RECLAMATION 


Managing Water in the West 


Colorado River Basin 

Water Supply and Demand Study 

Technical Report D-System Reliability Metrics 

U.S. Department of the Interior 

Bureau of Reclamation December 2012 
Mission Statements

The U.S. Department of the Interior protects America’s natural 

resources and heritage, honors our cultures and tribal communities, 

and supplies the energy to power our future. 

The mission of the Bureau of Reclamation is to manage, develop, 

and protect water and related resources in an environmentally and 

economically sound manner in the interest of the American public.
U.S. Department of the Interior

Bureau of Reclamation December 2012

Colorado River Basin 

Water Supply and Demand Study

Technical Report D — System 

Reliability Metrics

December 2012 D-iii

Contents

Page

1.0 Introduction ........................................................................................................... D-1

2.0 Approach for Metric Development ..................................................................... D-2

2.1 Step 1 – Resource Categories ..................................................................... D-2

2.2 Step 2 – Attribute of Interest ....................................................................... D-4

2.3 Step 3 – Location of Interest ....................................................................... D-4

2.4 Step 4 – Metric Types (Quantitative or Qualitative) .................................. D-5

2.5 Step 5 – Methods for Quantifying Metrics ................................................. D-5

2.6 Step 6 – Identify Reference Value (if appropriate) ..................................... D-6

2.6.1 Physical Constraint ......................................................................... D-6

2.6.2 Prescribed Condition ....................................................................... D-6

2.6.3 Estimated Condition........................................................................ D-6

2.6.4 Historical Condition ........................................................................ D-6

2.7 Step 7 – Documentation .............................................................................. D-6

2.8 Examples of Using the Step-wise Approach to Metric Development ........ D-7

2.8.1 Quantitative Type with Direct Measurement .................................. D-7

2.8.2 Quantitative Type with Indirect Measurement ............................... D-7

2.8.3 Qualitative Type.............................................................................. D-7

3.0 Sources of Data and Information Used in Metric Development ....................... D-8

4.0 Water Deliveries Metrics ...................................................................................... D-8

4.1 Metrics for the Consumptive Uses and Shortages Attribute of Interest ..... D-8

4.1.1 Tribal Water Rights......................................................................... D-9

4.2 Metrics for the Other Water Deliveries Attribute of Interest ...................... D-9

4.3 Metrics for the Socioeconomic Impacts of Shortages Attribute of Interest D-10

5.0 Electrical Power Resources Metrics .................................................................... D-10

5.1 Metrics for the Electrical Power Generated Attribute of Interest ............... D-11

5.2 Metrics for the Economic Value of Electrical Power Generated Attribute 

of Interest .................................................................................................... D-12

5.3 Metrics for the Available Generation Capacity Attribute of Interest ......... D-12

5.4 Metrics for the Impact on Power Rates Attribute of Interest ...................... D-12

5.5 Metrics for the Water Supply System Pumping Costs Attribute of 

Interest......................................................................................................... D-14

5.6 Metrics for the Impact on Basin Funds Attribute of Interest ...................... D-14

6.0 Water Quality Metrics .......................................................................................... D-14

6.1 Metrics for the Salinity Attribute of Interest ............................................... D-15

6.2 Metrics for the Sediment Transport Attribute of Interest ........................... D-15

6.3 Metrics for the Temperature Attribute of Interest ....................................... D-16

6.4 Other Water Quality Attributes of Interest ................................................. D-17

6.5 Metrics for Socioeconomic Impacts Related to Salinity Attribute of 

Interest......................................................................................................... D-17
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Water Supply and Demand Study

D-iv December 2012

7.0 Flood Control Metrics .......................................................................................... D-17

7.1 Metrics for the Flood Control Releases and Reservoir Spills Attribute of 

Interest......................................................................................................... D-17

7.2 Metrics for the Critical River Stages Related to Flooding Risk Attribute 

of Interest .................................................................................................... D-18

8.0 Recreational Resources Metrics .......................................................................... D-19

8.1 Metrics for the Shoreline Public Use Facilities Attribute of Interest.......... D-19

8.2 Metrics for the River and Whitewater Boating Attribute of Interest .......... D-20

8.3 Other Recreational Attributes of Interest .................................................... D-22

8.4 Metrics for the Socioeconomic Impacts Attribute of Interest ..................... D-22

9.0 Ecological Resources Metrics ............................................................................... D-22

9.1 Metrics for Flows to Support Threatened and Endangered Species 

Attribute of Interest ..................................................................................... D-23

9.2 Metrics for Aquatic and Riparian Habitat Attribute of Interest .................. D-24

9.2.1 Instream Flow Rights ...................................................................... D-26

9.2.2 Cottonwood Recruitment Metric .................................................... D-26

9.2.3 Flow-Dependent Ecological Systems ............................................. D-28

9.3 Metrics for Wildlife Refuges and Fish Hatcheries Attribute of Interest ..... D-29

10.0 Summary and Limitations ................................................................................... D-30

11.0 References .............................................................................................................. D-33

Tables

D-1 Resource Categories and Attributes of Interest ................................................. D-4

D-2 Attribute of Interest: Other Water Deliveries.................................................... D-10

D-3 Attribute of Interest: Electrical Power Generated ............................................ D-11

D-4 Attribute of Interest: Available Generation Capacity ....................................... D-13

D-5 Attribute of Interest: Salinity .............................................................................. D-16

D-6 Attribute of Interest: Critical River Stages Related to Flooding ..................... D-18

D-7 Attribute of Interest: Shoreline Public Use Facility .......................................... D-19

D-8 Attribute of Interest: River and Whitewater Boating ....................................... D-22

D-9 Attribute of Interest: Flows to Support Threatened and Endangered 

Species ........................................................................................................ D-25

D-10 Attribute of Interest: Aquatic and Riparian Habitat ........................................ D-27

D-11 Attribute of Interest: Wildlife Refuges and Fish Hatcheries ............................ D-30
Technical Report D — System

Reliability Metrics

December 2012 D-v 

Figures

D-1 Approach for Metric Development ......................................................................... D-3

D-2 Study Area with Locations of Defined Metrics ...................................................... D-32

Appendices 

D1 Metrics Sub-Team Members

D2 Boating Flow Days Metrics

D3 Threatened and Endangered Species Metrics

D4 Cottonwood Recruitment Metrics 

D5 Estimated Conditions for Flow-Dependent Ecological Systems

D6 Estimated Conditions for Upper Basin Wildlife Refuges 

December 2012 D-vii

Acronyms and Abbreviations

2007 Interim Record of Decision for Colorado River Interim

Guidelines Guidelines for Lower Basin Shortages and Coordinated Operations for 

Lake Powell and Lake Mead 

2007 Interim Colorado River Interim Guidelines for Lower Basin

Guidelines Final Shortages and Coordinated Operations for Lake Powell

EIS and Lake Mead Final Environmental Impact Statement 

af acre-feet

AMP Adaptive Management Program 

Basin Colorado River Basin 

Basin States Colorado River Basin States 

CAP Central Arizona Project

cfs cubic feet per second

CRSS Colorado River Simulation System

DOI U.S. Department of the Interior 

EIS Environmental Impact Statement

EPA U.S. Environmental Protection Agency 

Forum Colorado River Basin Salinity Control Forum 

kaf thousand acre-feet

kafy thousand acre-feet per year

LCR MSCP Lower Colorado River Multi-Species Conservation Program 

M&I municipal and industrial 

maf million acre-feet

metrics system reliability metrics

Mexico United Mexican States

mg/L milligram(s) per liter

msl above mean sea level

MWh megawatt-hour 

NGS Navajo Generating Station

NWR National Wildlife Refuge

Partnership Ten Tribes Partnership

PBO Programmatic Biological Opinion
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Water Supply and Demand Study

D-viii December 2012

Reclamation Bureau of Reclamation

Recovery Upper Colorado River Endangered Fish Recovery Program and 

Programs .San Juan River Basin Recovery Implementation Program 

ROD Record of Decision

Secretary Secretary of the Interior

SNWA Southern Nevada Water Authority 

Study Colorado River Basin Water Supply and Demand Study 

TNC The Nature Conservancy

tribes federally recognized tribes

USACE U.S. Army Corps of Engineers

USFWS U.S. Fish and Wildlife Service 

Western Western Area Power Administration
December 2012 D-1 

Technical Report D — System Reliability 

Metrics

1.0 Introduction

The Colorado River Basin Water Supply and Demand Study (Study), initiated in January 2010, 

was conducted by the Bureau of Reclamation’s (Reclamation) Upper Colorado and Lower 

Colorado regions, and agencies representing the seven Colorado River Basin States (Basin 

States) in collaboration with stakeholders throughout the Colorado River Basin (Basin). The 

purpose of the Study is to define current and future imbalances in water supply and demand in 

the Basin and the adjacent areas of the Basin States that receive Colorado River water over the 

next 50 years (through 2060), and to develop and analyze adaptation and mitigation strategies to 

resolve those imbalances. The Study contains for major phases to accomplish this goal: Water 

Supply Assessment, Water Demand Assessment, System Reliability Analysis, and Development 

and Evaluation of Options and Strategies for Balancing Supply and Demand.

Spanning parts of the seven states of Arizona, California, Colorado, New Mexico, Nevada, Utah, 

and Wyoming, the Colorado River is one of the most critical sources of water in the western 

United States. The Colorado River is also a vital resource to the United Mexican States 

(Mexico). It is widely known that the Colorado River, based on the inflows observed over the 

last century, is over-allocated and supply and demand imbalances are likely to occur in the 

future. Up to this point, this imbalance has been managed, and demands have largely been met as 

a result of the considerable amount of reservoir storage capacity in the system, the fact that the 

Upper Basin States are still developing into their apportionments, and efforts the Basin States 

have made to reduce their demand for Colorado River water. 

Concerns regarding the reliability of the Colorado River system to meet future needs are even 

more apparent today. The Basin States include some of the fastest growing urban and industrial 

areas in the United States. At the same time, the effects of climate change and variability on the 

Basin water supply has been the focus of many scientific studies, which project a decline in the 

future yield of the Colorado River. Increasing demand, coupled with decreasing supplies, will 

certainly exacerbate imbalances throughout the Basin. 

It is against this backdrop that the Study was conducted to establish a common technical 

foundation from which important discussions can begin regarding possible strategies to reduce 

future supply and demand imbalances. The content of this report is a key component of that 

technical foundation and describes the system reliability metrics identified in the Study. System 

reliability metrics (metrics) are measures that indicate the ability of the Colorado River system to 

meet the needs of Basin resources1 under multiple future conditions. Metrics were used to 

measure (quantitatively or qualitatively) the potential impacts to Basin resources from current 

and future water supply and demand imbalances and to measure the effectiveness of options and 

strategies at resolving those imbalances. These results are described in Technical Report G – 

System Reliability Analysis and Evaluation of Options & Strategies.

 

1 Resources include water allocations and deliveries for municipal, industrial, and agricultural use; hydroelectric power generation; recreation; 

fish wildlife, and their habitats (including candidate, threatened, and endangered species); water quality including salinity; flow and water 

dependent ecological systems; and flood control.
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This report describes the approach used to develop the system reliability metrics and the set of 

metrics resulting from implementing that approach. Initially published in June 2011 under 

Interim Report No. 1 and then updated and reissued in February 2012, this report replaces these 

two previously published versions. There were no substantial changes or additions to the metrics 

since February 2012, although several metrics were changed from using a quantitative to 

qualitative measurement as a result of data and tool limitations and time constraints. 

2.0 Approach for Metric Development 

Metrics were developed through a collaborative process involving representatives of numerous 

organizations, including the Reclamation, the Basin States, U.S. Fish and Wildlife Service 

(USFWS), National Park Service, Western Area Power Administration (Western), federally 

recognized tribes (tribes), conservation and recreation organizations, water delivery contractors, 

contractors for the purchase of federal power, and others interested in the Basin. A Metrics 

Sub-Team, composed of representatives from some of these organizations, was established to 

carry out the task of metric development. The Metrics Sub-Team coordinated with points of 

contact designated by the other organizations, who provided data, information, and expertise 

critical to metric development. 

The Metrics Sub-Team members and the points of contact from the other organizations are listed 

in appendix D1 of this report.

The general approach used to develop the metrics is presented in figure D-1. As shown, metric 

development was a multi-step process, in which each metric presented in this report was fully 

defined by applying steps 1 through 7. In the subsequent sub-sections, the individual steps used 

to develop the metrics are described, and examples are provided to illustrate the development 

approach. 

2.1 Step 1 – Resource Categories

As stated in the Plan of Study (see Study Report, Appendix 1 – Plan of Study):

The Study will characterize current and future water supply and demand 

imbalances in the Basin and assess the risks to Basin resources. Resources include 

water allocations and deliveries consistent with the apportionments under the Law 

of the River; hydroelectric power generation; recreation; fish, wildlife, and their 

habitats (including candidate, threatened, and endangered species); water quality 

including salinity; flow and water-dependent ecological systems; and flood 

control. 

The following resource categories were developed to reflect these groups of identified resources:

• Water Deliveries

• Electrical Power Resources 

• Water Quality

• Flood Control 

• Recreational Resources

• Ecological Resources 
Technical Report D — System

Reliability Metrics

December 2012 D-3 

FIGURE D-1 

Approach for Metric Development
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Water Supply and Demand Study

D-4 December 2012

Socioeconomic impacts were not considered an independent resource category in the Study. 

Instead, socioeconomic impacts resulting from water supply and demand imbalances were 

considered within the principal resource categories, as appropriate. 

2.2 Step 2 – Attribute of Interest

An attribute is a specific property or trait that can be associated with a resource category. Several 

attributes were identified in each resource category that are informative when evaluating system 

reliability for that category. These attributes are presented in table D-1 by resource category.

TABLE D-1 

Resource Categories and Attributes of Interest 

Resource Category Attribute of Interest

Water Deliveries ● Consumptive Uses

1 and Shortages2

● Water Levels Related to Intake Facilities

● Socioeconomic Impacts Related to Shortages

Electrical Power Resources ● Electrical Power Generated

● Economic Value of Electrical Power Generated

● Available Generation Capacity

● Impact on Power Rates

● Water Supply System Pumping Costs

● Impacts on Basin Funds 

Water Quality ● Salinity

● Sediment Transport

● Temperature

● Other Water Quality Attributes

● Socioeconomic Impacts Related to Salinity

Flood Control ● Flood Control Releases and Reservoir Spills

● Critical River Stages Related to Flooding Risk

Recreational Resources ● Shoreline Public Use Facilities

● River and Whitewater Boating

● Other Recreational Attributes

● Socioeconomic Impacts Related to Recreation

Ecological Resources ● Threatened and Endangered Species

● Aquatic and Riparian Habitats

● Wildlife Refuges and Fish Hatcheries

1 Consumptive use is water used, diminishing the available supply. 

2 Shortage is unmet demand. 

 Note that Demand is water needed to meet identified uses. 

2.3 Step 3 – Location of Interest

Specific locations were selected where a metric would be evaluated, including several points 

along the Colorado River, its major tributaries, and at selected facilities such as mainstem 

reservoirs or power generation facilities. Although at this step any location within the Study Area 

(the hydrologic boundaries of the Colorado River Basin within the United States, plus the 

adjacent areas of the Basin States that receive Colorado River water) could have been selected, 

the spatial and temporal scales of available data (through simulation modeling and other sources) 

restricted the locations and/or the analysis that could be performed at a specific location. 
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December 2012 D-5 

The Colorado River Simulation System (CRSS) is the primary modeling tool that was used in the 

Study. It simulates the operation of the major Colorado River system reservoirs on a monthly 

time step and provides information regarding the projected future state of the system in terms of 

output variables. Outputs include the amount of water in storage, reservoir elevations, releases 

from the dams, the amount of water flowing at various points in the system, the total dissolved 

solids content, and diversions to and return flows from water users in the system. Twelve Upper 

Basin and Lower Basin reservoirs are modeled in CRSS: Fontenelle, Flaming Gorge, Starvation 

(a representation of several reservoirs within the Central Utah Project in western Utah), Taylor 

Park, Blue Mesa, Morrow Point, Crystal, Navajo, Powell, Mead, Mohave, and Havasu. 

Approximately 250 diversions and return flows are represented in CRSS. Natural flow is input to 

the model at 29 locations in the Basin (20 in the Upper Basin upstream of and including the Lees 

Ferry, Arizona gaging station, and nine below Lees Ferry, Arizona, including the Paria River and 

other inflow points in the Lower Basin).2

2.4 Step 4 – Metric Types (Quantitative or Qualitative)

Metrics were evaluated in either a quantitative or qualitative fashion. A metric was evaluated

quantitatively if: a) direct evaluation was possible using output from CRSS or results from postprocessing of CRSS output data; or b) an indicator of the attribute of interest at the specified 

location could be developed, based on output from CRSS or post-processing of CRSS output 

data.

If a particular attribute of interest could not be represented either directly in CRSS or through the 

development of an indicator, the potential performance of an attribute under various future 

scenarios was discussed qualitatively. Qualitative metrics bypass steps 5 and 6 and are 

documented in step 7. 

Qualitative discussion vary in detail depending on the level of information available. In some 

cases, quantitative model results were used to qualitatively assess the metrics using known 

system variables, e.g., reservoir elevations or streamflow. Although these metrics were evaluated 

in a qualitative manner in the Study, information developed in the Study may be used to guide 

quantitative assessments in future studies.

2.5 Step 5 – Methods for Quantifying Metrics

If a metric was identified as quantitative, a specific method for quantifying that metric was 

selected. Two methods for quantifying metrics were identified:

1. Reference Value Method: In many cases, comparing the attribute of interest at a particular 

location to a reference value (that may also be specific to the location of interest) informed

the assessment of system reliability. The method used to quantify the reference value then 

defined the method for quantifying the metric. Because the Study addressed a wide range of 

Basin resources, no single method for quantifying reference values was applicable to all 

metrics. Therefore, four different methods for quantifying reference values (and the 

subsequent metrics) were defined, as outlined below. 

 

2 Natural flow represents the flow that would have occurred at the location had depletions and reservoir regulation not been present upstream of 

that location. However, CRSS uses historical inflows based on U.S. Geological Survey streamflow records as estimates of natural flows for the 

Paria, Little Colorado, Virgin and Bill Williams Rivers. In addition, the Gila River is not included in CRSS. See Technical Report C – Water 

Demand Assessment, Appendix C11 – Modeling of Lower Basin Tributaries in the Colorado River Simulation System, for more detail. 
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Water Supply and Demand Study

D-6 December 2012

2. Relative Comparison Method: In some cases, an informative reference value did not exist for 

an attribute of interest. In such cases, the attribute of interest was strictly compared across the 

range of future water supply and demand scenarios. For example, metrics related to flood 

control releases or spills to manage reservoir levels may not have an associated reference 

value. In this case, metrics related to flood control releases or spills were quantified through a 

comparative analysis between future scenarios.

2.6 Step 6 – Identify Reference Value (if appropriate)

If the reference value method was selected in step 5, an appropriate reference value was then

selected. As described below, reference values could be based on physical constraints in the 

Basin, prescribed conditions, estimated resource needs, or historical or simulated conditions. 

2.6.1 Physical Constraint

Some metrics were quantified based on physical constraints in the river system. For example, the 

elevation of a facility’s water intake represents a physical constraint and provided the reference 

value that was used to quantify a metric in the Water Deliveries resource category.

2.6.2 Prescribed Condition

Some metrics were quantified based on specific values that are prescribed in contracts and 

agreements between resource management agencies, Environmental Impact Statement (EIS) 

Records of Decision (ROD), Biological Opinions issued by USFWS, and other regulatory 

actions. For example, recommendations of flows for endangered species (as defined in a 

Biological Opinion) provided reference values that were used to quantify metrics in the 

Ecological Resources resource category. 

2.6.3 Estimated Condition

Some metrics were quantified using an estimated condition for a water-dependent resource. 

Estimated conditions typically were developed by interested stakeholders or were defined within 

published reports and articles. For example, the projected demand for municipal, industrial, and 

agricultural water at a specific location was used to quantify metrics in the Water Deliveries 

resource category. 

2.6.4 Historical Condition

Some metrics were quantified based on values derived from historical conditions, particularly 

when it was important to measure the change in the attribute of interest over time. Historical 

values were based on recorded information, where the period of interest may have covered a 

relatively short timeframe (such as the last 10 years) or a longer timeframe (such as the last 

100 years or longer). For example, the minimum hydroelectric generation data over the past 10 

years provided reference values that were used to quantify a metric in the Electrical Power 

Resources resource category. 

2.7 Step 7 – Documentation

Metric definitions developed by applying steps 1 through 6 are documented in tabular fashion. 

The tables, which appear by attribute of interest throughout the report, list the information shown 

as step 7 in figure D-1. 
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December 2012 D-7 

2.8 Examples of Using the Step-wise Approach to Metric Development

The following discussion provides examples of the approach to implementing each step for 

metric development. The examples were specifically selected to show the different paths that 

may be taken when following the steps shown in figure D-1. 

2.8.1 Quantitative Type with Direct Measurement

In the resource category Electrical Power Resources, electrical power generated was identified as 

an attribute of interest. In step 3, the locations of interest were identified as the major Colorado 

River Storage Project power plants3 in the Upper Basin and Hoover Dam and the Parker-Davis 

project in the Lower Basin. In step 4, it was determined that the attribute of interest is directly 

measurable at the selected locations (CRSS simulates power generation at each of the identified 

locations); therefore, a quantitative-type metric was used for this attribute. 

In step 5, the reference value method was selected based on stakeholder input as the method for 

metric quantification. In step 6, the reference values vary by location. For example, the Historical 

Condition method was used at Hoover with the minimum power generation over the previous 10 

years selected as the reference value, whereas the Prescribed Condition method was selected for 

use in the Upper Basin with the firm power contract utilized as the reference value.

2.8.2 Quantitative Type with Indirect Measurement

In the resource category Ecological Resources, aquatic and riparian habitat was identified as an 

attribute of interest. In step 3, the locations of interest were identified based on stakeholder input. 

In step 4, it was determined that this attribute could not be directly measured (CRSS does not 

represent specific ecological and biological characteristics related to aquatic and riparian 

habitat). However, flow conditions at the monthly time step simulated in CRSS could be an 

indication of the functioning of aquatic and riparian habitat, thus providing an indirect 

measurement for this attribute.

In step 5, the reference value method was chosen at locations where in-stream flow water rights 

exist (another reference value method was used at several other locations where such rights do 

not exist). In step 6, the minimum target flows defined by instream flow water rights (such as 

those held by the Colorado Water Conservation Board) were selected as the reference value 

using the prescribed conditions method. 

2.8.3 Qualitative Type

In the resource category Recreational Resources, socioeconomics related to recreation was

identified as an attribute of interest based on stakeholder input. In step 3, the locations of interest 

were identified throughout the Basin where there is a significant economic benefit from 

recreation. In step 4, it was determined that this attribute could not be directly measured and 

furthermore, an indirect measurement was not possible in the Study (an economic analysis would 

require additional economic data and modeling that are not currently available). Therefore, a 

qualitative-type metric was selected for this attribute. 

 

3 Power plants at Lake Powell, Flaming Gorge, Blue Mesa, Morrow Point, and Crystal Reservoirs.
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Water Supply and Demand Study

D-8 December 2012

3.0 Sources of Data and Information Used in Metric 

Development

Data sources used in the development of the system reliability metrics included recently 

published reports relevant to Basin water resources and data and information provided by 

representatives of organizations either participating directly in the Metrics Sub-Team or as 

designated point of contact. The use of these data and information sources was referenced where 

appropriate, and a list of these sources is provided in the References section of this report. 

4.0 Water Deliveries Metrics 

The water deliveries attributes of interest are: 

• Consumptive uses and shortages

• Other water deliveries

• Socioeconomic impacts related to shortages 

4.1 Metrics for the Consumptive Uses and Shortages Attribute of Interest

Consumptive uses and shortages metrics were evaluated at locations throughout the Basin where 

demand nodes exist within CRSS. All consumptive uses and shortages metrics are quantitative 

metrics whose reference values are defined by the Estimated Condition quantification method. 

Specifically, the Estimated Condition reference values are based on demand projections for the 

particular water demand scenario being modeled (see Technical Report C – Water Demand 

Assessment).

CRSS simulates shortages differently for the Upper and Lower Basin. For the Lower Basin, 

CRSS computes shortages as specified in the Colorado River Interim Guidelines for Lower 

Basin Shortages and Coordinated Operations of Lakes Powell and Mead (2007 Interim 

Guidelines) (U.S. Department of the Interior [DOI], 2007) through 2026. Beyond 2026, 

additional modeling assumptions were made: 1) the 2007 Interim Guidelines were assumed to 

extend through 2060, and 2) the operations of Lake Powell and Lake Mead reverted to the No 

Action Alternative in the Colorado River Interim Guidelines for Lower Basin Shortages and 

Coordinated Operations of Lakes Powell and Mead Final Environmental Impact Statement

(2007 Interim Guidelines Final EIS) (Reclamation, 2007) through 2060. Both assumptions4 were 

used in the system reliability analysis. 

The quantified demand scenarios in the Lower Basin include demands above the Lower Division 

states’ basic apportionments. As part of the system reliability analysis, select options were 

implemented to, in part, reduce demands above apportionment. Therefore, the remaining 

demands above Lower Division States’ basic apportionment were included as a metric. For the 

Upper Basin, CRSS does not simulate the complex water rights systems in each state that are

needed to model shortages to individual water right holders. At any particular node (location), 

the model tracks shortages when the flow is insufficient to meet the local demands. Such a broad 

simulation greatly underestimates shortages for the major Upper Basin tributaries; however, 

given the relative comparison nature of the Study, reporting shortages as modeled can still 

provide insights to benefits or reductions to deliveries within the Upper Basin. An area identified 

 

4 Technical Report G – System Reliability Analysis and Evaluation of Options and Strategies, Appendix G2 – Colorado River Simulation System 

Modeling provides a detailed description of these and other CRSS modeling assumptions used in the system reliability analysis.
Technical Report D — System

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December 2012 D-9 

for future work after the Study includes enhancements to CRSS to better estimate Upper Basin 

shortages. Additionally, the 10-year moving aggregate flow volume at Lee Ferry is tracked in 

CRSS. Anytime the 10-year flow volume is less than 75 million acre-feet (maf), the shortfall is 

reported as a Lee Ferry deficit.

4.1.1 Tribal Water Rights

The assessment of the ability of the system to satisfy tribal water rights, including tribal Central 

Arizona Project (CAP) entitlements, was not explicitly evaluated for two reasons. First, model 

limitations described previously with respect to not simulating water rights in the Upper Basin 

limited the ability to track deliveries to tribes in the Upper Basin. Second, at the request of the 

Ten Tribes Partnership (Partnership), opportunities to conduct a future joint planning study with 

Reclamation that will focus on tribal issues are being explored. It is envisioned that through this 

future study, coupled with CRSS enhancements, a detailed assessment of the ability of the 

system to satisfy tribal water rights would be performed. 

With respect to tribes with CAP entitlements, CRSS aggregates all deliveries to CAP users 

into one node, with the exception of the Ak-Chin and Salt River Pima-Maricopa Indian 

Communities. However, the ability of the system to deliver water to tribes with 

CAP entitlements could be determined based on CAP's ability to divert a sufficient 

quantity of water to meet these entitlements. Therefore, a qualitative discussion on the ability 

of the system to satisfy tribal water rights was included in the Study. 

4.2 Metrics for the Other Water Deliveries Attribute of Interest

There are several other attributes of interest related to water deliveries that are important to 

various stakeholders. These attributes of interest were evaluated at locations other than where 

CRSS demand nodes exist (e.g., reservoir elevations) and were therefore placed in this category. 

These include flows arriving at Morelos Diversion Dam, the Navajo Indian Irrigation Project 

Diversion at Navajo Reservoir, and Lake Mead at elevation 1,000 feet above mean sea level 

(msl). 

CRSS assumes a delivery to Mexico of 1.5 maf per year, with additional deliveries of up to 

200,000 acre-feet (af) per year when Lake Mead is in flood control operations. Reductions in 

deliveries to Mexico are simulated consistent with the modeling assumptions noted in the 2007 

Interim Guidelines Final EIS (Reclamation, 2007)5. CRSS extends to just south of the Northerly 

International Boundary to include the Morelos Diversion Dam (Mexico’s principal diversion) 

and accounts for the entire 1944 Treaty delivery at that point. Flows arriving at Morelos 

Diversion Dam in excess of the 1944 Treaty delivery were tracked as a relative comparison 

metric under the other water deliveries attribute of interest.

Water is extracted from the Colorado River at numerous locations using instream diversion 

facilities or reservoir intake structures. Intake structures cannot operate if reservoir water levels 

are below their respective minimum service elevations. Therefore, the frequency of potential 

conditions in which water levels drop below minimum intake service elevations are important 

measures of system reliability. The Navajo Indian Irrigation Project Diversion at Navajo 

 

5 Reclamation’s modeling assumptions are not intended to constitute an interpretation or application of the 1944 Treaty or to represent current 

U.S. policy or a determination of future U.S. policy regarding deliveries to Mexico. The United States will conduct all necessary and 

appropriate discussions regarding the proposed federal action and implementation of the 1944 Treaty with Mexico through the International 

Boundary and Water Commission in consultation with the Department of State.
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Reservoir was identified as an intake where water level data are critical and was quantitatively 

evaluated with a physical constraint of 5,990 feet msl. This is the minimum allowable water level 

where diversion facilities are still operable.

Elevation 1,000 feet msl in Lake Mead is important to water deliveries for multiple reasons. At 

elevation 1,000 feet msl, there are less than 4.5 maf of water remaining in Lake Mead. According 

to the 2007 Interim Guidelines (DOI, 2007), the Secretary of the Interior (Secretary) shall consult 

with the Basin States whenever Lake Mead is below elevation 1,025 feet msl and is projected to 

fall below 1,000 feet msl, to discuss further measures that may be undertaken at such time. This 

elevation is also of interest to the operation of the Southern Nevada Water Authority’s (SNWA) 

intake structures in Lake Mead. Currently, 1,000 feet msl is the minimum allowable water level 

at which the intake facilities are still operable. For these reasons, Lake Mead elevation at 

1,000 feet msl was evaluated quantitatively with its reference value defined by an Estimated 

Condition. All metrics for the other water deliveries attributes of interest are shown in table D-2. 

TABLE D-2 

Attribute of Interest: Other Water Deliveries

Location Metric Type Quantification Method

Reference Value

(feet msl)

Morelos Diversion Dam

Quantitative

Relative Comparison Not Applicable

Navajo Indian Irrigation Project Diversion 

at Navajo Reservoir Physical Constraint 5,990

Lake Mead Estimated Condition 1,000

4.3 Metrics for the Socioeconomic Impacts of Shortages Attribute of Interest

To quantitatively evaluate socioeconomic impacts of shortage conditions, an economic model 

that relates delivery shortages to employment, income, and tax revenue would be required. This 

model would need to be regional in nature and have the capability to allocate shortages among 

agricultural and municipal and industrial (M&I) users. Economic models of this type have been 

built and used in the past (USFWS, 1994). However, updating these models to evaluate 

socioeconomic impacts related to delivery shortages is beyond the scope of the Study. For this 

reason, socioeconomic impacts related to shortages is discussed in a qualitative manner. 

5.0 Electrical Power Resources Metrics 

The electrical power resources attributes of interest are:

• Electrical power generated 

• Economic value of electrical power generated

• Available generation capacity

• Impact on power rates

• Water supply system pumping costs 

• Impacts on Basin funds 
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December 2012 D-11

5.1 Metrics for the Electrical Power Generated Attribute of Interest

Hydroelectric power generation is directly related to the head on the generating units and the 

quantity of water flowing through the turbines. The net effective head is the difference between 

the water level elevation of the reservoir behind a dam and in the tail water below the dam. The 

net effective head and flow are the two variables that influence hydroelectric power generation of 

the power plant, measured in megawatts. 

Hydroelectric power is generated at numerous locations throughout the Basin. Hydropower 

plants in the Upper Basin that are modeled in CRSS include the Colorado River Storage Project 

facilities located at the Lake Powell, Flaming Gorge, Blue Mesa, Morrow Point, and Crystal 

reservoirs, as well as the power plant at Fontenelle. Hydropower plants in the Lower Basin 

include the Hoover, Parker, Davis, and Headgate Rock facilities. Metrics were developed to 

assess the impact to electrical power generated from these facilities (or an aggregate of) due to 

their inclusion in CRSS. Headgate Rock Dam is not explicitly modeled in CRSS. However, 

because it is located just downstream of Parker Dam, the releases from Parker Dam were used to 

qualitatively assess the effects on power generation at Headgate Rock Dam using the relative

comparison method. There are numerous other hydropower plants located throughout the Basin. 

Metrics for these other hydropower facilities were not developed; however, readers who have a 

particular interest in other hydropower plants may be able to use the results from facilities 

evaluated in the Study as indicators for facilities not evaluated in the Study. 

Western is a power marketing administration responsible for marketing and transmitting 

electricity from multi-use water projects in the central and western United States. Western 

markets power from all Upper Basin power plants as a single power resource; therefore, 

electrical power generated by Upper Basin facilities was measured by a single aggregate metric.

In the Lower Basin, power is marketed separately for Hoover, the Parker-Davis Project, and 

Headgate Rock hydropower plants. Individual metrics were used to measure electrical power 

generated at these three locations. Table D-3 summarizes the metrics related to electric power

generated.

TABLE D-3 

Attribute of Interest: Electrical Power Generated

Location Metric Type

Quantification 

Method

Reference Value

Megawatt-hours 

(MWh) per year

Upper Basin Power Plants1

Quantitative – Direct

Prescribed Condition 4,948,7803 

Hoover Power Plant Historical Condition 3,426,1494 

Parker and Davis Power Plants2 Relative Comparison Not Applicable

Headgate Rock Power Plant Qualitative Relative Comparison Not Applicable

1 Upper Basin power plants include: Fontenelle, Flaming Gorge, Blue Mesa, Morrow Point, Crystal, and Glen 

Canyon.

2 Parker and Davis power plants were aggregated for the purposes of the Study. Power marketed through the 

Parker-Davis Project consists of all of the power generated from Davis plus half the power generated from 

Parker, but this metric presents the entire power generated from both hydropower facilities.

3 Reference value is the firm power contract for all Upper Basin power plants.

4 Reference value is the minimum power generation that occurred during the 10-year reference period of 2000 

through 2009 selected by Western.
Colorado River Basin

Water Supply and Demand Study

D-12 December 2012

5.2 Metrics for the Economic Value of Electrical Power Generated Attribute of 

Interest

Western markets power and administers power contracts for power produced at Reclamationowned and -operated hydropower facilities. The economic value of electrical power produced by 

these facilities is an important measure of system reliability. CRSS calculates the quantity of 

electrical power generated, and this information could be used in post-processing analyses to 

calculate economic value. However, the necessary steps to compute the economic value of the 

electrical power generated was beyond the scope of the Study. Therefore, a qualitative analysis 

of the economic value was included in the Study. 

5.3 Metrics for the Available Generation Capacity Attribute of Interest

Available generation capacity is a measure of the maximum amount of power that could be 

produced based on reservoir level and the physical design capacity of the hydropower facility. 

The available generation capacity affects hydropower ramping operations and overall power 

system reliability. Ramping is the change in water release from the reservoir that passes through 

the turbine to meet the electrical load. Both scheduled and unscheduled ramping occur to meet 

variations in real-time electrical loads. Western depends on ramping operations to ensure 

electrical service reliability and an uninterrupted power supply. The higher the available 

generation capacity, the more flexibility is available in the ramping operations. Therefore, 

available generation capacity is an important attribute of electrical power resources.

Historical information about available generation capacity (by month) was evaluated. Available 

generation capacity in future scenarios was compared to this historical reference, both monthly 

and annually (computed by summing the monthly values). Table D-4 summarizes the metrics 

related to available generation capacity.

5.4 Metrics for the Impact on Power Rates Attribute of Interest

Western has contracts in place to deliver specified amounts of power to its customers in the 

Upper Basin. If Upper Basin hydroelectric power facilities cannot produce the contracted power 

during any given month, Western must buy energy at the market rate to make up these shortfalls. 

The amount of power that must be purchased at the market rate directly affects the long-term 

power rates to contract customers. In the Lower Basin, firm contract power delivery agreements 

are limited to the Parker-Davis Project. Although Western does not have firm contract power 

delivery agreements for power produced from the Hoover power plant, decreased power plant 

production would require increased purchases of market rate power by contract customers. 

Therefore, power generation at all power plants could affect power rates, regardless of whether 

they have firm contract power delivery agreements.

Varying degrees of power generation shortfalls would occur under the various future scenarios 

evaluated. Understanding the impacts of potential generation shortfalls (which may occur with or 

without the implementation of options and strategies) to power rates is an attribute of interest for 

electrical power resources. Power rates paid by contract customers are not directly measurable by 

CRSS, and updating third-party models to perform this analysis is outside the scope of the Study. 

Therefore, a qualitative evaluation of the relationship between generation shortfalls and power 

rates was included in the Study.
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December 2012 D-13

TABLE D-4 

Attribute of Interest: Available Generation Capacity

Location Metric Type

Quantitative 

Method

Reference Value2 

(all values are in MWh per month)

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep 

Upper Basin1

Quantitative – 

Direct

Historical 

Condition

769 672 757 781 874 869 856 783 688 677 670 795

Hoover 856 848 982 889 913 1,029 1,248 1,357 1,233 1,353 1,265 1,107

Parker and Davis 275 213 203 198 224 269 270 317 318 319 318 320

1 Upper Basin power plants include: Fontenelle, Flaming Gorge, Blue Mesa, Morrow Point, Crystal, and Glen Canyon.

2 Reference values are the minimum available generation capacity that occurred during the selected 10-year reference period of 2000 through 2009. 
Colorado River Basin

Water Supply and Demand Study

D-14 December 2012

5.5 Metrics for the Water Supply System Pumping Costs Attribute of Interest

Utilities that pump water to their service areas may be affected by increased energy requirements 

for pumping associated with lower water levels in source water reservoirs. Examples include the 

Salt River Project, which extracts cooling water from Lake Powell for the Navajo Generating 

Station (NGS); SNWA, which diverts water from Lake Mead; the Metropolitan Water District of 

Southern California, which diverts water from Lake Havasu through the Colorado River 

Aqueduct; and the Central Arizona Water Conservation District, which also diverts water from 

Lake Havasu to supply the CAP delivery area. Current operating practices maintain relatively 

constant lake levels in Lake Havasu regardless of hydrologic conditions. Pumping costs for the 

Colorado River Aqueduct and CAP, therefore, do not fluctuate significantly with hydrologic 

conditions. For this reason, quantitative metrics at these locations were deemed unnecessary. 

Alternatively, wide fluctuations in water levels in Lake Mead and Lake Powell could affect 

pumping costs for water providers that pump from these reservoirs. For example, SNWA uses 

variable-speed pumping equipment that has the ability to adjust power usage with varying lake 

levels. Therefore, the effects of varying lake levels on SNWA pumping costs were included as a 

qualitative metric. Conversely, the Salt River Project uses constant speed pumping equipment for 

the NGS, which is lower-cost equipment, but does not have the ability to adjust power usage 

with lake levels. Therefore, electrical costs for pumping water to the NGS will not fluctuate 

significantly with hydrologic conditions. For this reason, metrics for the NGS were deemed 

unnecessary. 

5.6 Metrics for the Impact on Basin Funds Attribute of Interest

A portion of the revenue from the sale of power generated at hydropower facilities is used to 

finance Basin funds, which include the Upper Colorado River Basin Fund, Lower Colorado 

River Basin Development Fund, Colorado River Dam Fund, and the Parker-Davis Account. 

These funds provide revenue for a variety of uses, including the operation and maintenance of 

hydroelectric facilities and associated dams and/or repayment of specific Basin projects or 

programs. Western is responsible for marketing and collecting payment for power and transfer of 

revenues to Basin funds. A change in the amount of available capacity or energy generation 

could potentially affect the revenue derived from the sale of power and the contributions to the 

Basin funds. 

The impact to Basin funds depends on numerous factors, including amount of power sold, 

economic value of that power, and revenue allocation agreements. CRSS does not directly 

calculate any of these quantities. However, it does calculate hydropower generation, and varying 

degrees of hydropower generation shortfalls would occur under the various future scenarios 

evaluated. Therefore, qualitative metrics were used to relate power generation shortfalls to 

increased risk of funding shortfalls. 

6.0 Water Quality Metrics 

The water quality attributes of interest are: 

• Salinity

• Sediment transport 

• Temperature
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December 2012 D-15

• Other water quality attributes

• Socioeconomic impacts related to salinity

6.1 Metrics for the Salinity Attribute of Interest

The U.S. Environmental Protection Agency (EPA) suggested the development of water quality 

criteria for salinity in the Basin following passage of the Federal Water Pollution Control Act 

(Clean Water Act) of 1972. In response, the Basin States formed the Colorado River Basin 

Salinity Control Forum (Forum) to develop numeric salinity criteria and an implementation plan 

to ensure compliance while allowing the Basin States to continue to develop their Compactallocated water. The Forum recommends, the States adopt, and EPA approves the flow-weighted 

average annual numeric salinity criteria for three locations on the lower Colorado River (table D5). The criteria, first established in 1975, are reviewed every 3 years; the latest review was 

completed in 2011. 

Minute No. 242 of the International Boundary and Water Commission provides that the United 

States shall adopt measures to ensure that the approximately 1.36 maf delivered to Mexico 

upstream of Morelos Dam have an annual average salinity of no more than 115 parts per million 

±30 parts per million over the average annual salinity of Colorado River waters which arrive at 

Imperial Dam. Real-time water operations ensure that the salinity differential is met each year. 

CRSS performs salinity calculations for select locations in the Lower Basin, including below 

Hoover Dam, below Parker Dam, and at Imperial Dam. Therefore, quantitative metrics for 

salinity were identified at these locations based on the Forum-developed numeric salinity 

criteria. CRSS does not include the complex surface water/groundwater interactions in the 

Yuma, Arizona region from Imperial Dam to the Northerly International Boundary. 

Although numeric salinity criteria in the Upper Basin and at other locations in the Lower Basin 

have not been developed, salinity levels are monitored at 17 locations throughout the Basin by 

the Colorado River Basin Salinity Control Program6 in cooperation with the U.S. Geological 

Survey, with 15 of those locations being in the Upper Basin. These locations are represented in 

CRSS and are used as relative comparison metrics to compare salinity levels across scenarios. 

Table D-5 summarizes the Basin salinity metrics and the associated quantification methods and 

reference values. 

6.2 Metrics for the Sediment Transport Attribute of Interest

Reservoirs behind dams throughout the Basin retain the vast majority of the inflowing sediment. 

Following the completion of the dams, large sediment deltas formed near the inflow areas. When 

the reservoirs are drawn down during droughts, rivers cut new channels through the sediment 

deltas to reach the reservoirs. Generally the greater the reservoir drawdown, the greater the 

sediment delta headcut and the finer the sediment exposed. The resuspended sediments have a 

significant oxygen demand and also temporarily release nutrients, which can result in greater 

algal growth. 

 

6 Authorized through Public Laws 93-320, 98-569, 104-20, 104-127, 106-459, 107-171, and 110-246.
Colorado River Basin

Water Supply and Demand Study

D-16 December 2012

TABLE D-5 

Attribute of Interest: Salinity

Location Metric Type Quantification Method

Reference Value1 

milligram(s) per 

liter (mg/L)

Below Hoover Dam

Quantitative Prescribed Condition

723

Below Parker Dam 747

At Imperial Dam 879

Colorado River near Glenwood Springs, CO

Quantitative Relative Comparison Not Applicable

Colorado River near Cameo, CO

Gunnison River near Grand Junction, CO

Dolores River near Cisco, CO

Colorado River near Cisco, CO

Green River at Green River, WY

Green River near Greendale, UT

Yampa River near Maybell, CO

Duchesne River near Randlett, UT

White River near Watson, UT

Green River at Green River, UT

San Rafael River near Green River, UT

San Juan River near Archuleta, NM

San Juan River near Bluff, UT

Colorado River at Lees Ferry, AZ

Colorado River near Grand Canyon, AZ

Virgin River near Littlefield, AZ

1 For locations with numeric criteria developed by the Forum, salinity is measured as flow-weighted average 

annual total dissolved solids at designated locations on the Colorado River. 

Riverine sediment transport, therefore, can have recreation and biological resource impacts. 

Sediment transport in the Basin is not modeled by CRSS. Although sediment transport models 

exist for some locations, there is no Basin-wide sediment transport model. The relation between 

beach formation in reservoirs and within river reaches, and the recreational experience was

addressed qualitatively in the Recreational Resources resource category. 

6.3 Metrics for the Temperature Attribute of Interest

Impounding water in reservoirs affects the water temperature of dam releases as a result of 

thermal stratification. During the summer, the surface layers of the reservoirs are typically warm 

as the result of inflows, ambient air temperature, and solar radiation. Conversely, lower reservoir 

layers remain cooler year-round. For these reasons, water temperatures downstream of reservoirs 

are influenced by reservoir water level, release facility location, and release volumes. 
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December 2012 D-17

Water temperature can affect the health of flow- and water-dependent species in the Basin. 

Water temperature is not modeled by CRSS and therefore was not quantitatively evaluated in the 

Study. 

6.4 Other Water Quality Attributes of Interest

Numerous other water quality attributes are of interest to various stakeholders. Water quality 

attributes such as selenium, dissolved oxygen, nutrients, algae, metals, perchlorate, and emerging 

contaminants were qualitatively addressed in the Study. 

6.5 Metrics for Socioeconomic Impacts Related to Salinity Attribute of 

Interest

Economic impacts of elevated salinity levels in the Colorado River and its tributaries are not 

calculated by CRSS. Reclamation and the Forum use the Lower Colorado Salinity Damage 

Model to estimate economic damages that result from elevated salinity levels in the Basin. 

Economic damages estimated by this model include changes to crop yields related to agricultural 

water use and impacts due to M&I water use, such as reduced useful life of water-dependent 

appliances, increased use of water-softening chemicals, and increased purchase of bottled water. 

The necessary steps to run this economic model using all of the Study’s results is beyond the 

scope of the Study. Therefore, the economic effects due to salinity levels were included as a 

qualitative metric. In addition, EPA has set voluntarily guidelines for salinity levels in drinking 

water supplies with a target of less than 500 mg/L, measured as total dissolved solids. Some 

water providers, notably the Metropolitan Water District of Southern California, blend Colorado 

River water with other water supplies that have lower salinity in an attempt to meet these 

guidelines. When salinity levels are elevated in the Colorado River, the ability of M&I water 

suppliers to meet their target blended salinity is diminished. Qualitative discussions of this item 

were provided in addition to the discussion of economic damages.

7.0 Flood Control Metrics

The flood control attributes of interest are: 

• Flood control releases and reservoir spills 

• Critical river stages related to flooding risk 

7.1 Metrics for the Flood Control Releases and Reservoir Spills Attribute of 

Interest

The term “flood control releases” is unique to the operation of Hoover Dam because Lake 

Mead’s annual release is governed by strict flood control regulations. The current flood control 

regulations were implemented under the Field Working Agreement between Reclamation and the 

U.S. Army Corps of Engineers (USACE) for Flood Control Operation of Hoover Dam and Lake 

Mead, signed February 8, 1984 as prescribed by the 1982 Water Control Manual for Flood 

Control, Hoover Dam and Lake Mead, Colorado River (USACE, 1982). Under this agreement, 

criteria are set forth to meet system space requirements from August through December and to 

determine reservoir releases from January through July. During all months of the year, the top 

1.5 maf of space (the space above elevation 1,219.6 feet msl) is reserved exclusively for flood 
Colorado River Basin

Water Supply and Demand Study

D-18 December 2012

control purposes. Lake Mead is considered to be under flood control operations when releases in 

excess of those necessary to meet water use demands are required to make this flood control 

space available.

Reclamation also makes “spill avoidance” decisions at other reservoirs that it manages and 

operates. The primary objective of spill avoidance is to minimize the amount of water that does 

not pass through hydropower facilities. Reclamation typically defines a spill as any amount of 

water that does not pass through the hydropower facilities, including water that is diverted 

around the dam through bypass piping, as well as water that physically passes over the dam 

spillway.

CRSS was used to quantify the frequency and magnitude of both flood control releases at Lake 

Mead and reservoir spills. These metrics were quantified at Fontenelle, Flaming Gorge, Blue 

Mesa, Lake Powell, and Lake Mead using the relative comparison quantification method. 

7.2 Metrics for the Critical River Stages Related to Flooding Risk Attribute of 

Interest

CRSS does not directly calculate water levels (stages) in river reaches. In select locations, 

empirical relationships between river flow and river stage can be used to assess the potential for

flooding. Specifically, empirical relationships between flow and flood risk (safe channel 

capacity) exist downstream of Lake Mead, Navajo Dam, and the Aspinall Unit. Additional 

analysis of CRSS output data was performed to estimate flooding potential. Table D-6 

summarizes the metrics for the critical river stages related to flooding risk. 

TABLE D-6 

Attribute of Interest: Critical River Stages Related to Flooding

Location Metric Type

Quantitative 

Method

Reference Value1 

cubic feet per 

second (cfs) Reference

Gunnison River at Delta, 

Colorado

Quantitative Estimated 

Condition

15,000

Water Control Manual Blue 

Mesa Dam and Reservoir 

(USACE, 1988)

San Juan River below 

Navajo Dam 5,000 Water Control Manual 

Navajo Dam and Reservoir 

(USACE, 1970) San Juan River near 

Farmington, New Mexico 12,000

Colorado River below 

Hoover Dam 28,000

Water Control Manual 

Hoover Dam and Lake 

Mead

(USACE, 1982)

1 Maximum safe channel capacity
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December 2012 D-19

8.0 Recreational Resources Metrics 

The recreational resources attributes of interest are: 

• Shoreline public use facilities

• River and whitewater boating

• Other recreation attributes

• Socioeconomic impacts related to recreation

8.1 Metrics for the Shoreline Public Use Facilities Attribute of Interest

Access to boat launch ramps and marinas is directly related to reservoir water levels. CRSS 

calculates water levels for all major Basin reservoirs, so access to shoreline facilities can be 

evaluated directly with CRSS output. Low reservoir levels can also limit reservoir boating 

navigation and affect ferry service. Table D-7 summarizes the metrics for shoreline access.

 

TABLE D-7

Attribute of Interest: Shoreline Public Use Facility

Location1 Metric Type

Quantitative 

Method

Reference 

Value2 

(feet msl)

Flaming Gorge 

Quantitative Physical 

Constraint

Firehole Boat Ramp 6,019

Cedar Springs Marina 6,018

Antelope Flat, Anvil Draw, Buckboard, Sheep Creek, 

Squaw Hollow Boat Ramps 6,015

Lucerne Valley Marina 6,010

Mustang Ridge and Upper Marsh Creek Boat Ramps 6,000

Lucerne Valley Boat Ramp 5,994

Blue Mesa 

Ponderosa Boat Ramp 7,468

Stevens Creek Boat Ramp 7,462

Lake Fork Marina and Boat Ramp 7,440

Iola and Elk Creek Boat Ramps 7,433

Navajo 

Arboles Boat Ramp 6,025

Sims Mesa Boat Ramp 6,000

Pine Boat Ramp 5,997

Lake Powell

Hite Public Boat Ramp 3,620

Castle Rock Cut 3,613

Antelope Point Public Boat Ramp 3,588

Wahweap, Stateline, Bull Frog Low Water Alternative, 

Halls Crossing Ramps 3,560

Wahweap, Antelope Point, Bull Frog, Halls Crossing 

Marinas 3,555
Colorado River Basin

Water Supply and Demand Study

D-20 December 2012

TABLE D-7

Attribute of Interest: Shoreline Public Use Facility

Location1 Metric Type

Quantitative 

Method

Reference 

Value2 

(feet msl)

Lake Mead

Pearce Bay Boat Ramp and Ferry 1,175

Las Vegas Bay and Government Wash Boat Ramps 1,150

Overton Beach Marina, Callville and South Cove Boat 

Ramps 1,125

Overton Boat Ramp 1,110

Lake Mead Marina 1,100

Lake Mead, Hemenway, Temple Bar Boat Ramps 1,080

Echo Bay Boat Ramp 1,050

1 Other locations, such as boat access camp sites, swim beaches, and natural features, are recognized as 

attractions but not included as reference values for the shoreline public use facilities attribute of interest.

2 Minimum reservoir levels required for use of designated shoreline public use facilities. Below these levels, 

facilities would have to be extended, closed, or relocated.

8.2 Metrics for the River and Whitewater Boating Attribute of Interest

Many different recreational activities are supported by rivers and streams throughout the Basin. 

The river and whitewater boating attribute of interest was designed to measure the impact to one 

of those activities, specifically river and whitewater boating. 

River and whitewater boating experiences vary with flow conditions, as well as with other nonflow related factors. For use in the Study, American Whitewater developed relationships that 

relate flow conditions to the quality of the boating experience by applying methodology 

developed by Whittaker et al. (2005). Under this methodology used by American Whitewater, 

flow translates to an “acceptable” or “optimal” boating day, depending on the flow condition and 

user survey responses. While this approach has been used in other Federal Energy Regulatory 

Commission-related studies, significant uncertainties exist related to its use in the Study. 

Additionally, it should be recognized that there are alternative study options to the one applied 

here that relate flow and recreation quality. The inclusion of the results from this particular 

approach should not be construed as an endorsement of this method by the Basin States or 

Reclamation. 

A key component of this methodology is user surveys that ask the recreational boating 

community to identify flows ranging from totally unacceptable to totally acceptable 

based on their skill level and craft type. American Whitewater independently conducted 

these surveys and due to resource constraints and the Study timeline, these surveys were 

conducted over a much shorter timeframe (1 month) than others typically conducted by 

American Whitewater. As such, there are limitations in the data collected by these surveys, 

in particular related to low response numbers and non-response bias. Non-response bias 
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December 2012 D-21

can result when surveys are only filled out by a small percentage of the people who were asked 

to fill out the survey, and has the potential to skew results (Whittaker et al., 1993)7. 

Survey limitations affect the flow-experience relationships derived from these surveys. 

Correspondingly, the flow ranges that define these relationships also contain limitations. Some of 

these are quite obvious given the extremely broad range of acceptable flows at some locations. 

For example, as shown in table D-8, for the Colorado River near Cisco, Utah, the range for an 

acceptable boating experience is from 1,800 to 100,000 cfs. The results of the user survey, as 

well as the methods applied to develop acceptable and optimal flow ranges, are described in 

detail in appendix D2. 

Notwithstanding these limitations, information retained from these surveys and the subsequent 

analysis resulting in estimated flow conditions to support the boating experience were included 

in the Study because the information may provide an understanding of the impacts to river and 

whitewater boating under the multiple future conditions assessed in the Study. This information 

provides a useful broad view of these impacts; however, it is recommended that future efforts 

that incorporate this information carefully consider the limitations described here and in further 

detail in appendix D2. 

Because CRSS operates at a monthly time step and the flow-experience relationships are 

developed based on average daily flows, a method was developed that uses the flow-experience 

relationships for the Study. This method develops daily flow patterns that translate monthly 

volumes projected by CRSS into “boating flow days” using the flow-experience relationships 

developed through user surveys. The daily flow patterns are not meant to predict actual daily 

flows in the future; rather, they are an intermediate step in obtaining the number of boating flow 

days in a month. The number of boating flow days is compared across future scenarios. As such, 

the utility is in the relative comparison of the metric between scenarios. A detailed description of 

this method is provided in appendix D2. 

Table D-8 lists the locations at which the metric was evaluated (locations explicitly modeled in 

CRSS), the corresponding recreational boating reach, and the estimated range of “acceptable” 

and “optimal” flows for boating as determined from the user surveys. It is important to note that 

these flow ranges are estimated to support river and whitewater boating and do not necessarily 

support other recreational activities, for example, fishing. The acceptable and optimal ranges

listed in this table are not the metrics’ reference value; rather, they were used to calculate the 

number of acceptable and optimal boating flow days. 

In cases where CRSS does not explicitly represent the recreational boating reach of interest, the 

nearest downstream location represented in CRSS was chosen as an indirect approximation of 

the location of interest. The locations were selected by evaluating three criteria: 1) the proximity 

of a location explicitly represented in CRSS to a whitewater boating resource; 2) an assessment 

of the CRSS ability to model flow at the desired locations; and 3) an acceptable number of 

respondents (30 per Whitaker et al. [1993]) for the user surveys. It should be recognized that the 

locations in table D-7 are not a complete list of locations that are important to the recreational 

boating community. Rather, they are the locations surveyed by American Whitewater and fit the 

evaluation criteria previously described and were evaluated in the Study. Appendix D2 lists all 

the locations surveyed by American Whitewater.

 

7 Whittaker et al. (1993) suggests that non-response bias may be an issue if the survey response rate is less than 65 percent. In the surveys 

conducted by American Whitewater, the response rates were typically much lower than 65 percent. 
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Water Supply and Demand Study

D-22 December 2012

TABLE D-8 

Attribute of Interest: River and Whitewater Boating

Location

Whitewater Boating 

Resources

Acceptable 

Range (cfs)

Optimal 

Range (cfs)

Colorado River at Glenwood Springs, CO GW Play Park, South Canyon 1,600–50,000 7,000–20,000

Dolores River near Cisco, UT Lower Dolores 900–20,000 1,800–3,000

Colorado River near Cisco, UT Hittle Bottom, Moab Daily 1,800–100,000 4,000–15,000

Green River near Greendale, UT Lodore Canyon 1,000–12,000 2,000–8,000

Yampa River near Maybell, CO1 Little Yampa Canyon, Cross 

Mountain Canyon

800–10,000 1,700–4,500

Yampa River at Deerlodge Park, CO Yampa Canyon 1,500–50,000 2,500–25,000

Green River at Jensen, UT Split Mountain Canyon 1,200–50,000 2,500–25,000

San Juan River near Bluff, UT Lower San Juan Canyon 800–50,000 1,400–7,500

1 The Cross Mountain segment is a very technical whitewater boating resource, and is defined by a narrow range of 

boating flows, as compared to other segments on the Yampa. Because of the technical and advanced nature of the 

resource, responses from experienced paddlers were less than 30.

8.3 Other Recreational Attributes of Interest

Sediment transport affects the recreational experience along Basin rivers and in Basin reservoirs. 

Significant additional analyses (beyond CRSS) are required to model sediment transport. 

Therefore, in lieu of detailed quantitative analyses, qualitative evaluations relating sediment 

transport to river flows were provided as part of the Study.

8.4 Metrics for the Socioeconomic Impacts Attribute of Interest

A reduction in the number of recreational visitors as a result of limited shoreline access could 

adversely affect local socioeconomics. Rough estimates that relate reservoir levels or flow 

conditions to socioeconomic impacts exist for some areas in the Basin. Significant additional 

analyses (beyond CRSS) are required to model the socioeconomic impacts related to reduced 

recreational use. For this reason, socioeconomic impacts related to reduced recreational use of 

Basin water resources were evaluated qualitatively.

9.0 Ecological Resources Metrics 

Colorado River ecosystems support a wide array of native species, each with diverse needs. To 

assess the response of these ecosystems to changed conditions under future scenarios, extensive 

data and models that examine the complex interactions of the physical environment and specific 

species’ needs are required. This detailed level of assessment is beyond the scope of the Study; 

however, metrics that approximate the flow-based conditions to support these resources were 

developed to facilitate the understanding of how these hydrologic conditions vary under future 

conditions. 

The locations at which these metrics are applied do not represent all of the ecologically 

important locations in the Basin. Rather, they represent locations that are both explicitly modeled 

in CRSS and have ecological relevance. Many limitations exist with respect to the tools and data 
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December 2012 D-23

that can be reasonably used given the Study’s time and resources. Acknowledging these 

limitations, metrics that approximate the location and estimate the flow conditions to support 

ecological resources were developed for the purpose of the Study. As such, the utility of the 

metrics described in this section is primarily to understand the relative comparison within an 

attribute of interest across a wide range of future scenarios8. 

Ecological resources specified in the Plan of Study (see Study Report, Appendix 1 – Plan of 

Study) include fish, wildlife, and their habitats; candidate, threatened, and endangered species; 

and flow- and water-dependent ecological systems. The ecological resources attributes of interest 

are:

• Flows to support threatened and endangered species

• Aquatic and riparian habitats 

• Wildlife refuges and fish hatcheries

9.1 Metrics for Flows to Support Threatened and Endangered Species 

Attribute of Interest 

The Upper Colorado River Endangered Fish Recovery Program and San Juan River Basin

Recovery Implementation Program (Recovery Programs) are designed to help recover several 

fish species listed as endangered under the federal Endangered Species Act (the Colorado pike 

minnow, the razorback sucker, the bonytail, and the humpback chub), while allowing water 

development to continue in the Upper Colorado and San Juan River Basins. The Recovery 

Programs provide water for these endangered fish species in accordance with all applicable laws 

through means that include the modification of operations at federal and non-federal facilities, 

conservation, and the development of additional supplies. Flow recommendations9 are defined as 

part of the Recovery Programs; therefore, flows are used as indicators for metrics for these fish 

species, and the Recovery Programs’ recommendations provide the reference values. Providing 

flows is only one part of the recovery efforts that include activities such as habitat development, 

non-native fish control, and monitoring and research. The combination of flow and non-flow 

recovery actions is anticipated to increase endangered fish populations to achieve recovery. As 

such, the relative difference in achieving these flow recommendations across various scenarios 

should not be viewed as the sole means to recover the species.

The 1996 Glen Canyon Dam ROD (Reclamation, 1996) guides the operations of Glen Canyon 

Dam regarding downstream ecological resources. The ROD sets very specific limits on daily 

operations (ramp rates and fluctuation limits). Most sub-monthly constraints cannot be 

effectively modeled in CRSS; however, the ROD specifies minimum allowable releases of 

8,000 cfs from 7:00 a.m. to 7:00 p.m. and 5,000 cfs from 7:00 p.m. to 7:00 a.m. When coupled 

with the down-ramp restrictions of 1,500 cfs per hour (Reclamation, 1996), the minimum 

average daily release is constrained to 6,438 cfs. The minimum daily release was converted to a 

minimum monthly release for Glen Canyon Dam and used as a reference value. 

 

8 For example, metrics for riparian habitat, under the aquatic and riparian habitats attribute of interest, should be used to show that scenario “X” 

meets the estimated flow conditions for cottonwood recruitment 95 percent of the time and scenario “Y” meets the criteria 98 percent of the 

time, so scenario “Y” is relatively better at meeting the flow conditions. An incorrect interpretation of the metric would be to infer that if 

scenario “X” is realized, cottonwood recruitment will not exist 5 percent of the time because data and tool limitations inhibit that level of detail.

9 The flow recommendations were developed based on the best available information at the time. They are subject to change based on continued 

research and adaptive management processes integral to the ongoing recovery efforts. 
Colorado River Basin

Water Supply and Demand Study

D-24 December 2012

The ROD also established the Glen Canyon Dam Adaptive Management Program (AMP) to 

monitor the effects of Glen Canyon Dam operations on the downstream ecological resources. 

The AMP is responsible for making recommendations to the Secretary regarding ways to fulfill 

the resource protection requirements of the Grand Canyon Protection Act while complying with 

all applicable federal laws. Each year the AMP recommends flows that the Secretary may adopt 

for these purposes. At times these have included changes in monthly release patterns; however, 

this is done annually on an ad hoc basis and therefore was not included as a metric. 

In the Lower Basin, the Lower Colorado River Multi-Species Conservation Program 

(LCR MSCP) provides Endangered Species Act compliance for specific federal ongoing and 

future flow and non-flow related actions in the Lower Basin through 2055, as well as the 

conservation plan for a non-federal section 10(a)(1)(B) permit over the same period of time. The 

LCR MSCP-covered activities include changes in points of diversion that could result in reduced 

flows in amounts up to 845 thousand acre-feet per year (kafy) in the reach below Hoover Dam to 

Davis Dam, up to 860 kafy in the reach below Davis Dam to Parker Dam, and up to 1,574 kafy 

in the reach below Parker Dam to Imperial Dam. Reductions in flow may occur from actions 

such as water transfers, conservation activities, and shortages to Lower Basin water users 

(Reclamation, 2004). The flow reduction values at these locations provide the reference values 

for metrics associated with threatened and endangered species in the Lower Basin.

Table D-9 summarizes the metrics related to flows to support threatened and endangered fish, 

including the location, flow target(s), and reference document from which these flows were 

taken. Many of the Recovery Program flow recommendations are for average daily flow rates, 

whereas CRSS operates at the monthly time step; however, recent research and development 

efforts resulted in the ability to evaluate daily flow targets below Navajo and Flaming Gorge 

Reservoirs. For other locations, monthly volumetric targets were developed based on the 

Recovery Program’s flow recommendations. Appendix D3 details the methods used to develop

these monthly approximations. Assumptions (e.g., hydrologic period of record chosen for year 

type determination) were made to develop those approximations that in some cases resulted in 

flows different than those specified in the reference documents and that exist for regulatory 

purposes. The inclusion of these approximated flows in the Study should not in any way change 

or affect the flow recommendations that are used for regulatory purposes. 

9.2 Metrics for Aquatic and Riparian Habitat Attribute of Interest

At some locations of interest, specific habitat needs have not been expressed in terms of flow 

recommendations for endangered fish recovery. Nonetheless, there is interest in examining how 

aquatic and riparian habitat for species not currently threatened or endangered may change with 

time under varying future scenarios. Although flow is not the only variable that influences 

changes to the aquatic and riparian habitat, it is the main output variable of CRSS. The flow 

conditions represent an indirect measurement of how the habitats could function in the future. 

Metrics for this attribute of interest were developed under each of the following groups: 

• Instream flow rights

• Cottonwood recruitment conditions 

• Flow-dependent ecological systems
Technical Report D — System

Reliability Metrics

December 2012 D-25

TABLE D-9 

Attribute of Interest: Flows to Support Threatened and Endangered Species

Location

Metric 

Type

Quantitative 

Method Reference Value2 Reference

Colorado River near 

Cameo, CO

Quantitative Prescribed 

Condition1

Average monthly flows ranging 

from about 1,560–17,160 cfs, 

depending on month and 

hydrologic year type

Recovery Program 

(Osmundson, 2001)

Gunnison River near 

Grand Junction, CO

Spring peak volumes ranging 

from about 347–2,090 kaf and 

summer through winter base 

flows ranging from 42–154 kaf, 

depending on hydrologic year 

type

Recovery Program 

(McAda, 2003)

Final Gunnison River 

Programmatic Biological 

Opinion (PBO) (USFWS, 

2009)

Colorado River near 

the Colorado-Utah 

Stateline

Spring peak volumes ranging 

from 871–5,271 kaf and summer 

through winter base flows 

ranging from 100–369 kaf, 

depending on hydrologic year 

type

Recovery Program 

(McAda, 2003)

Yampa River near 

Maybell, CO

Base flow of 120 cfs Recovery Program 

(USFWS, 2008)

Green River near 

Greendale, UT

Summer through winter base 

flows ranging from 800–1,800 

cfs, depending on hydrologic 

year type

Flaming Gorge 

Operations Final EIS 

(Reclamation, 2005)

Green River at 

Jensen, UT

Spring peak flows ranging from 

8,300–26,400 cfs and summer 

through winter base flows 

ranging from 900–3,000 cfs, 

depending on hydrologic year 

type

Flaming Gorge 

Operations Final EIS 

(Reclamation, 2005)

Green River at Green 

River, UT

Quantitative Prescribed 

Condition1

Spring peak volumes ranging 

from 1,092–4,700 kaf and 

summer through winter base 

flows ranging from 80–289 kaf, 

depending on hydrologic year 

type

Flaming Gorge 

Operations Final EIS 

(Reclamation, 2005)

Duchesne River near 

Randlett, UT

Spring peak volumes ranging 

from 47.6–535 kaf and summer 

through winter base flows 

ranging from 2.8–7.1 kaf, 

depending on hydrologic year 

type

Recovery Program 

(Modde and Keleher, 

2003)

San Juan River near 

Bluff, UT3 Spring peak flows ranging from 2,500–10,000 cfs and summer 

through winter base flows 

ranging from 500–1,000 cfs

Navajo Reservoir 

Operations Final EIS 

(Reclamation, 2006a) 

Glen Canyon Dam Minimum average daily release 

of 6,438 cfs

Glen Canyon Dam ROD 

(Reclamation, 1996)
Colorado River Basin

Water Supply and Demand Study

D-26 December 2012

TABLE D-9 

Attribute of Interest: Flows to Support Threatened and Endangered Species

Location

Metric 

Type

Quantitative 

Method Reference Value2 Reference

Hoover Dam to Davis 

Dam

Flow reductions up to 845 kafy LCR MSCP 

(Reclamation, 2004)

Davis Dam to Parker 

Dam

Flow reductions up to 860 kafy

Parker Dam to 

Imperial Dam

Flow reductions up to 1,574 kafy

1

 These flow targets are one component of the Upper Colorado River Endangered Fish Cooperative Agreement 

between DOI and the States of Colorado, Utah, and Wyoming; and several PBOs and EISs that are based on that 

agreement and the underlying program. These flow targets may change in the future as a result of new 

information or changes in this Recovery Program or the underlying PBOs and EISs.

2

 If the Recovery Programs’ flow recommendations are in terms of monthly flows or are at locations that daily flows 

can be evaluated using CRSS, the reference values are directly from the referenced document. Otherwise, the 

reference values are monthly approximations of the flow recommendations from the supplied references.

3

 CRSS does not presently have the appropriate resolution to measure base flow recommendations at the precise 

locations specified in the Navajo Reservoir Operations ROD (Reclamation, 2006b). Methods have been 

developed, in collaboration with Navajo Reservoir operators, to provide a quantitative approximation of the Navajo 

ROD flow recommendations that assume the recommendations are measured at the San Juan River near Bluff, 

Utah.

Table D-10 summarizes the metrics (both the locations and the reference values) considered 

under each of the above groups. The following sections describe these metrics in further detail. 

9.2.1 Instream Flow Rights

The Colorado Water Conservation Board has secured many instream flow rights10 to benefit the 

aquatic and riparian habitat across Colorado. Many of these locations are on tributaries that are 

not modeled in CRSS; however, where the locations coincide with gage locations in CRSS, the 

modeled flow was compared with the in-stream flow right. Table D-10 presents the locations and 

their reference values.

9.2.2 Cottonwood Recruitment Metric

Healthy cottonwood stands are an indicator of healthy riparian systems and the many species that 

depend on them. The recruitment of new cottonwoods is important in maintaining the 

cottonwood stands, and thus a healthy riparian system. The metric is based on the biological 

premise that conditions that could lead to a successful cottonwood recruitment event, should 

occur approximately once every 10 years, to sustain the cottonwoods and the many riparian 

facultative species depending on them. In coordination with the USFWS and The Nature 

Conservancy (TNC), a metric was developed that incorporates this concept. 

 

10 Available at: http://cwcb.state.co.us/environment/instream-flow-program/Pages/main.aspx. 
Technical Report D — System

Reliability Metrics

December 2012 D-27

TABLE D-10

Attribute of Interest: Aquatic and Riparian Habitat

Location Metric Type

Quantification 

Method Reference Value

Instream Flow Rights

Taylor River near Taylor Park, CO

Quantitative Prescribed

Condition

100 cfs in May through September 

and 50 cfs in October through April.

Gunnison River below Crystal 

Reservoir, CO

300 cfs in January through 

December

Cottonwood Recruitment Metric

Dolores River near Cisco, UT

Quantitative Estimated 

Condition

Positive conditions occurring once 

every 10 years1 

San Juan River near Archuleta, NM

Green River below Fontenelle 

Reservoir, WY

Green River near Green River, WY

San Rafael near Green River, UT

Colorado River near Cisco, UT

Flow-Dependent Ecological Systems

Yampa River near Maybell, CO

Quantitative Estimated 

Condition

Spring peak volumes ranging from 

369–1,459 kaf and summer through 

winter base flows ranging from 7.1–

73 kaf, depending on hydrologic 

year type2 

Little Snake River near Lily, CO Spring peak volumes ranging from 

100–531 kaf and summer through 

winter base flows ranging from 

0.36–33.7 kaf, depending on 

hydrologic year type2 

Yampa River at Deerlodge Park, CO Spring peak volumes ranging from 

458–1,994 kaf and summer through 

winter base flows ranging from 7.1–

118 kaf, depending on hydrologic 

year type2 

White River near Watson, UT Spring peak volumes ranging from 

120–504 kaf and summer through 

winter base flows ranging from 

12.3–36.9 kaf, depending on 

hydrologic year type2 

1 See appendix D4 for the detailed approach to this reference value.

2 See appendix D5 for the detailed approach to this reference value.
Colorado River Basin

Water Supply and Demand Study

D-28 December 2012

The metric employs the cottonwood recruitment box model (Mahoney and Rood, 1998), which 

has been applied in many western river systems, including the Bill Williams River (Shafroth et 

al., 1998) and the Sacramento River (ESSA Technologies Ltd., 2007). As described in Mahoney 

and Rood (1998), a successful recruitment event depends on four variables: timing of peak flow, 

the river stage corresponding to the peak flow, the rate of decline from when the peak flow 

occurs to when the peak has attenuated, and a flood large enough to create the appropriate seed 

beds. The metric is an estimated condition quantification method; it is estimated that positive 

recruitment conditions should occur once every 10 years to maintain healthy cottonwood stands. 

All the above conditions are required to create the opportunity for a successful recruitment event.

The approach to determine whether or not these conditions have occurred using CRSS is 

described in appendix D4. Table D-10 provides the locations at which the cottonwood metric is 

evaluated. 

The locations selected for the cottonwood recruitment method have not necessarily had sitespecific surveys to relate flow to floodplain inundation. Detailed site-specific surveys are 

necessary to recommend flows for cottonwood recruitment. However, the adopted method relies 

on documented rules of thumb to approximate positive recruitment conditions and is appropriate 

for a relative comparison across scenarios. Furthermore, the locations have been selected at 

existing gage sites, which may not be precisely located where ideal conditions exist for 

cottonwood growth; however, this approximation was necessary given CRSS spatial limitations. 

These assumptions are useful in providing a general understanding of the relative comparison of 

cottonwood recruitment under multiple future conditions; however, it is recommended that future 

efforts that incorporate this information carefully consider these limitations.

Additionally, there are other locations in the Basin where this metric would be appropriate; 

however, current modeling limitations have limited the inclusion of those locations. In particular, 

the Bill Williams River has existing flow recommendations (U.S. Geological Survey, 2006), has 

operations and hydraulic models applied to it for ecological flow needs (Shafroth et al., 2010), 

and had the cottonwood recruitment box model applied to it in previous efforts (Shafroth et al., 

1998). It would be beneficial to include similar metrics on the Bill Williams River; however, this 

inclusion is limited by the treatment of the Lower Basin tributaries within CRSS (Technical 

Report C – Water Demand Assessment, Appendix C11 – Modeling of Lower Basin Tributaries in 

the Colorado River Simulation System) in that there is little variation projected on the Bill 

Williams River between future scenarios. 

9.2.3 Flow-Dependent Ecological Systems

Metrics were developed to consider flow-dependent ecological systems (aggregation of fish 

health and riparian and aquatic habitat) for locations throughout the Basin that are important 

ecologically but for which no prescribed flow conditions exist. For example, the recommended 

flows for the Yampa River (described in table D-10) consider flow needs only during the base 

flow period. In coordination with the USFWS and TNC, metrics were developed for estimated 

flow conditions at this location in addition to two other locations in the Yampa River Basin. The 

White River near Watson, Utah, is another location with documented flow needs (Haines et al., 

2004; Lentsch et al., 2000), although they have not been fully prescribed through a biological 

opinion. Table D-10 presents the locations and a summary of the reference values for these

metrics, while appendix D5 describes the full set of estimated flow conditions and the methods to 

develop those flows for the flow-dependent ecological systems attribute of interest. 
Technical Report D — System

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December 2012 D-29

Several limitations exist with respect to the estimation of these flow conditions. First, these 

ecological systems are supported by many non-flow parameters (for example water quality, 

temperature, etc.) that are not considered in the estimated flow-based conditions. Secondly, these 

flow conditions must be aggregated to a monthly time step to meet that of CRSS. Additionally, 

the methodology used to develop these flow conditions (appendix D5) depends on assumptions 

behind the hydrologic year-typing. Acknowledging these limitations, the estimated flow 

conditions shown in table D-10 have been adopted for the purpose of the Study because they 

provide a general understanding of the relative comparison of these specific ecological systems; 

however, it is recommended that future efforts that incorporate this information carefully 

consider these limitations. 

9.3 Metrics for Wildlife Refuges and Fish Hatcheries Attribute of Interest

Table D-11 summarizes wildlife refuge and fish hatcheries in the Basin that have water rights

and their reference values. The determination of the reference values was done in coordination 

with USFWS. In the Upper Basin, reference values are based on both the associated water right 

within the state and historical diversion records and vary by hydrologic year type. A description 

of the computation of these reference values can be found in appendix D6. 

In the Lower Basin, reference values are based on the wildlife refuges’ entitlements and 

historical use and vary by water demand scenario (Technical Report C – Water Demand 

Assessment). Under a specific water demand scenario, the reference value may be less than or 

equal to the refuges’ entitlement. It is recognized that a refuge’s demand for water is not 

necessarily limited to that refuge’s entitlement; however, the quantification of that demand 

remains an ongoing effort within USFWS. 
Colorado River Basin

Water Supply and Demand Study

D-30 December 2012

TABLE D-11

Attribute of Interest: Wildlife Refuges and Fish Hatcheries

Location Metric Type

Quantification 

Method

Reference Value

(af)

Colorado

Browns Park National 

Wildlife Refuge Quantitative Estimated

Condition

Monthly flows up to 2,520 af, depending 

on month and hydrologic year type1

Wyoming

Seedskadee National 

Wildlife Refuge Quantitative EstimatedCondition

Monthly flows up to 5,700 af, depending 

on month and hydrologic year type1

Utah

Ouray National Wildlife 

Refuge Quantitative EstimatedCondition

Monthly flows up to 8,800 af, depending 

on month and hydrologic year type1

Arizona

Havasu National Wildlife 

Refuge

Quantitative Estimated 

Condition

Annual depletions ranging from 4,542–

37,339 af and annual diversions ranging 

from 37,850–41,839 af2

Cibola National Wildlife 

Refuge

Annual depletions ranging from 8,822–

16,793 af and annual diversions ranging 

from 14,230–27,000 af

2 

Imperial National Wildlife 

Refuge

Annual depletions ranging from 1,039–

23,000 af and annual diversions ranging 

from 1,676–28,000 af2 

Willow Beach Fish Hatchery Quantitative Estimated

Condition Annual depletions of about 290 af3

1

 See appendix D6 for monthly flow conditions that vary by hydrologic year type. 2 Annual diversion and depletion varies across water demand scenarios (Technical Report C – Water Demand 

Assessment). The lower ends represent the average diversion and depletion from 2005–2009 (4,542 af 

diversion for Havasu National Wildlife Refuge. The upper end represents the refuge entitlement (37,339 af 

diversion for Havasu National Wildlife Refuge). 3

 This amount reflects Lake Mead National Recreational Area annual depletion, which includes Temple Bar, 

Katherine, and Willow Beach. CRSS does not represent these locations explicitly and treats them as one 

diversion by the Lake Mead National Recreational Area. 

10.0 Summary and Limitations

Many metrics have been defined, and descriptions of these metrics have been provided in this 

report. The map shown in figure D-2 displays the Study Area and denotes the locations of the 

metrics that have been defined. The locations of the water deliveries metrics are not denoted 

because there are more than 200 locations throughout the Study Area. 

Metrics were developed to assess the impacts to water deliveries, electrical power resources, 

water quality, flood control, recreational resources, and ecological resources under multiple 

future conditions. Some metrics used information directly from CRSS (for example, 

consumptive uses and reservoir releases), while others used indirect measurements using flow to 

estimate the impact to the resource (for example, aquatic and riparian habitats). Still other

metrics, such as socioeconomic impacts, were evaluated qualitatively. 
Technical Report D — System

Reliability Metrics

December 2012 D-31

The ability to assess impacts to Basin resources is limited by the spatial and temporal detail of 

CRSS. For example, CRSS tracks shortages in the Upper Basin when the flow is insufficient to 

meet the local demands, as opposed to simulating the complex water rights system in each state 

that would be needed to appropriately model shortages to individual water rights holders. This 

representation affects the ability of the Study to assess the impacts to deliveries in the Upper 

Basin. 

Another example is that several ecological resources metrics were evaluated through 

approximations at larger spatial scales and longer time steps, e.g., monthly versus daily, than 

preferred because of model limitations. Additionally, ecosystems are composed of complex 

interactions influenced by many variables besides flow, e.g., sediment transport, water quality, 

temperature, etc. The ecological resource metrics developed for the Study are flow-based, which 

indicate whether or not a certain flow condition exists, but do not indicate that the expected 

impact on a species will be realized. Likewise, the flow-based metric may indicate lesser 

achievement, but other habitat measures not directly measured in the Study may improve, 

resulting in the improvement of the overall ecosystem. 

Despite these limitations, the metrics described in this report represent a good first step towards 

the identification of a comprehensive set of metrics to measure the potential impacts to Basin 

resources. Using these metrics and through the development of system vulnerabilities, Technical 

Report G – System Reliability Analysis and Evaluation of Options and Strategies presents the 

projected impacts to these Basin resources and the effectiveness of various options and strategies 

at mitigating these impacts. 

In efforts beyond the Study, additional CRSS developments and enhancements to improve the 

model’s ability to simulate the system under future conditions will occur. These improvements 

will help to further the understanding of the potential future impacts to Basin resources in future 

studies. 
Colorado River Basin

Water Supply and Demand Study

D-32 December 2012

FIGURE D-2 

Study Area with Locations of Defined Metrics
Technical Report D — System

Reliability Metrics

December 2012 D-33

11.0 References 

Bureau of Reclamation (Reclamation). 1996. Record of Decision Operation of Glen Canyon 

Dam Final Environmental Impact Statement. October. 

Bureau of Reclamation (Reclamation). 2004. Lower Colorado River Multi-Species Conservation 

Program. Volume I: Programmatic Environmental Impact Statement/Environmental 

Impact Report. Final. December.

Bureau of Reclamation (Reclamation). 2005. Operation of Flaming Gorge Dam Environmental 

Impact Statement. Final. September.

Bureau of Reclamation (Reclamation). 2006a. Navajo Reservoir Operations. Environmental 

Impact Statement. Final. April. 

Bureau of Reclamation (Reclamation). 2006b. Record of Decision for the Navajo Reservoir 

Operations, Navajo Unit-San Juan River New Mexico, Colorado, Utah, Final 

Environmental Impact Statement. 

Bureau of Reclamation (Reclamation). 2007. Colorado River Interim Guidelines for Lower 

Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead Final 

Environmental Impact Statement. November 2. 

ESSA Technologies Ltd. 2007. Sacramento River Ecological Flows Tool (SacEFT): Design & 

Guidelines (v.1.00.018). 

Haines, G.B., Irving, D., Modde, T. 2004. White River Base Flow Study for Endangered Fishes, 

Colorado and Utah, 1995-1996. Lentsch, L.D., B.G. Hoskins, L.M. Lubomudrov. 2000. 

The White River and Endangered Fish Recovery: A Hydrological, Physical and 

Biological Synopsis. 

Lentsch, L.D., Hoskins, B.G., Lubomudrov, L.M. 2000. The White River and Endangered Fish 

Recovery: A Hydrological, Physical and Biological Synopsis. Utah Division of Wildlife 

Resources, Salt Lake City, Utah.

Mahoney, J. and S. Rood, S. 1998. “Streamflow Requirements for Cottonwood Seedling 

Recruitment—An Integrative Model.” Wetlands,18(4), 634-645. 

DOI:10.1007/BF03161678. 

McAda, C. 2003. Flow Recommendations to Benefit Endangered Fishes in the Colorado and 

Gunnison Rivers. 

Modde, T., and C. Keleher. 2003. Flow Recommendations for the Duchesne River with a 

Synopsis for Information Regarding Endangered Fish. 

Osmundson, D.B. 2001. Flow Regimes for Restoration and Maintenance of Sufficient Habitat to 

Recover Endangered Razorback Sucker and Colorado Pike Minnow in the Upper 

Colorado River: Interim Recommendations for the Palisade-to-Rifle Reach.

Shafroth, P.B., G.T. Auble, J.C. Stromberg, and D.T. Patten. 1998. “Establishment of Woody 

Riparian Vegetation in Relation to Annual Patterns of Streamflow, Bill Williams River, 

Arizona.” Wetlands, 18(4), 577-590. DOI: 10.1007/BF03161674. 
Colorado River Basin

Water Supply and Demand Study

D-34 December 2012

Shafroth, P.B., A.C. Wilcox, D.A. Lytle, J.T. Hickey, D.C. Andersen, V.B. Beauchamp, A. 

Hautzinger, L.E. McMullen, and A. Warner. 2010. “Ecosystem Effects of Environmental 

Flows: Modeling and Experimental Floods in a Dry Land River.” Freshwater Biology,

55, 68-85. DOI:10.1111/j.1365-2427.2009.02271.x. 

U.S. Army Corps of Engineers (USACE). 1970. Water Control Manual, Navajo Dam and 

Reservoir, San Juan River Basin, Colorado and New Mexico. 

U.S. Army Corps of Engineers (USACE). 1982. Water Control Manual for Flood Control, 

Hoover Dam and Lake Mead, Colorado River. 

U.S. Army Corps of Engineers (USACE). 1988. Blue Mesa Dam and Reservoir Gunnison River, 

Colorado Water Control Manual. 

U.S. Department of the Interior (DOI). 2007. Record of Decision for Colorado River Interim 

Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and 

Lake Mead. December. 

U.S. Fish and Wildlife Service (USFWS). 1994. Recovery Program: Endangered and 

Threatened Species. 

U.S. Fish and Wildlife Service (USFWS). 2008. Rationale for Management of Water Releases 

from the Elkhead Reservoir Endangered Fish Pool to Augment August-October Base 

Flows in the Yampa River. 

U.S. Fish and Wildlife Service (USFWS). 2009. Final Gunnison River Basin Programmatic 

Biological Opinion. 

U.S. Geological Survey (USGS). 2006. Defining Ecosystem Flow Requirements for the Bill 

Williams River, Arizona. Whittaker, D., B. Shelby, W. Jackson, and R. Beschta. 1993. 

Instream Flows for Recreation: A Handbook on Concepts and Research Methods. 

Whittaker, D., B. Shelby, and J. Gangemi. 2005. Flows and Recreation, A Guide to Studies for 

River Professionals. 

Whittaker, D., Bo Shelby, William Jackson, and Robert Beschta. 1993. Instream Flows for 

Recreation: A Handbook on Concepts and Research Methods. U.S. Dept. of the Interior, 

National Park Service, Rivers Trails and Conservation Program. 
Technical Report D — System

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December 2012 D-35

Disclaimer

The Colorado River Basin Water Supply and Demand Study (Study) is funded jointly by the Bureau of 

Reclamation (Reclamation) and the seven Colorado River Basin States (Basin States). The purpose of 

the Study is to analyze water supply and demand imbalances throughout the Colorado River Basin and 

those adjacent areas of the Basin States that receive Colorado River water through 2060; and develop, 

assess, and evaluate options and strategies to address the current and projected imbalances. 

Reclamation and the Basin States intend that the Study will promote and facilitate cooperation and 

communication throughout the Basin regarding the reliability of the system to continue to meet Basin 

needs and the strategies that may be considered to ensure that reliability. Reclamation and the Basin 

States recognize the Study was constrained by funding, timing, and technological and other limitations, 

and in some cases presented specific policy questions and issues, particularly related to modeling 

and interpretation of the provisions of the Law of the River during the course of the Study. In such 

cases, Reclamation and the Basin States developed and incorporated assumptions to further complete 

the Study. Where possible, a range of assumptions was typically used to identify the sensitivity of the 

results to those assumptions.

Nothing in the Study, however, is intended for use against any Basin State, any federally recognized 

tribe, the federal government or the Upper Colorado River Commission in administrative, judicial or 

other proceedings to evidence legal interpretations of the Law of the River. As such, assumptions 

contained in the Study or any reports generated during the Study do not, and shall not, represent a legal 

position or interpretation by the Basin States, any federally recognized tribe, federal government or 

Upper Colorado River Commission as it relates to the Law of the River. Furthermore, nothing in the 

Study is intended to, nor shall the Study be construed so as to, interpret, diminish or modify the rights 

of any Basin State, any federally recognized tribe, the federal government, or the Upper Colorado River 

Commission under federal or state law or administrative rule, regulation or guideline, including without 

limitation the Colorado River Compact (45 Stat. 1057), the Upper Colorado River Basin Compact 

(63 Stat. 31), the Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande, 

Treaty Between the United States of America and Mexico (Treaty Series 994, 59 Stat. 1219), the 

United States/Mexico agreement in Minute No. 242 of August 30, 1973 (Treaty Series 7708; 24 UST 

1968), or Minute No. 314 of November 26, 2008, or Minute No. 318 of December 17, 2010, or Minute 

No. 319 of November 20, 2012, the Consolidated Decree entered by the Supreme Court of the United 

States in Arizona v. California (547 U.S 150 (2006)), the Boulder Canyon Project Act (45 Stat. 1057), 

the Boulder Canyon Project Adjustment Act (54 Stat. 774; 43 U.S.C. 618a), the Colorado River 

Storage Project Act of 1956 (70 Stat. 105; 43 U.S.C. 620), the Colorado River Basin Project Act of 

1968 (82 Stat. 885; 43 U.S.C. 1501), the Colorado River Basin Salinity Control Act (88 Stat. 266; 

43 U.S.C. 1951) as amended, the Hoover Power Plant Act of 1984 (98 Stat. 1333), the Colorado River 

Floodway Protection Act (100 Stat. 1129; 43 U.S.C. 1600), the Grand Canyon Protection Act of 1992 

(Title XVIII of Public Law 102-575, 106 Stat. 4669), or the Hoover Power Allocation Act of 2011 

(Public Law 112-72). In addition, nothing in the Study is intended to, nor shall the Study be construed 

so as to, interpret, diminish or modify the rights of any federally recognized tribe, pursuant to 

federal court decrees, state court decrees, treaties, agreements, executive orders and federal trust 

responsibility. Reclamation and the Basin States continue to recognize the entitlement and right of 

each State and any federally recognized tribe under existing law, to use and develop the water of the 

Colorado River system.
Appendix D1

Metrics Sub-Team Members

December 2012 D1-1

Appendix D1 — Metrics Sub-Team Members

The information presented in Technical Report D – System Reliability Metrics is the outcome of 

a collaborative process involving representatives of numerous organizations.

A list of Metrics Sub-Team members and their affiliations is presented below. 

• Klint Reedy, Black & Veatch

• Alan Butler, Bureau of Reclamation

• Carly Jerla, Bureau of Reclamation

• Martin Einert, Bureau of Reclamation

• Kara Gillon, Defenders of Wildlife

• Jason John, Navajo Nation 

• Colby Pellegrino, Southern Nevada Water Authority

• Jan Matusak, The Metropolitan Water District of Southern California

• Robert Wigington, The Nature Conservancy

• John Shields, Wyoming State Engineers Office 

Points of contact with other organizations that provided additional information are presented 

below. 

• Nathan Fey, American Whitewater

• Katrina Grantz, Bureau of Reclamation

• Robert Radtke, Bureau of Reclamation

• Jack Barnett, Colorado River Basin Salinity Control Forum

• Norm Henderson, National Park Service

• Bill Jackson, National Park Service

• Kent Turner, National Park Service

• David Slick, Salt River Project

• Janet Bair, U.S. Fish and Wildlife Service

• Tom Chart, U.S. Fish and Wildlife Service

• Andrew Hautzinger, U.S. Fish and Wildlife Service

• Jana Mohrman, U.S. Fish and Wildlife Service

• Mike Roberts, The Nature Conservancy

• John Sanderson, The Nature Conservancy

• Xavier Gonzalez, Western Area Power Administration 

• Sam Loftin, Western Area Power Administration 

Appendix D2 

Boating Flow Days Metrics

December 2012 D2-1 

Appendix D2 — Boating Flow Days Metrics

1.0 Introduction

This appendix describes the method used to implement the boating flow days metric for the river 

and whitewater boating attribute of interest. Relationships were developed at several Upper 

Colorado River Basin locations to link average daily flow to the quality of boating experience. In 

this context, flow translates to an acceptable, optimal, or other (flows below or above the 

acceptable thresholds) boating day, depending on the flow magnitude and the survey 

respondents. The flow-experience relationships (Whittaker et al., 2005) were developed by 

American Whitewater based on user surveys that asked users to identify flows ranging from 

totally unacceptable to totally acceptable based on their skill level and craft type. Because the 

Colorado River Simulation System (CRSS) operates at a monthly time step and the flowexperience relationships are developed based on average daily flows, an additional step is 

necessary to resolve the time step discrepancy.

Significant uncertainties exist related to the use of the approach taken by American Whitewater 

in the Colorado River Basin Water Supply and Demand Study (Study), as there are several 

limitations stemming from resource constraints and the Study timeline. Nevertheless, the 

information resulting from this approach has been included in the Study because it provides a 

broad view of the impacts to river and whitewater boating under multiple future conditions. It is 

recommended that future efforts carefully consider the limitations and assumptions of this 

approach if this information is used in future efforts. 

The methodology section details the process of performing user surveys and developing flowexperience relationships. Additionally, the procedure that is used to resolve the time step 

discrepancy between CRSS output and flow-recreation relationships is presented. The summary 

section describes results of the user survey procedure. A report developed by American 

Whitewater describing the user-survey approach and survey results is provided in attachment A.

2.0 Methodology

2.1 Establish Flow Ranges

To establish flow ranges for survey-based acceptable and optimal recreational opportunities, 

American Whitewater collected and organized personal evaluations of recreational resource 

conditions and recreation-relevant hydrology, consistent with standard methods (Whittaker et al., 

2005). An online survey conducted during November and December 2011 involved 

382 volunteer paddlers representing a range of experience and skill levels. The survey asked 

respondents to evaluate flows at each location, although few respondents had experience with 

every segment surveyed. 

Study respondents were asked to evaluate overall recreation quality for each measured flow at 

each Study segment, using a seven-point “acceptability” scale (ranging from very unacceptable 

[-3] to very acceptable [3]). Using a survey-based normative approach, individual evaluations of 

flows were aggregated into social norms, which described the group’s collective evaluation of 

those same stream flows (Shelby et al., 1996; Whittaker et al., 1993). Structural norm 

characteristics were used to graphically represent the range of acceptable flows for whitewater 
Colorado River Basin 

Water Supply and Demand Study

D2-2 December 2012

boating opportunities. Mean evaluation for each flow condition was plotted graphically to create 

the social norm or flow-acceptability curves (see figure D2-1 for an example). These curves were

analyzed in terms of certain characteristics, including:

• Acceptable flows: the range of flows represented above the neutral line of the curve starting 

at the minimum acceptable flow

• Optimal flows: flows that are represented by the peak of the curve

FIGURE D2-1 

Example Flow Acceptability Agreement Index Curve 

The size of symbols represents the variability within the responses (smaller symbols represent greater relative agreement among 

respondents). 

Impact acceptability curves and the Flow Acceptability Agreement Index (also known as 

Potential for Conflict Index, or FAAI) were used to help determine minimum acceptable, 

optimal, and the range of acceptable flows, and to estimate respondent agreement regarding the 

acceptability of each specific flow level. A detailed report on the methods used to determine the 

flow ranges is included as attachment A.

2.2 Obtain Boating Flow Days from CRSS Output

CRSS is operated on a monthly time step with flow outputs reported as average monthly flow or 

as monthly volumes. During the course of a month, the daily flow rates may change considerably 

and have a significant impact on the recreational whitewater resource. Therefore, the metric 

required a temporal disaggregation of modeled monthly flow volumes to daily average flow rates 

before computing the number of acceptable, optimal, and other boating days in a month. The 

disaggregated flow rates were then compared to the acceptable and optimal flow ranges for each 

location to develop statistics on the number of acceptable and optimal boating days in each 

month. 

The daily disaggregation of flow was performed external to the CRSS model using software 

developed specifically for this metric. The disaggregation technique uses historical patterns of 

flow variability from observed gage data and applies the variability to the modeled monthly flow 
 Appendix D2 — Boating Flow Days Metrics

December 2012 D2-3 

volume. Stream gages used to develop the historical patterns were evaluated for significant 

changes in upstream operations. Gages with significant changes over the past 30 years and gages

that were projected to have significantly different flow patterns in the future (e.g., re-operation of 

upstream reservoir) were screened from further consideration. 

Figure D2-2 shows the overall process of the temporal disaggregation using an example CRSS 

model output for a May flow volume. For the past 30 years of daily gage data at each location, 

each month was normalized by its monthly volume to develop coefficients that represent the 

historical pattern of variability (figure D2-2B). Each of the 30 sequences of coefficients was then 

applied to the simulated monthly flow to produce an ensemble of plausible daily flows 

(figure D2-2C). The daily flows patterns were then compared to the desired flow ranges for the 

specific location to develop statistics on the number of acceptable and optimal boating days in 

the month. 

3.0 Summary

Table D2-1 summarizes the number of respondents for each surveyed location and the acceptable 

and optimal flow ranges as identified by the user surveys. Locations immediately below Taylor 

Reservoir and the Aspinall Unit were excluded from the process due to the current representation 

of the operating logic of these reservoirs in CRSS. The Colorado River near Cameo, Colorado; 

Colorado River near the Colorado–Utah state line; Green River near Green River, Wyoming; 

White River near Watson, Utah; Gunnison River near Grand Junction, Colorado; and the Green 

River at Green River, Utah, were not included as metrics because there was not adequate user 

response to the surveys at these locations. Whittaker et al. (1993) recommends approximately 

30 respondents for statistical significance. For all other locations, high levels of agreement on 

optimal flows were recorded and minimum acceptable flows were identified for each segment by 

the respondents. For many segments, respondents reported no maximum acceptable flow, 

defining a wide range of acceptable flows, up to 100,000 cubic feet per second (cfs) for certain 

high-volume reaches. 

The boating flow days metric made it possible to quantify the relative trade-offs among 

recreation opportunities and between recreation and other resources during the System 

Reliability Analysis. The daily flow patterns are not meant to predict actual daily flows in the 

future; instead, they are an intermediate step in estimating the number of boating flow days in a 

month that were then compared across scenarios. 
Colorado River Basin 

Water Supply and Demand Study

D2-4 December 2012

FIGURE D2-2 

Example Steps for Computing Number of Boating Flow Days from CRSS Monthly Output

9 years from the 1981–2010 gage record are shown as an example.
 Appendix D2 — Boating Flow Days Metrics

December 2012 D2-5 

TABLE D2-1 

Summary of the Surveyed Locations, Respondent Numbers, and Acceptable and Optimal Flow Ranges

Attribute Location

Whitewater 

Boating 

Resource

Acceptable 

Boating Flow 

Range 

(cfs) 

Optimal Boating 

Flow Range 

(cfs) 

Respondent 

Numbers

Colorado River at Glenwood 

Springs, Colorado

GW Playpark

South Canyon

1,600–50,000 7,000–20,000 42 Responses –

328 Skipped

Colorado River near Cameo, 

Colorado

Big Sur 20,000–50,000 27,500–50,000 26 Responses – 

364 Skipped

Colorado River near ColoradoUtah state lineRuby-Horsethief 

Westwater

Not Applicable Not Applicable No data

Gunnison River near Grand 

Junction, Colorado

Lower Gunnison

DominguezEscalante

900–15,000 2,000–12,500 7 Responses – 

383 Skipped

Dolores River near Cisco, Utah Lower Dolores 900–20,000 1,800–3,000 48 Responses –

342 Skipped

Colorado River near Cisco, Utah Hittle Bottom

Moab Daily

1,800–100,000 4,000–15,000 35 Responses –

355 Skipped

Green River near Green River, 

Wyoming

Green River 

Whitewater park

Not Applicable Not Applicable 6 Responses –

384 Skipped

Green River near Greendale, Utah Lodore Canyon 1,000–12,000 2,000–8,000 93 Responses – 

199 Skipped

Yampa River near Maybell, 

Colorado

Little Yampa 

Canyon

Cross Mountain 

Canyon

800–10,000 1,700–4,500 22 Responses –

270 Skipped

51 Responses – 

241 Skipped

Yampa River at Deerlodge Park, 

Colorado

Yampa Canyon 1,500–20,000 5,000–15,000 102 Responses –

190 Skipped

Green River at Jensen, Utah Split Mountain 

Canyon

1,200–50,000 2,500–25,000 32 Responses – 

358 Skipped

White River near Watson, Utah Lower White Not Applicable Not Applicable 2 Responses –

388 Skipped

Green River at Green River, Utah Gray, Desolation, 

Labyrinth, and

Stillwater 

Canyons

1,600–50,000 3,000–20,000 26 Responses – 

364 Skipped

San Juan River near Bluff, Utah Lower San Juan 800–50,000 1,400–7,500 37 Responses –

353 Skipped

4.0 References 

Shelby, B., J.J. Vaske, and M.P. Donnely. 1996. “Norms, standards and natural resources.” 

Leisure Sciences, 18:103–123. 

Whittaker, D., B. Shelby, and J. Gangemi. 2005. Flows and Recreation, A Guide to Studies for 

River Professionals. U.S. Department of the Interior, National Park Service. 

Whittaker, D., B. Shelby, W. Jackson, and R. Beschta. 1993. Instream Flows for Recreation: A 

Handbook on Concepts and Research Methods. U.S. Department of the Interior, National 

Park Service.

Appendix D2 

Attachment A 

American Whitewater Draft Report

American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

December 2012 D2-A-1 

DRAFT SUMMARY REPORT 

Evaluating Recreational Flow-Needs in the Upper Colorado River Basin 

Defining Low, Acceptable, and Optimal Flows for Whitewater Boating 

Nathan Fey 

American Whitewater 

Evan Stafford 

CK Consulting 

Abstract: 

 Effects of in-stream flows on river-based recreational attributes, such as whitewater 

boating, have profound impacts on recreation opportunities. In many watersheds, streamflows 

necessary to provide the full range of whitewater boating opportunities are often not clearly 

defined - presenting a challenge to resource managers seeking to balance water supply and 

demand strategies. In this study, an online survey was designed and conducted to allow 

whitewater enthusiasts to evaluate flows for whitewater boating on rivers within the Upper 

Colorado River basin, and identify low, acceptable and optimum flows for 10 targeted river 

segments. Flow Acceptability Agreement Index curves summarizes the quality of boating 

opportunities for each measured stream-flow. Respondents also reported flows that provide 

certain recreation experiences, from technical low water to challenging high water trips. 

American Whitewater conducted this study to provide information on flows needed to sustain 

the whitewater boating resource in the Upper Colorado River basin. This information is being 

reported with the express intent of developing a quantitative metric for evaluating impacts to 

existing recreational flow-needs under various management opportunities currently being 

investigated under the US Bureau of Reclamation’s Colorado River Basin Study. 
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

D2-A-2 December 2012 

Contents 

I. Introduction 

II. Recreational Flow Assessment – Locations and Methods 

 - Recreational Whitewater Attribute Locations Table A 

 - Recreational Whitewater Attribute Locations and Respondent Numbers Table B 

 

III. Results and Discussion 

 A. Flow Evaluation Curves 

 - Acceptable and Optimal Flows for Whitewater Boating Table C 

 - Impact Acceptability Curve Acceptable and Optimal Flows by Craft-type Table D 

 

 B. Specific Flow Evaluations 

 - Median Whitewater Boating Flow Evaluations Table E 

 - Mean Whitewater Boating Flow Evaluations Table F 

 C. Discussion 

IV. Conclusion 

 - Integrating Overall and Specific Flow-Evaluations Figure A 

Appendix A 

 Online Flow-Evaluation Survey Attachment 

Appendix B 

 Overall Flow Evaluations 

 - Flow-Evaluation Curves Figures 1-8 

 - Mean Acceptability Agreement and FAAI data Tables 1-8 

Appendix C 

A subset listing of projects at which whitewater boating has been analyzed. 
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

December 2012 D2-A-3 

I. Introduction

 Whitewater boating is a flow dependent recreational use of rivers, and considerable work 

evaluating flow-recreation relationships has occurred over the last several decades (Brown et 

al., 1991; Shelby, Brown, & Taylor, 1992; Whittaker and Shelby, 2002). Many of the flowrecreation studies focus on whitewater boating, such as rafting, kayaking, and canoeing, as flow 

often determines whether people have opportunities to take a trip and what level of challenge or 

social value is provided (Whittaker & Shelby, 2000). Different flow levels provide for varied 

whitewater boating opportunities. As flows increase from zero, different paddling opportunities 

and challenges exist within ranges of flows on a spectrum: too low, minimal acceptable, 

technical, optimal, high challenge, and too high. Standard methodologies are used to define 

these flow ranges based on individual and group flow-evaluations. The various opportunities 

provided by different flow ranges are described as occurring in “niches” (Shelby et al., 1997). 

 

 Whitewater Boating is enjoyed in different crafts, such as canoes, kayaks, and rafts. 

Different craft types provide different opportunities for river-based recreation, from individual or 

small group trips, to large group multi-day excursions. Flows that provide greater social value for 

one type of craft, such as canoes, may not provide equivalent social value for rafting. Changes 

in streamflow can have direct effects on the quality of whitewater boating, for every craft type. 

Direct effects may change quickly as flows change, such as safety in running rapids, number of 

boat groundings, travel times, quality of rapids, and beach and camp access (Brown, Taylor, & 

Shelby, 1991; Whittaker et al., 1993; Whittaker & Shelby, 2002). Indirectly, flow effect wildlife 

viewing, scenery, fish habitat, and riparian vegetation over the long term as a result of changes 

in flow regime (Bovee, 1996; Richter et al., 1997; Jackson & Beschta, 1992; Hill et al., 1991). 

 Streamflow is often manipulated through controlled reservoir releases, unanticipated 

spills from dams, and in-channel diversions. Additional scenarios, such as climate change and 

drought, water rights development, or conservation and the associated decreases in water 

demands, can all impact flows and recreation quality. Decision-makers within land and resource 

management and regulatory agencies, are increasingly interested in assessing the impacts of 

flow regimes on recreation resources. This has been most notable in the Federal Energy 

Regulatory Commission’s (FERC) relicensing process, and where decision-makers, resource 

managers, and interest groups consider the extent that flow regimes can be managed to provide 

desirable recreational resource conditions. Appendix C lists a subset of projects where 

Whitewater Boating Flows have been analyzed. In these decision-making settings, specific 

evaluative information on how flow affects recreation quality is critical, particularly where social 

values are often central to decision-making (Kennedy and Thomas 1995). 

 Researchers collecting and organizing evaluative information, often employ a normative 

approach using survey-based techniques. This approach is particularly useful for developing 

thresholds, or standards, that define low, acceptable, and optimal resource conditions for 

whitewater boating. Thresholds are crucial elements in any effective management or decisionmaking process (Shelby et al. 1992). The approach examines individuals’ evaluations of a range 

of conditions (personal norms). Social Norms, defined by aggregate personal norms, describe a 

group’s collective evaluation of resource conditions. This approach has been used to 

understand streamflows for whitewater boating on the Grand Canyon (Shelby et al. 1992), as 

well as several others rivers in Colorado (Vandas et al. 1990, Shelby & Whittaker 1995, Fey & 

Stafford 2009, Fey & Stafford 2010). 

 American Whitewater designed and conducted this study to collect evaluative 

information on whitewater boating attributes for 10-targeted recreational resources in the 

Colorado River Basin. Using overall flow-evaluation data, we developed flow-evaluation curves 
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

D2-A-4 December 2012 

that identify low, acceptable, and optimum flows for whitewater boating. In addition, specific flow 

evaluations were collected to aid in “calibrating” points along each curve. The present paper 

integrates both types of information in order to assist the Protect the Flows Campaign and the 

U.S. Bureau of Reclamation, in the development of quantitative recreational System Reliability 

Metrics that can be implemented in the Colorado River Basin Study. 

II. Recreational Flow Assessment – Locations and Methods

 To define normative standards for whitewater boating flows in the Upper Colorado River 

basin, American Whitewater collected and organized personal evaluations of recreational 

resource conditions, and recreation-relevant hydrology, consistent with NPS methodologies1

. 

Using a web-based survey tool2, American Whitewater designed two sets of questions asking 

respondents to evaluate flows for ten rivers, relative to specific U.S. Geological Survey 

streamflow gage locations and Colorado River Simulation System Nodes. 

Table A: Recreational Whitewater Attribute Locations

Whitewater Resource Location USGS 

Gage

Whitewater Boating Attribute

Colorado River At Glenwood Springs 9072500 Glenwood Springs Playpark & South Canyon

Colorado River Near Cameo – CO 9095500 Big Sur

Gunnison River Near Grand Junction 9152500 Lower Gunnison (Dominguez-Escalante)

Dolores River Near Cisco - UT 9180000 Lower Dolores River

Colorado River Near Cisco – UT 9180500 Hittle Bottom & Moab Daily

Green River Near Green River - WY 9217000 Green River Whitewater Park

Green River at Jensen – UT 9261000 Split Mountain Canyon

White River Near Watson – UT 9306500 Lower White River

Green River At Green River – UT 9315000 Desolation-Gray, Labyrinth & Stillwater Canyons

San Juan River Near Bluff - UT 9379500 Lower San Juan

An online approach to the flow comparison survey was used in this study for several reasons: 

- The study timeframe was too short to use other approaches, such as mail-in surveys or inperson ballots. 

- Many whitewater boaters that have taken trips on these target rivers hail from around the 

United States. An online approach makes it easier to access this knowledge base. 

- Electronic announcements and links to the survey website facilitate broader participation and 

higher respondent numbers. 

 The Flow-Evaluation Survey was based on the normative approach discussed above. 

One set of survey questions was used to develop overall flow-evaluations curves, and another 

set of questions helped identify and explain various points on those same curves. Overall Flow 

evaluation questions asked respondents to evaluate overall recreation quality for specific 

measured flows on each study segment, using a seven-point “acceptability” scale (unacceptable 

-3 and acceptable 3). This type of Survey contrasts with surveys that evaluate a single flow, or 

surveys conducted while flows are manipulated by controlled releases over a short period of 

time (Whittaker et al. 1993). 

 Another set of six specific flow evaluation questions asked respondents to report: 1) the 

minimum whitewater flow, 2) lowest preferred whitewater flow, 3) technical whitewater flow, 4) 

optimal whitewater flow, 5) high whitewater flow, and 6) highest safe whitewater flow. Each 

respondent reported flows with respect to their preferred craft-type. A copy of the online Flow-

 

1

 Whittaker, D., B. Shelby, J. Gangemi. 2005. Flows and Recreation, A guide to studies for river professionals. 

U.S. Department of the Interior, National Park Service, Anchorage, AK. 

2

 www.surveymonkey.com
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

December 2012 D2-A-5 

Evaluation Survey, including both sets of questions, is attached as Appendix A. 

An announcement of the flow-evaluation study was sent to over 5,000 American 

Whitewater members, including a link to the online survey website. The announcement was 

also posted to several online river-related discussion forums and various regional paddling club 

websites. The online format allowed whitewater boaters of all skill-levels and craft-types to 

report personal evaluations. The survey sample included outfitters currently permitted to operate 

commercially on targeted rivers, and non-commercial boaters. Because there were few 

differences between these groups, the data was combined in the analysis. 

 In all, 382 volunteer paddlers responded to the survey, although very few respondents 

had experience with every segment in the study. Table B summarizes the number of survey 

responses for each study segment. For this study, 93% of respondents identified themselves as 

private paddlers, 78% of respondents identified themselves as advanced or expert paddlers, 

and 73% reported paddling at least 20+ days per season. A wide-range of craft types was 

surveyed, with rafters (23%), kayakers (72%), canoeists (5%) all represented. 

Most respondents (42%) reported living in six Colorado basin states, such as Wyoming, 

Colorado, Utah, New Mexico, Arizona, and Nevada, though paddlers from 38 states participated 

in the survey. 65% of respondents felt “very comfortable” estimating flows in cfs (cubic feet per 

second) on targeted river segments, while no respondents reported feeling “uncomfortable” or 

even “somewhat uncomfortable” estimating flows on their favorite stretch.

Table B:

Recreational Whitewater Attribute Locations and Respondent Numbers 

Whitewater Boating Location USGS 

Gage 

Whitewater Boating 

Attribute

Respondent 

Numbers

Colorado River At Glenwood Springs 9072500

Glenwood Springs -

South Canyon

42 Responses 

Colorado River Near Cameo 9095500 Colorado River - Big Sur 26 Responses 

Gunnison River Near Grand Junction 9152500

Lower Gunnison

Dominguez-Escalante

7 Responses 

Dolores River Near Cisco 9180000 Lower Dolores 48 Responses 

Colorado River Near Cisco 9180500 Hittle Bottom- Moab Daily 35 Responses

Green River Near Green River WY 9217000

Green River Whitewater 

Park 6 Responses 

Green River at Jensen 9261000 Split Mountain Canyon 32 Responses 

White River Near Watson 9306500 Lower White 2 Responses 

Green River At Green River UT 9315000

Desolation-Gray, 

Labyrinth & Stillwater 

Canyons 26 Responses 

San Juan River Near Bluff 9379500 Lower San Juan 37 Responses 

 For most segments studied, responses provided sufficient information to proceed with 

data analysis and organization. For both the Green River Whitewater Park, and Lower White 

River Attributes, not enough information was provided to develop FAAI curves. While 

responses for the Lower Gunnison River were less than 10 in aggregate, most evaluations show 

a high level of agreement, and supported flow-curve development. 

III. Results and Discussion 

 

A. Overall Flow Evaluations 

 

 Mean responses from the overall flow evaluation questions were plotted for each flow 
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

D2-A-6 December 2012 

level, and connected to create a curve. In most cases, the curves show inverted U shapes 

where low flows and high flows provide low quality recreation conditions, while medium flows 

provide more optimal conditions. Utilizing Flow Acceptability Agreement Index (FAAI) curves, 

the range of acceptable and optimal flows for whitewater boating were identified for most 

segments. Table B summarizes overall flow-evaluations for whitewater boating, including all 

craft-types. 

Table C: Acceptable and Optimal Flows for Whitewater Boating 

Whitewater Boating Attribute Minimum 

Flow (cfs)

Optimal Flows 

(cfs) 

Acceptable Flows 

(cfs) 

Glenwood Springs Playpark & South Canyon 1600 7,000-20,000 1,600-50,000

Big Sur 20,000 27,500-50,000 20,000-50,000

Lower Gunnison (Dominguez-Escalante) 900 2,000-12,500 900-15,000

Lower Dolores River 900 1,800-3,000 900-20,000

Hittle Bottom & Moab Daily 1800 4,000-15,000 1,800-100,000

Green River Whitewater Park Insufficient data

Split Mountain Canyon 1200 2,500-25,000 1,200-50,000

Lower White River Insufficient data

Desolation-Gray, Labyrinth & Stillwater Canyons 1600 3,000-20,000 1,600-50,000

Lower San Juan 800 1,400-7,500 800-50,000

For two study reaches (Green River Whitewater Park (WY), and Lower White River 

(UT)), response numbers were too low and did not provide sufficient data for curve 

development. For all other study segments, where evaluations of higher flows never drop below 

the neutral line, recreation quality may decline but may not drop below acceptable levels. Open 

response questions, discussed in Section B, were used to help identify flows that provide 

minimum, optimal, and high acceptable flows for each segment. 

The Flow Acceptability Agreement Index determines respondent agreement regarding 

the acceptability of each specific flow level (Figures and Tables 1-8, Appendix B). FAAI statistics 

show extremely high agreement levels for optimal flows (FAAI statistics range between 0 

complete agreement, to 1 complete disagreement) while some level of disagreement between 

respondents exists in regard to the range of acceptable flows. The level of disagreement can be 

attributed to variability between craft types, although other factors likely play a role including 

preferred experience and skill levels of respondents. Results show that for most study 

segments, acceptable flows for kayaks may not provide equal value for rafts. 

 Table D lists acceptable and optimal flows for both rafts and kayaks to illustrate the 

variability by craft-type. 
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

December 2012 D2-A-7 

Table D 

Colorado River Basin Segments FAAI Summary 

Minimum, Optimal and Acceptable Flows by Craft-Types 

Colorado River 

Basin Segment

Minimum Flow 

(CFS)

Optimal Flows 

(CFS)

Acceptable Flow 

(CFS)

Glenwood Park & 

South Canyon

Raft 1000 2800-16000 1000-25000

Kayak 1600 12000-25000 1600-50000

Big Sur 

Raft NA NA NA

Kayak 20000 25000-50000 20000-50000

Lower Gunnison

Raft 800 2000-12500 800-20000

Kayak NA NA NA

Lower Dolores

Raft 1000 2000-4000 1000-20000

Kayak 800 1400-2500 800-20000

Moab Daily

Raft 1800 5000-40000 1800-100000

Kayak 1800 5000-20000 1800-100000

Split Mountain

Raft 1200 4000-25000 1200-50000

Kayak 1000 2000-20000 1000-50000

Desolation/Gray

Raft 1600 5000-20000 1600-50000

Kayak 1400 4000-30000 1400-50000

Lower San Juan

Raft 1000 2000-7500 1000-20000

Kayak 800 1800-1000 800-20000

 

 For most study segments, respondents reported flows for both rafts and kayaks. Results 

show that for most segments, kayaks identify lower flows as more acceptable than similar flows 

for rafts. These results are typical for smaller craft-types where lower flows are sufficient for 

acceptable whitewater boating opportunities, while low flows do not provide enough flow for 

larger crafts, like rafts. Results for Glenwood Whitewater Park and South Canyon do not show 

similar results between craft types. Empirical data describe kayak evaluations as targeting key 

experiences at the Glenwood Wave, while rafting flows were evaluated for a longer downriver 

experience, where lower flows are sufficient for floating through South Canyon. 

B. Specific Flow Evaluation 

 In order to further refine the overall flow-evaluation curves, a second set of single-flow 

evaluations were presented to survey respondents. For each study segment, survey 

respondents reported a single flow value that provides a distinct paddling experience or “niche” 

along a spectrum: minimum, low, technical, optimal, high challenge, and highest safe flow. 

These “niches” relate stream flow to the full range of whitewater boating opportunities and aid in 

refining the flow-recreation relationship described in each Flow-Curve. Overlaying the specific 

and overall flow-evaluation results is a helpful approach to analyzing the results of specific flowevaluations. 

 With single preference norms reported as specific flow evaluations, measures of central 

tendency, such as the mean and median, are useful representations of the flow in question. 

Median flow evaluations for each study segment are described in Table E. For comparison, 

mean flow evaluations are summarized in Table F. 
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

D2-A-8 December 2012 

Table E 

MEDIAN Minimum, Low, Technical, Optimal, High and Maximum Flows 

Whitewater Boating 

Attribute

Minimum 

Flow 

(CFS)

Low 

Flow 

(CFS)

Technical 

Flow 

(CFS)

Optimal 

Flow 

(CFS)

High 

Flow 

(CFS)

Maximum 

Flow 

CFS)

1) Glenwood Springs & South 

Canyon 1000 2000 1500 4000 20000 30000

2) Big Sur 20000 20000 20000 22000 30000 30000

3) Lower Gunnison 

(Dominguez-Escalante) 700 900 800 3000 9000 15000

4) Lower Dolores River 700 1000 800 1500 3500 5000

5) Hittle Bottom & Moab Daily 1200 2000 1600 4000 20000 40000

- Green River Whitewater Park - - - - - -

6) Split Mountain Canyon 900 1300 1100 3000 20000 30000

- Lower White River - - - - - -

7) Desolation-Gray, Labyrinth 

& Stillwater Canyons 1200 2200 1100 5000 20000 35000

8) Lower San Juan 650 1000 900 2000 7000 20000

Table F 

MEAN Minimum, Low, Technical, Optimal, High and Maximum Flows 

Whitewater Boating 

Attribute

Minimum 

Flow 

(CFS)

Low 

Flow 

(CFS)

Technical 

Flow 

(CFS)

Optimal 

Flow 

(CFS)

High 

Flow 

(CFS)

Maximum 

Flow 

CFS)

1) Glenwood Springs & South 

Canyon 2281 3412 2502 6009 17624 29175

2) Big Sur

3) Lower Gunnison 

(Dominguez-Escalante) 686 1286 1083 2743 9167 14833

4) Lower Dolores River 783 1048 847 1549 3978 6788

5) Hittle Bottom & Moab Daily 1379 2588 2029 5372 23933 42306

- Green River Whitewater Park - - - - - -

6) Split Mountain Canyon 1053 1745 1346 3843 14603 19089

- Lower White River - - - - - -

7) Desolation-Gray, Labyrinth 

& Stillwater Canyons 1354 2757 1633 6631 20857 38181

8) Lower San Juan 709 1070 930 2594 8050 15432

Note: mean flow-values have been rounded to the nearest whole number. 

C. Discussion 

 

 For most segments, single-flow evaluations are shown to closely mimic relative values 

identified by the FAAI curves for minimum acceptable, optimal, and maximum acceptable flows. 

While differences between mean and median flow evaluations for open-ended responses have 

been established, these values help describe specific flow-dependant “niches” for whitewater 

boating experiences along each FAAI curve. For the Green River Whitewater Park and Lower 

White River attributes, insufficient data provided during the study period precluded analysis of 

FAAI curves, and did not provide enough data to analyze specific flow-evaluations for those 

attributes. 
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

December 2012 D2-A-9 

 Overlaying the specific and overall flow-evaluation results is a helpful approach to 

analyzing the results of the study. An example of this integration, using the Glenwood Springs 

and South Canyon Attribute is provided in Figure A. Following along the curves for both kayaks 

and rafts, the mean flow identified for minimum whitewater boating, for both craft-types is 1000 

cfs (average of both flow-curves). This is close to the point on the overall flow-evaluation curve 

(Figure 1, Appendix B) where the neutral line between un-acceptable and acceptable valuation 

is crossed. Integrating results from both overall and specific flow-evaluation questions provides 

more information than either format by itself. For more on integrating the results from Overall 

and Specific Flow Evaluations, refer to the Final Report of our Flow-Evaluation Study. 

Figure A 

Flow Acceptability Curves for Kayaks and Rafts - Glenwood Wave and South Canyon 

IV. Conclusion 

 To establish flow ranges for acceptable and optimal recreational opportunities, American 

Whitewater collected and organized personal evaluations of recreational resource conditions, 

and recreation-relevant hydrology, consistent with standard methodologies. An online survey 

conducted in 2011, involved 382 volunteer paddlers representing a range of experience and skill 

level. 

 Study respondents were asked to evaluate overall recreation quality for each measured 

flow at each study segment, using a seven-point “acceptability” scale. Using a survey-based 

normative approach, individual evaluations of flows are aggregated into social norms, which 

describe the group’s collective evaluation of those same stream flows. Impact Acceptability 

Curves and the Flow Acceptability Agreement Index were used to help determine minimum, 
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

D2-A-10 December 2012 

optimal and the range of acceptable flows, and respondent agreement regarding each specific 

flow level. For each of the river segments surveyed, high levels of agreement on optimal flows 

were recorded. Minimum acceptable flows were identified for each segment. For many 

segments, respondents reported no maximum acceptable flow; defining a wide range of 

acceptable flows, up to 100,000 cfs for certain high volume runs. 

 Good whitewater conditions require higher flows than those identified as providing 

minimum boatable flows. Good whitewater conditions for each target river segment have been 

identified in this study. For each study segment, the median response for minimum whitewater 

corresponds to the point where the overall flow-evaluation crosses the neutral line. The median 

response for optimal flows however corresponds with the peak of the curve where ratings are 

highest. Overall Flow-evaluation curves are relatively flat at the top of most segments, which is 

attributed to the multiple tolerance norms captured in the study results. 

 Whitewater flow-preferences described in this summary report make it possible to 

analyze and evaluate the impacts to whitewater boating under future water supply scenarios 

being developed under the U.S. Bureau of Reclamation’s Colorado River Basin Study. A 

quantitative metric of “boatable days” can be developed using the reported flow-evaluations 

from this study. This metric can aid in developing a relative comparison (boatable days) to 

quantify effects of flow manipulation under various scenarios for future supply and demand 

scenarios in the Colorado River basin. 
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

December 2012 D2-A-11

Literature Cited 

Bovee, K.D. (editor). (1996) The Complete IFIM: A Coursebook for IF250. Fort Collins, CO: 

U.S. Geological Survey. 

Brown, T.C., Taylor, J.G., & Shelby, B. (1991). Assessing the direct effects of Stream flow on 

recreation: A literature review. Water Resources Bulletin, 27(6), 979-989. 

Fey, N. & Stafford, E. (2009) Flow-Recreation Evaluations for the Upper Colorado River basin. 

Report to Upper Colorado River Wild and Scenic Stakeholders Group & U.S. Bureau of Land 

Management (unpublished) American Whitewater 

Fey, N. & Stafford, E. (2010) Defining Streamflows for Whitewater Boating in the Yampa River 

basin. Report to the Yampa-White Basin Roundtable and Colorado Department of Natural 

Resources (unpublished) American Whitewater 

Hill, M.T., Platts, W.S., and Beschta, R.L. (1991) Ecological and geomorphological concepts for 

instream and out-of-channel flow requirements. Rivers 2(3): 198-210

Jackson, W.L. & Beschta, R.L. (1992) Instream flows for rivers: Maintaining stream form and 

function as a basis for protecting dependant uses. In M.E. Jones and A. Laenen (editors), 

Interdisciplinary Approaches in Hydrology and Hydrogeology. St. Paul, MN: American Institute 

of Hydrology. 

Kennedy, J.J. & Thomas, J.W. (1995) Managing natural resources as social value. Pages 311-

322 in R.L. Knight and S.F. Bates (editors), A New Century for Natural Resources Management. 

Island Press, Washington D.C. 

Richter, B.D., Baumgartner, J.V., Wigington, R., and Braun, D.P. (1997) How much water does 

a river need? Freshwater Biology 37:231-249 

Shelby, B., Brown, T. C., & Taylor, J. G. (1992). Streamflow and Recreation. Ft. Collins, CO: 

USDA Forest Service, Rocky Mountain Forest and Range Experiment Station (General 

Technical Report RM-209). 

Shelby, B., Brown, T.C., and Baumgartner, R. (1992) Effects of streamflows on river trips on the 

Colorado River in Grand Canyon, Arizona. Rivers 3(3): 191-201

Shelby, B., Stankey, G., and Schindler, B. (1992) Introduction: the role of standards in 

wilderness management. Pages 1-4 in B. Shelby, G. Stankey, and B. Shindler (editors) 

Defining wilderness quality: The role of standards in wilderness management. Portland, OR: 

U.S. Forest Service, Pacific Northwest Research Station (General Technical Report PNW-GTR305). 

Shelby, B. & Whittaker, D. (1995) Flows and Recreation Quality on the Dolores River: 

Integrating overall and Specific Evaluations Rivers 5(2) 121-132

Shelby, B., Vaske, J.J., & Donnely, M.P. (1996). Norms, standards and natural resources. 

Leisure Sciences, 18, 103-123

Shelby, B., Whittaker, D. & Hansen, W. (1997). Streamflow effects on hiking in Zion National 

Park, Utah. Rivers, 6(2), 80-93
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

D2-A-12 December 2012 

Vandas, S., Whittaker, D., Murphy, D., Prichard, D., and others. (1990) Dolores River Instream 

Flow Assessment. Denver, Co: U.S. Bureau of Land Management (BLM/YA/PR-90-003). 

Whittaker, D., Shelby, B., Jackson, W., & Beschta, R. (1993). Instream Flows for recreation: A 

handbook on concepts and research methods. Anchorage, AK: Us National Park Service, 

Rivers, Trails, and Conservation Program. 

Whittaker, D., & Shelby, B. (2001). Flows and recreation on the Clackamas River, Oregon. 

Report prepared for Portland General Eclectic. May 

Whittaker, D. and B. Shelby. (2002) Evaluating instream flows for recreation: a handbook on 

concepts and research methods. U.S. Department of Interior, National Park Service, 

Anchorage, AK 
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

December 2012 D2-A-13

Appendix A – Online Flow-Evaluation Survey 

Appendix A presented screen shots of the online flow-evaluation surveys. To save paper, the 

screen shots have not been reprinted. The survey can be viewed online at 

http://www.americanwhitewater.org/content/Article/view/articleid/31219/. 

American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

December 2012 D2-A-15

Appendix B – Overall Flow Evaluation Results 

Figure 1 

Flow Acceptability Agreement Index Curve for Glenwood Springs and South Canyon 

(Flows represented are at the USGS Colorado River At Glenwood Springs, CO) 
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

D2-A-16 December 2012 

Table 1 

Glenwood Springs and South Canyon 

Mean Acceptability Scores and Flow Acceptability Agreement Index 

Specific Flow CFS Mean Acceptability FAAI

100 -2.74 0.06

200 -2.74 0.06

300 -2.71 0.06

400 -2.66 0.08

500 -2.46 0.08

600 -2.26 0.08

700 -1.86 0.11

800 -1.56 0.20

900 -1.29 0.27

1000 -0.77 0.38

1200 -0.34 0.53

1400 -0.26 0.55

1600 0.35 0.50

1800 0.46 0.46

2000 1.06 0.31

2200 1.12 0.30

2400 1.35 0.29

2600 1.51 0.30

2800 1.73 0.27

3000 1.95 0.19

3200 2.03 0.19

3400 2.03 0.19

3600 2.06 0.21

3800 2.11 0.21

4000 2.32 0.18

4500 2.32 0.19

5000 2.38 0.18

6000 2.39 0.19

7000 2.47 0.19

8000 2.47 0.19

9000 2.5 0.20

10000 2.45 0.22

12000 2.53 0.23

14000 2.55 0.24

16000 2.53 0.23

18000 2.53 0.25

20000 2.47 0.29

25000 2.39 0.33

30000 1.78 0.54

50000 1.47 0.61
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

December 2012 D2-A-17

Figure 2 

Flow Acceptability Agreement Index Curve for Big Sur 

(Flows represented are flow levels at USGS Colorado River near Cameo, CO) 

Table 2 

Big Sur Mean Acceptability Scores and 

Flow Acceptability Agreement Index 

Specific Flow CFS Mean Acceptability FAAI

100 -3 0.00

500 -3 0.00

1000 -3 0.00

1500 -3 0.00

2000 -3 0.00

2500 -3 0.00

3000 -3 0.00

4000 -2.91 0.00

5000 -2.86 0.00

10000 -2.73 0.00

12500 -2.55 0.03

15000 -2.18 0.18

17500 -1.04 0.41

20000 0.83 0.42

22500 1.88 0.19

25000 2.29 0.18

27500 2.71 0.11

30000 2.88 0.04

40000 2.67 0.06

50000 2.57 0.08
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

D2-A-18 December 2012 

Figure 3 

Flow Acceptability Agreement Index Curve for Lower Gunnison 

(Flows represented are at the USGS Gunnison River Near Grand Junction, CO) 

Table 3 

Lower Gunnison 

Mean Acceptability Scores and Flow Acceptability Agreement Index 

Specific Flow CFS Mean Acceptability FAAI

100 -3 0.00

200 -3 0.00

300 -3 0.00

400 -2.86 0.00

500 -2.14 0.00

600 -1.86 0.10

700 -0.57 0.38

800 -0.29 0.48

900 0.71 0.38

1000 1.29 0.29

1200 1.71 0.19

1400 1.71 0.19

1600 1.86 0.10

1800 2 0.10

2000 2.29 0.00

2500 2.29 0.05

3000 2.57 0.10

4000 2.57 0.14

5000 2.71 0.19

7500 2.71 0.24

10000 2.57 0.29

12500 2.57 0.33

15000 2.14 0.38
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

December 2012 D2-A-19

Figure 4 

Flow Acceptability Agreement Index Curve for Lower Dolores (Flows 

represented are flow levels at the USGS Dolores River Near Cisco, CO) 

Table 4 

Lower Dolores 

Mean Acceptability Scores and Flow Acceptability Agreement Index 

Specific Flow CFS Mean Acceptability FAAI

100 -3 0.00

200 -2.98 0.00

300 -2.9 0.00

400 -2.83 0.02

500 -2.37 0.05

600 -1.8 0.11

700 -1.2 0.16

800 -0.16 0.42

900 0.56 0.34

1000 1.28 0.19

1200 1.79 0.14

1400 2.16 0.11

1600 2.36 0.08

1800 2.4 0.05

2000 2.6 0.03

2500 2.56 0.04

3000 2.5 0.06

4000 2.22 0.14

5000 1.69 0.27

7500 1.5 0.32

10000 0.92 0.56

15000 0.58 0.68

20000 0.34 0.79
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

D2-A-20 December 2012 

Figure 5 

Flow Acceptability Agreement Index Curve for Colorado River above Moab 

(Flows represented are flow levels at the USGS Colorado River Near Cisco, CO) 

Table 5 

Colorado River above Moab 

Mean Acceptability Scores and Flow Acceptability Agreement Index 

Specific Flow CFS Mean Acceptability FAAI

100 -3 0.00

500 -2.91 0.00

700 -2.63 0.00

900 -2.13 0.08

1000 -1.45 0.28

1200 -1.19 0.29

1400 -0.67 0.40

1600 -0.18 0.46

1800 0.24 0.48

2000 0.97 0.31

2500 1.56 0.16

3000 1.91 0.08

4000 2.35 0.04

5000 2.62 0.01

7500 2.82 0.02

10000 2.82 0.03

15000 2.71 0.06

20000 2.41 0.13

25000 2.34 0.17

30000 2.19 0.22

40000 2.16 0.22

50000 1.72 0.38

75000 1.36 0.48

100000 1.07 0.58
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

December 2012 D2-A-21

Figure 6 

Flow Acceptability Agreement Index Curve for Split Mountain 

(Flows represented are flow levels at USGS Green River at Jensen, UT) 

Table 6 

Split Mountain 

Mean Acceptability Scores and Flow Acceptability Agreement Index 

Specific Flow CFS Mean Acceptability FAAI

100 -3 0.00

300 -2.78 0.00

500 -2.57 0.09

700 -2.09 0.09

900 -0.87 0.23

1000 -0.29 0.39

1200 0.43 0.35

1400 1.08 0.17

1600 1.83 0.22

1800 2 0.06

2000 2.25 0.03

2500 2.58 0.04

3500 2.63 0.04

4000 2.74 0.06

5000 2.48 0.15

7500 2.46 0.15

10000 2.36 0.20

15000 2.59 0.15

20000 2.5 0.25

30000 2.16 0.37

40000 1.53 0.51

50000 1.06 0.65
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

D2-A-22 December 2012 

Figure 7 

Flow Acceptability Agreement Index Curve for Desolation and Gray Canyons 

(Flows represented are flow levels at USGS Green River at Green River, UT) 

Table 7 

Desolation and Gray Canyons 

Mean Acceptability Scores and Flow Acceptability Agreement Index 

Specific Flow CFS Mean Acceptability FAAI

100 -3 0.00

300 -3 0.00

400 -2.94 0.00

500 -2.88 0.00

600 -2.63 0.00

700 -2.41 0.00

800 -1.82 0.04

900 -1.41 0.08

1000 -1.22 0.15

1200 -0.47 0.36

1400 -0.06 0.56

1600 0.47 0.46

1800 0.71 0.39

2000 1.35 0.24

2500 1.61 0.17

3000 2.05 0.07

4000 2.33 0.06

5000 2.68 0.07

7500 2.68 0.09

10000 2.84 0.11

15000 2.68 0.12

20000 2.47 0.245614

30000 2.28 0.2777778

40000 1.59 0.3137255

50000 1.5 0.3125
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

December 2012 D2-A-23

Figure 8 

Flow Acceptability Agreement Index Curve for Lower San Juan 

(Flows represented are flow levels at the USGS San Juan River Near Bluff, CO) 

Table 8 

Lower San Juan 

Mean Acceptability Scores and Flow Acceptability Agreement Index 

Specific Flow CFS Mean Acceptability FAAI

100 -3 0.00

300 -2.77 0.00

400 -2.45 0.00

500 -2.03 0.02

600 -1.35 0.06

700 -0.71 0.26

800 0.12 0.46

900 0.61 0.34

1000 1.25 0.17

1200 1.75 0.13

1400 2.19 0.09

1600 2.4 0.04

1800 2.48 0.04

2000 2.67 0.02

2500 2.7 0.03

3000 2.8 0.02

4000 2.87 0.03

5000 2.84 0.06

7500 2.57 0.15

10000 2.32 0.21

15000 2.04 0.17

20000 1.88 0.19

30000 2.28 0.28

40000 1.59 0.31

50000 1.5 0.31

American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

December 2012 D2-A-25

Appendix C 

A subset of FERC regulated hydropower projects at which discrete usable boating days 

have been scheduled and/or provided as mitigation for impacts to whitewater boating, 

and/or analyzed as part of a whitewater flow study.

River Project Name State FERC 

Project #

COOSA RIVER JORDAN DAM AL 00618

COOSA RIVER MITCHELL AL 00082

BUTTE CREEK FORKS OF BUTTE CA 06896

FEATHER RIVER FEATHER RIVER CA 02100

KERN RIVER BOREL CA 00382

KERN RIVER ISABELLA CA 08377

KERN RIVER KERN CANYON CA 00178

KERN RIVER KERN RIVER NO 1 CA 01930

KERN RIVER KERN RIVER NO 3 CA 02290

KINGS RIVER PINE FLAT CA 02741

MIDDLE FORK AMERICAN R MIDDLE FORK AMERICAN 

RIVER

CA 02079

MIDDLE FORK STANISLAUS 

RIVER

BEARDSLEY/DONNELLS CA 02005

N FK KINGS R HAAS-KINGS RIVER CA 01988

NORTH FORK FEATHER 

RIVER

POE CA 02107

NORTH FORK FEATHER 

RIVER

ROCK CREEK-CRESTA CA 01962

NORTH FORK FEATHER 

RIVER

UPPER NORTH FORK 

FEATHER RIVER

CA 02105

NORTH FORK MOKELUMNE 

RIVER

MOKELUMNE RIVER CA 00137

PIRU CREEK SANTA FELICIA CA 02153

PIT RIVER MCCLOUD-PIT CA 02106

PIT RIVER PIT 3, 4, & 5 CA 00233

PIT RIVER PIT NO. 1 CA 02687

SAN JOAQUIN R KERCKHOFF CA 00096

SAN JOAQUIN RIVER BIG CREEK NO 3 CA 00120

SAN JOAQUIN RIVER BIG CREEK NO 4 CA 02017

SAN JOAQUIN RIVER BIG CREEK NO.1 & NO.2 CA 02175

SOUTH FORK AMERICAN R UPPER AMERICAN RIVER CA 02101

SOUTH FORK AMERICAN 

RIVER

CHILI BAR CA 02155

SOUTH FORK FEATHER 

RIVER

SOUTH FEATHER POWER CA 02088

SOUTH FORK OF THE 

AMERICAN RIVER

EL DORADO CA 00184

SOUTH YUBA RIVER DRUM-SPAULDING CA 02310

SOUTH YUBA RIVER YUBA-BEAR CA 02266

STANISLAUS R MIDDLE FORK SAND BAR CA 02975

STANISLAUS RIVER SPRING GAP-STANISLAUS CA 02130

WEST BRANCH FEATHER 

RIVER

DESABLA-CENTERVILLE CA 00803

TALLULAH RIVER NORTH GEORGIA GA 02354

BEAR RIVER BEAR RIVER ID 00020
American Whitewater – DRAFT Report 

Stream-flow Evaluations – Colorado River Basin Study 

D2-A-26 December 2012 

DEAD RIVER FLAGSTAFF STORAGE ME 02612

KENNEBEC RIVER INDIAN POND ME 02142

MAGALLOWAY RIVER AZISCOHOS [?] ME 04026

RAPID RIVER UPPER & MIDDLE DAMS 

STORAGE

ME 11834

S BR PENOBSCOTT R CANADA FALLS ME

W BR PENOBSCOT R PENOBSCOT ME 02458

W BR PENOBSCOT R RIPOGENUS ME 02572

SWAN RIVER BIGFORK MT 02652

WEST ROSEBUD CREEK MYSTIC LAKE MT 02301

PIGEON RIVER WALTERS NC 00432

TUCKASEGEE RIVER DILLSBORO NC 02602

WEST FORK TUCKASEGEE 

RIVER

WEST FORK NC 02686

NANTAHALA RIVER NANTAHALA NC 02692

EF TUCKASEGEE EAST FORK NC 02698

ANDROSCOGGIN RIVER PONTOOK NH 02861

PEMIGEWASSET RIVER AYERS ISLAND NH 02456

HOOSIC RIVER HOOSIC NY 02616

MONGAUP RIVER RIO NY 09690

MOOSE RIVER MOOSE RIVER NY 04349

RAQUETTE RIVER [STONE VALLEY REACH] NY

RAQUETTE RIVER PIERCEFIELD NY 07387

SACANDAGA RIVER STEWARTS BRIDGE NY 02047

SALMON R SALMON RIVER NY 11408

SARANAC RIVER SARANAC RIVER NY 02738

BEAVER RIVER BEAVER FALLS NY 02593

BEAVER RIVER BEAVER RIVER NY 02645

BLACK RIVER GLEN PARK NY 04796

BEAVER RIVER LOWER BEAVER FALLS NY 02823

BLACK RIVER WATERTOWN NY 02442

KLAMATH RIVER KLAMATH OR 02082

SOUTH FORK ROGUE RIVER PROSPECT NO 3 OR 02337

SUSQUEHANNA RIVER HOLTWOOD PA 01881

SALUDA RIVER SALUDA SC 00516

WATEREE RIVER CATAWBA-WATEREE SC 02232

LITTLE TENNESSEE RIVER TAPOCO TN 02169

DEERFIELD RIVER DEERFIELD RIVER VT 02323

LITTLE RIVER WATERBURY VT 02090

LAKE CHELAN LAKE CHELAN WA 00637

SPOKANE RIVER SPOKANE RIVER WA 02545

SULLIVAN CREEK SULLIVAN LAKE (STORAGE) WA 02225

SULTAN RIVER HENRY M JACKSON 

(SULTAN)

WA 02157

TIETON RIVER TIETON DAM WA 03701

BLACK RIVER HATFIELD WI 10805

CHIPPEWA RIVER JIM FALLS WI 02491

GAULEY RIVER SUMMERSVILLE WV 10813
Appendix D3 

Threatened and Endangered Species Metrics

December 2012 D3-1 

Appendix D3 — Threatened and Endangered 

Species Metrics 

1.0 Introduction

This appendix describes the methods used to formulate the metrics for the threatened and 

endangered species attribute of interest. The following locations were selected based on existing 

flow recommendations and their compatibility with existing modeling capabilities: the Colorado 

River near Cameo, Colorado (Cameo); Gunnison River near Grand Junction, Colorado (Grand 

Junction); Colorado River near the Colorado-Utah state line (State Line); Yampa River near 

Maybell, Colorado (Maybell); Green River near Greendale, Utah (Greendale); Green River at 

Jensen, Utah (Jensen); Green River at Green River, Utah (Green River, Utah); Duchesne River 

near Randlett, Utah (Randlett); and San Juan River near Bluff, Utah (Bluff).

All selected locations have existing flow recommendations that specify suggested flows varying 

by month/season and hydrologic year type. The hydrologic year type varies based on the 

hydrologic conditions in the sub-basin as indicated by some reference value—for example, the 

forecasted inflow into a reservoir or the projected flow at a gage. In general, the 

recommendations include a base flow period and a spring peak flow period. In most cases, the 

recommendations are specified at the daily time step, though there are recommendations for 

average monthly flows at several locations. The distinction between the two is important. If the 

recommendations are stated in terms of average monthly flows, they can be directly incorporated 

into the Colorado River Simulation System (CRSS); only Cameo and Maybell have these direct

monthly recommendations. Although CRSS operates at a monthly time step, recent 

modifications to the model allow for plausible daily flow sequences to be generated at certain 

gage locations. At Greendale, Jensen, and Bluff, the daily recommendations can be directly 

compared to the stochastically generated daily flow sequences. At the remaining locations 

(Grand Junction, State Line, Green River, Utah, and Randlett), the daily flow recommendations 

were approximated as monthly volumes so that CRSS output could be used to evaluate the 

metrics. The methodology section details how the quantified flow targets were estimated for use 

in the Colorado River Basin Study (Study). In the quantified flow targets section, the target 

monthly volumes that were developed are presented. 

2.0 Methodology

2.1 Direct Use of Monthly Recommendations

The flow recommendations for Cameo (Osmundson, 2001) and Maybell (Modde and Smith, 

1995) are stated in terms of average monthly flow rates; therefore, they can be directly 

incorporated into a monthly time step model without any additional modifications. The monthly 

recommendations are presented in a later section. 

2.2 Monthly Approximations of Daily Recommendations

At locations where flow recommendations are expressed as daily values and where CRSS 

does not have the ability to produce daily flow sequences, historical gage data were 
Colorado River Basin

Water Supply and Demand Study

D3-2 December 2012

used to create an estimated daily flow sequence. This daily flow sequence was then 

converted to a monthly volume, as described in detail below.

Although the details of the flow recommendations vary between locations, they have many 

common elements. The flow recommendations are expressed as target ranges for the rate and/or 

the duration of flow, for example, 7 to 10 days at 3,000 to 3,500 cubic feet per second (cfs). Low 

and high target volumes were developed, which use the lower and upper bounds of the ranges, 

respectively. Additionally, flow recommendations define different hydrologic year types. 

Typically, the hydrologic year types are defined by the exceedance probability of the current 

year’s forecasted runoff conditions compared to the historical record1. The flow 

recommendations vary between year types to resemble the natural variability, so for each 

location there are low and high target volumes for every month and every hydrologic year type. 

Because the timing of the peak runoff varies between years, the monthly targets for April 

through July are combined for an overall spring target volume. The peak flow recommendations 

are typically for 1 to 4 weeks of the April through July period, so historical gage data are used as 

the pattern for the ascending and descending limbs of the hydrograph. The following steps 

outline the procedure to develop the monthly flow targets, which were repeated at each location. 

1. Obtain all historical, daily gage data. 

2. Rank each year based on annual (water year) volume. 

Compute the exceedance for each year as:

Exceedance = 

m

n + 1

where m = rank and n = the number of years in the record 

3. Categorize each year based on the exceedance percentages of each hydrologic year type. 

4. Depending on location, between 4 and 6 year types can exist2. 

5. Compute the average daily flow for each hydrologic year type from April 1 through July 31. 

6. Assign a daily flow rate for each day as follows:

a. During the base flow period, assign the minimum target base flow from the respective 

flow recommendation (Figure D3-1). 

b. Using the peak flow date as the center of the hydrograph, assign each day’s flow as 

the minimum target flow for the minimum number of days in the respective flow 

recommendation: 

i. Denote the start day of this peak target as Pstart and the ending day as Pend

(Figure D3-1). 

 

1 The year types are dependent on the length of the historical record. As such, the flows presented here may differ 

from the flow recommendations that exist for regulatory purposes. The inclusion of these approximated flows 

should not in any way change or affect the flow recommendations that are used for regulatory purposes.

2 The number of year types varies among locations because the respective flow recommendation documents do not 

use the same number of year types at all locations. The method here uses the same year types as the respective 

documentation.
Appendix D3 — Threatened and

Endangered Species Metrics

December 2012 D3-3 

c. Starting on April 1 and going through , assign each daily flow as the maximum 

of the base flow tar

P

g

e

et

nd

 and the average daily flow (from step 5) for the current day: 

i. Repeat for through July 31. 

7. Sum the daily flows for each month. 

8. Sum the monthly volumes for April through July. 

9. This results in the “low” target monthly and seasonal volumes. 

10. Repeat steps 6 to 8 selecting the maximum target flows and the maximum number of days at 

the target flows to compute the “high” monthly targets.

11. Repeat steps 6 to 10 for each hydrologic year type. 

FIGURE D3-1 

April through July Flow Schematic

Historical average daily flow is modified to meet the low and high base flow and peak flow recommendations. 

The peak flow recommendations are centered on the single day peak of the average daily flow. 

Pstart

1-Apr8-Apr

15-Apr22-Apr29-Apr

6-May

13-May20-May27-May

3-Jun

10-Jun17-Jun24-Jun

1-Jul8-Jul

15-Jul22-Jul29-Jul

Average daily flow Low target flows met High target flows met

Ensure the base 

flow target is met

Peak flow of X 

cfs for 14 days Peak flow of Y 

cfs for 10 days

Single day peak

of W-Z cfs

Pstart Pend

2.3 Direct Use of Daily Recommendations

Model upgrades allow for daily flow recommendations to be directly used as metrics at several 

locations within the Colorado River Basin. The operating rules within CRSS for Flaming Gorge 
Colorado River Basin

Water Supply and Demand Study

D3-4 December 2012

and Navajo were updated to reflect the recent Records of Decision (Bureau of Reclamation

[Reclamation], 2006a, 2006b) which modify the reservoir operations to help meet the respective 

flow recommendations below both reservoirs. The peak flow targets below both reservoirs are 

daily in nature, for example, 7 days at 18,600 cfs. Therefore, to adequately reflect the true 

operations of the reservoirs, CRSS aggregates daily operations to a total monthly volume 

released from the reservoirs. In doing so, the daily releases are stored in the CRSS results and 

can be compared with the daily flow recommendations during the peak flow period. 

Additionally, the flow requirements below both reservoirs are for locations that aggregate 

reservoir releases with other tributary inflows. Daily tributary flows are stochastically generated 

from monthly volumes in the model to produce a plausible daily tributary flow sequence for the 

peak flow period (April through July). When the tributary flows are combined with the reservoir 

releases, this total flow can be directly compared to the daily flow recommendations (Butler, 

2011). The daily flow sequences are not intended to be predictive; rather, in the framework of the 

probabilistic nature of CRSS, they produce a plausible daily flow sequence and provide 

variability in the daily flows for each model run. Average monthly releases are used during the 

base flow periods (August through March) because the reservoir releases are relatively constant 

during these periods. 

3.0 Quantified Flow Targets

The direct monthly and daily flow recommendations are presented in the following sections. The 

computed monthly volumes for the monthly approximations of daily recommendations are also 

provided. 

3.1 Direct Use of Monthly Recommendations

The flow recommendations from Osmundson (2001) are used directly for the threatened and 

endangered species metric at Cameo. Table D3-1 presents these recommendations. 

TABLE D3-1 

Average Monthly Flow Recommendations, in cfs, for the Colorado River near Cameo, Colorado 

Category Dry

Below 

Average

Above 

Average Wet

Rate 20% 30% 25% 25%

Exceedance 81–100% 51–80% 26–50% 0–25%

January 1,555 1,600 1,600 1,600

February 1,555 1,600 1,600 1,600

March 1,555 1,600 1,600 1,600

April 3,010 3,410 3,590 4,360

May 8,710 9,160 10,530 12,170

June 8,350 12,850 15,750 17,160

July 2,980 4,650 6,870 8,560

August 2,460 2,890 3,280 3,280

September 2,460 2,890 3,280 3,280

October 2,460 2,890 3,280 3,280

November 1,555 1,600 1,600 1,600

December 1,555 1,600 1,600 1,600

Source: Osmundson, 2001
Appendix D3 — Threatened and

Endangered Species Metrics

December 2012 D3-5 

For the Yampa River near Maybell, Colorado, Modde and Smith (1995) and the subsequent 

Yampa River Programmatic Biological Opinion (U.S. Fish and Wildlife Service [USFWS], 2005 

and 2008) recommend baseflows ranging from 120 cfs to 134 cfs throughout the year. Given the 

spatial and temporal scale of CRSS, the model will not be able to meaningfully distinguish 

between this range. For this reason, the Study assumed a baseflow target of 120 cfs for this 

metric.

3.2 Monthly Approximations of Daily Recommendations

After following the procedure described earlier for Grand Junction, State Line, Green River, 

Utah, and Randlett, the following volumetric targets were developed. The low targets for 

Grand Junction were developed from USFWS data (2009), and the high targets were developed 

from the upper bounds found in McAda (2003); the Grand Junction targets are presented in 

table D3-2. Table D3-3 presents the high and low targets for the State Line, both of which were 

developed from McAda (2003). Table D3-4 shows the high and low targets for Green River, 

Utah, which were developed based on the ranges in Reclamation (2005). Table D3-5 presents the 

monthly approximations for the Randlett flow recommendations from Modde and Keleher 

(2003). 

The goal of aggregating the April through July flow targets was to capture the runoff volume in 

one target. The historical data show that the runoff tends to occur earlier in drier years than in the 

wetter years for the Duchesne River near Randlett. To reflect this, the runoff volume was 

aggregated from March through June in dry and average years and the wet and extremely wet 

years were aggregated from April through July.

3.3 Direct Use of Daily Recommendations

The flow targets for Greendale, Jensen, and Bluff are presented in this section. Because CRSS 

can produce daily flow values at these sites, the tables presented are identical to those in the 

documents that establish the recommended flows. Table D3-6 presents both the base flow and 

peak flow recommendations for Greendale, and 
Colorado River Basin

Water Supply and Demand Study

D3-6 December 2012

Table D3-7 presents the recommendations for Jensen. Table D3-8 presents the peak flow 

recommendations for Bluff. The base flow recommendations below Navajo are stated to be 500 

to 1,000 cfs using a three-gage average (Reclamation, 2006c). Due to modeling constraints, Bluff 

is the only gage available below Navajo. It is assumed that if the base flow is met at Bluff, then 

the base flow recommendation is met (Butler, 2011). 
Appendix D3 — Threatened and

Endangered Species Metrics

December 2012 D3-7 

TABLE D3-2 

Low and High Monthly Approximations (acre-feet [af]) of Flow Recommendations for the Gunnison River near Grand 

Junction, Colorado

Year Type

Exceedance

Dry

90–100%

Moderately Dry

70–90%

Average Dry

50–70%

Low High Low High Low High

January 46,116 64,562 46,116 64,562 64,562 122,975

February 41,653 58,314 41,653 58,314 58,314 111,074

March 48,575 64,562 48,575 64,562 64,562 122,975

April–July 346,518 349,836 652,198 718,906 920,874 971,017

August 54,724 64,562 64,562 64,562 64,562 122,975

September 52,959 62,479 52,959 62,479 62,479 119,008

October 48,575 64,562 48,575 64,562 64,562 122,975

November 47,008 62,479 47,008 62,479 62,479 119,008

December 46,116 64,562 46,116 64,562 64,562 122,975

Year Type

Exceedance

Average Wet

30–50%

Moderately Wet

10–30%

Wet

0–10%

Low High Low High Low High

January 64,562 122,975 64,562 153,719 64,562 153,719

February 58,314 111,074 58,314 138,843 58,314 138,843

March 64,562 122,975 64,562 153,719 64,562 153,719

April–July 1,320,185 1,339,779 1,621,987 1,734,757 1,800,077 2,091,909

August 64,562 122,975 92,231 153,719 92,231 153,719

September 62,479 119,008 62,479 148,760 62,479 148,760

October 64,562 122,975 64,562 153,719 64,562 153,719

November 62,479 119,008 62,479 148,760 62,479 148,760

December 64,562 122,975 64,562 153,719 64,562 153,719
Colorado River Basin

Water Supply and Demand Study

D3-8 December 2012

TABLE D3-3 

Low and High Monthly Approximations (af) of Flow Recommendations for the Colorado River near the Colorado-Utah State Line

Year Type

Exceedance

Dry

90–100%

Moderately Dry

70–90%

Average Dry

50–70%

 Low High Low High Low High

January 110,678 110,678 153,719 245,950 153,719 245,950

February 99,967 99,967 138,843 222,149 138,843 222,149

March 110,678 110,678 153,719 245,950 153,719 245,950

April–July 870,512 882,380 1,511,575 1,727,954 2,102,851 2,240,154

August 110,678 110,678 153,719 245,950 153,719 245,950

September 107,107 107,107 148,760 238,017 148,760 238,017

October 110,678 110,678 153,719 245,950 153,719 245,950

November 107,107 107,107 148,760 238,017 148,760 238,017

December 110,678 110,678 153,719 245,950 153,719 245,950

Year Type

Exceedance

Average Wet

30–50%

Moderately Wet

10–30%

Wet

0–10%

Low High Low High Low High

January 184,463 295,140 184,463 295,140 184,463 368,926

February 166,612 266,579 166,612 266,579 166,612 333,223

March 184,463 295,140 184,463 295,140 184,463 368,926

April–July 3,008,537 3,228,714 4,095,964 4,220,322 4,843,930 5,270,515

August 184,463 295,140 184,463 295,140 184,463 368,926

September 178,512 285,620 178,512 285,620 178,512 357,025

October 184,463 295,140 184,463 295,140 184,463 368,926

November 178,512 285,620 178,512 285,620 178,512 357,025

December 184,463 295,140 184,463 295,140 184,463 368,926
Appendix D3 — Threatened and

Endangered Species Metrics

December 2012 D3-9 

TABLE D3-4 

Low and High Monthly Approximations (af) of Flow Recommendations for the Green River at Green River, Utah. 

Year Type

Exceedance

Dry

90–100%

Moderately Dry

70–90%

Average

30–70%

Low High Low High Low High

January 79,934 159,868 92,231 209,058 110,678 258,248

February 72,198 144,397 83,306 188,826 99,967 233,256

March 79,934 159,868 92,231 209,058 110,678 258,248

April–July 1,092,416 1,144,000 1,728,100 1,755,882 2,827,360 2,893,744

August 79,934 159,868 92,231 209,058 110,678 258,248

September 77,355 154,711 89,256 202,314 107,107 249,917

October 79,934 159,868 92,231 209,058 110,678 258,248

November 77,355 154,711 89,256 202,314 107,107 249,917

December 79,934 159,868 92,231 209,058 110,678 258,248

Year Type

Exceedance

Moderately Wet

10–30%

Wet

0–10%

Low High Low High

January 166,017 288,992 196,760 288,992

February 149,950 261,025 177,719 261,025

March 166,017 288,992 196,760 288,992

April–July 3,813,639 3,813,639 4,699,530 4,699,530

August 166,017 288,992 196,760 288,992

September 160,661 279,669 190,413 279,669

October 166,017 288,992 196,760 288,992

November 160,661 279,669 190,413 279,669

December 166,017 288,992 196,760 288,992
Colorado River Basin

Water Supply and Demand Study

D3-10 December 2012

TABLE D3-5 

Monthly Approximations (af) of Flow Recommendations for the Duchesne River near Randlett, Utah

Year Type

Exceedance

Dry

70–100%

Average

40–70%

Wet

10–40%

Extremely Wet

0–10%

January 3,074 3,074 7,071 7,071

February 2,777 2,777 6,387 6,387

March

47,619 173,642

7,071 7,071

April

368,554 534,897

May

June 

July 3,074 3,074

August 3,074 3,074 7,071 7,071

September 2,975 2,975 6,843 6,843

October 3,074 3,074 7,071 7,071

November 2,975 2,975 6,843 6,843

December 3,074 3,074 7,071 7,071

TABLE D3-6 

Flow Recommendations for Green River near Greendale, Utah 

Year Type

Exceedance

Dry

90–100%

Moderately Dry

70–90%

Average

30–70%

Moderately Wet

10–30%

Wet

0–10%

Maximum Spring 

Peak Flow (cfs)

4,600 4,600 4,600 4,600 8,600

Peak Flow Duration Depends on inflows into the Green River and the flows needed to achieve 

recommended flows at Jensen and Green River, Utah

Summer-to-Winter 

Base Flow (cfs)

800– 

1,000

800–1,300 800–2,200 1,500–2,600 1,800–2,700

Source: Reclamation, 2005
Appendix D3 — Threatened and

Endangered Species Metrics

December 2012 D3-11

TABLE D3-7 

Flow Recommendations for Green River near Jensen, Utah

Year Type

Dry

90–100%

Moderately Dry

70–90%

Average

30–70%

Moderately Wet

10–30%

Wet

0–10%

Max Spring 

Peak Flow 

(cfs)

8,300 8,300 18,6001

; 8,3002 20,300 26,400

Peak Flow 

Duration

Flows greater than 

8,300 cfs should 

be maintained for 

2 days or more 

except in 

extremely dry 

years (98% 

exceedance). 

Flows greater than 

8,300 cfs should 

be maintained for 

at least 1 week

Flows greater 

than 18,600 cfs 

should be 

maintained for 2 

weeks in at least 

1 of 4 average 

years. 

Flows greater 

than 18,600 cfs 

should be 

maintained for 2 

weeks or more. 

Flows greater 

than 22,700 cfs 

should be 

maintained for 2 

weeks or more 

and flows 

greater than

18,600 cfs for 4 

weeks or more. 

Summer-toWinter Base 

Flow (cfs)

900–1,100 1,100–1,500 1,500–2,400 2,400–2,800 2,800–3,000

Source: (Reclamation, 2005)

1 Recommended flows: 18,600 cfs in 1 of 2 average years.

2 Recommended flows: 8,300 cfs in other average years.

TABLE D3-8 

Peak Flow Recommendations for the San Juan River near Bluff, Utah 

Target Peak Flow 

(cfs) 

Minimum 

Duration 

(days)

Frequency

Maximum interval 

between occurrences 

(years)

> 10,000 5 20% 11

> 8,000 10 33% 7 

> 5,000 21 50% 5 

> 2,500 10 80% 3 

Source: Reclamation, 2006b

4.0 Summary

The flow targets presented here were included in CRSS to track the threatened and endangered 

species attribute of interest at the discussed locations. The monthly approximations of the daily 

flow targets are neither prescriptive in nature nor an interpretation of a flow need. Rather, they 

are coarse approximations of the cited flow recommendations developed to fit into the available 

modeling resources. All target flows are well suited to compare how flow metrics perform across 

scenarios, although they are not meant to identify specific years in the future that flow targets are

or are not met. 
Colorado River Basin

Water Supply and Demand Study

D3-12 December 2012

5.0 References 

Bureau of Reclamation (Reclamation). 2005. Operation of Flaming Gorge Dam Final 

Environmental Impact Statement. 

Bureau of Reclamation (Reclamation). 2006a. Record of Decision Operation of Flaming Gorge 

Dam Final Environmental Impact Statement. 

Bureau of Reclamation (Reclamation). 2006b. Record of Decision for the Navajo Reservoir 

Operations, Navajo Unit - San Juan River New Mexico, Colorado, Utah Final 

Environmental Impact Statement.

Bureau of Reclamation (Reclamation). 2006c. Final Environmental Impact Statement Navajo 

Reservoir Operations. 

Butler, R. A. 2011. Modeling Techniques to Assess Long-term Reliability of Environmental 

Flows in Basin Scale Planning (Master's Thesis). University of Colorado. 

McAda, C. 2003. Flow Recommendations to Benefit Endangered Fishes in the Colorado and 

Gunnison Rivers. 

Modde, T., & Keleher, C. 2003. Flow Recommendations for the Duchesne River with a Synopsis 

of Information Regarding Endangered Fishes. 

Modde, T., & Smith, G. 1995. Flow Recommendations for Endangered Fishes in the Yampa 

River. 

Osmundson, D. B. 2001. Flow Regimes for Restoration and Maintenance of Sufficient Habitat to 

Recover Endangered Razorback Sucker and Colorado Pikeminnow in the Upper 

Colorado River: Interim Recommendations for the Palisade-to-Rifle Reach. 

U.S. Fish and Wildlife Service (USFWS). 2005. Final Programmatic Biological Opinion on the 

Management Plan for Endangered Fishes in the Yampa River Basin. 

U.S. Fish and Wildlife Service (USFWS). 2008. Rationale for Management of Water Releases 

from the Elkhead Reservoir Endangered Fish Pool to Augment August-October Base 

Flows in the Yampa River. 

U.S. Fish and Wildlife Service (USFWS). 2009. Final Gunnison River Basin Programmatic 

Biological Opinion. 
Appendix D4 

Cottonwood Recruitment Metrics 

December 2012 D4-1 

Appendix D4 — Cottonwood Recruitment 

Metrics 

1.0 Introduction

This appendix describes the method used to implement the cottonwood recruitment metric for 

the aquatic and riparian habitats attribute of interest. The metric is used because healthy 

cottonwood stands are an indicator of healthy riparian systems and the many species that depend 

on them; recruitment of new cottonwoods is important in maintaining cottonwood stands as older 

trees die. As described in Mahoney and Rood (1998), a successful recruitment event is dependent 

on four main variables: timing of peak flow, the river stage corresponding to the peak flow, the 

rate of decline from when the peak flow occurs to when the peak has attenuated, and a flood 

magnitude large enough to create appropriate seed beds for the cottonwood seeds. It is also 

estimated that a recruitment event should occur about once every 5 to 10 years to maintain a 

healthy cottonwood stand. Each of these variables has biological importance in the recruitment 

process, and the metric aims to represent these criteria.

For cottonwood recruitment to take place, many processes must properly align. The recruitment 

events rely on hydrological processes to prepare the seed beds and maintain proper water levels 

for the growing seedlings. A large flood magnitude creates the appropriate seed beds: bare, 

moist sites above the base flow stage of the river (Scott et al., 1997). Research suggests that a 

1 in 5-year to 1 in 10-year flood event is associated with successful recruitment in the Rocky 

Mountain region (Mahoney and Rood, 1998). D4-1 depicts each of the remaining criteria. The 

peak flow should also properly coincide with seed dispersal (late May through July in most of 

the western United States) and reach a stage high enough to wet the elevation at which

cottonwoods grow. Typically, cottonwood stands are established about 2 to 5 feet above the base 

flow stage elevation of the stream. Finally, the receding limb should decline slowly enough that a 

seedling’s growing roots maintain contact with the water table or, more specifically, with freely 

available water in the phreatic zone and capillary fringe above this zone as both recede through 

the summer. Studies document cottonwoods surviving with the water table dropping about 1 inch 

per day. The occurrence of all the above conditions are required to create the opportunity for a 

successful recruitment event. The following section describes the translation of these criteria to 

parameters that can be modeled as best as possible given current limitations posed by the 

monthly time-step in the Colorado River Simulation System (CRSS). The approach described 

below cannot replace a site-specific study on a reach. The recruitment process is complex, and 

site-specific studies are important to accurately identify the conditions that support recruitment at 

each individual location. 
Colorado River Basin

Water Supply and Demand Study

D4-2 December 2012

FIGURE D4-1 

The Timing, Stage Height, and Rate of Decline Criteria for Positive Recruitment Conditions

Source: Mahoney and Rood, 1998. 

2.0 Methodology

The four criteria that must be met for cottonwood recruitment to be possible were approximated 

for use in CRSS. The four approximate criteria that were used to identify positive conditions and 

the process they represent are as follows: 

• April through July volume with a 5-year return period: 

– Assumed from the 1 in 5-year to 1 in 10-year range

– The 5-year flood event was determined based on the April through July volume for each 

year from historical gage data. Although peak instantaneous flow is typically used to 

characterize the 5-year flood (Scott et al., 1997), only monthly data are available in 

CRSS. 

• The peak monthly volume should occur in May or June: 

– Because the peak instantaneous flow typically occurs in the month with the peak monthly 

volume, this approximates that the peak occurs when seeds are dispersed. 

• The stage must reach at least 4 feet above the average base flow stage elevation: 

– Assumed from the 2 to 5 feet range. 

• Stage should drop by no more than 2.5 feet per month: 

– 1 inch per day converted to a monthly rate. 
Appendix D4 — Cottonwood

Recruitment Metrics

December 2012 D4-3 

Using the above criteria that must be met, the following steps list the procedure for determining 

if all four criteria are met within the CRSS modeling framework:

1. Compute S̅

low (the average base flow stage) from historical gage data and a stage-flow table. 

2. Compute Q5: the magnitude of an April through July volume with a return period of 5 years. 

3. Check that the peak monthly volume occurs in May or June. 

4. If it does not, the remaining criteria do not need to be checked. 

5. Is qApr−Jul (modeled April through July volume) ≥ Q5? 

6. If it is not, the remaining criteria do not need to be checked. 

7. Is Scurrent (the modeled stage in the current month) ≥ S̅

low + 4′? 

8. If it is not, the remaining criterion does not need to be checked. 

9. Is Scurrent+1 month ≥ Smax − 2.5′ and Scurrent+2months ≥ Scurrent+1 month − 2.5′? 

10. If (3), (5), (7), and (9) are all true, then positive conditions exist for cottonwood recruitment. 

Note that whenever stage is referenced, the modeled flow is converted to an elevation using a 

stage-flow table.

The above procedures identify which years have positive conditions. It is estimated that these 

positive conditions should occur approximately once every 10 years. The frequency with which 

the positive conditions occur were compared across scenarios and to the estimated need of 

occurring once every 10 years.

3.0 Summary

The biological processes that are necessary for cottonwood recruitment had to be approximated 

for use in a monthly time-step, Colorado River Basin-scale planning model. When all four 

conditions are met, the conditions are such that recruitment could take place, although 

recruitment is not guaranteed. Therefore, the metric should not be used to identify specific years 

in the future that recruitment will occur; rather, it is used to compare the frequency with which 

the recruitment could take place across scenarios. Furthermore, the variability (or lack of) in the 

metric’s results could be as much due to the coarseness of approximations as the differences 

between scenarios. That is, if the metric shows there is no change to the frequency of the 

favorable recruitment conditions between two scenarios, it is unclear if there are truly no 

differences between scenarios, or if the metric is not sensitive enough to identify the subtle 

differences between scenarios. Furthermore, this approach does not replace the benefits of sitespecific studies on these reaches. The recruitment process is complex, and site-specific studies 

are important to accurately identify the conditions that support recruitment at each individual 

location. 
Colorado River Basin

Water Supply and Demand Study

D4-4 December 2012

4.0 References 

Mahoney, J. M., Rood, S. B. 1998. "Streamflow Requirements for Cottonwood Seedling 

Recruitment—An Integrative Model." Wetlands 18(4), 634-645. 

DOI:10.1007/BF03161678. 

Scott, M. L., G.T. Auble, , J.M. Friedman. 1997. Flood Dependency of Cottonwood 

Establishment along the Missouri River, Montana, USA. Ecological Applications, 7(2), 

677-690. doi:10.1890/1051-0761(1997)007[0677:FDOCEA]2.0.CO; 2. 
Appendix D5

Estimated Conditions for 

Flow-Dependent Ecological Systems

December 2012 D5-1

Appendix D5 — Estimated Conditions for 

Flow-Dependent Ecological Systems

1.0 Introduction

The Nature Conservancy (TNC) developed approximations of flow conditions to support 

ecological systems for the Yampa River near Maybell, Colorado (Maybell), Yampa River near 

Deerlodge Park, Colorado (Deerlodge Park), and the Little Snake River near Lily, Colorado 

(Lily). These quantifications are based on TNC’s interpretation of how the Yampa River 

Programmatic Biological Opinion (PBO) (U.S. Fish and Wildlife Service [USFWS], 2005) could 

be expanded to quantify flow conditions for the full flow regime for Maybell and two additional 

locations in the Yampa River Basin: Deerlodge Park and Lily. It should be noted that these 

quantifications are not required under the PBO. 

Additionally, TNC developed approximations of flow conditions to support ecological systems at 

White River near Watson, Utah. These quantifications include estimated flow conditions based 

on USFWS flow recommendations that are currently under development through the Upper 

Colorado River Endangered Fish Recovery Program.

The methodology section describes how the monthly flow conditions were quantified, and the 

results of these quantifications are presented in the section on estimated flow conditions.

2.0 Methodology

2.1 Yampa River Basin

The PBO covers specified levels of future increases in water use through 2045 within the Yampa 

River Basin. The methodology described here assumes that depletions from the Yampa River 

expand to these levels by the year 2045. The range of simulated future flows in the river, 

assuming historical hydrology and the specified future depeltions, are the basis for computing the 

estimated flows for ecological systems. The additional depletions specified in the PBO include 

23,428 acre-feet (af) above Lily and 30,104 af above Maybell, for a total of 53,532 af above 

Deerlodge Park. The year-round flows are estimated for the entire Yampa River Basin (at the 

Maybell, Lily and Deerlodge Park gages), while ensuring that the base flow target at Maybell 

(USFWS, 2008) is met. The method used to develop the estimated flow targets is detailed below.

TNC used the 2009 update to the State of Colorado’s Statemod1 model to simulate future flows 

within the Yampa River Basin which formed the basis of estimating the year-round flows for 

ecological systems. The model was run using data representing the depletions specified in the 

PBO (2045-level demands) and assumed future flows according to the historical 84-year period 

1922 to 20052 to simulate flows in the year 2045. The following steps were then taken to develop 

flow targets based on model results from the Statemod simulations:

 1 Statemod is the State of Colorado’s surface water allocation and accounting model.

2 Statemod results are sensitive to the chosen period of record, and as such, any resulting estimated flow condition 

would require further analysis to quantify this sensitivity. 
Colorado River Basin

Water Supply and Demand Study

D5-2 December 2012

1. Sum all simulated monthly flows in 2045 at Deerlodge to compute annual total 

volumes. Rank the annual volumes to determine the probability of exceedance and

classify each year as shown in table D5-1. The years are separated by exceedance

level to allow the flow targets to vary based on hydrologic year type. 

TABLE D5-1

Probability of Exceedance

Year Type Probability of Exceedance

Wet 0–10%

Moderately Wet 10–30%

Average 30–70%

Moderately Dry 70–90%

Dry 90–100%

2. Retrieve the simulated shortages in 2045 above each gage.

3. Adjust the simulated flow in 2045 to assume no shortages will occur (for each month 

at each gage) as: 2045 simulated flow at the gage minus the 2045 shortage from (2) 

above the gage3. Adjusted flow must be > 0.

4. Further adjust monthly flows computed in (3) to ensure that base flows at Maybell are 

at least equal to 120 cubic feet per second4.

5. Average all simulated then further adjusted flows (4) within a given year type, then 

aggregate the April through July flows to a total runoff-season target. Targets for a 

particular month do not always increase from dry to wet year types due to the 

elimination of negatives in (3).

2.2 White River

The Upper Colorado River Endangered Fish Recovery Program is in the process of developing 

flow recommendations for the White River near Watson, Utah. The current draft flow 

recommendations include daily targets. These draft recommendations were aggregated to 

monthly flow targets consistent with methods used for the monthly approximations of daily 

recommendations for the threatened and endangered species attribute of interest appendix D3.

3.0 Estimated Flow Conditions

The monthly estimated flow conditions for Maybell, Lily, and Deerlodge Park are presented in 

tables D5-2, D5-3, and D5-4, respectively. Table D5-5 lists the targets for the White River near 

Watson. The purpose of aggregating the April through July flow targets was to capture the runoff 

volume in one target value.

 3 Shortages are subtracted to follow the assumption in the PBO that they will be satisfied in 2045 and decrease the 

remaining flow.

4 See appendix D3 for the simplification of the base flow targets at Maybell. The base flow targets at Maybell are 

assumed to extend downstream to Deerlodge Park in this quantification.
Appendix D5 — Estimated Conditions for

Flow-Dependent Ecological Systems

December 2012 D5-3

TABLE D5-2

Estimated Flow Conditions (af) for the Yampa River near Maybell, Colorado

Category

Exceedance

Dry

90–100%

Moderately Dry

70–90%

Average

30–70%

Moderately Wet

10–30%

Wet

0–10%

January 9,248 10,915 13,635 14,374 22,341

February 13,489 13,684 16,243 16,548 25,824

March 25,180 40,997 36,046 44,670 73,206

April–July 368,981 604,472 870,646 1,179,492 1,458,585

August 7,379 7,379 8,438 16,316 31,482

September 7,141 7,141 7,141 7,141 23,472

October 8,320 13,101 15,444 17,028 31,916

November 11,895 15,588 16,541 16,913 30,254

December 8,580 12,960 14,819 15,687 22,470

TABLE D5-3

Estimated Flow Conditions (af) for the Little Snake River near Lily, Colorado

Category

Exceedance

Dry

90–100%

Moderately Dry

70–90%

Average

30–70%

Moderately Wet

10–30%

Wet

0–10%

January 2,758 3,983 5,330 6,065 7,823

February 4,121 5,236 6,054 7,517 10,938

March 12,416 22,196 19,732 26,924 33,688

April–July 100,287 199,559 318,873 444,742 530,698

August 564 1,146 2,386 2,240 6,320

September 361 900 1,230 2,277 6,492

October 1,288 3,824 6,145 7,635 11,981

November 3,813 4,833 7,170 8,469 11,153

December 3,752 4,809 6,258 7,155 8,399

TABLE D5-4

Estimated Flow Conditions (af) for the Yampa River near Deerlodge Park, Colorado

Category

Exceedance

Dry

90–100%

Moderately Dry

70–90%

Average

30–70%

Moderately Wet

10–30%

Wet

0–10%

January 11,861 13,865 17,671 19,068 31,769

February 17,891 17,449 21,844 22,255 39,675

March 34,061 56,019 49,568 61,300 118,118

April–July 457,535 772,084 1,150,079 1,570,554 1,993,638

August 7,379 7,379 11,635 22,697 44,258

September 7,141 7,141 7,141 8,248 29,901

October 11,900 18,890 21,818 24,363 44,280

November 16,910 21,537 23,487 24,244 44,678

December 12,307 17,989 20,964 22,272 32,739
Colorado River Basin

Water Supply and Demand Study

D5-4 December 2012

TABLE D5-5

Estimated Flow Conditions (af) for the White River near Watson, Utah

Category

Exceedance

Dry

90–100%

Moderately Dry

70–90%

Average

30–70%

Moderately Wet

10–30%

Wet

0–10%

January 18,447 18,453 19,051 22,605 25,365

February 16,661 19,128 18,656 25,483 28,397

March 18,447 21,521 24,595 30,744 36,777

April–July 120,233 203,189 237,841 362,771 503,589

August 12,348 19,005 21,916 30,437 36,893

September 16,618 18,926 19,122 27,537 35,703

October 18,447 21,521 22,608 30,623 35,860

November 17,852 20,803 20,377 27,409 32,372

December 18,284 18,797 18,878 24,223 25,021

4.0 References

U.S. Fish and Wildlife Service (USFWS). 2005. Final Programmatic Biological Opinion on the 

Management Plan for Endangered Fishes in the Yampa River Basin. 

U.S. Fish and Wildlife Service (USFWS). 2008. Rationale for Management of Water Releases 

from the Elkhead Reservoir Endangered Fish Pool to Augment August-October Base 

Flows in the Yampa River. 
Appendix D6

Estimated Conditions for 

Upper Basin Wildlife Refuges

December 2012 D6-1

Appendix D6 — Estimated Conditions for 

Upper Basin Wildlife Refuges

1.0 Introduction

The Seedskadee, Browns Park, and Ouray National Wildlife Refuges (NWR), located in the 

Upper Basin, hold water rights that help to preserve the health of those refuges. The refuges’ 

water rights are typically diversion rights, and the Colorado River Simulation System has the 

ability to track whether the requested diversion amount is present in reaches approximating the 

locations of the Upper Basin NWRs. The following sections present the method to estimate the 

flow conditions for the NWRs and the resulting estimated conditions.

2.0 Methodology

Historically, the NWRs’ diversions vary annually based on hydrologic conditions, so for each 

refuge, the estimated conditions vary with hydrologic year type. The estimated diversions were 

developed based on the NWRs’ state water rights and historical diversion records.

Approximately 20 years of annual water usage reports from the refuges maintained by the 

U.S. Fish and Wildlife Service were used to develop the estimated diversions. Monthly diversion 

records or a total annual diversion amount were reported in the water usage reports, depending 

on refuge and year. The full record of annual diversion amounts were ranked and then separated 

by exceedance probability to come up with diversion needs that vary with hydrologic year type.

Wet, moderately wet, average, and dry year types were defined as 0 to 10 percent, 10 to 

30 percent, 30 to 70 percent, and 70 to 100 percent exceedance probabilities, respectively. The 

full diversion right was used as the annual need in wet years. For other year types, the annual 

diversion amount was determined based on the middle exceedance probability for that year 

type—for example, the year with a 20 percent exceedance probability for the average wet year.

Monthly needs were then computed based on the average historical monthly diversion pattern.

3.0 Estimated Conditions

The estimated conditions for Seedskadee, Browns Park, and Ouray NWRs are listed in 

tables D6-1, D6-2, and D6-3, respectively.
Colorado River Basin

Water Supply and Demand Study

D6-2 December 2012

TABLE D6-1

Estimated Conditions (acre-feet [af] per month) for the Seedskadee NWR

Year Type

Exceedance

Dry

100–70%

Average

70–30%

Moderately Wet

30–10%

Wet

10–0%

January 250 300 360 700

February 250 300 360 700

March 1,300 1,700 1,900 3,650

April 1,600 2,000 2,300 4,450

May 2,060 2,550 2,700 5,700

June 1,640 2,040 2,330 4,600

July 900 1,150 1,300 2,500

August 700 850 1,200 2,200

September 850 1,000 1,200 2,200

October 450 570 650 1,300

November 0 0 0 0

December 0 0 0 0

Annual 10,000 12,460 14,300 28,000

TABLE D6-2

Estimated Conditions (af per month) for the Browns Park NWR

Year Type

Exceedance

Dry

100–70%

Average

70–30%

Moderately Wet

30–10%

Wet

10–0%

January 90 130 200 320

February 90 130 200 310

March 460 680 1,100 1,615

April 560 830 1,300 1,970

May 720 1,070 1,700 2,520

June 570 850 1,340 2,020

July 320 480 750 1,130

August 240 360 570 855

September 220 330 520 800

October 230 340 520 810

November 0 0 0 0

December 0 0 0 0

Annual 3,500 5,200 8,200 12,350
Appendix D6 — Estimated Conditions for

Upper Basin Wildlife Refuges

December 2012 D6-3

TABLE D6-3

Estimated Conditions (af per month) for the Ouray NWR

Year Type

Exceedance

Dry

100–70%

Average

70–30%

Moderately Wet

30–10%

Wet

10–0%

January 0 0 0 0

February 0 0 0 0

March 600 1,100 1,500 2,000

April 800 1,200 1,100 2,300

May 2,500 4,500 6,500 8,800

June 800 1,200 1,500 2,200

July 600 1,100 1,500 2,100

August 600 1,100 1,500 2,050

September 600 1,100 1,500 2,000

October 600 1,100 1,500 2,000

November 0 0 0 0

December 0 0 0 0

Annual 7,100 12,400 16,600 23,450