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 G — System 

Reliability Analysis and Evaluation 

of Options and Strategies

December 2012 G-iii

Contents

1.0 Introduction .................................................................................................................... G-1

2.0 Approach ......................................................................................................................... G-2

3.0 System Reliability Methodology ................................................................................ G-4

3.1 Scenarios Reflecting Uncertain Future Conditions..................................... G-4

3.2 Simulating the Colorado River System....................................................... G-6

3.3 Performance Measures ................................................................................ G-6

3.3.1 System Response Variables ............................................................ G-7

3.3.2 System Reliability Metrics .............................................................. G-7

3.3.3 Indicator Metrics ............................................................................. G-10

3.4 Interpreting Scenario Outcomes ................................................................. G-11

4.0 Evaluation of System Reliability Without Options and Strategies 

(Baseline Conditions) .................................................................................................... G-12

4.1 Upper Basin Tributary Flow ....................................................................... G-12

4.2 Upper Basin Shortage ................................................................................. G-16

4.3 Lake Powell Pool Elevation ........................................................................ G-18

4.4 Lee Ferry Deficit ......................................................................................... G-19

4.5 Lake Mead Pool Elevation .......................................................................... G-21

4.6 Lower Basin Shortage ................................................................................. G-22

4.7 Summary ..................................................................................................... G-24

5.0 Defining Vulnerable Outcomes and Vulnerable Conditions ............................... G-25

5.1 Vulnerability Definitions ............................................................................ G-25

5.1.1 Metrics and Vulnerability Thresholds ............................................ G-25

5.1.2 Vulnerability Results Without Options and Strategies ................... G-27

5.2 Vulnerable Conditions ................................................................................ G-34

5.2.1 Defining Vulnerable Conditions ..................................................... G-34

5.2.2 Vulnerable Conditions Without Options and Strategies ................. G-36

6.0 Evaluation of System Reliability With Options and Strategies .......................... G-40

6.1 Portfolios of Options to Address System Imbalances................................. G-42

6.1.1 Individual Options .......................................................................... G-42

6.1.2 Static Portfolio of Options .............................................................. G-42

6.2 Improving System Benefits Through Dynamic Portfolios ......................... G-49

6.2.1 Dynamic Portfolios ......................................................................... G-49

6.2.2 Strategies and Study Portfolios ....................................................... G-52

6.3 Study Portfolio Evaluation .......................................................................... G-54

6.3.1 Improvements in System Performance ........................................... G-54

6.3.2 Changes in Water Delivery Vulnerabilities .................................... G-61

6.3.3 Changes in Electrical Power Resource Vulnerabilities .................. G-72

6.3.4 Changes in Flood Control Vulnerabilities ...................................... G-72

6.3.5 Changes in Water Quality Resource Vulnerabilities ...................... G-74

6.3.6 Changes in Recreational Resource Vulnerabilities ......................... G-74
G-iv December 2012

Page

6.3.7 Changes in Ecological Resource Vulnerabilities ............................ G-78

6.3.8 Summary of System Reliability Results ......................................... G-80

6.3.9 Costs and Other Characteristics of Implemented Options .............. G-82

6.3.10 Vulnerability Reduction Versus Cost Tradeoffs ............................. G-90

6.3.11 Implemented Options for Different Portfolios ................................ G-92

6.4 Summary of System Reliability with Options and Strategies ..................... G-100

7.0 Summary ......................................................................................................................... G-102

8.0 References ....................................................................................................................... G-104

Disclaimer ...................................................................................................................................... G-107 

Figures

G-1 Overall Study Approach ................................................................................................. G-3

G-2 10th, 50th, 90th Percentiles for Annual Flow at Green River, Utah, at 

 Colorado River near Cisco, Utah and San Juan River near Bluff, Utah .................. G-13

G-3 10th, 50th, 90th Percentiles for Magnitude of Upper Basin Annual Shortage........ G-17

G-4 10th, 50th, 90th Percentiles for Lake Powell End-of-December Pool Elevation ... G-18

G-5 10th, 50th, 90th Percentiles for Lee Ferry Deficit in Years in Which a Deficit 

Occurs and Percent of Traces with a Lee Ferry Deficit ............................................ G-20

G-6 10th, 50th, 90th Percentiles for Lake Mead End-of-December Pool Elevation ..... G-21

G-7 10th, 50th, 90th Percentiles for Lower Basin Shortages when Present 

(Regulatory, Hydrologic, and Remaining Demand above Lower Division 

 States’ Basic Apportionments), and Percent of Traces with Lower Basin 

Shortages .......................................................................................................................... G-23

G-8 Summary of Vulnerability Without Options and Strategies for Water 

Delivery Metrics .............................................................................................................. G-29

G-9 Percent of Traces Vulnerable Without Options and Strategies by Scenario 

 and Time Period, Lake Mead Elevation Indicator Metric (Below 1,000 feet 

 in any One Month) .......................................................................................................... G-30

G-10 Percent of Traces Vulnerable Without Options and Strategies by Scenario 

 and Time Period, Remaining Demand Above Lower Division States’ Basic 

 Apportionments for a Subset of All Scenarios ............................................................ G-31

G-11 Summary of Vulnerability Without Options and Strategies for Electric Power 

Indicator Metrics ............................................................................................................. G-31

G-12 Summary of Vulnerability Without Options and Strategies for Flood Control 

Indicator Metrics ............................................................................................................. G-32

G-13 Summary of Vulnerability Without Options and Strategies for Recreational 

Indicator Metrics ............................................................................................................. G-33
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-v 

Figures (continued)

Page

G-14 Summary of Vulnerability Without Options and Strategies for Ecological 

Indicator Metrics ............................................................................................................. G-34

G-15 Scatter Plot of Vulnerable Conditions for the Lee Ferry Deficit Indicator 

Metric Without Options and Strategies ........................................................................ G-37

G-16 Proportion of Supply Scenario Within Each Set of Vulnerable Conditions 

 Without Options and Strategies, by Water Delivery Indicator Metric ..................... G-41

G-17 Percent of Vulnerable Years for Each Indicator Metric Across Three Time 

 Periods for the Baseline and Static Portfolio A. Includes only system benefits ..... G-46

G-18 Percent of Vulnerable Years for Each Indicator Metric Across Three Time

Periods for the Baseline and Static Portfolio A. Includes System and Demands 

 Above Lower Division States’ Basic Apportionments Benefits. .............................. G-47

G-19 Percent of Vulnerable Traces for the Lake Mead Elevation Indicator Metric 

Across Three Time Periods for the Baseline and Static Portfolio A, by Supply 

and Demand Scenario ..................................................................................................... G-48

G-20 Total Yields over Time for Average Costs for Portfolios .......................................... G-54

G-21 10th, 50th, 90th Percentiles for Magnitude of Upper Basin Annual Shortage 

 for the Baseline and Four Dynamic Portfolios ............................................................ G-55

G-22 10th, 50th, 90th Percentiles for Lake Powell End-of-December Pool Elevation 

for the Baseline and Four Dynamic Portfolios ............................................................ G-56

G-23 10th, 50th, 90th Percentiles for Lee Ferry Deficit in Years in Which a Deficit 

Occurs and Percent of Traces (bottom) with a Lee Ferry Deficit for the 

 Baseline and Four Dynamic Portfolios......................................................................... G-57

G-24 10th, 50th, 90th Percentiles for Lake Mead End-of-December Pool Elevation 

 for the Baseline and Four Dynamic Portfolios ............................................................ G-58

G-25 10th, 50th, 90th Percentiles for Lower Basin Annual Shortages (Regulatory 

 plus Hydrologic) Magnitude, and Percent of Traces with Lower Basin 

 Shortage for the Baseline and Four Dynamic Portfolios .......................................... G-59

G-26 10th, 50th, 90th Percentiles for Remaining Demands Above Lower Division 

 States’ Basic Apportionments Magnitude and Percent of Traces When 

 This Occurs for the Baseline and Four Dynamic Portfolios ...................................... G-59

G-27 10th, 50th, 90th Percentiles for the Sum of Lower Basin Regulatory and 

 Hydrologic Shortages plus Remaining Demands Above Lower Division 

 States’ Basic Apportionments for the Baseline and Four Dynamic Portfolios ....... G-60

G-28 Percent of Vulnerable Traces for Each Water Delivery Indicator Metric 

 Across Three Time Periods for the Baseline And Four Simulated Portfolios ........ G-62

G-29 Percent of Vulnerable Years for Each Water Delivery Indicator Metric 

Across Three Time Periods for the Baseline And Four Simulated Portfolios ........ G-63
G-vi December 2012

Figures (continued)

Page

G-30 Number of Vulnerable Years Across Traces 2012–2060 for All Scenarios, 

Lee Ferry Deficit Indicator Metric, In Vulnerable Conditions 

(Long-Term Flow < 14 mafy and Drought < 11 mafy) ............................................. G-65

G-31 Number of Vulnerable Years Across Traces 2012–2060 for a Subset of 

 All Scenarios, Lake Mead Elevation Indicator Metric, In Vulnerable 

 Conditions (Long-Term Flow < 15 mafy & Drought < 13 mafy) ............................ G-66

G-32 Reduction in Vulnerable Traces with Selected Portfolios in Place, 

Lee Ferry Deficit Indicator Metric ................................................................................ G-67

G-33 Percentage of Each Supply Scenario Within Each Set of Vulnerable 

Conditions with Portfolio A in Place, by Water Delivery Indicator Metric ............ G-71

G-34 Percent of Vulnerable Traces for Each Electric Power Indicator Metric 

 Across Three Time Periods for the Baseline and Four Simulated Portfolios ......... G-72

G-35 Percent of Vulnerable Years for Each Electric Power Indicator Metric 

Across Three Time Periods for the Baseline and Four Simulated Portfolios ......... G-73

G-36 Percent of Vulnerable Traces for Each Flood Control Indicator Metric 

 Across Three Time Periods for the Baseline and Four Simulated Portfolios ......... G-73

G-37 Percent of Vulnerable Years for Each Flood Control Indicator Metric 

 Across Three Time Periods for the Baseline and Four Simulated Portfolios ......... G-73

G-38 Percent of Vulnerable Traces for Each Recreational (Boating Flow Days) 

 Indicator Metric Across Three Time Periods for the Baseline and Four 

Simulated Portfolios........................................................................................................ G-75

G-39 Percent of Vulnerable Years for Each Recreational (Boating Flow Days) 

 Indicator Metric Across Three Time Periods for the Baseline and Four 

Simulated Portfolios........................................................................................................ G-76

G-40 Percent of Vulnerable Traces for Each Recreational (Shoreline Facilities) 

 Indicator Metric Across Three Time Periods for the Baseline and Four 

Simulated Portfolios........................................................................................................ G-77

G-41 Percent of Vulnerable Years for Each Recreational (Shoreline Facilities) 

 Indicator Metric Across Three Time Periods for the Baseline and Four 

Simulated Portfolios........................................................................................................ G-78

G-42 Percent of Vulnerable Traces for Each Ecological Indicator Metric Across 

Three Time Periods for the Baseline and Four Simulated Portfolios ....................... G-79

G-43 Percent of Vulnerable Years for Each Ecological Indicator Metric Across 

 Three Time Periods for the Baseline and Four Simulated Portfolios ....................... G-80

G-44 Percent of Years Vulnerable for Upper Basin Reliability and Lower Basin

Reliability in 2041–2060 with Portfolios Implemented, by Supply Scenario ......... G-82
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-vii

Figures (continued)

Page

G-45 Total Annual Cost by Supply Scenario Resulting from Implementation 

of the Dynamic Portfolios Over Time .......................................................................... G-84

G-46 Total Annual Cost for All Traces and Low Streamflow and Lowest 

Streamflow Conditions Resulting from Implementation of the Dynamic 

 Portfolios over Time ....................................................................................................... G-85

G-47 Average Annual Cost by Supply Scenario Resulting From Implementation

of the Dynamic Portfolios over Time ........................................................................... G-86

G-48 Average Annual Cost for All Traces and Low Streamflow and Lowest 

Streamflow Conditions Resulting from Implementation of the Dynamic 

 Portfolios over Time ....................................................................................................... G-87

G-49 Amount of Annual Yield with Reliability Group Characteristics Scores 

 A–E for Each Portfolio in 2060 ..................................................................................... G-88

G-50 Amount of Annual Yield with Environment Group Characteristics Scores 

 A–E for Each Portfolio In 2060 .................................................................................... G-89

G-51 Percent of Years Vulnerable for Upper Basin and Lower Basin 

Vulnerabilities from 2041–2060 and Range In Total Annual Cost In 

 2060 Across Supply Scenarios for Four Portfolios .................................................... G-90

G-52 Percent of Years Vulnerable from 2041–2060 and Range In Total Annual 

 Cost In 2060 for All Water Supply Sequences, Sequences with Low 

 Streamflow Conditions, and Sequences with Lowest Streamflow 

 Conditions Across Upper Basin and Lower Basin Vulnerabilities, 

for Four Portfolios ........................................................................................................... G-91

G-53 Percent of Traces in Which Options are Implemented over Time for 

 Each Portfolio .................................................................................................................. G-94

G-54 Percentage of Traces Implemented by year for Select Options with 

 Portfolio B and Portfolio C ............................................................................................ G-96

Tables

G-1 Summary of Scenarios and Number of Traces Used to Evaluate System Reliability ........ G-6

G-2 System Response Variables ............................................................................................... G-8

G-3 System Reliability Metrics and Number of Locations ....................................................... G-9

G-4 Indicator Metrics by Resource Category ........................................................................... G-10

G-5 Indicator Metrics and Vulnerability Thresholds ................................................................ G-26

G-6 Characterizations of Uncertainty For Vulnerable Conditions (All Futures) ...................... G-35
G-viii December 2012

Tables (continued)

Page

G-7 Vulnerable Conditions Defined for Each Water Delivery Indicator Metric ...................... G-36

G-8 Vulnerable Conditions Defined for Each Water Delivery Indicator Metric ...................... G-38

G-9 Criteria Used to Characterize Representative Options....................................................... G-43

G-10 Summary of the Type, Number, and Yields of Options Included in Static 

 Portfolio A .......................................................................................................................... G-44

G-11 Definitions of the Vulnerability Signposts Developed for Each Indicator Metric ............. G-50

G-12 Options that Address Different Vulnerabilities ................................................................. G-51

G-13 Strategies and Portfolio Descriptions Explored in the Study ............................................. G-53

G-14 Summary of Included Options for Portfolios B and C ....................................................... G-53

G-15 Vulnerable Conditions Defined for Each Water Delivery Indicator Metric 

 for Portfolio A.................................................................................................................... G-69

G-16 Summary of System Reliability Outcomes (Percent of Years Vulnerable) 

 for Baseline and Portfolios for All Scenarios, 2041–2060 Period .................................... G-81

G-17 Summary of Costs and Option Characteristics Differences Among Portfolios ................. G-89

G-18 Percent of Traces in Which Options are Implemented from Option Group and the 

Minimum Delay Between Availability and Median Implementation Delay ..................... G-97

G-19 Percentage of Traces within Low Streamflow conditions In which Options 

 are Implemented from Option Group and the Minimum Delay between 

 Availability and Median Implementation Delay ................................................................ G-98

G-20 Percentage of Traces within Lowest Streamflow conditions in which Options 

 are Implemented from Option Group and the Minimum Delay between 

 Availability and Median Implementation Delay ................................................................ G-99

G-21 Portfolios in Which Option Groups Have Short Delay and Long Delay 

Options Across All Traces ................................................................................................. G-101

Appendices

G1 Modeling Sub-Team Members

G2 Colorado River Simulation System Modeling Assumptions 

G3 Additional Methodology and Results 

G4 Supplemental Results 
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-ix

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 EIS Shortages and Coordinated Operations for Lake Powell

and Lake Mead Final Environmental Impact Statement 

af acre-feet

Ag agricultural

Basin Colorado River Basin 

Basin States Colorado River Basin States

CDF Cumulative Density Function

cfs cubic feet per second

Compact Colorado River Compact 

CRSS Colorado River Simulation System 

desal desalination

DOI U.S. Department of the Interior 

EC extraordinary conservation 

EIS Environmental Impact Statement

ft feet

GCM General Circulation Model

GWh gigawatt-hour 

Gulf Gulf of California

ICS Intentionally Created Surplus 

kaf thousand acre-feet

kafy thousand acre-feet per year

M&I municipal and industrial 

maf million acre-feet

mafy million acre-feet per year

Mexico United Mexican States

msl above mean sea level

MWD Metropolitan Water District of Southern California
G-x December 2012

PBO Programmatic Biological Opinion 

Reclamation Bureau of Reclamation

ROD Record of Decision

SJCP San Juan Chama Project

SNWA Southern Nevada Water Authority 

SoCal Southern California 

SSI self-served industrial 

Study Colorado River Basin Water Supply and Demand Study 

USFWS U.S. Fish and Wildlife Service 

WAPA Western Area Power Administration

YDP Yuma Desalting Plant
December 2012 G-1 

Technical Report G — System Reliability 

Analysis and Evaluation of Options and

Strategies

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 four 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 that 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 Study’s analysis of system reliability. 

This technical report includes an evaluation of the system reliability without options and 

strategies, identification and an assessment of vulnerable conditions, an evaluation of system 

reliability with implementation of different combinations (portfolios) of future potential options,

and an assessment of those portfolios in terms of cost and timing of option implementation. 
Colorado River Basin

Water Supply and Demand Study

G-2 December 2012

2.0 Approach 

The overall analytical Study approach and the technical reports that correspond with elements of 

that approach are shown in figure G-1. As outlined in Technical Report E – Approach to 

Develop and Evaluate Options and Strategies, the Study objectives are centered on addressing 

the two focal questions of the Study: 

1. What is the future reliability of the Colorado River system to meet the needs of Basin 

resources1 through 2060? 

2. What are the options and strategies required to mitigate future risks to these resources?

The first question requires an understanding of the underlying components of future reliability: 

water supply and water demand. Specifically, what are the factors that will determine the future 

availability of water, and what are the factors that will determine the future demand for water? 

The scenario development process, described in Technical Report A – Scenario Development, 

addresses these questions and results in scenarios that define a range of plausible future water 

supply and water demand. The scenarios for both water supply and water demand are described 

in Technical Report B – Water Supply Assessment and Technical Report C – Water Demand 

Assessment. The first question also requires an understanding of the needs of Basin resources. 

These needs are identified via the system reliability metrics described in Technical Report D – 

System Reliability Metrics. Combined, Technical Reports A – D describe the components 

needed, i.e., future scenarios of water supply and demand and resource metrics, to address the 

first question. 

The process to address the first question required evaluation of the system reliability without 

options and strategies and the assessment of the outcome through the characterization of system 

vulnerabilities. Both are presented in this report along with the findings related to the first 

question, as indicated by the first two shaded boxes in figure G-1. 

The second question relates to water management responses to mitigate and adapt to the potential 

impacts to Basin resources under plausible scenarios of the future. The main components in 

addressing this question are first, the identification and characterization of options and second, 

the development of portfolios of options. The outcomes of these two steps are the focus of 

Technical Report F – Development of Options and Strategies. 

This report further presents the findings related to the second question describing the 

effectiveness of the portfolios at reducing system vulnerabilities through evaluation of system 

reliability with options and strategies, as indicated in the third shaded box in figure G-1.

 

1 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.
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-3 

FIGURE G-1 

Overall Study Approach

The activities documented in this report were carried out through a collaborative process 

involving representatives of numerous organizations, including Reclamation, the Basin States, 

federally recognized tribes (tribes), and conservation organizations. A Modeling Sub-Team and

Options and Strategies Sub-Team, composed of representatives from these organizations, were

established to review key modeling assumptions and results from this phase. The Modeling 

Sub-Team members are listed in appendix G1 of this report. Options and Strategies Sub-Team 

members are listed in Technical Report F – Development of Options and Strategies, Appendix 1 

– Options and Strategies Sub-Team Members. 

This report presents the methods and analysis for the 1) evaluation of system reliability without 

options and strategies, 2) characterization of system vulnerabilities, and 3) evaluation of system

reliability with options and strategies, all shaded in figure G-1. 

The general approach for the system reliability analysis and evaluation of options and strategies 

are summarized as follows.

• Evaluation of System Reliability without Options and Strategies – The Baseline system 

reliability without options and strategies was evaluated to understand current risk for 

comparison to system reliability with options and strategies. Under the Baseline system 

reliability, plausible supply, demand and operational assumption combinations were

considered. 
Colorado River Basin

Water Supply and Demand Study

G-4 December 2012

• Define Vulnerable Outcomes and Vulnerable Conditions – Based on the six resource 

categories, definitions of vulnerability were developed for a group of system reliability 

metrics. System conditions often preceding or associated with these system vulnerabilities

were explored, and findings from this analysis were used to guide the implementation of 

options by Colorado River Simulation System (CRSS) as part of the system reliability 

analysis with options and strategies. 

• Evaluation of System Reliability with Options and Strategies – The system reliability was 

evaluated with the inclusion of options and strategies to quantify reliability improvements. A 

progression of four steps was taken within this analysis: 

o Evaluate how the system reliability could be improved using a portfolio in which a 

large set of feasible options are implemented as soon as they are available – the static 

framework. Within this step, demands above Lower Division States’ basic

apportionments were met only during Surplus Conditions2. 

o Evaluate how the system reliability could be improved using a portfolio in which a 

large set of feasible options are implemented as soon as they are available. Demands 

above Lower Division States’ basic apportionments can also be met by options. 

o Evaluate how the system reliability could be improved using a portfolio that triggers 

options in response to evolving conditions suggestive of increasing vulnerability—the 

dynamic framework. Demands above Lower Division States’ basic apportionments 

can also be met by options. 

o Analyze the frequency and timing of option implementation in the dynamic portfolios 

gaining insight toward effectiveness of options at improving system reliability. 

Define common, short delay options; common, long delay options; and contingency 

options and explore changes in option definition based on different vulnerable 

conditions. 

3.0 System Reliability Methodology 

The Study developed an analytical framework that balances the capability for evaluating 

numerous future scenarios with providing sufficient model resolution to represent Basin 

resources. This section presents the main components of such a framework: 1) the inputs that 

define a wide range of plausible future conditions, or scenarios; 2) an appropriate Basin-wide 

model; and 3) a means to evaluate system performance. This section concludes with a discussion 

of how the study analyzes and interprets the simulation results and a description of key figures. 

3.1 Scenarios Reflecting Uncertain Future Conditions 

The Study evaluates uncertainty about future management conditions through water supply and 

demand scenarios, and two assumptions regarding Lakes Powell and Mead operations post-2026 

(see Technical Report A – Scenario Development).

The supply uncertainty is represented through four water supply scenarios and associated 

themes, each comprising many individual sequences of streamflow: 

 

2 In accordance with the Consolidated Decree and Article III of the Long-Range Operating Criteria, the Secretary of the Interior determines 

yearly the water supply condition for the Lower Division states.
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-5 

• Observed Resampled: Future hydrologic trends and variability are similar to the past 

approximately 100 years—comprises 103 sequences. 

• Paleo Resampled: Future hydrologic trends and variability are represented by 

reconstructions of streamflow for a much longer period in the past (nearly 1,250 years) that 

show expanded variability—comprises 1,244 sequences. 

• Paleo Conditioned: Future hydrologic trends and variability are represented by a blend of 

the wet-dry states of the longer paleo-reconstructed period (nearly 1,250 years), but 

magnitudes are more similar to the observed period (about 100 years)—comprises 

500 sequences.

• Downscaled General Circulation Model (GCM) Projected: Future climate will warm, 

with regional precipitation and temperature trends represented by an ensemble of future 

downscaled GCM projections—comprises 112 sequences. 

Collectively, these four supply scenarios are modeled by approximately 1,960 future supply 

sequences.

Demand uncertainty is represented by six water demand scenarios, each reflecting different 

assumptions about future demographics and land use, technology and economics, and social 

values and governance. Each demand scenario is modeled by a single time sequence of water 

demand across the Basin, except when evaluated along with a Downscaled GCM Projected trace. 

In these cases, demand is calculated to vary in accordance with the climate conditions reflected 

by the supply trace. These storylines and their associated themes are:

• Current Projected (A): Growth, development patterns, and institutions continuing along 

recent trends

• Slow Growth (B): Low growth with emphasis on economic efficiency 

• Rapid Growth (C1 and C2): Economic resurgence (population and energy) and current 

preferences toward human and environmental values 

• Enhanced Environment (D1 and D2): Expanded environmental awareness and stewardship 

with growing economy 

Under the storylines, two logical branches or directions were considered for the Rapid Growth 

(slower technology adoption—C1 and rapid technology adoption and slight increase in social 

values—C2) and Enhanced Environment (current growth trend—D1 and higher growth and 

technology—D2) scenarios. 

Two operating assumptions reflect different Lakes Powell and Mead operations beyond 2026, 

when the Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated 

Operations for Lake Powell and Lake Mead (2007 Interim Guidelines) (U.S. Department of the 

Interior [DOI], 2007), provided in the Colorado River Interim Guidelines for Lower Basin 

Shortages and Coordinated Operations for Lake Powell and Lake Mead Final Environmental 

Impact Statement (2007 Interim Guidelines Final Environmental Impact Statement [EIS]) 

(Reclamation, 2007), expire. In one assumption, the 2007 Interim Guidelines are assumed to be 

extended through 2060; in the other assumption, operations revert to the No Action Alternative 

from the 2007 Interim Guidelines Final EIS. 
Colorado River Basin

Water Supply and Demand Study

G-6 December 2012

Collectively, these scenarios and the post-2026 operations assumption describe a wide range of 

plausible future conditions and can be used to develop quantitative estimates of the range of 

system performance and Basin resource conditions. The specific way in which the Study 

interprets these results is provided below. 

3.2 Simulating the Colorado River System

CRSS, Reclamation’s long-term planning model, was the simulation tool utilized in the Study. 

CRSS simulates operations at a monthly time step and is developed in the RiverWare® modeling 

software (Zagona et al., 2001). Within this framework, rule-based simulation represents 

management policy using “If -Then” logic. This capability allows for evaluation of alternative 

operations and has been used in numerous Colorado River policy and environmental impact 

studies by both Reclamation and stakeholders. 

CRSS includes a total of 12 reservoirs (Fontenelle, Flaming Gorge, Starvation, Taylor Park, Blue 

Mesa, Morrow Point, Crystal, Navajo, Powell, Mead, Mohave and Havasu), each with unique 

operational rules. In addition to policy rules for the modeled facilities, streamflow and demand 

input data are also required. These data constitute the various supply and demand scenarios 

developed as part of the Study. For streamflow, the model has 29 input nodes in the Basin, 

corresponding with the reaches used by Reclamation for natural flow and salt computations. 

Each quantified demand scenario contains data for the more than 400 water users in the model. 

Appendix G2 describes the key assumptions common to all simulations. 

CRSS simulates future conditions based on the future supply and demand sequences, resulting in 

thousands of individual traces; one trace for each combination of supply, demand, and 

assumption regarding Lakes Powell and Mead operations beyond 2026. Table G-1 summarizes 

the total traces resulting from combinations of the water supply and demand scenarios and the 

post-2026 Lakes Powell and Mead operations assumptions. The analysis of these traces 

constitutes the basis for the system reliability analysis. 

TABLE G-1 

Summary of Scenarios and Number of Traces Used to Evaluate System Reliability

Supply Scenarios Demand 

Scenarios

Post-2026 Operation of 

Lakes Powell and Mead Traces

Observed Resampled 103 x 6 x 2 = 1,236

Paleo Resampled 1,244 x 6 x 2 = 14,928

Paleo Conditioned 500 x 6 x 2 = 6,000

Downscaled GCM 

Projected

112 x 6 x 2 = 1,344

Total 1,959 x 6 x 2 = 23,508

3.3 Performance Measures 

Performance measures are critical for evaluating system reliability and facilitating the 

comparison of different strategies to address imbalances. Collectively referenced as system

reliability metrics (metrics), these measures are distributed geographically throughout the Basin 

and span the six Basin resource categories considered in the Study (water deliveries, electrical 
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-7 

power, water quality, flood control, recreational, and ecological). The metrics were developed 

through a collaborative process involving representatives of numerous organizations, including 

Reclamation, the Basin States, U.S. Fish and Wildlife Service (USFWS), National Park Service, 

Western Area Power Administration (WAPA), tribes, U.S. Forest Service, conservation 

organizations, water delivery contractors, contractors for the purchase of federal power, and 

others interested in the Basin. 

The Study utilizes three types of metrics: 

• System response variables representing a high-level depiction of the system operation and 

response to varying hydrologic, demand, and operating criteria. 

• System reliability metrics representing more-detailed, targeted measures that aim to evaluate 

specific attributes of interest within each resource category. These were developed primarily 

through the work detailed in Technical Report D – System Reliability Metrics. 

• Indicator metrics presenting a high-level view of system resources by either elevating an 

existing metric that is particularly telling or by combining multiple metrics into one, thus 

reflecting a larger area or broader scope. 

Each metric type in the system reliability analysis is described in more detail below.

3.3.1 System Response Variables

System response variables describe Basin conditions for the various scenarios. System response 

variables are a first step in investigating system performance under plausible future conditions. 

The variables are primarily direct model trace results such as pool elevations, hydropower 

generation or flow. 

When describing results across the multiple traces consisting of water supply, water demand, and 

operational assumptions quantitative summaries of the distribution of results are often presented. 

For example, for a given simulated year, a figure could present the 10th, 50th, and 90th 

percentile results. The 10th percentile result is the level at which 10 percent of the traces have 

not exceeded the value shown. This output provides a gross estimate of possible future trends 

and operational ranges for major Basin components. The results should not be interpreted as 

probabilistic estimates of what could happen and therefore are more useful as measures for 

comparisons of different strategies rather than providing a definitive assessment of a particular 

resource of the Basin. Table G-2 lists the system response variables examined in the Study. 

3.3.2 System Reliability Metrics

As described in Technical Report D – System Reliability Metrics, metrics were defined for

6 resource categories and 25 attributes of interest that can be quantified directly or indirectly 

based on CRSS results at one or more of 47 locations throughout the Basin. In total, 

approximately 100 individual metrics were developed. Table G-3 lists the resource categories 

and individual metrics as well as the number of locations for which each metric is quantified. 

The full suite of metric results is available in appendix G4. 

Metrics vary considerably in development complexity; some metrics only expand the type of 

reporting described for the system response variables, while others required specific model 

development and significant post-processing. 
Colorado River Basin

Water Supply and Demand Study

G-8 December 2012

TABLE G-2 

System Response Variables

System Response Variable

Annual Flow of Green River at Green River, Utah

Annual Flow of Colorado River near Cisco, Utah

Annual Flow of San Juan River near Bluff, Utah

Total Storage Above Lake Powell

Upper Basin Annual Shortage

Lake Powell Pool Elevation above mean sea level (msl)

Total Upper Basin Energy Production (Cumulative Density Function [CDF] and by year)

Lake Powell Water Year Release

Lee Ferry Deficit

Lake Mead Pool Elevation msl

Lower Basin Annual Total Shortage (includes remaining demands above Lower Division States’ basic

apportionments) 

Lower Basin Annual Regulatory Shortage

Lower Basin Surplus Probability

Hoover Energy Production (CDF and by year)

Parker and Davis Energy Production (CDF and by year)
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-9 

TABLE G-3 

System Reliability Metrics and Number of Locations 

Resource Metric No. of Locations

Water Delivery Resource Category

Upper Basin Shortage 1 

Lee Ferry Deficit 1 

Lower Basin Shortage 1 

Lake Mead Pool Elevation < 1,000 feet msl 1 

Remaining Demands above Lower Division States’ Basic Apportionments 1 

Upper Basin Delivery 1 

Navajo Reservoir Pool Elevation < 5,990 feet msl 1 

Lower Basin Delivery 1 

Annual Flows at Morelos Diversion Dam Above Treaty Delivery 1 

Electrical Power Resources Category

Electrical Power Generated 3 

Available Generation Capacity 3 

Water Quality Resource Category

Salinity Concentration 20

Flood Control Resource Category

Flood Control 1 

Reservoir Spill 6 

Critical River Stage Related to Flooding Risk 3 

Recreational Resource Category

Shoreline Public Use Facility 5 

Boating Flow Days 8 

Ecological Resource Category

Flows to Support Threatened and Endangered Species 13

Instream Flow Rights 2 

Cottonwood Recruitment 6 

Flow-Dependent Ecological Systems 4 

Wildlife Refuges and Fish Hatcheries 7 
Colorado River Basin

Water Supply and Demand Study

G-10 December 2012

3.3.3 Indicator Metrics

To provide a summary view of resource performance in different parts of the Basin, indicator 

metrics were developed. These indicator metrics either elevate a single metric that is particularly 

significant for a given Basin resource in a particular area or combine multiple metrics to provide 

a more regional average perspective on the Basin resource. In total, 30 indicator metrics across 

the 6 resource categories were developed, as detailed in table G-4. The disparate number of 

indicator metrics amongst resource categories is not reflective of importance, but rather the 

relative ease or difficulty associated with a high-level representation of a given category. For 

example, in the water quality resource category, the Parker to Davis reach was identified as a 

reasonable indicator of water quality conditions in the Lower Basin and represents a concise 

depiction of Basin water quality conditions. Recreation, on the other hand, includes different 

metrics such as river boating and lake-based recreation, which are largely dependent upon the 

hydrology of Upper Basin tributaries and reservoir operations. As such, a single site cannot be 

used to indicate the reliability of the recreational resources. Therefore, more indicator metrics are

needed to represent the vulnerability of some resources. 

TABLE G-4 

Indicator Metrics by Resource Category

Water Delivery Electric Power Recreation 

Upper Basin Shortage 

Lee Ferry Deficit

Lake Mead Pool Elevation

< 1,000 feet msl

Lower Basin Shortage 

Remaining Demand Above 

Lower Division States’ Basic

Apportionment 

Lake Powell Pool Elevation

< 3,490 feet msl

Upper Basin Electrical 

Power Generated

Lake Mead Pool Elevation

< 1,050 feet msl

Colorado River Optimal Boating Flow Days

Green River Optimal Boating Flow Days

San Juan Optimal Boating Flow Days

Colorado River Total Boating Flow Days

Green River Total Boating Flow Days

San Juan Total Boating Flow Days

Blue Mesa Shoreline Public Use Facility

Navajo Shoreline Public Use Facility

Flaming Gorge Shoreline Public Use Facility

Powell Shoreline Public Use Facility

Mead Shoreline Public Use Facility

Ecological Water Quality Flood Control 

Colorado River1

Green River

San Juan River

Yampa River

Hoover Dam to Davis Dam

Flow reductions 

Numeric Salinity Criterion

below Parker Dam 

Lake Mead Downstream Safe Channel 

Capacity

1 Target flows or flow recommendations from Programmatic Biological Opinions (PBOs) to support 

threatened and endangered species. 
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-11

3.4 Interpreting Scenario Outcomes

The scenario planning approach considered in the Study resulted in scenarios for water supply 

and water demand. Combining these scenarios, along with operational assumptions related to the 

operation of Lakes Powell and Mead, results in a large set of plausible future conditions. Each 

individual combination is simulated in CRSS and the results for each combination thus define a 

range of plausible outcomes. 

It is common practice, when using supply data based on resampled historical conditions, to 

weight the results of each trace equally and interpret the distribution of results probabilistically

(Groves et al., 2008). For example, system reliability in a given year could be calculated as the 

percentage of traces in which supply was sufficient to meet demand. This approach may also be 

valid when using supply data based on directly sampled paleo data, such as the Paleo Resampled 

scenario or data conditioned on paleo sequencing, such as the Paleo Conditioned scenario. 

Reliability in this context is relevant to the conditions that occurred during the portion of the 

paleo record that was sampled and the resampling techniques are ground in accepted time series 

analysis (Ouarda et al., 1997; Prairie et al., 2008). 

When using downscaled GCM data (i.e. Downscaled GCM Projected scenario), however, there 

is no theoretical basis for assuming that each sequence is equally likely. The distribution of 

sequences reflects the data available from GCM simulations, which is determined by different 

research teams and the assumptions they used. When using this type of data, the distribution of 

simulation results should only be interpreted as representative of the distribution of results that 

could be experienced under the conditions described by the scenarios. 

This information, while not useful for simulating absolute outcomes, can be very useful for

comparative purposes. For example, two different sets of options could be compared to 

understand the distribution of results across a set of GCM scenario traces. More favorable shifts 

in the distribution due to one set of options would suggest more favorable impacts on the system 

for that set of options. 

The scenarios can also be pooled together to compare how distributions change. The traces 

should not be considered as equally likely, but simply as plausible. Note that how the scenarios 

are pooled will determine the final distribution. For example, if one scenario includes more 

traces than another, then the pooled distribution will emphasize the scenario with a greater 

number of traces. 

The study uses the scenario results for comparative purposes only. To summarize these 

distributions, statistics are used that specify the level above which a particular percentage of 

results have not been exceeded. For example, the 10th percentile results for flows at a particular 

location for a specific year would be the level of flow not exceeded by 10 percent of the traces.

Similarly, the 50th percentile, or median, is the level of flow not exceeded by 50 percent of the 

traces. The median value should not be interpreted as an average or most likely outcome—rather 

it is simply the central tendency of the distribution.

When pooling scenarios, the Study resampled the results so that each supply scenario contributes 

the same number of observations to the pool. The Paleo Resampled scenario at 1,244 traces has 

the largest pool and all other scenarios are resampled to match when describing system response 

outcomes or vulnerabilities. Practically, this means replicating results for the other scenarios 

such that the number of traces is equal for each scenario. For example, for the system response 

results presented below, the 112 Downscaled GCM Projected results are each replicated 11 times 
Colorado River Basin

Water Supply and Demand Study

G-12 December 2012

to increase the sample size to 1,232. Then 12 more sequences are randomly selected to bring the 

total to 1,244. To create a manageable sample set for the analysis of option implementation, 

results are replicated and/or sampled so that each scenario contributes 500 observations, rather 

than 1,244 traces. This means 500 observations were randomly sampled from the Paleo 

Resampled results for the options analysis, and the result from Observed Resampled at 104 

traces and Downscaled GCM Projected results were replicated and/ or sampled so that each 

scenario contributes 500 observations, thereby matching the sample size for the Paleo 

Conditioned scenario. Options analysis was them performed on the equally weighted and pool 

scenarios.

Pooled scenario data are first evaluated in a later section using robust decision methods (Lempert 

et al., 2003; Groves and Lempert, 2007; Dessai and Hulme, 2007; Lempert and Groves, 2010). 

This approach views the scenario results not as predictions of the future, but rather a means to 

expansively trace out the plausible futures that may be faced by the Basin. Analysis of these 

results then defines those future conditions that represent vulnerabilities to the system. These 

vulnerabilities represent the future conditions in which the system performance is not achieving 

predefined goals. The options and strategies analysis, described later, then evaluates different 

ways to alleviate these vulnerabilities. This information can support decisions without an explicit 

assignment of probabilities to the scenarios.

4.0 Evaluation of System Reliability Without Options and 

Strategies (Baseline Conditions) 

Results for select system response variables are shown across the Basin for each combination of 

supply and demand scenario and assumption regarding Lakes Powell and Mead operations 

beyond 2026 building—a total of 48 combinations. These combinations are explored across five

system response variables: Upper Basin tributary flow, Upper Basin shortage, Lake Powell pool 

elevation, Lee Ferry deficit, Lake Mead pool elevation, and Lower Basin shortage. 

4.1 Upper Basin Tributary Flow

Results are presented for three key system response variables, specifically, percentiles for annual 

flow for three major Upper Basin tributaries. Figure G-2 presents simulated 2012 through 2060 

gaged annual flow at (a) the Colorado River at Cisco, Utah ; (b) Green River near Green River, 

Utah; and (c) San Juan River near Bluff, Utah. Results are presented for the 48 scenario 

combinations. Both sides display 24 lines resulting from the combination of 4 water supply and 6 

water demand scenarios. With each panel further splitting the scenarios by post-2026 operation 

of Lakes Powell and Mead, where the left panel is based on extension of the 2007 Interim 

Guidelines operation and the right panel is based on reverting to the No Action Alternative (DOI, 

2007). Five scenario combinations that generally bound and fill out the results spread are 

highlighted and the remaining combinations are presented in gray. 
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-13

FIGURE G-2 

10th, 50th, 90th Percentiles for Annual Flow at Green River, Utah (a), at Colorado River near Cisco, Utah (b) and San Juan River 

near Bluff, Utah (c) 

(a) 
Colorado River Basin

Water Supply and Demand Study

G-14 December 2012

(b)
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-15

All sites exhibit a reduction in annual flow over the simulation period across all percentiles, 

primarily as a result of the increasing demands, as exhibited by the highlighted Observed 

Resampled, Rapid Growth (C1) scenario. The supply scenarios show the widest range of 

variability with the demands providing additional variability exhibited through further spread 

around each supply cluster. Demand variability is slightly more pronounced at the 10th and 90th

percentiles, compared with the 50th percentile indicating demand variability is more pronounced 

at the extreme high and low flows rather than at the median. 

(c)
Colorado River Basin

Water Supply and Demand Study

G-16 December 2012

The Green River exhibits a similar central tendency (represented by the 50th percentile) of flow 

magnitudes across all scenarios, indicating little change in annual flow across the four supply 

scenarios. Whereas for the Colorado and San Juan rivers, the Downscaled GCM Projected 

supply scenario has a lower central tendency than the Observed Resampled, Paleo Resampled 

and Paleo Conditioned scenarios indicate reduced flows in these tributaries under a Downscaled 

GCM projected scenario. 

The highlighted Paleo Conditioned, Enhanced Environment (D1) scenarios generally provide the 

upper bound for the 90th percentile resulting from the more-frequent and longer-duration surplus 

spells exhibited by the scenario. Whereas on the Green and Colorado Rivers, the Paleo 

Resampled (shown as the bottom cluster of smooth gray lines) generally provides the lower 

bound indicative of the reduced variance seen with the Paleo Resampled scenario, with years 

when Downscaled GCM scenario dips below this bound. Of note, on the San Juan River, the 

Downscaled GCM Projected scenario indicates a stronger reduction in high flows (displayed by 

the reduced 90th percentile) than any other scenario; showing the starkest change in flow under 

the Downscaled GCM Projected scenario across all sites. 

At the 10th percentile, the Downscaled GCM Projected flows again tends to provide the lower 

bound across most sites, indicating a shifted distribution of lower flows produced by the 

Downscaled GCM Projected scenario, especially on San Juan River, where the lower 10th

percentile, coupled with reduced 90th percentile flows, indicate a shift to lower flows along with 

a reduced variance compared with the other supply scenarios. The Paleo Resampled (shown as 

the cluster of smooth gray lines) generally bounds the higher 10th percentile flows, except on the 

San Juan River, where the Paleo Conditioned scenario serves this role, indicating higher low 

flows in the Paleo Conditioned scenario than the Paleo Resampled scenario. The post-2026 

management assumption does not impact this response variable because no impacts are realized 

above Lake Powell.

4.2 Upper Basin Shortage

Figure G-3 presents the total Upper Basin 2012 through 2060 annual shortage, defined as 

requested demand minus actual delivery. However, there are significant limitations associated 

with CRSS when calculating annual shortages in the Upper Basin because most of the shortages 

are hydrologic shortages that occur on the tributaries within the Upper Basin. Therefore, this 

figure significantly underestimates the shortages in the Upper Basin. 

Upper Basin median shortage increases significantly across all scenarios as a result of median 

supplies decreasing in the future, coupled with median demands increasing. Similar to historical 

conditions, there is always some amount of Upper Basin shortage for all traces and all years, 

largely due to hydrologic supply limitations on the smaller Upper Basin tributaries in the late 

irrigation season. In many tributaries, downstream senior rights and physical flows do not make 

storage a feasible option. These shortages are not affected by operation of the CRSP reservoirs. 

Nor do the post-2026 management assumptions impact this response variable because no impacts 

are realized above Lake Powell.
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-17

FIGURE G-3 

10th, 50th, 90th Percentiles for Magnitude of Upper Basin Annual Shortage

Note that there is always some amount of upper basin shortage for all years and all traces.

The Downscaled GCM Projected scenario results in the highest shortage increase due to its 

strong reduction in median flow. The Downscaled GCM Projected scenario’s flow reduction, 

coupled with the demand increases exhibited by the Rapid Growth (C1) demand scenario, result 

in the largest shortages across all scenarios. The lower bound of the Downscaled GCM Projected 

supply scenarios cluster is defined by the Enhanced Environment (D1) demand scenario. Even 

though Slow Growth (B) scenario demands were lower than the Enhanced Environment (D1) 

scenario demands, the latter exhibits less shortage because Enhanced Environment (D1) has 

lower demands in the Upper Basin than Slow Growth (B). 
Colorado River Basin

Water Supply and Demand Study

G-18 December 2012

4.3 Lake Powell Pool Elevation

Figure G-4 presents Lake Powell end-of-December pool elevation. At the 90th percentile level 

after reservoir elevations have stabilized from initial 2010 conditions, variability across supply 

and demand scenarios is insignificant. This stable elevation represents the approximate peak 

elevation seen in December as Lake Powell begins to spill. All scenarios produce sufficient 

flows to maintain Lake Powell at peak end-of-December conditions. 

FIGURE G-4 

10th, 50th, 90th Percentiles for Lake Powell End-of-December Pool Elevation
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-19

At the 50th percentile, the Downscaled GCM Projected scenario across all demand scenarios 

results in lower Lake Powell levels than any other supply demand combination. The decline in 

elevation from 2012 levels range from 80 to 140 (-7.6 million acre-feet [maf] to -11.4 maf) feet 

msl by 2060, whereas across all other scenarios reservoir elevations either increase about 10 feet 

msl or decrease by up to 50 feet msl. 

Meanwhile, the 10th percentile shows a continual decline across most scenarios. At the 10th

percentile, the Downscaled GCM Projected scenario exhibits little variability across all demand 

scenarios after 2025. Lake Powell pool elevation (before 2030) is simulated at extremely low 

levels (3,400 feet msl, 0.7 acre-feet [af]), well below minimum power pool (3,490 feet msl). The 

Paleo Conditioned scenario shows more spread across demand scenarios by 2060 bound by the 

Enhanced Environment (D1) scenario (3,480 feet msl) at higher elevations and the Rapid Growth 

(C1) scenario at lower elevations (3,420 feet msl),which is below power pool. These extreme 

levels are simulated under two supply scenarios (Downscaled GCM and Paleo Conditioned) and 

result from the increased probability of lower flow displayed through the Downscaled GCM 

Projected scenario and drought sequences that are plausible based on the paleo record but have 

not yet occurred since the filling of Lake Powell. 

Lakes Powell and Mead operation assumptions post-2026 show some influence on pool 

elevation. Under the assumed extension of the 2007 Interim Guidelines, generally lower 

elevations are seen at Lake Powell after 2026, at the 50th and 10th percentiles. This occurs due 

to Lake Powell balancing operations at various levels with Lake Mead, in addition to 

equalization operations. This is in contrast to only equalizing lake storage contents when 

reverting to the No Action Alternative.

4.4 Lee Ferry Deficit

Figure G-5 presents the magnitude (bottom panel) and percent of traces (top panel) with a Lee 

Ferry Deficit, defined for purposes of the Study as the amount of flow less than an aggregate of 

75 maf over 10 years. Lee Ferry is the division point between the Upper and Lower Basins 

specified in the Colorado River Compact (Compact) and is located below the Paria River.

The percent of traces exhibiting a deficit is primarily dependent on the supply scenario, with the 

demand scenario producing some variation around each supply. The Observed and Paleo 

Resampled scenarios show little increase (1 percent) by 2060 in percent of traces with a Lee 

Ferry Deficit. This result is consistent with this constrained sampling technique, which cannot 

produce drought spells or magnitudes not found in the observed or paleo reconstructed record. 

The increased percent of traces with a Lee Ferry Deficit exhibited under the Paleo Conditioned 

scenario is a result of drought sequences consistent with the paleo sequences but not found 

directly in the reconstructed record. The Paleo Conditioned scenario Lee Ferry Deficit results in 

2 percent of traces in Deficit under Enhanced Environment (D1) demands to 8 percent under 

Rapid Growth (C1) demands. 

The Downscaled GCM Projected scenario stresses the Upper Basin more than any other 

scenario; the Downscaled GCM Project scenario deficit begins at zero, and increases to 

25 percent under Rapid Growth (C1) demands and 17 percent under Enhanced Environment 

(D1) demands. 

The magnitude of deficit is generally not influenced by supply or demand scenarios. Across each 

percentile, the scenarios crisscross each other through time but are about 3.5 maf at the 90th 
Colorado River Basin

Water Supply and Demand Study

G-20 December 2012

percentile, 2 maf at the 50th percentile, and 500 kaf at the 10th percentile. Once a trace enters 

these extreme hydrologic conditions that cause a deficit, magnitudes are limited to a particular 

response. The post-2026 management assumption does not significantly impact this response 

variable.

FIGURE G-5 

10th, 50th, 90th Percentiles for Lee Ferry Deficit in Years in Which a Deficit Occurs (top) and Percent of Traces with a Lee Ferry 

Deficit (bottom) 
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-21

4.5 Lake Mead Pool Elevation

Figure G-6 presents Lake Mead end-of-December pool elevation. 

At the 90th percentile, pool elevation generally increases from initial 2010 conditions 

before dropping at different magnitudes for each supply scenario. The Paleo Resampled scenario 

(lowest cluster of smooth gray lines) shows the largest pool elevation drop by 2060, ranging 

from 0 to 60 feet msl. The variance in this water supply scenario is reduced compared to the 

observed record and does not generate the frequency of surplus spells of the observed record. 

Nor does it produce the magnitudes of high annual flows also seen in the observed record. The 

next-lowest supply scenario is the Downscaled GCM Projected scenario, with a pool elevation 

drop by 2060 ranging from 0 to 30 feet msl. The remaining two supply scenarios realize an 

increase in pool elevation ranging from 30 to 40 feet msl by 2060 across all demand scenarios. 

FIGURE G-6 

10th, 50th, 90th Percentiles for Lake Mead End-of-December Pool Elevation
Colorado River Basin

Water Supply and Demand Study

G-22 December 2012

These declines are a result of less-frequent equalization and balancing releases from Lake 

Powell, primarily resulting from reduced supplies coupled with increasing Upper and Lower 

Basin demands. 

At the 50th percentile, the Downscaled GCM Projected scenario across all demand scenarios 

projects Lake Mead elevations at lower levels than any other supply demand combination. This 

indicates that the reduced supply simulated under a plausible climate assumption sharply 

diminishes the Basin storage. The drop from 2012 levels ranges from 90 to 140 feet msl by 2060, 

whereas across all other scenarios the levels range from an increase of about 5 feet to a decrease

of 75 feet msl. 

At the 10th percentile, the Downscaled GCM Projected supply scenario exhibits little variability 

across all demand scenarios. It also shows pool elevation reaching extremely low levels (900 feet 

msl), which is below the current Southern Nevada Water Authority (SNWA) minimum pumping 

level (1,000 feet msl). The Paleo Conditioned scenario shows a much greater spread across 

demand scenarios by 2060 when the 2007 Interim Guidelines (DOI, 2007) are extended. They are 

bound by the Enhanced Environment (D1) scenario (970 feet msl) at higher elevations and the 

Rapid Growth (C1) scenario a lower elevations (930 feet msl), also both below SNWA’s current 

intake minimum pumping level. These extreme levels are produced under these two supply 

scenarios as a result of an increased number of traces, with lower elevations displayed through the 

Downscaled GCM Projected scenario and drought sequences that are plausible based on the paleo 

record but have not yet occurred since the filling of Lake Mead The remaining supply scenarios 

2060 pool elevations range from 950 to 1,020 feet msl. 

The Lakes Powell and Mead operation assumptions post-2026 again influence results. Under the 

2007 Interim Guidelines, generally lower elevations occur at both reservoirs by 2026, resulting 

from no change in shortage guideline assumptions once Lake Mead reaches elevation 1,025 feet 

msl. At this level, the Basin States have agreed to consultation to determine actions. When 

reverting to the No Action Alternative, an operational assumption to attempt to avoid Lake Mead 

declining below elevation 1,000 feet msl is implemented and effective under all but the worst 

supply scenario, the Downscaled GCM Projected.

4.6 Lower Basin Shortage

Figure G-7 presents the magnitude (top panel) and percent of traces (bottom panel) with the 

Lower Basin 2012 through 2060 annual total shortage, determined as regulatory and hydrologic 

shortages plus remaining demands above the Lower Division States’ basic apportionments. The 

percent of traces with shortage begins at 100 percent in 2012. This results primarily from 

remaining demands above the Lower Division States’ basic apportionment initially not being met 

under any traces until a few years into the future, when demands above Lower Division States’ 

apportionments can be met in a limited number of traces through surplus events (approximately 

10 percent) until 2044. After 2044, surplus events cannot cover increasing demands above the 

Lower Division States’ basic apportionments under all traces. 

Across all percentiles, the Downscaled GCM Projected scenario results in the highest shortage 

increase from 530 thousand acre-feet (kaf) in 2012 to a range in 2060 of about 4 maf to 5.4 maf 

at the 90th percentile and 2 maf to 3.2 maf at the 50th percentile. This range was defined by the 

demand variability where the Rapid Growth (C1) scenario exhibited the highest shortage and the 

Slow Growth (B) scenario exhibited the lowest. 
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-23

FIGURE G-7 

10th, 50th, 90th Percentiles for Lower Basin Shortages when Present (Regulatory, Hydrologic, and Remaining Demand above 

Lower Division States’ Basic Apportionments) (upper panel), and Percent of Traces with Lower Basin Shortages (lower panel)

At the 50th percentile the supply scenarios show less difference. The Downscaled GCM 

Projected scenario is generally higher, with certain of the other scenarios bound by the demand 

variability of the Downscaled GCM Projected scenario. The remaining supply scenarios show 

little difference in the magnitude of shortage based on supply scenarios but show that the 

differences are still influenced by demand scenario variability. As a result, shortages generally 

increase from 550 kaf in 2012 to a range of 1.8 maf to 4 maf by 2060 at the 50th percentile. This 

initial 2012 shortage and continual increase in shortage is primarily driven by remaining 

demands above the Lower Division States’ apportionments, which can only be met under surplus 

conditions. 

The 10th percentile is similar to the 50th in that the Downscaled GCM Projected scenario is 

generally higher, with certain of the other scenarios bound by the demand variability of the 

Downscaled GCM Projected scenario. Shortage magnitudes range from 550 kaf in 2012 to a 

range of 100 kaf to 2.8 kaf by 2060. 
Colorado River Basin

Water Supply and Demand Study

G-24 December 2012

The Lakes Powell and Mead operation assumptions post-2026 influence Lower Basin shortage. 

The 90th percentile shortage increases to 3.70 maf, and the 10th percentile shortage climbs at a 

slower rate to 1.2 maf. The jump in shortage magnitude observed around 2027 results from both 

the assumed reversion to the No Action Alternative from the Interim Guidelines Final EIS 

(Reclamation, 2007) for half the traces, and the reduced supplies represented under the 

Downscaled GCM Projected scenario.

It is important to note that the reasons for Lower Basin shortages are different than the reason for 

Upper Basin shortages. Lower Basin shortages are influenced by large demands, coupled with 

Compact allocations available to meet those demands as well as contrived operational rules that 

define shortages. Upper Basin shortages are caused by the lack of physical water supply, 

especially on the smaller tributaries.

4.7 Summary

System response variable results explored 48 different scenarios—4 supply, 6 demand, and 

2 post-2026 Lakes Powell and Mead operation assumptions. 

In summary, without options and strategies, key system response variables indicate diminished 

system performance across most system measures. The findings based on this analysis are 

summarized below: 

• Upper Basin Tributary flows exhibit a reduction in annual flow primarily as a result of the 

increasing demands. This reduction is further strengthened on the Colorado and San Juan 

rivers by the Downscaled GCM Projected scenario’s reduced supplies. Further reduction 

resulting from the Downscaled GCM Projected scenario is minimal on the Green River. 

• Upper Basin median shortage increases significantly across all scenarios as a result of 

median supplies decreasing in the future, coupled with median demands increasing. Similar 

to historical conditions, there is always some amount of Upper Basin shortage for all traces

and all years, largely due to hydrologic supply limitations on the smaller Upper Basin 

tributaries in the late irrigation season. In many tributaries, downstream senior rights and 

physical flows do not make storage a feasible option. 

• Percent of traces with a Lee Ferry Deficit shows little increase (1 percent) by 2060 under the 

Observed and Paleo Resampled scenarios. The Paleo Conditioned scenario Lee Ferry Deficit 

results in 2 percent of traces in Deficit under Enhanced Environment (D1) demands to 8 

percent under Rapid Growth (C1) demands. Under the Downscaled GCM Project scenario, 

the deficit increases to 25 percent under Rapid Growth (C1) demands and 17 percent under 

Enhanced Environment (D1) demands as a result of the diminishing supply. The magnitude 

of deficit is generally not influenced by supply or demand scenarios and ranges from about 

500 kaf to 4 maf at the 50th percentile. 

• Lakes Powell and Mead pool elevations both indicate a wide range of future levels. At Lake 

Mead under all scenarios, except the Downscaled GCM Projected, from 2012 conditions, 

elevations range from an increase of about 5 feet to a decrease of 75 feet msl by 2060. Under 

the Downscaled GCM Projected, this range shifts down to elevations dropping from 90 to 

140 feet msl. 

• Lower Basin shortage magnitudes reflect the increasing gap between supply and demand. As 

a result, shortages generally increase from 550 kaf in 2012 to a range of 1.8 maf to 4 maf by 
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-25

2060 at the 50th percentile. This initial 2012 shortage and continual increase in shortage is 

primarily driven by remaining demands above the Lower Division States’ apportionments, 

which can only be met under surplus conditions. 

5.0 Defining Vulnerable Outcomes and Vulnerable 

Conditions 

The Study uses the concept of vulnerability to aid in summarizing the future conditions in which 

the system’s performance falls below acceptable thresholds across the wide range of indicator 

metrics. The performance of the Basin resources, as measured by a set of indicator metrics, 

varies considerably across changing and uncertain conditions. Some performance outcomes can 

be characterized as a largely linear or proportional response, whereas others are more aptly 

described in a binary manner. As a result, a unique threshold for undesirable or unacceptable 

performance or vulnerability was established for each of the indicator metrics. This process 

involved members of the Metrics and Modeling Sub-Teams as well as outreach to resource 

experts. The resulting vulnerability thresholds range from long-term minimum average 

performance to comparison against a historical range to a single-value criterion. By adding these 

thresholds to the process, two benefits were realized. First, by adding a vulnerability threshold to 

results, perspective is given as to the health/viability of the resource (e.g., is the resource close to 

being vulnerable?). Further, by tracking the number and persistence of vulnerable events with 

and without options over time, portfolio efficacy comparisons can be made using a variety of 

methods. 

5.1 Vulnerability Definitions

5.1.1 Metrics and Vulnerability Thresholds

In collaboration with the Metrics and Modeling Sub-Teams and resource experts, one or more 

vulnerability thresholds for each indicator metric were identified. Thresholds for the Water 

Delivery category were identified through an iterative process. Information from the WAPA was 

used to determine Electric Power Generation thresholds based in part on historical energy 

production from the Hoover, Glen Canyon, and other key hydropower facilities in the Basin. The 

Water Quality (salinity) and Flood Control thresholds are based on existing planning criteria for 

their respective indicator metrics.

Vulnerability thresholds for the Recreational and Ecological resource categories were more 

difficult to identify. To develop thresholds for these metrics, a comparative control-run was 

simulated with CRSS using constant 2015 water demand and historical hydrology to define 

quasi-Baseline levels for each metric. Using those results, in conjunction with input from 

resource experts/managers, vulnerability thresholds were established based on deviation from 

these control-run outcomes. 

Vulnerability thresholds are listed with their corresponding indicator metrics in table G-5. 

Additional descriptions of these thresholds, including source and rationale, can be found in 

appendix G3 of this document.
Colorado River Basin

Water Supply and Demand Study

G-26 December 2012

TABLE G-5 

Indicator Metrics and Vulnerability Thresholds

Resource Category/ 

Indicator Metric Vulnerability Threshold

Water Delivery

Upper Basin Shortage Shortage exceeds 25 percent of requested depletions in any 1 year

Lee Ferry Deficit Running 10-year sum of deliveries falls below 75 maf in any 1 month

Lake Mead Pool Elevation

< 1,000 feet msl

Reservoir storage is less than 1,000 feet msl elevation (SNWA current 

lower intake minimal pumping level) in any 1 month

Lower Basin Shortage Two different thresholds are used, either of which indicates vulnerability

to shortage (difference between Lower Basin basic apportionment of 

7.5 maf and actual depletions)

(1) Exceeds 1 maf over any 2-year window

(2) Exceeds 1.5 maf over any 5-year window

Demand Above the Lower 

Division States’ basic

Apportionments 

Demand above the Lower Division States’ basic apportionments exceeds 

1 maf in any year through 2035. Threshold decreases linearly from 1 maf

in 2035 to 0.250 maf (250 kaf) in 2060.

Electric Power Resources

Upper Basin Generation Power generation falls below 4,450 gigawatt-hours per year (GWh/yr) for 

more than 3 consecutive years

Lake Powell Pool Elevation, 

3,490 feet msl

Reservoir elevation falls below power pool of 3,490 feet msl in any 

1 month

Lake Mead Pool Elevation, 

1,050 feet msl

Lake Mead pool elevation falls below power pool of 1,050 feet msl in any 

1 month in any year

Water Quality Resources

Numeric Salinity Criteria below 

Parker Dam

Salinity exceeds 747 milligrams per liter in at least 1 year in more than 

50 percent of traces, for a given supply scenario and time period

Flood Control Resources

Lake Mead Downstream Safe 

Channel Capacity

Streamflow below Hoover Dam greater than 28,000 cubic feet per second 

(cfs) in any 1 month

Recreational Resources

Optimal Boating Flow Days At least 1 year in which the number of boating flow days on the Green 

River, San Juan River, and Upper Colorado River is less than the 10th

percentile of the control run1 

Total Boating Flow Days At least 1 year in which the number of boating flow days on the Green 

River, San Juan River, and Upper Colorado River is less than the 

minimum of the control run1

Public Use Facility Recreation 

Shoreline Elevation

Elevation of reservoirs drops below certain elevations in any 1 month:

• Blue Mesa Elevation below 7,440 feet msl

• Navajo Pool Elevation below 6,025 feet msl Flaming Gorge 

Elevation below 6,019 feet msl Powell Pool Elevation below 

3,560 feet msl Mead Pool Elevation below 1,080 feet msl
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-27

TABLE G-5 

Indicator Metrics and Vulnerability Thresholds

Resource Category/ 

Indicator Metric Vulnerability Threshold

Ecological

Streamflow on Yampa River 

near Maybell, Colorado 

Deviation beyond control run1 results range for (1) base flow target 

success rate (based on USFWS, 2008)

Streamflow on Green River at 

Green River, Utah 

Deviation beyond control run1 results range for (1) year type distribution 

(2) peak flow target success rate (3) base flow target success rate (based 

on Reclamation, 2005)

Streamflow on Colorado River at 

State Line, Colorado

Deviation beyond control run1 results range for (1) year type distribution 

(2) peak flow target success rate (3) base flow target success rate (based 

on McAda, 2003) 

Streamflow on San Juan near 

Bluff, Utah

Deviation beyond control run1 results range for (1) year type distribution 

(2) year type frequency (3) base flow target success rate (based on 

Reclamation, 2006)

Lakes Mead to Davis flow 

reductions

Streamflow greater than 845 kaf in any 1-year (based on Reclamation, 

2004)

1 The control run helps understand current system variability and model biases. Demands were held constant for the 

entire modeling horizon at the 2015, current projected levels in the control run, and the equalization line is held 

constant at the 2015 level. Hydrology conditions were simulated for the 49-year period using the Observed 

Resampled supply scenario. For some indicator metrics, vulnerability was defined relative to control run results. For 

example, vulnerability could be defined as meeting a flow target less frequently than the control run results (see 

appendix G-3 for vulnerability detail on each indicator metric).

5.1.2 Vulnerability Results Without Options and Strategies

Using the vulnerability thresholds described above, vulnerability was summarized for each 

indicator metric in two ways: 1) the proportion of simulation traces in which the threshold was 

exceeded at least once during the time period considered, and 2) the proportion of all years in the 

simulation in which the threshold was exceeded. Because each supply scenario includes a 

different number of individual traces, these statistics were calculated by resampling traces from 

each supply scenario to ensure that each scenario received equal weight. Rather than provide an 

average value for each trace, the proportion of years summarizes the overall frequency of the 

vulnerability across all traces. This helps to distinguish between, for instance, traces in which the 

vulnerability threshold is exceeded only once versus traces in which there are many vulnerable 

years.

Summaries of vulnerability from CRSS simulations shown in this section are aggregated into 

three future time periods: 2012 through 2026, 2027 through 2040, and 2041 through 2060. The 

end of the first time period was selected to coincide with the expiration date of the 2007 Interim 

Guidelines (DOI, 2007), after which two scenarios were considered to represent different 

assumptions regarding the future operation of Lakes Powell and Mead. Figure G-8 shows a 

summary of vulnerability results without options and strategies across all scenarios for the six 

indicator metrics in the Water Delivery Resource Category. The figure provides bar plots of the 

proportion of traces (left) and years (right) in which a metric crosses the vulnerability threshold. 

Similar results for the remaining resource categories are provided in subsequent paragraphs after 

the Water Delivery vulnerability discussion below. 
Colorado River Basin

Water Supply and Demand Study

G-28 December 2012

Figure G-8 shows that, in general, water delivery reliability is decreasing over time, resulting in 

increasing vulnerability. All water delivery indicator metrics show increasing vulnerability 

across the time periods, although the magnitude varies with each metric and the magnitude of 

vulnerability is much greater in the Lower Basin. For instance, the proportion of traces in which 

at least one Lee Ferry Deficit occurs increases from 2 percent in the period 2012 through 2026 to 

16 percent in the period 2041 through 2060, with 6 percent of years in the last period yielding a 

nonzero deficit. By comparison, Lake Mead storage is also declining a greater proportion of the 

time, with the percent of traces in which lake levels fall below the 1,000-foot elevation threshold 

more than doubling from the first to the last period (13 to 40 percent) and the percent of years in 

which levels fall below 1,000 feet msl more than quadrupling (4 to 19 percent).

Water delivery shortages to Lower Basin states also occur with greater frequency over time, with 

shortage vulnerabilities (i.e., exceeding 1 maf over any 2 years or 1.5 maf over any 5 years) 

occurring in 80 percent or more of the traces, with more than half of all years yielding a 

vulnerable outcome, by the 2041 through 2060 time period. Remaining demand above the Lower 

Division States’ basic apportionment also increases past acceptable thresholds in CRSS 

simulations: by the period 2041 through 2060, all traces exceed the threshold at some point, and 

nearly all years after 2041 would be considered vulnerable. CRSS simulations show that water 

delivery reliability is threatened by the effects of climate change, but the increasing vulnerability 

noted above also emerges in simulations derived from the historical or paleo climate record. For 

example, figure G-9 shows the percent of traces in which Lake Mead pool elevation is projected 

to be below 1,000 feet msl. These results are disaggregated by time period, supply scenario 

(columns), demand scenario (symbols), and whether the 2007 Interim Guidelines are extended 

for Lakes Mead and Powell reservoir operation after 2026 (colors). For each supply scenario 

subset, the grey region shows range and the middle black bar the scenario median. Similar results 

for all water delivery indicator metrics can be found in appendix G3.

Figure G-9 shows that in the first time period (2012 through 2026), vulnerability in the Lower 

Basin varies primarily with the supply scenario. The Observed Resampled and Paleo Resampled 

scenarios cause a lower proportion of vulnerable traces, whereas the Paleo Conditioned and 

Downscaled GCM Projected results present a step change in percent of vulnerable traces. Little 

to no variation with demand scenario is noted in the first period (indicated by minimal variation 

in the demand scenario medians). 

In the second and third periods, results continue to vary across supply scenarios, but the variation 

between demand scenarios (same-colored symbols) increases in the Lower Basin, and a greater 

change is noted between traces in which the 2007 Interim Guidelines (DOI, 2007) are extended 

(blue) and those in which management reverts to the 2007 Interim Guidelines Final EIS 

(Reclamation, 2007) No Action Alternative (orange). In the final period, the relative difference 

between supply scenarios is of the same approximate magnitude as shown for the demand 

scenarios. Other water delivery metrics generally show similar patterns over variation across 

scenarios and over time (see appendix G3). 
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-29

FIGURE G-8 

Summary of Vulnerability Without Options and Strategies for Water Delivery Metrics 
Colorado River Basin

Water Supply and Demand Study

G-30 December 2012

FIGURE G-9 

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, Lake Mead Elevation Indicator 

Metric (Below 1,000 feet in any One Month)

The exception to this pattern is remaining demand above Lower Division States’ basic

apportionments (figure G-10). Here, a wide range of results across the demand scenarios are 

seen, from 43 percent to 100 percent of traces vulnerable in the 2027 through 2040 time period. 

The rate of demand increase in the Lower Division States, coupled with a threshold that drops 

over time, drives most of the vulnerability in this instance. Further, demands above basic

apportionments are only met during surplus conditions. In the Slow Growth (B) scenario, for 

instance, many traces do not exceed the vulnerability threshold until the final time period, 

whereas in scenarios with higher rates of demand growth, 75 to100 percent of traces are 

vulnerable by 2040. The threshold is exceeded in all scenarios by the last time period, suggesting 

a clear vulnerability related to growing Lower Basin demand.

Figure G-11 shows a summary of vulnerability results without options and strategies across all 

scenarios for the four indicator metrics in the Electric Power Resource category. The figure 

shows bar plots of the proportion of traces (left) and years (right) in which a metric crosses the 

vulnerability threshold. 

Figure G-11 shows that, in general, electric power reliability is decreasing over time. All electric 

power indicator metrics show increasing vulnerability across the time periods, although the 

magnitude varies with each metric. For instance, the proportion of traces in which Lake Mead 

pool elevation falls below 1,050 feet msl in any one month in any year increases from 31 percent 

in the 2012 through 2026 time period to 70 percent in the 2041 through 2060 time period, with 

42 percent of years in the last period falling below the 1,050 foot elevation threshold 
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-31

FIGURE G-10

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, Remaining Demand Above Lower 

Division States’ Basic Apportionments for a Subset of All Scenarios

FIGURE G-11

Summary of Vulnerability Without Options and Strategies for Electric Power Indicator Metrics
Colorado River Basin

Water Supply and Demand Study

G-32 December 2012

Figure G-12 shows a summary of the vulnerability results without options and strategies across a 

subset of all scenarios for the one indicator metric in the Flood Control Resource Category. The 

flood control vulnerabilities were few and actually decreased over time due to the increase in 

available storage associated with growing demand and reduced supply. 

FIGURE G-12

Summary of Vulnerability Without Options and Strategies for Flood Control Indicator Metrics 

Figure G-13 shows a summary of the vulnerability results without options and strategies across a 

subset of all scenarios for the 11 indicator metrics in the Recreational Resource Category. River 

boating indicator metrics (top panel) are based on the shift in long-term average availability of 

flows deemed acceptable (total days) and optimal (optimal days) as determined from an 

American Whitewater survey analysis documented in Technical Report D – System Reliability 

Metrics. Between the total and optimal flow metrics, the optimal metrics were consistently more 

vulnerable. This is because the window for optimal flows is more stringent and thus more 

sensitive to changes in flow. For reservoir recreation (bottom panel), Flaming Gorge reservoir 

performs notably well. This is due to a combination of less reduction in flow projections in the 

Upper Green River compared to other tributaries and slower growth relative to other regions. 

Blue Mesa and Navajo reservoirs exhibit the most stress under future demands without options 

and strategies.

Due to model constraints, the metric for the Water Quality Resource Category, salinity below 

Parker Dam, is only available in the Observed Resampled and Paleo Resampled supply 

scenarios. Without options enacted, across the available supply scenarios, salinity below Parker 

Dam does not violate the numeric criteria. 

Figure G-14 shows a summary of the vulnerability results without options and strategies across 

all scenarios for the five indicator metrics in the Ecological Resource Category. As detailed in 

Technical Report D – System Reliability Metrics, ecological metrics are multi-faceted. In order to 

establish vulnerability criteria, the performance of each metric’s components (e.g., meeting base

flow or peak flow recommendations) was quantified in a control run based on the historical

hydrology scenario and demands fixed at 2015 projected levels. Thus, during the course of a 

simulation, should the performance of a metric facet become degraded beyond the performance 

range of the control run, that outcome was deemed vulnerable. The specific details and nuances 

of the process for each of the metrics presented below can be found in appendix G3. All 

ecological indicator metrics show increasing vulnerability across the time periods, although the 

magnitude varies with each metric. For instance, the proportion of traces in which the San Juan 

River ecological indicator metric is vulnerable increases from 22 percent in the 2012 through 

2026 period to 77 percent in the 2041 through 2060 period, with 52 percent of years in the last 
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-33

FIGURE G-13

Summary of Vulnerability Without Options and Strategies for Recreational Indicator Metrics 
Colorado River Basin

Water Supply and Demand Study

G-34 December 2012

FIGURE G-14

Summary of Vulnerability Without Options and Strategies for Ecological Indicator Metrics 

period indicating vulnerability. Increased vulnerability is primarily a result of decreasing overall 

flows, increasing demands and shifting monthly flow distributions that may violate existing flow 

recommendations. 

5.2 Vulnerable Conditions 

5.2.1 Defining Vulnerable Conditions

Resources of the Basin are deemed vulnerable for futures in which an indicator metric violates 

its respective vulnerability threshold. These futures are a product of specific supply, demand, and 

management combinations, and vulnerable conditions may be present in any of these future 

combinations. Rather than defining a specific scenario combination as vulnerable, it is beneficial 

to identify the shared characteristics that stress the system under vulnerable futures. 

A key step in the analysis is to identify vulnerable conditions—concise descriptions of the 

combination of future external conditions that lead the system to underperform relative to the 

vulnerability thresholds for each metric. This analysis is particularly important because some 

conditions or combinations thereof may be significantly more telling in whether a threshold is 

likely to be violated. Vulnerable conditions help focus decision makers’ attention on the 
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-35

uncertain future conditions most pertinent to the challenges of concern and help facilitate 

discussions regarding the best ways to respond to those challenges. Appendix G3 provides more 

details and an example of this analysis.

An analysis was performed on all five of the water delivery indicator metrics. The process began 

with the simulation model results under each plausible future generated using CRSS3. For each 

indicator metric evaluated, vulnerability thresholds define futures as either vulnerable or not 

vulnerable. The Study then identified vulnerable conditions for each metric. The analysis 

considered the following uncertainties:

• Multiple characterizations of future hydrologic conditions (Supply Scenarios) 

• Demand (Demand Scenarios)

• Post-2026 operations for Lakes Powell and Mead uncertainty (i.e., future management after 

the expiration of the 2007 Interim Guidelines) 

Except where noted, these uncertainties were characterized and summarized over the 50-year 

period of analysis in order to capture the long-term averages or trends that appear to lead to 

vulnerabilities. Hydrologic uncertainty is represented with a variety of different statistical 

characterizations of water supply over time. 

Vulnerabilities were first evaluated for all futures by characterizing hydrologic conditions based 

on Basin-wide flow statistics (table G-6). 

TABLE G-6 

Characterizations of Uncertainty For Vulnerable Conditions (All Futures)

Uncertainty Characterization

Lees Ferry Natural Flow Annual Mean (2012–2060)

Trend (2012–2060)

Variance (2012–2060)

Annual Mean of Driest N-year Period (examined 5-, 8-, 10-year periods) 

Year of Driest N-year Period (examined 5-, 8-, 10-year periods) 

Annual Mean Flow of Wettest N-year period (examined 5-, 8-, 10-year 

periods) 

Year of Wettest N-year period (examined 5-, 8-, 10-year periods) 

Demand Mean Annual Post-2040 Demand1

Post 2026-Management 

Conditions

Extend Interim Guidelines or Revert to 2007 Interim Guidelines Final EIS 

No Action Alternative (Reclamation, 2007)

1 Multiple characterizations of demand over a range were considered, but because of the small number of 

demand scenarios, alternative characterizations would result in equivalent descriptions of vulnerability.

Analytically defining vulnerable future conditions serves several important purposes for the 

Study. Vulnerable conditions help to communicate clearly which plausible futures lead to 

 

3 For each supply scenario, some randomly selected traces were included more than once so that each scenario contained the same number of 

traces (1,244). This, in effect, weights each supply scenario equally in the vulnerability analysis. Sensitivity tests using different weighting 

approaches (i.e., no weighting and partial weighting) showed only modest difference in these analytically derived vulnerabilities.
Colorado River Basin

Water Supply and Demand Study

G-36 December 2012

vulnerability, describing a large set of plausible futures as a small, understandable set of 

conditions. Also, upon implementation of portfolios, the change in vulnerable conditions (i.e., 

how the pool of still vulnerable traces are best described) offers a quantitative method for 

evaluation of efficacy.4

5.2.2 Vulnerable Conditions Without Options and Strategies

Results from the analysis of vulnerable conditions in a future without options and strategies are 

shown below. First, the Lee Ferry Deficit indicator metric is described in detail, and then a 

tabular summary of the vulnerable conditions defined for the remaining water delivery indicator 

metrics is provided. Additional detail can be found in appendix G3. 

Table G-7 provides a summary of the vulnerable conditions identified for the Lee Ferry Deficit 

indicator metric using the methodology described in appendix G3. Across all traces considered, 

approximately 19 percent yielded at least one non-zero Lee Ferry Deficit over the 50-year 

simulation period. This represents the overall proportion of vulnerable traces in CRSS analysis. 

Using only two characterizations of uncertainty—the long-term mean natural flow and driest 8-

year mean natural flow, both measured at Lees Ferry—a vulnerable condition is defined that 

included 85 percent of these vulnerable traces (coverage). Lees Ferry is the site of the Colorado 

River gaging station located above the Paria River. In addition, the vulnerable condition has a 

density of 87 percent; meaning that 87 percent of traces with these flow characteristics yielded a 

vulnerable outcome at some point during the simulation. 

TABLE G-7 

Vulnerable Conditions Defined for Each Water Delivery Indicator Metric

Indicator Metric: Lee Ferry Deficit 

Vulnerable Condition Description: Low long-term average flow (< 13.8 maf) and 8-year drought below 

11.2 mafy

Vulnerable Traces: 19% Vulnerability Definition:

• Annual Mean Natural Flow at Lee Ferry 2012–

2060 < 13.8 mafy 

• Driest 8-Year Period of Annual Mean Natural Flow 

at Lee Ferry 2012–2060 < 11.2 mafy

Vulnerability Statistics:

• Coverage: 85%

• Density: 87%

This vulnerable condition is described as Low long-term average flow (<13.8 maf) and 

8-year drought below 11.2 million acre-feet per year (mafy). The characteristics include low 

long-term natural flow of 13.8 mafy, well below the observed historical average, and an 8-year 

drought with flows averaging below 11.2 mafy. These two conditions capture the vulnerable 

traces with high coverage and density, and are not sensitive to the range of demand scenarios 

considered or the possibility of changing operation assumptions after the 2007 Interim 

Guidelines (DOI, 2007) expire in 2026. 

 

4 For example, a portfolio that is vulnerable in a smaller percentage of futures is more resilient to those vulnerable conditions.
Technical Report G — System Reliability Analysis and

Evaluation of Options and Strategies

December 2012 G-37

A visual summary of Low long-term average flow (<13.8 maf) and 8-year drought below 

11.2 mafy is shown in figure G-15. Each point in the figure represents one trace in the analysis, 

characterized according to long-term mean annual flow (y-axis) and mean annual flow during the 

driest 8-year period (x-axis). Red points indicate traces with at least one Lee Ferry deficit 

vulnerability during the simulation, and gray points mark traces in which no vulnerability occurs. 

The yellow region (lower left) in the figure summarizes the vulnerable condition boundaries 

identified in the analysis; each trace that falls within this region is denoted with an X, and each 

trace outside is marked with an O. This figure shows that, despite the strong correlation between 

long-term and drought flows, a combination of restrictions in both dimensions is important to 

identifying a set of vulnerable conditions with high coverage and density. For instance, removing 

the long-term mean restriction would include all traces in the upper-left quadrant. Although there 

are some vulnerable traces in this quadrant not captured in Low long-term average flow 

(<13.8 maf) and 8-year drought below 11.2 mafy, a majority of these traces are not vulnerable, 

and therefore density would drop dramatically were this region included.

FIGURE G-15

Scatter Plot of Vulnerable Conditions for the Lee Ferry Deficit Indicator Metric Without Options and Strategies 

Summaries of the identified vulnerable conditions for all water delivery indicator metrics are 

shown in table G-8. For each indicator metric, the table provides a brief description of the 

vulnerable conditions and specifies the percentage of total traces that are vulnerable. Next, the 

table indicates the set of one or more restrictions on uncertain future system conditions that 

together describe the vulnerability. For quantitative inputs (e.g., annual mean natural flow at 

Lees Ferry from 2012 through 2060), the cells include a graphical illustration of the restrictions.

In these plots, the blue line shows the range of input values across all traces. Annual mean 

natural flow from 2012 through 2060, for example, ranges from 10 to 18.5 mafy. The 
Colorado River Basin 

Water Supply and Demand Study

G-38 December 2012

Table G-8 

Vulnerable Conditions Defined for Each Water Delivery Indicator Metric 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-39

Table G-8 

Vulnerable Conditions Defined for Each Water Delivery Indicator Metric 
Colorado River Basin

Water Supply and Demand Study

G-40 December 2012

superimposed red line shows the subset of this range included in the definition of the vulnerable 

condition (e.g., all traces with mean 2012 through 2060 flow less than 13.8 maf). Finally, the 

words in between the columns indicate whether just one of the conditions needs to be met to fall 

within the vulnerable conditions (“OR”) or whether all conditions must be met to fall within the 

vulnerable conditions (“AND”). 

Additional information about the vulnerable conditions, including summaries of the statistical 

results from the clustering algorithm applied, is provided in appendix G3. 

In general, vulnerable conditions for the majority of the water delivery indicator metrics 

described in table G-8 can be concisely described using two main drivers: 1) Lees Ferry natural 

flow and 2) post-2026 operations for Lakes Powell and Mead. Furthermore, the analysis shows 

that natural flow is best described with two of the many characterizations considered: a) annual 

mean (2012 through 2060) and b) annual mean of driest 8-year period. 

The specific thresholds for these inputs vary by metric, but a combination of these two flow 

characterizations and the post-2026 operations for Lakes Powell and Mead fully describe the 

vulnerable conditions for four of the six indicator metrics in the Baseline simulations.

The exceptions to this are Upper Basin shortage and remaining demand above Lower Division 

States’ basic apportionments. Conditions that typically produce an Upper Basin shortage above 

the vulnerability threshold are generally related to natural hydrologic flow conditions, not nondepletive flow requirements at Lees Ferry. For remaining demand above Lower Division States’ 

basic apportionments, all traces yield at least 1 vulnerable year in the Baseline simulations, and 

therefore no non-vulnerable conditions can be identified. 

Figure G-16 relates the vulnerable conditions defined for each metric back to the supply 

scenarios developed as inputs to the analysis. For each water delivery indicator metric, the 

percentage of traces within vulnerable conditions is shown. Further, of those traces, the percent 

from each water supply scenario is specified. Because the total percent of traces in vulnerable 

conditions is rather high for most, their contributions from different supply scenarios are largely 

comparable (100 percent of traces vulnerable would produce exactly equal contributions from 

each scenario). The Lee Ferry Deficit and Lake Mead pool elevation indicator metrics are the 

exception and show a higher percent of traces being from the Downscaled GCM Projected

scenario. This indicates that those metrics are more likely to be vulnerable under that particular 

supply and less so under the others. 

6.0 Evaluation of System Reliability With Options and 

Strategies

The Baseline system reliability evaluation section revealed a wide range of plausible future 

outcomes for the Study Area. The recurrent tendency of these outcomes, however, suggests 

increasingly challenging future conditions. For example, the median pool elevation at Lake Mead 

declines significantly across all scenarios evaluated. This discussion was followed by a 

characterization the external conditions in which the system was vulnerable. For example, Lake 

Mead levels are likely vulnerable if long-term average natural flow is slightly lower than the 

mean, and 8-year drought natural flows at Lees Ferry are below 13 mafy. These conditions 

occurred in almost half of all traces evaluated in the Study.
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-41

FIGURE G-16

Proportion of Supply Scenario Within Each Set of Vulnerable Conditions Without Options and Strategies, by Water Delivery 

Indicator Metric

Given these findings, the key remaining important question the Study strives to address what it 

will take to solve the supply and demand imbalance problem. In light of increasing demand and 

possibly diminishing supply, exploration of system imbalances and resource impacts is an 

important component of the Study. Another challenge not included in the Baseline modeling is 

the significant demands above Lower Division States’ basic apportionment, as quantified in 

Technical Report C – Water Demand Assessment. Over the Study horizon, these additional water 

needs grow to nearly 2.8 mafy in some scenarios. Understanding the capacity of the system to 

address this extra demand is also a key part of the Study. 

This section begins by summarizing options that are available to address both system needs and 

remaining demands above Lower Division States’ basic apportionment. Next, it evaluates how 

the system could be improved using a portfolio in which a large set of feasible options are 

implemented as soon as they are available. The simulations first consider improvements and 

incurred costs when options only address Lower Division States’ demands within basic

apportionments. Thereafter, improvements and cost are re-evaluated when also addressing 

demands above Lower Division States’ basic apportionments. The simulations of these static 
Colorado River Basin

Water Supply and Demand Study

G-42 December 2012

portfolios provide an upper bound for potential system vulnerability reduction by implementing

the options modeled quantitatively in the Study. This section describes an analysis of dynamic 

portfolios, which trigger options in response to evolving conditions.. 

6.1 Portfolios of Options to Address System Imbalances

From November 2011 through February 2012, the Study solicited public input on options and 

strategies for helping to resolve future water supply and demand imbalances in the Basin. The 

Study cost-share partners sought input from a broad range of stakeholders and interested parties 

located within as well as external to the Basin. Through this processes approximately 160 

individual option submissions were received. Technical Report F – Development of Options and 

Strategies is a comprehensive documentation of the solicitation and collection process, option 

organization and classification, and a 17-criteria rating. The following is an overview of the 

detailed content contained therein and how those options were incorporated into the system 

modeling. 

6.1.1 Individual Options 

Of the many submissions received, all were classified as one of four high-level groupings: those 

that increase supply, those that reduce demand, those that are related to system operations, and 

those that are primarily related to governance and implementation. Although many of the options 

are conducive to the quantitative framework employed in the Baseline modeling, others were less 

amenable and thus were evaluated in a qualitative manner or via a more appropriate, alternate 

quantitative method. 

Because many of the submissions were similar in spirit, these options were combined when 

possible, as a representative option. The motivation for doing this is largely three-fold. By 

summarizing like ideas as a representative option, one is not given preference over another. 

Further, the associated details of timing, yield and implementation can be quantified consistently

across all representative options. Last, representative options ensure that the potential benefit of a 

particular type of option is not overstated or understated by determining yield based on objective 

review, not relative popularity. 

Each of the submitted options was evaluated based on 17 characterization criteria shown in 

table G-9. The criteria were selected to capture important attributes for the Study and to provide 

a relative comparison among options. Each option was assigned either a quantitative value (e.g., 

dollars per af for the cost of water) or a five-point rating (“A” through “E”) for each of the 

criteria, where “A” represents the most favorable rating and “E” the least favorable. A detailed 

description of the options and characterization process is described in Technical Report F – 

Development of Options and Strategies. The characterization criteria results were used to 

determine if an option was realistically feasible given the Study time window, and therefore 

whether it should be included in the system modeling with options and strategies. 

6.1.2 Static Portfolio of Options

In many plausible future conditions, the implementation of more than one option will be required 

to address Basin challenges. To evaluate the potential for available options to reduce or eliminate 

vulnerabilities, a single, static portfolio of options was developed—Static Portfolio A. This 

portfolio includes a large set of options submitted by the public and characterized as described 

above. The portfolio implementation is static in that it specifies that each option is to be 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-43

TABLE G-9 

Criteria Used to Characterize Representative Options

Criteria Summary Description of Criteria

Quantity of Yield The estimated long-term quantity of water generated by the option— either an 

increase in supply or a reduction in demand

Timing Estimated first year that the option could begin operation 

Technical Feasibility Technical feasibility of the option based on the extent of the underlying technology 

or practices

Cost The annualized capital, operating, and replacement cost per af of option yield

Permitting Level of anticipated permitting requirements and precedent of success for similar 

projects

Legal Consistency with current legal frameworks and laws, or precedent with success in 

legal challenges

Policy Considerations Extent of potential changes to existing federal, state, or local policies that concern 

water, water use, or land management

Implementation Risk Risk of achieving implementation and operation of option based on factors such as 

funding mechanisms, competing demands for critical resources, challenging 

operations, or challenging mitigation requirements

Long-term Viability Anticipated reliability of the option to meet the proposed objectives over the long 

term 

Operational Flexibility Flexibility of option to be idled from year to year with limited financial or other 

impacts

Energy Needs Energy required to permit full operation of the option, including treatment, 

conveyance, and distribution

Energy Source Anticipated energy source to be used to allow option to be operational

Hydropower Anticipated increases or decreases in hydroelectric energy generation associated 

with implementation of the option

Water Quality Anticipated improvements or degradation in water quality associated with 

implementation of the option.

Recreation Potential impacts to recreational activities including in-river and shoreline activities

Other Environmental 

Factors

Other environmental considerations, such as impacts to air quality, or aquatic, 

wetland, riparian, or terrestrial habitats

Socioeconomics Potential impacts to socioeconomic conditions in regions within or outside of the 

Basin as a result of implementing the option

implemented when available, regardless of the simulated system conditions. Therefore, the static 

portfolio represents an upper bound as to how much improvement the system could experience 

using the options in the portfolio, even though in many future conditions, the system may not 

require all the options to be implemented.

Table G-10 summarizes the type, number, and yield of the options included in Static Portfolio A, 

by time period—near-term (years 1 through 25), long-term (years 26 through 50), and total 

(years 1 through 50). This portfolio considers 36 options, and, when completely implemented, 

could yield approximately 6.3 maf in increased supply or reduced demand at an annualized cost 
Colorado River Basin

Water Supply and Demand Study

G-44 December 2012

estimated at $7.9 billion. Although all of these options either increase supply or reduce demand, 

the spatial differences of the options and methods of integrating within the system may limit the 

ability to address vulnerabilities. This limitation is particularly true for addressing Upper Basin 

shortages on tributaries. 

TABLE G-10

Summary of the Type, Number, and Yields of Options Included in Static Portfolio A

Option 

Category Option Type

Near-Term Long-Term Total

Number of 

Options

Sum of 

Yield 

(kafy) 

Number of 

Options

Sum of 

Yield 

(kafy) 

Number 

of 

Options

Sum of 

Yield 

(kafy)

Augment 

Supply

Desalination 8 1,176 2 300 10 1,476

Import 0 0 1 600 1 600

Local Supply 2 175 0 2 175

Reuse 4 618 3 532 7 1,150

Watershed 

Management 4 610 1 120 5 730

Total 18 2,579 7 1,552 25 4,131

Reduce 

Demand

Agricultural 

Conservation 5 1,000 0 0 5 1,000

Energy Sector 

Water Use 

Efficiency

1 160 0 0 1 160

M&I 

Conservation 3 600 2 400 5 1,000

Total 9 1,760 2 400 11 2,160

Grand Total 27 4,339 9 1,952 36 6,291

Based on results presented in the previous section on system reliability without options and 

strategies, significant vulnerabilities exist. In that modeling, demands above Lower Division 

States’ basic apportionments were only met under quantified, domestic, flood control or 70R 

surplus conditions. Therefore, upon consideration of options, the first undertaking is to explore 

their capacity to ameliorate those previously identified vulnerabilities. To accomplish this, 

modeling assumptions remain unchanged and the Static Portfolio A is used. However, of the 

many options included therein, several have capacity to benefit demands above Lower Division 

States’ basic apportionments, and are not included in this exercise. The resulting portfolio has an 

annual yield of approximately 4 mafy by 2060 with an annualized cost estimated at $5 billion. 

As option yield enters the system, it is allocated in accordance with the operational framework 

utilized in the modeling without options. Recall that pursuant to this assumption, deliveries to 

demand above Lower Division States’ basic apportionments only occur during periods of 

surplus. 

Because sizeable demands above Lower Division States’ basic apportionments exist, the capacity 

of options to resolve system vulnerabilities while also delivering to demands above Lower 

Division States’ basic apportionments is also analyzed. The entire Static Portfolio A, including 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-45

options that only address demands above Lower Division States’ basic apportionment as 

described in table G-10, is now considered. This constitutes an additional yield/benefit of about 

2.3 mafy by 2060 at an estimated annualized cost of $2.7 billion. When considering the 

additional options, which directly address demands above Lower Division States’ basic

apportionments, additional modeling assumptions pertaining to the allocation of the Lower Basin 

option benefits are required between those demands and the system. Appendix G3 describes an 

approach and sensitivity analysis of how this might be accomplished. For the results presented in 

the remainder of this report, when demands above Lower Division States’ basic apportionments 

are met by options, benefits are assumed to offset demands above Lower Division States’ basic

apportionments until the Lake Mead pool elevation falls below 1,050 feet msl. At this point, 

options with capacity to do so benefit the system until Lake Mead’s pool elevation has recovered 

above the 1,050–foot threshold. 

To simulate the above described portfolio, the functionality to augment supply and reduce 

demands at the appropriate spatial locations was built into CRSS framework (see appendix G2 

for additional model details). At the onset of a simulation, a list of the various options, 

containing their quantified yield and year available, is passed to the model. Under the static 

portfolio, each option is implemented at the earliest possible year and for the full yield. At the 

end of each simulation with the full Static Portfolio A, all options are implemented with a total 

annual yield of approximately 6.3 mafy at an annualized cost estimated at $7.7 billion. 

Results from these modeling simulations are presented in the sections below and compared with 

outcomes of the system reliability modeling without options and strategies (referred to as 

Baseline from here on). In doing so, the capacity to resolve system imbalances is made apparent, 

both for assumptions that limit deliveries to basic apportionments and those extending it to 

demands beyond. 

Figure G-17 shows the effects of the Static Portfolio A on water delivery vulnerabilities for three 

time periods when not addressing demands above Lower Division States’ basic apportionments, 

across all scenarios. The implementation of all the options in the portfolio significantly reduces 

the number of years in which the system is vulnerable for all the water delivery indicator metrics. 

It nearly eliminates years in which there is a Lee Ferry Deficit across all time periods. The 

number of years in which Lake Mead drops below 1,000 feet msl is reduced from 22 percent to 

2 percent, as are the number of years in which a Lower Basin Shortage occurs; from around 

50 percent of the years to around 5 percent of the years. 

Although the analysis shows the percent of vulnerable years resulting in an Upper Basin shortage 

decreasing with the portfolio options, this may be a result of CRSS-simplified representation of 

smaller tributaries in the Upper Basin. Because the smaller tributary demand is placed on the 

mainstem of the larger tributaries (Yampa, Colorado, Gunnison, and San Juan), the model tends 

to overestimates the ability of many options to reduce the associated shortages. For example, 

municipal conservation on the Front Range or in large cities along the mainstem Colorado will 

not increase flow on smaller tributaries where many of the shortages exist. This observation is 

true for each of the portfolios considered. 
Colorado River Basin

Water Supply and Demand Study

G-46 December 2012

FIGURE G-17

Percent of Vulnerable Years for Each Indicator Metric Across Three Time Periods for the Baseline and Static Portfolio A. 

Includes only system benefits. 

 

Graph reflects a subset of all scenarios evaluated for the portfolio analysis—Supply Scenarios: Observed Resampled, Paleo 

Conditioned, and Downscaled GCM Projected; Demand Scenarios: Current Projected (A), Rapid Growth (C1), Enhanced 

Environment (D1); Management Scenarios: Interim Guidelines Continued, Revert to 2007 Interim Guidelines Final EIS No Action 

Alternative.

Figure G-18 shows the effects that Static Portfolio A would have when providing both a system 

benefit and addressing demands above Lower Division States’ basic apportionments, across all 

scenarios for three time periods. The implementation of all the options in the portfolio 

significantly reduces the number of years in which the system is vulnerable for all the water 

delivery indicator metrics. The portfolio completely eliminates the vulnerability associated with 

remaining demand above Lower Division States’ basic apportionments. For other indicator 

metrics, nearly identical vulnerability reductions were achieved, relative to the portfolio only 

addressing system benefits, but at an increased $2.7 billion annualized cost. However, the 

additional cost eliminates the remaining demands above Lower Division States’ basic 

apportionments vulnerability.

To illustrate the static portfolio’s effect on outcomes relative to the various demand, supply, and 

management scenarios, figure G-19 shows the range of traces in which Lake Mead is vulnerable 

across three time periods for the Baseline case and Static Portfolio A across a subset of the 

demand, supply, and management scenarios. The static portfolio has minimal effect in the first 

time period, due to the time required to bring on most of the options. In the second period, the 

portfolio completely eliminates vulnerabilities derived from the Observed Resampled supply 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-47

FIGURE G-18

Percent of Vulnerable Years for Each Indicator Metric Across Three Time Periods for the Baseline and Static Portfolio A. 

Includes System and Demands Above Lower Division States’ Basic Apportionments Benefits. 

Graph reflects a subset of all scenarios evaluated for the portfolio analysis—Supply Scenarios: Observed Resampled, Paleo 

Conditioned, and Downscaled GCM Projected; Demand Scenarios: Current Projected (A), Rapid Growth (C1), Enhanced 

Environment (D1); Management Scenarios: Interim Guidelines Continued, Revert to 2007 Interim Guidelines Final EIS No Action 

Alternative.
Colorado River Basin

Water Supply and Demand Study

G-48 December 2012

FIGURE G-19

Percent of Vulnerable Traces for the Lake Mead Elevation Indicator Metric Across Three Time Periods for the Baseline and 

Static Portfolio A, by Supply and Demand Scenario

Graph reflects a subset of all scenarios evaluated for the portfolio analysis—Supply Scenarios: Observed Resampled, Paleo 

Conditioned, and Downscaled GCM Projected; Demand Scenarios: Current Projected (A), Rapid Growth (C1), Enhanced 

Environment (D1); Management Scenarios: Interim Guidelines Continued, Revert to 2007 Interim Guidelines Final EIS No Action 

Alternative.

scenario, but only modestly reduces vulnerabilities from traces derived from the Downscaled 

GCM Projected scenario. In the long term, the only remaining vulnerabilities are due to traces 

from the Downscaled GCM Projected scenario. The vulnerabilities are slightly higher from 

traces simulated with the Rapid Growth scenario as well as the management scenario in which 

the 2007 Interim Guidelines (DOI, 2007) are extended past 2026. 

This modeling showcases the upper bound of the portfolio’s potential to improve vulnerabilities 

under two assumptions. First, it addresses benefits to the system and demands within Lower 

Division States’ basic apportionment and second, benefits to the system along with remaining 

demand above Lower Division States’ basic apportionments. Both assumptions address 

vulnerabilities similarly and showed vulnerability could be significantly reduced when applying 

all options as soon as they are available. To address remaining demands above Lower Division 

States’ basic apportionments, an additional $2.7 billion of options needed to be added. 

Implementing Static Portfolio A implies that all options would need to begin the permitting 

process immediately. Further, options would be implemented regardless of the system status at 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-49

the time they are available, creating the potential for over-investment in many cases. The next 

section describes how the Basin can improve system benefits using portfolios that are dynamic 

and implement options only under conditions in which they are simulated to be needed. All 

portfolios benefit system demands within the existing basic apportionments as well as attempt to 

satisfy demands above Lower Division States’ basic apportionments under specific conditions. 

6.2 Improving System Benefits Through Dynamic Portfolios

6.2.1 Dynamic Portfolios 

The Study recognizes that Basin needs will depend upon future conditions that are highly 

uncertain. Successful strategies for addressing system imbalances must be adaptive and 

implement new options under future conditions in which they are most likely needed and are 

most effective for preventing vulnerabilities. Called dynamic portfolios, this approach aims to 

explore the timing and magnitude of options required to mitigate vulnerabilities on a trace- bytrace basis. The goal of this approach is to better understand the range of investment needs across 

scenarios and also improve the benefit to system resources given those investments. This affords 

a quantitative perspective of the magnitude of the overinvestment associated with Static Portfolio 

A (in which no dynamic implementation was considered). The basic principle is to construct 

model logic such that option implementation is delayed when conditions are favorable while 

investments are accelerated as vulnerabilities emerge. In order to do this, additional tools, model 

functionalities, and assumptions were required. 

From the option characterization, many options require significant time to plan and construct, 

which is reflected by their “earliest date available.” From a dynamic perspective, one cannot wait 

for vulnerability to occur before beginning the planning and implementation activities. The result 

would be a sizeable response lag and likely little improvement with regard to resource 

vulnerability. Therefore, in order to realize more timely benefits, it is assumed that the planning 

and construction process for all options begins in 2013. The length of time to conduct feasibility, 

permitting, and construction was estimated for each option as part of the characterization process 

(see Technical Report F – Development of Options and Strategies). This duration is added to 

2013 to estimate the earliest possible operational year. As a result, all options are available by 

their respective earliest possible dates. With this assumption, during a model simulation, 

vulnerabilities can now be more effectively addressed by implementing appropriate options from 

those available in a given year. Obviously it is unrealistic that the planning and construction 

process for all options would begin effective immediately with the goal to make them available 

by the earliest possible date. However, by tracking the options implemented and the timing 

thereof, a trace-by-trace “best case investment” could be hind-cast. For example, if only one 

option was required for a particular trace and it was implemented much later than the earliest 

possible date, that particular “best case investment” would perhaps be to begin planning for the 

option, but defer additional significant investment until conditions suggest that it is required. By 

analyzing the options selected and their timing and cost, across all scenarios, insight can be 

gained as to how often and when each option might be needed, which is likely to be useful 

information when faced with making actual Basin investments. 

Building upon the assumption and framework discussed above, the most effective way to 

mitigate vulnerabilities is preemptive option investment to avoid vulnerability instead of simply 

reacting to it. As a result, the ability to anticipate vulnerability, at some lead time, helps to guide 

and inform the actual timing of when an option should be implemented to effectively hedge 
Colorado River Basin

Water Supply and Demand Study

G-50 December 2012

against vulnerability. This capacity is referred to as signposting. For the purpose of the Study, it 

was assumed that option implementation only occurs to address water supply vulnerabilities. As 

such, signposts were developed only for specific vulnerabilities that were used to trigger option 

implementation. Through an objective analysis of system conditions that tend to precede 

vulnerable events, signposts were developed. When a signpost is observed, options are 

implemented from those available at that particular time. In taking preemptive steps, the benefit 

of a single option is allowed to accrue, possibly reducing the need for a larger, more reactive 

investment. By design, signposts are based on system factors that can change in response to the 

already implemented options, helping to avoid over-investment. The specifics of each signpost, 

detailed in table G-11, balance lead time and predictive skill. In the case of the Upper Basin 

shortage vulnerability, little predictive skill was achieved given the high degree of inter-annual 

flow variability. Therefore, the signpost is simply one vulnerable event. The lead time is the 

longest period between the triggering of a signpost and occurrence of a vulnerability that still 

retained sufficient predictive skill. Appendix G3 provides an illustration of signposts and how 

they were developed. 

TABLE G-11

Definitions of the Vulnerability Signposts Developed for Each Indicator Metric

Indicator Metric/ 

Vulnerability

Lead 

Time

(years)

Conditions

Lake 

Powell

Lake 

Mead

Natural 

5-year 

Mean Flow

at Lees 

Ferry

Upper 

Basin

Shortage

Lower Division 

States’ Demand 

Above Basic 

Apportionments 

Lee Ferry Deficit 5 3490’ NA 12.39 maf NA NA

Lower Basin Shortage 

(>1 maf over 2 years) 

3 NA 1060’ 13.51 maf NA NA

Lower Basin Shortage 

(>1.5 maf over 5 years)

3 NA 1075’ 13.51 maf NA NA

Mead Pool Elevation 

(< 1,000 feet msl) 

3 NA 1040’ 13.35 maf NA NA

Upper Basin Shortage 

(>25%) 

0 NA NA NA 25% NA

Demand Above Lower 

Division States’ Basic 

Apportionments 

Varies NA NA NA NA Demand above basic

apportionments is 

within 100 kaf of 

permissible level

Driven by the needs of dynamic option implementation, a secondary assessment of each 

representative option was performed. Specifically, the capacity of an option to address the 

various water supply vulnerabilities was quantified. This was accomplished by modeling the 

representative options and monitoring changes in the aforementioned vulnerabilities. The 

purpose of this is to inform dynamic option selection given the vulnerability at hand. Table G-12 

shows the results of this analysis. It should be noted that some judgment was exercised in this 

process, particularly when vulnerability improvements were found to be marginal or protracted. 

Note that because Upper Basin shortages are largely agricultural shortages on smaller tributaries, 

municipal conservation is not likely to reduce shortages. 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-51

TABLE G-12

Options that Address Different Vulnerabilities

Representative Option

Year 

Available

Vulnerability Addressed by Representative 

Option

UB ShortageLee Ferry DeficitMead Pool 

Elevation

Lower Basin Shortage 1Lower Basin Shortage 2Lower Division States’Demand Above BasicApportionments 

Agriculture (Ag) Conservation 2016 X X X X X X 

M&I Conservation 2016 X X X X X X 

Local-Rainwater Harvesting 2016 X X X X X X 

Reuse-Grey Water 2021 X X X X X X 

Reuse-Industrial 2021 X X X X X X 

Reuse-Municipal (Steps 1 and 2) 2021 X X X X X X 

Reuse-Municipal (Steps 3-5) 2036 X X X X 

Desalination (Desal)-Gulf of California (Gulf) 2028 X X X X 

Desal-Pacific Ocean-CA 2031 X X X X 

Desal-Pacific Ocean-Mexico 2026 X X X X 

Desal-Salton Sea Drainwater 2026 X X X X 

Desal-Southern California (SoCal)

Groundwater 2021 X X X X 

Desal-Yuma Area Groundwater 2021 X X X X 

Import-Front Range-Missouri 2041 X X X X X 

Energy Water Use Efficiency-Air Cooling 2021 X X 

Watershed-Dust 2026 X X 

Watershed-Tamarisk 2023 X X X X 

Watershed-Weather Modification (Weather 

Mod) 2016 X X 

Local-Coal Bed Methane 2021 X X 
Colorado River Basin

Water Supply and Demand Study

G-52 December 2012

Option and signpost information is passed to the model at the onset of each simulation. 

Additional model logic was implemented to monitor for the vulnerability signposts. Upon 

detection of a signpost, options that are 1) available (timing) and 2) address the anticipated 

vulnerability (quantity) are implemented in accordance with the following logic:

(1) In a single year, no more than four options total may be implemented Basin-wide. This 

aims to reduce over-investment while ensuring that enough options could be 

implemented to address all vulnerabilities in a single year, should that be required. 

(2) In a single year, additional options are implemented to address the same vulnerability 

until their total yield equals or exceeds 100 kafy, subject to the limitation described in 

(1). 

(3) If multiple signposts are triggered in the same year, an option is implemented for the first 

vulnerability. If the selected option(s) do not address the other vulnerabilities, additional 

options are implemented until all vulnerabilities are addressed, subject to the limitation in 

(1). This helps to prevent over-investment.

(4) Once an option is implemented, it remains in effect for the remainder of the simulation. 

At the conclusion of each model run/simulation, a summary of the selected options and their 

implementation timing is included in the results output. 

For each portfolio, specific data on option implementation such as timing and yield are output on 

a trace by trace basis, in addition to the standard suite of performance metrics. These data afford 

the ability to perform numerous analyses such as portfolio impact on system response variables, 

metrics, and indicator metrics. As an alternate and complementary measure, the improved 

resiliency can be quantified for a portfolio; for example, given some action taken, how bad of a 

drought can now be tolerated without incurring a vulnerable event, as compared to the system 

without options and strategies. When coupled with cost information, the trade-off between 

capital investment and performance can be considered. Option implementation frequency can 

also be assessed, both within and across portfolios. 

6.2.2 Strategies and Study Portfolios

The Study developed four exploratory portfolios to reflect different strategies for selecting and 

combining options to address Colorado River imbalances between water supply and water 

demand, as described in Technical Report F – Development of Options and Strategies. Each 

portfolio consists of a unique selection of options that are considered to address vulnerabilities 

(e.g., declining Lake Mead pool elevation) that may exist under future combinations of supply 

and demand. The portfolios were implemented dynamically in CRSS, meaning options were 

implemented based on the portfolio strategy depending on the timing and nature of the 

vulnerabilities. Portfolios were then analyzed to assess the effects of the strategy on resolving 

vulnerabilities to Basin resources. As a result, for a given portfolio, the sequencing and timing of 

options will be unique to each supply/demand scenario. 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-53

Table G-13 describes each of the four strategies and portfolios developed for the Study. Table G14 summarizes the number and yield of options by 2060 by type for Portfolios A and C. 

Technical Report F – Development of Options and Strategies provides additional detail on 

included options for each portfolio. 

TABLE G-13

Strategies and Portfolio Descriptions Explored in the Study

Strategy and 

Portfolio Name Portfolio Description

Portfolio A Includes options with high technical feasibility, excludes options with highest 

permitting, legal, policy, and long-term viability risks. Is the least restrictive in terms of 

options, and contains all options that are in both Portfolio B and Portfolio C.

Portfolio B Includes options with high technical feasibility and high long-term reliability; excludes 

options with high permitting, legal, or policy risks

Portfolio C Includes only options with relatively low energy intensity; includes options that result in 

increased instream flows; excludes options that have low feasibility or high permitting 

risk 

Portfolio D Is the most selective in terms of options and contains only those options that are 

included in both Portfolio B and Portfolio C

TABLE G-14

Summary of Included Options for Portfolios B and C 

Option 

Category Option Type

Portfolio B Portfolio C

Number of 

Options

Sum of 

Yield (kafy)

Number of 

Options

Sum of 

Yield (kafy)

Increase 

Supply

Desalination 10 1,476 5 620

Import 1 600 0 0 

Local Supply 1 100 1 75

Reuse 6 972 7 1,150

Watershed Management 2 300 5 730

Total 20 3,448 18 2,575

Reduce 

Demand

Agricultural Conservation 5 1,000 5 1,000

Energy Water Use Efficiency 1 160 1 160

M&I Conservation 5 1,000 5 1,000

Total 11 2,160 11 2,160

Grand Total 31 5,608 29 4,735
Colorado River Basin

Water Supply and Demand Study

G-54 December 2012

Figure G-20 shows the potential yield of the four portfolios over time for three different limits on 

the portfolio average cost. Portfolios are limited by including only those options that keep the 

average cost of the portfolio below the specified limit. On the right, the portfolios are essentially 

unconstrained by cost (average costs less than $1,250 per af). Not surprisingly, Portfolio A has 

the highest potential yield (~6.3 maf) and Portfolio D has the lowest potential yield (~4.0 maf). 

Portfolios B and C yields are similar through 2042. At that point, Portfolio B yield increases 

significantly more than Portfolio C. For lower average costs, the differences between the four 

portfolios are less significant (figure G-20, left), particularly between Portfolios B and C. 

FIGURE G-20

Total Yields over Time for Average Costs for Portfolios

Less than $750 per af (left), less than $1,000 per af (middle) and less than $1,250/af (right) 

6.3 Study Portfolio Evaluation

6.3.1 Improvements in System Performance 

The effects of the dynamic portfolios were simulated in CRSS for the entire suite of supply, 

demand, and management scenarios. This section describes how the portfolios affect the 

performance of the system across these scenarios. Each figure is composed of five vertical 

panels. The first panel displays the Baseline runs, which do not include new actions considered 

in the portfolios. The remaining four panels present results from one of four simulated portfolios 

discussed above. 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-55

The figures present either magnitude and percent of traces with occurrence, or 10th, 50th and 

90th percentile results for each of the key system response variables. The percentiles represent a 

level of non-exceedance for a given percentage of traces—i.e., the 10th percentile indicates the 

level at which 10 percent of the traces have not exceeded the value shown. In each of the figures, 

all traces for all combined scenarios are incorporated such that the results represent an ensemble 

of plausible future conditions. 

Summaries of system performance across traces presented in this section do not describe 

probabilistic outcomes. They describe plausible ranges and distributions for the baseline or a 

portfolio, corresponding to a wide range of plausible hydrologic, demand, and management 

traces. The underlying traces are the same across all portfolios and as such enable a consistent 

comparison of outcome differences across the portfolios. 

Figure G-21 presents Upper Basin annual shortage as calculated by CRSS, which consistently 

and significantly underestimates shortages in the Upper Basin. Under the Baseline conditions,

median shortage reaches 390 kaf by 2060. Portfolio B reduces 2060 median shortage to 230 kaf, 

a 40 percent reduction, followed closely by the Portfolio A (240 kaf), Portfolio D (250 kaf), and 

Portfolio C (250 kaf) portfolios (a 35 percent reduction). 

FIGURE G-21

10th, 50th, 90th Percentiles for Magnitude of Upper Basin Annual Shortage for the Baseline and Four Dynamic Portfolios

In all years under each of the portfolios, a shortage is projected in more than 99 percent of all traces.

The 90th percentile results suggest approximately 1.42 maf of Upper Basin shortage in 2060 

under the Baseline. These shortages are projected to be reduced by approximately 36 percent in 

Portfolio C and by approximately 49 percent with Portfolio B. The other two portfolios fall 

between these bounds. 

Again, this graphic likely overestimates the reduction in Upper Basin shortages under each 

portfolio, as a result of CRSS-simplified representation of smaller tributaries in the Upper Basin. 

Because the smaller tributary demand is placed on the mainstem of the larger tributaries (Yampa, 

Colorado, Gunnison, and San Juan), the model tends to overestimate the ability of many options 
Colorado River Basin

Water Supply and Demand Study

G-56 December 2012

to reduce the associated shortages. For example, municipal conservation on the Front Range or 

in large cities along the mainstem Colorado will not increase flow on smaller tributaries where 

many of the shortages exist.

Figure G-22 presents Lake Powell end-of-December pool elevation. Under the Baseline, median 

pool elevation decreased 29 feet by 2060, from 3,643 feet msl in 2012 to 3,614 feet msl by 2060. 

Implementation of any portfolio reversed this drop. The increase in pool elevation from 2060 

Baseline conditions was bound by Portfolio A (51-foot increase) and Portfolio D (39-foot 

increase). With Portfolio B, pool elevation increased by 49 feet msl and with Portfolio C pool 

elevation increased by 46 feet msl. 

FIGURE G-22

10th, 50th, 90th Percentiles for Lake Powell End-of-December Pool Elevation for the Baseline and Four Dynamic Portfolios

The 10th percentile indicated a 218-foot drop in elevation by 2060 under the Baseline. This drop 

is reduced to 145 feet under Portfolio D, 123 feet under Portfolio C, 96 feet under Portfolio B, 

and 82 feet under Portfolio A. It is noteworthy that even with such an improvement, levels are 

quite low, indicating that some scenarios still pose a challenge to the system, even with options 

in place. 

Figure G-23 presents the magnitude (top panel) and percent of traces (bottom panel) with a Lee 

Ferry Deficit defined as less than 75 maf of flow over 10 years. As was the case with Lake 

Powell pool elevation, all portfolios show improvements compared to the Baseline. In some 

cases, the number of traces in which a deficit occurs appears to have stabilized at less than 2

percent. Under the Baseline, the median deficit oscillates between approximately 1 and 3 maf 

between 2012 and 2040 then stabilizes at approximately 2 maf through 2060. A spike in deficit 

magnitude after 2050 is a result of reduced natural flows present in the Downscaled GCM 

Projected supply scenario. This spike is present under all portfolio results. Although the risk of a 

Lee Ferry Deficit was notably lowered, the median magnitude was impacted less (average 

magnitude reduction of 5.4 kafy across portfolios). In fact, at the 90th percentile, there appear to 

be some slight increases in shortage magnitudes. This is likely an artifact of reducing the number 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-57

FIGURE G-23

10th, 50th, 90th Percentiles for Lee Ferry Deficit in Years in Which a Deficit Occurs (top) and Percent of Traces (bottom) with a 

Lee Ferry Deficit for the Baseline and Four Dynamic Portfolios

of shortage events, particularly those of smaller magnitudes, thereby shifting some of the moreextreme conditions to the 90th percentile. Importantly, the portfolios that stabilize the probability 

of a Lee Ferry Deficit contain an option for an Upper Basin water bank, with certain assumptions 

about how a water bank would operate, that is used to help meet Compact delivery obligations 

when needed. The water bank concept is one of the best ways at reducing vulnerability of the 

Upper Basin to a Lee Ferry deficit. Because water banking concepts involve large institutional, 

legal, and policy issues, work must continue with deliberate speed to explore Upper Basin water 

banking options. 

Figure G-24 presents Lake Mead end-of-December pool elevation. Under the Baseline, median 

pool elevation decreased 69 feet, from 1,135 feet msl in 2012 to 1,066 feet msl by 2060. Pool 

elevations improved under all portfolios, relative to the Baseline, albeit not as immediate and to a 

lesser magnitude compared with the results at Lake Powell. The delayed recovery of the median 

pool elevation is a combination of option availability for implementation and the additional 

demands above Lower Division States’ basic apportionments that were not addressed in the 

Baseline run. These demands all originate in the Lower Division States, and therefore add 

demand on Lake Mead by calling for greater releases. In 2060, relative to the Baseline, median 

pool elevations rose from 60 to 90 feet msl depending on the specific portfolio. Not surprisingly, 

Portfolio A, which has the largest maximum potential yield, saw the largest increase (90 feet), 

and Portfolio D, with smallest maximum potential yield, showed the smallest gains (60 feet). 

Further, the 10th percentile indicates a 177-foot decline by 2060 under the Baseline. This decline

is reduced to 75 feet under Portfolio D, 71 feet under Portfolio C, 48 feet under Portfolio B, and 

43 feet under Portfolio A. The 90th percentile indicates an approximate 20-foot increase from 

Baseline conditions by 2060 across all portfolios. 
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G-58 December 2012

FIGURE G-24

10th, 50th, 90th Percentiles for Lake Mead End-of-December Pool Elevation for the Baseline and Four Dynamic Portfolios

Figure G-25 presents the magnitude (top panel) and percent of traces (bottom panel) with the 

Lower Basin 2012 through 2060 annual regulatory shortage. Under the Baseline, the Lower 

Basin median regulatory shortage begins at 400 kaf, indicating 50 percent of traces are under 

level 1 shortage; raises to 500 kaf by 2019 (level 2 shortage); reaches 600 kaf by 2027 (level 3 

shortage); and maintains this through 2060. The 90th percentile shortage increases to 600 kaf by 

2018, then jumps to approximately 1.72 maf by 2027, and rises to 1.78 maf by 2060. 

With the implementation of portfolios, the availability of options to address Lower Basin 

regulatory shortage is insufficient until 2032, at which time all portfolios show a drop in median 

shortage to as low as 241 kaf under Portfolio C by 2060. There is also a substantial decrease in 

shortage at the 90th and 10th percentile levels. At the 90th percentile, Portfolio A shows a 

reduction by 2060 to 584 kaf and the 10th percentile shows a reduction to 88 kaf. 

Figure G-26 presents the Lower Basin 2012–2060 annual remaining demands above Lower 

Division States’ basic apportionments as distribution of magnitudes and percent of traces 

when that occurs. Under the Baseline, median remaining demands above Lower Division 

States’ basic apportionments (top panel) increases from 536 kaf in 2012 to 1,687 kaf by 

2060. The 90th percentile increases from 536 kaf in 2012 to 2,507 kaf by 2060, while the 

10th percentile begins at 529 kaf in 2012, dips to a low of 0 kaf in 2022, and then grows to a 

high of 1,168 kaf by 2060. The percent of traces with remaining demands above Lower Division 

States’ basic apportionments in 2012 (bottom panel) begins at 100 percent, dips to 90 percent 

around 2020, then climbs back to 100 percent by 2044 and remains at that percentage through 

2060. This behavior is related to the similar pattern observed at the 10th percentile magnitude. 

Recall that under the Baseline, the only time Lower Division States’ demands above basic 

apportionments are met is during surplus. The near-term probability of surplus is negligible, so 

Lower Division States’ demands above basic apportionments often goes unmet. As the percent of 

traces with surplus increases in the near future, the percent of traces in which above basic 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-59

FIGURE G-25

10th, 50th, 90th Percentiles for Lower Basin Annual Shortages (Regulatory plus Hydrologic) Magnitude (top), and Percent of

Traces with Lower Basin Shortage (bottom) for the Baseline and Four Dynamic Portfolios

FIGURE G-26

10th, 50th, 90th Percentiles for Remaining Demands Above Lower Division States’ Basic Apportionments Magnitude (top) and 

Percent of Traces When This Occurs (bottom) for the Baseline and Four Dynamic Portfolios
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G-60 December 2012

apportionments are not met drops modestly, as does the remaining demands above basic 

apportionments magnitude at the 10th percentile. Ultimately, however, the percent of traces 

returns to 100 percent and the 10th percentile magnitudes begin to increase. This is due to the 

demands above Lower Division States’ basic apportionments increasing with time to a level that 

cannot be satisfied with surplus conditions alone. 

Implementation of any portfolio shows a reduction in magnitude after 2016 and percent of traces

after 2030. By 2060, the median remaining demands above Lower Division States’ basic 

apportionments is reduced to 0 kaf under Portfolio A, 16 kaf under Portfolio B, 77 kaf under 

Portfolio D, and 97 kaf under Portfolio C. The percent of traces is reduced to 48 percent under 

Portfolio A, 51 percent under Portfolio B, 63 percent under Portfolio D, and 66 percent under 

Portfolio C. 

Figure G-27 presents the Lower Basin 2012 through 2060 annual total shortage determined as 

regulatory and hydrologic shortages plus remaining demands above Lower Division States’ basic

apportionments. The figure shows the magnitude (top panel) and percent of traces when that 

occurs (bottom panel). Under the Baseline, median shortage in 2012 is 536 kaf and climbs to 

2.274 maf by 2060. The 90th percentile increases to 3.720 maf, while the 10th percentile climbs 

at a slower rate to 1.167 maf. The percent of traces with shortage begins at 100 percent in 2012, 

dipping to 90 percent from 2020 through 2024, then climbing back to 100 percent by 2044 and 

through 2060. This is the same behavior discussed in the previous section. When reservoirs are 

full (i.e., surplus conditions exist), there are no regulatory shortages and occasionally the surplus 

is sufficient to satisfy all demands above basic apportionments.

FIGURE G-27

10th, 50th, 90th Percentiles for the Sum of Lower Basin Regulatory and Hydrologic Shortages plus Remaining Demands Above 

Lower Division States’ Basic Apportionments for the Baseline and Four Dynamic Portfolios
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December 2012 G-61

Implementation of portfolios consistently reduces median shortage from 2030 to a magnitude of 

150 kaf under Portfolio A, 154 kaf under Portfolio B, 162 under Portfolio D, and 181 kaf under 

Portfolio C by 2060 in all portfolios. The 90th percentile is reduced to about 1 maf by 2060. The 

percent of traces with shortage in 2060 is reduced to 60 percent under Portfolio A, 65 percent 

under Portfolio B, 75 percent under Portfolio D, and 76 percent under Portfolio C. 

Improvements in system performance are demonstrated across all portfolios when compared 

with the Baseline analyses. Comparison of the four portfolios with 2060 Baseline conditions 

showed: 

• Due to CRSS simplification, the reduction in Upper Basin median shortage magnitude is 

likely overstated. Still, while the magnitude of shortage was reduced, nearly all traces still 

contained some shortages. 

• Lake Powell end-of-December median pool elevation increased between 39 and 51 feet msl 

under implementation of the dynamic portfolios. 

• Lee Ferry median deficit magnitude was reduced by 265 kaf, and the percent of traces with 

deficit was reduced to between 1 and 4 percent versus 8 percent for the Baseline. 

• Lake Mead end-of-December storage shows declines through 2030 in all portfolios, but 

increases between 60 and 90 feet by 2060 as options are implemented to reduce demand or 

increase Basin supply.

• Lower Basin regulatory shortage was similar to the Baseline through 2030 then dropped to 

a low of 241 kaf by 2060, a 60 percent reduction from 2060 Baseline conditions. Similarly, 

the percent of traces with shortage dropped from a high of 48 percent in 2033 to a low of 

32 percent by 2060, compared with 67 percent under the Baseline. Remaining demand above 

Lower Division States’ basic apportionments showed a steady median decline from a high of 

820 kaf in 2015 to between 0 and 100 kaf by 2060. By 2060, the percent of traces with 

remaining demands above Lower Divisions’ States basic apportionments is reduced to 

between 48 and 66 percent from 100 percent under the Baseline. 

6.3.2 Changes in Water Delivery Vulnerabilities 

Simulation results from the evaluation of portfolios were also used to estimate to what degree 

these new investments could reduce vulnerability in the Basin across all water delivery indicator 

metrics. The results of this analysis are shown in the figures following. Shown below are two 

figures for each resource category: one figure for the percentage of traces and one for the 

percentage of years in which vulnerability occurs. Each figure shows a barplot with the 

percentage of traces or years vulnerable, separated by indicator metric and time period. In 

addition, the results from each dynamic portfolio simulation are shown across the x-axis, with 

the baseline (no action) simulations shown in the left-most pane and the portfolio simulations

shown in sequence to the right. 

Figures G-28 and G-29 shown the change in vulnerability for the water delivery indicator metrics 

with portfolios in place compared with the Baseline. The next section provides these same 

summary results for the other indicator metrics. 
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G-62 December 2012

FIGURE G-28

Percent of Vulnerable Traces for Each Water Delivery Indicator Metric Across Three Time Periods for the Baseline And Four 

Simulated Portfolios 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-63

FIGURE G-29

Percent of Vulnerable Years for Each Water Delivery Indicator Metric Across Three Time Periods for the Baseline And Four 

Simulated Portfolios 

For all metrics shown, vulnerabilities in the first period tend to change little from the Baseline

results. This is a combination of often low vulnerability risk in the early period and few options 

available to address vulnerabilities when they occur. The middle time period is the first period in 

which results significantly diverge from the Baseline for most indicator metrics. However, this 

period, in some cases, is also the most vulnerable window, because options may have only been 

available for a short time and little benefit has yet accrued. As discussed earlier, demands above 

apportionment were not addressed in the Baseline modeling and therefore show a marked 

improvement under the portfolios. Also, one might expect Portfolio A to show the greatest 

reduction in vulnerabilities simply by having the greatest yield available to address imbalances. 

However, this is not always the case. Because this portfolio includes the Upper Basin banking 

option, water generated by conservation is not immediately available to address vulnerabilities, 

but is instead “banked” to help hedge against future water use curtailments as specified in the 

Upper Colorado River Basin Compact. 

For this same reason, Portfolio A was particularly effective at reducing frequency of Lee Ferry 

Deficits. It is noteworthy that in general, the relative reduction in percent of years in which

vulnerable conditions existed was greater than the reduction in percent of traces vulnerable. For 

example, with regard to the Lower Basin Shortage indicator metric (1.5 maf per 5 years), percent 
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G-64 December 2012

of years vulnerable in the 2041 through 2060 time period are reduced from about 59 percent to 

less than 25 percent, whereas percent of traces vulnerable are lowered from 87 percent to about 

58 to 66 percent, depending on the portfolio. 

This indicates that it is difficult to completely eliminate the vulnerability in each trace due to 

significant hydrologic variability. 

The following paragraphs address specific changes in water delivery indicator metric 

vulnerability with portfolios in place (in order of water delivery metrics listed).

Upper Basin Shortage

Due to CRSS simplification, the reduction in Upper Basin median shortage magnitude is likely 

overstated. Still, while the magnitude of shortage was reduced, nearly all traces still contained 

some shortages. 

Lee Ferry Deficit

Portfolio investments appear to substantially reduce the occurrence of a Lee Ferry deficit in 

many simulated traces. In particular, Portfolios A and C, which include an Upper Basin banking 

option, reduce the percent of vulnerable traces in the 2041 through 2060 time period from 

16 percent to 4 to 5 percent. Similarly, these portfolios reduce the percent of vulnerable years 

from 6 percent in the final time period to 1 percent with options implemented. Portfolios B and D

also reduce the proportion of traces or years with a Lee Ferry Deficit occurring (vulnerability 

remains in 9 to 11 percent of traces or 2 to 3 percent of years in the 2041 through 2060 time 

period). 

Lake Mead Elevation

Lake Mead elevation is better maintained above the 1,000-foot vulnerability threshold with 

portfolios in place. All four dynamic portfolios reduce the proportion of years or traces in which 

vulnerability occurs, although Portfolios A and B yield the most substantial vulnerability 

reduction for this indicator metric. This is due to the inclusion of additional desalination options 

for the Lower Basin in these portfolios. One note here is that the portfolios do not perform as 

well in the middle time period (2027 through 2040), generally yielding a larger percent of 

vulnerable traces and years in the middle period when compared with the final period despite 

growing vulnerability over time. This result is because the options needed to augment Lake 

Mead storage levels—particularly additional system water gained by offsetting Lower Basin 

demand with new coastal desalination—only become available after 2040, resulting in very low 

Lake Mead levels during the interim decades in 15 to 17 percent of traces (7 percent of years). 

Lower Basin Shortage

The portfolios generally reduce the percent of time in which Lower Basin shortages occur. 

However, shortages exceeding the vulnerability thresholds specified by Lower Basin users still 

occur in many traces or years with the portfolios in place. For example, with Portfolio A in place, 

the proportion of traces/years with a shortage exceeding 1 maf over 2 years declines from 80 

percent of traces/51 percent of years in the Baseline to 35 percent/10 percent in the 2041 through 

2060 time period. When considering a shortage of 1.5 maf over 5 years, alternately, the reduction 

is from 87 percent of traces/59 percent of years to 61 percent/23 percent with Portfolio A in place. 

In general, the 5-year shortage metric is more sensitive, and shows a larger proportion of 

vulnerable traces and years both in the Baseline and with dynamic portfolios implemented. As 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-65

with Lake Mead elevation, for these metrics, a greater reduction in vulnerability is observed in the 

third time period compared with the first and second periods due to the number of options 

available and called by the portfolio by this point in time. 

Lower Basin shortages are driven by Lake Mead storage levels, so these results reiterate that, 

despite the improvement in storage levels with the dynamic portfolios, a substantial fraction of 

traces or years remain in which Lake Mead levels trigger Lower Basin shortages that could 

exceed users’ capacity for short-term adaptation. As noted above, the most significant reduction 

in vulnerability occurs with remaining demand above basic apportionments in the Lower 

Division States. Due to increasing demand and the declining moving threshold over time, 

100 percent of traces and 93 percent of years are vulnerable for this indicator metric by the 2041 

through 2060 time period in the Baseline. With the portfolios implemented, however, the 

outcome is substantially improved in the middle and final time periods. In particular, in the final 

period the proportion of vulnerable traces is reduced dramatically (20 to 26 percent with 

portfolio), as is the proportion of vulnerable years (5 to 7 percent with portfolio). All portfolios 

help to reduce unmet demand above Lower Division States’ basic apportionments, although due 

to the desalination options, Portfolios A and B generally yield the greatest reduction in 

vulnerable traces or years for this metric across all time periods. 

A subset of the traces included in CRSS, particularly those drawn from the Downscaled 

GCM Projected hydrology, yield a large number of vulnerable years in a given trace. In these 

cases, portfolio investments may not fully eliminate vulnerable years (i.e., may not yield zero 

vulnerability in a trace), but may nevertheless reduce the number of years in which a 

vulnerability occurs. Figure G-30 illustrates this result for the Lee Ferry Deficit indicator metric 

by showing a histogram with bins for the number of vulnerable years (y-axis) summarized as a 

proportion of traces (x-axis). As above, this figure shows results from the Baseline (left column) 

as well as those from the four dynamic portfolios. For further sensitivity, this figure focuses on 

those traces included in the low long-term annual average flow below 14 maf and 8-year drought 

below 11 mafy vulnerable conditions defined for this metric in the previous section. 

FIGURE G-30

Number of Vulnerable Years Across Traces 2012–2060 for All Scenarios, Lee Ferry Deficit Indicator Metric, In Vulnerable 

Conditions (Long-Term Flow < 14 mafy and Drought < 11 mafy)
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G-66 December 2012

For traces in this set of vulnerable conditions, 13 percent of traces have no years with a Lee 

Ferry Deficit in the Baseline from 2012 through 2060. However, 25 percent of traces show a 

deficit in 1 to 5 years, 28 percent show a deficit in 6 to 10 years, and 33 percent (18 + 7 + 

8 percent) have a deficit in 11 or more years. This distribution shifts substantially, however, with 

the portfolios in place. Implementing Portfolio A, for instance, shifts many traces to zero 

vulnerability (69 percent within the vulnerable condition). Other traces still include at least one 

vulnerable year, but the upper tail—the proportion of traces with a large number of vulnerable 

years—is dramatically reduced. Using Portfolio A again, the proportion of traces with a deficit in 

11 or more years is reduced from 33 percent to 6 percent.

Similar results can be observed using the Lake Mead elevation indicator metric (figure G-31). 

Once again, the figure shows the subset of traces within the vulnerable conditions previously 

defined for this metric (Long-term average flow below 15 mafy and 8-year drought below 

13 mafy). Note that, in this set of vulnerable conditions, a large proportion of traces in the 

Baseline show Lake Mead elevation below 1,000 feet msl in 11 or more years, with nearly onequarter of traces (22 percent) showing Lake Mead at critically low levels in 21 or more years. 

With Portfolio B implemented, however, the entire distribution is shifted—from 28 percent to 

63 percent of traces with zero vulnerable years at one end, and 22 percent to 4 percent with 21 or 

more years vulnerable. Although a large fraction of traces with at least one vulnerable year 

remain within this set of vulnerable conditions (44 percent with the best-performing portfolio), 

the general pattern is a reduction in the number of vulnerable years and improved performance 

even in highly adverse traces. Similar results for other water delivery indicator metrics are 

provided in appendix G3. 

FIGURE G-31

Number of Vulnerable Years Across Traces 2012–2060 for a Subset of All Scenarios, Lake Mead Elevation Indicator Metric, In 

Vulnerable Conditions (Long-Term Flow < 15 mafy & Drought < 13 mafy)

However, another key question is how the portfolios perform in terms of reducing vulnerability 

within the set of vulnerable conditions defined for each metric. Ideally, a portfolio would shift 

the definitions or thresholds for vulnerable conditions altogether, yielding a range of conditions 

that were previously vulnerable under the Baseline but no longer produce vulnerable outcomes 

with the portfolio implemented. This type of change does in fact occur in the simulated portfolio 

results for the water delivery metrics. For example, the top pane of figure G-32 below shows the 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-67

same scatter plot of vulnerable conditions for the Lee Ferry Deficit indicator metric also shown 

in figure G-15. The axes show the two dimensions that define the vulnerable conditions: longterm average annual natural flow at Lees Ferry (y-axis) and average annual natural flow at Lees 

Ferry during the lowest 8-year period (x-axis). Each point in the plot shows one trace outcome 

across the 2012-2060 time span, with vulnerable traces colored red and non-vulnerable traces 

colored gray. Points within the low long-term average flow and 8-year drought below 11.2 mafy

vulnerable conditions are marked with X’s, and points outside are marked with O’s.

FIGURE G-32

Reduction in Vulnerable Traces with Selected Portfolios in Place, Lee Ferry Deficit Indicator Metric

The middle and bottom panes show the same plot with the same vulnerable conditions defined, 

but with results from Portfolio A or Portfolio B implemented, respectively, instead of the 

Baseline. This figure shows that, with the portfolios in place, a large fraction of traces and 

corresponding region of the vulnerable conditions has changed from red (vulnerable) to gray (not 

vulnerable). For instance, significantly few traces with a mean flow of 10 mafy or greater during 

the driest 8-year period are vulnerable with either of these portfolios implemented, whereas in 

the Baseline traces with average flows during an 8-year drought of 10 to 11.2 mafy were nearly 

always vulnerable when coupled with a low long-term overall flow. This suggests that the 

conditions that cause this vulnerability have shifted with the portfolios in place, and the new 

investments have provided a hedge against vulnerability in plausible simulated futures. 
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G-68 December 2012

To test the potential shift in vulnerability with a portfolio in place, the vulnerable conditions 

were re-evaluated for all water delivery indicator metrics with Portfolio A in place. The results of 

this reanalysis are provided in table G-15. In this table, results are provided from the Baseline

and also show the change in vulnerability with the portfolio in place. The second column shows 

the change in the overall proportion of vulnerable traces, while the rightmost columns describe 

how the vulnerable conditions shift when Portfolio A is implemented. In each cell, the blue bars 

again show the full range of the flow characterization or other quantitative input to the modeling 

across all scenarios; the red bars show the range of the restriction that helps to define the new 

vulnerable condition; and the yellow bars (with subscript values) show where the restriction 

identified for the Baseline simulations was previously defined. 

For example, the first row shows the vulnerable conditions for Upper Basin Shortage with the 

portfolio in place. In the Baseline, 86 percent of traces include at least one vulnerable year during 

the 2012 through 2060 timeframe, and the vulnerable conditions are defined by a 1-year 

minimum natural flow at Lees Ferry less than or equal to 8.3 maf. With Portfolio A

implemented, however, the percentage of vulnerable traces is reduced to 73 percent, and the new 

threshold for minimum natural flow shifts to 7.0 maf. This indicates that the additional supply 

and/or reduced demand in the Upper Basin with the portfolio in place provides additional 

capacity to handle single years with very low natural flows of between 7.0 and 8.3 maf without 

yielding a shortage of more than 25 percent of requested depletions for Upper Basin users. This 

result suggests that Portfolio A could introduce new resiliency to the system and allow the Upper 

Basin to better hedge against low-flow years. 

With respect to the other water delivery indicator metrics, the following changes in vulnerable 

conditions with the portfolio implemented are noted: 

• The conditions producing a Lee Ferry Deficit shift farther into the tail: with the portfolio 

implemented, these vulnerabilities most often occur in traces with a long-term flow mean of 

13.2 mafy and an 8-year drought mean of 10 mafy, compared with 13.8 mafy and 11.2 mafy 

in the Baseline, respectively. 

• Lake Mead elevation vulnerability shows a similar shift towards the extreme cases, with the 

long-term flow threshold reduced by about 500 kaf and the drought mean reduced by 700 kaf 

to 1 maf compared with the Baseline, depending on the post-2026 operation assumption for 

Lakes Powell and Mead. 

Two different patterns occur in the Lower Basin shortage indicator metrics. First, the “ORs” 

change to “ANDs,” meaning that within each portfolio the domain of the vulnerable condition is 

reduced and all conditions across the row must now be met within the vulnerable conditions. By 

contrast, in the Baseline, meeting either flow condition was sufficient to predict a vulnerable 

trace. In addition, for both metrics both the long-term mean and 8-year drought mean thresholds 

shift downwards, but only if management reverts to the 2007 Interim Guidelines Final EIS No 

Action Alternative (i.e., the 2007 Interim Guidelines (DOI, 2007) expire) after 2026. However, 

the new vulnerable conditions for these metrics with Portfolio A in place still include a large 

proportion of traces from CRSS simulations, and the long-term mean thresholds remain above 

the observed historical average of Lees Ferry natural flow. 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-69

TABLE G-15

Vulnerable Conditions Defined for Each Water Delivery Indicator Metric for Portfolio A
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G-70 December 2012
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-71

In general, portfolio implementation narrows the range of conditions that typically produced 

vulnerability when projecting plausible future water delivery reliability using CRSS simulations. 

Although vulnerability is not eliminated, the additional resiliency introduced by Portfolio A

reduces the risk of future vulnerabilities under current operational assumptions in many plausible 

futures. Figure G-33 includes the baseline vulnerable condition results of figure G-16 and the 

new vulnerable conditions associated with the Portfolio A results.

It shows the distribution of traces and total number of traces in vulnerable conditions broken out 

by supply scenario. As to be expected, the number of traces in vulnerable conditions was reduced 

for all indicator metrics. Most notable were reductions in the number of traces in the Lake Mead 

and Lower Division States’ demand above basic apportionments vulnerable conditions. 

Interestingly, for Upper Basin shortage, overall reductions were moderate, and all supply 

scenarios contribute a roughly equally number of traces. This is likely because most traces have 

at least one low-flow year, which is the condition for Upper Basin vulnerability. Further, when 

comparing the distribution of traces within vulnerable conditions, between the Baseline and with 

Portfolio A, a higher percentage tends to be from the Downscaled GCM Projected supply 

scenario. This is particularly noteworthy for the Lake Mead vulnerable conditions. 

FIGURE G-33

Percentage of Each Supply Scenario Within Each Set of Vulnerable Conditions with Portfolio A in Place, by Water Delivery 

Indicator Metric 
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6.3.3 Changes in Electrical Power Resource Vulnerabilities 

Figures G-34 (percent of traces) and G-35 (percent of years) shown the change in vulnerability 

for the electric power indicator metrics with portfolios in place compared with the Baseline. 

Electric power resources exhibited moderate performance improvements, as were seen in the 

water delivery indicator metrics. As more options are implemented, increased flow helps to raise 

pool elevations and in some cases, greater downstream demand requires larger releases. This 

combination is a two-fold benefit to hydropower. 

6.3.4 Changes in Flood Control Vulnerabilities 

Figures G-36 and G-37 show the change in vulnerability for the flood control indicator metrics 

with portfolios in place and compared with the Baseline. Under the Baseline modeling, flood 

control vulnerabilities were few and actually decreased over time due to the increase in available 

storage associated with growing demand. Under the various portfolios, the vulnerability 

incidence rate remained low, but did increase slightly. This is a direct result of option benefit

increasing pool elevations, which in turn, reduces capacity to absorb extreme flow events. 

Logically, these increased risks are most notable in the third time window, when the most 

options have been implemented. These increases are considerably more notable in the percent of 

traces vulnerable view (figure G-36) compared to the percent of years vulnerable (figure G-37). 

FIGURE G-34

Percent of Vulnerable Traces for Each Electric Power Indicator Metric Across Three Time Periods for the Baseline and Four 

Simulated Portfolios 
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and Evaluation of Options and Strategies

December 2012 G-73

FIGURE G-35

Percent of Vulnerable Years for Each Electric Power Indicator Metric Across Three Time Periods for the Baseline and Four 

Simulated Portfolios 

FIGURE G-36

Percent of Vulnerable Traces for Each Flood Control Indicator Metric Across Three Time Periods for the Baseline and Four 

Simulated Portfolios 

FIGURE G-37

Percent of Vulnerable Years for Each Flood Control Indicator Metric Across Three Time Periods for the Baseline and Four 

Simulated Portfolios 
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G-74 December 2012

6.3.5 Changes in Water Quality Resource Vulnerabilities

Due to model constraints, the metric for the Water Quality Resource category, salinity below 

Parker Dam, is only available in the Observed Resampled and Paleo Resampled supply 

scenarios. With options enacted, across the available supply scenarios, salinity below Parker 

Dam does not violate the numeric criteria. 

6.3.6 Changes in Recreational Resource Vulnerabilities 

Figures G-38 through G-41 shown the change in vulnerability for the recreational indicator 

metrics with portfolios, compared to the Baseline. Specifically, the metrics in figures G-38 and 

G-39 are river boating vulnerabilities, and those in figures G-40 and G-41 pertain to reservoir 

recreation. River boating indicator metrics are based on the shift in long-term average 

availability of PBO-based flows deemed acceptable (total days) and optimal (optimal days). 

Between the total and optimal flow metrics, the optimal were consistently more vulnerable. This 

is because the window for optimal flows is more stringent and thus more sensitive to changes in 

flow. All portfolios demonstrate improvements in the number of vulnerabilities for the boating 

indicator metrics. However, Portfolios A and C showed the most improvement. This is due to the 

Upper Basin banking option, found in both, which shepherds conserved water from across the 

major tributaries to the bank in southern Utah. By shepherding the conserved water, resources 

that depend on in-stream flows tend to benefit, including river boating recreation. 

For reservoir recreation, Flaming Gorge performs notably well, even under the Baseline

simulations. This is due to a combination of increases in streamflow projections in the Upper 

Green and slower growth relative to other regions. On the other hand, Blue Mesa and Navajo 

show significant vulnerability and little improvement even with portfolios. Based on their 

respective vulnerability definitions, both locations experienced multiple vulnerable years in the 

historical record. Therefore, it is not surprising that with increasing demands, vulnerabilities 

would continue and be challenging to mitigate in these locations, compared to other sites. 

Reductions to vulnerabilities at other locations in the Upper Basin are largely due to conservation 

and weather modification options. These options serve to either increase reservoir inflow or 

reduce the required release.
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-75

FIGURE G-38

Percent of Vulnerable Traces for Each Recreational (Boating Flow Days) Indicator Metric Across Three Time Periods for the 

Baseline and Four Simulated Portfolios 
Colorado River Basin

Water Supply and Demand Study

G-76 December 2012

FIGURE G-39

Percent of Vulnerable Years for Each Recreational (Boating Flow Days) Indicator Metric Across Three Time Periods for the 

Baseline and Four Simulated Portfolios 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-77

FIGURE G-40

Percent of Vulnerable Traces for Each Recreational (Shoreline Facilities) Indicator Metric Across Three Time Periods for the 

Baseline and Four Simulated Portfolios 
Colorado River Basin

Water Supply and Demand Study

G-78 December 2012

FIGURE G-41

Percent of Vulnerable Years for Each Recreational (Shoreline Facilities) Indicator Metric Across Three Time Periods for the 

Baseline and Four Simulated Portfolios 

6.3.7 Changes in Ecological Resource Vulnerabilities 

Figures G-42 and G-43 show the change in vulnerability for the ecological resource indicator 

metrics within portfolios, compared with the Baseline. Based on the discussion of river boating 

vulnerabilities, it would be logical to expect that the portfolios with the Upper Basin Banking 

option and associated shepherding of flows would benefit ecological resources more so than 

other portfolios. In the case of the Yampa and San Juan rivers, this is exactly the case. However, 

for the Green and Upper Colorado rivers, the improvements are largely commensurate with other 

portfolios. This is due to the particular PBO-based flow recommendations at those sites. The 

Green River and Colorado River flow prescriptions are specific with regard to timing and 

volume. As such, increases in flow as a result of shepherding water to the bank may not help to 

resolve vulnerabilities if the transfer is not managed consistently with the flow 

recommendations. Coordinated shepherding and re-regulation may be required to achieve the 

maximum benefit to those more-detailed flow requirements.
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-79

FIGURE G-42

Percent of Vulnerable Traces for Each Ecological Indicator Metric Across Three Time Periods for the Baseline and Four 

Simulated Portfolios 
Colorado River Basin

Water Supply and Demand Study

G-80 December 2012

FIGURE G-43

Percent of Vulnerable Years for Each Ecological Indicator Metric Across Three Time Periods for the Baseline and Four 

Simulated Portfolios

6.3.8 Summary of System Reliability Results

Table G-16 summarizes the system reliability results with the four portfolios in place. As shown 

in the table, portfolios are projected to improve the ability to meet Basin resources needs 

(reduction in vulnerabilities). The vulnerabilities related to critical Upper Basin and Lower Basin 

water delivery metrics—Lee Ferry Deficit and Lake Mead pool elevation below 1,000 feet msl—

were reduced by 50 percent or more. The results for metrics related to electrical power, water 

quality, recreation, and ecological resources demonstrate reductions of a similar percentage in 

vulnerabilities. Only the metric related to flood control below Hoover Dam shows a slight 

increase in vulnerability due to the potential for higher reservoir storage (and higher likelihood of 

high release) when portfolios were included. 

Although the portfolio analysis successfully demonstrated that system reliability can be 

improved, it is not without significant cost and performance tradeoffs. Figure G-44 illustrates the 

performance across portfolios by supply scenario in terms of addressing the Upper Basin water 

delivery reliability and Lower Basin water delivery reliability vulnerabilities.
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-81

TABLE G-16

Summary of System Reliability Outcomes (Percent of Years Vulnerable) for Baseline and Portfolios for All Scenarios, 2041–2060 

Resource System Vulnerability Baseline Portfolio A Portfolio B Portfolio C Portfolio D

Water Delivery Lee Ferry Deficit (Upper Basin Reliability) 7% 2% 2% 3% 3% 

Lake Mead pool elevation below 1,000 feet msl (Lower 

Basin Reliability) 

19% 3% 3% 5% 6% 

Electrical Power Upper Basin Generation (below 4,450 gigawatts per hour 

per year for 3 consecutive years)

18% 9% 10% 10% 11% 

Lower Basin Generation (Lake Mead pool elevation below 

1,050 feet msl) 

42% 14% 14% 29% 20% 

Flood Control Critical River Stage below Hoover Dam (greater than 

28,000 cfs) 

1% 4% 4% 3% 34%

Water Quality Salinity below Parker Dam (greater than numeric criteria)1 0% 0% 0% 0% 0%

Recreation Colorado River Boating (days less than control run) 30% 14% 16% 17% 19% 

Powell Shoreline Facilities (pool elevation less than 

3,560 feet msl)

24% 11% 11% 12% 13% 

Mead Shoreline Facilities (pool elevation less than 

1,080 feet msl) 

57% 31% 30% 37% 39%

Ecological Colorado River Flow (less than reference value) 38% 40% 28% 28% 31%

Lake Mead to Lake Mohave Flow (annual flow change 

greater than 845 kaf) 

12% 4% 4% 7% 8% 

1 Due to modeling limitations, results reported do not include results from the Downscaled GCM Projected scenario. 
Colorado River Basin

Water Supply and Demand Study

G-82 December 2012

FIGURE G-44

Percent of Years Vulnerable for Upper Basin Reliability (left) and Lower Basin Reliability (right) in 2041–2060 with Portfolios 

Implemented, by Supply Scenario

Portfolio B favors options believed to have higher certainty of available water supply once 

implemented. As shown in figure G-44 (on the right), this portfolio performs as well or better 

than all the other portfolios for addressing the Lower Basin reliability vulnerability shown in 

table 4 across all supply scenarios. The portfolio is less effective than Portfolios A and C for the 

Upper Basin reliability vulnerability (figure G-44, left), particularly in the Downscaled GCM 

Projected supply scenario (bottom row). 

Portfolio C, while focused on options that favor lower energy needs and less environmental 

impacts, is more dependent on shifting social values towards additional conservation and reuse. 

Choosing to implement options characterized as having low energy needs (as a surrogate for 

potential environmental impacts) might come at the expense of having a less certain long-term 

water supply. However, this portfolio performs well for addressing the Upper Basin reliability 

vulnerability (figure G-44, left) and is particularly effective under the Downscaled GCM 

Projected supply scenario (figure G-44, bottom row). The effectiveness of this portfolio for 

addressing Upper Basin reliability vulnerabilities is largely attributable to the inclusion of an 

Upper Basin water bank that specifically targets this vulnerability. Portfolio C is less effective; 

however, at addressing the Lower Basin reliability vulnerabilities (figure G-44, right). 

6.3.9 Costs and Other Characteristics of Implemented Options 

The costs of addressing the Basin’s vulnerabilities differ across portfolios and traces, and depend 

on which options are implemented. Figures G-45 through G-48 summarize the total annual cost 

($) and average annual cost per unit of water ($ per af) across different subsets of traces over 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-83

time. Total annual cost is calculated as the sum of the annual costs associated with each of the 

options implemented up to that point in time. Annual costs reflect capital and operation and 

maintenance costs in 2012 dollars, using 4.125 percent interest over the beneficial life of the 

option. Average cost per unit of water is computed as the quotient of annual cost and average 

annual yield. One set of figures summarizes across the traces within the four scenarios (figures 

G-45 and G-47). The other set (figures G-46 and G-48) summarizes across traces inside and 

outside two vulnerable conditions—those vulnerable for Lake Mead pool elevation < 1,000 feet 

msl and the Lee Ferry Deficit.

Total annual costs increase over time for all portfolios and supply scenario (figure G-45). The 

costs across the traces diverge significantly over time. In 2060, the 25th to 75th percentile costs 

range between about $2 billion to $5 billion for the Observed Resampled, Paleo Conditioned, 

and Paleo Resampled supply scenarios, and increases to potentially $7.0 billion under the GCM 

Projected scenario. Portfolio A is the most costly due to the inclusion of the greatest number of 

options and Portfolio D is the least costly due to the inclusion of the least number of options. 

These wide ranges of costs reflect the large differences in types of conditions evaluated for each 

supply scenario. For example, about 25 percent of the traces within the Downscaled GCM 

Projected scenario require only modest investment, and costs generally do not exceed $3 billion 

per year for all portfolios. Reciprocally, 25 percent of the traces require much more investment 

in options, pushing costs to as high as $5 billion for Portfolio C and more than $6 billion for the 

Portfolios A and B. Portfolio C is similar in cost range to Portfolio B except under the GCM 

Projected scenario, where it is less expensive largely due to exclusion of some options that are 

only triggered under more–challenging water supply conditions within Portfolio A and 

Portfolio B. The range of costs for Portfolio C is lower for the Downscaled GCM Projected 

scenario than the costs for Portfolio B, largely due to the exclusion of some option that are only 

triggered under more challenging water supply conditions within Portfolio A and Portfolio B, 

and the inclusion of focused-options such as the water bank, that more cost effectively address 

severe regional conditions. 

The total annual costs are also summarized across all traces and those within the vulnerable 

conditions (figure G-46). This shows more clearly how stressing conditions lead to higher costs 

across all portfolios. In general the Lake Mead Pool Elevation vulnerable conditions describe 

low streamflow conditions and the Lee Ferry Deficit vulnerable conditions describe even lower 

streamflow conditions (table G-8):

• Lake Mead vulnerable conditions: Long-term average flow below 15 mafy and 8-year 

drought below 13 mafy—or “Low Streamflow” conditions. 

• Lee Ferry Deficit vulnerable conditions: Long-term average flow below 13.8 maf and 8-

year drought below 11.2 mafy—or “Lowest Streamflow” conditions.

Recall that the Lee Ferry Deficit vulnerable conditions are more stressing conditions than the 

Lake Mead pool elevation < 1,000 feet msl vulnerable conditions. As expected, for all portfolios, 

costs are significantly lower and grow more slowly over time when considering all traces. For 

traces within vulnerable conditions, however, costs increase more rapidly in the early and middle 

periods as available options are quickly brought on line. Again, Portfolio C is less costly for the 

Lowest Streamflow conditions (i.e., traces with Long-Term Flow < 14 mafy and Drought Below 

11 mafy) than Portfolios A and B. Note that the wide range in costs for traces within the Lowest 

Streamflow conditions reflects the mixture of very stressing and moderately stressing traces.
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Water Supply and Demand Study

G-84 December 2012

FIGURE G-45 

Total Annual Cost by Supply Scenario Resulting from Implementation of the Dynamic Portfolios over Time 

The spread between the 25th and 75th percentile is indicated by shading. The 10th and 90th percentile values are indicated by the 

‘x’s.
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-85

FIGURE G-46 

Total Annual Cost for All Traces and Low Streamflow and Lowest Streamflow Conditions Resulting from Implementation of the 

Dynamic Portfolios over Time

The spread between the 25th and 75th percentile is indicated by shading. The 10th and 90th percentile values are indicated by the 

‘x’s. Low Streamflow conditions are those in which long-term mean natural flows are less than 15 mafy and the 8-year dry period 

flows are less than 13 mafy. Lowest Streamflow conditions are those in which long-term mean natural flows are less than 14 mafy 

and the 8-year dry period flows are less than 11 mafy.

The next two figures show the distribution of average costs over time for the four portfolios and 

the scenarios (figure G-47) and the vulnerable conditions (figure G-48). Across all groups of 

traces, the pattern of average costs for the Portfolios A and C is distinct from Portfolios B and D. 

Specifically, the former portfolios lead to markedly higher costs in the near term. These higher 

costs are due to the relatively high cost of the Energy Sector Conservation option ($2,000 per af) 

and some of the later increments of M&I Conservation ($700 to $950 per af), which are specified 

to be implemented when available. Average costs for all portfolios are roughly similar by 2060, 

ranging from about $750 to $1,250 per af for the Observed Resampled traces (top panels, 

figure G-47) and from $1,000 to $1,250 per af for the Lee Ferry Deficit vulnerable traces 

(bottom panels, figure G-48).
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Water Supply and Demand Study

G-86 December 2012

FIGURE G-47 

Average Annual Cost by Supply Scenario Resulting From Implementation of the Dynamic Portfolios over Time 

The spread between the 25th and 75th percentile is indicated by shading. The 10th and 90th percentile values are indicated by the 

‘x’s.
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-87

FIGURE G-48 

Average Annual Cost for All Traces and Low Streamflow and Lowest Streamflow Conditions Resulting from Implementation of 

the Dynamic Portfolios over Time

The spread between the 25th and 75th percentile is indicated by shading. The 10th and 90th percentile values are indicated by the 

‘x’s. Low Streamflow conditions are those in which long-term mean natural flows are less than 15 mafy and the 8-year dry period 

flows are less than 13 mafy. Lowest Streamflow conditions are those in which long-term mean natural flows are less than 14 mafy 

and the 8-year dry period flows are less than 11 mafy.

The options implemented within the portfolios also vary in terms of their characteristics (see the 

individual options section). Figures G-49 and G-50 summarize the range across the traces of 

yield in 2060 by each of the five characteristics ratings (A through E) for two groupings of 

criteria. These two criteria groups are representative of the overall strategy used to develop the 

portfolios. The Reliability group, which includes Technical Feasibility, Long-Term Viability, 

and Implementation Risk criteria, is used to represent the technical feasibility and long-term 

reliability preferences of Portfolio B. Similarly, the Environment group, comprising Energy 

Needs, Permitting, and Other Environmental Factors criteria, is used as a surrogate for reduced 

potential environmental impacts that are preferred in Portfolio C. For each grouping, the total 

yield by options with scores of A through C and D through E are summed for each three criteria 

and divided by three.
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Water Supply and Demand Study

G-88 December 2012

Figure G-49, for example, shows that Portfolio B implements mostly options with reliability

characteristics of A, B, or C. Portfolio C, however, provides a modest about of yield using 

options that score D or E on these criteria. 

FIGURE G-49 

Amount of Annual Yield with Reliability Group Characteristics Scores A–E for Each Portfolio in 2060 

Figure G-50 shows that Portfolio B implements up to about 1.5 maf of options that received 

either a D or E score in terms of energy needs for some traces. Portfolio C, in contrast, provides 

less yield through options that received a D or an E score for the Environment group 

characteristics. 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-89

FIGURE G-50

Amount of Annual Yield with Environment Group Characteristics Scores A–E for Each Portfolio In 2060 

In summary, there is much similarity across the portfolios in terms of the costs incurred across 

the traces and the characteristics of the options. Some modest differences are summarized in 

table G-17. 

TABLE G-17 

Summary of Costs and Option Characteristics Differences Among Portfolios

Portfolio A Portfolio B Portfolio C Portfolio D

Costs Highest cost Higher annual 

costs in later years

High average cost in 

early years, lower 

cost, particularly for 

more stressing 

traces, in later years 

Lowest cost

Option 

characteristics

Use of broadest 

range in terms of 

characteristics of 

options

Options with higher 

reliability

Fewer energyintensive optionsNo low reliability 

options; fewer 

energy-intensive 

options
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Water Supply and Demand Study

G-90 December 2012

6.3.10 Vulnerability Reduction Versus Cost Tradeoffs

It is important to consider the costs of implementing portfolios in relationship to their effects on 

reducing basin vulnerabilities. Figures G-51 and G-52 combines the information presented in 

figure G-29 (percent of vulnerable years for each water delivery indicator metric) and figure G45 (total annual cost by vulnerable condition) for different groups of traces.

As shown in figure G-51 (top row) the annual cost, in 2012 dollars, for implementing the 

portfolios ranges from approximately $2.5 billion to $3.5 billion in the year 2060 when 

considering the median of the Observed Resampled supply sequences, and from $3.6 billion to 

$5.8 billion when considering the median of the Downscaled GCM Projected supply sequences. 

The inter-quartile ranges of cost are significantly larger. However, because of the appraisal-level 

option cost estimating used in the Study, the cost values contain additional uncertainty not 

directly reflected in these estimates. 

FIGURE G-51 

Percent of Years Vulnerable for Upper Basin and Lower Basin Vulnerabilities from 2041–2060 and Range In Total Annual Cost 

In 2060 Across Supply Scenarios for Four Portfolios 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-91

FIGURE G-52 

Percent of Years Vulnerable from 2041–2060 and Range In Total Annual Cost In 2060 for All Water Supply Sequences (top), 

Sequences with Low Streamflow Conditions (middle), and Sequences with Lowest Streamflow Conditions (bottom) Across Upper 

Basin and Lower Basin Vulnerabilities, for Four Portfolios 

(1) Conditions in which long-term mean natural flows are less than 15 mafy and the 8-year dry period flows are less than 13 mafy. 

(2) Conditions in which long-term mean natural flows are less than 14 mafy and the 8-year dry period flows are less than 11 mafy. 

Across the top three supply scenarios (Observed Resampled, Paleo Resampled, and Paleo 

Conditioned), one can see that Portfolios B and D are generally less costly than Portfolios A and 

C. For the Downscaled GCM Projected water supply scenario tradeoffs begin to become 

apparent. Specifically, Portfolio C leads to fewer vulnerable years with respect to Upper Basin 

reliability than Portfolios A and B, with an upper range of costs that is also lower than those for 

Portfolios A and B. Conversely, Portfolio A generally leads to the fewest vulnerable years with 

respect to Lower Basin reliability than other portfolios. 

The differences among the portfolios become even more apparent in terms of costs and ability to 

reduce vulnerability as one focuses on the future conditions that are particularly stressing to the 

basin. Figure G-52 shows that across all traces, each portfolio reduces the years in which the 

Basin is vulnerable similar amounts. As was seen in figure G-45, the 2060 cost ranges are wide, 

reflecting the diversity of conditions across all traces. 
Colorado River Basin

Water Supply and Demand Study

G-92 December 2012

For sequences that are less favorable, such as in the “Low Streamflow” conditions, tradeoffs 

among the portfolios more pronounced. For the Lower Basin Vulnerability (Lake Mead Pool 

Elevation < 1,000 feet msl) (right column), Portfolios A and B are the most effective in reducing 

vulnerability, yet the range in costs are lower for the former. In this case, Portfolio B could be 

considered more favorable to the others in terms of these two dimensions. For the Upper Basin 

Vulnerability (Lee Ferry Deficit) (left column), however, the portfolios that reduce vulnerability 

more, lead to higher ranges in cost. Note, however, that Portfolio C reduces vulnerabilities more 

than the Portfolios B and D, and has a lower high cost range than Portfolio B. 

When considering the “Lowest Streamflow” subset of sequences (figure G-52, bottom row), two 

distinct tradeoffs between reduction in vulnerability and cost across the portfolios are seen. For 

the Upper Basin Reliability system vulnerability, Portfolio C both performs better than 

Portfolios B and D in terms of reducing this vulnerability and has a lower range of costs than 

Portfolios A and B. For the Lower Basin Reliability System Vulnerability, however, Portfolio B

reduces vulnerability more than Portfolios C and D and also results in lower costs than 

Portfolio A. 

6.3.11 Implemented Options for Different Portfolios 

The four portfolios evaluated in the Study represent different approaches for addressing the 

projected imbalances between water supply and demand and associated vulnerabilities. These 

portfolios were developed as exploratory strategies and should not be considered as individual 

suggestive pathways. Rather, they were developed to explore the range of options, different 

preferences for option characteristics, and different levels of option inclusion. Analysis of the 

frequency and timing of option implementation in the dynamic portfolios provides insight toward 

development of long-term strategies for the Basin.

Successful strategies for the Basin will need to consider near-term actions, conditions that should 

be monitored over time, and options that can be implemented contingent on future conditions. 

The results presented in this section can be analyzed to identify for which options implementation 

should begin soon, and which options may be necessary only if conditions warrant them. The 

vulnerable conditions described in this report can provide a starting point for developing a 

monitoring approach to inform future investment needs. However, some actions have sufficiently 

long implementation timelines that action will need to be taken well in advance of the shorterduration monitoring metrics. Some options are needed soon after availability only in futures 

consistent with the vulnerable conditions identified in the Study. In such cases, implementation of 

such options would hedge against the possible vulnerable conditions. Last, due to the particularly 

severe nature of some scenarios, the elimination of all vulnerabilities is not possible given the 

current range of options and the extreme nature of certain hydrologic futures. 

Evaluation of options across the range of uncertain futures and exploratory portfolios considered 

in the Study can be summarized in terms of three main outcomes: 

• The percentage of traces in which an option is implemented: The higher percentage of 

traces, the less contingent the need for the option is on future conditions. 

• The time delay between when individual options could be available and when they are 

implemented in CRSS simulations: Options with no or little time delay require planning to 

begin soon. 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-93

• The differences in implementation percentage and delay across portfolios and 

vulnerable conditions: Options with similar implementation percentage and delay across the 

portfolios represent common groups between the preferences behind the different portfolios; 

options implemented soon in vulnerable conditions represent potential hedging actions. 

CRSS implements options according to the ordering defined by the portfolio preferences and cost 

effectiveness (described in Technical Report F – Development of Options and Strategies) and in 

response to vulnerable conditions, according to defined signposts. Some options, therefore, are 

implemented by all four portfolios, whereas other options are only implemented in some of the 

portfolios. Within each portfolio, options are implemented more frequently and at different timing 

depending on the particular trace conditions. Figure G-53 shows the frequency of option 

implementation for all four portfolios by year. The black vertical line indicates the first year in 

which an option could be available. Green diamonds indicate years in which those options are 

implemented in few traces, and yellow and red diamonds indicate years in which options are 

increasingly implemented within the traces. Note that these results aggregate results across all the 

supply, demand, and management scenarios. 

Several key observations can be made from this figure: 

• Almost all of the conservation options are implemented in nearly all traces by 2060, although 

Portfolios A and C implement these options more frequently, and earlier in the Study period. 

The exception is the fifth step of M&I conservation, which is only implemented in some 

traces by 2060 in Portfolio B. 

• The only options that are always implemented the year in which they are available are those 

that are specified to begin immediately by portfolio design—e.g., M&I Conservation UB, 

which is part of the specified water bank in Portfolios A and C; Watershed-Weather Mod 

(Steps 1 and 2) for Portfolio B; and Energy Sector Conservation for Portfolio C and 

Portfolio A. 

• The Portfolios A and B, in general, implement more options than the other two portfolios in 

some traces, largely due to the greater availability of options in these portfolios to meet 

stressing traces. 

Common options can be defined as those that are frequently selected for implementation across 

the range of scenarios included in the Study. Similarly, short delay options can be described as 

those that are implemented at or near the earliest dates that they are assumed to be available. 

Common, short delay options are then those that are frequently selected for implementation and 

which are implemented soon after they are available. The implementation of these options 

suggests that feasibility may need to be investigated soon. Common, long delay options are those 

that are implemented in most traces, but only after a delay from the time in which they are 

available. A delay in feasibility assessment of these options may be warranted in these cases. 

Last, contingency options are those that are implemented in only some traces.
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Water Supply and Demand Study

G-94 December 2012

FIGURE G-53 

Percent of Traces in Which Options are Implemented over Time for Each Portfolio 

Note: Color indicates percentage of traces in which options are implemented. Vertical lines indicate year in which options are available. 

Ag=agricultural, UB=Upper Basin, LB=Lower Basin, M&I=Municipal and Industrial, Mod=Modification, Desal=Desalination, SoCal=Southern California.
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-95

To identify common, short delay options; common, long delay options; and contingency options, 

the percent of traces in which an option is implemented and the delay in option implementation 

is evaluated for each portfolio. The percent of traces in which the option is implemented is 

computed by considering all traces in all scenarios. The option implementation delay is 

computed as the median difference between the dynamic implementation timing and the year in 

which the option is assumed to be available in traces where the option is on. The implementation 

delay threshold between short and long delay options was 5 years.

Figure G-54 expands on figure G-53 for a few select options in Portfolios B and C to show the 

timing in which options are implemented at increasing frequency. Options in which this 

relationship is vertical are needed in most traces immediately and are common, short delay 

options. Options with a more sloped relationship are only required soon in some traces, and for 

other traces the options are not needed until later. These are either common, long delay or 

contingency options. For example, M&I Conservation (Step 1) is implemented in all traces 

immediately after it is available in Portfolio C. However, it is only implemented in 25 percent of 

the traces by 2018 and in 100 percent of the traces by 2060 for Portfolio B. This option is a 

common, short delay option for Portfolio C and a common, long delay option for Portfolio B. 

The Desal-Pacific Ocean-CA (Step 1) and Import-Front Range-Missouri portfolios, in contrast, 

are contingency options—they are only needed in about 15 percent and 30 percent of the traces 

evaluated, respectively.

To summarize these results for all options, table G-18 shows the percent implemented by 2060 

(color and label) and the minimum delay (across options) between availability and median 

implementation (size) for eight representative option groups. Large, red squares indicate option 

groups in which options are implemented frequently across the sequences and have a short delay 

(e.g., Ag Conservation, M&I Conservation, and Weather Mod for Portfolio B). These groups 

include common, short delay options. Smaller red squares indicate option groups in which 

options are implemented in most traces by 2060, but only after a long delay from availability. 

These groups include common, long delay options. Large green squares include options that are 

less frequently implemented and have a short delay. Small green squares include options that are 

less frequently implemented and have a long delay (e.g., Local-Coal Bed Methane). These are 

contingency options. 

Interpretation of common, short delay options is straightforward. These options were found by 

CRSS to be most effective in addressing system imbalances in most traces, and would need to be 

implemented soon to meet Basin needs. There is more ambiguity about options identified to be 

long delay or contingency options (those implemented soon after availability in a smaller 

percentage of traces). 

To better understand whether implementation of long delay or contingency options should 

proceed soon, looking to the vulnerable conditions identified earlier can provide insight. 

Identifying options that are needed soon after availability within the vulnerable conditions 

provides guidance on options to invest in to increase the system’s resilience to these conditions. 

Tables G-18 and G-19 show similar information as table G-18 but based on only those within 

Low Streamflow conditions (table G-19) and within Lowest Streamflow conditions (table G-20). 
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G-96 December 2012

FIGURE G-54 

Percentage of Traces (vertical axis) Implemented by year (horizontal axis) for Select Options with Portfolio B and Portfolio C
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-97

TABLE G-18 

Percent of Traces in Which Options are Implemented from Option Group (label and color) and the Minimum Delay (across the 

options) Between Availability and Median Implementation Delay (size) 
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G-98 December 2012

TABLE G-19 

Percentage of Traces within Low Streamflow conditions In which Options are Implemented from Option Group (label and color) 

and the Minimum Delay (across options) between Availability and Median Implementation Delay (size)

Low Streamflow conditions are those in which long-term mean natural flows are less than 15 mafy and the 8-year dry period flows 

are less than 13 mafy. 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-99

TABLE G-20

Percentage of Traces within Lowest Streamflow conditions in which Options are Implemented from Option Group (label and 

color) and the Minimum Delay (across options) between Availability and Median Implementation Delay (size) 

Lowest Streamflow conditions are those in which long-term mean natural flows are less than 14 mafy and the 8-year dry period 

flows are less than 11 mafy. 

Table G-18 shows that several more option groups include common, short delay options. For 

example, Ag Conservation with Transfers is a short delay option for all portfolios, not just 

Portfolio B. Reuse-Municipal is also implemented in most traces across all traces with short 

delays. Many option groups show more options becoming common, long delay options. 

Desal-Pacific Ocean-Mexico is now implemented in about 90 percent of traces in the Long-Term 

Reliability and Portfolio A. Watershed-Weather Mod projects also move to a long delay option, 

being implemented in between 66 and 100 percent of traces across the four portfolios. 

When considering the within Lowest Streamflow conditions, even more option groups become 

short delay (table G-20). For example, more desalination options are implemented in most traces, 

although not immediately after availability. Reuse and watershed management options are also 

implemented in most traces within this vulnerability.

Planning for short delay options across all traces should ideally begin immediately because these 

actions will be necessary to meet future challenges. If Basin planners believe that the vulnerable 
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Water Supply and Demand Study

G-100 December 2012

conditions are likely to occur, planning for the short delay options in the vulnerable conditions 

should also begin immediately. With long delay options, Basin planners can monitor signpost 

conditions and begin implementation if conditions degrade. 

6.4 Summary of System Reliability with Options and Strategies 

Several key findings emerge from the modeling and analysis discussed in this section:

• The modeling of a single static portfolio (Static Portfolio A) shows that significant system 

improvements are possible given the set of options characterized in the Study. These 

improvements led to a substantial reduction in vulnerabilities for most, but not all scenarios. 

Not all vulnerabilities could be mitigated for some extreme scenarios. 

• Four dynamic portfolios helped determine a more realistic range of action across the wide 

variety of supply/demand scenarios quantified. These results indicate that full investment in 

the Static Portfolio A is not required for many scenarios in order to effectively mitigate a 

large number of vulnerabilities. Of the traces that the system is still vulnerable with the 

implementation of portfolios, most are from the Downscaled GCM Projected supply 

scenario.

• A comparison of dynamic portfolio model simulations revealed several relationships. In 

many traces, portfolios with more available options improved system performance at higher 

costs. For some indicator metrics and traces, different portfolios were both more effective at 

reducing vulnerabilities and containing costs. The portfolio analysis also showed the 

differences in reliability and environmental characteristics of the options used to address 

vulnerabilities across the portfolios.

This section provided insight into which options are common across traces and implemented 

with only short delays after availability. Table G-21 summarizes these findings by classifying 

which representatives option have short or long delay in more than 75 percent of the traces by 

2060. These results are calculated for all traces and by vulnerable conditions. The 

implementation delay threshold between short and long delay options was 5 years. The coloring 

in the table indicates the number of portfolios that are short or long delay (Darker reds indicate 

short delay for more portfolios; darker greens indicate longer delay for more portfolios.) 

Table G-19 highlights the following key findings: 

• Options that are always short delay: M&I Conservation (for all portfolios); Ag 

conservation and Weather Mod (for Portfolio B); Energy Water Use Efficiency (for 

Portfolios A and B)—implementation of these options now, per preferences for different 

portfolios, is most consistent to the findings of this analysis. 

• Additional short delay options in Low Streamflow conditions (Long-Term Flow < 15 

mafy and Drought < 13 mafy): Desal-Salton Sea; Ag Conservation (all portfolios); Reuse 

Municipal (Portfolio C and D)—these options would need to be implemented soon in order 

to hedge against these challenging conditions. 
Technical Report G—System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-101

TABLE G-21 

Portfolios in Which Option Groups Have Short Delay and Long Delay Options Across All Traces (Left Two Columns)

Darker reds and darker greens indicate more portfolios with specified delay. 

Option Category Option Group

Common Across All 

Traces

Common Across Low 

Streamflow Conditions1 Common Across Lowest 

Streamflow Conditions2 

Short Delay Long Delay Short Delay Long Delay Short Delay Long Delay

Ag Conservation Ag Conservation with Transfers B A, C, D A, B, C, D A, B, C, D

Desalination Desal-Groundwater A, B, C, D A, B, C, D A, B, C, D

Desal-Gulf A, B

Desal-Pacific Ocean-California

Desal-Pacific Ocean-Mexico A, B A, B

Desal-Salton Sea A, B, C, D ALL A, B, C, D

Desal-Yuma A, B, C, D A, B, C, D A, B, C, D

Energy WUE Energy Water Use Efficiency A, C A, C A, C B, D

Import Import Front Range A, B

Local Supply Local-Coal Bed Methane A, B

Local-Rain A, C

M&I Conservation M&I Conservation A, B, C, D A, B, C, D A, B, C, D

Reuse Reuse-Grey Water A, C

Reuse-Industrial A, B, C, D

Reuse-Municipal A, B, C, D

Watershed 

Management

Watershed-Brush Control A, C A C A, C

Watershed-Dust Control A, C

Watershed-Weather Mod. B B B A, C, D

1 Low Streamflow conditions are those in which long-term mean natural flows are less than 15 mafy and the 8-year dry period flows are less than 13 mafy. 2 Lowest Streamflow conditions are those in which long-term mean natural flows are less than 14 mafy and the 8-year dry period flows are less than 11 mafy.
Colorado River Basin

Water Supply and Demand Study

G-102 December 2012

• Additional short delay options in Lowest Streamflow conditions (Long-Term Flow < 14 

mafy and Drought < 11 mafy): Desal-Yuma; Import-Front Range (Portfolios A and B)—

near-term implementation of these options would be required only to hedge against the more 

severe conditions.

• Key contingent options within Low Streamflow conditions (Long-Term Flow < 15 mafy 

and Drought < 13 mafy) include: Desal-Gulf of California, Desal-Pacific Ocean-California, 

Reuse-Grey Water, and Watershed-Dust Control, and Local-Coal Bed Methane—

implementation of these options can wait and be triggered in response to signposts 

anticipating these challenging conditions.

7.0 Summary

The results of the system reliability analysis without options and strategies indicate the potential 

for continued and significant stress on Basin resources. Lake Mead and Lake Powell storage was 

shown to be declining. With declining lake levels, resources such as hydropower and shoreline 

recreation are affected, while the probability of water delivery shortages is increased. Flow in 

many key tributaries decreased based on projections of reduced r reduced natural flow and 

growing demands, which had implications for flow-dependent resources such as boating 

recreation and ecological needs. These findings fully support the need to develop and evaluate 

options for balancing future supply and demand. 

Based on additional analysis of modeling results without options and strategies, it was found 

that no single combination of water supply, water demand, and operational assumptions is 

responsible for the aforementioned challenges. In fact, most combinations have the capacity 

to stress at least some Basin resources. However, more noteworthy is the relative importance 

of various vulnerability drivers depending on a particular combination of water supply, water 

demand, and operational assumptions and the time period. For the first period in the Study 

horizon (2012–2026), all scenarios follow the operational policies established by the 2007 

Interim Guidelines (DOI, 2007). At the same time, demands are not appreciably different across 

the scenarios. Therefore, the largest driver of vulnerability in the early time period is associated 

with projections of water supply. In the later two time periods, assumptions for the operation of 

Lakes Powell and Mead and demand scenarios are increasingly important with regard to 

vulnerability rates. In fact, by the third time window, some resources show roughly equal 

vulnerability caused by the water supply, water demand, and operational assumptions. The 

exception to this observation is the Downscaled GCM Projected water supply scenario. The 

increased variability and declining trend in flow in this scenario increase are substantial enough 

that vulnerability is elevated under these hydrologic conditions, regardless of the demand and 

operational assumptions. In most cases, the lowest vulnerability for scenarios with the 

Downscaled GCM Projected supply is still greater than any other supply, demand, operational 

assumption combination. 

System modeling with options and strategies demonstrated that all portfolios have capacity to 

reduce vulnerabilities across resources and in doing so, making a sizeable reduction in the 

supply-demand imbalance. In the 2012 through 2026 period, reductions in vulnerabilities tend to 

be small, owing to generally low risks early on, even in the baseline and also, in some cases, a 

lack of options available to address vulnerabilities that may occur. In the latter two time 

windows, vulnerability reductions of 50 percent or more (relative to Baseline results) are seen in 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-103

all resource categories. The one exception is the flood control indicator metric. A consequence 

of increased Basin yield and greater storage in reservoirs is a slight increase in flood control 

vulnerabilities. These events remain fairly infrequent; reaching a maximum frequency of 

5 percent of years in the later period, when the most options have been implemented. 

These reductions in vulnerability are encouraging, but vulnerabilities are never completely 

eliminated, even when every option considered is implemented as soon as it becomes available. 

Further, given the uncertainty of future conditions, it is impossible to predict the actual 

vulnerability distribution. Because of this, the percent of years or traces that are vulnerable 

does not translate to a future probability of occurrence. Rather the suite of projections of 

future conditions was used to evaluate the effectiveness of various portfolios for reducing 

vulnerabilities. The effectiveness of the portfolios is summarized for two subsets of the scenarios 

considered: by water supply scenario and by specific conditions that tend to accompany certain 

vulnerabilities. In the case of a Lee Ferry Deficit, an 8-year drought with average flow less than 

or equal to 11.2 mafy (natural flow at Lees Ferry) was one of the conditions that was found to 

accompany that particular vulnerability. When repeated for results with portfolios, the 8-year 

drought magnitude associated with a Lee Ferry Deficit was found to be as low as 10 mafy in 

some cases. This provides a quantitative assessment of portfolio performance by defining the 

change in severity of conditions that can be tolerated. 

Of the four strategies and associated portfolios considered, notable differences extend beyond 

portfolio performance. As discussed earlier, portfolios differ based on the options used to address 

supply/demand imbalances. From analysis of the characterization criteria, the portfolios 

differentiate most notably on cost, environmental effects, and long-term reliability. Portfolio cost 

is largely driven by the total potential yield considered in the portfolio, the unit cost of the 

options, and the water supply and water demand conditions for which the portfolio was 

evaluated. As such, by 2060, annual portfolio costs range from approximately $2 billion to 

$5 billion, but could increase to potentially $7 billion under the GCM Projected scenario. The 

differences in cost across portfolios result from the preference of option types versus increased 

ability to reduce vulnerabilities. Two examples of this are portfolio preferences for options with 

higher long-term reliability and preferences for lower environmental impacts. By choosing to 

only consider options that were characterized as moderate to high long-term viability, lower unit 

cost alternatives may be excluded, but the options increased the total potential yield. In contrast, 

options characterized as having lower potential environmental impacts may come at the expense 

of yield certainty. The purpose of exploring these differences is not to identify a “best” portfolio 

or strategy, but to acknowledge that there are various approaches to address the future supply and 

demand imbalance and that each has associated implications that must be considered in the 

decision making process. 

Although the portfolios explored in the Study address Basin imbalances differently, they also 

have commonalities. For example, all portfolios incorporate significant agricultural water 

conservation, M&I water conservation, energy water use efficiency, and some levels of weather 

modification because they are available relatively early in the Study horizon and address many of 

the vulnerabilities. However, some options were implemented more frequently in response to 

challenging water supply conditions. For example, ocean and brackish water desalination, 

wastewater reuse, and importation options were implemented for the most challenging water 

supply conditions in portfolios. It is also important to note that option selection and 

implementation depends upon the option characterization process and results. As a result, it 
Colorado River Basin

Water Supply and Demand Study

G-104 December 2012

is possible that of two similar options, one may be relied on often while the other is almost never 

implemented due to cost differences, permitting difficulty, technical feasibility, or other factors. 

Robust planning requires careful consideration with regard to timing, location and magnitude of 

anticipated future Basin needs in addition to the frequency with which options are implemented 

as suggested in the Study.

The Study confirms that without action, the Colorado River system will become increasingly 

challenged to sustain the communities and resources that rely on Colorado River system 

water supply. The Study demonstrates that many of the Basin imbalances and resulting 

vulnerabilities to Basin resources can be greatly improved or mitigated through option and 

portfolio implementation. However, due to the particularly severe nature of some projected 

scenarios, the elimination of all vulnerabilities was not possible given the range of options 

considered and the extreme nature of certain plausible hydrologic futures. This raises significant 

questions regarding the acceptable levels of risks to Basin resources and the appropriate tradeoffs in terms of options, costs, resources, and other implications to achieve those acceptable 

levels. Even though these questions are beyond the scope of the current effort, they will need to 

be addressed as part of the implementation of options as well as in subsequent planning efforts. 

8.0 References 

Bureau of Reclamation (Reclamation). 2004. Bureau of Reclamation, U.S. Fish and Wildlife 

Service, and The Metropolitan Water District of Southern California. Lower Colorado 

River Multi-Species Conservation Program. Volume I: Programmatic Environmental 

Impact Statement/Environmental Impact Report. Final. December 17. 

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

Impact Statement. Final. September.

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

Impact Statement. Final. April.

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. 

Dessai, S. and M. Hulme. 2007. “Assessing the Robustness of Adaptation Decisions to Climate 

Change Uncertainties: A Case Study on Water Resources Management in the East of 

England.” Global Environmental Change 17(1), 59–72. 

Groves, D. G. and R. J. Lempert. 2007). “A New Analytic Method for Finding Policy- Relevant 

Scenarios.” Global Environmental Change, 17: 73–85. 

Groves, D. G., D. Yates, C. Tebaldi. 2008. “Developing and Applying Uncertain Global Climate 

Change Projections for Regional Water Management Planning.” Water Resources 

Research, 44 (W12413). 

Lempert, R. and D. G. Groves. 2010. “Identifying and Evaluating Robust Adaptive Policy 

Responses to Climate Change for Water Management Agencies in the American West, 

Technological Forecasting and Social Change.” 77: 960–974. 

Lempert, R. J., S. W. Popper and S. C. Bankes. 2003. Shaping the Next One Hundred Years: 

New Methods for Quantitative, Long-term Policy Analysis. 
Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-105

McAda, C. 2003. Flow Recommendations to Benefit Endangered Fishes in the Colorado and 

Gunnison Rivers. 

Ouarda, T., J.W. Labadie, and D.G. Fontane.1997. “Index sequential hydrologic modeling for 

hydropower capacity estimation.” Journal of the American Water Resources Association, 

33(6), 1337–1349. 

Prairie, J., Nowak, K., Rajagopalan, B., Lall, U., Fulp, T. 2008. “A Stochastic Nonparametric 

Approach for Streamflow Generation Combining Observational and Paleoreconstructed 

Data.” Water Resources Research Volume 44, W06423, DOI: 10.1029/2007WR006684. 

U.S. Department of the Interior (DOI), 2007. Record of Decision for Colorado River Interim 

Guidelines for Lower Basin Shortages and Coordinated Operations of Lakes Powell and 

Mead.

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. Department of the Interior, U.S. Fish and Wildlife 

Service, Upper Colorado River Endangered Fish Recovery Program. 

Zagona, E., T. Fulp, R. Shane, T. Magee, and H. Goranflo. 2001. “RiverWareTM: A Generalized 

Tool for Complex Reservoir Systems Modeling.” Journal of the American Water 

Resources Association. 37(4):913–929. 

Technical Report G — System Reliability Analysis

and Evaluation of Options and Strategies

December 2012 G-107

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 G1

Modeling Sub-Team Members

December 2012 G1-1

Appendix G1 — Modeling Sub-Team 

Members

The information presented in Technical Report G – System Reliability Analysis and 

Evaluation of Options and Strategies is the outcome of a collaborative process involving 

representatives of numerous organizations. 

A list of Modeling Sub-Team members and their affiliations is presented below. 

• Don Gross, Arizona Department of Water Resources

• Alan Butler, Bureau of Reclamation

• Carly Jerla, Bureau of Reclamation

• Ken Nowak, Bureau of Reclamation

• James Prairie, Bureau of Reclamation

• Dave Trueman, Bureau of Reclamation

• Chuck Cullom, Central Arizona Project

• Mohammed Mahmoud, Central Arizona Project

• Greg Gates, CH2M HILL

• Armin Munévar, CH2M HILL

• Jennifer Pitt, Environmental Defense Fund

• Evan Bloom, RAND Corporation

• Jordan Fischbach, RAND Corporation

• David Groves, RAND Corporation

• Kay Brothers, Southern Nevada Water Authority

• Tom Maher, Southern Nevada Water Authority

• Colby Pellegrino, Southern Nevada Water Authority

• Chuck Lawler, Ten Tribes Partnership

• Bill Hasencamp, The Metropolitan Water District of Southern California

• Karen Murphy, The Metropolitan Water District of Southern California

• Kevin Wheeler, Water Balance Consulting

• Erin Wilson, Wilson Water Group
Appendix G2

CRSS Modeling Assumptions 

December 2012 G2-1 

Appendix G2 — CRSS Modeling

Assumptions

1.0 Background 

The Colorado River Simulation System (CRSS), the Bureau of Reclamation’s (Reclamation)

long-term planning model that covers the entire Colorado River Basin (Basin), is the primary 

model used in the Colorado River Basin Water Demand and Supply Study (Study) to simulate 

future conditions. The model framework used for this process is a commercial river modeling 

software called RiverWareTM (Zagona et al., 2001); a generalized river basin modeling software 

package developed by the University of Colorado through a cooperative arrangement with 

Reclamation and the Tennessee Valley Authority. CRSS was originally developed by 

Reclamation in the early 1970s and was implemented in RiverWareTM in 1996. 

CRSS simulates the operation of the major reservoirs on the Colorado River and provides 

information regarding the projected future state of the system on a monthly basis in terms of 

output variables including the amount of water in storage, reservoir elevations, releases from the 

dams, the amount of water flowing at various points throughout the system, and the diversions to 

and return flows from the water users throughout the system. The basis of the simulation is a 

mass balance (or water budget) calculation that accounts for water entering the system, water 

leaving the system (e.g., from consumptive use of water, trans-basin diversions, evaporation), 

and water moving through the system (i.e., either stored in reservoirs or flowing in river 

reaches). The model was used to project the future conditions of the Colorado River system on a 

monthly time-step for the period 2012 through 2060. 

The input data for the model includes monthly natural inflows, various physical process 

parameters such as the evaporation rates for each reservoir, initial reservoir conditions on 

January 1, 2012, and the future diversion and depletion schedules for entities in the Basin States 

and for the United Mexican States (Mexico). These future schedules were based on the six 

demand scenario quantified in the Study (Technical Report C – Water Demand Assessment). 

The rules of operation of the Colorado River mainstream reservoirs including Lake Powell and 

Lake Mead are also provided as input to the model. This set of operating rules describes how 

water is released and delivered under various hydrologic conditions and aim to reflect actual 

operations. Rules that guide the portfolio implementation are also input to the model and reflect a 

“dynamic” implementation that triggers options to be implemented only when needed as 

determined by the occurrence of a set of pre-defined vulnerability signposts. These signposts 

consist of combinations of certain Lees Ferry natural flow conditions and Lakes Powell and 

Mead reservoir elevations that are correlated to the occurrence undesirable conditions (e.g. Lake 

Mead less than 1,000 feet above mean sea level [msl]) or vulnerabilities.

The future hydrology used as input to the model consisted of sequences that comprise the 

Study’s four water supply scenarios (Technical Report B – Water Supply Assessment). Each 

sequence (a total of 1,959 when combining all four water supply scenarios) is input as natural 

flow at 29 individual inflow points (or nodes) on the system. The locations of the hydrologic 
Colorado River Basin

Water Supply and Demand Study

G2-2 December 2012

input sites are shown and the methodologies used to generate future inflow sequences are 

discussed in Technical Report B – Water Supply Assessment. 

The following sections describe the CRSS modeling assumptions and configuration associated 

with the modeling of the system reliability without options and strategies (Baseline system 

reliability) and those for the modeling of the system reliability with options and strategies.

2.0 System Reliability without Options and Strategies 

(Baseline) Modeling Assumptions

For the modeling of the Baseline system reliability, the state of the system was simulated from 

2012–2060 with all combinations of the supply and demand scenarios. The four supply 

scenarios are Observed Resampled, Paleo Resampled, Paleo Conditioned, and Downscaled GCM 

(General Circulation Model) Projected. See Technical Report B – Water Supply Assessment for 

further descriptions of the supply scenarios. The six demand scenarios are Current Projected 

(A), Slow Growth (B), Rapid Growth (C1 and C2), and Enhanced Environment (D1 and D2). 

Additional details are available in Technical Report C – Water Demand Assessment. 

Additionally, two assumptions regarding Lakes Powell and Mead operations after the expiration 

of the Record of Decision for Colorado River Interim Guidelines for Lower Basin Shortages and 

Coordinated Operations of Lake Powell and Lake Mead (2007 Interim Guidelines 

[U.S. Department of the Interior (DOI), 2007]) in 2026 were considered and are described more 

in the reservoir operations section below. The combination of all water supply and demand 

scenarios and two operational assumptions for Lakes Powell and Mead result in 48 Baseline 

simulations, each with multiple future sequences that reflect water supply uncertainty. For 

combinations in which a demand scenario is coupled with the downscaled GCM projected

hydrology, agriculture, outdoor municipal and industrial (M&I), and phreatophyte demands, 

along with reservoir evaporation are adjusted to reflect increased water needs under a warmer 

climate, see Technical Report C for additional details. The following sections detail the 

assumptions and model configuration for the Baseline simulations.

2.1 Initial Conditions

The model was initialized with observed 2011 end-of-calendar-year (EOCY) reservoir conditions 

shown in table G2-1. 

2.2 Reservoir Operations

2.2.1 Upper Basin Reservoirs above Lake Powell

The Taylor Park, Fontenelle, and Starvation reservoirs are operated in accordance with their 

existing rule curves (Reclamation, 2007), although Fontenelle’s operating rules in CRSS have 

been updated since the 2007 Interim Guidelines (DOI, 2007). The Aspinall Unit operations do 

not reflect the Record of Decision (ROD) for the Aspinall Unit Operations Final Environmental 

Impact Statement (FEIS) (Reclamation, 2012) because the modeling in the Study began before 

the signing of the ROD. Instead, Aspinall Unit operations are also operated in accordance with 

their previous rule curves (Colorado River Interim Guidelines for Lower Basin Shortages and 

Coordinated Operations of Lake Powell and Lake Mead Final Environmental Impact Statement

[Reclamation, 2007]). 
Appendix G2 — CRSS Modeling Assumptions

December 2012 G2-3 

TABLE G2-1 

2011 End-of-Calendar-Year Reservoir Storage Conditions used as Initial Conditions

Reservoir

Elevation 

(feet msl) Storage (af)

Fontenelle 6,486.86 207,381

Flaming Gorge 6,031.41 3,403,746

Starvation 5,734.92 255,000

Taylor Park 9,307.93 66,655

Blue Mesa 7,489.07 574,132

Morrow Point 7,154.97 112,986

Crystal 6,750.95 6,359

Navajo 6,057.10 1,311,371

Powell 3,639.74 15,972,410

Mead 1,132.83 14,883,261

Mohave 638.82 1,585,878

Havasu 445.69 537,515

CRSS was modified to reflect the Navajo and Flaming Gorge RODs (Reclamation, 2006a and

2006b, respectively). In general, both RODs contain downstream flow targets that the reservoirs 

must attempt to meet according to the rules within the RODs. In summary, Flaming Gorge 

operations are governed by the April through July unregulated inflow into the reservoir, which 

determines which downstream flow targets should be met—e.g., in a wet year (larger inflow into 

the reservoir), higher downstream flows are targeted. The flow targets are specified at the submonthly time step, which historically could not be reflected within CRSS. In order to capture the 

sub-monthly component of the flow targets, and thus Flaming Gorge’s operations, the model was 

programmed to determine typical daily operations before summing to a monthly release (Butler, 

2011). 

Similarly, Navajo’s ROD contains multiple downstream flow targets, specified at sub-monthly 

time intervals. In this case, a September 30th storage target guides Navajo’s operations. A 

release pattern is selected to bring Navajo closest to the September 30th storage target while 

helping meet the downstream flow targets stated in the ROD (Butler, 2011). 

2.2.2 Lake Powell and Lake Mead

For 2012 through 2026, Lake Powell and Lake Mead are operated according to the 2007 Interim 

Guidelines. For modeling purposes, after the expiration of the 2007 Interim Guidelines in 2026, 

two operational assumptions, a. and b. below, were considered.

1) the Shortage, Surplus, and Coordinated Operations provisions of the 2007 Interim 

Guidelines are extended
Colorado River Basin

Water Supply and Demand Study

G2-4 December 2012

a. The Equalization Line at Powell from 2027 through 2060 is determined by 

assuming the slope of the Equalization Line from 2012 through 2026 extends 

through 2060. 

2) the operating rules revert to the rules of the 2007 Interim Guidelines Final EIS No Action 

Alternative. The No Action Alternative assumes the following for Shortage, Surplus and 

Coordinated Operations. There is no Intentionally Created Surplus (ICS) assumed in the 

No Action Alternative.

a. Shortage: Stage 1 Shortage is triggered to prevent Mead from declining below 

1,050 feet msl. Stage 1 Shortages range in volume from approximately 350 to 

500 kaf. If Lake Mead’s elevation continues to decline, a Stage 2 Shortage is 

imposed to keep Mead above 1,000 feet msl. Stage 2 Shortages can be up to 

3.0 maf.

b. Surplus: Surplus determinations are per Flood Control Surplus conditions or the 

70R Strategy1. 

c. Coordinated Operations: Three factors affecting Lake Powell’s release are: 1) the 

minimum objective release of 8.23 maf, 2) equalization; and 3) spill avoidance. 

For equalization to occur the 602(a) storage requirement must be met. 

In both cases, Lake Mead flood control procedures are in effect. Also, if Lake Mead elevation 

falls below 1,000 feet msl, deliveries to the Southern Nevada Water Authority (SNWA) are 

assumed to continue. 

If Lake Mead is sufficiently low such that after the maximum shortage (per the 2007 Interim 

Guidelines or No Action Alternative post 2026) is applied water is still unavailable to meet the 

remaining deliveries, the remaining deliveries were shorted hydrologically with respect to their 

physical location on the river. 

2.2.3 Lake Mohave and Lake Havasu

Lake Mohave and Lake Havasu are operated in accordance with their existing rule curves.

2.3 Intentionally Created Surplus

Intentionally Created Surplus (ICS) may be created through various mechanisms, including 

extraordinary conservation, tributary conservation, system efficiency projects, and importation of 

non-Colorado River water. The 2007 Interim Guidelines detail the different types of ICS and the 

rules that govern the creation, storage, and use of ICS credits. In addition to contractor-specific 

creation, several Lower Basin projects have been completed since 2007. In 2010, the Warren H. 

Brock Reservoir became operational. Based on the funding agreement, the Metropolitan Water 

District of Southern California (MWD) and the Central Arizona Project (CAP) were credited 

with 100 kaf, and SNWA with 400 kaf of system efficiency ICS (referred to as Brock ICS to 

 

1 Under the 70R Strategy, a surplus condition is based on the system space requirement at the beginning of each year. Based on the 70th 

percentile historical runoff, a normal 7.5 maf delivery to the Lower Division states, the Upper Basin scheduled use, and Lake Powell and Lake 

Mead volumes at the beginning of the year, the volume of water in excess of the system space requirement at the end of the year is estimated. If 

that volume is greater than zero, a Surplus is declared. See appendix A of the 2007 Interim Guidelines Final EIS (Reclamation, 2007) for the 

full 70R computation.
Appendix G2 — CRSS Modeling Assumptions

December 2012 G2-5 

distinguish from other system efficiency ICS). Additionally, the same three agencies funded an 

18-month pilot-run of the Yuma Desalting Plant (YDP). Based on the pilot run, MWD, CAP, 

and SNWA were credited with 24,397 af; 3,050 af; and 3,050 af of system efficiency ICS 

(referred to as YDP ICS), respectively. Under the 2007 Interim Guidelines, ICS cannot be 

created after 2026 and must be used by 2036. Under the modeling assumption that the 2007 

Interim Guidelines expire in 2026, ICS is subject to these constraints. However, under the 

assumption that the 2007 Interim Guidelines are extended through 2060, it is assumed that ICS 

activity is also extended through 2060. The remaining sections detail the state-specific modeling 

assumptions for creation and delivery of ICS. 

2.3.1 Arizona

Arizona has an initial credit of 100 kaf from Brock and 3,050 af from the YDP pilot project. In 

CRSS, it is assumed that starting in 2018, the CAP will take delivery of 10 kaf per year (kafy) of 

the Brock ICS credits in any non-shortage year (Lake Mead > 1,075 feet msl) as defined by the 

2007 Interim Guidelines until the credits have been exhausted or the ICS mechanism expires. 

Additionally, Arizona will use its 3,050 af of YDP credits in the first normal year (Lake Mead > 

1,075 feet msl and < 1,145 feet msl) after 2017. 

2.3.2 California

California has an initial credit of 66 kaf from Brock, 24,396 af from YDP, and 344,439 af from 

extraordinary conservation (EC), which are the December 31, 2011 balances. It is assumed that 

all deliveries of California’s ICS credits are made to MWD and that any creation of ICS credits 

through extraordinary conservation is also made by MWD. Because ICS expires at different 

times depending on the post-2026 operations assumption, the logic for creation and delivery of 

ICS differs depending on which policy is in effect. 

When it is assumed that the 2007 Interim Guidelines expire in 2026 and operations revert to the 

FEIS No Action Alternative, ICS must be completely recovered by 2036. Under this operating 

assumption, the 66 kaf of Brock ICS is recovered at a rate of 20 kafy, beginning in 2026, except 

during Shortage and Surplus conditions, or when EC-ICS is created. Once all Brock ICS credits 

are exhausted, the YDP ICS credits are used to bring the total ICS delivery between Brock and 

YDP to 20 kafy until all YDP credits are also exhausted. Again, the YDP credits are not 

delivered during Shortage and Surplus conditions or when EC-ICS is created. When the 2007 

Interim Guidelines are assumed to extend through 2060, the Brock and YDP ICS is recovered 

using the same logic, although the initial recovery does not begin until 2041. 

The creation and delivery of EC-ICS again depends on the post-2026 operations assumption and 

also varies with the natural flow conditions at Lees Ferry. EC can be created in Surplus and 

Shortage conditions and is assumed to not be delivered during Shortage conditions. The 

provided demand schedules (see Technical Report C) include an assumed creation of 200 kaf of 

EC-ICS, which is reflected in the model by increasing the initial balance to 544,439 kaf (the 

2011 end-of-calendar-year balance plus the assumed creation minus the system assessment). 

Additionally, it is assumed that another 200 kaf of EC-ICS is created in 2013. For the period 

2014 through 2060, the creation and delivery amounts vary with post-2026 operations and the 

annual Lees Ferry natural flow. The annual natural flow at Lees Ferry is compared with the 

1906 through 2008 observed natural flow to determine the quantity of EC-ICS (table G2-2). The 

maximum amount of EC-ICS that can be stored in Lake Mead is 1.5 million acre-feet (maf), so 
Colorado River Basin

Water Supply and Demand Study

G2-6 December 2012

any creation amount is constrained to not exceed the maximum storage constraint. When the 

2007 Interim Guidelines are assumed to expire in 2026, the delivery amounts no longer depend 

on the natural flow conditions. Beginning in 2031, ICS is delivered in any surplus year that 

delivery to MWD is less than 1.25 maf. In normal years the EC-ICS delivery is computed as the 

end of the previous year’s ICS balance divided by the number of years before 2037. This 

amount in constrained to be no larger than the remaining balance nor more than the remaining 

Colorado River Aqueduct capacity. For example, if the 2030 balance is 1.5 maf, then the 2031 

delivery is 250 kaf in Normal conditions. 

TABLE G2-2 

California Extraordinary Conservation ICS Creation and Delivery Amounts

2007 Interim Guidelines 

Expire in 2026

2007 Interim Guidelines Extend through 

2060

Lees Ferry Natural 

Flow Percentile

Creation 

(kaf) 2014–

2026

Delivery (kaf) 

2014–20301 

Creation (kaf) Delivery (kaf)

2014–

2040

2041–

2060

2014–

2040

2041–

2060

>= 80th 200 0 200 150 0 0 

< 80th and >= 60th 200 0 200 75 0 0 

< 60th and >= 40th 75 0 75 0 0 100

< 40th and >= 20th 0 0 0 0 0 250

< 20th 0 150 0 0 150 250

1 ICS deliveries can continue through 2036. For the period 2031–2036, the EC-ICS delivery is computed as the end 

of the previous year’s ICS balance divided by the number of years left before 2037.

2.3.3 Nevada

In the state of Nevada, SNWA accounts for all ICS activity. The 2011 end-of-year balances for 

Brock and YDP ICS are 400,000 and 3,050 af, respectively. SNWA also had a non-zero 2011 

end-of-year balance for EC-ICS; however, for the purposes of modeling, these credits were not 

considered. In addition to EC, YDP and Brock ICS, SNWA takes advantage of tributary 

conservation and imported ICS and has access to 1.25 maf of stored water in an Arizona 

groundwater bank. It is assumed that SNWA has access to 30 kaf of tributary conservation ICS 

in 2012 through 2015 and 15 kaf in 2015 through 2060 with access to an additional 9 kafy of 

imported ICS. This section describes the modeled logic for utilizing these multiple resources. 

Based on the quantification of demands (Technical Report C), SNWA has demands above 

Nevada’s basic apportionment of 300 kaf that increase through time. The logic presented here 

focuses on using ICS credits to help offset the demands above apportionment. The system 

conditions, i.e., Normal, Surplus, or Shortage, and the differing constraints on the different types 

of ICS, necessitate logic that differs with system condition.

The logic describes how all sources would be utilized in priority order; however, if at any stage 

there is no more remaining demand above apportionment, then the remaining sources are not 

used. In Normal conditions, SNWA starts by utilizing the tributary conservation and imported 
Appendix G2 — CRSS Modeling Assumptions

December 2012 G2-7 

ICS2. If there is more tributary and imported ICS than demand above apportionment, then the 

remaining ICS credits are converted to EC-ICS and are stored in Lake Mead; if the 2007 Interim 

Guidelines are assumed to expire in 2026, then the remaining credits cannot be stored after 2026. 

The next source utilized is stored EC-ICS credits in Lake Mead. The withdrawals from EC-ICS

can occur 10 years after the 2007 Interim Guidelines expire and cannot exceed 300 kaf in any 

one year. Next, Brock ICS will be recovered at a rate of up to 40 kafy until the 400 kaf are fully 

recovered, or 10 years after the 2007 Interim Guidelines expire, whichever occurs first. Finally, 

the Arizona groundwater credits are recovered at a rate of up to 40 kafy until fully utilized. 

During a Domestic and Quantified Surplus, the Normal conditions logic is applied, although 

before doing so, the surplus deliveries are applied to the demand above apportionment. During 

Flood Control Surplus, no ICS deliveries are made and any EC-ICS credits stored in Lake Mead 

are lost. The flood control delivery to SNWA contains an additional 30 kaf of water that is 

assumed to be deposited into a groundwater bank. The use of this water is not modeled; 

however, the total deposits are recorded. 

During Shortage Conditions, the tributary conservation and imported ICS are recovered up to 

their respective maximum values. Because EC and Brock ICS cannot be recovered during 

shortage years, the Arizona groundwater bank is the next source available; it is recovered up to 

40 kafy. 

2.4 Other Key Assumptions

2.4.1 Upper Colorado River Water Rights

Historically, CRSS has not modeled water rights in the Upper Basin. Deliveries were made to all 

users if there is water in the reach, regardless of whether there was a downstream user with a 

more senior water right. Although this can affect the modeled deliveries and shortages to various 

users, it also can skew modeled streamflow. During the Study, an effort was made to improve 

the Upper Colorado River reach upstream of the confluence with the Gunnison River by 

incorporating two senior water rights on the Upper Colorado main stem. The reach above the 

confluence with the Gunnison River is largely governed by two senior rights: the senior right of 

the Shoshone Power Plant and the senior users from the Grand Valley Irrigation Company. 

CRSS was modified to ensure that Shoshone Power Plant had access to 1,250 cubic feet per 

second by shorting users above Shoshone. Then, all users above the Grand Valley Irrigation 

Company, except for Shoshone Power Plant, are shorted to ensure that the senior users’ demands 

are fully met before meeting any other demands. The existing demand node that represented the 

Grand Valley Irrigation Company included senior and junior user demands. It was assumed that 

half of the existing demands were senior demands, which total 106.5 kafy of consumptive 

demand under the Current Projected (A) demand scenario. Incorporating the simple priority 

deliveries into CRSS more accurately reflects shortages to Upper Colorado main stem users 

while improving the modeled flows at the Colorado River near Glenwood Springs and Cameo 

gages.

 

2 Tributary conservation and imported ICS are described together throughout the document; however, in practice and in CRSS, tributary ICS is 

used before imported ICS.
Colorado River Basin

Water Supply and Demand Study

G2-8 December 2012

2.4.2 Lee Ferry Deficit

Logic has been implemented such that when the monthly, 10-year moving aggregate flow 

volume at Lee Ferry falls below 75 maf, water is injected into the system just above Lake 

Powell, and then released from Lake Powell during the same month. The magnitude of the 

injection and subsequent release is computed to bring the 10-year total volume at Lee Ferry to 75 

maf. The injected water is reported as Lee Ferry deficit3 throughout the Study. When water is 

assumed to be supplied to the system in this manner, the uncertainty regarding metric results

increases, particularly in the Upper Basin. However, due to the infrequent occurrence of a Lee 

Ferry deficit across all traces, these results are not disregarded. This uncertainty, however, 

should be considered carefully when viewing metric results, particularly in the Upper Basin, that 

have been impacted by this modeling assumption. 

2.4.3 Deliveries to Mexico

For modeling purposes, future water deliveries to Mexico are made as follows: 

1. The model accounts for the entire delivery to Mexico at the Northerly International 

Boundary (NIB). 

2. Water deliveries to Mexico are pursuant to the provisions of the 1944 Treaty. This 

provides annual deliveries of 1.5 maf to Mexico and up to 1.7 maf during Lake Mead 

flood control release conditions. 

3. For modeling purposes it is assumed that during Shortage Conditions, Mexico shares 

shortage in proportion to U.S. users in the Lower Basin (16.67 percent). This assumption 

is consistent with that used in the modeling supporting 2007 Interim Guidelines Final EIS 

(Reclamation, 2007)4. 

4. Neither Minute No. 318 (through 2013) nor Minute No. 319 (through 2017) were 

modeled in the Study due to their limited duration. 

2.4.4 Warren H. Brock Reservoir

Brock reservoir is assumed to operate every year beginning in 2012 and is assumed to conserve 

approximately 90 percent of non-storable flows. This reduces the average annual volume of nonstorable flows delivered to Mexico from 73 kafy (historical average from 1964 through 2010, 

excluding flood years on the Gila or flood control releases) to 7 kafy. 

2.4.5 Welton-Mohawk Return Flows

Bypass of return flows from the Welton-Mohawk Irrigation and Drainage District to the Cienega 

de Santa Clara in Mexico is assumed to be 109 kafy (historical average from 1990 through 2010) 

and is not counted as part of the 1944 Treaty delivery to Mexico. 

 

3 Article III(d) of the Colorado River Compact stipulates that the Upper Division States will not cause the flow of the river at the Lee Ferry 

Compact Point to be depleted below an aggregate of 75 maf for any period of 10 consecutive years. For the purpose of the Study, a Lee Ferry 

deficit is defined as the difference between 75 maf and the 10-year total flow arriving at Lee Ferry.

4 Allocation of Colorado River water to Mexico is governed by the 1944 Treaty. Reclamation’s modeling assumptions are not intended to 

constitute an interpretation or application of the 1944 Treaty or to represent current United States policy or a determination of future United 

States policy regarding deliveries to Mexico.
Appendix G2 — CRSS Modeling Assumptions

December 2012 G2-9 

2.4.6 Yuma Desalting Plant

The YDP is not assumed to operate during the Study period. 

2.5 Control Run

The control run helps understand current variability of the system and model bias, which informs 

the development of several indicator metrics (see appendix G3). Demands were held constant 

for the entire modeling horizon at the 2015, current projected levels for the control run, and the 

equalization line is held constant at the 2015 level. The conditions were simulated for the 

49-year period using the Observed Resampled supply scenario. 

3.0 System Reliability with Options and Strategies 

Modeling Assumptions

3.1 Modeling Representative Options

Each characterized option (see Technical Report F – Development of Options and Strategies) 

that was contained within one of the portfolios was implemented in CRSS. The following 

sections describe how each representative option was implemented in CRSS and any 

assumptions that were made in the implementation. In some instances, multiple representative 

options are modeled identically, with only magnitudes varying—this is noted where applicable. 

When options introduce new water into the system, e.g., desalination projects, assumptions were 

necessary to determine how this water would be used. For example, in the Lower Basin the 

water could be used to benefit the system, i.e., improve reservoir elevations and help meet 

demands within basic apportionment. Conversely, the new water could be used to meet the 

demand above the Lower Division States’ basic apportionments. Ultimately, a hybrid approach 

was used. In the hybrid approach, new water goes towards meeting the demands above the 

Lower Division States’ basic apportionments and offsetting shortages when Lake Mead elevation 

is greater than 1,050 feet above msl. Once Lake Mead elevations drop below 1,050 feet above 

msl, the water is assumed to go to the system until the next time Lake Mead is at or above 

elevation 1,050 feet above msl. The determination of whether the new water goes towards 

meeting demands above the Lower Division States’ basic apportionments or to the system is an 

annual decision made in January based on the end of the previous year’s Lake Mead elevation. 

Appendix G3 includes a sensitivity analysis which tested several elevations for determining 

whether the options’ yield goes towards the system or demands above the Lower Division States’ 

basic apportionment. Each option in which this approach is used is noted in the following 

sections.

3.1.1 Importations to the Front Range

Importations to the Front Range are modeled as a reduction in diversions by Front Range exports 

and the San Juan Chama Project (SJCP) export. The total project amount is split between the 

Front Range exports and the SJCP by computing the amount going to SJCP and assuming the 

remainder goes to the Front Range. SJCP’s portion of the project is computed as the minimum 

of one-quarter of the total amount and the current year’s SJCP demand. The reduction in the 

SJCP goes to demands above apportionment, in New Mexico, when they exist; otherwise, the 

reduction in SJCP’s diversion becomes system water. 
Colorado River Basin

Water Supply and Demand Study

G2-10 December 2012

3.1.2 Southern California Desalination Options

Both the Pacific Ocean desalination and the Southern California groundwater desalination 

options are modeled as reductions in deliveries to MWD. For these options, it was assumed that 

MWD would reduce its diversions from the Colorado River to a minimum diversion of 450 kafy 

so that others could benefit from Southern California desalination options via an exchange with 

Colorado River water. The Pacific Ocean and the Southern California groundwater desalination 

options help meet the demands above the Lower Division States’ basic apportionments when 

Lake Mead is greater than 1,050 feet msl; otherwise they go towards a system benefit. 

3.1.3 Gulf of California Ocean Desalination

The Gulf of California (Gulf) ocean desalination option is modeled as an injection of water into 

the system above Imperial Dam. The injected water was assumed to have a salinity 

concentration of 750 milligrams per liter (mg/L). The Gulf of California ocean desalination 

helps meet the demands above the Lower Division States’ basic apportionments when Lake 

Mead is greater than 1,050 feet msl; otherwise it goes towards a system benefit.

3.1.4 Yuma Brackish Water Desalination

The Yuma brackish water desalination option is modeled as an injection of water into the system 

below Imperial Dam. The Yuma brackish water desalination helps meet the demands above the 

Lower Division States’ basic apportionments when Lake Mead is greater than 1,050 feet msl; 

otherwise it goes towards a system benefit.

3.1.5 Coal Bed Methane-produced Water

Although coal bed methane-produced water would be distributed over large areas in reality, it is 

modeled as a point injection at four locations in the Upper Basin. Table G2-3 lists the locations 

and the percent of the total project water that is injected at each location. The percentages were 

computed using the characterization of this option found in Appendix F6. All injections are 

assumed to have a salinity concentration of 250 mg/L and the injected water becomes system 

water.

TABLE G2-3 

Coal Bed Methane-Produced Water Injection Locations

Injection Location in CRSS Percent of Total

San Juan River Below Navajo Reservoir 57

White River above Watson, Utah 2.7

Green River above Green River, Utah 28

Green River at Green River, Wyoming 12.3

3.1.6 Tamarisk Control

Tamarisk control in the Upper Basin is modeled as an injection of water just above Lake Powell. 

For modeling purposes, the injected water is assumed to have a salinity concentration of 0 mg/L 

and is considered system water.
Appendix G2 — CRSS Modeling Assumptions

December 2012 G2-11

Tamarisk control on the Lower Colorado River mainstem is modeled as a reduction in demand of 

existing phreatophyte nodes. The assumed savings from tamarisk control are proportionally 

distributed to the three demand objects. 

3.1.7 Conversion of Power Plants to Air Cooling

The characterization of the conversion of power plants to air cooling estimated 160 kaf of yield 

potential (appendix F10). This option is modeled as an 89.5-percent reduction in demand of 

several Upper Basin energy users. The percentage reduction was computed to yield a savings of 

approximately 160 kaf in 2015, although this same percentage is applied for every year the 

option is used. 

3.1.8 M&I Conservation

M&I conservation is modeled as a proportional reduction in the consumptive demand of M&I 

users Basin-wide. This proportional application results in roughly 25 percent of each phase of 

conservation being applied to Upper Basin M&I users while the remaining 75 percent is applied 

to Lower Basin M&I users. Appendix F8 describes how the conservation amounts were 

quantified, including how and why they vary amongst demand scenarios. In the appendix, three 

levels of conservation are identified. For modeling purposes, these levels were further split into 

five phases, so that the effects of conservation could be more widely distributed through time and 

so the phases equate to roughly 200-kaf steps for consistency with other projects. Table G2-4 

lists the five phases of M&I conservation by demand scenario. In the Lower Basin, it was 

assumed that M&I conservation be used to first meet demand above the Lower Division States’ 

basic apportionment. 

TABLE G2-4 

M&I Conservation Quantities and Timing by Modeling Phase 

Conservation 

Level

Modeling 

Phase

Year 

Available

Conservation Magnitudes (kaf)

Current 

Projected 

(A)

Slow 

Growth 

(B)

Rapid 

Growth 

(C1)

Rapid 

Growth 

(C2)

Enhanced 

Environment 

(D1)

Enhanced 

Environment 

(D2)

1 1 2016 200 200 200 50 50 50

2 2 2021 200 150 250 200 100 150

3 2031 200 150 250 200 100 150

3 4 2041 200 200 275 250 200 275

5 2051 200 200 275 250 200 275

Total Conservation 1,000 900 1,250 950 650 900

3.1.9 M&I Reuse Options

Municipal Wastewater Reuse

Municipal wastewater reuse is modeled as a reduction in diversion of the M&I exports in 

California, Arizona, New Mexico, Colorado, Wyoming, and Utah. The municipal wastewater 

reuse consists of both non-potable and indirect potable reuse (see appendix F5 for more 
Colorado River Basin

Water Supply and Demand Study

G2-12 December 2012

information). Table G2-5 lists the reuse amounts by state and 200-kaf phase (fifth phase is only 

132 kaf). Phase 1 is solely composed of non-potable reuse, and phases 3 through 5 are only 

indirect potable reuse. Phase 2 consists of the remaining available yield of non-potable reuse and 

enough indirect potable reuse in California and Arizona to bring the entire phase to 200 kaf. 

In the Lower Basin, it was assumed that municipal reuse be used to first meet demand above the 

Lower Division States’ basic apportionment. When reuse is combined with the M&I 

conservation option in portfolios the following assumption is made: if enough conservation takes 

place, then M&I reuse can indeed reduce the diversions from the Colorado River. Municipal 

reuse in California is modeled by reducing MWD’s diversion from the Colorado River; MWD 

cannot reduce its Colorado River diversion below 450 kafy, which constrains the benefit to 

California. When MWD’s diversion cannot be reduced further, the municipal wastewater reuse 

option is still implemented in the other states because it is applied to all states at once.

TABLE G2-5 

Municipal Wastewater Reuse by State 

Phase

Amount of Reuse (af)

California Arizona Colorado Utah

New 

Mexico Wyoming

1 109,200 45,500 27,600 11,100 5,500 1,100

2 115,300 48,000 22,400 8,900 4,500 900

3 141,000 59,000 0 0 0 0 

4 141,000 59,000 0 0 0 0 

5 93,500 38,500 0 0 0 0 

Industrial Wastewater Reuse

Industrial wastewater reuse is modeled as a reduction in M&I demand for users with self-served 

industrial (SSI) demand in Colorado, Arizona, California, and Nevada. In Arizona, industrial 

demands exist in both the Central Arizona and the Mainstem planning areas. Rather than 

distributing a small savings to every M&I user in the Mainstem planning area, it was assumed 

that the reduction in demand occurred at the City of Yuma demand node. The total estimated 

demand reductions from industrial wastewater reuse were distributed between Colorado, 

Arizona, California, and Nevada as 26, 56, 15, and 3 percent of the total savings, respectively. 

The percentages were computed from the average SSI demand in each state among all demand 

scenarios. Within each state, the reduction in demand is proportionally distributed to all SSI 

users. 

3.1.10 Grey Water Recycling

Grey water recycling is modeled by reducing M&I demands for the same users as municipal 

wastewater reuse. The total quantified yield from grey water recycling is proportionally 

distributed to the identified M&I exports. 
Appendix G2 — CRSS Modeling Assumptions

December 2012 G2-13

3.2 Agricultural Conservation

Agricultural conservation is modeled as a proportional reduction in agricultural demands Basinwide. This proportional application results in roughly 40 percent of each phase of conservation 

being applied to Upper Basin agricultural users while the remaining 60 percent is applied to 

Lower Basin agricultural users. Five phases of agricultural conservation exist, with savings of 

200 kaf at each phase. Phase 1 is available in 2016, phase 2 in 2021, and phases 3 through in 

2026. 

3.3 Watershed Management

The dust control and weather modification options were modeled as percent increases in April 

through July natural flow at applicable natural flow nodes. Only April through July were 

selected because both programs focus on increasing runoff from snow pack. These options are 

modeled as percent increases instead of static values to help capture some of the uncertainty in 

these programs in the model. Additionally, weather modification will likely result in higher 

yields in years that already have above average snow pack; modeling the additional water as a 

percentage helps capture this characteristic as well. The percent increases were computed to 

result in the assumed yield from the options characterization when applied to the 1908–2008 

average April through July natural flow at the applicable natural flow nodes. Table G2-6 lists 

the assumed percent increases for each phase of weather modification and dust mitigation. 

Weather modification percent increases are applied to the following natural flow nodes: 

Colorado at Glenwood Springs, Colorado; Colorado at Cameo, Colorado; Taylor above Taylor 

Park, Colorado; Gunnison at Blue Mesa, Colorado; Gunnison at Grand Junction, Colorado; 

Dolores at Cisco, Utah; Green above Fontenelle, Wyoming; Green at Green River, Wyoming; 

Green at Greendale, Utah; Yampa at Maybell, Colorado; Little Snake near Lily, Colorado; 

Duchesne at Randlett, Utah; White near Watson, Utah; San Rafael near Green River, Utah; San 

Juan at Archuletta, New Mexico; and San Juan at Bluff, Utah. Dust control percent increases are 

applied to the following natural flow nodes: Colorado at Cameo, Colorado; Taylor above Taylor 

Park, Colorado; Gunnison at Blue Mesa, Colorado; Gunnison at Grand Junction, Colorado; 

Dolores at Cisco, Utah; San Juan at Archuleta, New Mexico; and San Juan at Bluff, Utah. 

The natural salt loads will increase at the affected locations by assuming that the salinity 

concentration does not change due to weather modification or dust control. These options are 

assumed to be implemented for system benefit.

TABLE G2-6 

Watershed Management Options with the Percent Increases to Natural Flow 

Representative Option

Percent Increase in 

Natural Flow

Watershed-Weather Modification (step 1) 1.02

Watershed-Weather Modification (step 2) 2.03

Watershed-Dust (step 1) 6.12

Watershed-Dust (step 2) 2.62
Colorado River Basin

Water Supply and Demand Study

G2-14 December 2012

3.4 Upper Basin Banking

This option created an Upper Basin water bank designed to help reduce the magnitude of a Lee 

Ferry deficit. In conjunction with the water bank, various conservation (M&I, agricultural, and 

energy) efforts across the Upper Basin would be coordinated for the purpose of yielding water to 

store in the bank. In order to ensure the conserved water is credited to the bank entirely, the 

water is routed to the designated storage facility, i.e., downstream users are not allowed to use 

water generated through upstream conservation. For modeling purposes it was assumed that a 

program could be in place by 2019, which is two years before the earliest occurrence of a Lee 

Ferry deficit under any supply/demand scenario combination. The following sections describe 

the modeling assumptions developed for the purposes of including the banking option in the 

Study. The provided modeling assumptions were based on the option submission and were 

further developed through the Modeling Sub-Team.

3.4.1 Bank Details and Administration 

The Upper Basin Bank was assumed to be stored in a conceptual off-stream storage location just 

upstream of Lake Powell. The bank was constrained to a 5-maf storage capacity, and a 3 percent

tax was applied to the bank’s storage at the end of each year to account for various losses from 

seepage, transmission, etc.

Regarding the administration of water accumulated in the bank, when the 10-year Lee Ferry flow 

was less than 75 maf, banked water was released from the off-stream storage facility and passed 

through Lake Powell in order to ensure a 10-year flow of 75 maf at Lee Ferry. This 

supplementation continued until the 10-year volume was at or greater than 75 maf without 

supplementation from the bank or the bank was fully depleted. If the bank was fully depleted 

and the 10-year volume was still less than 75 maf, then water was injected upstream of Powell 

and reported as Lee Ferry deficit consistent with the Baseline modeling discussed earlier. 

3.4.2 Generation of Water for the Bank

A two-tiered approach was assumed to generate water for use in the bank in order to 1) make 

annual contributions aimed at growing the balance over time under Tier 1 and 2) yielding 

additional water for the bank as the 10-year flow at Lee Ferry approaches 75 maf under Tier 2. 

The generated water was assumed to be from a combination of M&I, agricultural, and energy 

water conservation. From the quantification of conservation options independent of this specific 

option, there is the Basin-wide potential for approximately 1 mafy of conservation each in the 

agricultural and M&I sectors by 2060. A discussion of methods applied to determine the 

maximum values of conservation are provided in the agriculture and M&I conservation 

characterization documentation (see Technical Report F – Development of Options and 

Strategies). When benefits of such efforts are assumed to be distributed geographically in 

proportion to water use for those sectors, there is Upper Basin potential for approximately 

250 kafy of M&I conservation and 400 kafy of agricultural conservation by 2060 under the 

current projected demand scenario. Additionally, according to the option characterization, there 

is at least 160 kafy of water conservation potential in the energy sector by 2060 within the Upper 

Basin. 

As stated earlier, Tier 1 conservation aimed to build a balance in the bank over time via annual 

contributions. To accomplish this, conservation efforts to benefit the bank increased from the 

implementation date, reaching an annual yield of approximately 400 kaf by 2060. Contributions 
Appendix G2 — CRSS Modeling Assumptions

December 2012 G2-15

to the bank increased in five steps consistent with the five different phases of M&I conservation, 

previously discussed. The first increment of M&I conservation begins in 2016, though it is not 

routed to the bank until 2019. In 2021, the second increment of M&I conservation, and the 

energy conservation options are implemented and routed to the bank. Increments three through 

five use the remaining phases of M&I conservation, and begin in 2031, 2041, and 2051, 

respectively, totaling approximately 400 kaf in 2060 under the current projected demand 

scenario. With banking, M&I conservation was assumed to always be in effect in the Upper 

Basin. Tier 2 conservation aimed to produce additional water for the bank when conditions 

indicated a Lee Ferry deficit was likely to occur in the short term. Specifically, when the Lee 

Ferry deficit signpost occurred, Tier 2 conservation was triggered. Agricultural conservation, 

including short-term fallowing, was used for the purpose of Tier 2 water generation. When Tier 

2 conservation was necessary, the maximum available agricultural conservation yields were used 

to generate water for the bank. Given this logic, the maximum annual bank contribution was the 

combination of Tiers 1 and 2 in 2060, amounting to just over 800 kafy. Once the Lee Ferry

deficit signpost was no longer active, Tier 2 is turned off and contributions from Tier 1 continue 

according to schedule. Once the bank’s capacity is reached, Tier 1 conservation measures 

continue; however, the water is no longer routed to the bank—it simply becomes system water. 

A further discussion of how the banking option behaves in the dynamic portfolio framework is 

included in a later section.

3.4.3 Routing of Water

As water was generated for the purpose of benefitting the bank, it was routed to the conceptual 

off-stream storage location above Lake Powell. Conservation under this option was not for the 

purpose of meeting downstream shortages or unmet demands within the Upper Basin. To ensure 

that the water reached Lake Powell and was credited to the bank, logic and rules were built into 

CRSS to prevent users from diverting and using the conservation yield.

4.0 Modeling Dynamic Portfolios

The final phase of the study evaluates system reliability with options and strategies. In this 

phase, multiple options were combined together (portfolio) to collectively help address system 

vulnerabilities. A static set of options were selected and multiple dynamic portfolios were used 

to select options. In the static portfolio, 36 options were modeled together. Under the static 

portfolio, it was assumed that each option ‘turned on’ in the first year that it was available as 

defined by the options characterization (Technical Report F). 

Dynamic portfolios were used to select options to preemptively address water delivery

vulnerabilities while attempting to prevent over-investment. In order to address the 

vulnerabilities before they occurred, system conditions are monitored within CRSS and are 

described as signposts in the Study (appendix G3 describes the development of signposts). 

When a signpost is observed, e.g., Lake Powell falls below some elevation, then an option is

turned on to prevent a future vulnerability from occurring. Logic was added to CRSS to react to 

the signposts and select options from a particular portfolio. A priority list of options, i.e., the 

portfolio, and a list of which vulnerabilities are addressed by each option was necessary model 

input. Tables G2-7 through G2-10 present the model input used for each of the four portfolios. 

In several portfolios, certain options are assumed to be implemented in all traces rather than 

reacting to system conditions. These options are effectively removed from the portfolio list and 
Colorado River Basin

Water Supply and Demand Study

G2-16 December 2012

are statically turned on through other logic in CRSS. Table G2-11 lists which vulnerabilities are 

addressed by each option. From this input, once a signpost or an actual vulnerability occurs, 

CRSS selects the first option that is (1) available and (2) addresses the particular vulnerability in 

accordance with the following logic:

• In a single year, no more than four options total may be implemented Basin-wide. This aims 

to reduce over-investment while ensuring that enough options could be implemented to 

address all vulnerabilities in a single year.

• In a single year, additional options are implemented to address the same vulnerability until 

their total yield equals or exceeds 100 kafy, subject to the limitation described in (1). 

• If multiple signposts are triggered in the same year, an option is implemented for the first 

vulnerability. If the selected option(s) do not address the other vulnerabilities, additional 

options are implemented until all vulnerabilities are addressed, subject to the limitation in 

(1).

TABLE G2-7 

CRSS Input for Portfolio A1 

Representative Option Cost ($/af)

2 Earliest Year Available Magnitude (kaf)

Watershed-Weather Mod 1 30 2016 100

Watershed-Weather Mod 2 35 2021 200

Watershed-Dust 1 220 2026 280

Ag Conservation-Transfer 1 250 2016 200

Ag Conservation-Transfer 2 400 2021 200

Watershed-Tamarisk 400 2023 30

Ag Conservation-Transfer 3 500 2026 200

M & I Conservation 13 500 2016 200

Watershed-Dust 2 520 2036 120

Ag Conservation-Transfer 4 600 2026 200

Desal-Yuma Area Groundwater 600 2021 100

M & I Conservation 23 700 2021 200

Ag Conservation-Transfer 5 750 2026 200

Desal-SoCal Groundwater 750 2021 20

M & I Conservation 33 750 2031 200

M & I Conservation 43 900 2041 200

M & I Conservation 53 900 2051 200

Desal-Salton Sea Drainwater 1 1,000 2026 200

Desal-Salton Sea Drainwater 2 1,150 2031 200

Desal-Salton Sea Drainwater 3 1,300 2036 100
Appendix G2 — CRSS Modeling Assumptions

December 2012 G2-17

TABLE G2-7 

CRSS Input for Portfolio A1 

Representative Option Cost ($/af)

2 Earliest Year Available Magnitude (kaf)

Desal-Pacific Ocean-Mexico 1,500 2026 56

Reuse-Municipal 1 1,500 2021 200

Reuse-Municipal 2 1,600 2031 200

Import-Front Range-Missouri 1,700 2041 600

Reuse-Municipal 3 1,800 2036 200

Reuse-Municipal 4 1,800 2041 200

Reuse-Municipal 5 1,800 2046 132

Desal-Pacific Ocean-CA 1 1,850 2031 200

Desal-Pacific Ocean-CA 2 1,850 2036 200

Energy Water Use Efficiency-Air Cooling4 2,000 2021 160

Local-Coalbed Methane 2,000 2021 100

Reuse-Industrial 2,000 2021 40

Desal-Gulf1 2,100 2028 200

Desal-Gulf2 2,100 2033 200

Local-Rain 3,150 2016 75

Reuse-Grey Water 4,200 2021 178

1 This portfolio also includes the Upper Basin banking option.

2 Cost is not input into CRSS; however, it is included in this table for clarity because it is the basis for the priority 

sorting of options.

3 M&I conservation options are assumed to be on in the Upper Basin in all traces starting in the earliest year 

available, regardless of system conditions. The conserved amount is typically routed to the bank. M&I conservation 

in the Lower Basin is still turned on in response to system conditions; therefore, only the Lake Mead pool elevation, 

Lower Basin shortage, and Lower Basin demand above apportionment vulnerabilities will trigger M&I conservation.

4 Energy Water Use Efficiency-Air Cooling is assumed to be on in all traces starting in the earliest year available,

regardless of system conditions and is typically routed to the bank. Therefore this option is removed from the priority 

option list before loading into CRSS and is turned on through other logic in CRSS. 

Ag – agricultural

Desal – desalination

SoCal –Southern California

Weather Mod - weather modification
Colorado River Basin

Water Supply and Demand Study

G2-18 December 2012

TABLE G2-8 

CRSS Input for Portfolio B 

Representative Option Cost ($/af)

1 Earliest Year Available Magnitude (kaf)

Watershed-Weather Mod 12 30 2016 100

Watershed-Weather Mod 22 35 2021 200

Ag Conservation-Transfer 12 250 2016 200

Ag Conservation-Transfer 2 400 2021 200

Ag Conservation-Transfer 3 500 2026 200

M & I Conservation 1 500 2016 200

Ag Conservation-Transfer 4 600 2026 200

Desal-Yuma Area Groundwater 600 2021 100

M & I Conservation 2 700 2021 200

Ag Conservation-Transfer 5 750 2026 200

Desal-SoCal Groundwater 750 2021 20

M & I Conservation 3 750 2031 200

M & I Conservation 4 900 2041 200

M & I Conservation 5 900 2051 200

Desal-Salton Sea Drainwater 1 1,000 2026 200

Desal-Salton Sea Drainwater 2 1,150 2031 200

Desal-Salton Sea Drainwater 3 1,300 2036 100

Desal-Pacific Ocean-Mexico 1,500 2026 56

Reuse-Municipal 1 1,500 2021 200

Reuse-Municipal 2 1,600 2031 200

Import-Front Range-Missouri 1,700 2041 600

Reuse-Municipal 3 1,800 2036 200

Reuse-Municipal 4 1,800 2041 200

Reuse-Municipal 5 1,800 2046 132

Desal-Pacific Ocean-CA 1 1,850 2031 200

Desal-Pacific Ocean-CA 2 1,850 2036 200

Energy Water Use Efficiency-Air Cooling 2,000 2021 160

Local-Coal Bed Methane 2,000 2021 100

Reuse-Industrial 2,000 2021 40

Desal-Gulf 1 2,100 2028 200

Desal-Gulf 2 2,100 2033 200

1 Cost is not input into CRSS, however, it is included in this table for clarity because it is the basis for the priority 

sorting of options. 2 These options are assumed to be on in all traces regardless of system conditions and are not implemented in 

response to signposts. Therefore these options are removed from the priority option list before loading into CRSS 

and are turned on through other logic in CRSS.
Appendix G2 — CRSS Modeling Assumptions

December 2012 G2-19

TABLE G2-9 

CRSS Input for Portfolio C1 

Representative Option Cost ($/af)

2 Earliest Year Available Magnitude (kaf)

Watershed-Weather Mod 1 30 2016 100

Watershed-Weather Mod 2 35 2021 200

Watershed-Dust 1 220 2026 280

Ag Conservation-Transfer 1 250 2016 200

Ag Conservation-Transfer 2 400 2021 200

Watershed-Tamarisk 400 2023 30

Ag Conservation-Transfer 3 500 2026 200

M & I Conservation 13 500 2016 200

Watershed-Dust 2 520 2036 120

Ag Conservation-Transfer 4 600 2026 200

Desal-Yuma Area Groundwater 600 2021 100

M & I Conservation 24 700 2021 200

Ag Conservation-Transfer 5 750 2026 200

Desal-SoCal Groundwater 750 2021 20

M & I Conservation 34 750 2031 200

M & I Conservation 44 900 2041 200

M & I Conservation 54 900 2051 200

Desal-Salton Sea Drainwater 1 1,000 2026 200

Desal-Salton Sea Drainwater 2 1,150 2031 200

Desal-Salton Sea Drainwater 3 1,300 2036 100

Reuse-Municipal 1 1,500 2021 200

Reuse-Municipal 2 1,600 2031 200

Reuse-Municipal 3 1,800 2036 200

Reuse-Municipal 4 1,800 2041 200

Reuse-Municipal 5 1,800 2046 132

Energy Water Use Efficiency-Air Cooling5 2,000 2021 160

Reuse-Industrial 2,000 2021 40

Local-Rainwater Harvesting 3,150 2016 75

Reuse-Grey Water 4,200 2021 178

1 This portfolio also includes the Upper Basin banking option.

2 Cost is not input into CRSS; however, it is included in this table for clarity because it is the basis for the priority 

sorting of options. 3 M&I conservation step 1 is assumed to be on in all traces, Basin-wide, regardless of system conditions. In the 

Upper Basin, the conserved amount is typically routed to the bank. Therefore this option is removed from the priority 

option list before loading into CRSS and is turned on through other logic in CRSS.

4 The remaining M&I conservation options are assumed to be on in the Upper Basin in all traces starting in the 

earliest year available, regardless of system conditions, and the conserved amount is typically routed to the bank. 

M&I conservation in the Lower Basin is still turned on in response to system conditions; therefore, only the Lake 

Mead pool elevation, Lower Basin shortage, and Lower Basin demand above apportionment vulnerabilities will 

trigger M&I conservation. 5 Energy Water Use Efficiency-Air Cooling is assumed to be on in all traces starting in the earliest year available

regardless of system conditions and is typically routed to the bank. Therefore this option is removed from the priority 

option list before loading into CRSS and is turned on through other logic in CRSS. 
Colorado River Basin

Water Supply and Demand Study

G2-20 December 2012

TABLE G2-10

CRSS Input for Portfolio D 

Representative Option Cost ($/af)

1 Earliest Year Available Magnitude (kaf)

Watershed-Weather Mod 1 30 2016 100

Watershed-Weather Mod 2 35 2021 200

Ag Conservation-Transfer 1 250 2016 200

Ag Conservation-Transfer 2 400 2021 200

Ag Conservation-Transfer 3 500 2026 200

M & I Conservation 1 500 2016 200

Ag Conservation-Transfer 4 600 2026 200

Desal-Yuma Area Groundwater 600 2021 100

M & I Conservation 2 700 2021 200

Ag Conservation-Transfer 5 750 2026 200

Desal-SoCal Groundwater 750 2021 20

M & I Conservation 3 750 2031 200

M & I Conservation 4 900 2041 200

M & I Conservation 5 900 2051 200

Desal-Salton Sea Drainwater 1 1,000 2026 200

Desal-Salton Sea Drainwater 2 1,150 2031 200

Desal-Salton Sea Drainwater 3 1,300 2036 100

Reuse-Municipal 1 1,500 2021 200

Reuse-Municipal 2 1,600 2031 200

Reuse-Municipal 3 1,800 2036 200

Reuse-Municipal 4 1,800 2041 200

Reuse-Municipal 5 1,800 2046 132

Energy Water Use Efficiency-Air Cooling 2,000 2021 160

Reuse-Industrial 2,000 2021 40

1 Cost is not input into CRSS; however, it is included in this table for clarity because it is the basis for the priority 

sorting of options.
Appendix G2 — CRSS Modeling Assumptions

December 2012 G2-21

TABLE G2-11

Options that Address Different Vulnerabilities

Representative Option

Year 

Available

Vulnerability Addressed by Representative Option UB Shortage Lee Ferry Deficit Low Lake Mead 

Pool 

Elevations 

Lower Basin Shortage 1Lower Basin Shortage 2Lower Division States’Demand Above Basic Apportionment

Ag Conservation 2016 X X X X X X 

M & I Conservation 2016 X1 X1 X X X X 

Local-Rainwater Collection 2016 X X X X X X 

Reuse-Grey Water 2021 X X X X X X 

Reuse-Industrial 2021 X X X X X X 

Reuse-Municipal Step 1-2 2021 X X X X X X 

Reuse-Municipal Step 3-5 2036 X X X X 

Desal-Gulf 2028 X X X X 

Desal-Pacific Ocean 2031 X X X X 

Desal-Pacific Ocean-MX 2026 X X X X 

Desal-Tribs 2026 X X X X 

Desal-SoCal groundwater 2021 X X X X 

Desal-Yuma 2021 X X X X 

Import-Front Range-Missouri 2041 X X X X X 

Energy Conservation 2021 X X 

Watershed-Dust Management 2026 X X 

Watershed-Tamarisk 2023 X X X X 

Watershed-Weather Mod 2016 X X 

Local-Coalbed Methane 2021 X X 

1 For Portfolios A and C, only Lower Basin M&I conservation steps are implemented based on signposts. Therefore, 

the M&I conservation options under these scenarios do not address the Upper Basin shortage and Lee Ferry deficit 

vulnerabilities. 
Colorado River Basin

Water Supply and Demand Study

G2-22 December 2012

Options are selected at the beginning of each year based on system conditions at the end of the 

previous year. When the Upper Basin Banking option is not part of the portfolio, all options are 

brought online Basin-wide. For example, conservation is applied Basin-wide, and once an option 

is selected, it is assumed to be on for the remainder of the simulation. 

When a portfolio includes banking, there are several exceptions to these rules. The Upper Basin 

Banking option assumes that M&I conservation is always on in order to generate water for the 

bank. Because the bank is only applied in the Upper Basin, the Lower Basin M&I conservation 

portion is split out as a separate option and selected based on signposts monitoring Lower Basin 

water delivery vulnerabilities. Furthermore, while M&I conservation in the Upper Basin is 

always in place, the conserved water does not always go to the bank. Once the bank is at its 

capacity of 5 maf, the water yielded from M&I conservation is assumed to be system water for 

the given year. Once the bank is significantly below its capacity, the water is again routed to the 

bank. Analogous logic is applied to energy conservation when banking is used, although it is 

less nuanced because there is no energy conservation option in the Lower Basin. 

Additionally, agricultural fallowing supplies water to the bank during Tier 2 operations, which 

can be turned on and off as necessary. When banking is in place, agricultural fallowing can still 

be turned on Basin-wide if necessitated by a signpost. If any phases of agricultural fallowing are 

already on when Tier 2 banking is needed, then the Upper Basin portion of the fallowing options 

switch from system benefit to targeted benefit, i.e., it is routed to the bank. Conversely, if any

agricultural fallowing phases are not currently on, but are available when Tier 2 banking is 

needed, then they are turned on, at the maximum yield potential for the current year, for the 

Upper Basin only and the conservation yield is routed to the bank. In this case, agricultural 

fallowing phases in the Upper Basin are turned off once Tier 2 banking is no longer necessary. 

5.0 References 

Bureau of Reclamation (Reclamation). 2006a. 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). 2006b. Record of Decision for the Operation of Flaming 

Gorge Dam 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.

Bureau of Reclamation (Reclamation). 2012. Record of Decision for the Aspinall Unit 

Operations, Final Environmental Impact Statement. 

Butler, R. A. 2011. Modeling Techniques to Assess Long-term Reliability of Environmental 

Flows in Basin Scale Planning (Master's Thesis). University of Colorado. 

U.S. Department of the Interior (DOI). 2007. Record of Decision for Colorado River Lower 

Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead. 

Zagona, E., T. Fulp, R. Shane, T. Magee, and H. Goranflo. 2001. “RiverWareTM: A Generalized 

Tool for Complex Reservoir Systems Modeling.” Journal of the American Water 

Resources Association. 37(4):913–929. 
Appendix G3 

Additional Methodology and Results

December 2012 G3-1 

Appendix G3 — Additional Methodology and 

Results 

1.0 Introduction

This appendix provides additional methodology discussion and results related to the system 

reliability analysis presented in Technical Report G – System Reliability Analysis and Evaluation 

of Options and Strategies. The appendix structure largely follows that of Technical Report G . A 

complete suite of system response variable results is provided, indicator metrics and 

vulnerability are further explored, and definitions and associated vulnerability thresholds are 

detailed, followed by a full set of indicator metric vulnerability figures without options and 

strategies. Also pertaining to vulnerability, a discussion of additional vulnerable condition 

methodology is presented that includes an example, and vulnerable condition results for all water 

supply indicator metrics are provided. This appendix supplements the methods and results for 

system reliability presented in the main report with options and strategies. Therein, modeling 

assumptions are discussed, including signpost selection methods. Following that, results with 

options and strategies for all system response variables and indictor metric vulnerable conditions 

are provided. 

2.0 Evaluation of System Reliability without Options and 

Strategies

2.1 System Response Variables

System response variables describe Colorado River Basin (Basin) conditions for the various 

scenarios. These are primarily direct model trace results such as pool elevations, hydropower 

generation, or flow. This output provides a gross estimate of possible future trends and 

operational ranges for major Basin components. System response variables (listed in table G-1 of 

the main report) are a first step in investigating system performance under plausible future 

conditions; however, they are not tailored to assess specific Basin resources and may lack a 

frame of reference for readers seeking to review a particular Basin resource.

Colorado River Simulation System (CRSS) simulations provide thousands of trace results used 

to estimate the system reliability across scenarios without options and strategies revealing a wide 

range of outcomes. This section presents either magnitude and percent of traces with occurrence 

or statistics that specify the level that a particular percentage of results has not exceeded. For 

example, the 10th percentile results for flows at a particular location for a specific year would be 

the level of flow not exceeded by 10 percent of the traces. Similarly, the 50th percentile, or 

median, is the level of flow not exceeded by 50 percent of the traces. The median value should 

not be interpreted as an average or most likely outcome, but as the central tendency of the 

distribution of these results. 

These variables are presented for each supply and demand scenario and either of two 

assumptions regarding Lakes Powell and Mead operations beyond 2026 to explore differences. 

Figures G3-1 to G3-7, G3-9 to G3-15, and G3-17 show time series of 10th, 50th and 90th

percentiles for the following types of system response variables: river flow, reservoir storage, 
Colorado River Basin

Water Supply and Demand Study

G3-2 December 2012

reservoir release, reservoir pool elevation, shortage, surplus, and energy production. In addition, 

figures G3-8, G3-16, and G3-18 use cumulative distribution functions to further explore energy 

production results.Select scenarios are highlighted for reference.

FIGURE G3-1 

10th, 50th, 90th Percentiles for Annual Flow of Green River at Green River, Utah, by Scenario, Without Options and Strategies
Appendix G3 — Additional

Methodology and Results

December 2012 G3-3 

FIGURE G3-2 

10th, 50th, 90th Percentiles for Annual Flow of Colorado River near Cisco, Utah, by Scenario, Without Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-4 December 2012

FIGURE G3-3 

10th, 50th, 90th Percentiles for Annual Flow of San Juan River near Bluff, Utah, by Scenario, Without Options and Strategies
Appendix G3 — Additional

Methodology and Results

December 2012 G3-5 

FIGURE G3-4 

10th, 50th, 90th Percentiles for Total Storage Above Lake Powell by Scenario, Without Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-6 December 2012

FIGURE G3-5 

10th, 50th, 90th Percentiles for Upper Basin Annual Shortage by Scenario, Without Options and Strategies
Appendix G3 — Additional

Methodology and Results

December 2012 G3-7 

FIGURE G3-6 

10th, 50th, 90th Percentiles for Lake Powell Pool Elevation by Scenario, Without Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-8 December 2012

FIGURE G3-7 

10th, 50th, 90th Percentiles for Total Upper Basin Energy Production by Scenario, Without Options and Strategies

terawatt hour (tWh) 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-9 

FIGURE G3-8 

Cumulative Density Function for Total Upper Basin Energy Production by Scenario, Without Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-10 December 2012

FIGURE G3-9 

10th, 50th, 90th percentiles for Lake Powell Water Year Release by Scenario, Without Options and Strategies
Appendix G3 — Additional

Methodology and Results

December 2012 G3-11

FIGURE G3-10

Percent Traces and 10th, 50th, and 90th Percentiles for Lee Ferry Deficit by Scenario, Without Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-12 December 2012

FIGURE G3-11

10th, 50th, 90th Percentiles for Lake Mead Pool Elevation by Scenario, Without Options and Strategies
Appendix G3 — Additional

Methodology and Results

December 2012 G3-13

FIGURE G3-12

Percent Traces and 10th, 50th, and 90th Percentiles for Lower Basin Annual Total Shortage (including remaining demands 

above Lower Division States’ basic apportionments) by Scenario, Without Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-14 December 2012

FIGURE G3-13

Percent Traces and 10th, 50th, and 90th Percentiles for Lower Basin Annual Regulatory Shortage by Scenario, Without Options 

and Strategies
Appendix G3 — Additional

Methodology and Results

December 2012 G3-15

FIGURE G3-14

Percent Traces with a Lower Basin Surplus by Scenario, Without Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-16 December 2012

FIGURE G3-15

10th, 50th, 90th Percentiles for Hoover Dam Energy Production by Scenario, Without Options and Strategies
Appendix G3 — Additional

Methodology and Results

December 2012 G3-17

FIGURE G3-16

Cumulative Density Function for Hoover DamEnergy Production by Scenario, Without Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-18 December 2012

FIGURE G3-17

10th, 50th, 90th Percentiles for Parker Dam and Davis Dam Energy Production by Scenario, Without Options and Strategies
Appendix G3 — Additional

Methodology and Results

December 2012 G3-19

FIGURE G3-18

Cumulative Density Function for Parker Dam and Davis Dam Energy Production by Scenario, Without Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-20 December 2012

3.0 Defining Vulnerable Outcomes and Vulnerable 

Conditions

3.1 Vulnerability Definitions

3.1.1 Indicator Metric Vulnerability

This section provides additional information regarding the indicator metric definitions and 

associated vulnerability thresholds described in Technical Report G – System Reliability Analysis 

and Evaluation of Options and Strategies. Some of the selected indicator metrics required 

additional assumptions and/or additional processing in order to generate a suitable indicator for 

vulnerability. Field and resource experts were consulted in developing vulnerability thresholds 

and were instrumental in the process. Because vulnerability is unique to each resource/location 

combination, the thresholds and associated methods varied. Generally, the approach was to 

capture a condition that would result in a significant degradation for the resource and/or require 

sizeable capital/infrastructure investment to mitigate. The rationale, assumptions, and methods 

for these metrics are described below. 

Water Delivery

Water delivery indicator metrics were developed with the Modeling Sub-Team. Flow at Lee 

Ferry was selected as an indicator metric; vulnerability was defined as flow less than an 

aggregate of 75 million acre-feet (maf) over any 10-year period. Lake Mead’s pool elevation was 

also was selected as an indicator metric. Elevation 1,000 feet above mean sea level (msl) in Lake 

Mead is important to water deliveries for multiple reasons. This is significant both in terms of 

deliveries to the Southern Nevada Water Authority and is of importance in the 2007 Interim 

Guidelines. For these reasons, vulnerability was defined as any month in which pool elevation 

falls below that threshold. 

Delivery shortages are of considerable concern and unique to the various regional water users 

throughout the Basin.The following indicator metrics were developed to reflect this geographic 

heterogeneity: (1) Upper Basin shortage as percent of requested depletion, (2) Lower Basin 

2-year moving window shortage volume sum, and (3) Lower Basin 5-year moving window 

shortage volume sum. Drawing from expertise of the Modeling Sub-Team, respective 

vulnerabilities were selected to be (1) annual shortage volume greater than 25 percent of 

requested depletion, (2) cumulative shortage volume exceeding 1 maf in any 2-year window, and 

(3) cumulative shortage volume exceeding 1.5 maf in any 5-year window. From Technical 

Report C – Water Demand Assessment, demand exists for Colorado River water in excess of 

Lower Divison States’ basic apportionments. Because this is a considerable portion of the overall 

Lower Division States’ demand in several scenarios, annual demand above Lower Division 

States’ basic apportionment was also selected as a water delivery indicator metric. Vulnerability 

for this indicator was developed based on estimated sustainability of existing and identified 

future supplies that could be used to meet those demands. Through this effort, it was decided 

that, for the period of 2012 to 2035, demand above Lower Division States’ basic apportionment 

up to 1 maf would not indicate a vulnerability, but exceeding this threshold would indicate a

vulnerability. For the period 2035 to 2060, the non-vulnerable demand above Lower Division 

States’ basic apportionment decreased linearly from 1 maf to 0.25 maf, reflecting reduced 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-21

availability of other supplies. As was the case for the first period, any year in which the demand 

above Lower Division States’ basic apportionment exceeded its corresponding threshold value 

was deemed vulnerable. 

Electric Power

Electric power indicator metrics and associated vulnerabilities were developed with guidance 

from Western Area Power Administration. Based on key facilities, power markets and contracts, 

three indicator metrics were developed. Owing to the relationship between head and generation 

capacity, two of the indicator metrics are pool elevation at Lakes Powell and Mead. The third 

indicator developed was annual aggregate Upper Basin generation (defined as the sum of Blue 

Mesa, Morrow Point, Crystal, Flaming Gorge, Fontenelle, and Glen Canyon). For the Lake 

Powell indicator metric, vulnerability was defined as pool elevation below power pool in any 

month (pool elevation less than 3,490 feet msl. For Lake Mead, vulnerability was defined as pool 

elevation below 1,050 feet msl, which is the turbine rough water threshold. For the Upper Basin 

aggregated indicator metric, vulnerability was defined as 3 consecutive years with generation 

less than 4,450 gigawatt-hours (GWh) per year. This threshold was developed by Western Area 

Power Administration, taking into consideration its power contracts in markets served by Upper 

Basin facilities and its capacity to secure supplemental power from other sources. 

Flood Control

The flood control indicator metric was selected to be Hoover Dam release. Because substantial 

downstream infrastructure and agriculture are close to the river and floodplain, this area has 

potential for considerable damages should the safe channel capacity (28,000 cubic feet per 

second [cfs]) be exceeded (Bureau of Reclamation [Reclamation], 2000). Given the 

aforementioned consequences of flow exceeding the critical river stage, vulnerability was 

defined as any month in which the Hoover Dam release violates that threshold. 

Recreation 

Recreation indictor metrics were developed for (1) shoreline public use facilities and (2) river 

and whitewater boating. Metrics pertaining to shoreline public use facilities were developed in 

conjunction with appropriate federal and state management agencies. The thresholds are pool 

elevations that would necessitate relocation or infrastructure work (e.g., siltation removal or boat 

ramp extension) to maintain viability of major shoreline public use facilities during the high-use 

season. Because reservoir conditions vary considerably across the Upper Basin, locations in the 

three major tributaries (Green, Upper Colorado, and San Juan basins) were selected in addition to

Lakes Powell and Mead. 

For the Green River Basin, pool elevation at Flaming Gorge Reservoir during May to September 

served as the indicator of shoreline public facilities in that region. The resource is deemed

vulnerable when pool elevation drops below 6,019 feet msl during that period. According to

Operation of Flaming Gorge Dam Final Environmental Impact Statement (Reclamation, 2005), 

over 75 percent of visitation occurs from May to September. Further, in appendix 4 of the 

aforementioned Flaming Gorge Final Environmental Impact Statement, the low-end threshold 

for most recreation was identified as a pool elevation of 6,017 feet msl; the vulnerability 

threshold selection was informed by this, but ultimately chosen to be slightly higher (6,019 feet

msl) to reflect the point at which the first major boat ramp would no longer be useable. 

In the Upper Colorado Basin, the largest reservoir is Blue Mesa on the Gunnison River. From the 

Aspinall Unit Operations Final Environmental Impact Statement (Reclamation, 2012), the peak 
Colorado River Basin

Water Supply and Demand Study

G3-22 December 2012

visitation season is very similar to that of Flaming Gorge, making the indicator metric May to 

September pool elevation. Through discussions with the National Park Service at Curecanti 

National Recreation Area, the vulnerability threshold was chosen to be 7,440 feet msl; this is the 

current minimum elevation at which Lake Fork Marina/boat ramp can operate (Stahlnecker, 

2012). The Lake Fork Marina/boat ramp would be the first of the three major public use facilities 

at Blue Mesa to be significantly impacted by declining reservoir levels.

Navajo Reservoir is the major shoreline recreation destination in the San Juan Basin. As 

described in the 2006 Navajo Reservoir Operations Final Environmental Impact Statement 

(Reclamation, 2006), the recreation season generally extends from April to October. As such, the 

San Juan Basin Shoreline Public Use Facility indicator metric is Navajo pool elevation during 

that period. One of the three major marina/boat ramp facilities at the reservoir, Two Rivers 

Marina near Arboles, Colorado, was constructed with a concrete boat ramp serviceable to pool 

elevations as low as 5,978 feet msl (Reclamation, 2006). However, over the years, due to shifts 

in the main river channel and substantial siltation, considerable work would be required to 

maintain usability below 6,025 feet. Therefore, the vulnerability threshold for this indictor metric 

is pool elevation below 6,025 feet msl; other Navajo shoreline public use facilities still provide 

recreation access at this elevation. The selection was guided by discussion with Colorado State 

Park staff at Navajo State Park in Arboles (Secrist, 2012) Further; this is supported by the New 

Mexico State Park description of boating at elevations below 6,030 feet msl as being in the 

lowest-quality tier.1

Lake Powell receives considerable year-round visitation; however, like the other Upper Basin 

reservoirs, the majority of recreational use occurs during the summer months—approximately 

75 percent during the May-to-September window—sothe indicator metric for Lake Powell is 

pool elevation during that period. The majority of shoreline public use facilities are currently 

serviceable to pool elevations as low as 3,560 feet msl; below that point, additional infrastructure 

would be required to maintain most public boat ramps. Further, all major marinas would face 

sizeable challenges to maintain operation below a pool elevation of 3,555 feet msl (Reclamation, 

2000). Therefore, the vulnerability threshold is defined as pool elevation below 3,560 feet msl. 

Recreation at Lake Mead occurs year-round; therefore, the indicator metric is pool elevation in 

all months. Over the past decade, due to declining lake levels some shoreline public use facilities 

have been relocated or closed. Given the economic reliance of surrounding communities on 

shoreline access-centric industry, selecting a vulnerability threshold for the entire resource is 

particularly tenuous. From discussions with the National Park Service, the majority of shoreline 

public use facilities offering lake access and recreation in 2012 have capacity to operate to a pool 

elevation of 1,080 feet msl; many facilities have plans to enable operation at lower levels. 

However, a considerable portion of these strategies require non-trivial infrastructure investment 

(e.g., moving marinas or extending boat ramps). Owing to the prospect of significant 

restructuring to maintain recreation opportunities commensurate with current access below 

1,080 feet msl, this was chosen as the vulnerability threshold (Turner, 2012). 

Metrics pertaining to river and whitewater boating estimate the number of days per month with 

flows that are below acceptable, acceptable low, optimal, acceptable high and above acceptable 

for supporting river boating recreation (see Technical Report D – System Reliability Metrics,

Appendix D2 – Boating Flow Days Metrics). From these results, two indicator metrics were 

 

1 Available at: http://www.emnrd.state.nm.us/SPD/BOATINGWeb/NavajoLake.html. 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-23

developed for each major Upper Basin tributary (Green, Colorado, and San Juan rivers). The first 

deals exclusively with optimal boating flow days and the second captures total boating flow days 

(sum of acceptable low, optimal, and acceptable high days). In both cases, the indicator metric 

aggregates across all metric locations within a particular basin to give, for example, total optimal 

boating flow days in the Green River Basin. As was the case with the shoreline public facility 

use attribute of interest, each of the three regions captured by boating flow days indicator metrics 

have peak seasons. In the Green River Basin, based on a review of commercially offered boating 

activities and the Operation of Flaming Gorge Dam Final Environmental Impact Statement 

(Reclamation, 2005), the key months were found to be May to September. For the Colorado 

mainstem, a similar review of commercially scheduled trips indicated the same peak season. The 

San Juan River, due to its more southerly location, has a slightly longer river recreation season; 

March to October, confirmed by the Navajo Reservoir Operations Final Environmental Impact 

Statement (Reclamation, 2006) and commercial trip offerings. Therefore, for each sub-basin, a 

peak season aggregation of optimal and total boating flow days was produced, offering a 

condensed view of the monthly five flow tiers at eight locations across the Upper Basin. 

Working with representatives from American Whitewater, a framework for indicator metric 

vulnerability threshold criteria was developed. The foundation of this concept is that boating 

recreation would become vulnerable if the future number of boating flow days deviates 

substantially from historical levels. Unfortunately, boating flow days computed from gage data 

are not appropriate for comparison with model projected future conditions due to model biases 

and reservoir construction or reoperation over time. To capture the spirit of estimating historical

levels of boating flow days, a modeling control run was proposed. For the control run, the Study 

model, CRSS, was run with the historical Observed Resampled supply scenario and demands 

static at the 2015 Current Projected (A) scenario levels. The result of this run is an 

approximation of historical boating flow days, driven by observed hydrologic variability and 

present-day demands, which lends itself to comparison with future projected conditions. Due to 

considerable inter-annual hydrologic variability in the Basin, simulation results from the control 

run were compared with future projected conditions based on 10-year running averages. In the 

case of the total boating flow days indicator metrics, vulnerability was defined as a future period 

for which the 10-year average boating flow days is below the control run minimum 10-year 

average. For the optimal boating flow days indicator metric, vulnerability was defined as a future 

period for which the 10-year average falls below the 10th percentile of the respective control run 

results. The optimal boating flow days vulnerability threshold is more rigorous, compared with 

the total boating flow days threshold, because optimal flow days afford the most recreation 

opportunities and therefore have the greatest value. 

Ecological

A wide range of ecological metrics were developed and discussed in Technical Report D – 

System Reliability Metrics. Due to the number and complexity of these metrics, it was not 

feasible to develop an indicator metric that encompasses several locations within a particular 

region. As a result, a single metric was selected as an indicator for four regions in the Upper 

Basin: Yampa, Colorado mainstem, Green, and San Juan. The locations selected tend to be more 

downstream in their respective regions to offer some aggregation of upstream conditions. Further 

descriptions of these metrics and the development of vulnerability thresholds follows in the 

sections below. 
Colorado River Basin

Water Supply and Demand Study

G3-24 December 2012

For the Yampa River near Maybell, the flows to support threatened and endangered species calls 

for maintaining a baseflow of 120 cfs at all times (U.S. Fish and Wildlife Service, 2008). Similar 

to earlier discussion regarding recreation, comparing a flow recommendation derived from gage 

data with model-simulated flows may not always be appropriate. Further, the development of an 

ecologically based vulnerability threshold is beyond the scope of the Study, so the control run 

comparison approach for establishing vulnerability was employed. In this control run, modeled 

Yampa River flow near Maybell was first checked against the 120 cfs to identify years in which 

the recommendation was violated. Following, for each trace, a running percent of years with a 

violation was computed (i.e., if the first year in a trace violated the recommendation but years 

two and three did not, the percent of years with a violation would be 100 percent in year one, 50 

percent in year two and 33 percent in year three). From these data, the annual maxima of percent 

violation across all control run traces were selected, thereby defining a time series threshold for 

permissible frequency of flow recommendation violations. The same percent of years with a 

violation statistic was computed for each model projected future trace. If the value in a given 

year exceeded the threshold derived from the control run, it was deemed vulnerable. 

For the Green and Colorado rivers, the flow recommendations are more complex. At those sites, 

flow recommendations are monthly and tied to year type categories (Reclamation, 2005; McAda, 

2003). For example, during a dry year type, lower flows are targeted while higher flows are 

prescribed for average or wet years. Further, there is a target distribution for the year types. For 

the purpose of developing indicator metrics, these were distilled into three components: (1) year 

type distribution, (2) April to July peak flow compliance, and (3) September baseflow 

compliance. For the same reasons discussed above, the control run approach was employed for 

these locations in developing indicator metric vulnerability thresholds. Changing monthly and 

seasonal flow recommendations and year type distribution targets made this more complicated 

than the Yampa modeling, but the concept of quantifying some permissible frequency of noncompliance remains the same. The procedure described below examines each of the 

aforementioned flow recommendation components individually, and should any one of the three 

components perform worse than observed in the control run, the year is deemed vulnerable. 

The target year-type distribution specifies the percent of years that should be classified in each 

category. Using the control run results, the year-type distribution variability was first quantified 

to establish a unit-less measure of deviation from the target distribution. For each year, the 

percent of years falling into each category up to that year were computed. These values were 

then compared with the target percentages and summarized by taking the sum of the absolute 

differences. The following is an example calculation for a hypothetical target distribution that 

specified three year types and equal occurrence frequency (i.e., 0.33 for each). Consider the tenth 

year of a trace; at this point, 2 years have been classified as wet; 3 years have been average; and 

5 years have been dry. The corresponding frequencies would be 0.20, 0.30, and 0.50, with the 

respective absolute differences being 0.13, 0.03, and 0.17, and the index (sum of absolute 

differences) would be 0.33. As the trace evolves over time, with more values contributing to the 

distribution, the expectation is that the percentages converge toward the targets and the index 

values become smaller and smaller. With this completed for all traces in the control run, the 

annual maxima were computed, establishing a maximum permissible deviation from the target

distribution time series. The index computation was performed for all model projected future 

traces, and any year that exceeded the threshold derived from the control run was deemed 

vulnerable. 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-25

The success of meeting flow recommendations associated with each year type was quantified in 

a similar manner to the distribution of year types. As mentioned earlier, the two aspects of the 

flow recommendations examined were the peak flow period (April through July) and the 

September baseflow. For each year in the control run results, the number of years falling into 

each year type category were computed, as was done for the target distribution. Next, the peak 

flow and September baseflow values for each year were analyzed to assess which year-type flow 

was actually seen in each of those years. The result is two lists – one of year types that should 

have been met and a second of the year type flows that were actually met. Subsequently, for each 

year in those two lists, the percent of years up to that point in each classification was calculated. 

The average of the absolute differences (by percent of year types, actual versus classified) was 

computed as a unitless measure of flow recommendation non-compliance. With this completed 

for all traces in the control run, the annual maxima were computed, thus establishing a maximum 

permissible flow recommendation non-compliance time series for peak and September flows. 

The index computation was performed for all model projected future traces with regard to both 

peak and September flow recommendations, and any year that exceeded either threshold derived 

from the control run was deemed vulnerable. 

The flow recommendation to benefit threatened and endangered species on the San Juan near 

Bluff, Utah, is similar to those previously discussed; it has peak and base flow targets, in 

addition to year-type frequencies (Reclamation, 2006). However, the flow targets are not tied to 

year-type classification; instead the four tiers of flow magnitude-duration combinations are given 

occurrence frequencies and maximum intervals between occurrence. The baseflow 

recommendation is static and applies for each month. Hence, three aspects were also identified 

for this site: (1) baseflow compliance, (2) frequency of magnitude-duration, and (3) tiers interval 

between tier occurrence. Using the control run results, thresholds for each of these were 

developed. The baseflow component was evaluated in the same manner as was done for the 

Yampa baseflow prescription. Flow tier frequency compliance was analogous to the 

Green/Colorado target distribution calculation. The unique aspect of the Bluff recommendation 

was the maximum interval between tier occurrence. This index was developed by first computing 

the compliance for each tier; a year within the permissible interval was flagged as compliant, and 

each year exceeding the permissible interval was flagged as in violation. The result for each trace 

was four time series of violation/compliance. To summarize a single trace, for each year, the 

average number of violations across all tiers up to that point was computed. Last, as was done for 

all of the previously described indices, for each year, the annual maxima across all control run 

traces was computed, giving a maximum permissible interval violation. These indices were

computed for all model projected future traces, and any year that exceeded one of the thresholds 

derived from the control run was deemed vulnerable. 

Water Quality

In order to comply with the Clean Water Act, the Colorado River Basin Salinity Control Forum 

develops numeric salinity criteria below Hoover and Parker Dams and at Imperial Dam. The 

water quality indicator metric was selected to be the numeric salinity criterion below Parker 

Dam. Parker Dam was chosen because of the three locations on the lower Colorado River where 

annual salinity criteria have been established, the Parker Dam location has historically shown the 

highest damages resulting from salinity (e.g., early replacement of household water heaters, 

reduced agricultural production). Average annual salinity concentrations and salt loads were 

determined on a flow-weighted basis. The flow-weighted average annual salinity concentration is 

calculated by dividing the flow-weighted average annual salt load passing a measuring station by 
Colorado River Basin

Water Supply and Demand Study

G3-26 December 2012

the total annual volume of water passing the same point during a calendar year. The flowweighted average annual salt load is calculated by first multiplying the daily salinity 

concentration values by the daily flow rates. These values are then summed over a calendar year. 

The total annual volume of water is calculated by calculating the sum of the daily flow rate. 

Below Parker Dam the numeric salinity criteria is 747 milligrams per liter.

Exceedance of the flow-weight average annual salinity criteria defines vulnerability. Unlike 

other resource categories, salinity vulnerably can only be defined for a given year across traces 

or a specified time period (e.g., 2012 through 2026) and not for an individual trace. At Parker 

Dam, if 50 percent of the traces in any one year for a given period (e.g., 2012 through 2026) 

exceeds 747 milligrams per liter, the period was vulnerable. 

3.1.2 Vulnerability Results Without Options and Strategies

Technnical Report G provides vulnerability results without options and strategies, summarized 

across all scenarios, for all indicator metrics. These results are broken out by scenario and 

described in further detail in figures G3-19 through G3-70. Each figure shows the simulation 

results for one indicator metric, with each point representing the median result from one 

scenario. The figures are disaggregated by time period, supply scenario (columns), demand 

scenario (symbols), and whether the Record of Decision for Colorado River Interim Guidelines 

for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead (2007 

Interim Guidelines) (U.S. Department of Interior [DOI], 2007) are extended after 2026 (colors). 

For sites above Lake Powell, post 2026 reservoir operations do not impact results. As such, there 

will be no difference between results for the extend 2007 Interim Guidelines (DOI, 2007) and

revert to the No Action Alternative options presented in the Colorado River Interim Guidelines 

for Lower Basin Shortages and Coordinated Operations of Lake Powell and Lake Mead Final 

Environmental Impact Statement (2007 Interim Guidelines Final EIS) (Reclamation, 2007). For 

each supply scenario subset (column), the gray region shows range and the black bar the scenario 

median.
Appendix G3 — Additional

Methodology and Results

December 2012 G3-27

FIGURE G3-19

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Upper Basin Shortage Indicator Metric (exceeds 25% of requested depletion in any 1 year)

FIGURE G3-20

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Upper Basin Shortage Indicator Metric (exceeds 25% of requested depletion in any 1 year)
Colorado River Basin

Water Supply and Demand Study

G3-28 December 2012

FIGURE G3-21

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Lee Ferry Deficit Indicator Metric (exceeds zero in any 1 year)

FIGURE G3-22

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Lee Ferry Deficit Indicator Metric (exceeds zero in any 1 year)
Appendix G3 — Additional

Methodology and Results

December 2012 G3-29

FIGURE G3-23

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Lake Mead Pool Elevation <1,000 feet msl Indicator Metric (below 1,000 feet msl in any 1 month)

FIGURE G3-24

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Lake Mead Pool Elevation <1,000 feet msl Indicator Metric (below 1,000 feet msl in any 1 month)
Colorado River Basin

Water Supply and Demand Study

G3-30 December 2012

FIGURE G3-25

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Lower Bain Shortage Indicator Metric (exceeds 1 maf over any 2-year window)

FIGURE G3-26

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period,

Lower Basin Shortage Indicator Metric (exceeds 1 maf over any 2-year window)
Appendix G3 — Additional

Methodology and Results

December 2012 G3-31

FIGURE G3-27

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Lower Bain Shortage Indicator Metric (exceeds 1.5 maf over any 5-year window)

FIGURE G3-28

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Lower Basin Shortage Indicator Metric (exceeds 1.5 maf over any 5-year window)
Colorado River Basin

Water Supply and Demand Study

G3-32 December 2012

FIGURE G3-29

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, Remaining Demand Above Lower 

Division States’ Basic Apportionment Indicator Metric (exceeds moving threshold in any one year)

FIGURE G3-30

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, Remaining Demand Above Lower 

Division States’ Basic Apportionment Indicator Metric (exceeds moving threshold in any one year)
Appendix G3 — Additional

Methodology and Results

December 2012 G3-33

FIGURE G3-31

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Lake Powell Pool Elevation < 3,490 Indicator Metric (below power pool of 3,490 feet in any 1 month)

FIGURE G3-32

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Lake Powell Pool Elevation < 3,490 Indicator Metric (below power pool of 3,490 feet msl in any 1 month)
Colorado River Basin

Water Supply and Demand Study

G3-34 December 2012

FIGURE G3-33

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Upper Basin Electrical Power Generated Indicator Metric (below 4,450 GWh per year for more than three consecutive years) 

FIGURE G3-34

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Upper Basin Electrical Power Generated Indicator Metric (below 4,450 GWh per year for more than three consecutive years)
Appendix G3 — Additional

Methodology and Results

December 2012 G3-35

FIGURE G3-35

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Lake Mead Pool Elevation <1,050 feet Indicator Metric (below 1,050 feet in any 1 month of any year)

FIGURE G3-36

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Lake Mead Pool Elevation <1,050 feet Indicator Metric (below 1,050 feet in any 1 month of any year)
Colorado River Basin

Water Supply and Demand Study

G3-36 December 2012

FIGURE G3-37

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Lake Mead Downstream Safe Channel Capacity Indicator Metric (flow greater than 28,000 cfs in any 1 month)

FIGURE G3-38

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Lake Mead Downstream Safe Channel Capacity Indicator Metric (flow greater than 28,000 cfs in any 1 month)
Appendix G3 — Additional

Methodology and Results

December 2012 G3-37 

FIGURE G3-39

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Colorado River Optimal Boating Flow Days Indicator Metric (below 10th percentile of control run)

FIGURE G3-40

Percent of Year Vulnerable Without Options and Strategies by Scenario and Time Period, 

Colorado River Optimal Boating Flow Days Indicator Metric (below 10th percentile of control run)
Colorado River Basin

Water Supply and Demand Study

G3-38 December 2012

FIGURE G3-41

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Green River Optimal Boating Flow Days Indicator Metric (below 10th percentile of control run)

FIGURE G3-42

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Green River Optimal Boating Flow Days Indicator Metric (below 10th percentile of control run)
Appendix G3 — Additional

Methodology and Results

December 2012 G3-39

FIGURE G3-43

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

San Juan River Optimal Boating Flow Days Indicator Metric (below 10th percentile of control run)

FIGURE G3-44

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

San Juan River Optimal Boating Flow Days Indicator Metric (below 10th percentile of control run)
Colorado River Basin

Water Supply and Demand Study

G3-40 December 2012

FIGURE G3-45

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Colorado River Acceptable Boating Flow Days Indicator Metric (below minimum of control run)

FIGURE G3-46

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Colorado River Acceptable Boating Flow Days Indicator Metric (below minimum of control run)
Appendix G3 — Additional

Methodology and Results

December 2012 G3-41

FIGURE G3-47

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Green River Acceptable Boating Flow Days Indicator Metric (below minimum of control run)

FIGURE G3-48

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Green River Acceptable Boating Flow Days Indicator Metric (below minimum of control run)
Colorado River Basin

Water Supply and Demand Study

G3-42 December 2012

FIGURE G3-49

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

San Juan River Acceptable Boating Flow Days Indicator Metric (below minimum of control run)

FIGURE G3-50

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

San Juan River Acceptable Boating Flow Days Indicator Metric (below minimum of control run)
Appendix G3 — Additional

Methodology and Results

December 2012 G3-43

FIGURE G3-51

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Blue Mesa Shoreline Pubic Use Facility Indicator Metric (pool elevation below 7,433 feet in any 1 month May through Sept)

FIGURE G3-52

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Blue Mesa Shoreline Pubic Use Facility Indicator Metric (pool elevation below 7,433 feet in any 1 month May through Sept)
Colorado River Basin

Water Supply and Demand Study

G3-44 December 2012

FIGURE G3-53

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Navajo Shoreline Public Use Facility Indicator Metric (pool elevation below 6,025 feet in any 1 month April through Oct) 

FIGURE G3-54

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Navajo Shoreline Public Use Facility Indicator Metric (pool elevation below 6,025 feet in any 1 month April through Oct) 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-45

FIGURE G3-55

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Flaming Gorge Shoreline Public Use Facility Indicator Metric (pool elevation below 6,019 feet in any 1 month May through Sept) 

FIGURE G3-56

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Flaming Gorge Shoreline Public Use Facility Indicator Metric (pool elevation below 6,019 feet in any 1 month May through Sept)
Colorado River Basin

Water Supply and Demand Study

G3-46 December 2012

FIGURE G3-57

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Powell Shoreline Public Use Facility Indicator Metric (pool elevation below 3,560 feet in any 1 month May through Sept)

FIGURE G3-58

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Powell Shoreline Public Use Facility Indicator Metric (pool elevation below 3,560 feet in any 1 month May through Sept)
Appendix G3 — Additional

Methodology and Results

December 2012 G3-47

FIGURE G3-59

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Mead Shoreline Public Use Facility Indicator Metric (pool elevation below 1,080 feet in any 1 month)

FIGURE G3-60

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Mead Shoreline Public Use Facility Indicator Metric (pool elevation below 1,080 feet in any 1 month)
Colorado River Basin

Water Supply and Demand Study

G3-48 December 2012

FIGURE G3-61

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Colorado River Indicator Metric (ecological vulnerability)

FIGURE G3-62

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Colorado River Indicator Metric (ecological vulnerability)
Appendix G3 — Additional

Methodology and Results

December 2012 G3-49

FIGURE G3-63

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Green River Indicator Metric (ecological vulnerability)

FIGURE G3-64

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Green River Indicator Metric (ecological vulnerability)
Colorado River Basin

Water Supply and Demand Study

G3-50 December 2012

FIGURE G3-65

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

San Juan River Indicator Metric (ecological vulnerability)

FIGURE G3-66

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

San Juan River Indicator Metric (ecological vulnerability)
Appendix G3 — Additional

Methodology and Results

December 2012 G3-51

FIGURE G3-67

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Yampa River Indicator Metric (ecological vulnerability)

FIGURE G3-68

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Yampa River Indicator Metric (ecological vulnerability)
Colorado River Basin

Water Supply and Demand Study

G3-52 December 2012

FIGURE G3-69

Percent of Traces Vulnerable Without Options and Strategies by Scenario and Time Period, 

Hoover Dam to Davis Dam Flow Reductions Indicator Metric (greater than 845 thousand acre-feet (kaf) in any 1 year)

FIGURE G3-70

Percent of Years Vulnerable Without Options and Strategies by Scenario and Time Period, 

Hoover Dam to Davis Dam Flow Reductions Indicator Metric (greater than 845 kaf in any 1 year)
Appendix G3 — Additional

Methodology and Results

December 2012 G3-53

3.2 Vulnerable Conditions 

Additional detail regarding the vulnerable conditions analysis in the Study is provided below. 

Included are the statistical algorithm used to identify vulnerable conditions for each water 

delivery indicator metric as well asan example application of the algorithm. In addition, results 

from the vulnerable conditions analysis for each metric, including a summary table and scatter 

plot, and statistics summarizing the performance of the algorithm are provided. 

3.2.1 Defining Vulnerable Conditions Using the Patient Rule Induction Method 

The Study uses the Patient Rule Induction Method (PRIM) (Friedman and Fisher, 1999) to 

identify vulnerable conditions. PRIM employs statistical algorithms to evaluate CRSS results and 

define different descriptions of vulnerable conditions. Each definition comprises a set of range 

restrictions for a set of variables. PRIM both (1) identifies those variables that are useful to 

describe vulnerabilities and (2) defines specific threshold values for each variable. 

PRIM calculates possible descriptions of the vulnerabilities that differ based on the variables 

included and their assigned thresholds. PRIM computes three measures of merit to help 

determine how well a particular description explains vulnerable futures: 

• Coverage: The fraction of all the vulnerable futures that have the vulnerable conditions. 

(A vulnerable future is one where the strategy does not meet its objectives.) Ideally, the 

vulnerable conditions would contain all the vulnerable futures and coverage would be 

100 percent. 

• Density: The fraction of all the futures in which the vulnerable conditions hold that are 

actually vulnerable (fail to meet their objectives). Ideally, all the futures within the 

vulnerable conditions would be vulnerable and density would be 100 percent. 

• Interpretability: The ease with which users can understand the information conveyed by 

the vulnerable conditions. The number of conditions in the set serves as a proxy for 

interpretability. The smaller the number of conditions, the higher the interpretability.

These three measures are generally in tension with one another. For instance, choosing a set of 

conditions that explains more-vulnerable outcomes (higher coverage) will also likely explain a 

higher percentage of non-vulnerable outcomes (lower density). 

3.2.2 Patient Rule Induction Method Example

Consider a set of 20 simulations, 4 of which are considered vulnerable. Each simulation is 

defined by inputs (X, Y, and Z) that can take a value between 0 and 1, as shown in figure G3-71. 

Figure G3-72 shows each simulation result graphically with respect to inputs X (horizontal axis), 

Y (vertical axis), and Z (size of symbol). The red lines and yellow shading indicate the input 

range restrictions for one set of vulnerable conditions. 
Colorado River Basin

Water Supply and Demand Study

G3-54 December 2012

FIGURE G3-71 

Example Input Values (X, Y, and Z) for 20 Simulations and Ranges Defining the Vulnerable Conditions 

Red symbols indicate simulations that are vulnerable. X’s indicate simulations described by the vulnerable conditions. Vertical red 

lines and yellow shading indicate ranges of one characterization of the vulnerable conditions. 

FIGURE G3-72 

Graphical Representation of 20 Simulation Outcomes with Thresholds for Vulnerable Conditions 

Red symbols indicate simulations that are vulnerable. X’s indicate simulations described by the vulnerable conditions. X and Y 

thresholds are shown by the red lines. The size of each point is defined by the Z variable. The yellow shaded region represents the 

region of the input space that defines the vulnerability. There is no restriction on the Z variable for this vulnerability description.
Appendix G3 — Additional

Methodology and Results

December 2012 G3-55

PRIM can define different vulnerable conditions for these results. Table G3-1 lists the definition, 

coverage, and density results for four different sets of vulnerable conditions. The conditions 

shown in figure G3-71, for example, restricts the X and Y variables and describe three of the 

four vulnerable simulations (75 percent coverage) and three out of the four simulations described 

by the definition are vulnerable (75 pecent density). The other vulnerability definitions shown in 

table G3-1 show the tradeoff between coverage, density, and number of restrictions. PRIM 

presents the user with a set of vulnerable conditions on the frontier of the density coverage tradeoff, and the user then selects the set of conditions most appropriate for the analysis.

TABLE G3-1 

Example Statistics for Several Different Example PRIM Vulnerable Conditions 

Definition Coverage Density

X < 0.2

Y < 0.4

2/4 = 50% 2/2 = 100%

X < 3.75

Y < 4.35

3/4 = 75% 3/4 = 75%

X < 3.75

Y < 4.35

Z < 0.6

3/4 = 75% 3/3 = 100%

X < 0.5

Y < 0.55

4/4 = 100% 4/6 = 67%

Note: Shaded row describes results shown in figures G3-71 and G3-72.

3.2.3 Vulnerable Conditions Without Additional Options and Strategies

Results from the analysis of vulnerable conditions in a future without additional options and 

strategies are shown in table G3-2 for all water delivery indicator metrics. For quantitative inputs 

(e.g., annual mean natural flow at Lees Ferry from 2012 to 2060), the cells include a graphical 

illustration of the restrictions. In these plots, the blue line shows the range of input values across 

all traces. Annual mean natural flow from 2012 to 2060, for example, ranges from 10 to 18.5 

million acre-feet per year (mafy). The superimposed red line shows the subset of this range 

included in the definition of the vulnerable condition (e.g., all traces with mean 2012 to 2060 

flow less than 13.8 maf). Finally, the words in between the columns indicate whether just one of 

the conditions needs to be met to fall within the vulnerable conditions (“OR”) or whether all 

conditions must be met to fall within the vulnerable conditions (“AND”). 
Colorado River Basin

Water Supply and Demand Study

G3-56 December 2012

TABLE G3-2 

Vulnerable Conditions Defined for Each Water Delivery Indicator Metric
Appendix G3 — Additional

Methodology and Results

December 2012 G3-57

TABLE G3-2 

Vulnerable Conditions Defined for Each Water Delivery Indicator Metric
Colorado River Basin

Water Supply and Demand Study

G3-58 December 2012

Statistics from the PRIM analysis are summarized in table G3-3. In general, the algorithm 

provided usable results in all cases, with greater than 80 percent coverage and density for all but 

one metric and a small number of restricted dimensions to allow for better interpretation. It 

should be noted, however, that the large proportion of vulnerable traces for the four shortage 

metrics complicate the overall analysis, because it is more difficult to distinguish conditions 

producing vulnerability when a vulnerability occurs in a large majority of the CRSS simulations. 

TABLE G3-3 

Coverage and Density Results for Water Delivery Vulnerable Conditions in Baseline

Indicator Metric

Vulnerable 

Traces Coverage Density

Upper Basin Shortage 86% 98% 95%

Lee Ferry Deficit 19% 85% 87%

Lake Mead Pool Elevation 47% 86% 72%

Lower Basin Shortage (1 maf over 2 years) 86% 99% 90%

Lower Basin Shortage (1.5 maf over 5 years) 92% 100% 94%

Remaining Demand Above Lower Division States’ Basic 

Apportionment 100% 100% 100%

In the visual summaries below, each point represents one trace in the analysis, characterized 

according to long-term mean annual flow (y-axis) or mean annual flow during the driest 8-year 

period (x-axis). Red points indicate traces with at least one vulnerability during the simulation, 

while gray points mark traces in which no vulnerability occurs. The yellow region (lower left) in 

the figure summarizes the vulnerable condition boundaries identified in the analysis; each trace 

that falls within this region is denoted with an x, while each trace outside is marked with an o.

Figures G3-73 through G3-78 present scatter plots that provide a visual summary of the 

vulnerable condition for each water delivery indicator metric. 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-59

FIGURE G3-73

Scatter Plot of Vulnerable Conditions for the Upper Basin Shortage (exceeds 25% of requested depletion in any 1 year) Indicator 

Metric Without Options and Strategies 

FIGURE G3-74

Scatter Plot of Vulnerable Conditions for the Lee Ferry Deficit (exceeds zero in any 1 year) Indicator Metric Without Options and 

Strategies 
Colorado River Basin

Water Supply and Demand Study

G3-60 December 2012

FIGURE G3-75

Scatter Plot of Vulnerable Conditions for the Lake Mead Pool Elevation <1,000 feet msl (below 1,000 feet msl in any 1 month) 

Indicator Metric Without Options and Strategies 

FIGURE G3-76

Scatter Plot of Vulnerable Conditions for the Lower Basin Shortage (exceeds 1 maf over any 2-year window) Indicator Metric 

Without Options and Strategies 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-61

FIGURE G3-77

Scatter Plot of Vulnerable Conditions for the Lower Basin Shortage (exceeds 1.5 maf over any 5-year window) Indicator Metric 

Without Options and Strategies 

FIGURE G3-78

Scatter Plot of Vulnerable Conditions for the Remaining Demand Above Lower Division States’ Basic Apportionment (exceeds 

moving threshold in any 1 year) Indicator Metric Without Options and Strategies 
Colorado River Basin

Water Supply and Demand Study

G3-62 December 2012

4.0 Evaluation of System Reliability with Options and 

Strategies

4.1 Allocating Benefits from Options to the System Versus Regions 

The system reliability modeling with options and strategies first aimed to quantify the range of 

action that might be required to reduce/mitigate system vulnerabilities meeting demand of the 

Lower Division States above 7.5 maf only during Surplus Conditions. For this assessment, 

Portfolio A was evaluated to estimate the level of system improvement that could be achieved 

were most options implemented. 

The water demand assesessment confirmed that the Lower Division States have demand above 

their basic apportionment of 7.5 maf. As a result, further investigation was necessary to quantify 

the potential range of option magnitudes needed to address demands within and beyond Lower 

Division States’ basic apportionment. As with the system benefit assessment, the same Portfolio 

A was evaluated to estimate the amount of demand above Lower Division States’ basic 

apportionment that could be met were most options implemented. 

To implement these two approaches, CRSS used two sets of assumptions aimed at evaluating

option implementation for maximum system benefit:

• Options are implemented according to the static schedule (implemented as soon as options is 

available) 

• Demands above Lower Division States’ basic apportionment are only met during Surplus 

Conditions or via implementation of local options such as conservation (the effect of 

conservation is that more demand can be met with a given delivery, and some of the new 

demand satisfied would otherwise be considered demand above Lower Division States’ basic 

apportionment). 

The following alternative set of assumptions were used to evaluate option implementation that 

maximized meeting demand above Lower Division States’ basic apportionment: 

• Options are implemented according to the static schedule and whenever possible, yield is 

directed toward meeting demands above Lower Division States’ basic apportionment. 

• If demands above Lower Division States’ basic apportionment are completely satisfied, any 

remaining option yield is put towards system benefit.

Any Basin-wide strategy must take into consideration that the Lower Division States have 

demand above 7.5 maf when aiming to reduce system vulnerabilities. Thus, an approach was 

developed in which demands above Lower Division States’ basic apportionment and system 

resources both benefit from option yield. Such a situation could be realized by various avenues. 

One simple approach is to assume that option yield would first be used to replenish Lake Mead 

to some level. Beyond that, remaining water would be delivered to demands above Lower 

Division States’ basic apportionment. By solidifying a storage base, future risk is mitigated while 

benefitting other system resources such as hydropower or water deliveries. As discussed earlier, 

numerous mechanism/threshold combinations could be crafted to achieve a balance between 

system and demand above Lower Division States’ basic apportionment benefit. In reality, this 

would likely to be determined by a host of factors yet to be identified, such as option specifics, 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-63

realized demand, and project funding. Owing to the aforementioned uncertainty and in the 

interest of simplicity, it was concluded that a minimum pool elevation at Lake Mead would need 

to be maintained before option yield could benefit demands above Lower Division States’ basic 

apportionment. Analysis and selection of the minimum pool elevation threshold is provided in 

the following section. It is important to emphasize that the policy modeled here is to demonstrate 

a concept only. 

4.1.1 System vs. Regional Benefit Threshold Sensitivity Analysis

To inform the selection of the pool elevation threshold in the above mentioned hybrid, 

system/regional benefit framework, a sensitivity analysis was performed. The analysis consisted 

of running CRSS with a range of potential thresholds for a small subset of the quantified supply, 

demand, and reservoir operations scenario combinations (specifically, Downscaled GCM 

(general circulation model) Projected and Observed Resampled hydrologies with the Current 

Projected demand scenario and the 2007 Interim Guidelines extended). Elevations for potential 

thresholds were identified matching the current shortage tier elevations (Reclamation, 2007) of 

(1,025 feet, 1,050 feet, and 1,075 feet msl). Overall, results showed minimal sensitivity between 

the three values considered. Figure G3-79 shows water supply indicator metric vulnerabilities for 

the Baseline and three thresholds. Portfolio capacity to reduce the Lake Mead below 1,000 feet 

msl vulnerability was essentially the same across all thresholds. Shortage vulnerability frequency 

actually increases slightly with higher thresholds. This is because changing to system benefit 

precludes the option water from being available to offset shortages. In contrast, the lower 

thresholds allow water to be available longer to offset shortages (recall that option water 

delivered to each state first meet any shortage volumes then demands above Lower Division 

States’ basic apportionment). For the remaining demand above Lower Division States’ basic 

apportionment vulnerability, all three thresholds show strong improvements. The lowest 

threshold does show the greatest improvement because more option water is available to meet 

those demands. However, threshold selection does not appear to be significantly altering 

portfolio performance. In light of these observations, the threshold was selected to be 1,050 feet 

msl. This elevation allows for some option yield to address shortage volumes (between pool 

elevations 1,050 and 1,075 feet msl), but does not wait until mandatory reconsultation (pool 

elevation 1,025 feet msl) to switch to a system benefit (Reclamation, 2007). 
Colorado River Basin

Water Supply and Demand Study

G3-64 December 2012

FIGURE G3-79

Water Delivery Indicator Metrics; Baseline and Portfolio A results for Downscaled GCM and Observed Resampled Scenario

Hydrologies with Current Projected Demand Scenario and 2007 Interim Guidelines extended. 

Note: The three thresholds considered for system versus regional benefit were Lake Mead at 1,025 feet, 1,050 feet, and 

1,075 feet msl. 

4.2 Signposts 

Technical Report G – System Reliability Analysis and Evaluation of Options and Strategies

describes the development of dynamic portfolios for the study. In contrast to static investments, 

dynamic portfolios are designed to be adaptive to changing conditions in the Basin and to invest 

in additional options when vulnerabilities become more likely. Key to these dynamic portfolios 

are signposts based on observable conditions that occur in advance of a one or more water 

delivery vulnerabilities. The development of these signposts is described below. The discussion 

includes a further description of signposts and an example of signpost implementation. The 

results from the analysis performed using CRSS simulations are provided to identify effective 

and accurate signposts occurring in advance of water delivery vulnerabilities. 

4.2.1 Signpost Implementation Example

In the Study, signposts were developed only for water delivery vulnerabilities that were used to 

trigger option implementation. When a signpost is observed, options are implemented from those 

available at that particular time. In taking preemptive steps, the benefit of a single option is 

allowed to accrue, possibly reducing the need for a larger, more reactive investment. By design, 

signposts are based on system factors that can change in response to the already implemented 

options, helping to avoid over-investment. 

For example, the 5-year running mean natural streamflow at Lees Ferry, coupled with the 

current-year level of Lake Mead, could be an effective signpost to project those futures in which 

Lake Mead pool elevation is vulnerable. When Lake Mead is below a certain level and natural 

streamflow appears to be consistently low, options to address an impending vulnerability could 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-65

be implemented. Figure G3-80 shows a simple example of a signpost successfully triggering a 

new option in 2043 to prevent a Lake Mead pool elevation vulnerability (pool elevation below 

1,000 feet msl) from occurring later in the simulation.

FIGURE G3-80

Illustration of a Signpost that Triggers Augmentation to Prevent Lake Mead Levels from Dropping Below 1,000 Feet msl 

The red line represents Lake Mead elevations for a single CRSS simulation under the Baseline management. The green line reflects 

augmentation that increases Lake Mead levels. The signpost is set at a level of 1,050 feet msl. As a simple approximation, the 

augmentation adds 100 feet to Lake Mead levels each year after signpost is triggered (2043).

4.2.2 Signpost Selection

To choose signposts for the dynamic portfolios, a large set of potential signposts (around 200) 

for the five of the six water delivery indicator metrics were first generated.2 Each signpost is a 

unique combination of streamflow and reservoir elevation level thresholds, drawn from a wide 

range of possible values. For each metric, the signpost was evaluated in terms of how well it 

predicts vulnerabilities and non-vulnerabilities. A true positive calculation for a signpost reports 

the percent of years with a vulnerability in which the signpost is triggered in advance by a 

specified amount of lead time. A given signpost can be evaluated for different lead times, for 

example, between 3 and 10 years. The true negative rate for a signpost, conversely, reports the 

percent of futures with no vulnerability in which the signpost is also not measured. Lead times 

do not affect the true negative rates. Larger numbers for both these rates indicate more useful 

signposts for water planner. A low true positive rate would cause under investment in options, 

while a low true negative rate would likely result in over-investment.

 

2 No leading signpost was developed for remaining demand above apportionment, because all traces produce a vulnerability for this indicator 

metric at some point in the simulation in a future without additional options and strategies. Instead, the amount of remaining demand above 

apportionment itself serves as a signpost for future vulnerability, triggering options when demand is with 100 kaf of the vulnerability threshold.
Colorado River Basin

Water Supply and Demand Study

G3-66 December 2012

For example, Figure G3-81 shows the signpost analysis results for the Lake Mead vulnerability 

for a 5-year lead time. Each point represents one possible signpost, and each signpost has two 

components: 

• The Lake Mead pool elevation threshold (differentiated with symbols) 

• The 5-year running mean natural streamflow threshold (differentiated by color)

Charts such as this one were reviewed to select signposts that struck a favorable balance between 

true positive and true negative rates. In general, this involved selecting a point along the upperright edge of the results (the optimal frontier). 

FIGURE G3-81

True Positive/True Negative Tradeoff Curve for Possible Lake Mead Pool Elevation <1,000 feet msl Signposts 

Each point is one possible signpost, defined here as unique combination of a threshold for 5-year running mean natural streamflow 

at Lees Ferry (colors) and a threshold for Lake Mead pool elevation (symbols), measured 3 years prior to the vulnerability occurring. 

True positive and true negative rates are shown on the y- and x-axis, respectively.

Similar scatter plots used to develop signposts for the other water delivery indicator metrics are 

shown in the figures G3-82 through G3-84. 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-67

FIGURE G3-82 

True Positive/True Negative Tradeoff Curve for Possible Lee Ferry Deficit Signposts

Each point is one possible signpost, defined here as unique combination of a threshold for 5-year running mean natural streamflow 

at Lees Ferry (colors) and a threshold for Lake Powell pool elevation (symbols), measured 5 years prior to the vulnerability 

occurring. True positive and true negative rates are shown on the y- and x-axis, respectively.

FIGURE G3-83

True Positive/True Negative Tradeoff Curve for Possible Lower Basin Shortage (greater than 1 maf over 2 years) Signposts 

Each point is one possible signpost, defined here as unique combination of a threshold for 5-year running mean natural streamflow 

at Lees Ferry (colors) and a threshold for Lake Mead pool elevation (symbols), measured 3 years prior to the vulnerability occurring. 

True positive and true negative rates are shown on the y- and x-axis, respectively.
Colorado River Basin

Water Supply and Demand Study

G3-68 December 2012

FIGURE G3-84

True Positive/True Negative Tradeoff Curve for Possible Lower Basin Shortage (> 1.5 maf over 5 years) Signposts 

Each point is one possible signpost, defined here as unique combination of a threshold for 5-year running mean natural streamflow 

at Lees Ferry (colors) and a threshold for Lake Mead pool elevation (symbols), measured 3 years prior to the vulnerability occurring. 

True positive and true negative rates are shown on the y- and x-axis, respectively.

4.3 Study Portfolio Evaluation

This section includes selected additional results from CRSS with options and strategies not 

otherwise provided in Technical Report G. Included are subsections showing the potential 

changes in system response variables, reductions in water delivery vulnerabilities with portfolios 

implemented, and implemented options, respectively. 

4.3.1 System Response Variables

Figures G3-85 to G3-102 show system response variable results from CRSS modeling with 

options and strategies. These variables include river flow, reservoir storage, reservoir release, 

reservoir pool elevation, shortage, surplus, and energy production. Percentile time series plots 

and cumulative distribution functions used to present these results show scenarios combined on a 

by portfolio basis. 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-69

FIGURE G3-85

10th, 50th, 90th Percentiles for Annual Flow of Green River at Green River, Utah, With Options and Strategies

FIGURE G3-86

10th, 50th, 90th Percentiles for Annual Flow of Colorado River near Cisco, Utah, With Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-70 December 2012

FIGURE G3-87

10th, 50th, 90th Percentiles for Annual Flow of San Juan River near Bluff, Utah, With Options and Strategies

FIGURE G3-88

10th, 50th, 90th Percentiles for Total Storage Above Lake Powell With Options and Strategies
Appendix G3 — Additional

Methodology and Results

December 2012 G3-71

FIGURE G3-89

10th, 50th, 90th Percentiles for Upper Basin Annual Shortage with Options and Strategies

FIGURE G3-90

10th, 50th, 90th Percentiles for Lake Powell Pool Elevation With Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-72 December 2012

FIGURE G3-91

10th, 50th, 90th Percentiles for Total Upper Basin Energy Production with Options and Strategies
Appendix G3 — Additional

Methodology and Results

December 2012 G3-73

FIGURE G3-92

Cumulative Density Function for Total Upper Basin Energy Production With Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-74 December 2012

FIGURE G3-93

10th, 50th, 90th Percentiles for Powell Water Year Release With Options and Strategies

FIGURE G3-94

Percent Traces and 10th, 50th, and 90th Percentiles for Lee Ferry Deficit With Options and Strategies
Appendix G3 — Additional

Methodology and Results

December 2012 G3-75

FIGURE G3-95

10th, 50th, 90th Percentiles for Lake Mead Pool Elevation With Options and Strategies

FIGURE G3-96

Percent Traces and 10th, 50th, and 90th Percentiles for Lower Basin Annual Total Shortage (including remaining demands 

above Lower Division States’ basic apportionments) With Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-76 December 2012

FIGURE G3-97

Percent Traces and 10th, 50th, 90th Percentiles of Lower Basin Annual Regulatory Shortage With Options and Strategies

FIGURE G3-98

Percent Traces with Lower Basin Surplus With Options and Strategies
Appendix G3 — Additional

Methodology and Results

December 2012 G3-77

FIGURE G3-99

10th, 50th, 90th Percentiles for Hoover Energy Production With Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-78 December 2012

FIGURE G3-100

Cumulative Density Function for Hoover Energy Production With Options and Strategies
Appendix G3 — Additional

Methodology and Results

December 2012 G3-79

FIGURE G3-101

10th, 50th, 90th Percentiles for Parker and Davis Energy Production With Options and Strategies
Colorado River Basin

Water Supply and Demand Study

G3-80 December 2012

FIGURE G3-102

Cumulative Density Function for Parker and Davis Energy Production With Options and Strategies

4.3.2 Indicator Metrics

Figures G3-103 through G3-113 are histograms showing the percent of simulated traces with 

vulnerable years, in 5-year bins (e.g., 1 to 5 years vulnerable, 6 to 10 years vulnerable). Bins for 

the number of vulnerable years are shown on the y-axis, and the proportion of vulnerable traces 

is shown on the x-axis. Results are further subdivided to show the set of traces inside (top panel) 

or outside (bottom panel) the vulnerable conditions previously defined for each water delivery 

indicator metric. 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-81

FIGURE G3-103

Number of Vulnerable Years Across Traces 2012–2060 for All Scenarios Upper Basin Shortage (exceeds 25% of requested 

depletion in any 1 year) Indicator Metric, Inside Vulnerable Conditions

FIGURE G3-104

Number of Vulnerable Years Across Traces 2012–2060 for All Scenarios Upper Basin Shortage (exceeds 25% of requested 

depletion in any 1 year) Indicator Metric, Outside Vulnerable Conditions

FIGURE G3-105

Number of Vulnerable Years Across Traces 2012–2060 for All Scenarios Lee Ferry Deficit (exceeds zero in any 1 year) Indicator 

Metric, Inside Vulnerable Conditions
Colorado River Basin

Water Supply and Demand Study

G3-82 December 2012

FIGURE G3-106

Number of Vulnerable Years Across Traces 2012–2060 for All Scenarios Lee Ferry Deficit (exceeds zero in any 1 year) Indicator 

Metric, Outside Vulnerable Conditions

FIGURE G3-107

Number of Vulnerable Years Across Traces 2012–2060 for All Scenarios Lake Mead Pool Elevation <1,000 feet msl (below 

1,000 feet msl in any 1 month) Indicator Metric, Inside Vulnerable Conditions

FIGURE G3-108 

Number of Vulnerable Years Across Traces 2012–2060 for All Scenarios Lake Mead Pool Elevation <1,000 feet msl (below 

1,000 feet msl in any 1 month) Indicator Metric, Outside Vulnerable Conditions
Appendix G3 — Additional

Methodology and Results

December 2012 G3-83

FIGURE G3-109

Number of Vulnerable Years Across Traces 2012–2060 for All Scenarios Lower Basin Shortage (exceeds 1 maf over any 2-year 

window) Indicator Metric, Inside Vulnerable Conditions

FIGURE G3-110

Number of Vulnerable Years Across Traces 2012–2060 for All Scenarios Lower Basin Shortage (exceeds 1 maf over any 2-year 

window) Indicator Metric, Outside Vulnerable Conditions
Colorado River Basin

Water Supply and Demand Study

G3-84 December 2012

FIGURE G3-111

Number of Vulnerable Years Across Traces 2012–2060 for All Scenarios Lower Basin Shortage (exceeds 1.5 maf over any 

5-year window) Indicator Metric, Inside Vulnerable Conditions

FIGURE G3-112

Number of Vulnerable Years Across Traces 2012–2060 for All Scenarios Lower Basin Shortage (exceeds 1.5 maf over any 

5-year window) Indicator Metric, Outside Vulnerable Conditions

FIGURE G3-113

Number of Vulnerable Years Across Traces 2012–2060 for All Scenarios Remaining Demand Above Lower Division States’ 

Basic Apportionment (exceeds moving threshold in any 1 year) Indicator Metric, All Traces (all traces are vulnerable)
Appendix G3 — Additional

Methodology and Results

December 2012 G3-85

Another way to visualize these results is by looking for patterns of vulnerable traces across the 

dimensions that define the vulnerable conditions for each water delivery indicator metric. 

Figures G3-114 through G3-119 present the same scatter plots showing vulnerable conditions as 

shown earlier in this appendix, but with portfolios implemented. The axes show the dimensions 

that define the vulnerable conditions, which vary by water delivery metric. Each point in the plot 

shows one trace outcome across the 2012 to 2060 time span, with vulnerable traces colored red 

and non-vulnerable traces colored gray. Points inside the vulnerable conditions for a given metric 

are marked with x’s, and points outside are marked with o’s.

In these figures, the vulnerable conditions definitions are constant across all portfolios for 

comparison with the Baseline, but the pattern of vulnerable traces varies by portfolio to show 

where vulnerable traces (red points) become non-vulnerable (gray points) with the portfolio. 
Colorado River Basin

Water Supply and Demand Study

G3-86 December 2012

FIGURE G3-114

Reduction in Vulnerable Traces with Portfolios in Place, Upper Basin Shortage (exceeds 25% of requested depletion in any 

1 year) Indicator Metric
Appendix G3 — Additional

Methodology and Results

December 2012 G3-87

FIGURE G3-115

Reduction in Vulnerable Traces with Portfolios in Place, Lee Ferry Deficit (exceeds zero in any 1 year) Indicator Metric
Colorado River Basin

Water Supply and Demand Study

G3-88 December 2012

FIGURE G3-116

Reduction in Vulnerable Traces with Portfolios in Place, Lake Mead Pool Elevation <1,000 feet msl (below 1,000 feet msl in any 

1 month) Indicator Metric
Appendix G3 — Additional

Methodology and Results

December 2012 G3-89

FIGURE G3-117

Reduction in Vulnerable Traces with Portfolios in Place, Lower Basin Shortage (exceeds 1 maf over any 2-year window) 

Indicator Metric
Colorado River Basin

Water Supply and Demand Study

G3-90 December 2012

FIGURE G3-118

Reduction in Vulnerable Traces with Portfolios in Place, Lower Basin Shortage (exceeds 1.5 maf over any 5-year window) 

Indicator Metric
Appendix G3 — Additional

Methodology and Results

December 2012 G3-91

FIGURE G3-119

Reduction in Vulnerable Traces with Portfolios in Place, Remaining Demand Above Lower Division States’ Basic Apportionment 

(exceeds moving threshold in any 1 year) Indicator Metric
Colorado River Basin

Water Supply and Demand Study

G3-92 December 2012

Results from the analysis of vulnerable conditions in a future with Portfolio A implemented 

strategies are shown in table G3-4 for all water delivery indicator metrics. In this table, results 

are provided from the Baseline and also show the change in vulnerability with the portfolio in 

place. The second column shows the change in the overall proportion of vulnerable traces, and

the columns to the right describe how the vulnerable conditions shift when Portfolio A is 

implemented. In each cell, the blue bars again show the full range of the flow characterization or 

other quantitative input to the modeling across all scenarios; the red bars show the range of the 

restriction that helps to define the new vulnerable condition; and the yellow bars (with subscript 

values) show where the restriction identified for the Baseline simulations was previously 

defined. Table G3-5 provides the density and coverage statistics for the vulnerable conditions 

presented in table G3-4. 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-93

TABLE G3-4

Vulnerable Conditions Defined for Each Water Delivery Indicator Metric for Portfolio A
Colorado River Basin

Water Supply and Demand Study

G3-94 December 2012

TABLE G3-4 

Vulnerable Conditions Defined for Each Water Delivery Indicator Metric for Portfolio A 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-95

TABLE G3-4 

Vulnerable Conditions Defined for Each Water Delivery Indicator Metric for Portfolio A 
Colorado River Basin

Water Supply and Demand Study

G3-96 December 2012

TABLE G3-5 

Coverage and Density Results for Water Delivery Vulnerable Conditions in Portfolio A

Indicator Metric Vulnerable 

Traces Coverage Density

Upper Basin Shortage 69% 96% 85%

Lee Ferry Deficit 6% 77% 57%

Lake Mead Pool Elevation 24% 53% 80%

Lower Basin Shortage (1 maf over 2 years) 62% 84% 80%

Lower Basin Shortage (1.5 maf over 5 years) 83% 77% 89%

Remaining Demand Above Lower Division States’

Basic Apportionment 26% 57% 57%

5.0 Summary 

This appendix offers supplementary content for Technical Report G – System Reliability Analysis 

and Evaluation of Options and Strategies. The results and methods presented herein focus on 

system response variables, indicator metrics, vulnerability and vulnerable conditions. For 

individual metric results, see appendix G4. 
Appendix G3 — Additional

Methodology and Results

December 2012 G3-97

6.0 References 

Bureau of Reclamation (Reclamation). 2012. Aspinall Unit Operations Final Environmental 

Impact Statement. January. 

Bureau of Reclamation (Reclamation). 2007. Colorado River Interim Guidelines for Lower 

Basin Shortages and Coordinated Operations of Lake Powell and Lake Mead Final 

Environmental Impact Statement. 

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

Impact Statement. April.

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

Environmental Impact Statement. September. 

Bureau of Reclamation (Reclamation). 2000. Colorado River Interim Surplus Criteria. 

Environmental Impact Statement. Final. December. 

Friedman, J. H., & Fisher, N. I. (1999). Bump hunting in high-dimensional data. Statistics and 

Computing, 9(2), 123–143.

McAda, C. 2003. Flow Recommendations to Benefit Endangered Fishes in the Colorado and 

Gunnison Rivers. Prepared by U.S. Fish and Wildlife Service. Grand Junction, Colorado. 

Secrist, Doug. 2012. Personal Communication. Doug Secrist, Colorado State Parks and Wildlife. 

August. 

Stahlnecker, Ken. 2012. Personal Communication. Ken Stahlnecker, National Park Service, 

August. 

Turner, Kent. 2012. Personal Communication. Kent Turner, National Park Service. July. 

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.

U.S. Fish and Wildlife Service. 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 G4

Supplemental Results

December 2012 G4-1

Appendix G4 — Supplemental Results

This appendix provides supplemental discussion and results related to the system reliability

analysis presented in Technical Report G – System Reliability Analysis and Evaluation of 

Options and Strategies for metrics identified in Technical Report D – System Reliability Metrics.

Results are presented with (portfolios) and without (Baseline) the implementation of options and 

strategies. The analysis is presented by category and subsequent attributes of interest in a series 

of six attachments, as follows:

Attachment A, Water Deliveries Metrics’ Results

o Consumptive Uses and Shortages, Other Water Deliveries 

Attachment B, Electrical Power Resources Metrics’ Results

o Electrical Power Generated, Economic Value of Electrical Power Generated, 

Available Generation Capacity, Impact on Power Rates, Water Supply System 

Pumping, Impact on Basin Funds

Attachment C, Water Quality Metrics’ Results

o Salinity, Sediment Transport, Temperature, Other Water Quality Constituents, 

Socioeconomic Impacts Related to Salinity

Attachment D, Flood Control Metrics’ Results

o Flood Control Release, Reservoir Spills, Flooding Risk

Attachment E, Recreational Resources Metrics’ Results

o Shoreline Public Use Facilities, River and Whitewater Boating, Other Recreational, 

Socioeconomic Impacts

Attachment F, Ecological Resources Category Metrics’ Results

o Flows to Support Threatened and Endangered Species, Instream Flow Rights, 

Cottonwood Recruitment Metric, Flow-Dependent Ecological Systems, Wildlife 

Refuges and Fish Hatcheries

Results are presented by portfolio with all scenario combinations grouped together. In 

accordance with the scenario planning approach employed in the Colorado River Basin Water 

Supply and Demand Study, all scenarios are plausible and results are presented to reflect the 

distribution of outcomes associated with the various scenarios considered. All scenarios have 

been resampled such that each scenario contributes equally to the distribution. Results are 

intended to be used to make relative comparisons. They are not intended to specify absolute 

values.

Information for each attribute of interest and subsequent metrics is discussed qualitatively or is 

discussed and presented as quantitative information in figures that reflect key outcomes. Where 

applicable, figures display reference values from Technical Report D – System Reliability 

Metrics. Figures include: 
Colorado River Basin

Water Supply and Demand Study

G4-2 December 2012

(1) Box and whisker type plots that show the median, 25th and 75th percentiles and 

include “whiskers” representing the 10th and 90th percentiles. The statistical data for 

a given “box” represent the metric over all combined supply and demand scenarios, 

unless otherwise noted. The boxes are presented for the Baseline as well as each 

scenario for time periods representing 2012 through 2026, 2027 through 2040, and 

2041 through 2060.

(2) Frequency and magnitude plots showing line plots relating the frequency of 

occurrence (typically the percentage of years) of an event compared to the magnitude 

of the event. These plots are also presented over time periods representing 2012

through 2026, 2027 through 2040, and 2041 through 2060.

(3) Bar charts are used to display the percent of years that met a desired target or the 

percent of years that are within a given category. The bars are also presented for the 

Baseline as well as each portfolio for time periods representing 2012 through 2026, 

2027 through 2040, and 2041 through 2060.

Quantitative discussion focuses on either the relative performance or the performance versus a 

prescribed value for individual indicator metrics. In each case, the performance over time 

without options and strategies (Baseline) is discussed first and then compared to the performance 

with options and strategies (portfolios). In many cases, the performance of individual metrics is 

gauged versus system vulnerabilities. Qualitative discussions generally use quantitative data 

indirectly to make inferences about potential system performance with respect to the attribute of 

interest. 
Appendix G4 

Attachment A

Water Deliveries Metrics’ Results

December 2012 G4-A-1 

Attachment A — Water Deliveries Metrics’ 

Results

1.0 Introduction

System reliability metrics (metrics), defined in Technical Report D – System Reliability Metrics,

were developed to assess the performance of Colorado River Basin (Basin) resources with and 

without the implementation of options and strategies. Metrics were developed for six resource 

categories (Water Deliveries, Electrical Power Resources, Water Quality, Flood Control, 

Recreational Resources, and Ecological Resources) and for numerous attributes of interest within 

each category. 

This attachment presents summary results for both the quantitative and qualitative metrics 

associated with the Water Deliveries resource category. The Water Deliveries resource attributes 

of interest are shown in table A-1. 

Results are presented by portfolio with all scenario combinations grouped together. In 

accordance with the scenario planning approach employed in the Colorado River Basin Water 

Supply and Demand Study (Study), all scenarios are plausible and results are presented to reflect 

the distribution of outcomes associated with the various scenarios considered. All scenarios have 

been resampled such that each scenario contributes equally to the distribution. Results are 

intended to be used to make relative comparisons. They are not intended to specify absolute 

values.

Information for each attribute of interest and subsequent metrics is discussed qualitatively or is 

discussed and presented as quantitative information in figures that reflect key outcomes. Where 

applicable, figures display reference values from Technical Report D – System Reliability 

Metrics. Figures include: 

(1) Box and whisker type plots that show the median, 25th and 75th percentiles and

include “whiskers” representing the 10th and 90th percentiles. The statistical data 

for a given “box” represent the metric over all combined supply and demand 

scenarios, unless otherwise noted. The boxes are presented for the Baseline as 

well as each portfolio for time periods representing 2012 through 2026, 2027 

through 2040, and 2041 through 2060. 

(2) Frequency and magnitude plots showing line plots relating the frequency of 

occurrence (typically the percentage of years) of an event compared to the 

magnitude of the event. These plots are also presented over time periods 

representing 2012 through 2026, 2027 through 2040, and 2041 through 2060. 
Colorado River Basin

Water Supply and Demand Study

G4-A-2 December 2012

TABLE A-1 

Water Delivery Metrics

Attribute of 

Interest Resource Metric Section 

Quantitative 

or Qualitative

Plot 

Type Location

Figure 

Number

Consumptive 

Uses and 

Shortages

Upper Basin 

Delivery 2.1 Quantitative Annual Upper Basin 

Aggregate A-1 

Upper Basin 

Shortage 2.1 Quantitative Annual Upper Basin 

Aggregate A-2 

Lower Basin 

Shortage 2.1 Quantitative Annual Lower Basin A-3 

Lower Basin 

Delivery 2.1 Quantitative Annual Lower Basin 

Aggregate A-4 

Lee Ferry Deficit 2.1 Quantitative Annual Colorado River at 

Lee Ferry, AZ A-5 

Remaining 

Demands above 

Lower Division 

States’ Basic 

Apportionment

2.1 Quantitative Annual Lower Basin 

Aggregate A-6 

Tribal Water 

Right Satisfaction 2.2 Qualitative NA Basin-wide NA

Other Water 

Deliveries

Navajo Reservoir 

Pool Elevation 3 Quantitative Monthly Navajo Reservoir A-7 

Lake Mead Pool 

Elevation 3 Quantitative Monthly Lake Mead A-8 

Annual Flows at 

Morelos 

Diversion Dam 

Above the 1944 

Treaty Delivery

3 Quantitative Annual Morelos Diversion 

Dam A-9 

Socioeconomic 

Impacts of 

Shortages

Socioeconomic 

Impacts of 

Shortages

4 Qualitative NA Basin-wide NA
Attachment A — Water

Deliveries Metrics’ Results

December 2012 G4-A-3 

2.0 Metrics for the Consumptive Uses and Shortages 

Attribute of Interest 

2.1 Quantitative Consumptive Uses and Shortages Metrics

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

demand nodes exist within the Colorado River Simulation System (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).

Upper and Lower Basin delivery and shortage are measures of aggregate CRSS-simulated 

consumptive use (delivery) and shortage. Increasing delivery results in better realization of full 

demand and reduction in shortage. Figures A-1 through A-4 show results associated with Upper 

and Lower Basin shortage and delivery. In addition, figures A-5 and A-6 show the Lee Ferry 

deficit (defined for purposes of the Study as the amount of flow less than an aggregate of 75 maf 

over 10 years) and the remaining demand above Lower Division States’ basic apportionment. 

For the Upper Basin, delivery increases over time under the Baseline as demand increases. 

However, shortage also increases under the Baseline, reflecting both the increased demand and 

future supply limitations. Implementation of each portfolio results in both increased delivery and 

decreased shortage. Portfolio A and Portfolio B show slightly better performance (increasing 

delivery and reducing shortage) than the other portfolios, likely due to augmentation. In 

addition, the range of potential shortage and magnitude of shortage appears to be significantly 

reduced with each portfolio. Of particular interest is that with the implementation of each 

portfolio, shortage in the 2041 to 2060 time period is similar to shortages in the 2012 through 

2026 (first) time period, even with , in general, future increase in demand and reduction in 

supply. 

Figure A-5 shows the number of years where there is a Lee Ferry deficit and the associated 

magnitude. Under the Baseline, the deficit increases in both frequency and magnitude over time. 

Implementation of each portfolio reduces both deficit frequency and magnitude, with markedly 

better performance under Portfolio A and Portfolio C. Each of these portfolios includes the 

implementation of banking through routing conserved water to a conceptual off-stream storage 

location above Lake Powell. 

For the Lower Basin, delivery decreases and shortage increases under the Baseline over time. 

This reflects future reduced supplies, while demands remain at or above apportionment. 

Implementation of each portfolio increases delivery over time to near the first time period levels 

and reduces median shortage to the first time period levels. Although median shortage across the 

scenarios is near first time period levels, there is potential for a higher magnitude of shortage 

under more-challenging scenarios. The Lower Division States currently have demands above 

basic apportionment. Under the Baseline, these demands increase through time. As each 

portfolio is implemented, these remaining demands above Lower Division States’ basic 

apportionment are reduced over time from the Baseline. Further, by the 2041 through 2060 

period, remaining demand above Lower Division States’ basic apportionment is reduced well 

below first time period levels to near zero.
Colorado River Basin

Water Supply and Demand Study

G4-A-4 December 2012

FIGURE A-1 

Annual Upper Basin Delivery 

FIGURE A-2 

Annual Upper Basin Shortage

FIGURE A-3 

Annual Lower Basin Shortage 
Attachment A — Water

Deliveries Metrics’ Results

December 2012 G4-A-5 

FIGURE A-4 

Annual Lower Basin Delivery

FIGURE A-5 

Annual Lee Ferry Deficit (10-year flow volume less than 75 million acre-feet)

FIGURE A-6 

Annual Remaining Demands Above Lower Division States’ Basic Apportionment
Colorado River Basin

Water Supply and Demand Study

G4-A-6 December 2012

2.2 Tribal Water Right Satisfaction

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

Project entitlements, was not explicitly evaluated due to CRSS’s inability to simulate water 

rights in the Upper Basin and because CRSS does not include individual Central Arizona Project 

users. Tribal deliveries will be further analyzed in future studies—see the Study Report section 

on future considerations and next steps for additional details.

3.0 Metrics for the Other Water Deliveries Attribute of 

Interest 

Several other attributes of interest related to water deliveries are important to various 

stakeholders. These attributes were evaluated for locations other than where CRSS demand 

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

the Navajo Indian Irrigation Project Diversion at Navajo Reservoir, Lake Mead at elevation 

1,000 feet above mean sea level (msl), and flows arriving at Morelos Diversion Dam. 

Figure A-7 shows CRSS simulated monthly Navajo Pool Elevation. In general, the median pool 

elevation declines over time across the scenarios for the Baseline. In addition, the 10th

percentile pool elevations drop by more than 20 feet above msl. Implementation of each 

portfolio results in higher median pool elevations across the scenarios and an increase in the 10th

percentile elevations. Note that the median elevations under Baseline and the portfolios are well 

above the minimum elevation for Navajo Irrigation Project diversion. 

Figure A-8 shows the monthly Lake Mead pool elevation. Under the Baseline there is a marked 

drop in every month over time in pool elevation. Implementation of each portfolio results in an 

increase in pool elevation over time across the scenarios. Portfolio A appears to produce 2041 

through 2060 time period pool elevations at or above the first time period elevations. However, 

for each of the portfolios, the range in potential elevations increases when compared to the first 

time period; this reflects increasing differences between scenarios through time. 

Figure A-9 presents the annual flows at Morelos Diversion Dam that are above the required 1944 

Treaty delivery. Under the Baseline, these flows decrease slightly in both magnitude and 

frequency over time. Implementation of each of the portfolios results in an increase in 

magnitude and frequency over time. 
Attachment A — Water

Deliveries Metrics’ Results

December 2012 G4-A-7 

FIGURE A-7 

Monthly Navajo Reservoir Pool Elevation 

Minimum Pool Elevation for Navajo Irrigation Project Diversion Reference Value Shown as Solid Red Line

 

FIGURE A-8 

Monthly Lake Mead Pool Elevation 

Elevation 1,000 ft msl Reference Value Shown as Solid Red Line
Colorado River Basin

Water Supply and Demand Study

G4-A-8 December 2012

FIGURE A-9 

Annual Flows at Morelos Diversion Dam Above the 1944 Treaty Delivery

4.0 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 users. Economic models of this type have been built 

and used in the past. 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 are discussed qualitatively. 

An unsure or stressed water supply could increase the potential for reduced economic activity. 

Unsure or reduced water supplies could result in new and existing water-reliant industries to 

locate elsewhere. Frequent shortage could result in reduced agricultural yield, impacting farm 

income as well as all of the associated industries. Additionally, as discussed in attachment E to 

appendix G4, reduced reservoir levels and flows could result in a reduction of recreation and 

associated income. 

Figures A-2 and A-3 present Upper and Lower Basin shortage, respectively. As shown, shortage 

is anticipated to increase in frequency and magnitude over time under the Baseline. 

Implementation of the portfolios indicates that shortage can be mitigated. For the Lower Basin, 

median shortage over time is similar to the first time period. However, the range of shortage 

increases significantly as a result of low flow/high demand scenarios. 
Appendix G4 

Attachment B

Electrical Power Resources Metrics’ Results

December 2012 G4-B-1 

Attachment B — Electrical Power Resources 

Metrics’ Results

1.0 Introduction

System reliability metrics (metrics), defined in Technical Report D – System Reliability Metrics,

were developed to assess the performance of Colorado River Basin (Basin) resources with and 

without the implementation of options and strategies. Metrics were developed for six resource 

categories (Water Deliveries, Electrical Power Resources, Water Quality, Flood Control, 

Recreational Resources, and Ecological Resources) and for numerous attributes of interest within 

each category. 

This attachment presents summary results for both the quantitative and qualitative metrics 

associated with the Electrical Power Resources category. The Electrical Power Resources 

attributes of interest are shown in table B-1. 

Results are presented on a portfolio basis, in which all scenarios are grouped together. In 

accordance with the scenario planning approach employed in the Colorado River Basin Water 

Supply and Demand Study (Study), all scenarios are plausible and results are presented to reflect 

the distribution of outcomes associated with the various scenarios considered. All scenarios have 

been resampled such that each scenario contributes equally to the distribution. Results are 

intended to be used to make relative comparisons. They are not intended to specify absolute 

values.

Information for each attribute of interest and subsequent metrics is discussed qualitatively or is 

discussed and presented as quantitative information in figures that reflect key outcomes. Where 

applicable, figures display reference values from Technical Report D – System Reliability 

Metrics. Figures include: 

(3) Box and whisker type plots that show the median, 25th and 75th percentiles and 

include “whiskers” representing the 10th and 90th percentiles. The statistical data for 

a given “box” represent the metric over all combined supply and demand scenarios, 

unless otherwise noted. The boxes are presented for the Baseline as well as each 

portfolio for time periods representing 2012 through 2026, 2027 through 2040, and 

2041 through 2060. 
Colorado River Basin

Water Supply and Demand Study

G4-B-2 December 2012

TABLE B-1 

Resource Categories and Attributes of Interest

Attribute of Interest Section 

Quantitative or 

Qualitative Plot Type Location

Figure 

Number

Electrical Power 

Generated

2 Quantitative Annual Upper Basin Aggregate B-1 

Hoover B-2 

Parker and Davis B-3 

Qualitative Headgate Rock Power 

Plant

NA

Economic Value of 

Electrical Power 

Generated

3 Qualitative NA Basin-wide NA

Available Generation 

Capacity

4 Quantitative Monthly 

and Annual

Upper Basin Aggregate B-4, B-5 

Hoover B-6, B-7 

Parker and Davis B-8, B-9 

Impact on Power 

Rates

5 Qualitative NA Basin-wide NA

Water Supply 

System Pumping 

Costs

6 Qualitative NA Basin-wide NA

Impact on Basin 

Funds

7 Qualitative NA Basin-wide NA

2.0 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 tailwater 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 Colorado River Basin 

(Basin). Hydropower plants in the Upper Basin that are modeled in the Colorado River 

Simulation System (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, 

and Davis facilities.

Figures B-1 through B-3 present the annual electrical power generated as computed in CRSS. 

Upper Basin electrical power generated can be compared to the associated power generation 

contract held by Western Area Power Administration (WAPA) of 4,948 terrawatt-hours. Figure 

B-1 shows annual electrical power generation for the aggregation of all Upper Basin power 

plants. Median power generation under the Baseline declines through 2060 to near the contract 
Attachment B — Electrical Power

Resources Metrics’ Results

December 2012 G4-B-3 

value. Implementation of each portfolio increases power generation to conditions in the 2012 

through 2026 (first) time period. 

FIGURE B-1 

Annual Electrical Power Generated, Upper Basin Aggregate 

Power Generation Reference Value is shown as Solid Red Line. 

FIGURE B-2 

Annual Electrical Power Generated, Hoover 

Power Generation Reference Value is shown as Solid Red Line.
Colorado River Basin

Water Supply and Demand Study

G4-B-4 December 2012

FIGURE B-3 

Annual Electrical Power Generated, Parker and Davis

Figure B-2 shows the Hoover plant’s power generation. Under the Baseline, median 2041 

through 2060 power generation decreases to below the historical 10-year low reference provided 

by WAPA. Implementation of each portfolio improves power generation. However, historical 

generation rates are not achieved. 

Figure B-3 shows power generation at the Parker and Davis power plants. Baseline power 

generation decreases over time through 2060. Implementation of each portfolio exacerbates this 

reduction, resulting in nearly twice the reduction of power generation over time. Presumably, 

this reduction in power generation is due to the implementation of desalination and/or reuse 

projects and demand reduction. With portfolios in place, options such as desalination and reuse 

help meet demands below Parker, resulting in reduced Parker releases and decreased energy 

generation.

The Headgate Rock Power Plant is located in the Lower Basin below Parker Reservoir. It is not 

explicitly modeled in CRSS. However, because the reservoir is operated to maintain a relatively 

constant elevation, changes in flow below Parker Reservoir can be used to assess changes in 

power generation. 

Under the Baseline simulation, the median flow below Parker reduces over time, indicating some 

reduction in energy generated at Headgate Rock. Additionally, as portfolios implement options, 

there tend to be lower releases from Parker compared to the Baseline, once again indicating a 

reduction in energy generation at Headgate Rock. 

3.0 Metrics for the Economic Value of Electrical Power 

Generated 

WAPA markets power and administers power contracts for power produced at hydropower 

facilities owned and operated by the Bureau of Reclamation. 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. 
Attachment B — Electrical Power

Resources Metrics’ Results

December 2012 G4-B-5 

Economic value can be assessed qualitatively by examining electrical power generated and 

assuming that increases in power result in additional economic value and decreases in power 

result in a loss of economic value. Figures B-1 through B-3 present electrical power generation 

for the Upper Basin in aggregate, Hoover Dam, and Parker and Davis. Under the Baseline, 

power generation declines over time across the scenarios. Implementation of each portfolio 

results in an improvement in power generation over the Baseline. However, while Upper Basin 

power generation remains essentially unchanged over time from the first time period, Hoover 

power generation is slightly reduced, and Parker and Davis power generation appears to be 

reduced by around 5 percent. In aggregate, these results suggest a slight decrease in economic 

value. 

4.0 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. WAPA 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. 

Figures B-4 to B-9 show the monthly and annual generation capacity for the Upper Basin, 

Hoover Dam, and Parker and Davis dams through 2060, as modeled in CRSS. For the Upper 

Basin aggregate and Hoover Dam, the Baseline generation capacity declines over time, with 

particularly significant declines to at or near zero in the summer months when peak demands 

typically occur. Implementation of each portfolio results in significant improvements in 

available generation capacity over the Baseline, with most portfolios resulting in available 

generation capacity greater than conditions in the first time period. The portfolios also 

significantly increase the available power generation capacity in the worst conditions. In CRSS, 

Parker and Davis are operated to maintain relatively constant pool elevations, which results in a 

constant generating capacity. Although there is slight variation in the elevations at Parker and 

Davis across scenarios, it (1) generally does not greatly affect the generation capacity and (2) is 

not evident at the scale shown in figures B-8 and B-9. 
Colorado River Basin

Water Supply and Demand Study

G4-B-6 December 2012

FIGURE B-4 

Monthly Available Generation Capacity, Upper Basin Aggregate. Generation Capacity 

Reference Value is shown as Solid Red Line.

FIGURE B-5 

Annual Available Generation Capacity, Upper Basin Aggregate. Generation Capacity 

Reference Value is shown as Solid Red Line.
Attachment B — Electrical Power

Resources Metrics’ Results

December 2012 G4-B-7 

FIGURE B-6 

Monthly Available Generation Capacity, Hoover. Generation Capacity 

Reference Value is shown as Solid Red Line.

FIGURE B-7 

Annual Available Generation Capacity, Hoover. Generation Capacity 

Reference Value is shown as Solid Red Line.
Colorado River Basin

Water Supply and Demand Study

G4-B-8 December 2012

FIGURE B-8 

Monthly Available Generation Capacity, Parker and Davis. Generation Capacity 

Reference Value is shown as Solid Red Line.

FIGURE B-9 

Annual Available Generation Capacity, Parker and Davis. Generation Capacity 

Reference Value is shown as Solid Red Line.

5.0 Metrics for the Impact on Power Rates Attribute of 

Interest 

For the Upper Basin, WAPA has firm delivery contracts in place. When WAPA cannot meet 

these contract amounts, power must be purchased on the open market at substantially higher 

rates. Projected increased demand and reduced supplies will likely result in increased frequency 

of these power buys, potentially increasing the overall rate for power. As shown in figure B-1, 

CRSS simulations indicate significantly reduced power generation by 2060 for the Baseline. 

Improvement in power generation occurs with each of the portfolios. Implementation of each 
Attachment B — Electrical Power

Resources Metrics’ Results

December 2012 G4-B-9 

portfolio results in power generation similar to generation in the first time period, with slightly 

worse performance under Portfolio D. Implementation of each portfolio would likely result in 

little to no change in power rates due to changes in power generation. 

Reduced power generation in the Lower Basin will likely require power purchases on the open 

market. This increased demand on the market will likely result in an overall increase in market 

rates. As noted in figure B-2, median power generation at Hoover Dam decreases over the long 

term. Each of the portfolios reduces this decrease, with Portfolio B resulting in the best longterm power generation from Hoover Dam and overall generation only slightly reduced from 

generation in the first time period. This result implies that there may be the need for some 

additional power buys in the Lower Basin with some associated increase in power rates. 

6.0 Metrics for the Water Supply System Pumping Costs 

Attribute of Interest 

Lower water levels in reservoirs may affect pumping power requirements for some entities. 

Examples include the Salt River Project, which extracts cooling water from Lake Powell for the 

Navajo Generating Station; the Southern Nevada Water Authority (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 Central Arizona 

Project delivery area. Based on current reservoir operations and typical utility equipment and 

procedures, there should be little effect on power costs due to changing reservoir levels for most 

of these utilities. However, because SNWA uses variable speed pumps, changing Lake Mead 

levels could impact pumping costs. 

As shown in figure B-10, CRSS simulations indicate that the median Lake Mead elevation under 

the Baseline is significantly reduced over time. This reduced elevation would likely result in 

increased pumping costs for SNWA. All of the portfolios improve Lake Mead elevation and 

reduce the range of variability in elevations through 2060 compared to Baseline results. 

Portfolio A results in the most improvement of Lake Mead elevations through 2060. All of the 

portfolios except for Portfolio D result in 2060 median Lake Mead elevations higher than recent 

elevations, suggesting potential future decreased relative pumping costs for SNWA. 
Colorado River Basin

Water Supply and Demand Study

G4-B-10 December 2012

FIGURE B-10

Monthly Lake Mead Pool Elevation

Elevation 1,000 ft msl Reference Value shown as Solid Red Line

7.0 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. 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. 

Reduced power generation will likely result in a loss of revenue, potentially impacting the noted 

revenue uses.

As shown in figures B-1 to B-3, CRSS simulations indicate significantly reduced power 

generation and subsequent likely loss of revenue by 2060 for the Baseline. Improvement in 

power generation occurs with each of the portfolios. Power generation is essentially maintained 

at or near first time period levels in the Upper Basin and at Hoover Dam, with significant 

reductions at Parker and Davis Dam. These results suggest a likely reduction in overall revenue 

and impact to Basin Funds. 
Appendix G4 

Attachment C 

Water Quality Metrics’ Results

December 2012 G4-C-1 

Attachment C — Water Quality Metrics’ 

Results

1.0 Introduction

System reliability metrics (metrics), defined in Technical Report D – System Reliability Metrics,

were developed to assess the performance of Colorado River Basin (Basin) resources with and 

without the implementation of options and strategies. Metrics were developed for six resource 

categories (Water Deliveries, Electrical Power Resources, Water Quality, Flood Control, 

Recreational Resources, and Ecological Resources) and for numerous attributes of interest within 

each category. 

This attachment presents summary results for both the quantitative and qualitative metrics 

associated with the Water Quality resource category. The Water Quality resource attributes of 

interest are shown in table C-1. 

Results are presented on a portfolio basis, in which all scenarios are grouped together. In 

accordance with the scenario planning approach employed in the Colorado River Basin Water 

Supply and Demand Study (Study), all scenarios are plausible and results are presented to reflect 

the distribution of outcomes associated with the various scenarios considered. All scenarios have 

been resampled such that each scenario contributes equally to the distribution. Results are 

intended to be used to make relative comparisons. They are not intended to specify absolute 

values.

Information for each attribute of interest and subsequent metrics is discussed qualitatively or is 

discussed and presented as quantitative information in figures that reflect key outcomes. Where 

applicable, figures display reference values from Technical Report D – System Reliability 

Metrics. Figures include: 

(4) Box and whisker type plots that show the median, 25th and 75th percentiles and 

include “whiskers” representing the 10th and 90th percentiles. The statistical data 

for a given “box” represent the metric over all combined supply and demand 

scenarios, unless otherwise noted. The boxes are presented for the baseline as well 

as each scenario for time periods representing 2012 through 2026, 2027 through 

2040, and 2041 through 2060. 

(5) Frequency and magnitude plots showing line plots relating the frequency of 

occurrence (typically the percentage of years) of an event compared to the 

magnitude of the event. These plots are also presented over time periods 

representing 2012 through 2026, 2027 through 2040, and 2041 through 2060. 
Colorado River Basin

Water Supply and Demand Study

G4-C-2 December 2012

TABLE C-1 

Water Quality Metrics

Attribute of 

Interest Section 

Quantitative or 

Qualitative

Plot 

Type Locations

Figure 

Number

Salinity 2 Quantitative Annual Colorado River Below Hoover Dam C-1 

Colorado River Below Parker Dam C-2 

Colorado River At Imperial Dam C-3 

Colorado River near Glenwood 

Springs, CO C-4 

Colorado River near Cameo, CO C-5 

Gunnison River near Grand Junction, 

CO C-6 

Dolores River near Cisco, CO C-7 

Colorado River near Cisco, CO C-8 

Green River at Green River, WY C-9 

Green River near Greendale, UT C-10

Yampa River near Maybell, CO C-11

Duchesne River near Randlett, UT C-12

White River near Watson, UT C-13

Green River at Green River, UT C-14

San Rafael River near Green River, 

UT C-15

San Juan River near Archuleta, NM C-16

San Juan River near Bluff, UT C-17

Colorado River at Lees Ferry, AZ C-18

Colorado River near Grand Canyon, 

AZ C-19

Virgin River near Littlefield, AZ C-20

Sediment 

Transport

3 Qualitative NA Basin-wide NA

Temperature 4 Qualitative NA Basin-wide NA

Other Water 

Quality

constituents

5 Qualitative NA

Basin-wide NA

Socioecono

mic Impacts 

Related To 

Salinity

6 Qualitative NA

Basin-wide NA
Attachment C — Water

Quality Metrics’ Results

December 2012 G4-C-3 

2.0 Metrics for the Salinity Attribute of Interest 

In order to comply with the Clean Water Act, the Colorado River Basin Salinity Control Forum 

(Forum) develops numeric salinity criteria for water below Hoover and Parker dams and at 

Imperial Dam. The most recent criteria are 723, 747, and 879 milligrams per liter1, respectively 

and were developed in 2011. In addition, Minute No. 242 of the International Boundary and 

Water Commission provides that the United States ensure that waters 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 that arrive at 

Imperial Dam. 

Colorado River Simulation System (CRSS) output for these locations, along with 17 additional 

monitoring locations, is shown in figures C-1 to C-20. Due to modeling limitations, the results 

shown include only the Observed Resampled and the Paleo Resampled supply scenarios. In 

examining these results the following broad observations are made: 

1. Negative concentrations – Negative concentrations were reported in some simulations 

for the locations shown in figures C-12 and C-15, which is clearly unrealistic. CRSS 

models water quality improvements projects (WQIPs), which remove salinity from the 

system, using a constant mass removal. A negative concentration results if, in any given 

month, the salinity mass in the reach is less than the WQIP’s set removal amount. This 

modeling limitation will be addressed in the future. 

2. Prescribed conditions (Hoover, Parker, and Imperial, figures C-18 to C-20) – Salinity 

increases under the Baseline, likely due to the increasing demand coupled with reduced 

supply. The increases are less than 10 percent and do not approach the prescribed 

concentrations. Implementation of each of the portfolios reduces salinity concentrations 

from the Baseline but does not reduce to 2012 through 2026 concentrations. 

3. Lower concentrations – Three of the locations—Delores River near Cisco, CO 

(figure C-7), Duchesne River near Randlett, UT (figure C-12), and San Rafael River near 

Green River, UT (figure C-15)—result in future salinity concentration reductions under 

the Baseline. The decrease in Baseline salinity may be due to decreases in demand 

resulting in more available flow for dilution. Implementation of each portfolio results in 

small future reductions from the Baseline. At these locations Portfolio B tends to reduce 

concentrations more than the other portfolios. 

4. Same concentrations – In two cases, the White River near Watson, UT (figure-C-13) 

and the Virgin River near Littlefield, AZ (figure C-20), there is little to no change in 

salinity concentration under the Baseline or with implementation of each portfolio. For 

the White River near Watson, UT, consistent concentrations appear to be due to relatively 

small changes in demand or supply from the Baseline scenario. For the Virgin River near 

Littlefield, AZ, this effect is due to the fact that this location only considers natural flow 

and is outside of the locations that demands are specifically modeled. 

5. Higher concentrations – For the remaining locations, salinity steadily increases under 

the Baseline and is significantly reduced with the implementation of each portfolio. 

These decreases are due to either demand reduction and/or augmentation, resulting in 

 

1 Flow-weighted average annual salinity.
Colorado River Basin

Water Supply and Demand Study

G4-C-4 December 2012

greater overall flow and subsequently more dilution and lower salinity concentrations. 

Two distinct patterns emerge in comparing future portfolio performance related to 

location. These distinctions are represented by the Colorado River near Glenwood 

Springs, CO and by the Green River at Green River, WY. For the Colorado River near 

Glenwood Springs, CO, the salinity is reduced from the Baseline but appears to increase 

from Portfolio A to Portfolio D. This effect is likely due to varying degrees of increased 

dilution in Portfolio A and Portfolio B due to the inclusion of importation options. For 

the Green River at Green River, WY, salinity is reduced from the Baseline, but Portfolio 

A and Portfolio C appear to perform better with respect to salinity concentration. This 

effect is likely due to the inclusion of banking in these portfolios which routes conserved 

water to a conceptual off-stream storage location above Lake Powell. The routing 

increases flow in the reaches resulting in increased dilution. 

FIGURE C-1 

Annual Salinity, Colorado River below Hoover Dam

Numeric Salinity Criteria Reference Value Shown as Solid Red Line. 
Attachment C — Water

Quality Metrics’ Results

December 2012 G4-C-5 

FIGURE C-2 

Annual Salinity Colorado River below Parker Dam 

Numeric Salinity Criteria Reference Value Shown as Solid Red Line.

FIGURE C-3 

Annual Salinity, Colorado River at Imperial Dam

Numeric Salinity Criteria Reference Value Shown as Solid Red Line.

FIGURE C-4 

Annual Salinity, Colorado River near Glenwood Springs, CO
Colorado River Basin

Water Supply and Demand Study

G4-C-6 December 2012

FIGURE C-5 

Annual Salinity, Colorado River near Cameo, CO

FIGURE C-6 

Annual Salinity, Gunnison River near Grand Junction, CO

FIGURE C-7 

Annual Salinity, Dolores River near Cisco, CO
Attachment C — Water

Quality Metrics’ Results

December 2012 G4-C-7 

FIGURE C-8 

Annual Salinity Colorado River near Cisco, CO

FIGURE C-9 

Annual Salinity, Green River at Green River, WY

FIGURE C-10

Annual Salinity, Green River near Greendale, UT
Colorado River Basin

Water Supply and Demand Study

G4-C-8 December 2012

FIGURE C-11

Annual Salinity, Yampa River near Maybell, CO

FIGURE C-12

Annual Salinity, Duchesne River near Randlett, UT

FIGURE C-13

Annual Salinity, White River near Watson, UT
Attachment C — Water

Quality Metrics’ Results

December 2012 G4-C-9 

FIGURE C-14

Annual Salinity, Green River at Green River UT

FIGURE C-15

Annual Salinity, San Rafael River near Green River, UT

FIGURE C-16

Annual Salinity, San Juan River near Archuleta, NM
Colorado River Basin

Water Supply and Demand Study

G4-C-10 December 2012

FIGURE C-17

Annual Salinity, San Juan River near Bluff, UT

FIGURE C-18

Annual Salinity, Colorado River at Lees Ferry, AZ

FIGURE C-19

Annual Salinity, Colorado River near Grand Canyon, AZ
Attachment C — Water

Quality Metrics’ Results

December 2012 G4-C-11

FIGURE C-20

Annual Salinity, Virgin River near Littlefield, AZ

3.0 Metrics for the Sediment Transport Attribute of Interest

Reservoirs 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. 

These impacts can affect overall water quality.

These potential effects can be qualitatively assessed by examining the variability and magnitude 

of reservoir drawdown. In examining Lake Mead, pool elevation is shown to reduce over time 

under the Baseline, with very low elevations reached under the 10th percentile (figure C-21). 

Implementing each portfolio increases the expected elevation and dramatically improves the 

potential low elevations over time. These increased elevations imply that there could be less 

downcutting and subsequent sediment transport issues in the portfolios relative to the Baseline. 

By 2060, implementation of each portfolio results in a higher median elevation than that seen 

today. This increase implies that in the future, there could be less downcutting than is seen 

presently and therefore less impact due to sediment. 
Colorado River Basin

Water Supply and Demand Study

G4-C-12 December 2012

FIGURE C-21

Monthly Lake Mead Pool Elevation

4.0 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. Water 

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

With decreasing storage volumes, water temperatures will generally trend closer to influent flow 

temperatures. This change reflects a rise in overall temperature from releases. Under some 

future climate scenarios, this effect will be combined with an increase in ambient temperatures. 

This change could result in reduced habitat for cold water fish species, such as trout, and an 

increase in invasive species predation. 

These potential effects can be qualitatively assessed by examining the variability and magnitude 

of reservoir drawdown. In examining figure C-21, Lake Mead elevation is shown to reduce over 

time under the Baseline, with very low elevations reached under the 90th percentile. 

Implementing each portfolio increases the expected elevation and dramatically reduces the range 

in elevations over time compared to the Baseline. This change implies that water temperatures 

from reservoir releases could be cooler under the portfolios when compared to the Baseline. By 

2060, implementation of each portfolio results in a greater median elevation than seen today, 

implying more storage and potentially cooler temperatures. However, under the downscaled 

GCM supply scenario, ambient temperature would likely increase, potentially diminishing any 

benefit from increased storage volume. 
Attachment C — Water

Quality Metrics’ Results

December 2012 G4-C-13

5.0 Other Water Quality Attribute of Interest 

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

conditions could potentially affect other water quality attributes such as selenium, dissolved 

oxygen, nutrients, algae, metals, perchlorate, and emerging contaminants. 

As noted in the sediment transport section, lower reservoir volumes and level variability can 

result in greater dissolved oxygen demand, nutrient release, and subsequent algal growth. 

Increased temperatures due to either or both reduced reservoir levels and climate change can also 

exacerbate these issues due to a reduced capacity of warmer water to dissolve oxygen and higher 

potential algal growth rates. In addition, downcutting of reservoir deltas and sediment release 

could result in resuspension of deposited selenium and metals. Selenium, metals, perchlorate, 

and emerging contaminants could also have higher concentrations due to lower flows and less 

dilution. 

These potential effects can be qualitatively assessed by examining the variability and magnitude 

of reservoir drawdown. In examining figure C-21, Lake Mead elevation is shown to reduce over 

time under the Baseline with very low elevations reached under the 10th percentile. 

Implementing each portfolio increases the expected elevation and dramatically improves 

elevations in the worst case supply scenarios. These improvements imply that there could be less 

downcutting and subsequent sediment transport issues and water temperature issues (e.g., 

dissolved oxygen demand, nutrient release, algal growth, and resuspension of metals). 

Potential changes in concentration of selenium, metals, perchlorate, and emerging contaminates 

can be qualitatively assessed by examining changes in flow. Lee Ferry deficit can be used as a 

surrogate for flow at Lee Ferry. Figure C-22, shows Lee Ferry deficit under Baseline and the 

portfolios over time. In general, Lee Ferry deficit is shown to be more frequent and of greater 

magnitude over time under the Baseline. Implementing each portfolio increases the expected 

flow over time or rather reduces the frequency and magnitude of Lee Ferry deficit, although 

future flows with the portfolios implemented are still reduced when compared to current 

conditions. This result implies that less water would be available for dilution of selenium, 

metals, perchlorate, and emerging contaminants. 

Figure C-22

Annual Lee Ferry Deficit
Colorado River Basin

Water Supply and Demand Study

G4-C-14 December 2012

6.0 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 Municipal and Industrial (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. 

Potential socioeconomic impacts were evaluated qualitatively by examining CRSS results for 

changes in salinity. Figures C-1 to C-20, illustrate that salinity could increase at almost every 

monitoring point under the Baseline over time. In most cases, implementing each portfolio 

reduces future salinity compared to the Baseline. However, in most cases, future salinity 

levels are greater than current levels. Of particular interest is the salinity at Imperial Dam 

(figure C-20). It appears that the median salinity could increase by about 25 milligrams per 

liter over current conditions. This increase could result in negative socioeconomic 

consequences. However, the predicted values, even for the 10th percentile, are well below 

the numeric criteria of 879 milligrams per liter established for water quality at Imperial Dam.

Potential economic damages due to increased salinity could 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. 
Appendix G4 

Attachment D

Flood Control Metrics’ Results

December 2012 G4-D-1 

Attachment D — Flood Control Metrics’ 

Results

1.0 Introduction

System reliability metrics (metrics), defined in Technical Report D – System Reliability Metrics,

were developed to assess the performance of Colorado River Basin (Basin) resources with and 

without the implementation of options and strategies. Metrics were developed for six resource 

categories (Water Deliveries, Electrical Power Resources, Water Quality, Flood Control, 

Recreational Resources, and Ecological Resources) and for numerous attributes of interest within 

each category. 

This attachment presents summary results for the quantitative metrics associated with the Flood 

Control resource category. The Flood Control resource attributes of interest are shown in table 

D-1. 

Results are presented by portfolio with all scenario combinations grouped together. In 

accordance with the scenario planning approach employed in the Colorado River Basin Water 

Supply and Demand Study (Study), all scenarios are plausible and results are presented to reflect 

the distribution of outcomes associated with the various scenarios considered. All scenarios have 

been resampled such that each scenario contributes equally to the distribution. Results are 

intended to be used to make relative comparisons. They are not intended to specify absolute 

values.

Information for each attribute of interest and subsequent metrics is discussed qualitatively or is 

discussed and presented as quantitative information in figures that reflect key outcomes. Where 

applicable, figures display reference values from Technical Report D – System Reliability 

Metrics. Figures include: 

(6) Box and whisker type plots that show the median, 25th and 75th percentiles 

and include “whiskers” representing the 10th and 90th percentiles. The 

statistical data for a given “box” represent the metric over all combined supply 

and demand scenarios, unless otherwise noted. The boxes are presented for 

the Baseline as well as each portfolio for time periods representing 2012 

through 2026, 2027 through 2040, and 2041 through 2060. 

(7) Frequency and magnitude plots showing line plots relating the frequency of 

occurrence (typically the percentage of years) of an event compared to the 

magnitude of the event. These plots are also presented over time periods 

representing 2012 through 2026, 2027 through 2040, and 2041 through 2060. 
Colorado River Basin

Water Supply and Demand Study

G4-D-2 December 2012

TABLE D-1 

Flood Control Metrics

Attribute of 

Interest

Resource 

Metric Section 

Quantitative 

or Qualitative Plot Type Location

Figure 

Number

Flood Control 

Releases and 

Reservoir 

Spills

Flood Control 

Release

2.1 Quantitative Percent 

Exceedance Lake Mead D-1 

Reservoir 

Spills

2.2 Quantitative Percent 

Exceedance

Fontenelle D-2 

Flaming Gorge D-3 

Blue Mesa D-4 

Lake Powell D-5 

Lake Mead D-6 

Critical River 

Stages Related 

to Flooding 

Risk

Flooding Risk 3 Quantitative Monthly Downstream of 

Aspinall Unit D-7 

Downstream of 

Navajo Dam D-8 

Downstream of 

confluence with 

Animas River

D-9 

Downstream of 

Lake Mead D-10

2.0 Metrics for the Flood Control Releases and Reservoir 

Spills Attribute of Interest 

For Lake Mead, criteria are developed for flood control releases under agreement between the 

U.S. Army Corps of Engineers and the Bureau of Reclamation (Reclamation). These criteria are 

used to develop system space requirements from August through December and determine 

reservoir releases from January through July. During all months of the year, the top 1.5 million 

acre-feet of space (the space above elevation 1,219.6 feet above mean sea level) is reserved 

exclusively for flood 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. 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. The primary objective of spill 

avoidance is to minimize the amount of water that does not pass through hydropower facilities. 

The Colorado River Simulation System (CRSS) was used to quantify the frequency and 

magnitude of both flood control releases at Lake Mead and reservoir spills. The reservoir spill 

metrics were quantified at Fontenelle, Flaming Gorge, Blue Mesa, Lake Powell, and Lake Mead 

using the relative comparison quantification method. 

Figure D-1 shows the magnitude and frequency of flood control releases at Mead. Under the 

Baseline, these releases decrease marginally in both magnitude and frequency over time. 
Attachment D — Flood Control

Metrics’ Results

December 2012 G4-D-3 

Implementation of each portfolio results in a slight increase in both magnitude and frequency of 

flood control releases compared to the Baseline.

Figures D-2 through D-6 show the magnitude and frequency of reservoir spills for Fontenelle, 

Flaming Gorge, Blue Mesa, Lake Powell, and Lake Mead, respectively. For Fontenelle and 

Flaming Gorge, there is little discernible difference over time in the Baseline and with the 

implementation of each portfolio. This consistency is likely due to minimal upstream demands 

and lack of augmentation in the Green River Basin. Blue Mesa, Lake Powell, and Lake Mead all 

show increases in magnitude and frequency of spills over time under the Baseline. This likely 

results from operating below hydropower capacity, such that continuing to release when 

hydropower generation capacity is reduced is counted as a spill in the same way that exceeding 

reservoir capacity is counted as a spill. Implementation of each portfolios results in a reduction 

in spills over time – likely due to demand reduction and augmentation that primarily reduce the 

likelihood of low elevations and subsequent low elevation spills. 

2.1 Flood Control Releases from Lake Mead

FIGURE D-1 

Lake Mead Flood Control Release Percent of Years Exceeding Magnitude
Colorado River Basin

Water Supply and Demand Study

G4-D-4 December 2012

2.2 Reservoir Spills

FIGURE D-2 

Fontenelle Spill Percent of Years Exceeding Magnitude

FIGURE D-3 

Flaming Gorge Spill Percent of Years Exceeding Magnitude

FIGURE D-4 

Blue Mesa Spill Percent of Years Exceeding Magnitude
Attachment D — Flood Control

Metrics’ Results

December 2012 G4-D-5 

FIGURE D-5 

Lake Powell Spill Percent of Years Exceeding Magnitude

FIGURE D-6 

Lake Mead Spill Percent of Years Exceeding Magnitude

3.0 Metrics for the Critical River Stages Related to 

Flooding Risk Attribute of Interest

Empirical relationships between flow and flood risk (safe channel capacity) exist downstream of 

Navajo Dam, the Aspinall Unit, and Lake Mead. Reference safe channel capacity values include 

15,000 cubic feet per second (cfs) for the Gunnison River at Delta, Colorado; 5,000 cfs for the 

San Juan River below Navajo Dam; 12,000 cfs for the San Juan near Farmington, NM; and 

28,000 cfs for the Colorado River below Hoover Dam;. Additional analysis of CRSS output data 

was performed to estimate flooding potential. Navajo and Mead release in CRSS were used for 

the metrics below Navajo Dam, and below Hoover Dam. For the San Juan River near 

Farmington, NM, the flow was approximated as the releases from Navajo, plus the natural flow 

above Bluff, Utah minus Colorado’s demands in the San Juan Basin. Additionally, a gage for 

the Gunnison River at Delta, Colorado does not exist in CRSS; however, a gage location in 

CRSS does exist for the Gunnison River near Grand Junction, Colorado. A linear model was 
Colorado River Basin

Water Supply and Demand Study

G4-D-6 December 2012

used to estimate flow at Delta from flow at the Grand Junction gage2. The model is based on 

historical data and assumes the historical flow relationship between both sites will continue in 

the future. This may not be an appropriate assumption under all future supply/demand 

combinations. However, the approximation provides a view of possible flows at Delta 

commensurate with the relative comparison nature of the metrics.

Figures D-7 through D-10 present monthly flows for Gunnison River at Delta, Colorado; the San 

Juan River below Navajo Dam; the San Juan near Farmington, NM; and the Colorado River 

below Hoover Dam. In general, peak flows occur in May and June, with some significant peaks 

in July. Under the Baseline, flows decrease over time at all locations. Implementation of each 

portfolio results in increases in flow over time compared to the Baseline. Only maximum flows 

(exceeding the 90th percentile) on the San Juan River below Navajo Dam approach or exceed the 

safe channel capacity. These flows occur in May and June from the present period (2012 

through 2026) to the 2041 through 2060 period for the Baseline and each of the portfolios. 

FIGURE D-7 

Monthly Flooding Risk Downstream of Aspinall Unit 

Safe Channel Capacity Reference Value is shown as Solid Red Line. 

 

2 The linear model used to relate Grand Junction flow to Delta flow in cubic feet per second (cfs) was: Delta Flow = .8306*Grand Junction Flow 

– 180.3 cfs. The R2 value of the model fit to the historical data is 0.98.
Attachment D — Flood Control

Metrics’ Results

December 2012 G4-D-7 

FIGURE D-8 

Monthly Flooding Risk Downstream of Navajo Dam

Safe Channel Capacity Reference Value is shown as Solid Red Line.

FIGURE D-9 

Monthly San Juan Flooding Risk Downstream of confluence with Animas River

Safe Channel Capacity Reference Value is shown as Solid Red Line.
Colorado River Basin

Water Supply and Demand Study

G4-D-8 December 2012

FIGURE D-10

Monthly Flooding Risk Downstream of Lake Mead 

Safe Channel Capacity Reference Value is shown as Solid Red Line.
Appendix G4 

Attachment E

Recreational Resources Metrics’ Results

December 2012 G4-E-1 

Attachment E — Recreational Resources 

Metrics’ Results

1.0 Introduction

System reliability metrics (metrics), defined in Technical Report D – System Reliability Metrics, 

were developed to assess the performance of Colorado River Basin (Basin) resources with and 

without the implementation of options and strategies. Metrics were developed for six resource 

categories (Water Deliveries, Electrical Power Resources, Water Quality, Flood Control, 

Recreational Resources, and Ecological Resources) and for numerous attributes of interest within 

each category. 

This attachment presents summary results for both the quantitative and qualitative metrics 

associated with the Recreational Resources category. The Recreational Resources attributes of 

interest are shown in table E-1. 

Results are presented on a portfolio basis, in which all scenarios are grouped together. In 

accordance with the scenario planning approach employed in the Colorado River Basin Water 

Supply and Demand Study (Study), all scenarios are plausible and results are presented to reflect 

the distribution of outcomes associated with the various scenarios considered. All scenarios have 

been resampled such that each scenario contributes equally to the distribution. Results are 

intended to be used to make relative comparisons. They are not intended to specify absolute 

values. 

Information for each attribute of interest and subsequent metrics is discussed qualitatively or 

discussed and presented as quantitative information in figures that reflect key outcomes. Where 

applicable, figures display reference values from Technical Report D – System Reliability 

Metrics. Figures include: 

(8) Box and whisker type plots that show the median, 25th and 75th percentiles and 

include “whiskers” representing the 10th and 90th percentiles. The statistical data for 

a given “box” represent the metric over all combined supply and demand scenarios, 

unless otherwise noted. The boxes are presented for the Baseline as well as each 

portfolio for time periods representing 2012 through 2026, 2027 through 2040, and 

2041 through 2060. 
Colorado River Basin

Water Supply and Demand Study

G4-E-2 December 2012

TABLE E-1 

Recreational Metrics

Attribute of 

Interest Section 

Quantitative or 

Qualitative Plot Type Location

Figure 

Number

Shoreline Public 

Use Facilities 2 Quantitative Monthly

Flaming Gorge E-1 

Blue Mesa E-2 

Navajo E-3 

Lake Powell E-4 

Lake Mead E-5 

River and 

Whitewater 

Boating

3 Quantitative

Monthly by 

Boating 

Flow Day 

Type

Colorado River at Glenwood 

Springs, CO E-6 

Dolores River near Cisco, UT E-7 

Colorado River near Cisco, 

UT E-8 

Green River near Greendale, 

UT E-9 

Yampa River near Maybell, 

CO E-10

Yampa River at Deerlodge 

Park, CO E-11

Green River at Jensen, UT E-12

San Juan River near Bluff, UT E-13

Other 

Recreational 4 Qualitative NA Basin-Wide NA

Socioeconomic 

Impacts 5 Qualitative NA Basin-Wide NA

2.0 Metrics for the Shoreline Public Use Facilities Attribute 

of Interest

Figures E-1 through E-5 show box plots of pool elevation at the following reservoirs: Flaming 

Gorge, Blue Mesa, Navajo, Lake Powell, and Lake Mead. Additionally, reference values for 

Shoreline Public Use Facilities, as identified in Technical Report D – System Reliability Metrics, 

are provided for reference. These values represent the current minimum pool elevation for 

operation of major marinas and boat ramps. For Recreational Resources, it is beneficial to 

maintain pool elevations above these reference values. Flaming Gorge (figure E-1) infrequently 

falls below any reference elevation, across all time periods. Further, the impact of portfolios is 

minimal; reflecting the limited option yield above that reservoir. Under the Baseline, Blue Mesa 

pool elevation (figure E-2) spans the four reference elevations, particularly in the second (2027 

through 2040) and third (2041 through 2060) periods. All portfolios show pool elevation 
Attachment E — Recreational

Resources Metrics’ Results

December 2012 G4-E-3 

improvements, by about 20 feet in the third time period; the lack of difference between portfolios 

is because most options impacting Blue Mesa are common to all portfolios. Baseline Navajo 

median pool elevations (figure E-3) are above all reference values for all months. However, in 

the second and third time periods, the 25th percentile begins to fall below the first reference 

elevation for several months. All portfolios bring the 25th percentile above that threshold, with 

Portfolio A showing the largest change in pool elevation relative to the Baseline. Similar results 

are seen for Lake Powell (figure E-4). Portfolios increased pool elevations enough that the 25th 

percentiles are generally near or above the first reference elevation, while over time the Baseline 

25th percentile fell below several reference elevations. Figure E-5 shows results for Lake Mead. 

Across the three time periods, the Baseline median pool elevation falls from being about 

centered in the reference elevations to being below most. Portfolios show the greatest impact at 

Lake Mead; by the third time period, pool elevation improved relative to the Baseline by about 

60 feet above mean sea level (msl), bringing median pool elevation generally higher than the first 

time period (2012 through 2026), particularly for Portfolio A and B. 

FIGURE E-1 

Monthly Flaming Gorge Reservoir Pool Elevation

Shoreline Public Use Facilities Reference Elevations Show as Solid Red Lines.
Colorado River Basin

Water Supply and Demand Study

G4-E-4 December 2012

FIGURE E-2 

Monthly Blue Mesa Reservoir Pool Elevation

Shoreline Public Use Facilities Reference Elevations Show as Solid Red Lines.

FIGURE E-3 

Monthly Navajo Reservoir Pool Elevation

Shoreline Public Use Facilities Reference Elevations Show as Solid Red Lines.
Attachment E — Recreational

Resources Metrics’ Results

December 2012 G4-E-5 

FIGURE E-4 

Monthly Lake Powell Pool Elevation

Shoreline Public Use Facilities Reference Elevations Show as Solid Red Lines.

FIGURE E-5 

Monthly Lake Mead Pool Elevation

Shoreline Public Use Facilities Reference Elevations Show as Solid Red Lines.
Colorado River Basin

Water Supply and Demand Study

G4-E-6 December 2012

3.0 Metrics for the River and Whitewater Boating Attribute 

of Interest

Figures E-6 through E-13 show monthly river and whitewater metrics by boating flow day types: 

below acceptable, acceptable low, optimal, acceptable high, and above acceptable boating flow 

days. The boating flow days increase monotonically with flow; that is, acceptable high boating 

flow days will always be for higher flows than optimal boating flow days. These values reflect 

the flow aspect of river and whitewater boating quality. The process for computing flow day 

types is described in Technical Report D – System Reliability Metrics. Generally, under the 

Baseline, flows reduce over time and a shift is observed from one flow day type to another. For 

example, the month of June in figure E-8 shows a reduction in the number of acceptable high 

days and an increase in the number of optimal days. Locations that do not follow this trend are 

those directly impacted by reservoir releases (e.g., figure E-9, Green River near Greendale, UT) 

or those locations with limited upstream flow changes (e.g., figure E-10, Yampa River near 

Maybell, CO). These types of locations tend to be the least impacted by the implementation of 

portfolios (e.g., figure E-7, Dolores River near Cisco, UT). Locations with greater upstream 

option influence generally showed a shift toward higher flow day types with the implementation 

of portfolios. For example, in May of the third time period, the Colorado River at Glenwood 

Springs (figure E-6) shows a substantial shift from mostly below-acceptable boating flow days to 

acceptable-low boating flow days when portfolio results are compared with the Baseline. Similar 

shifts to more-acceptable and optimal boating flow days are evident for the San Juan River near 

Bluff, UT (figure E-13). This was most notable for Portfolio A and Portfolio C, which both route 

conserved water to a conceptual off-stream storage location above Powell as part of the banking 

option. It is noteworthy that across all locations, many of the below acceptable boating flow days 

occur during winter months that are generally less popular for river and whitewater boating. 

While some sites may show a slight shift over time toward more early season (March or April) 

acceptable or optimal boating flow days, most of these boating flow days still occur during the 

summer months, even in the third time period. 
Attachment E — Recreational

Resources Metrics’ Results

December 2012 G4-E-7 

FIGURE E-6A

Monthly River and Whitewater Boating by Boating Flow Day Type, Colorado River at Glenwood Springs, CO
Colorado River Basin

Water Supply and Demand Study

G4-E-8 December 2012

FIGURE E-6B

Monthly River and Whitewater Boating by Boating Flow Day Type, Colorado River at Glenwood Springs, CO
Attachment E — Recreational

Resources Metrics’ Results

December 2012 G4-E-9 

FIGURE E-7A

Monthly River and Whitewater Boating by Boating Flow Day Type, Dolores River near Cisco, UT
Colorado River Basin

Water Supply and Demand Study

G4-E-10 December 2012

FIGURE E-7B

Monthly River and Whitewater Boating by Boating Flow Day Type, Dolores River near Cisco, UT
Attachment E — Recreational

Resources Metrics’ Results

December 2012 G4-E-11

FIGURE E-8A

Monthly River and Whitewater Boating by Boating Flow Day Type, Colorado River near Cisco, UT
Colorado River Basin

Water Supply and Demand Study

G4-E-12 December 2012

FIGURE E-8B

Monthly River and Whitewater Boating by Boating Flow Day Type, Colorado River near Cisco, UT
Attachment E — Recreational

Resources Metrics’ Results

December 2012 G4-E-13

FIGURE E-9A

Monthly River and Whitewater Boating by Boating Flow Day Type, Green River near Greendale, UT
Colorado River Basin

Water Supply and Demand Study

G4-E-14 December 2012

FIGURE E-9B 

Monthly River and Whitewater Boating by Boating Flow Day Type, Green River near Greendale, UT
Attachment E — Recreational

Resources Metrics’ Results

December 2012 G4-E-15

FIGURE E-10A

Monthly River and Whitewater Boating by Boating Flow Day Type, Yampa River near Maybell, CO
Colorado River Basin

Water Supply and Demand Study

G4-E-16 December 2012

FIGURE E-10B

Monthly River and Whitewater Boating by Boating Flow Day Type, Yampa River near Maybell, CO
Attachment E — Recreational

Resources Metrics’ Results

December 2012 G4-E-17

FIGURE E-11A

Monthly River and Whitewater Boating by Boating Flow Day Type, Yampa River at Deerlodge Park, CO
Colorado River Basin

Water Supply and Demand Study

G4-E-18 December 2012

FIGURE E-11B

Monthly River and Whitewater Boating by Boating Flow Day Type, Yampa River at Deerlodge Park, CO
Attachment E — Recreational

Resources Metrics’ Results

December 2012 G4-E-19

FIGURE E-12A

Monthly River and Whitewater Boating by Boating Flow Day Type, Green River at Jensen, UT
Colorado River Basin

Water Supply and Demand Study

G4-E-20 December 2012

FIGURE E-12B

Monthly River and Whitewater Boating by Boating Flow Day Type, Green River at Jensen, UT
Attachment E — Recreational

Resources Metrics’ Results

December 2012 G4-E-21

FIGURE E-13A

Monthly River and Whitewater Boating by Boating Flow Day Type, San Juan River near Bluff, UT
Colorado River Basin

Water Supply and Demand Study

G4-E-22 December 2012

FIGURE E-13B

Monthly River and Whitewater Boating by Boating Flow Day Type, San Juan River near Bluff, UT
Attachment E — Recreational

Resources Metrics’ Results

December 2012 G4-E-23

4.0 Other Recreational Attributes of Interest 

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

Significant additional analyses (beyond the Colorado River Simulation System [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.

As reservoirs are significantly drawn down, sediment can be re-suspended and may result in the 

release of nutrients, possibly enhancing algal blooms. Riverine sediment transport, therefore, 

can have implications for the quality of recreation experience. In addition, sediment transport can 

affect beach formation and maintenance. Significant and/or frequent drawdown can lead to 

erosion, loss of beaches, and subsequent negative effects on recreation. These potential effects 

were qualitatively assessed by examining the variability and magnitude of reservoir drawdown. 

In figure E-5, Lake Mead elevation is shown to be lower in general and exhibit a broad range of 

elevations under the Baseline. Further, sedimentation, coupled with lower reservoir levels can 

reduce recreation opportunities by limiting access to certain areas or by creating operational 

challenges to boat ramps and marinas. 

Implementing portfolios increases the expected elevations and reduces the range in elevations 

over time. These improvements imply that there could be less downcutting and subsequent 

sediment transport issues in the portfolios relative to the Baseline. By 2060, implementation of 

each portfolio results in a higher median elevation than that of today. This increase implies that 

in the future, there could be less downcutting than at present and therefore less impact due to 

sediment.

5.0 Metrics for the Socioeconomic Impacts Attribute of 

Interest 

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

reduced river flows could adversely affect local socioeconomics. Rough estimates exist that 

relate reservoir levels or flow conditions to socioeconomic impacts 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.

CRSS simulations indicate that both reservoir levels and flow could be reduced under the 

Baseline. Figures E-1 through E-5 show portfolio implementation generally increases reservoir 

levels, and figures E-6 through E-13 suggest higher flows over time when compared to the 

Baseline. However, a portfolio is unlikely to exactly maintain historical reservoir levels or flow. 

Timing, magnitude, and location of portfolio options create uncertainty with regard to the 

socioeconomic impacts. In general, as reservoir levels decrease below the level for shoreline 

public use facilities, opportunities for visitation also decrease. However, sizeable fluctuations in 

pool elevation can be as important as an absolute decrease with regard to the maintenance and 

operation of shoreline public use facilities. As such, a reduction in the range of reservoir levels 

or flow could help to mitigate socioeconomic impacts associated with overall magnitude 

reductions. 

Appendix G4 

Attachment F 

Ecological Resource Metrics’ Results

December 2012 G4-F-1 

Attachment F — Ecological Resource 

Metrics’ Results

1.0 Introduction

System reliability metrics (metrics), defined in Technical Report D – System Reliability Metrics, 

were developed to assess the performance of Colorado River Basin (Basin) resources with and 

without the implementation of options and strategies. Metrics were developed for six resource 

categories (Water Deliveries, Electrical Power Resources, Water Quality, Flood Control, 

Recreational Resources, and Ecological Resources) and for numerous attributes of interest within 

each category. 

This attachment presents summary results for the quantitative metrics associated with Ecological 

Resources. The Ecological Resource attributes of interest are shown in table F-1. 

Results are presented by portfolio with all scenario combinations grouped together. In 

accordance with the scenario planning approach employed in the Colorado River Basin Water 

Supply and Demand Study (Study), all scenarios are plausible and results are presented to reflect 

the distribution of outcomes associated with the various scenarios considered. All scenarios have 

been resampled such that each scenario contributes equally to the distribution. Results are 

intended to be used to make relative comparisons. They are not intended to specify absolute 

values.

Information for each attribute of interest and subsequent metrics is discussed and presented as 

quantitative information in figures that reflect key outcomes. Where applicable, figures display 

reference values from Technical Report D – System Reliability Metrics. Figures include: 

(9) Box and whisker type plots that show the median, 25th and 75th percentiles and 

include “whiskers” representing the 10th and 90th percentiles. The statistical data for

a given “box” represent the metric over all combined supply and demand scenarios, 

unless otherwise noted. The boxes are presented for the Baseline as well as each 

portfolio for time periods representing 2012 through 2026, 2027 through 2040, and 

2041through 2060. 

(10) Bar charts are used to display the percent of years that met a desired target or the 

percent of years that are within a given category. The bars are also presented for the 

Baseline as well as each portfolio for time periods representing 2012 through 2026, 

2027 through 2040, and 2041through 2060. 
Colorado River Basin

Water Supply and Demand Study

G4-F-2 December 2012

TABLE F-1 

Ecological Resource Metrics

Attribute of 

Interest

Resource 

Metric Section

Quantitative 

or Qualitative Plot Type Location

Figure 

Number

Flows to 

Support 

Threatened 

and 

Endangered 

Species

Flows to 

Support 

Threatened 

and 

Endangered 

Species

2 Quantitative Monthly Yampa River near 

Maybell, CO

F-1 

Glen Canyon Dam F-2

Year Type 

Frequency 

and Flow 

by Year 

Type

Colorado River near 

Cameo, CO

F-3 and 

F-4

Gunnison River near 

Grand Junction, CO

F-5 and 

F-6

Colorado River near the 

Colorado-Utah Stateline

F-7 and 

F-8

Green River near 

Greendale, UT

F-9 and 

F-10

Green River at Green 

River, UT

F-11 and 

F-12

Duchesne River near 

Randlett, UT

F-13 and 

F-14

Year Type

Frequency 

and 

Percent of 

Years 

Meeting 

Target

Green River at Jensen, 

UT

F-9 and 

F-15

Monthly 

and Annual 

San Juan River near 

Bluff, UT

F-16 

through 

F-20

Annual Hoover Dam to Davis 

Dam

F-21

Davis Dam to Parker 

Dam

F-22

Parker Dam to Imperial 

Dam

F-23

Aquatic and 

Riparian 

Habitat

Instream 

Flow Rights

3.1 Quantitative Monthly Taylor River near Taylor 

Park, CO

F-24

Gunnison River below 

Crystal Reservoir, CO

F-25

Cottonwood 

Recruitment 

Metric

3.2 Quantitative Annual Dolores River near Cisco, 

UT

F-26

San Juan River near 

Archuleta, NM

F-27

Green River below 

Fontenelle Reservoir, WY

F-28

Green River near Green 

River, WY

F-29

San Rafael near Green 

River, UT

F-30

Colorado River near 

Cisco, UT

F-31
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-3 

TABLE F-1 

Ecological Resource Metrics

Attribute of 

Interest

Resource 

Metric Section

Quantitative 

or Qualitative Plot Type Location

Figure 

Number

Aquatic and 

Riparian 

Habitat

FlowDependent 

Ecological 

Systems

3.3 Quantitative Year Type 

Frequency 

and Flow 

by Year 

Type

Yampa River near 

Maybell, CO

F-32 and 

F-33

Little Snake River near 

Lily, CO

F-34 and 

F-35

Yampa River at 

Deerlodge Park, CO

F-36 and 

F-37

White River near Watson, 

UT

F-38 and 

F-39

Wildlife 

Refuges and 

Fish 

Hatcheries

Wildlife 

Refuges and 

Fish 

Hatcheries

4 Quantitative Flow by 

Year Type

Browns Park National 

Wildlife Refuge

F-40

Seedskadee National 

Wildlife Refuge

F-41

Ouray National Wildlife 

Refuge

F-42

Annual Havasu National Wildlife 

Refuge

Table F-2 

Cibola National Wildlife 

Refuge

Imperial National Wildlife 

Refuge

Willow Beach Fish 

Hatchery

2.0 Metrics for the 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. Flow 

recommendations3 are defined as part of the Recovery Programs; therefore, flows are used as 

metrics for these fish species, and the Recovery Programs’ recommendations provide the 

reference values. Providing flows is only one part of the recovery efforts, which include 

activities such as habitat development, non-native fish control, and monitoring and research. 

Therefore, the relative difference in achieving these flow recommendations across various 

scenarios should not be viewed as the sole means to recover the species. Many of the Recovery 

Program flow recommendations are for average daily flow rates, whereas the Colorado River 

Simulation System (CRSS) operates at the monthly time step. Recent research and development 

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

Reservoirs (see Technical Report D – System Reliability Metrics, Appendix D3 – Threatened and 

 

3 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

G4-F-4 December 2012

Endangered Species Metrics). For other locations, monthly volumetric targets were developed 

based on the Recovery Program’s flow recommendations. 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 those 

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. 

In addition to metrics based on Recovery Program flow recommendations, metrics also exist for 

Glen Canyon Dam and on the Colorado River below Hoover Dam. The metric at Glen Canyon 

Dam represents the minimum allowable release specified by the 1996 Glen Canyon Dam Record 

of Decision (Bureau of Reclamation [Reclamation], 1996). The metrics below Hoover Dam 

represent the permitted changes in point diversions in three reaches specified by the Lower 

Colorado River Multi-Species Conservation Program (Reclamation, 2004). 

The metrics for flows to support threatened and endangered species are separated into two main 

groups: those with single flow targets for all months (e.g. minimum base flows) and those with 

targets that vary by month and/or hydrologic year type. Figures F-1 and F-2 present results for 

the Yampa River near Maybell, Colorado, and the releases from Glen Canyon Dam, which both 

have minimum flow targets as reference values. 

Of those locations with flow targets that vary by month and/or hydrologic year type, most 

contain two figure types: (1) a year type frequency figure and (2) a figure showing flow volumes 

by month and hydrologic year type. With the exception of the Gunnison River near Grand 

Junction, Colorado, and the Green River near Greendale and Jensen, Utah, the year type 

frequency figures were developed as follows:

1. Using annual volumes at the specific gage from the control run (see appendix G3), 

percentiles that separate year types were computed (e.g., the 20th percentile separates the 

“dry” years from “below average” years on at the Colorado River near Cameo, 

Colorado). 

2. Using the annual volumes from the modeled scenarios, each year was binned in its 

respective year type classification, as separated by the thresholds computed in step 1.

3. The frequency that each year type occurred in each time period was computed.

For the Gunnison River near Grand Junction, Colorado, the Final Gunnison River Programmatic 

Biological Opinion (U.S. Fish and Wildlife Service [USFWS], 2009) indicates that year types are 

determined by the April through July forecasted inflow into Blue Mesa Reservoir. Therefore, 

step 1 above was skipped, and step 2 was modified to use the April through July volume and the 

thresholds defined in USFWS (2009) to bin the year types4. Similarly, the year types for the 

Green River near Greendale, Utah, and the Green River near Jensen, Utah (Jensen), are 

determined by the April through July unregulated inflow into Flaming Gorge Reservoir. All year 

type frequency figures include reference values indicating the expected frequency of each year 

type as defined by the respective flow recommendations.

At these locations, a complementary figure displays the flow (or flow volume) at each location 

for each year type and month. As explained in Technical Report D – System Reliability Metrics, 

 

4 The Aspinall Unit within CRSS is not operated to reflect the Record of Decision for the Aspinall Unit Operations Final Environmental Impact 

Statement (Reclamation, 2012); therefore, model results were not expected to reflect Record of Decision operations.
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-5 

the spring months (typically April though July) are aggregated together. For each time period 

and month, for each scenario, the flows representing the different year type percentiles were 

grouped together, e.g., the driest 10 percent of Januaries in 2012 though 2026 or the 30th through 

70th percentiles of April though July of 2041 through 2060. Then, each year type was grouped 

together for all scenarios before the statistics were computed for the box plot. These figures help 

show the flow variability between and within year types in comparison to the reference values.

The final metrics that are presented for flows to support threatened and endangered species are 

those for Jensen and the San Juan River near Bluff, Utah (Bluff). Although these locations are 

largely analogous to those previously described, the daily flow recommendations are able to be 

directly compared using CRSS by disaggregating monthly volumes to plausible daily flow 

patterns instead of having to aggregate daily recommendations to monthly volumes – see 

Technical Report D – System Reliability Metrics for more information. The ability to directly 

compare disaggregated flows to recommendations changes the way the results can be viewed. 

For the daily flow targets and durations at Jensen, figure F-15 indicates the percent of years that 

were able to meet each flow target. The flow targets for Bluff include a minimum frequency and 

a maximum interval between occurrences that each flow target should meet and not exceed, 

respectively. Each flow target at Bluff includes a figure for the frequency of meeting the target, 

and a figure presenting the years since the flow target was last met (years since last occurrence). 

For the years since last occurrence, the historical gage record at Bluff was analyzed to determine 

the last occurrence, rather than starting the count from zero in 2012 (the first modeled year). 

This helps to more accurately present the years since the last occurrence for the first time period 

(2012 through 2026). Finally, Bluff also includes a minimum base flow target that is presented 

identically to like metrics as previously described.

Several overarching results are observed at most locations for flows to support threatened and 

endangered species metrics. To begin, the flow is generally higher in all portfolios than in the 

Baseline, particularly at the 75th and 90th percentiles. At locations separated by hydrologic year 

type, this trend is more apparent in the wetter year types. Typically, Portfolios A and C increase 

the flow more than Portfolios B and D; figure F-1 exemplifies this observation, which is due to 

the inclusion of an Upper Basin bank and the routing of conserved water to a conceptual offstream storage location above Lake Powell. At most locations for which the year type frequency 

is shown, in the Baseline, there is an increase in the frequency of dryer year types and a decrease 

in the number of wetter year types through time. Again, all portfolios help stabilize or reduce the 

frequency of dry year types through time and stabilize or increase the frequency of wet year 

types, compared to the Baseline. In some cases (e.g., figure F-5), an increase in the frequency of 

wet year types through time within a single portfolio is achieved. 

For Jensen (figure F-15), the frequency that each of the flow targets is met decreases through 

time under the Baseline. With the implementation of portfolios, the frequency that the flow 

targets are met increases not only as compared to the Baseline, but through time as well. 

The average monthly flows at Bluff (figure F-16) follow the same trends in monthly flows 

discussed previously. In figures F-17 through F-20, the frequency that flow targets are met and 

the number of years between occurrences are shown for four different flow-duration targets. In 

all cases, portfolios perform better than the Baseline (i.e., increase the frequency of meeting the 

flow targets, and decrease the number of years between occurrences). For these metrics, the 

performance across portfolios is similar, with the exception those shown in figure F-18b, which 
Colorado River Basin

Water Supply and Demand Study

G4-F-6 December 2012

indicates slightly better performance in the third period (2041 through 2060) in Portfolio A, and 

figure F-17a, which indicates slightly worse performance in that period by Portfolio D. 

Figures F-21 through F-23 show the annual flow reductions in three reaches below Lake Mead. 

In all three reaches, the same general trend exists; the Baseline only exceeds the maximum 

allowable flow reduction at the 90th percentile in the third period, and the portfolios all decrease 

the flow reductions, compared to the Baseline. There is some variability across portfolios, with 

Portfolio B typically performing better and Portfolio D not performing as well.

FIGURE F-1 

Monthly Flow, Yampa River near Maybell, CO

Red Lines Indicate the Minimum Reference Value of 120 cubic feet per second (cfs) 
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-7 

FIGURE F-2 

Monthly Release from Glen Canyon Dam

Red Lines Indicate the Minimum Base Flow Reference Value of 6,438 cfs 

FIGURE F-3 

Year Type Frequency, Colorado River near Cameo, CO

Red Lines Indicate Frequency Reference Values 
Colorado River Basin

Water Supply and Demand Study

G4-F-8 December 2012

FIGURE F-4A

Flow Volume by Year Type, Colorado River near Cameo, CO

Red Lines Indicate the Average Monthly Flow Recommendations as Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-9 

FIGURE F-4B

Flow Volume by Year Type, Colorado River near Cameo, CO

Red Lines Indicate the Average Monthly Flow Recommendations as Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-10 December 2012

FIGURE F-5 

Year Type Frequency, Gunnison River near Grand Junction, CO

Red Lines Indicate Frequency Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-11

FIGURE F-6A

Flow Volume by Year Type, Gunnison River near Grand Junction, CO 

Red Lines Indicate the Low and High Flow Recommendation Approximations as Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-12 December 2012

FIGURE F-6B

Flow Volume by Year Type, Gunnison River near Grand Junction, CO 

Red Lines Indicate the Low and High Flow Recommendation Approximations as Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-13

FIGURE F-7 

Year Type Frequency, Colorado River near Colorado-Utah State Line

Red Lines Indicate Frequency Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-14 December 2012

FIGURE F-8A

Flow Volume by Year Type, Colorado River near Colorado-Utah State Line 

Red Lines Indicate the Low and High Flow Recommendation Approximations as Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-15

FIGURE F-8B

Flow Volume by Year Type, Colorado River near Colorado-Utah State Line 

Red Lines Indicate the Low and High Flow Recommendation Approximations as Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-16 December 2012

FIGURE F-9 

Year Type Frequency, Green River near Greendale and Jensen, UT

Red Lines Indicate Frequency Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-17

FIGURE F-10A

Flow by Year Type, Green River near Greendale, UT 

Red Lines Indicate the Low and High Flow Recommendation Approximations as Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-18 December 2012

FIGURE F-10B

Flow by Year Type, Green River near Greendale, UT 

Red Lines Indicate the Low and High Flow Recommendation Approximations as Reference Values 
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-19

FIGURE F-11

Year Type Frequency, Green River at Green River, UT

Red Lines Indicate Frequency Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-20 December 2012

FIGURE F-12A

Flow Volume by Year Type, Green River at Green River, UT

Red Lines Indicate the Low and High Flow Recommendation Approximations as Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-21

FIGURE F-12B

Flow Volume by Year Type, Green River at Green River, UT 

Red Lines Indicate the Low and High Flow Recommendation Approximations as Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-22 December 2012

FIGURE F-13

Year Type Frequency, Duchesne River near Randlett, UT

Red Lines Indicate Frequency Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-23

FIGURE F-14A

Flow Volume by Year Type, Duchesne River near Randlett, UT 

Red Lines Indicate the Flow Recommendation Approximations as Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-24 December 2012

FIGURE F-14B

Flow Volume by Year Type, Duchesne River near Randlett, UT 

Red Lines Indicate the Flow Recommendation Approximations as Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-25

FIGURE F-15

Percent of Years Meeting Green River near Jensen, UT, Flow Targets

(a) Represents Dry Year Type Target; (b) Represents Moderately Dry Year Type Target; (c) Represents Target for All 

Moderately Wet Year Types and 1 in 4 Average Years; (d) and (e) Represent Two Wet Year Type Targets; Red Lines Indicate 

Reference Values 
Colorado River Basin

Water Supply and Demand Study

G4-F-26 December 2012

FIGURE F-16

Monthly Flow, San Juan River near Bluff, UT

Red Lines Indicate the Minimum Reference Value of 500 cfs 
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-27

FIGURE F-17

San Juan River near Bluff, UT, 10 days >= 2,500 cfs 

(a) Percent of Years Meeting Target Flow and (b) Years since Last Occurrence of Target Flow-Duration; Red Lines Indicate (a) 

Minimum Frequency and (b) Maximum Interval Between Occurrences
Colorado River Basin

Water Supply and Demand Study

G4-F-28 December 2012

FIGURE F-18

San Juan River near Bluff, UT, 21 days >= 5,000 cfs 

(a) Percent of Years Meeting Target Flow and (b) Years since Last Occurrence of Target Flow-Duration; Red Lines Indicate (a) 

Minimum Frequency and (b) Maximum Interval Between Occurrences
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-29

FIGURE F-19

San Juan River near Bluff, UT, 10 days >= 8,000 cfs 

(a) Percent of Years Meeting Target Flow and (b) Years since Last Occurrence of Target Flow-Duration; Red Lines Indicate (a) 

Minimum Frequency and (b)Maximum Interval Between Occurrences
Colorado River Basin

Water Supply and Demand Study

G4-F-30 December 2012

FIGURE F-20

San Juan River near Bluff, UT, 10 days >= 10,000 cfs 

(a) Percent of Years Meeting Target Flow and (b)Years since Last Occurrence of Target Flow-Duration; Red Lines Indicate (a) 

Minimum Frequency and (b) Maximum Interval Between Occurrences
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-31

FIGURE F-21

Annual Flow Reductions, Hoover Dam to Davis Dam

Red Line Indicates Maximum Allowable Flow Reduction 

FIGURE F-22

Annual Flow Reductions, Davis Dam to Parker Dam

Red Line Indicates Maximum Allowable Flow Reduction 
Colorado River Basin

Water Supply and Demand Study

G4-F-32 December 2012

FIGURE F-23

Annual Flow Reductions, Parker to Imperial Dam

Red Line Indicates Maximum Allowable Flow Reduction 

3.0 Metrics for the Aquatic and Riparian Habitat Attribute 

of Interest

3.1 Instream Flow Rights

The Colorado Water Conservation Board has secured many instream flow rights5 to benefit the 

aquatic and riparian habitat across Colorado. Figures F-24 and F-25 present the results for the 

locations that instream flow rights coincide with gage locations in CRSS. Monthly flow at these 

two locations is presented along with reference values for the instream flow rights. 

Figure F-24 indicates that flow on the Taylor River near Taylor Park, Colorado, is generally 

increased by portfolios, compared to the Baseline. The portfolios also reduce variability (e.g., 

the inner quartile range is reduced), compared to the Baseline. Figure F-25 indicates that 

portfolios tend to increase flows on the Gunnison River below Crystal Reservoir, compared to 

the Baseline. However, the variability remains largely the same, owing to the regulated nature of 

the Gunnison River below the Aspinall Unit. 

 

5 Available at: http://cwcb.state.co.us/environment/instream-flow-program/Pages/main.aspx. 
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-33

FIGURE F-24

Monthly Flow Taylor River near Taylor Park, CO

Red Lines Indicate Instream Flow Rights

FIGURE F-25

Monthly Flow Gunnison River below Crystal Reservoir

Red Lines Indicate Instream Flow Rights
Colorado River Basin

Water Supply and Demand Study

G4-F-34 December 2012

3.2 Cottonwood Recruitment

The cottonwood recruitment metric, developed in coordination with the FWS and The Nature 

Conservancy, 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. The metric uses 

monthly approximations to estimate physical processes that lead to positive conditions for 

cottonwood recruitment events. Technical Report D – System Reliability Metrics includes 

additional description of the metric and the steps for computing when positive conditions exist. 

Figures F-26 through F-31 present a count of the years since positive recruitment conditions 

occurred. To remove the effects of initial conditions (i.e., starting the count at 0 in 2012), the 

historical gage records at the six locations were analyzed using the same methodology employed 

in CRSS to determine the last year that positive conditions existed. This led to counts greater 

than the 49-year modeling horizon (e.g., figure F-30). 

The Baseline trends vary across the different locations, with sites such as the San Juan River near 

Archuleta, New Mexico (figure F-27), changing very little through time and sites such as the 

Green River near Fontenelle, Wyoming (figure F-28), experiencing longer runs with no positive 

conditions occurring in later time periods. However, in most cases, portfolios reduce the number 

of years between positive conditions for recruitment occurring, compared to the Baseline. 

Generally, Portfolio B tends to perform better than other portfolios, though the Green River near 

Green River, Wyoming (figure F-29), is a noticeable exception. 

FIGURE F-26

Years since Positive Conditions Occurred, Dolores River near Cisco, UT

Red Line Indicates Estimated Condition that Positive Conditions for Recruitment Should Exist Once Every 10 Years
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-35

FIGURE F-27

Years since Positive Conditions Occurred, San Juan River near Archuleta, NM

Red Line Indicates Estimated Condition that Positive Conditions for Recruitment Should Exist Once Every 10 Years 

FIGURE F-28

Years since Positive Conditions Occurred, Green River Below Fontenelle, WY

Red Line Indicates Estimated Condition that Positive Conditions for Recruitment Should Exist Once Every 10 Years
Colorado River Basin

Water Supply and Demand Study

G4-F-36 December 2012

FIGURE F-29

Years since Positive Conditions Occurred, Green River near Green River, WY

Red Line Indicates Estimated Condition that Positive Conditions for Recruitment Should Exist Once Every 10 Years 

FIGURE F-30

Years since Positive Conditions Occurred, San Rafael River near Green River, UT

Red Line Indicates Estimated Condition that Positive Conditions for Recruitment Should Exist Once Every 10 Years 
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-37

FIGURE F-31

Years since Positive Conditions Occurred, Colorado River near Cisco, UT

Red Line Indicates Estimated Condition that Positive Conditions for Recruitment Should Exist Once Every 10 Years 

3.3 Flow-dependent Ecological Systems

Metrics were developed, in coordination with FWS and the Nature Conservancy, 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. 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 and temperature) that are not considered in the estimated flow-based 

conditions. Secondly, these flow conditions must be aggregated to a monthly time step to meet 

those of CRSS. Additionally, the methodology used to develop these flow conditions depends on 

assumptions behind the hydrologic year-typing. Acknowledging these limitations, figures F-32 

through F-39 present the year type frequency and the flow by year type for four locations: the 

Yampa River near Maybell, Colorado; the Little Snake River near Lily, Colorado; the Yampa 

River at Deerlodge Park, Colorado; and the White River near Watson, Utah. The year type 

frequency figures were developed as follows:

1. Using annual volumes at the specific gage from the control run, the percentiles that 

separate year types were computed (e.g., the 20th percentile separates the “dry” years 

from “below average” years at the Colorado River near Cameo, Colorado). 

2. Using the annual volumes from the modeled scenarios, each year was binned in its 

respective year type classification, as separated by the thresholds computed in step 1.

3. Last, the frequency that each year type occurred in each time period was computed.

For each time period and month, for each scenario, the flows representing the different year type 

percentiles were grouped together (e.g., the driest 10 percent of Januaries from 2012 to 2026 or 

the 30th through 70th percentiles of Aprils through Julys from 2041 to 2060). Then, each year 

type for all scenarios was grouped together before computing the statistics for the box plots. 

Regarding year type frequency (figures F-32, F-34, F-36, and F-38), the same general trends are 

observed at all four locations. Under the Baseline, the frequency of dry years increases through 

time, and the frequency of wet years decreases through time. However, portfolios generally 

increase the frequency of moderately wet and wet year types and decrease the number of 
Colorado River Basin

Water Supply and Demand Study

G4-F-38 December 2012

moderately dry and dry year types, both through time and compared to the Baseline. Typically, 

the frequency of moderately wet and wet year types is highest in Portfolios A and C. This is 

likely attributable to the banking mechanism that is in place in these portfolios and includes the 

routing of conserved water to a conceptual off-stream storage location above Lake Powell. 

When the conserved water is routed downstream, the flow in the reach increases, therefore 

classifying the year as a wetter year type than would be the case without conservation and 

routing. 

Figures F-33, F-35, F-37, and F-39 present the flow by year type at the four locations. For 

locations in the Yampa Basin (figures F-33 through F-37), portfolios tend to benefit the flows in 

most year types. For the White River near Watson, UT (figure F-39), there is little variability 

between portfolios and the Baseline, or across portfolios. This is attributed to the relatively 

small demands that exist and the lack of any large options or strategies being implemented in the 

White River Basin. 

FIGURE F-32

Year Type Frequency, Yampa River near Maybell, CO

Red Lines Indicate Frequency Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-39

FIGURE F-33A

Flow Volume by Year Type, Yampa River near Maybell, CO 

Red Lines Indicate the Estimated Target Flow Conditions as Reference Values; kaf = thousand acre-feet
Colorado River Basin

Water Supply and Demand Study

G4-F-40 December 2012

FIGURE F-33B

Flow Volume by Year Type, Yampa River near Maybell, CO 

Red Lines Indicate the Estimated Target Flow Conditions as Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-41

FIGURE F-34

Year Type Frequency, Little Snake River near Lily, CO

Red Lines Indicate Frequency Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-42 December 2012

FIGURE F-35A

Flow Volume by Year Type, Little Snake River near Lily, CO 

Red Lines Indicate the Estimated Target Flow Conditions as Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-43

FIGURE F-35B

Flow Volume by Year Type, Little Snake River near Lily, CO 

Red Lines Indicate the Estimated Target Flow Conditions as Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-44 December 2012

FIGURE F-36

Year Type Frequency, Yampa River at Deerlodge Park, CO

Red Lines Indicate Frequency Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-45

FIGURE F-37A

Flow Volume by Year Type, Yampa River at Deerlodge Park, CO 

Red Lines Indicate the Estimated Target Flow Conditions as Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-46 December 2012

FIGURE F-37B

Flow Volume by Year Type, Yampa River at Deerlodge Park, CO 

Red Lines Indicate the Estimated Target Flow Conditions as Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-47

FIGURE F-38

Year Type Frequency, White River near Watson, UT

Red Lines Indicate Frequency Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-48 December 2012

FIGURE F-39A

Flow Volume by Year Type, White River near Watson, UT 

Red Lines Indicate the Estimated Target Flow Conditions as Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-49

FIGURE F-39B

Flow Volume by Year Type, White River near Watson, UT 

Red Lines Indicate the Estimated Target Flow Conditions as Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-50 December 2012

4.0 Metrics for Wildlife Refuges and Fish Hatcheries 

Attribute of Interest 

Metrics and their reference values were developed, in coordination with FWS, for wildlife 

refuges and fish hatcheries in the Basin that have water rights. 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. In the Lower Basin, reference values are based on the 

wildlife refuges’ entitlements and historical use, and vary by water demand scenario.

Figures F-40 through F-42 present the monthly flow for the reaches where the three Upper Basin 

wildlife refuges exist (Browns Park, Seedskadee, and Ouray National Wildlife Refuges 

[NWRs]). Although the reference values appear to be zero because of the scale of the figures, 

they are, in fact, not zero (see Technical Report D – System Reliability Metrics). At all three 

locations, the flow is more than sufficient to meet the reference values, and the portfolios tend to 

increase the flow in the reaches.

The reference values for the three Lower Basin NWRs and the fish hatchery are the requested 

depletions and diversions quantified in the Study. These demands vary by demand scenario (see 

Technical Report C – Water Demand Assessment). Displaying results for comparison with the 

appropriate reference value would require a scenario-by-scenario presentation. Instead, for these 

metrics, table F-2 presents the percentage of years that do not meet the NWR and fish hatchery 

demands. Although there are some extreme instances under the Baseline in which the demands 

are not fully met, the demands are met in all years under all portfolios. 
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-51 

FIGURE F-40A

Flow by Year Type, Browns Park National Wildlife Refuge 

Red Lines Indicate the Estimated Conditions as Reference Values; kafm = thousand acre-feet per month 
Colorado River Basin

Water Supply and Demand Study

G4-F-52 December 2012

FIGURE F-40B

Flow by Year Type, Browns Park National Wildlife Refuge 

Red Lines Indicate the Estimated Conditions as Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-53

FIGURE F-41A

Flow by Year Type, Seedskadee National Wildlife Refuge 

Red Lines Indicate the Estimated Conditions as Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-54 December 2012

FIGURE F-41B

Flow by Year Type, Seedskadee National Wildlife Refuge 

Red Lines Indicate the Estimated Conditions as Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-55

FIGURE F-42A

Flow by Year Type, Ouray National Wildlife Refuge 

Red Lines Indicate the Estimated Conditions as Reference Values
Colorado River Basin

Water Supply and Demand Study

G4-F-56 December 2012

FIGURE F-42B

Flow by Year Type, Ouray National Wildlife Refuge 

Red Lines Indicate the Estimated Conditions as Reference Values
Attachment F — Ecological

Resource Metrics’ Results

December 2012 G4-F-57

TABLE F-2 

Lower Basin National Wildlife Refuges and Fish Hatcheries Percent of Years Not Meeting Requested Depletions and Diversions 

Baseline Portfolio A Portfolio B Portfolio C Portfolio D

Havasu NWR 0 0 0 0 0 

Cibola NWR < 1% 0 0 0 0 

Imperial NWR < 1% 0 0 0 0 

Willow Beach Fish Hatchery 0 0 0 0 0 

5.0 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). 2012. Record of Decision for the Aspinall Unit 

Operations, Final Environmental Impact Statement. 

U.S. Fish and Wildlife Service (FWS). 2009. Final Gunnison River Basin Programmatic 

Biological Opinion.