current and anticipated) in this basin. 

Development of the operations model required skill 

and experience in modeling with HSPF, the assembly 

of a large data base, and an extensive knowledge of current and proposed operations in the basin. The sheer 

size of the computer program, the necessary integration 

of complex code from several programmers, the need 

for critical review from a variety of Truckee River 

interests, and the ongoing nature of the TROA negotiations to define operational policy all point to a need for 

future revisions, upgrades, and maintenance. This 

model is expected to evolve and be improved through 

purposeful application and analysis of the output. 

The following bulleted items summarize some 

more general limitations, assumptions, or improvements that may be important to the reader in interpreting model output.

• All models are conceptual representations of the 

real world. Just as physically based models that 

simulate precipitation-runoff processes have 

inherent errors because detailed physical processes have been lumped together and averaged, 

so, too, will operational models of complex river 

basins. Further analysis of results will be necessary in order to refine the model logic, especially 

that logic that represents the human element 

rather than prescribed actions that are clearly 

spelled out in legal decrees and agreements.

• Although an attempt was made to include all significant aspects of draft TROA in the model, time 

constraints meant that some minor aspects in the 

draft TROA were not included. Where known, 

these omissions are mentioned in the assumptions 

listed for each section. It is possible that other 

aspects were inadvertently omitted and thus may 

be absent from the model and discussions in this 

report. Finally, some minor details may have been 

left out of the report for the sake of brevity but are 

present in the flowcharts and code and are, in fact, 

simulated by the model.

• With modification of the database, the operations 

model would have the capability to accept forecasted data for near-term simulations of current 

operations or draft TROA operations for planning 

purposes. This improvement would allow model 

simulations using near real-time data, such as 

forecasted streamflow data derived from current 

snowpack data and median climate conditions. 

Such capability would aid users in planning operations for an upcoming runoff season. However, 

without extensive changes to the model code, 

these planning simulations would be restricted to 

those operations coded in the model.

• Reliable data are unavailable to fully account for 

all inflows and outflows in the Truckee River 

Basin. These include measured reservoir and tributary inflows and meteorological data such as 

precipitation and evaporation. Errors in volume 

resulting from lack of data or inaccurate data may 

be either compensating or cumulative. Therefore, 

the magnitude of simulation differences resulting 

from the data are not fully known. 

• Some water rights in the Truckee River Basin 

may be satisfied with ground water rather than 

surface water. Various amounts and locations of 

ground-water pumping are not addressed by this 

model. To do so would require linking the operations model to a calibrated ground-water model 

similar to Maurer (1986).

• There are few quantitative data on irrigation 

return flows, which are estimated in the model 

simulations using factors applied to the diversion 

amounts. 

• Temporary diversions that return almost all water 

back to the river within a few miles, such as diversions to riverside power plants, are not simulated. 

• The flow-routing part of the model for the Truckee Canal (reaches 60–69) and the Little Truckee 

River (reaches 185–209) has not been tested 

against observed streamflow data. Methods to 

construct the Truckee Canal and Little Truckee 

River parts of the flow-routing model were similar to those used in the Truckee River (Berris, 

1996) and the Carson River (Hess, 1996) flow 

routing models. Very little observed flow data or 

diversion data are available to compare observed 

and simulated daily streamflows for these added 

reaches.
126 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

• For simulation of Lake Tahoe releases of pooled 

water for maintaining Floriston rates, the watersurface elevation of Tahoe includes all water 

categories in the lake, but does not reflect pooled 

water volume stored in any other reservoir as 

specified in draft TROA.

• The simulation period for which daily input data 

have been compiled or estimated for the operations model is currently October 1, 1932, to September 30, 1997. Simulations can be made for 

any period of time for which the user has complete daily data. However, the modeler would 

have to revise several dated variable assignments 

within the SPECL block. There are, for example, 

several computed flags, storage accumulators, 

and so forth that are computed on specific dates 

within the program code and used to guide operations in subsequent months. If the user opts to 

start a simulation on a day other than October 1, 

1932, initial values for these variables would 

have to be individually assigned. Inappropriate or 

overlooked assignments could result in errors that 

may carry through the simulation period. Other 

initial conditions required for simulations, such as 

reservoir storages and water category amounts in 

all reaches, inflows, and so forth, must be specified by the user. 

• To realize multiple-use benefits of reservoirs in 

the Truckee River Basin when determining 

releases, managers can utilize blending or seasonal foresight or some combination of the two 

concepts. Blending of reservoir releases satisfies 

a demand for one category of water by concurrent 

releases from more than one reservoir. Current 

examples of blending used by managers are multiple-reservoir releases to maintain Floriston 

rates, to meet Pyramid Lake fish flow targets, to 

maximize power generation, and to satisfy floodcontrol criteria. Methods describing current or 

draft TROA reservoir management for the purpose of blending are undocumented. 

• Seasonal foresight utilizes forecasts of both 

inflows and reservoir management to construct an 

operational forecast. Such a forecast can be used 

to “schedule” operations in advance, smoothing 

reservoir releases over weekly/monthly periods 

and thus avoiding large operational swings. As 

with blending of reservoir releases, methods 

describing reservoir management using seasonal 

foresight are undocumented. Examples of where 

seasonal foresight would be useful are storage of 

proposed water categories, maintaining preferred 

instream flows, and maintaining recreational 

pools. 

• In the USGS Truckee River Basin operations 

model, there are no specific subblocks that simulate scheduling, blending, or seasonal foresight 

procedures. Instead of blending releases, the 

operations model draws upon one reservoir at a 

time to satisfy demands, taking into account recreational pools. However, some blending is 

accomplished in model simulations of draft 

TROA operations by making exchanges to 

achieve various instream flows, recreational 

pools, and enhanced storage security. Additional 

blending in the model would require defining the 

relation between reservoir levels and releases for 

multiple-use benefits. To simulate the use of 

scheduling and seasonal foresight, would require 

pseudo-operation forecasts that, to be accurate, 

would require much more coding and would significantly increase model run times. 

SUMMARY

The demand for all uses of water in the Truckee 

River Basin, California and Nevada, commonly is 

greater than can be supplied. Droughts lasting several 

years, such as the recent drought of the late 1980’s and 

early 1990’s, can result in substantial water shortages 

for irrigation and municipal users and may stress fish 

and wildlife ecosystems. Truckee River water is used 

to enhance fishery and recreational resources in California, to generate power upstream from Reno, to provide municipal and industrial (M&I) water supply in 

the Truckee Meadows vicinity, to maintain Pyramid 

Lake levels, to conserve the Pyramid Lake fish species 

cui-ui and Lahontan cutthroat trout, and to provide irrigation water to the Truckee River Basin and, through 

transbasin diversion, the Carson River Basin. This 

diversity in interests results in a wide range of alternatives for planning, allocating, and managing the water 

resources and operating the various reservoirs and 

diversion systems. Decrees, agreements, and regulations generally define current water management in 

the basin.
SUMMARY 127

Title II of Public Law (P.L.) 101-618, the Truckee-Carson-Pyramid Lake Water Rights Settlement 

Act of 1990, provides direction, authority, and a 

mechanism for resolving conflicts over water rights 

in the Truckee and Carson River Basins. P.L. 101-618 

provides a foundation for the negotiation and development of reservoir and river operating criteria, known as 

the Truckee River Operating Agreement (TROA), to 

balance interstate and interbasin allocation of water 

rights among the many interests competing for Truckee 

River water. Additionally, the Truckee River Water 

Quality Settlement Agreement (WQSA), signed in 

1996, provides for acquisition of water rights to aid in 

resolving water-quality problems during periods of low 

flow on the Truckee River in Nevada while simultaneously providing additional water for fish and wildlife 

resources. Efficient execution of many of the planning, 

management, or environmental assessment requirements of TROA and WQSA will require detailed 

water-resources and hydraulic data, coupled with 

sound analytical tools. Models constructed and evaluated with reliable data will help assess effects of alternative operational scenarios related to reservoir and 

river operations, water-rights transfers, and changes in 

irrigation practices. The dynamic nature of certain reservoir and river operations, coupled with the interdependence of water-quality to dynamic flow regimes, 

dictate the use of a model that can characterize and represent the physical hydrologic and hydraulic features of 

the basins and the river/reservoir operations, and can 

simulate flow with a computation interval sufficient to 

represent these dynamics, such as a daily time step. 

However, available modeling tools have a monthly 

time step and cannot simulate dynamic flows. Such 

models cannot fully address the broad spectrum of 

water-resources issues associated with the dynamic 

nature of operations, flows, and water quality in the 

quantitative detail that is needed for evaluation of management options.

The Truckee–Carson Program of the U.S. Geological Survey, to support U.S. Department of the 

Interior implementation of P.L. 101-618, developed a 

modeling system to assist in the efficient planning, 

management, and allocation of water resources. The 

daily operations model discussed in this report is a 

part of the modeling system. The operations model 

utilizes flow-routing and operations modules. The 

operations model is capable of simulating lake/reservoir and river operations, including diversion of Truckee River water to the Truckee Canal for transport to 

the Carson River Basin. 

This report describes the chronology and background of decrees, agreements, and laws that affect 

Truckee River operational practices; the construction 

of the Truckee River daily operations model, including 

the data necessary for simulations; the simulation of 

Truckee River Basin operations, both current and proposed under TROA and WQSA; suggested model 

improvements and limitations; and a comparison 

between simulated and observed operations. The daily 

operations model simulates river and reservoir operations as well as streamflow in the Truckee River from 

Lake Tahoe to Pyramid Lake, the Truckee Canal, and 

Lahontan Reservoir in the Carson River Basin. The 

daily operations model was designed to provide simulations that allow comparison of the effects of alternative management practices or allocations on streamflow or reservoir storages in the Truckee River Basin. 

The model was not intended to reproduce historical 

values. A general overview of daily operations (current 

and proposed) and how they are simulated is provided 

in this report. In addition to this report, supplemental 

information that documents the extremely complex 

operating rules is available, including detailed flowcharts, original model code, and a listing of variable 

names and definitions found in the flowcharts and 

code.

The daily operations model uses the Hydrological 

Simulation Program–FORTRAN (HSPF) to simulate 

streamflow and reservoir and river operations. HSPF 

was chosen because it can (1) simulate continuously 

over time, including periods of storm runoff and low 

flows, (2) simulate at a daily time step, (3) simulate the 

hydraulics of complex natural and man-made drainage 

networks, (4) produce simulation results for many locations along the river and its tributaries, (5) simulate reservoir and river operations, and (6) compute a detailed 

water budget that accounts for inflows and diversions 

as well as different categories of water in the river and 

reservoirs. HSPF is an internationally used non-proprietary program maintained by the Environmental Protection Agency.

Reservoir and river operations for the Truckee 

River Basin are governed by complex rules in legal 

agreements, decrees, and regulations that specify 

numerous conditions for the distribution and use of 

water categories. The Truckee River Basin operations 

model simulates reservoir and river operations by 
128 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

evaluating specific conditions and executing the appropriate operations through the use of model code. Conditions that are typically evaluated during simulations 

include the time of year, reservoir stage, reservoir storage, volume of a given water category in a reservoir, 

streamflow magnitude, and fulfillment of demands.

The Truckee River daily flow-routing model 

developed by Berris (1996) is used within the operations model to model the movement of water into and 

through the reaches of the drainage network while the 

operations model simulates the man-made regulation 

of water movement within and out of the Truckee River 

Basin drainage network. The scope of the flow-routing 

model was expanded from 47 reaches to 72 reaches for 

use with the operations model.

External input data are required for streamflow and operations simulations. These include 

time series of daily reservoir inflows, river inflows, 

channel seepage losses, evapotranspirations losses 

from phreatophytes, precipitation, evaporation, M&I 

demand for the Truckee Meadows, and various types 

of runoff forecasts.

The constructed model simulates three major 

options regarding Truckee River operational practices. 

The first simulates current (1998) operational practices. The second combines current operations and 

those proposed in draft TROA and WQSA. The third 

simulates WQSA without draft TROA, and is not 

described separately in this report. All simulated operations are organized into subblocks of model code. 

Current and proposed operations, organized into subblocks of model code, can be grouped into the general 

classifications: (1) initial assignments and computations, (2) flood-control criteria, (3) storage priorities, 

(4) release adjustments to meet downstream demands, 

(5) merged reservoir releases for multiple objectives, 

(6) river diversions, and (7) exchanges or transfers of 

water categories among one or more reservoirs. 

Initial assignments and computations is a utility 

subblock in which miscellaneous constants and flags 

are assigned prior to the simulation of operations. 

These assignments include reservoir outlet capacities 

based on current reservoir stage; irrigation demands 

transferred to other uses, such as M&I demand or 

water-quality demand; minimum, enhanced, and preferred flow targets; recreation pool levels; Floriston 

rates targets; and M&I credit water base amounts. 

Current reservoir and river operations are implemented primarily by adjusting reservoir releases and 

diverting water of specific water categories from the 

main channel. Adjustment of reservoir releases allows 

the reservoir operator to pass inflows through to downstream reaches, store inflows, or release water from 

reservoir storage for a variety of objectives. River 

diversions to meet irrigation and M&I demands are 

based on water rights. Operations currently practiced 

and simulated are briefly described below.

Truckee River reservoirs are currently operated 

according to several types of flood-control criteria 

throughout a given year. Flood-control criteria are simulated by adjusting reservoir releases of precautionary 

drawdowns and uncontrolled spills.

A reservoir storage priority system is used in the 

Truckee River Basin to determine when a reservoir 

may or may not store water. Storage priorities must 

consider Floriston rates demands and Newlands Project 

demands for Truckee River water. Reservoir storage is 

simulated by adjusting reservoir releases.

Under current operations, several demands are 

described in legal decrees and simulated by the operations model. Satisfying these demands involves adjusting reservoir releases and river diversions. Demands 

met by operational simulations include Floriston rates, 

instream flows, Pyramid Lake fish, Newlands Project, 

and privately owned stored water (POSW), such as 

Power Company POSW (PCPOSW) and Truckee–

Carson Irrigation District POSW (TCIDPOSW). The 

water categories pooled water and Tahoe–Prosser 

Exchange water are used to maintain Floriston rates. 

The water categories fish water and uncommitted water 

(only that part not needed for the purposes of the 

Tahoe–Prosser Exchange Agreement) serve to benefit 

threatened and endangered fish of Pyramid Lake. The 

POSW categories, PCPOSW and TCIDPOSW, are 

used to meet, in part, Truckee Meadows M&I and 

Newlands Project demands, respectively.

For simulations, releases from a given reservoir 

that meet more than one objective may be consolidated 

as a “merged reservoir release.” Untagged releases that 

are not required to be of specific categories, such as 

uncontrolled spills and precautionary drawdown 

releases based on flood-control criteria, or maintenance 

of current minimum flows, may be combined with 

releases tagged to specific categories. If the demand for 

untagged releases is greater than for tagged releases, 

then water categories must be assigned to that part of 

the untagged releases that is greater than the tagged 

releases, according to a rank-order list.
SUMMARY 129

River operations involve the diversion of pooled 

water, POSW, or natural water as specified in legal 

decrees, such as the Sierra Valley Settlement Agreement or the Orr Ditch Decree. Simulated river operations include (1) the Sierra Valley Diversion, which 

diverts water from the Little Truckee River for agricultural demands in California outside of the Truckee 

River Basin, (2) Truckee River diversions between the 

Farad and Vista gaging stations for M&I and agricultural demands in the Truckee Meadows, (3) Truckee 

River diversions downstream from Vista gaging station 

for agricultural demands of adjacent agricultural lands, 

and (4) diversion of Truckee River water at Derby Dam 

to the Newlands Project via the Truckee Canal based 

on Operating Criteria and Procedures (OCAP). 

Water exchange and transfers allows reservoir 

operators to meet multiple-use goals by manipulating 

volumes of water categories in one or more reservoirs. 

Exchanges involve moving stored water of a given 

water category from one reservoir to another. There are 

three types of exchanges: (1) a paper exchange—nonphysical exchanges of a volume of water in one or more 

reservoirs for water in one or more other reservoirs; 

(2) in-lieu-of exchange—release of one or more categories of water from one or more reservoirs in lieu of a 

release of water of yet another category from one or 

more other reservoirs; and (3) re-storage—release of 

water from one reservoir for storage in a downstream 

reservoir. Two common exchanges currently practiced 

and simulated by the operations model are the Tahoe–

Prosser Exchange and the Donner–Boca Exchange. 

These exchanges are simulated as in-lieu-of exchanges. 

Transfers involve only one reservoir and result in the 

gain or loss of water in one category by transfer from 

another within that single reservoir.

The draft TROA agreement, unsigned as of 

1998, and the WQSA agreement, signed in 1996, are 

designed to make more effective and efficient use of 

water categories in reservoir operations to meet multiple objectives. Reservoir and river operations outlined 

in draft TROA and WQSA are intended to (1) increase 

the drought water supply for M&I uses in the Truckee 

River Basin in California and the Truckee Meadows, 

(2) increase the water supply to maintain adequate 

lake levels and spawning flows to promote the recovery 

of endangered and threatened Pyramid Lake fish, 

(3) increase instream flows for fish and water quality, 

and (4) maintain reservoir storage levels for recreation 

use. Achieving these objectives may be accomplished 

by revising many of the current operations regarding 

water storage and release practices. Two key elements 

of draft TROA and WQSA enable such changes to current operations. The first element involves reducing 

releases for Floriston rates, the required flow at the 

Farad gaging station. Water not released for Floriston 

rates would be retained in storage and transferred to 

new credit water categories available only to satisfy 

those objectives outlined in draft TROA and WQSA. 

The second element involves mandatory or voluntary 

exchanges of water categories between reservoirs to 

better coordinate releases to meet multiple objectives.

Draft TROA and WQSA specify procedures for 

storage of credit water categories in Lake Tahoe and 

reservoirs of the Truckee River Basin. These procedures allow for the storage of several categories of 

water within a reservoir. These procedures commonly 

involve a transfer of water categories retained in storage that would have been released under another set of 

circumstances, such as under current operations. The 

water retained would then be transferred to a new credit 

water category. Procedures for storage of credit water

categories also involve a variety of other types of mandatory exchanges and transfers. Policies and operational procedures regarding some of the proposed 

water categories are not yet defined in the draft TROA. 

As a result, the proposed water categories, referred to 

as Fernley credit water, Newlands Project credit 

water, and other credit water were not coded, are not 

simulated in the operations model, and are not 

described in this report.

Under draft TROA, California could store a part 

of its unused surface-water allocation in Truckee River 

reservoirs for M&I purposes. The new category, California M&I Credit water (CMICW) is created in 

Lake Tahoe to provide an additional water supply during droughts. CMICW is accumulated in simulations 

by determining if the projected demand for direct 

diversion of surface water is less than California’s surface-water allocation. If so, then the difference is available for accumulation of CMICW in Lake Tahoe. A 

new category, called Joint Program fish credit water

(JPFCW), may be available in simulations for accumulation, based on the remaining allocation of surface 

water after California M&I use and storage of 

CMICW. JPFCW is used to meet recreational and 

instream flow demands.

In addition to CMICW, draft TROA will provide 

procedures for storage and accumulation of a number 

of other categories, such as Power Company M&I 

credit water (PCMICW), fish credit water, water-
130 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

quality credit water (WQCW), and Joint Program fish 

credit water (JPFCW). PCMICW, used as M&I 

drought supply in the Truckee Meadows, is accumulated during simulations by (1) creating and accumulating the consumptive use portion of former Orr Ditch 

Decree agricultural water rights acquired by Power 

Company that would have been released to maintain 

Floriston rates, (2) re-storage of PCPOSW released 

from Independence Lake to another appropriate reservoir, or (3) implementing one of several mandatory and 

voluntary exchanges and transfers.

Fish credit water is water other than fish water 

that can be stored and used for the benefit of Pyramid 

Lake fish. Fish credit water can be accumulated during 

simulations by (1) retaining in storage that portion of 

pooled water not needed to immediately satisfy Orr 

Ditch Decree water rights and would have flowed to 

Pyramid Lake, and (2) implementing one of several 

mandatory and voluntary exchanges and transfers. A 

water category called Power Company emergency 

drought supply (PCEDS) consists of the first 7,500 

acre-ft of fish credit water stored in Stampede Reservoir. Additionally, half of the fish credit water created 

becomes JPFCW until (1) JPFCW in all reservoirs 

totals 20,000 acre-ft, or (2) California exhausts its 

annual surface-water allocation.

Water-quality credit water (WQCW) is dedicated 

to augmenting instream flow in the Truckee River from 

the Truckee Meadows to Pyramid Lake to enhance 

water quality and preserve wildlife and fish habitat 

along the Truckee River. WQCW can be accumulated 

during simulations by three methods based on draft 

TROA principles in conjunction with WQSA. The first 

method of simulation involves reducing releases corresponding to the consumptive use of Orr Ditch Decree 

rights acquired by WQSA that would have been 

released to maintain Floriston rates. The water retained 

would be transferred to WQCW. The second method of 

simulation involves the accumulation of WQCW during periods when cui-ui flow targets are in effect at 

Nixon, downstream from Derby Dam. The volume of 

WQCW accumulated corresponds to the volume of 

pooled water flowing directly to Pyramid Lake that 

augments flow used for the benefit of Pyramid Lake 

fish in accordance to the consumptive use portion of 

acquired Orr Ditch Decree rights. The third method of 

simulation is an instream creation of WQCW within 

the Truckee River by transferring to WQCW that part 

of pooled water obligated to Orr Ditch Decree rights 

purchased for uses specified in WQSA.

Under draft TROA and WQSA, releases of credit 

water are simulated to meet downstream demands. 

Credit waters simulated to meet demands include 

releases of firm and nonfirm PCMICW and CMICW 

to meet M&I and agricultural demands, releases of fish 

credit water to meet cui-ui flow targets, and releases 

of WQCW to meet water-quality targets. Additionally, 

direct diversions from Lake Tahoe and Donner and 

Independence Lakes are simulated to meet local 

M&I demands.

Mandatory exchanges and transfers are simulated 

for moving (physically or administratively) or converting water categories among one or more reservoirs. 

These required exchanges and transfers are specified 

for certain water categories and purposes in draft 

TROA to allow the storage and release of water categories to meet more than one objective. Mandatory 

exchanges and transfers are simulated to (1) achieve 

enhanced minimum instream flows and (2) favor the 

storage of selected new credit water categories, 

depending on specific conditions such as reservoir storage on specific dates and the presence or absence of a 

drought situation.

The first type of simulated mandatory exchange 

provides for the enhancement of minimum instream 

flows using current and credit water categories accumulated in reservoirs. Enhanced minimum instream 

flows are simulated by (1) increasing reservoir releases 

of water categories if the water can be re-stored in a 

downstream reservoir or if the water can be exchanged 

into another reservoir, or (2) releasing JPFCW without 

re-storage or exchange. The exchange and re-storage 

of water categories for enhancing minimum flows 

depends on their security in storage, once re-stored 

or exchanged, their availability and location in reservoir storage before re-storage or exchange, type of 

season (normal or dry), and the current status of 

streamflow with respect to enhanced flow targets at 

specified locations. 

Other mandatory exchanges and transfers are 

simulated based on category storage limits, drought situation, time of the year, or some combination of these 

criteria. These operations are simulated mostly as paper 

exchanges and transfers. These other exchanges and 

transfers are simulated to maintain firm PCMICW, 

nonfirm PCMICW, and PCEDS base amounts and to 

transfer PCPOSW and PCMICW stored in reservoirs 

on specific dates.
SUMMARY 131

Many exchanges are voluntary and are not specified individually in draft TROA. Voluntary exchanges 

would be requested by the parties interested in making 

the exchange and would be based on terms and conditions agreed to by the parties. Similar to mandatory 

exchanges, voluntary exchanges can satisfy several 

objectives. Because the number of potential voluntary 

exchanges is quite large, only four major types are simulated by the operations model and described in this 

report. These exchanges are used to (1) achieve preferred instream flows, (2) enhance storage security, 

(3) efficiently utilize precautionary drawdown releases, 

and (4) maintain recreational pools. For simulation, it 

is assumed that if conditions allow for a voluntary 

exchange, that voluntary exchange will be simulated.

One type of voluntary exchange provides for the 

achievement of preferred instream flows. Similar to 

enhanced instream flows, preferred flows are simulated as flow targets that vary by season and location. 

For most simulations, reservoir releases may be 

increased to achieve preferred flows only if the water 

can be re-stored or exchanged into another reservoir. 

Another type of voluntary exchange, enhanced 

storage security exchanges, involves exchanging water 

to a reservoir that is more likely to allow an owner to 

keep and access that water. A voluntary exchange may 

allow credit water categories to be exchanged to a reservoir with safer storage conditions. The operations 

model simulates the most likely exchanges for 

enhanced storage security: (1) an exchange of credit 

water categories from Lake Tahoe or Prosser Creek 

Reservoir to Boca Reservoir, and (2) an exchange of 

water categories from Boca Reservoir to Stampede 

Reservoir. These simulated exchanges assume that 

Stampede provides the most secure storage for water 

categories.

A third type of voluntary exchange, efficient use 

of releases for precautionary drawdowns, allows precautionary drawdowns from a reservoir during floodcontrol operations to meet other objectives, such as 

maintenance of Floriston rates. Simulations provide 

three exchange possibilities: (1) a Donner–Tahoe 

exchange when precautionary drawdowns from Donner Lake may be substituted for Lake Tahoe pooled 

water releases, (2) a Prosser–Tahoe exchange when 

precautionary drawdowns from Prosser Creek Reservoir may be substituted for Tahoe pooled water 

releases, and (3) a Prosser–Boca exchange when precautionary drawdowns from Prosser Creek Reservoir 

may be substituted for Boca Reservoir adverse-to-canal 

water releases.

A fourth type of voluntary exchange operation, 

maintenance of recreational pools, is the management 

of reservoir releases and exchanges to maintain recreational pools during the summer. Although recreational 

pool objectives are set for Donner and Independence 

Lakes and Prosser and Boca Reservoirs, exchanges are 

only simulated to maintain Boca recreational pool 

objectives. For reservoirs other than Boca, recreational 

pool objectives are simulated in consideration with the 

reservoir releases. For Boca, simulations provide inlieu-of exchange possibilities with Prosser Creek Reservoir and Lake Tahoe. The operations model does 

not simulate operations to meet Stampede Reservoir, 

Martis Creek Lake and Lake Tahoe recreational pools. 

Simulations adjust reservoir storage accounts of 

water categories for evaporation losses and precipitation gains on the basis of priority guidelines provided 

in draft TROA. Additionally, simulated releases due to 

flood-control criteria use water categories based on 

rank-order guidelines. Similar to current operations, 

these merged reservoir releases, required for uncontrolled spills and precautionary drawdowns based on 

flood-control criteria, satisfy a variety of other objectives under draft TROA and WQSA. Priority orders 

may change if a drought situation exists.

Simulations use forecasts to evaluate expected 

runoff conditions that affect operations. The determination of normal and dry seasons is used to specify 

enhanced instream flow releases. The determination of 

a drought situation is used to determine the order of 

water category releases required under flood-control 

criteria and to determine if mandatory exchanges 

should take place that involve various water categories. 

As a surrogate for human judgement needed in making 

some operational decisions, a runoff index of wet, dry, 

or average is established by comparing forecasted runoff to mean runoff from historical records. 

Traditional model development usually entails 

calibration and verification tasks in order to demonstrate the reliability of the model. However, testing of 

the Truckee River Basin operations model by comparison with historical data is difficult for several reasons. 

These include historical flexibility and lack of documentation in how operations were actually implemented, as well as the lack of past input data to 

simulate all of the details and system interactions of 

past operations. Thus, only limited testing of the USGS 
132 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

Truckee River Basin operations model by comparison 

with historical data can be accomplished. Because draft 

TROA has not yet been implemented, no observed data 

reflecting proposed operations are available for comparison to simulated data. 

With these limitations in mind, the periods 

1989–97 and 1933–97 were chosen to illustrate model 

simulations compared to historically observed 

streamflows.

The period 1989–97 was chosen to test simulation 

of reservoir and river operations because it includes all 

current reservoirs and is the most representative of the 

current operating strategy coded in the model. Current 

operations were simulated and simulated streamflows 

at the Farad, Vista, and Nixon gaging stations were 

graphically compared to observed values. Differences 

between observed and simulated flows at the gaging 

stations for the periods 1989 and 1994 were probably 

the result of simulated reservoir storages that were 

different from observed storages and single incident 

variances in actual operations or operations based 

on special permits or agreements not simulated by 

the model.

The period 1933–97 was chosen to illustrate longterm differences between simulated and observed 

streamflow volumes at the Farad gaging station. For 

the entire period, the percent bias of simulated streamflow was -13 percent. For the periods 1933–80 and 

1981–97, percent biases of simulated streamflow at 

the Farad gaging station were -18 and -2 percent, 

respectively. Differences between the inflow data used 

in model simulations and actual inflows between the 

outflow of Lake Tahoe and Farad are an important 

reason for the negative bias between simulated and 

observed flows. It is likely that errors from PRMS simulations of inflows to the operations model, the use 

of synthetic meteorological data used as input for 

PRMS simulations, and different reservoir configurations contribute toward the negative bias at Farad prior 

to 1981. Operational variables, such as different effective dates of decrees and agreements, flexible adherence to decrees and agreements, and other unknown 

or minor operational variables, may also influence simulation results, but their influence on simulation results 

is difficult to specify.

REFERENCES CITED

Berris, S.N., 1996, Daily flow-routing simulations for the 

Truckee River, California and Nevada: U.S. Geological 

Survey Water-Resources Investigations Report, 96-

4097, 83 p.

Berris, S.N., Hess, G.W., and Cartier, K.D., 1996, Simulation of selected reservoir operations in the upper 

Truckee River Basin, California: U.S. Geological 

Survey Fact Sheet FS-082-96, 4 p.

Berris, S.N., Hess, G.W., and Bohman, L.R., 2001, Hydrologic data used in the river and reservoir operations 

model, 1933–97, Truckee River Basin, California and 

Nevada: U.S. Geological Survey Open-File Report 

00-478, 48 p.

Bicknell, B.R., Imhoff, J.C., Kittle, J.L., Donigan, A.S., and 

Johanson, R.C., 1993, Hydrological simulation program-FORTRAN: User’s manual for release 10: 

EPA/600/R-93/174, Environmental Research Laboratory, 660 p.

Brown, W.M. III, Nowlin, J.O., Smith, L.H., and Flint, M.R., 

1986, River-quality assessment of the Truckee and Carson River System, California and Nevada—hydrologic 

characteristics: U.S. Geological Survey Open-File 

Report 84-576, 201 p. 

Buchanan, C.C., and Strekal, T.A., 1988, Simulated water 

management and evaluation procedures for cui-ui: 

U.S. Fish and Wildlife Service, 19 p.

Bureau of Reclamation, 1959, Agreement for water 

exchange operations of Lake Tahoe and Prosser Creek 

Reservoir: Contract No. 14-06-400-957, 10 p.

——— 1988, Secretarial record of decision on the Newlands 

Project Operation Criteria and Procedures: Mid-Pacific 

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134 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

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GLOSSARY

Selected technical terms used in this report are 

defined for convenience of the reader. See Langbein 

and Iseri (1960) for additional information regarding 

hydrological terminology.

additional supplemental storage water. Also referred to as 

non-adverse-to-canal (Truckee Canal) water, this term 

means all water diverted to and stored in Boca Reservoir in excess of supplemental storage water (adverseto-canal water), but not including credit water, privately 

owned stored water, and project water from another 

reservoir. See also supplemental storage water.

ANNIE. A time-series data-management system that allows 

a user to interactively store, retrieve, list, plot, check, 

update, or statistically analyze spatial, parametric, and 

time-series data for hydrologic models.

Boca pressure water. Fish water or fish credit water, 

released from Stampede Reservoir for temporary 

storage in Boca Reservoir, that provides sufficient 

hydraulic head at the outlet works to enable timely 

releases to achieve flow targets for the benefit of 

Pyramid Lake fish.

California M&I credit water (CMICW). Water that 

may be stored for M&I use in California according 

to draft TROA.

category. Any block of water that is individually accounted 

for in an observed or simulated water budget and that 

may have specific ownership, such as privately owned 

stored water, or a designated use, such as pooled water.

consumptive use duty. The total volume of irrigation water 

per year required to mature an acre of a particular type 

of crop. The duty is the annual amount of water supplied to the land, including transmission losses from the 

point of diversion at the river to the farm headgate, and 

is not the volume of water actually consumed by the 

plants. Transmission losses are not included in the 

consumptive use duty applied to M&I diversions. 

contract storage. Interim Storage Agreement as authorized 

under paragraph 205(b)(3) of P.L. 101-618 among the 

Secretary of the Interior, Sierra Pacific Power Company, Washoe County Water Conservation District, and 

the Pyramid Lake Paiute Tribe (Contract for Storage of 

SPPC Water in Stampede and Boca Reservoirs).

controlled spill. See precautionary drawdown.

credit water. Water that is accumulated, stored, and 

released in accordance with provisions in draft TROA. 

Categories included are fish credit water, firm Power 

Company M&I credit water, nonfirm Power Company 

M&I credit water, California M&I credit water, Water 

Quality credit water, Joint program fish credit water, 

Fernley credit water, Newlands Project credit water, 

and other credit water (water stored and used for beneficial uses that are not currently defined in draft TROA).

depletion. The amount of diverted water that is consumptively used and, therefore, not returned to the river or 

aquifer.

displacement. The forced release of one water category 

from a reservoir because of a higher priority for storage 

of another water category during a spill.

drought condition. As identified in draft TROA, a condition 

under which the Power Company’s normal water 

supply is not sufficient to satisfy normal M&I water 

year demand and a drought situation exists.

drought situation. As identified in draft TROA, situation in 

which the Truckee River runoff forecast indicates there 

would not be sufficient unregulated water and pooled 

water to maintain Floriston rates throughout the water 

year, or Lake Tahoe elevation is forecasted to drop 

below 6,223.5 ft (Lake Tahoe datum) before November 

15.

dry season. As identified in draft TROA, a range of forecasted runoff in the Truckee River Basin downstream 

from Lake Tahoe and the amount of water in Lake 

Tahoe at various times of the year, defined by figures 5 

and 6. Along with normal season, these thresholds were 

established to integrate forecasting into an operation 

that would assure that water rights would not be 

impaired while improving the prospects of enhancing 

minimum instream flow.

efficiency. Efficiency is computed as the total amount of 

water delivered to water-rights holders at the farm 

headgates divided by total diversion to the water-distri-
GLOSSARY 135

bution system. Low efficiencies mean that conveyance/transit losses, such as seepage, evaporation, or 

other operational losses, are large.

enhanced minimum instream flows. Mandatory target 

flows, identified in draft TROA, used to benefit fish 

and river habitat in California, to be achieved through 

the use of credit water, privately owned stored water, 

or fish water only if such waters could be re-stored in 

another reservoir or exchanged for water in another 

reservoir.

exchange. As identified in draft TROA, a transaction of 

specific quantities and water categories among reservoirs by any of three methods: (1) nonphysical 

exchange of a volume of water in one or more reservoirs for an equal volume of water in one or more other 

reservoirs, often called a “paper exchange;” (2) release 

of one or more categories of water from one or more 

reservoirs in lieu of a release of water of yet another 

category from one or more other reservoirs, often called 

an “in-lieu-of exchange” and; (3) release of water from 

one reservoir for storage in a downstream reservoir, 

often called “re-storage.”

Extended Streamflow Prediction (ESP). A computer 

program developed by the National Weather Service 

that uses existing snowpack conditions and applies 

historical temperature and precipitation values of a 

user-specified exceedance level over a future period of 

time (length of prediction also is user-specified) in 

order to predict streamflow rates or volumes.

F- Table. Function tables of the RCHRES block that contain 

relations between hydraulic properties of channel 

reaches, lakes, and reservoirs.

Fernley credit water. As identified in draft TROA, water 

that may be stored and utilized by the town of Fernley 

for M&I purposes.

firm Power Company M&I credit water (firm PCMICW). 

As identified in draft TROA, water stored in Stampede 

Reservoir that can be utilized for M&I purposes under 

drought conditions.

fish credit water (FCW). As identified in draft TROA, 

water, other than fish water, that can be stored and 

utilized for the benefit of Pyramid Lake fish.

fish water. Stampede Reservoir project water and uncommitted water in Prosser Creek Reservoir held or 

released into the Truckee River for the benefit of 

Pyramid Lake fish.

Floriston rates. Mandatory Truckee River flow rates, first 

established by the Truckee River General Electric 

Degree in 1915 as minimum-flow criteria for the 

Truckee River at the California-Nevada boundary.

former agricultural right. As identified in draft TROA, a 

water right from the Truckee River or its tributaries, 

originally used for irrigation in accordance with the 

Orr Ditch Decree, that has been purchased or otherwise 

acquired for uses other than agricultural.

gaging station. A gaging station where a continuous 

record of discharge, stage, or water-quality parameters 

is obtained.

GENeration and analysis of model simulation SCeNarios 

(GENSCN). The graphical user-interface developed 

to aid operational model simulations by creating, 

running, and analyzing alternative water-management 

scenarios.

in-lieu-of exchange. See exchange.

instream flow transfer. Creation of water-quality credit 

water instream (as flow within the river) rather than as 

water not released, and thus held as storage within a 

reservoir. Instream flow transfers are limited to those 

times when Truckee River flows are less than specified 

water-quality targets (see also transfer).

irrigation return flow. Excess surface water or ground 

water that returns to the river after diversion or application for irrigation.

irrigation season. Generally, the 7-month period beginning 

April 1 and ending October 31 of any year.

joint program fish credit water (JPFCW). As identified 

in draft TROA, fish credit water that may be stored 

and utilized for recreational pool and instream flow 

purposes in California, after which the water must flow 

unimpeded to Pyramid Lake.

municipal and industrial. Water supplied through a public 

water system for use in residential areas, commercial 

establishments, industry, landscape irrigation, or for 

other public needs.

natural water. Water that originates from flow in Truckee 

River tributary subbasins not regulated by a reservoir or 

from flow that is passed through a reservoir without 

detention, except Lake Tahoe.

Newlands Project credit water. Water that may be stored 

and utilized for use in satisfying OCAP requirements 

for the Newlands Project.

nondrought situation. See drought situation.

nonfirm Power Company M&I credit water (nonfirm 

PCMICW). As identified in draft TROA, any water 

other than Power Company POSW or firm Power 

Company M&I credit water that can be stored in 

any Truckee River reservoir and utilized for Power 

Company M&I purposes. 

normal season. See dry season. 

observed data. Lake-level or streamflow data computed 

from gage-height records collected at continuousrecorder or intermittent-observation gaging stations.
136 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998

Operating Criteria and Procedures (OCAP). Federal 

regulation governing diversion of water from the 

Truckee River for the Newlands project and operations 

for providing water to the Newlands Project, with the 

objective of maximizing use of Carson River water and 

minimizing diversion of Truckee River water.

other credit water. As identified in draft TROA, water 

that may be stored and utilized for beneficial uses not 

defined at this time.

paper exchange. See exchange.

pass-through. That part of reservoir inflow not allowed to 

be stored in order to meet demands or storage rights 

downstream having a higher legal priority. 

pondage. That portion of Boca Reservoir that provides 800 

acre-ft of storage capacity to facilitate the use of regulating flow for power generation and meeting Floriston 

rates as defined in the Truckee River Agreement. 

pooled water. Water stored pursuant to the Orr Ditch Decree 

and the Truckee River Agreement and allocated to the 

maintenance of Floriston rates.

Power Company emergency drought supply (PCEDS). 

As identified in draft TROA, water stored in Stampede 

Reservoir that can be utilized by the Power Company 

for M&I purposes under drought conditions.

Power Company M&I credit water. See firm Power 

Company M&I credit water and nonfirm Power 

Company M&I credit water.

 precautionary drawdown. For reservoirs with dedicated 

flood-control space, reservoir releases generally made 

during the period from about late summer to November 

1. Reservoirs that do not have dedicated flood-control 

space or other operating criteria requiring wintertime 

drawdown, such as Lahontan Reservoir or Lake Tahoe, 

typically have precautionary drawdown or reservoir 

releases in late winter or early spring. Also termed 

controlled spills, these releases are made to reduce 

reservoir levels to a prescribed limit that allows for 

emergency flood-control space, mostly during the 

winter and early spring months, but such releases could 

be made anytime that a situation merits (see also spill).

preferred flows. Target flows, identified in draft TROA, 

that are greater than enhanced minimum instream 

flows. 

priority date. Date a water right is established; used to 

chronologically determine the relative priority of 

water rights.

privately owned stored water (POSW). Water stored 

pursuant to water rights of Power Company in Independence Lake and the water rights of Power Company and 

TCID in Donner Lake.

project water. Water initially stored as pooled water in 

Lake Tahoe, supplemental storage water (adverse-tocanal), additional supplemental storage (non-adverseto-canal), and pondage water in Boca Reservoir, Stampede–Reservoir project water in Stampede Reservoir, 

Tahoe-Prosser Exchange water and uncommitted water 

in Prosser Creek Reservoir, and privately owned stored 

water in Donner and Independence Lakes.

re-storage. See exchange.

reach. A reservoir or a section of river having relatively 

uniform hydraulic properties and used within HSPF to 

simulate the movement of water within a hydrologic 

network.

recreational pool. Minimum reservoir storage levels that 

are maintained to promote or enhance public uses, such 

as boating and fishing. 

recreational season. The period between the dates April 1 

and September 3 (assumed to be the Labor Day 

holiday).

sidewater. Unregulated inflows of natural water from 

tributary subbasins in the Truckee River Basin.

spill. Spills can be either controlled or uncontrolled. 

Controlled spills (often termed precautionary drawdowns) are planned releases generally made in compliance with flood-control criteria or dam safety criteria. 

Uncontrolled spills are unplanned releases that occur 

when there is no reservoir storage capacity. In uncontrolled spills at reservoirs where river outlet works 

exist, reservoir inflows exceed the capacity of the river 

outlet works and water passes over the spillway without 

going through river outlet works.

spring filling season. The period when the reservoirs can be 

filled with spring runoff up to maximum allowable 

storage capacity.

supplemental storage water. Also referred to as adverse-tocanal water, this term refers to the first 25,000 acre-ft 

of water stored (or, if a lesser quantity is stored, then 

such lesser quantity) in Boca Reservoir during any year 

commencing October 1 and ending September 30 of the 

following year.

Tahoe-Prosser Exchange water (TPEW). Water stored in 

Prosser Creek Reservoir in accordance with the TahoeProsser Exchange Agreement that is classified as Lake 

Tahoe storage and used to maintain Floriston rates in 

conjunction with minimum releases from Lake Tahoe.

threshold volume. Daily storage volumes specified as 

constraints to mandatory exchange criteria in draft 

TROA and as constraints to several miscellaneous 

operations simulated by the operations model. The 

threshold volumes provide for the safety of stored, 

re-stored, or exchanged water from the threat of reservoir spill when reservoir volumes are large or of limited 

outlet capacity, recreation potential, or water category 

availability when reservoir volumes are small.

transfer. A mechanism in draft TROA for establishing 

storage of certain credit water categories in a reservoir. 

Transfers, unlike exchanges, involve only one reservoir, and the sum of the releases from all reservoirs may 
GLOSSARY 137

be modified as a result of this operation. In a transfer, 

there is a gain in volume for one water category, coincident with the loss of an equal volume of water from 

another water category in the same reservoir (see also 

instream flow transfer).

uncommitted water. Water stored in Prosser Creek Reservoir pursuant to its California water right and used for 

the purposes of the Tahoe-Prosser Exchange Agreement and the benefit of threatened and endangered fish 

of Pyramid Lake. Such water does not include dead 

storage and inactive storage, privately owned stored 

water, credit water, Tahoe-Prosser Exchange water, and 

project water from another reservoir. 

uncontrolled spill. See spill.

user’s control input (UCI). Computer file containing 

specifications that control HSPF simulations.

water balance. An accounting of the inflow to, outflow 

from, and storage in a hydrologic unit.

water-quality credit water (WQCW). As identified in 

draft TROA, water acquired and dedicated to waterquality purposes pursuant to the Truckee River Water 

Quality Agreement. 

water year. The 12-month period beginning October 1 and 

ending September 30, and designated by the calendar 

year of the ending date. 

wintertime cap. A prescribed, less-than-full reservoir 

storage level maintained usually from about November 

to March or April each year that provides adequate 

flood-control space to reduce the threat of downstream 

flood damage or provides space required by safety of 

dams criteria.
138 River and Reservoir Operations Model, Truckee River Basin, California and Nevada, 1998