Assessment of the Estimated Effects of Four 

Experimental Options on Resources Below Glen 

Canyon Dam 

Prepared by 

U.S. Geological Survey 

Southwest Biological Science Center 

Grand Canyon Monitoring and Research Center 

Flagstaff, Arizona 

Developed in cooperation with the 

Glen Canyon Dam Adaptive Management Program 

 

 

Draft for Review 

Glen Canyon Dam Adaptive Management Program 

Technical Work Group 

October 27, 2006 

U.S. Department of the Interior 
ii

Contents 

Chapter 1. Introduction.................................................................................................................................... 1 

 Background.................................................................................................................................... 1 

 General Methods .......................................................................................................................... 3 

 Report Organization...................................................................................................................... 4 

Chapter 2. Experimental Options Descriptions ........................................................................................... 5 

 Component Descriptions ............................................................................................................. 5 

 Experimental Options Descriptions ........................................................................................... 7 

Chapter 3. Estimated Effects of Proposed Flow Regimes on Downstream Resources.....................18 

 Part 1: Physical Resources ......................................................................................................18 

 Part 2: Aquatic and Fisheries Resources ..............................................................................29 

 Part 3: Terrestrial Biological Resources................................................................................37 

 Part 4: Recreation and Cultural Resources...........................................................................43 

 Part 5: Hydropower Resources ...............................................................................................56

 Summary Table............................................................................................................................57 

 

Chapter 4. Estimated Effects of Proposed Nonflow Actions on Downstream Resources................60 

 Temperature Control Device.....................................................................................................61 

 Nonnative Fish Control...............................................................................................................67 

 Translocation of Humpback Chub ...........................................................................................70 

 Humpback Chub Refuge, Propagation, and Genetics Management Planning................73 

 Summary Table............................................................................................................................74 

Chapter 5. Evaluation of Proposed Experimental Designs .....................................................................78 

 Introduction..................................................................................................................................78 

 Option A and Option A Variation Experimental Design........................................................79 

 Option B Experimental Design..................................................................................................79 

 Option C Experimental Design..................................................................................................80 

Chapter 6. Scientific “Take Home” Points for Selecting an Experimental Option .............................83 

References Cited.............................................................................................................................................88 

Appendix A. Methods for Determining Flows ...........................................................................................96 

Appendix B. Flow Variations ......................................................................................................................109 

Appendix C. Glen Canyon Dam Release Temperature Modeling........................................................123 

Appendix D. Mainstem Temperature Modeling .....................................................................................130 

Appendix E. Economic Analysis ................................................................................................................141
1

Chapter 1: Introduction 

This report is designed to provide a scientific assessment of the estimated effects of four experimental 

options currently being considered by the Glen Canyon Dam Adaptive Management Program 

(GCDAMP). Each of the four options outlines revised operating criteria for Glen Canyon Dam and 

various nonflow actions that would be implemented or tested during the next 10 years. The purpose of 

this assessment is to provide GCDAMP participants and Department of the Interior (DOI) decision 

makers with information about how each of the four experimental options is likely to (a) affect 

downstream biological, physical, and sociocultural resources of the Colorado River ecosystem (Glen 

Canyon Dam to upper Lake Mead) and (b) contribute to the understanding of the relationships between 

management actions and resource conditions. 

Background 

The GCDAMP was established in 1996 by the Secretary of the Interior to implement the Grand Canyon 

Protection Act of 1992 (GCPA), the 1995 Operation of Glen Canyon Dam Final Environmental Impact 

Statement (final EIS), and the 1996 Record of Decision (ROD). Adaptive management in Grand Canyon 

was envisioned as a new paradigm for addressing the complex environmental problems related to the 

operation of Glen Canyon Dam through the dynamic interplay of stakeholder collaboration, resources 

management, and scientific research. As a result, GCDAMP consists of five major components, 

including: 

• The Adaptive Management Work Group (AMWG) is a Federal Advisory Committee composed 

of 25 stakeholders that was established to facilitate the implementation of the GCDAMP. After 

careful review, the AMWG makes recommendations to the Secretary of the Interior on how to 

best alter dam operating criteria or other management actions in order to fulfill the Department of 

the Interior’s obligations under the GCPA. 

• The Secretary of the Interior’s Designee serves as the chair of the AMWG and provides a direct 

link between the AMWG and the Secretary of the Interior. 

• The Technical Work Group (TWG) translates AMWG policy and goals into information needs, 

provides questions that serve as the basis for long-term monitoring and research activities, and 

conveys research results to AMWG members. 

• The U.S. Geological Survey’s (USGS) Grand Canyon Monitoring and Research Center 

(GCMRC) provides credible, objective scientific information on the effects of the operation of 

Glen Canyon Dam and related factors on natural, cultural, and recreational resources along the 

Colorado River from Glen Canyon Dam to Lake Mead. 

• The independent review panels (IRPs) provide independent assessments of program proposals 

and accomplishments to ensure scientific objectivity and credibility. For example, a formal group 

of Science Advisors (SAs) consisting of academic experts in fields germane to studies within the 

scope of the GCDAMP serves as an IRP. 
2

This document will be reviewed by the SAs, TWG, and AMWG (in that order). AMWG 

recommendations concerning the experimental options will be forwarded to the Secretary’s Designee. 

The eventual preferred alternative will be implemented following completion of appropriate 

environmental compliance (e.g., National Environmental Policy Act, Endangered Species Act) and 

approval by the Secretary of the Interior.

The 1996 ROD implemented a modified low fluctuating flow (MLFF) regime as the basis for the 

operation of Glen Canyon Dam, following an extensive National Environmental Policy Act review 

process. In selecting the MLFF alternative (also known as ROD operations), the ROD noted that the goal 

was to “permit recovery and long-term sustainability of downstream resources while limiting hydropower 

capacity and flexibility only to the extent necessary to achieve recovery and long-term sustainability.” In 

the intervening decade, the MLFF operating regime and a variety of experimental projects have been 

implemented to meet this goal. In keeping with its role in the program, GCMRC and its cooperators have 

evaluated the effects of MLFF operations and various experimental efforts. The State of the Colorado 

River Ecosystem in Grand Canyon (Gloss and others, 2005), prepared by the GCMRC to meet the 

information needs of GCDAMP participants, summarizes the results of these studies and the state of the 

resources in the Grand Canyon based on relevant scientific data collected between 1991 and 2004. 

In 2005, an ad hoc Science Planning Group (SPG) was established to provide a forum for GCDAMP 

participants and GCMRC scientists to work collaboratively to develop an effective long-term direction for 

the future experimental research activities. Over the course of a year, three experimental options were 

developed by various GCDAMP participants through the SPG process. In October 2006, a fourth option 

was added to the list of options under consideration at the request of the TWG. As a result, this 

assessment considers four experimental options (table 1.1), referred to as Options A, A Variation, B, and 

C. Each option reflects very different philosophies and policies related to conservation and use of Grand 

Canyon resources, and the role of science in the GCDAMP. As a result of these differences, the primary 

flow regimes advocated by the four options vary greatly. For example, Options A and A Variation 

provide for wider fluctuating flows throughout the year primarily to benefit hydropower generation. By 

contrast, Option B proposes to incrementally implement and test steady flows and equalized monthly 

volumes of flows primarily to protect downstream resource values. Option C includes both steady flows 

in the late summer/early fall and wider fluctuating flows during other times of the year. 

In addition to variations in flow regime, the experimental options also have nonflow components that 

vary. However, all the options share several common flow and nonflow actions, including: 

• Implementation of a temperature control device (TCD) to elevate mainstem water temperatures 

and promote humpback chub spawning and recruitment; 

• Nonnative fish management to reduce predation on and competition with native fishes; and 

• Beach/habitat-building flows (BHBF), or controlled floods, under enriched sand supply 

conditions to conserve sand resources. 

A fundamental tenet of adaptive management is “learning by doing,” meaning that science is used to 

better understand the relationships between actions—natural events, anthropogenic change, or 

experimental treatments—and desired resource conditions. A properly designed experimental program 

implemented over a long time frame is most likely to yield definitive information on the relationships 

between specific actions and the condition of target resources. The four options vary significantly in their 

proposed experimental design or approach. Options A and A Variation provide for implementation of a 

suite of actions at the earliest possible time frame to achieve a positive resource response, and deem 

learning about the relationship between actions and resource responses to be a secondary priority. Options 
3

B and C advocate a more structured experimental design that is intended to improve downstream 

resources while facilitating an understanding of the effectiveness of different management actions. 
4

Table 1.1 Authors/proponents on the various experimental options, and approval mechanism. 

Option Author/Proponent Approved 

 

A Arizona Game and Fish Department SPG 

 Federation of Fly Fishers 

U.S. Department of Energy, 

Western Area Power Administration 

A Variation Colorado River Energy Distributors Association TWG 

B Grand Canyon River Guides SPG 

 Grand Canyon Trust 

C Bureau of Reclamation SPG 

National Park Service 

U.S. Fish and Wildlife Service 

It should be noted that the four experimental options that are the subject of this evaluation reflect different 

policy options related to the Glen Canyon Dam experimental program that were defined primarily by 

GCDAMP stakeholders. These experimental options should not be confused with an experimental science 

plan that articulates specific science questions, hypotheses, and technical approaches. These will be 

defined in detail in a long-term experimental plan (LTEP) that will be developed by GCMRC once the 

preferred experimental option is determined by the Secretary of the Interior. The LTEP will be integrated 

into the Monitoring and Research Plan to Support the Glen Canyon Dam Adaptive Management Program, 

Fiscal Years 2007–11, which describes the scope and objective of a 5-year monitoring and research 

program to address priority goals, questions, and information needs specified by the GCDAMP.

 

General Methods 

The assessment of the possible influence of the four options on downstream resources is made primarily 

through the use of information reported in the 2005 knowledge assessment final report (Melis and others 

2006b; KAR). In making their assessments, GCMRC scientists relied on the peer-reviewed literature, 

both sources cited in the KAR and elsewhere, and the range of expert opinions from well-known 

scientists that were shared during the 2005 workshop that culminated in the KAR. The estimated resource 

responses to the proposed experimental options are of a generalized nature and made with admission of 

the numerous uncertainties that were identified during the knowledge assessment workshop. 

New models for simulating the effects of downstream water temperature (see appendix D, this report) and 

diurnal stage variation (see appendix B, this report) have been completed since the KAR was finalized. 

The results generated by these models were used to inform the analysis presented in following chapters. 

Simulation results for diurnal stage variation, as derived from a new version of the HEC-RAS model 

containing 2,200 cross sections (Magirl, in press), were used in assessing the options. In addition, 

information pertaining to release temperatures from the dam and downstream thermal characteristics is 

derived from new and existing models for Lake Powell and downstream flow and temperature conditions. 
5

The temperature models are also being used to simulate the amount of downstream warming under 

several TCD design options. 

All options were evaluated over a range of simulated hydrologic conditions for the upper Colorado River 

Basin in order to evaluate the influences of the four options under a realistic range of variability. The 

hydrologic conditions included in the assessment range from 8.23 million acre-feet (MAF), the minimum 

amount of water needed to meet delivery requirements under various treaties and agreements, to mostprobable and wet conditions. The hydrologic scenarios for these three conditions were derived from 

output data generated by the Bureau of Reclamation using a Colorado River Storage System (CRSS) 

simulation model based on 20th century hydrologic conditions (see appendix A, this report). Monthly 

release volumes projected for each of the options under the 8.23 MAF annual release pattern, mostprobable conditions, and wet scenarios were used by the Western Area Power Administration to generate 

hourly hydrographs for each of the experimental scenarios over the 10-year simulation period. 

Finally, the 2005 KAR process identified a critical need to evaluate the economic implications to 

hydropower resources associated with various experimental plans. Following this recommendation, an 

economic assessment of the four options has also been undertaken independently by the Western Area 

Power Administration. The results of the economic evaluation are reported in appendix E; however, 

chapter 3 of this report presents a summary of those findings. This assessment and the economic 

evaluation will be subjected to external peer review by knowledgeable experts. 

Report Organization 

The report is designed to provide GCDAMP participants and DOI decision makers the relevant 

information that they need to evaluate the effects of the four options on downstream resources. To limit 

the primary report length and complexity, technical scientific discussions (e.g., methods used to develop 

models and estimate temperature change) have been placed in the appendices for readers who are 

interested in more detailed information. 

Chapter 2 of the report provides a description of each of the four options under consideration. Chapter 3 

evaluates the flow-related effects of each option on downstream resources, including physical resources 

(i.e., sediment, temperature, and diurnal stage variation), aquatic and fisheries resources, riparian 

biological resources, recreation and cultural resources, and hydropower. Chapter 4 assesses the influence 

of the nonflow experimental components of each option on downstream resources, while chapter 5 

compares the proposed experimental designs. Chapter 6 closes the report with a presentation of 

GCMRC’s most important conclusions that emerged for consideration during the preparation of this 

assessment. 
6

Chapter 2: Experimental Options Descriptions 

This chapter provides general descriptions of the four experimental options under consideration by the 

Glen Canyon Dam Adaptive Management Program (GCDAMP). Each option alters the current operating 

criteria for Glen Canyon Dam (flow component) and specifies other nonflow treatments to be 

implemented during the next 10 years. 

Because released water flows from Glen Canyon Dam vary with hydrological conditions, a detailed 

description of release patterns is provided in appendix B for each option under various conditions: (1) an 

annual release of 8.23 million acre-feet (MAF), the minimum amount of water needed to meet delivery 

requirements under various agreements and treaties; (2) most-probable hydrological conditions; (3) wet 

hydrological conditions. 

The nonflow treatments recommended by each option are based on modification of activities that have 

been developed over time through the GCDAMP process and are described generally in the first section 

of this chapter. Specific differences in nonflow actions among the options are identified in the individual 

experimental option descriptions. Many of the nonflow actions relate to the management and 

conservation of the Grand Canyon population of humpback chub (Gila cypha), a native fish species that is 

federally listed as endangered under the Endangered Species Act. The summary descriptions for 

experiments related to humpback chub were drawn from the September 2006 Draft Comprehensive Plan 

for the Management and Conservation of Humpback Chub in Grand Canyon. 

Component Descriptions 

Flow Components 

Beach/Habitat-Building Flows (BHBF) 

BHBFs are infrequent high releases that are at least 10,000 cubic feet per second (cfs) greater than 

currently allowable peak discharge in a minimum release year (30,000 cfs) but not greater than 45,000 

cfs. Under current Glen Canyon Dam operations, BHBFs occur under the hydrologic triggering criteria 

recommended by the GCDAMP in 1998, which restricted these high flows to years of high reservoir 

conditions and high inflows. Thus, under current operations, a BHBF would occur in years when there 

was an expectation of having a very full reservoir. However, in September 2002, the U.S. Department of 

the Interior approved for research purposes changes linking restoration floods to triggering thresholds 

based on sand inputs. Significant sand inputs to Marble Canyon that exceeded the triggering threshold for 

an experimental high flow occurred during September–November 2004. Approval of a supplemental 

environmental assessment paved the way for the experimental high flow (BHBF) that began on Sunday, 

November 21, 2004. 

Under all four of the experimental options, BHBFs could continue to be tested under a recently revised 

sediment trigger. The proposed sediment trigger would be met when 0.5 million metric tons of sand are 

introduced by the Paria River and retained above river mile (RM) 30, and an additional “weighted” 0.5 

million metric tons of sand are delivered by the Paria River, Little Colorado River (LCR), or sources in 

between these two primary tributaries. To calculate the weighted input, sand from the Paria River is given 
7

full value, and sand from the LCR and other sources is valued at 50% of the actual input. Thus, a BHBF 

could be triggered with an input of 1.0 to 1.5 million metric tons of sand depending on how much of the 

sand is derived from the Paria River. 

 

Nonflow Components 

Temperature Control Device 

Installation of a Glen Canyon Dam temperature control device (TCD), or selective withdrawal structure, 

would provide dam operators with flexibility to draw water from different depths of the reservoir, 

including warmer water from near the surface of the reservoir. The goal of the TCD would be to provide a 

combination of cold and warm water withdrawals to benefit the endangered humpback chub while 

minimizing negative impacts to other resources. The implementation of a TCD as part of the long-term 

experimental plan will be subjected to National Environmental Policy Act review. Construction and 

operation of a TCD will be dependent on the outcome of that process and the availability of construction 

funding. The Bureau of Reclamation proposes to modify two of the eight penstocks on Glen Canyon Dam 

and test the effects of using selective withdrawal through implementation of the long-term experimental 

plan. There is a high probability that low reservoir levels in the next several years, coupled with the two 

modified penstocks, will allow sufficiently warm dam releases to adequately test the effects of higher 

water temperatures on the downstream ecosystem. 

Control of Nonnative Coldwater Fish 

This project was implemented to test whether removal of rainbow trout (Oncorhynchus mykiss), brown 

trout (Salmo trutta), and other nonnative fish species would benefit humpback chub. The experiment was 

conducted in a 17-mile reach of the mainstem Colorado River above and below the confluence with the 

Little Colorado River for 4 years, 2003–6. Monitoring of humpback chub and nonnative fish continues in 

order to evaluate population responses to the removal of competitor and predator fishes. All four 

experimental options support continued control of nonnative, coldwater fish, but the options vary in detail 

provided on when and how control efforts would be implemented.

Control of Nonnative Warmwater Fish 

Because of the natural warming of the releases from Glen Canyon Dam that have occurred as a result of 

lowered reservoir levels in Lake Powell (2003–current), managers and scientists have expressed concern 

that populations of nonnative fishes adapted to warm water, most of whom are already present in Grand 

Canyon, may increase at the expense of native fishes. Species such as common carp (Cyprinus carpio),

fathead minnow (Pimephales promelas), plains killifish (Fundulus zebrinus), and channel catfish 

(Ictalurus punctatus) may pose the greatest risk to native species, but other nonnatives may also pose 

important threats, whether through direct predation, competition for resources, habitat alteration, or a 

combination of all three threats. All of the option proponents support continued research on how to best 

address this threat with concomitant monitoring of the native fishes, especially humpback chub.

Humpback Chub Disease/Parasite Research 

This project includes two phases: (1) development and implementation of a monitoring plan for fish 

diseases and parasites in the Colorado River and its tributaries, with emphasis on those infecting 
8

humpback chub and (2) investigation of mechanisms for control and suppression of important diseases 

and parasites. 
9

Humpback Chub Translocation 

This activity would transplant young-of-year humpback chub produced in the Little Colorado River to 

appropriate tributaries within Grand Canyon National Park and adjoining tribal lands. Based on 

evaluations conducted by Valdez and others (2000), the probability of establishing sustainable humpback 

chub populations in these tributaries is small, but proponents believe that any reproduction and/or survival 

in locations other than the Little Colorado River decreases the risk of losing the entire Grand Canyon 

humpback chub population to a catastrophic event 

Humpback Chub Refuge(s) 

This activity would create an off-river refuge population for the Grand Canyon population of humpback 

chub. Larval and young-of-year humpback chub currently experience high mortality and few survive to 

adulthood. Collection of young humpback chub for use in a refuge population provides a safeguard 

against future catastrophic loss with very low risk to the overall population. This activity will (1) refine 

the methods for transportation of wild-caught humpback chub to a refuge facility, (2) refine the methods 

for holding humpback chub in captivity, (3) establish a refuge to protect the genetic integrity of wild 

humpback chub from the Grand Canyon population, and (4) potentially provide a source of humpback 

chub for use in ex situ experiments. 

Humpback Chub Population Augmentation Planning 

This activity proposes to evaluate the efficacy and need for augmenting (stocking) humpback chub in 

Grand Canyon and developing an appropriate plan. Elements of the plan would include the completion of 

a genetics management plan, the identification of facilities to support an augmentation program (i.e., 

grow-out ponds), and the development of a stocking plan. Option A and A Variation call for the 

implementation of humpback chub population augmentation should the humpback chub population in 

Grand Canyon be reduced below a threshold, or trigger, that is yet to be determined. Option C focuses on 

planning and evaluation, with implementation to be determined based on the results of further study and 

the completion of the Comprehensive Plan for the Management and Conservation of Humpback Chub in 

Grand Canyon. Option B does not advocate the augmentation of the wild humpback chub population. 

Mini Experiments 

Mini experiments are short-term field experiments are intended to assist in providing answers to science 

questions related to the uncertainties of implementing an option. 

Experimental Options Descriptions 

This section provides descriptions of each of the four options under consideration. Hydrological modeling 

for all options was done under three different hydrologic conditions (see appendices A and B). Water 

temperature modeling was done for each of the four options based on the varying flow regimes, including 

the operation of two units on a proposed temperature control for water years 2012–16 (see appendix D). 

Table 2.1 provides the reader an overview of the flow and nonflow components of the four options 

considered by this assessment. 
10

Table 2.1 Summary of flow and nonflow components of the four experimental options under 

consideration by the Glen Canyon Dam Adaptive Management Program. BASE operations 

(modified low fluctuating flow regime) are provided for comparison. 

 Flow/Nonflow 

Treatment 

BASE 

operations 

Option A Option A 

Variation 

Option B Option C 

Flow 

Increased daily 

flow 

fluctuations 

No Yes (increased by 

50% to 66% in 

winter months and by 

25% in summer 

months) 

Yes (increased 

by 25% to 66% 

in all months 

except April 

and May) 

No Yes (increased by 

50% to 66% in 

winter months) 

Flow Stable flows 

No No No Yes, (tests of 

4, 8, and 12 

months) 

Yes, (September 

through October) 

Flow Beach/habitatbuilding flows 

Possible, 

but only 

under 

hydrologic 

triggers 

Yes, as tests under 

sediment input 

triggering 

Yes, as tests 

under sediment 

input triggering 

Yes, as tests 

under 

sediment input 

triggering 

Yes, as tests under 

sediment input 

triggering 

Flow Alternative 

ramping rates 

No Yes (hourly 

downramping rate 

increased 100% in all 

months) 

Yes (hourly 

downramping 

rate increased 

100% in Apr–

Oct and 167% 

in Nov–Mar ) 

No Yes (hourly 

downramping rate 

increased by 100% 

in Nov–Jul only) 

Nonflow Temperature 

control device 

No Yes Yes Yes Yes, 2 units 

assumed 

Nonflow Control of 

nonnative 

coldwater fish 

No Yes, as needed Yes, as needed Yes, as needed Yes 

Nonflow Control of 

nonnative 

warmwater 

Fish 

 

No Yes, as needed, with 

R&D starting in 2007 

Yes, as needed, 

with R&D 

starting in 2007 

Yes, as 

needed, with 

R&D starting 

in 2007 

Yes, with R&D 

starting 2007 

Nonflow Humpback 

chub 

disease/parasite 

research 

No Yes Yes Yes Yes, with R&D 

starting 2008 

Nonflow HBC 

translocation No Yes Yes No 1

Yes

Nonflow Humpback 

chub refuge(s) 

No Yes Yes Possibly 1Yes

Nonflow HBC 

population 

augmentation 

planning 

No 

Yes, Planning efforts 

toward 

implementation, as 

needed 

Yes, Planning 

efforts and 

implementation 

No 1Yes, planning 

phase

Flow and 

Nonflow 

2

Mini 

experiments 

No Yes Possibly Yes 1Yes

Experimental 

Design 

 Not 

applicable 

Reverse Titration Reverse 

Titration 

Factorial Forward Titration 

NOTE: 1) For Option C: Ancillary projects not considered part of the main experiment; implementation decision includes consideration of 

confounding the main experiment. 2) Mini experiments are short-term field experiments that do not confound main experimental treatment 

effects. For Option C: These experiments are considered undefined concepts and would be incorporated if defined and not in conflict with the 

main experiment. 
11

BASE Operations 

Dam operations under the modified low fluctuating flow (MLFF) alternative, which was implemented by 

the 1996 Record of Decision (ROD), are presented to provide an understanding of current baseline 

conditions and operations at Glen Canyon Dam. Referred to as BASE operations throughout this 

evaluation, current Glen Canyon Dam operations provide the basis for relative resource response 

evaluations for the four experimental options considered. 

The MLFF operating regime, or BASE operations, has been the dominant mode of Glen Canyon Dam 

operation since August 1991, when the interim operation criteria for Glen Canyon Dam were 

implemented. Given more than a decade of implementation and research, data associated with BASE 

operations have been accumulated relative to an array of resource performance measures. For these 

reasons, BASE operations provide a good baseline against which to compare the four experimental 

operations. BASE operations are generally treated as the “no action” alternative with respect to current 

GCDAMP experimental planning efforts. 

Daily and Hourly Operations 

Under normal BASE operations, the daily range in release rates is no more than 8,000 cubic feet per 

second (cfs) and the release peak fluctuation generally cannot exceed 25,000 cfs except during periods of 

high regional runoff or for experimental flows. The hourly rate at which flow changes can be made under 

current operations is 4,000 cfs/hr for upramp and 1,500 cfs/hr for downramp. 

Beach/Habitat-Building Flows 

Under BASE operations, beach/habitat-building flows might occur, but only under the hydrologic 

triggering criteria recommended by the GCDAMP in 1998. The trigger allows a BHBF if the January 

forecast for the April through July unregulated spring runoff into Lake Powell exceeds 13 MAF (about 

140% of normal) when the January 1 storage is 21.5 MAF, or if any later monthly forecast for spring 

runoff into Lake Powell would require a powerplant monthly release greater than 1.5 MAF. 

Option A 

Daily and Hourly Operations 

Option A would increase daily flow fluctuations compared to BASE operations for 5 of 12 months. These 

increases would be greatest in February with a 66% increase over BASE operations (10,000 vs. 6,000 cfs 

range), while December and January would increase 50% compared with BASE operations (12,000 vs. 

8,000 cfs). There would also be a 25% increase in the flow variations compared with BASE operations in 

July and August (10,000 vs. 8,000 cfs). The flow variations would remain the same as BASE operations 

from September through November and from March through June. 

Compared to BASE operations, the hourly upramp rate would remain unchanged at 4,000 cfs/hr under 

Option A, but the hourly downramp rate would be increased by 100% in all months of the year to 3,000 

cfs/hr instead of 1,500 cfs/hr. 
12

Beach/Habitat-Building Flows 

BHBFs could be tested under the recently revised sediment trigger. 

Additional Flow Experiments 

Option A includes a number of other experiments that could be used to refine operations to perform 

specific tasks. Examples are nonnative fish management flows (e.g., summer stranding flows) to reduce 

the Glen Canyon Dam rainbow trout population, and tests of the effects of ramp rate on sediment 

transport. The specifics of the flows that would be tested in these experiments would be subject to 

reservoir levels, powerplant maintenance, economic considerations, and the adaptive management 

process, but could include: 

1. Summer Stranding Flows: A stranding flow would maintain elevated flows (e.g., 15,000 cfs) for 

2 or 3 days, followed by a very sharp drop in flows to a minimum level (i.e., 7,000 cfs). A 

stranding flow would be considered in the period of June, July, or August. 

2. Ponding Flows: Ponding flows are those relatively high flows that produce slackwater areas in 

tributary mouths for the benefit of humpback chub. 

3. Electrical Power Production Experiments: Power production experiments are short-term flow 

experiments intended to investigate alternative fluctuating flow parameters that might be 

compatible with downstream resource objectives. 

Nonflow Components 

1. Temperature Control Device (two units) 

2. Humpback Chub Augmentation 

3. Humpback Chub Translocation with translocation efforts focused on other priority tributaries, 

such as Bright Angel and Shinumo Creeks, plus other possible side streams that are suitable 

4. Mechanical Removal of Nonnative Fishes, including both coldwater and warmwater nonnative 

species, as needed 

Experimental Design 

Option A seeks to implement as many treatments as possible as soon as feasible. In terms of design, 

Option A incorporates reverse titration, meaning that all treatments are implemented to achieve resource 

benefit until such time that a positive response in targeted resources is detected. That is, treatments may 

be systematically removed one at a time under continued monitoring until benefits are observed to 

diminish (learning by undoing). Although learning through this process may be more complicated, 

beneficial resource response is posited as a priority above establishing cause-effect science results. 

 
13

Option A Variation 

As its name implies, Option A Variation is a slightly modified version of Option A described above. The 

differences between the two experimental options are confined to the daily and hourly operations of Glen 

Canyon Dam designed to increase hydropower production during periods of high consumer demand. All 

other flow-based experiments and nonflow components are the same as Option A. 

Daily and Hourly Operations 

Option A Variation would increase daily flow fluctuations compared to BASE operations for 10 of 12 

months. These increases would be greatest in February with a 66% increase over BASE operations 

(10,000 vs. 6,000 cfs range), while December and January would increase 50% compared with BASE 

operations (12,000 vs. 8,000 cfs). In September through November and in March through June, Option A 

Variation would increase daily flow fluctuations by 25% compared to BASE operations (8,000 vs. 6,000 

cfs). A 25% increase would also occur in July and August (10,000 vs. 8,000 cfs). The release flows would 

remain unchanged relative to BASE operations only in April through May (6,000 cfs). 

The hourly upramp rate would remain unchanged at 4,000 cfs/hr under Option A Variation compared to 

BASE operations. However, the hourly downramp rate would be increased by 100% compared to BASE 

operations in April through October (3,000 csf/hr compared to 1,500 cfs/hr) and by 167% in November 

through March (4,000 cfs/hr compared to 1,500 cfs/hr). 

Beach/Habitat-Building Flows 

Same as Option A. 

Additional Flow Experiments 

Same as Option A. 

Nonflow Components 

Same as Option A. 

Experimental Design 

Same as Option A. 

 

 

Option B 

Daily and Hourly Operations 

Compared to BASE operations, Option B would gradually implement stable flows on a seasonally 

adjusted basis. Initially, Option B would implement fluctuating flows under current MLFF operations 

during periods when monthly release volumes are approximately equalized throughout the year. Over 
14

time, operations under this option would evolve to progressively increased implementation of seasonally 

stable flows. Table 2.2 summarizes the flows associated with Option B. 

Table 2.2 Summary of flows associated with Option B for WY2007 to WY2013. 

Dates Flow Monthly 

volume1

(KAF) 

Discharge (cfs) 2 BHBF3

October 2006 to July 2007 A 700 ROD fluctuations 

(7,500–13,500) 

No 

August 2007 to November 2007 B 620 Steady (10,000) No 

December 2007 to July 2008 C 720 Constrained fluctuations 

(: 4,000 daily) 

One or more if 

triggered 

August 2008 to November 2008 B 620 Steady (10,000) No 

December 2008 to July 2009 C 720 Constrained fluctuations 

(: 4,000 daily) 

One or more if 

triggered 

August 2009 to March 2010 B 620 Steady (10,000) No 

April 2010 to July 2010 C 820 Constrained fluctuations 

(: 4,000 daily) 

One or more if 

triggered 

August 2010 to March 2011 B 620 Steady (10,000) No 

April 2011 to July 2011 C 820 Constrained fluctuations 

(: 4,000 daily) 

One or more if 

triggered 

August 2011 to March 2012 620 Steady (10,000) No 

April 2012 1,060 Steady (14,285) One if triggered 

May 2012 800 Steady (13,300) No 

June 2012 

D 

790 Steady (13,160) No 

July 2012 to March 2013 620 Steady (10,000) No 

April 2013 1,060 Steady (14,285) One if triggered 

May 2013 800 Steady (13,300) No 

June 2013 790 Steady (13,160) No 

July 2013 to September 2013 

D 

620 Steady (10,000) No 

1

Monthly volume is based on the assumption of an 8.23 MAF release year. If more than 8.23 MAF will be released, 

then discharge will be adjusted proportionally so that monthly volumes remain approximately equal. 

2

 Minor fluctuations are allowed for Automatic Generation Control purposes. 

3

 BHBF are 41,000 to 45,000 for 1–3 days depending on research objectives. 

For water year (WY) 2007 through WY 2013, Option B starts by equalizing monthly volumes with MLFF 

fluctuations (Flow A), and then combines steady and constrained fluctuating flows of different durations 

(Flows B and C) with seasonally adjusted steady flows (Flow D). Flows B, C, and D are replicated twice; 

the pattern of flows is described in table 2.4. For the purposes of the 10-year evaluation, Option B design 

returns to MLFF operations after WY 2013, while results of the experiment are being evaluated. 
15

1. Flow A (Equalized monthly volumes): This pattern of flows tests the level of sediment 

accumulation under equalized monthly volumes and MLFF flows. Equalizing monthly volumes is 

intended to eliminate months with high sediment export rates, maintain a higher minimum flow 

throughout much of the year for increasing food base productivity, and retain daily MLFF 

fluctuations for load following. These flows are also aimed at creating conditions that would 

allow for some evaluation of the level of nearshore stability needed to restore mainstem rearing 

habitat for humpback chub. No BHBF will occur in conjunction with these flows. 

2. Flow B (Short-term steady flows): This pattern of flows tests whether 4 or 8 months of steady 

flows are sufficient to provide humpback chub rearing habitat in the mainstem. The short-term 

steady flows begin in August when the highest numbers of young-of-year normally enter the 

mainstem. The steady flows are intended to provide a stable nearshore environment and an 

increase in water temperature (especially in backwaters). These flows are intended to maximize 

food base productivity, but be low enough to allow for sediment accumulation. No BHBF will 

occur in conjunction with these flows. 

3. Flow C (Constrained fluctuations): Fluctuations are constrained to reduce sediment transport 

and enlarge the food base while still allowing some fluctuations to minimize impacts on 

hydropower generation. These flows are also intended to provide some indication of the level of 

nearshore stability needed to restore mainstem rearing habitat for humpback chub. 

4. Flow D (Seasonally adjusted steady flows): These flows are designed to mimic, in part, a 

“natural” hydrograph. A BHBF will occur in April of 2012 and 2013 when it is likely to have the 

least impact on young-of-year humpback chub and other native fish. The BHBF is contingent on 

the accumulation of 1.0 million metric tons of tributary supplied sand in Marble Canyon. No 

“supply conditioning” fluctuating flows will occur. 

Beach/Habitat-Building Flows 

BHBFs would be implemented under a new sediment trigger. Under Option B, a BHBF would occur 

immediately once the sediment input trigger was met. However, a BHBF would not occur if there was a 

high risk of unacceptable negative impacts to young-of-year humpback chub residing in the mainstem 

(the criteria for this determination are currently undefined). 

Experimentation with limited duration “supply conditioning” fluctuating flows could occur before the 

BHBF to test whether prescribed fluctuations would more evenly distribute the sediment input and thus 

conserve a larger proportion of the accumulated sediment. In addition, if a subsequent sediment input 

trigger was met during the same block of experimental flows, another BHBF test would immediately 

occur. 

Nonflow Components 

1. Temperature Control Device: Option B calls for the testing of a TCD with three or four units 

instead of two as currently proposed. 

2. Nonnative Species Control: Option B includes the control of warmwater and coldwater 

nonnative species control, as needed, through WY 2016. 
16

3. Humpback Chub Translocation: The translocation of humpback chub to other tributaries and 

the development and management of an off-site genetic refuge at Willow Beach (and/or other 

sites) could be considered under Option B pending a risk analysis and an evaluation of the options 

available to meet the perceived need. 

Experimental Approach 

Option B is intended to be a factorial approach with replication of stable and fluctuating flow elements. 

The approach was chosen to attempt the greatest degree of statistical rigor possible under large-scale field 

experimental conditions with as few confounding treatments as possible. Under the limited scope of the 

experiment considered in this evaluation, the treatments appear to be implemented as a forward titration 

for both temperature and habitat stability, but each annual stable flow period is replicated once during the 

sequence shown in table 2.2. 

For experimentation starting in WY 2014, Option B includes a reassessment of the status and trends of 

resource conditions; a reassessment of the effects of flows, temperature, and nonnative control; and 

further testing (as needed) of both daily and seasonal flow variability, temperature (using a TCD), 

BHBFs, and nonnative control in a factorial design. 

Option C 

Daily and Hourly Operations 

Compared to BASE operations, Option C relaxes the MLFF operating criteria in three months for daily 

fluctuations and nine months for ramping rates. Daily flow fluctuations would be increased from 

December through February compared to BASE operations, up from 8,000 cfs to 10,000 cfs or 12,000 

cfs. The downramp rate would be increased from 1,500 cfs/hr to 3,000 cfs/hr during November through 

July. At a minimum, stable flows (up to 2,000 cfs daily fluctuations) would occur during September and 

October of each year. The intent of implementing small fluctuations in September and October is to 

provide the opportunity for experiments to begin defining “ecologically stable flows” that would allow 

some hydropower generation, but also limits destabilization of downstream nearshore native fish rearing 

habitats. 

Option C would be implemented in three 5-year segments with the final year of each segment being used 

to evaluate, report, and determine whether to proceed as planned with the next experimental segment. The 

evaluation of experimental efforts would be accomplished through updating The State of the Colorado 

River Ecosystem in Grand Canyon report (SCORE, see Gloss and others, 2005) and knowledge 

assessment report, followed by tradeoff analysis in 2017 for use in planning the final 5-year segment 

(2017–21). Evaluation includes determination of whether resource triggers have been reached with 

subsequent expansion or contraction of factors (actions) determined to be impacting key resources. 

Option C includes consistent hydrology from WY 2007 through WY 2016 to allow for an assessment of 

the effects of the TCD, which is scheduled to be operational between the end of the first segment and the 

beginning of the second in WY 2012. Table 2.3 summarizes the flows proposed for the first two 5-years 

segments proposed by Option C to test the effects of a TCD. Option C assumes the number of units to be 

two and that the device will be operated from May through October at full capacity. 
17

The Option C approach includes a biological trigger for humpback chub to be determined by the GCMRC 

in coordination with other scientists and the Science Advisors. The trigger is to be based on numbers of 

humpback chub in the Grand Canyon population and the population trend of humpback chub, such that if 

the population declines to the trigger or below the trigger, the Bureau of Reclamation would immediately 

reinitiate consultation with U.S. Fish and Wildlife Service to determine a course of action to reverse the 

decline. One of the considerations of that consultation would be a determination of whether sufficient 

evidence exists to justify the expansion of the steady flow period from September and October into 

August. If the identified trigger is not realized during the first 10 years of the experiment, re-consultation 

would still occur prior to the initiation of the third segment in 2017 to determine what changes, if any, 

would be recommended for dam operations or other actions. 

Beach/Habitat-Building Flows

BHBFs would be implemented under a new sediment trigger and with experimentation to determine 

whether conditioning flows preceding the BHBF can be used to purposefully transport and deposit fine 

sediment to desired locations downstream of the input. 

Nonflow Components 

Actions described in the humpback chub comprehensive plan will be considered for implementation 

based on completion of planning, attainment of technology threshold, and prioritization of budget; the 

potential for confounding of the experimental plan would be considered prior to implementation of each 

action (WY 2007–WY 2012). Actions deeded likely for implementation at this time include: 

1. Control of Nonnative Coldwater Fish: Option C includes experimentation to determine relative 

efficacy of mainstream and tributary control, and evaluation of levels of control (WY 2007–WY 

2012). 

2. Temperature Control Device: Option C assumes the number of units to be two and that the 

device will be operated from May through October at full capacity. 

3. Control of Nonnative Warmwater Fish: This activity is considered in Option C to be a 

component of the experimental plan and one for which treatments will be developed; however, it 

is not sufficiently developed for treatments to be assigned at this time. Under Option C, this 

project is initially treated as research and development project and is then integrated as a 

treatment. After WY 2012, Option C would place emphasis on warmwater nonnative fish control 

with elevation of release temperatures from selective withdrawal (WY 2012–WY 2021). 

4. Humpback Chub Disease/Parasite Research: Option C considers this component a research 

and development activity, which likely will be conducted largely in laboratory settings during the 

first phase. Following the first 5-year phase of research and development, this activity could 

move to a field phase with well-defined treatments. 

Ancillary Projects 

Option C defines several experimental activities as ancillary projects, meaning that the individual activity 

is not a treatment in the experimental design, but one that would be analyzed for its confounding effect on 

the main experiment. The following activities are defined as ancillary projects: 
18

1. Humpback Chub Translocation: Appropriate precautions would be taken to minimize 

confounding the main experiment with the effect of translocation (e.g., it may be possible to mark 

humpback chub emerging from tributaries so that their contribution to the mainstream population 

could be documented). 

2. Humpback Chub Refuge(s): Removal of fish for this purpose and any repatriation would be 

accomplished under the guidelines and criteria identified in the humpback chub genetics 

management plan now being written. 

3. Humpback Chub Population Augmentation Planning: Option C supports planning for 

augmentation with a first step being completion of a genetics management plan. If the humpback 

chub trigger described above is met, augmentation may be considered as part of a suite of actions 

necessary to reverse the decline of humpback chub in Grand Canyon. 

Experimental Design 

Implemented in three 5-year segments, Option C makes use of an experimental approach referred to as a 

forward titration. New treatments would be added incrementally to improve knowledge of the 

relationships among treatments and the resources affected by those treatments. For example, steady flows 

in September and October would be implemented in segment 1, a TCD in segment 2, and an August 

steady flow trigger in segment 3 under certain conditions. Option C calls for the services of a biostatistician 

to identify much more specifically how this design, which is not to be found in the statistical literature, would 

actually be implemented. None of the treatments proposed under Option C are considered “management actions,” as 

defined by TWG and AMWG for the long-term experimental plan, in recognition of the large uncertainty associated 

with the effects of most actions as identified in the 2005 knowledge assessment report. The evaluation of 

experimental efforts would be accomplished through updating SCORE and knowledge assessment reports every 5 

years. Option C does not support mini experiments until they are better described and analyzed for their 

confounding effects on the main experiment. 
19

Table 2.3 Monthly and daily flows associated with the first two 5-year segments proposed by 

Option C. Flows assume 8.23 million acre-feet annual release volume. Daily ranges and ramping 

rates in green are consistent with current Record of Decision (ROD) limitations and those in red 

indicate changes proposed by Option C. 

Monthly 

Volume 

(acrefeet)

Mean 

Daily 

Flow 

(cfs) 

Max Monthly 

Flow (cfs)1 

Min 

Monthly 

Flow 

(cfs)2 

Daily 

Range 

(cfs)3 

Upramp/ 

Downramp 

(cfs/hr)3 

Within ROD 

Daily 

Fluctuation 

Limits? 

Yes/No

Within 

ROD 

Ramp 

Rates? 

Yes/No

 

Oct 500 8,100 9,100 7,100 ~2,000 4,000/1,500 Yes Yes 

Nov 650 10,900 13,900 7,900 6,000 4,000/3,000 Yes No 

Dec 800 13,000 18,500 6,500 12,000 4,000/3,000 No No 

Jan 800 13,000 17,000 5,000 12,000 4,000/3,000 No No 

Feb 675 11,000 15,000 5,000 10,000 4,000/3,000 No No 

Mar 650 10,600 13,600 7,600 6,000 4,000/3,000 Yes No 

Apr 625 10,500 13,500 7,500 6,000 4,000/3,000 Yes No 

May 625 10,200 13,200 7,200 6,000 4,000/3,000 Yes No 

Jun 725 12,200 15,200 9,200 6,000 4,000/3,000 Yes No 

Jul 825 13,400 17,400 9,400 8,000 4,000/3,000 Yes No 

Aug4 800 13,000 17,000 9,000 8,000 4,000/1,500 Yes Yes 

Sep 555 9,300 10,300 8,300 ~2,000 4,000/1,500 Yes Yes 

 

Annual 

(ac-ft X 

1000) 8230 1

 Beach/habitat-building flows of 41,000 cfs or more can occur January through April using combined Paria River-Little 

Colorado River input triggers proposed by the GCMRC; if dam releases can not be managed between attainment of triggers 

and BHBFs to conserve sediment adequately and not unduly impact other resources, earlier dates for BHBFs should be 

considered. 

2

 Assumes “no drop” Sunday operation as has characteristically occurred under the ROD. 

3

 Daily ranges and ramping rates in green are with ROD limitations; those in red are not. 4

Note that in any given year if triggers are met with regard to humpback chub steady. August flows might be a 

condition through re-consultation with U.S. Fish and Wildlife Service.

 
20

Chapter 3: Estimated Effects of Proposed Flow 

Regimes on Downstream Resources 

This chapter presents the estimated effects on downstream resources of the flow regimes proposed by the 

four experimental options under consideration by the Glen Canyon Dam Adaptive Management Program. 

Downstream resources considered by this assessment include physical resources (i.e., sediment, water 

temperature, and diurnal stage variation (DSV)), aquatic and fisheries resources, riparian biological 

resources, recreation and cultural resources, and hydropower. The estimates presented here rest primarily 

on information reported in the 2005 knowledge assessment workshop final report (Melis and others, 

2006b; KAR), but additional scientific information has also been considered, when appropriate. As a 

result, the estimates are of a generalized nature and made with the admission that numerous uncertainties 

were identified during knowledge assessment workshop. 

Since the knowledge assessment report was finalized, new models for simulating the effects of diurnal 

stage variation and downstream water temperature have been completed. The results generated by these 

models were used to inform the analysis presented in this chapter. All four options were evaluated over a 

range of simulated hydrologic conditions for the upper Colorado River Basin in order to estimate the 

influences of the four options under a more realistic range of variability (see appendix B, this report). 

Additionally, in modeling temperature responses, each of the experimental regimes is assumed to include 

operation of a TCD for 5 consecutive years starting in 2012 (see appendix D, this report). 

Part 1: Physical Resources 

Executive Summary 

In this section, evaluations are presented regarding the estimated effects of the four experimental options 

compared to BASE operations (modified low fluctuating flow, or MLFF) for fine-sediment storage, 

downstream water temperatures, and diurnal stage variation. Evaluations were conducted by sediment 

researchers and physical scientists from the GCRMC science staff on the basis of information contained 

in the 2005 knowledge assessment report and peer-reviewed literature referenced in that report. 

Numerical modeling was only used to estimate the information provided for DSV and for evaluations of 

downstream, main channel water temperature associated with dam releases without a temperature control 

device (TCD) for the first 5 years of the 10-year evaluation (2007–11). Numerical simulations for a twounit TCD were also conducted and evaluated and those results are reported in chapter 4 under nonflow 

treatments related to TCD operation in the last 5 years of the evaluation period (2012–16). 

For fine-sediment storage, the primary difference between BASE operations and the experimental options 

is related to the triggering mechanism for beach/habitat-building flows (BHBF). Under BASE operations, 

BHBFs may only be triggered by hydrologic conditions leading to full lake levels in Lake Powell. In 

contrast, under all experimental options, BHBFs are triggered by above average tributary sediment inputs 

and mainstem retention. Because previous research and monitoring have shown that BHBFs must be 

linked to sediment-enriched conditions in order to have any chance of building eddy sandbars at all 

elevations, all experimental options are considered superior to BASE operations from the standpoint of 

fine-sediment storage. In addition, BHBFs may temporarily (over timescales of months) reduce the 

subsequent transport/export of sand by coarsening the sand on the surface of the channel bed and lower 
21

parts of sandbars. Comparison of the flow regimes of the individual options indicates that Option B has 

the greatest likelihood of increasing sandbar volume over the long term because it contains significant 

periods of steady flows and constrained fluctuations such that it will have the slowest rate of sandbar 

erosion during periods between BHBFs and the greatest potential to retain tributary inputs leading up to 

BHBFs. Options A, A Variation, and C are thought to rank substantially behind Option B for their 

likelihood of increasing sandbar volume over the long term because of high-volume fluctuating releases 

in summer and winter, which are known to be significantly net erosional. Option C ranks above Options 

A and A Variation because of it includes steady flows in September and October, which are more 

conducive to retention of tributary inputs that typically occur during this time of year, and owing to lower 

fluctuations that likely reduce sandbar erosion during these months.

For downstream water temperatures in the main channel, it is known that lower release volumes promote 

downstream warming because of increased residence time, particularly in the late spring, summer, and 

early fall months when air temperatures are significantly warmer than release water temperatures. Based 

on numerical modeling results, the differences in monthly volumes between the options are not large 

enough to result in significant differences in mainstem temperatures. That is, the simulated differences in 

mainstem temperatures between the options are within the uncertainty of the model such that it cannot be 

concluded that there are significant differences between the options. 

It is also known that more stable flows result in warmer nearshore areas (particularly backwaters) during 

the late spring, summer, and early fall months when air temperatures are significantly warmer than release 

water temperatures, which results presumably because mixing with the colder mainstem is inhibited by 

stable flows. Because of this effect, Option B is expected to have warmer nearshore temperatures than the 

other options during much of the year because of the prevalence of steady flows and constrained 

fluctuating flows. Option C ranks second owing to stable flows in September and October. Because 

Options A and A Variation contain no stable flows, they rank behind Options B and C. However, because 

daily ranges are expanded in months where the daily ranges are relatively high under BASE operations as 

well, Options A and A Variation are not expected to result in significantly different nearshore water 

temperature from BASE operations. 

Diurnal stage variation is defined as the difference in stage between the daily low flow and the daily peak 

flow. Estimates of diurnal stage variation using a step-backwater numerical model indicate that Option B 

would result in decreases in stage variation compared to BASE operations of about 3 ft on average for 

steady flow months, and about 1.5 ft on average during constrained fluctuating months. Option C steady 

flow months (October and November) would result in similar decreases (~ 3 ft) compared to BASE 

operations. Increased fluctuations in winter months proposed by Option C would lead to an increased 

diurnal stage variation of about 2 ft on average compared to BASE operations. Options A and A Variation 

would lead to similar increased variation in the winter as well as approximately 1 ft increased variation in 

the summer expanded daily range months. These estimates are based on averages over the entire river 

corridor (from Glen Canyon Dam to Diamond Creek, river miles -15 to 226) and for minimum release 

hydrology. For the first 10 miles downstream from the Little Colorado River (LCR), the DSV is typically 

around 1 ft less than this average because of local geometry.
22

Fine-Sediment Storage (all flows up to 45,000 cfs) 

Options 

Options A and A Variation: Because Option A increases the hourly downramping rate by 100% 

compared to BASE operations, the resulting higher sand-export rates associated with expanded 

fluctuations or prolonged periods of peaking operations between BHBFs will most likely have the 

influence of accelerating erosion of sandbars. This is also estimated to be the case for Option A Variation 

because the DSV is increased by 25% to 66%, along with a 100% to 167% increase in the hourly 

downramping rate relative to BASE operations.

Option B: This option contains a combination of stable flows and fluctuating flows that are more 

constrained that those under BASE operations. As a result, annual sand inputs from tributaries are likely 

to be more effectively conserved before and after BHBF tests. Sandbars built during sand-enriched 

BHBFs are also likely to erode at slower rates between BHBF tests. During consecutive years of 8.23 

million acre-feet (MAF) releases, tributary sediment inputs are likely to accumulate over multiyear 

periods compared with BASE operations. Hence, BHBF tests that occur during protracted periods of 

minimal release hydrology when annual sediment inputs are likely to accumulate may result in more 

robust sandbar restoration responses than under BASE operations or other options having less constrained 

diurnal fluctuations. 

Option C: The stable flows that occur in September and October of each year in this option may allow 

for multiple tributary sediment inputs to accumulate in late summer and fall more than would occur under 

fluctuating flows for similar monthly volumes under BASE operations. The fall flow stability would be a 

larger influence in sediment accumulation before BHBF tests in fall through spring as hydrology becomes 

wetter and September and October monthly release volumes increase. This is particularly important for 

Paria River sediment inputs that occur mostly in late summer and fall. Summer fluctuations are similar to 

BASE operations, but sand-transport data collected under MLFF operations indicate that those summer 

operations result in elevated sand export, even under minimal annual release volumes of 8.23 MAF. 

Relaxed fluctuations in winter months are estimated to increase erosion rates of sandbars that might be 

formed during fall or winter BHBF tests. Such winter fluctuations may elevate sand export downstream 

prior to spring BHBF tests, but the downstream transport of new tributary sand could also effectively 

distribute new sediment throughout the ecosystem and result in more consistent patterns of sandbar 

deposition, compared with the results measured in the 2004 BHBF test. 

Fine-Sediment Summary 

Besides differences in how BHBF responses may vary under the four options, there are also substantial 

differences expected between Options A, A Variation, B, or C in terms of sand export during normal 

operations (i.e., non-BHBF), particularly during lower dam release years (i.e., ~8.23 MAF). Because 

stable flows transport less sand than fluctuating flows, Option B will transport less sand than Option C, 

and Option C will transport less sand than Options A or A Variation. Existing data indicate that the 

fluctuating and stable flows proposed in Option B tend to accumulate tributary sand in the mainstem, 

while the winter and summer fluctuations of Options A, A Variation, and C tend to be net erosional. As a 

result, during minimum release years with sediment-triggered BHBF tests, Option B would be the most 

likely to increase sandbar area and volume (over decades), Option C would be the second most likely, and 

Options A and A Variation, the third and fourth most likely, respectively. It is not yet possible to assign 
23

probabilities for increasing sandbar area and volume to each option. The basic differences between the 

options are expected to hold during wet hydrologic conditions, but the likelihood of increasing sandbar 

area and volume would decrease because sand export increases with higher flow releases. Because under 

wet hydrologic conditions the sand budget for Marble and Grand Canyons is predicted to be negative 

for all four options, the details of the hydrographs may be less important, except that deposition at higher 

elevations during frequent BHBFs may offset erosion occurring during the rest of the year. Also during 

wet years (when the reservoir is full) it may be desirable to test higher BHBFs under enriched conditions 

to evaluate whether depositing sand at higher elevations than is possible during 45,000 cfs BHBFs results 

in a more effective method for maintaining larger sandbars. 

In conclusion, the sediment conservation strategy of a BHBF consists essentially of three fluvial process 

responses: (1) transfer inputs of tributary-supplied sand from the channel of the Colorado River to where 

it is needed (on the parts of the sandbars that will be emergent at typical dam releases) and will persist for 

longer timescales than on the channel bed, (2) temporarily (over timescales of months) reduce the 

subsequent transport/export of sand by coarsening the sand on the surface of the channel bed and lower 

parts of sandbars, and (3) maintain the increased sandbar size and maintain sediment in upstream reaches 

of the river until a subsequent BHBF can be released from the dam. Releasing more-frequent BHBFs 

could benefit the sediment budget by enlarging sandbars and suppressing subsequent sand transport by 

coarsening the bed of the river. The next section provides additional insight on the proposed strategy for 

scientifically evaluating the BHBF concept so that managers can better identify management options that 

are likely to achieve identified resource objectives for sand resources below Glen Canyon Dam. 

Strategy for BHBF Tests Following Tributary Sand Enrichment 

The most important science question identified by sediment scientists at the 2005 knowledge assessment 

workshop was: Is there a “flow only” operation that will restore and maintain sandbar habitats over 

decadal timescales?

One significant outcome of the knowledge assessment workshop was that the information and models are 

not yet available to answer this question, despite the great deal of learning that has occurred regarding 

sediment transport, sandbars, and dam operations in this system. The question can only be answered 

through a program of rigorous experimentation that utilizes BHBF tests whenever triggered by large 

amounts of new sediment being supplied to the system by tributaries downstream from Glen Canyon 

Dam. The rationale for conducting BHBFs under sediment-enriched conditions has been documented in 

several peer-reviewed outlets, including Webb and others (1999), Topping and others (2000a), Rubin and 

Topping (2001), Rubin and others (2002), Schmidt and others (2004), Wright and others (2005), Hazel 

and others (2006), and Topping and others (2006). The flow chart below was developed at the knowledge 

assessment workshop to guide experimentation toward answering the sediment science question. 

In this sediment resource assessment, we consider eddy sandbar deposits as a whole (i.e., we do not 

differentiate strictly between different elevation ranges). This approach has been taken primarily for two 

reasons. First, because of the considerable uncertainty regarding system response to operations over 

decadal time scales, we have attempted to simplify the assessment as much as possible. Second, existing 

data (and general theory) indicate that sand deposits in different elevation ranges are not independent 

from each other, and that the system tends to erode from the bottom up. Thus, if a given operation is 

expected to be depositional (or erosional) in lower parts of eddies, then it’s likely to be depositional (or 

erosional) at high elevation as well (in the long term, with BHBFs). That said, in some instances we 

discuss eddies at “lower” elevation versus “higher” elevation; in these cases, we are referring to roughly 

below and above powerplant capacity, respectively. 
24

Figure 3.1. Flow chart developed at the knowledge assessment workshop to guide experimentation toward 

answering the sediment science question. 

For sand resources, the greatest difference between BASE operations and the four experimental options is 

that BHBF tests will occur based on sediment triggers under Options A, A Variation, B, and C, and only 

under hydrologic triggers under BASE operations (relatively high storage conditions in Lake Powell 

combined with forecasted April through July runoff from the upper Colorado River Basin of 30% or 

greater than average). Under BASE operations, with no chance of a BHBF until Lake Powell is full and 

no correlation between conducting a BHBF and the degree of sediment enrichment, the amount of sand in 

all three elevations is expected to decrease over decadal time scales because (1) during the powerplant 

releases until the reservoir fills, sand will continue to be eroded from sandbars at all elevations; (2) during 

the first BHBF (not tied to the degree of sediment enrichment), sand may be deposited at higher 

elevations (above 25,000 cfs) but eroded from the lower elevations of the sandbars (like during the 1996 

experiment); and (3) following this BHBF, the lower elevations of the sandbars that were scoured during 

the BHBF would not be expected to fully recover under normal powerplant releases (as observed after the 

1996 experiment). Therefore, over decades, BASE operations will probably result in there being less sand 

at all elevations. 

In contrast, Options A, A Variation, B, and C all include the possibility of BHBF tests when triggered by 

large new inputs of tributary sand. As observed during the 2004 experiment, BHBFs conducted under 

enriched conditions may increase the amount of sand in sandbars at all elevations. During the intervening 

powerplant releases, sand will be eroded from the lowest elevations in the sandbars first, but this erosion 

could be offset by new deposition during the next BHBF (if frequent enough). During the 2004 

experiment, we learned that more sand than was available during that test would be required to achieve 
25

increases in the total area and volume of eddy sandbars throughout all of Marble and Grand Canyons, not 

just in the upper 40 miles of Marble Canyon. Given that the sand budget in Marble and Grand Canyons is 

likely to be negative under all moderate and higher powerplant releases, the only possible “flow only” 

option to evaluate is whether frequent BHBFs conducted under enriched conditions can ultimately offset 

the erosion of sandbars occurring during the intervening powerplant releases. 

There are also substantial differences expected between Options A, A Variation, B, and C in terms of 

sand export during normal operations (i.e., non-BHBF), particularly during lower dam release years (i.e., 

~8.23 MAF). Because stable flows transport less sand than fluctuating flows, Option B will transport less 

sand than Option C, and Option C will transport less sand than Options A or A Variation. Existing data 

collected during consecutive 8.23 MAF annual releases under the MLFF regime (2000–5) indicate that 

the fluctuating and stable flows as proposed in Option B and associated with minimal annual releases, 

tend to accumulate tributary sand in the mainstem, while the winter and summer fluctuations of Options 

A, A Variation, and C tend to be net erosional. It is uncertain whether the constrained fluctuations and 

stable flows under Option B during most probable or wet hydrologic conditions would result in 

accumulation of tributary sand inputs. Thus, during minimum release years with sediment-triggered 

BHBF tests, Option B would be the most likely to increase sandbar area and volume (over decades), 

Option C would be the second most likely, and Options A and A Variation the third and fourth most 

likely. It is not yet possible to assign probabilities for increasing sandbar area and volume to each option. 

During wet hydrologic conditions, the basic differences between the options are expected to hold, but the 

likelihood of increasing sandbar area and volume would decrease because sand export increases with 

higher flow releases. Also during wet years (when the reservoir is full) it may be desirable to test higher 

BHBFs under enriched conditions to evaluate whether depositing sand at higher elevations than is 

possible during 45,000 cfs BHBFs results in a more effective method for maintaining larger sandbars. 

It is not yet possible to predict whether there is a “flow only” operation that can restore and maintain 

sandbar habitats over decadal time scales. Long-term experimentation (combined with monitoring and 

further numerical model development) is required to answer this question. Of the experimental options 

currently under consideration, all options with sediment-triggered BHBFs (A, A Variation, B, and C) are 

preferable to BASE operations, which incorporate only hydro-triggered BHBFs. Of the four options with 

sediment triggers, Option B has the greatest likelihood of increasing sandbar area and volume over 

decades because of the prevalence of steady flows and moderate fluctuations; Option C has a slightly 

greater likelihood than Options A and A Variation owing to fall steady flows. Though it is not possible to 

assign expected probabilities of increasing sandbar area and volume to each option, it is likely that 

Options A, A Variation, and C are more similar to each other than they are to Option B. During wet 

hydrologic conditions, the differences between the options become less important because the likelihood 

for increasing sandbar area and volume decreases as the total flow release from the dam increases (i.e. 

export is more likely to exceed tributary inputs during wet years, regardless of the dam operation). 

The benefits of BHBFs to the Grand Canyon native fish community remain undocumented. Published 

studies on humpback chub use of Little Colorado River habitats indicates that shallow, near-shore habitats 

are heavily used by young of the year and juvenile humpback chub (Stone and Gorman, 2006). If 

additional sediment delivered to the mainstem by a BHBF increased the frequency and/or extent of these 

habitats in the mainstem Colorado River, then BHBFs might be expected to support survival of these 

important life history stages. Recently completed analysis indicates that the Grand Canyon humpback 

chub population has stabilized, albeit below historic levels (Melis and others, 2006a). A secure humpback 

chub population would allow for increasing the amount of effort applied to conservation and protection of 

other resources, especially the retention of sediment in the system. More sediment in the Grand Canyon 

aquatic ecosystem may benefit humpback chub, as well as other resource areas, such as beaches for 
26

recreation, especially if shallow, slack water habitats are enhanced, as these have been shown to be of 

benefit to young humpback chub (Stone and Gorman, 2006). 

Downstream Water Temperatures: Main Channel and Nearshore (without 

temperature control device) 

Assessing Water Temperature for BASE Operations versus Experimental Options 

The objective of this experimental options assessment is to evaluate the four experimental flow options 

with respect to desired downstream water temperature regimes thought to be most beneficial to biological 

resources. To conduct the evaluations, we rely on our current understanding of the physical processes 

controlling downstream temperature patterns as described in the final 2005 knowledge assessment 

document (see 2005 Knowledge Assessment of the Effects of Glen Canyon Dam on the Colorado River 

Ecosystem: an experimental planning support document; Melis and others, 2006b), as well as a recently 

developed mainstem water temperature model to simulate the fate of flow releases stipulated in the four 

experimental flow options. These simulations provide a quantitative comparison of the effects of variable 

flow regimes and release temperatures on the fate of the mainstem thermal regime. Comparable numerical 

modeling capabilities are not currently available for nearshore environments (scheduled for development 

in FY 2007). Therefore, the effects of the experimental options are evaluated using a numerical model for 

the main channel, and using current state-of-knowledge for nearshore environments. 

 

Main channel: The detailed methods and results for the mainstem modeling component are contained in 

appendix D. The basic conclusion of the modeling is that the differences between the options are 

relatively small, and in most cases are probably within the uncertainty of the model calculations (~ 0.5–

1oC depending on location; see appendix D). Example model results are shown below. 

9

10

11

12

13

14

15

16

Release RM31 RM65 RM127 RM225

Average mainstem water

temperature over first 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

6

8

10

12

14

16

18

20

22

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

Average mainstem water

temperature over first 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

Figure 3.2 Average mainstem water temperatures at five locations (left) and average monthly 

temperatures at river mile 65 (right) for the first 5 years of the simulation period (i.e. 

period without temperature control device) for most probable hydrologic scenario. 

In April through June, when Option B contains higher volume releases than the other options, the greatest 

difference between options in terms of monthly average temperatures (~ 1oC) occurs. The higher volume 

releases lead to higher flow velocity in the mainstem, which decreases the amount of time available for 

warming as the water moves downstream leading to slightly cooler mainstem temperatures. These 

differences, however, should be interpreted with caution given how close they are to the model 
27

uncertainty, as well as because the model is still considered to be in the final stages of testing and 

validation. Indeed, some of the results generated by this study have revealed model components that need 

further investigation (in particular, the relationship between discharge and velocity during steady and 

fluctuating flows). Thus, the most appropriate interpretation of the modeling results is that there are not 

significant differences between the experimental options with respect to mainstem water temperatures. 

Here, significant is defined as being resolvable by the model given the uncertainty in the calculations. A 

further outcome of the modeling is related to the effects of hydrology on mainstem water temperatures. 

The reader should refer to appendix D for details. The effects of the TCD are considered separately in 

chapter 4. 

Nearshore Environments: It is generally known that steady flows promote more warming than 

fluctuating flows in nearshore areas, particularly backwaters. This is thought to be a result of less water 

exchange with the (typically colder) mainstem during stable flows, such that backwater temperatures can 

more closely equilibrate with atmospheric conditions. During fluctuating flows, backwaters may flush 

more quickly and the sandbars that isolate the backwaters may even be overtopped on a daily basis 

resulting in complete volume exchange with the mainstem. The exact relation between daily range in flow 

and amount of backwater warming is as yet undefined owing to a lack of data and numerical models 

(currently under development); also, this relation is expected to be highly variable and site-specific. 

Several studies have attempted to characterize the differences between mainstem and nearshore water 

temperatures, but all have been faced with similar obstacles in adequately quantifying these differences 

(e.g. Hoffnagle, 1996; Trammell and others, 2002; Korman and others, 2005a; Vernieu and others, 2005, 

Kaplinski, 2006). Confounding factors, such as highly variable Glen Canyon Dam release temperatures, 

ambient air temperatures, and release volumes, have made analysis and subsequent interpretation of the 

data complex. Despite these complexities, most of the data indicate that, in general, backwater 

environments have the potential to warm substantially compared to associated mainstem locations. 

Korman and others (2005a) found that, on average, maximum backwater temperatures at three locations 

during the fall of 2005 were 2–3°C warmer than the mainstem with instantaneous differences of up to 

7°C. Other studies have found similar ranges of differences between the mainstem and nearshore 

environments with maximum differences occasionally exceeding 7°C in specific locations. 

Common sense dictates that nearshore temperatures are directly linked to mainstem temperatures such 

that, in most instances, warmer mainstem temperatures will result in warmer nearshore temperatures. 

Finally, it is important to note that nearshore habitats are dynamic entities whose abundance and 

persistence are complicated functions of discharge, stage, and channel geometry and that further 

monitoring and modeling work is needed to expand our current knowledge of the complex linkages 

between the mainstem and the nearshore thermal environments of the Colorado River. 

Options 

Option A: Main channel temperatures are not expected to be significantly different from BASE 

operations or other options. Increased daily range in July and August reduces the potential for warming of 

nearshore areas during this time of year because increased fluctuations promote exchange of (typically 

colder) mainstem water with backwaters. However, the differences between this option and BASE 

operations will probably be small since relatively large fluctuations occur during these months under 

BASE operations. 

Option A Variation: Same as Option A except for the slightly reduced potential for nearshore warming 

is extended to June, September, and October because of expanded daily ranges during these months. 
28

Option B: Main channel temperatures are not expected to be significantly different from BASE 

operations or other options. This option, however, contains substantially more periods of stable flows and 

would thus be expected to result in generally warmer nearshore areas than BASE operations and other 

options. Constrained fluctuations occurring in non-stable flow months may also result in warmer 

nearshore temperatures, particularly in the spring and summer months. 

Option C: Main channel temperatures are not expected to be significantly different from BASE 

operations or other options. Steady flows proposed for September and October are expected to promote 

warming in nearshore environments. More warming is expected in September than October when little 

downstream warming typically occurs because release water temperatures are similar to air temperatures. 

Increased daily range in the winter months is not expected to have a large effect because very little 

warming, and sometimes slight downstream cooling, occurs during this time of year. 

Downstream Water Temperature Summary 

Numerical modeling of main channel water temperatures indicates that only small differences are 

expected to result from differences in flow releases between the options. Because these differences are in 

the same range as the model uncertainty, it cannot be concluded that there are differences between the 

options with respect to mainstem temperatures. Because it is generally thought that wider variation in 

daily fluctuating flows will tend to reduce warming in nearshore environments owing to increased 

exchange between colder mainstem water and warmer water in nearshore environments (such as 

backwaters), Option B ranks first in terms of nearshore temperatures because it has many more periods of 

steady flows than Options A, A Variation, and C. Option C ranks second owing to stable flows in 

September and October. Option A and Option A Variation rank third and fourth, respectively, and are not 

expected to result in significant differences in nearshore water temperatures compared to BASE 

operations. 

Estimates of Diurnal Stage Variations by Geomorphic Reach 

Diurnal stage variation is defined as the difference in stage between the daily low flow and the daily peak 

flow. To estimate DSV for each experimental option on a monthly basis, water surface (i.e., stage) 

profiles were computed for 1,000 cfs increments using the recently developed HEC-RAS model for the 

Colorado River between Glen Canyon Dam and Diamond Creek (Magirl, in press). The HEC-RAS model 

computes stage profiles for steady flow using more than 2,000 cross sections based on LiDAR-derived 

topography above 8,000 cfs. Model calibration was accomplished by constructing synthetic trapezoidal 

bathymetry at the LiDAR cross sections; the bathymetry was adjusted to achieve less than 65 cm 

differences between the model and the measured water surface profile at 8,000 cfs. Model validation was 

completed by comparing model predictions with measured stage-discharge relationships at 18 Northern 

Arizona University long-term sandbar monitoring sites. The average difference between the model and 

measurements at the 18 sites was about 75 cm for flows below powerplant capacity. 

The DSV was evaluated by computing the stage profile associated with the peak and low flows for each 

option for each month based on typical weekday operations (table 3.1). Subtracting one profile from the 

other results in a DSV for each cross section in the model. For simplified presentation of the results and 

comparison of the options, the average DSV was computed for two reaches: (1) the entire model domain 

(from the dam to Diamond Creek) and ( 2) the first 10 miles downstream from the LCR (i.e., known 

humpback chub habitat). The DSV deviates longitudinally from the two reach-based averages depending 
29

on specific reach geometry. The results of these calculations, averaged over the entire model domain, for 

minimum release years of 8.23 MAF, are plotted below (fig. 3.3) along with a table (table 3.1) 

summarizing the differences between each experimental option and BASE operations, followed by a 

summary of the differences for the reach downstream from LCR. 
30

Table 3.1: Comparison of average diurnal stage variation for each experimental option relative to BASE 

operations. Relative comparisons are segregated by season for presentation purposes (see fig. 3.3 for 

monthly values). 

No difference in fall (Sep–Nov) and spring (Mar–Jun) 

Increased in winter (Dec–Feb) by about 2 ft on average 

Option A 

(relative to 

BASE) Increased in summer (Jul–Aug) by about 1 ft on average 

Increased by about 1 ft on average in Oct–Nov, Mar, and Jul–Aug 

Increased in winter (Dec–Feb) by about 2 ft on average 

Option A 

Variation 

(relative to 

BASE) Increased by about 0.5 ft in Jun; decreased by about 0.6 ft in May 

For the first 10 months (block 1), reduced by about 0.5 ft on average 

For steady flow months, reduced to ~ 0 from about 3–3.5 ft on average 

Option B 

(relative to 

BASE) For fluctuating months (except 1st 10), reduced by about 1.5 ft on average 

Reduced during Sep–Oct steady flows, from about 3 ft to ~ 0 

Increased in winter (Dec–Feb) by about 2 ft on average 

Option C 

(relative to 

BASE) Very slight difference (~ 0.1 ft) in Nov, spring and summer (Mar–Aug) 

Figure 3.3: Average diurnal stage variation by month for BASE operations and the four experimental options 

for an 8.23 million acre-feet (MAF) annual release volume, or minimum release hydrology. 

0

1

2

3

4

5

6

7

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

Average Diurnal Stage Variation (feet)

Based on 8.23 MAF hydrology

Base

SPG A

SPG B (1st 10 months)

SPG B (4 months steady)

SPG B (8 months steady)

SPG B (12 months steady)

SPG C

A variation
31

Options 

Option A: Daily Stage Variation associated with experimental operations in this option is similar to 

BASE operations during fall and spring months each year. However, in winter months, the DSV increases 

by an average of about 2 ft throughout the river corridor. In summer months, the DSV also increases, but 

only by about 1 ft on average throughout the river corridor. 

Option A Variation: This is the only option that expands the daily range in October, November, and 

March, resulting in about 1 ft increased DSV as compared to BASE operations. The maximum daily 

range is expanded in June and September as well, but not fully implemented during 8.23 MAF years. 

Increased DSV in December through February and July and August are the same as Option A. 

Option B: This option results in decreased DSV when compared to BASE operations because of the 

stable flow elements in dam operations. During initial fluctuating flow tests under equalized monthly 

release volumes associated with 8.23 million acre-feet annual releases, there is a reduction in DSV of 

about 0.5 ft on average. With the onset of stable flows, DSV is reduced on average by about 3–3.5 ft. 

During fluctuating flows that occur following the initial test of equalized monthly release volumes, DSV 

is reduced by about 1.5 ft from BASE operations, on average. 

Option C: Experimental flows in this option reduce DSV by about 3 ft on average throughout the river 

corridor in fall stable flow months, but the DSV is increased on average by about 2 ft in winter months 

when experimental fluctuations occur. During late fall, spring, and throughout summer, there is little to no 

change in daily stage ranges when compared to BASE operations. 

Summary of Reach Downstream from LCR 

The diurnal stage variations over the first 10 miles downstream from the LCR are generally less than 

those averaged over the entire domain because of local reach geometry. For BASE operations, the DSV is 

about 0.6–0.7 ft less for the reach downstream from the LCR for all months. For Options A, A Variation, 

and C, the difference in DSV is greatest in the winter months when the daily range is expanded. In 

December through February, the DSV in the reach downstream from the LCR is 1.0–1.6 ft less than the 

average over the entire reach from the dam to Diamond Creek. In other months, the differences for Option 

C are similar to BASE operations. Options A and A Variation also have expanded daily ranges in July 

and August; during these months, the DSV is about 0.8 ft less in the reach downstream from the LCR. For 

Option B, DSV during fluctuating months is 0.3–0.5 ft less for the reach downstream from the LCR as 

compared to the entire model domain. 

Diurnal Stage Variation Summary 

Option B is expected to result in generally less diurnal variation in stage throughout the river corridor 

compared to the BASE operations as well as Options A, A Variation, and C because of the prevalence of 

stable flows and constrained fluctuating flows. Options A and A Variation would expand the diurnal stage 

variation in the summer and winter months. Option A Variation also expands the maximum daily range in 

September through November, March, and June. Option C would expand the diurnal stage variation in 

winter months and reduce the variation in stable flow months of September and October. 

During years when annual release volumes exceed 8.23 MAF, diurnal stage variations are expected, in 

general, to be less than for minimum hydrology. This is because (1) high steady flows may occur during 
32

summer months of high release years, and (2) when monthly volumes are increased, daily lows and peaks 

are increased while holding the daily range constant, and diurnal stage variations tend be slightly less for 

higher flows (with the same daily range) owing to canyon geometry (i.e., stage increases less rapidly with 

flow at higher flows). 

 

Part 2. Aquatic and Fisheries Resources 

Executive Summary 

Managers of Grand Canyon aquatic organisms need to determine the impacts of various dam operations 

on these organisms in the Colorado River and its tributaries to support management decision making. 

While the available literature allows for some informed predictions regarding how these organisms will 

respond to various flow options, the knowledge assessment workshop concluded with many areas of 

uncertainty that remain to be investigated. 

The available literature definitively concludes that cold water is limiting to primary and invertebrate 

productivity (Benke and others, 1988; Huryn and Wallace, 2000), native fish reproduction (Hamman, 

1982; Valdez and Ryel, 1995; Clarkson and Childs, 2000), and native fish swimming ability (Ward and 

others, 2002). Current temperatures of water released from Glen Canyon Dam are below optimum not 

only for native fishes but also for the population of rainbow trout introduced there. Warming dam release 

water temperatures would be expected to increase the growth and survival of aquatic organisms, including 

native and nonnative fishes. Because none of the four flow options considered results in measurably 

warmer water temperatures, the installation and operation of a temperature control device, continued 

natural warming of release temperatures because of drought, or both will be necessary if natural resource 

managers expect to realize any benefits to aquatic organisms from increased water temperatures. 

Reduced DSV can be expected to increase habitat stability, which allows for more permanently wetted 

area that can support algae and invertebrates. Option B proposes the most constrained flow fluctuations 

and, therefore, could be expected to increase habitat stability more than options A, A Variation, or C. 

Because there is reduced productivity in the winter, increased flow fluctuations would not be expected to 

have much measurable effect on the aquatic food base at this time of year. Of the aquatic organisms 

evaluated, rainbow trout would be most likely to suffer from increased winter fluctuations proposed in 

Options A, A Variation, and C because of habitat destabilization that can disrupt reproductive activities 

(Korman and others, 2005b). 

A number of large-scale experimental treatments have been implemented in Grand Canyon since 2000, 

including low summer steady flows (2000), beach/habitat-building flows (2004), and removal of rainbow 

trout and other nonnative fishes (2003–6). All of these treatments were implemented with the intention of 

benefiting multiple Grand Canyon resources, including aquatic organisms. Ecosystems generally take 

months to years to completely respond to such experiments and so the impacts of these treatments on the 

Colorado River ecosystem are still being assessed, especially regarding their effects on the food base and 

native fishes. During this time period, the population size of a nonnative snail has increased dramatically, 

further confounding analysis. While the dam operation options being considered may all be evaluated for 

their degree and direction of impact on the aquatic ecosystem, all except for BASE operations will 

introduce some confounding in the analysis of the impacts of previous treatments that will take additional 

years to completely resolve. The assessments presented below were largely based on the conclusions of 

the 2005 GCMRC knowledge assessment report (Melis and others, 2006b), unless otherwise stated. 
33
34

Aquatic Food Base: Glen Canyon and Grand Canyon 

While the response of the food base (primary and secondary producers in the aquatic food web) to some 

dam operations could be determined from information available to the knowledge assessment workshop 

participants, the food base response to factors could not be predicted with certainty (Melis and others, 

2006b). A strategic science question developed by the participants and presented below reflects this 

uncertainty. A multiyear food base monitoring project focused on tracking the fate of carbon in the 

Colorado River Ecosystem has been initiated and will provide information regarding the impacts of dam 

operations on this important resource. 

Science Question 

SSQ 5-2. How is invertebrate flux affected by water quality (e.g., temperature, nutrient concentrations, 

turbidity) and dam operations? 

Conducting analysis of the aquatic food base under the BASE operations will provide some information 

to answer this question. Implementation of one of the flow options being considered would provide 

comparative data for additional assessment, though implementation of any of the flow options will 

complicate efforts to determine specific cause and effect relationships. 

Options 

BASE Operations: Because the BASE operations are a continuation of the modified low fluctuating flow 

regime, they will not result in any changes to the aquatic food base. This flow scenario represents the best 

option for learning about the aquatic food base because the new food base research project has collected 1 

year of data with this operational regimen in place. 

Option A: This option is likely to reduce the productivity of the aquatic food base relative to the BASE 

operations because of lower daily low flows and a greater DSV. Daily low flows will be lower during the 

months of December through February and July and August and this will decrease the area of 

permanently wetted bottom available for algae and invertebrates (Melis and others, 2006b). Increasing the 

DSV during the same months will negatively affect the aquatic food base in Grand Canyon, but it is 

unclear how this will affect the food base in Glen Canyon (Melis and others, 2006b). The effects of a 

BHBF on the aquatic food base are unclear (Melis and others, 2006b). Changes in downramp rates 

associated with this option are unlikely to affect the aquatic food base. 

Option A Variation: The effects of this option relative to BASE operations are expected to be the same 

as Option A. Changes in ramping rates are unlikely to affect the aquatic food base. 

Option B: This option is likely to increase the productivity of the aquatic food base relative to BASE 

operations because of increases in daily low flows. Blinn and others (1995) estimated that increasing the 

daily low flow from 5,000 cfs to 8,000 cfs would increase the amount of Cladophora energy present in 

the Glen Canyon reach from ~12 billion joules to ~18 billion joules, a 50% increase. Daily low flows 

under this option are higher than BASE operations in 7 of the 10 months for Block 1, 22 of 24 months for 

Block 2, 22 of 24 months for Block 3, and 23 of 26 months for Block 4. Although the steady flows or 

lower fluctuations associated with this option may reduce rates of invertebrate drift, they are likely to be 

offset by substantial increases in invertebrate biomass associated with increases in the daily low flow. The 

effects of a BHBF on the aquatic food base are unclear (Melis and others, 2006b). 
35

Option C: This option is likely to increase the productivity of the aquatic food base relative to BASE 

operations because of higher daily low flows. Daily low flows are slightly higher in November and 

February through June, which will increase the total standing mass of algae and invertebrates. Although 

this option entails a greater DSV, which is likely to have a negative impact on the food base in Grand 

Canyon (Melis and others, 2006b), this increase in daily range will only occur for three months in the 

winter when primary productivity is typically reduced. The effects of a BHBF on the aquatic food base 

are unclear (Melis and others, 2006b). Changes in downramp rates associated with this option are unlikely 

to affect the aquatic food base. 

Fish 

Science questions 

While the knowledge assessment workshop concluded that increased mainstem water temperatures would 

have a positive impact on the spawning and rearing of young native fishes, the most important factor or 

factors limiting the overall humpback chub population have not been definitively determined (Melis and 

others, 2006b). The current uncertainty is reflected in the strategic science question developed at the 

knowledge assessment workshop and in a related question developed by the Science Advisors, both 

presented below. 

SSQ 1-1. To what extent are adult populations of native fish controlled by production of young fish from 

tributaries, spawning and incubation in the mainstem, survival of young-of-year and juvenile stages in the 

mainstem, or by changes in growth and maturation in the adult population as influenced by mainstem 

conditions? 

SA 1. What are the most limiting factors to successful humpback chub adult recruitment in the mainstem: 

spawning success, predation on young-of-year and juveniles, habitat (water temperature), pathogens, 

adult maturation, food availability, competition? 

The GCDAMP has also established a goal of supporting the recreational angling for rainbow trout in the 

Lees Ferry reach of the Colorado River below Glen Canyon Dam. The primary strategic science question 

regarding this resource is: 

SSQ 3-6. What GCD operations (ramping rates, daily flow range, etc.) maximize trout fishing 

opportunities and catchability? 

Maximization of trout fishing opportunities is related to the quality (i.e., size) of rainbow trout that can be 

caught. The need to manage this resource for high quality fish is reflected in the following GCDAMP 

research information need: 

RIN 4.1.1. What is the target proportional stock density (i.e., trade-off between numbers and size) for 

rainbow trout in the Lees Ferry reach? 

The primary effects of increased flow variations are expected to be the physical displacement of fishes 

and habitat instability. The larvae and young-of-year of both native and nonnative fish species are most 

susceptible to flow displacement because of their poorly developed swimming ability. Increased flow 

variability is expected to reduce the Glen Canyon rainbow trout population spawning success, especially 
36

regarding the deposition, development, and hatching of eggs, because the stationary redds (nests) and 

eggs are especially susceptible to displacement and desiccation (Korman and others, 2005b). 

 

Humpback Chub 

Options 

BASE Operations: Under BASE operations, the Grand Canyon adult (> 4 years old) humpback chub 

population appears to have stabilized beginning in about 2000 (Melis and others, 2006a). This is 

relatively new information that was not available to the knowledge assessment workshop participants, 

who did not reach any conclusions about the effects of various flows on the adult humpback chub 

population, indicating instead that additional research was needed before more definitive statements could 

be made. The observation that the adult humpback population has stabilized in recent years while 

mainstem temperatures have been warming (especially 2000 and 2003–6) is consistent with the 

knowledge assessment workshop conclusion that warmer temperatures would increase survival of young 

humpback chub. 

One metric of the mainstem spawning success of humpback chub is captures of young-of-year humpback 

chub in the mainstem. Monitoring of humpback chub in the mainstem Colorado River below the Little 

Colorado River is confounded because young fish may be produced in the mainstem or in the Little 

Colorado and washed into the mainstem. Catch rates of young humpback chub in the mainstem above the 

mouth of the Little Colorado River increased each year from 2003 through 2006, indicating an increase in 

mainstem spawning in this reach. This may be associated with increased mainstem water temperatures, 

stable flows in September in some years, and/or the mechanical removal of rainbow trout and other 

nonnative fishes. Temperature has been described as limiting to spawning of humpback chub by many 

authors, including Hamman (1982), Valdez and Ryel (1995), and Clarkson and Childs (2000), suggesting 

that this parameter may be of critical importance. However, numbers of young humpback chub are still 

very low. For example, sampling with seines and hoopnets of numerous backwater habitats above the 

Little Colorado River inflow in September 2006 captured only 57 humpback chub less than 100 mm total 

length. It will be difficult and/or expensive to determine where young humpback chub were spawned, 

whether in a tributary or the mainstem, when they are captured in the mainstem below the Little Colorado 

River. 

Option A: The increased fluctuations characteristic of this option cannot be determined to have a 

negative or positive effect on adult humpback chub at this time based on the results of the knowledge 

assessment. Humpback chub evolved in a system with great flow volume variability in most years, so this 

species might be expected to have some adaptations that help it resist physical displacement by high 

flows. 

The knowledge assessment workshop participants determined that young-of-year humpback chub would 

be negatively affected by increased fluctuations, owing to the high potential for displacement, habitat 

destabilization, and less than ideal temperatures, though additional study is warranted based on the level 

of uncertainty associated with this conclusion. 

High winter flows might temporarily displace young humpback chub, but this effect would not be 

predicted to depress the population over the long term because this species evolved in an environment 

where high spring flows occurred. Relatively high DSV is not an historical condition, and so may be 

expected to have greater potential to displace young humpback chub, especially during summer and fall, 
37

than options with a lower DSV. In the near term, if young humpback chub do not have habitats available 

to them that allow them to avoid high flows (e.g., backwaters, boulders, tributaries), and their population 

numbers are low, then high flows may interfere with maturation. 

Option A Variation: The potential for physical displacement and habitat destabilization described above 

for Option A would also apply to Option A Variation. Increased ramping rates might magnify this effect. 

Option B: The knowledge assessment participants could not conclude whether the reduced fluctuations 

that are the primary flow feature of this option would have a negative or positive impact on adult 

humpback chub. The knowledge assessment concluded that steady flows and reductions in monthly 

volume, as are described by this option, would favor growth and survival of young humpback chub in 

nearshore habitats. 

Option C: The knowledge assessment workshop participants could not draw conclusions about the 

impacts of flows on adult humpback chub. The steadier fall flows described in this option would, 

according to knowledge assessment participants, be expected to provide benefits to young humpback 

chub in nearshore habitats during September and October, habitats that are thought to be important to 

survival of young humpback chub (Stone and Gorman, 2006). The increased winter flows described in 

Option C would not be predicted to have much impact on young humpback chub because smaller 

numbers of this age class are in the system at that time of the year, though this might change if there were 

a large increase in the density of this age class of humpback chub. Because this species evolved in a 

system with occasional high-volume floods on an annual basis, it would be reasonable to predict that 

young fish would generally survive high winter flows, though high DSVs would not be expected to favor 

native fishes, especially younger fish. Under this option, ongoing monitoring of the humpback chub 

population will provide an assessment of this population that will help determine whether August steady 

flows are required. If the population is observed to be in decline, steady August flows may help increase 

survivorship of young humpback chub in the mainstem, which would in turn be expected to help the 

population size increase. Quantification of the exact population size trigger value(s) or parameter(s) 

remains to be determined. It should be noted that the population size of adult humpback chub appears to 

have stabilized from 2000 to 2005. 

Flannelmouth Sucker 

Options 

Base Operations: Flannelmouth sucker are common in Grand Canyon (Gloss and Coggins, 2005), 

generally spawning in tributaries but feeding and maturing in the mainstem Colorado River (Gloss and 

Coggins, 2005; Ward and others, 2002). They were found in all reaches of the river in Grand Canyon in 

2006. It cannot be determined whether individual flannelmouth sucker captured in the mainstem Colorado 

River were produced there or were produced in tributaries and have moved into the mainstem, so the 

current level of spawning success for this species cannot be readily assessed, though it is thought to occur 

in some years when conditions are favorable. There is no monitoring in place at this time to determine 

which of these fish were produced in tributaries and which were produced in the mainstem. The 

knowledge assessment concluded that flannelmouth sucker would have the same responses to nearshore 

rearing habitat conditions as humpback chub. 

Option A: Participants in the knowledge assessment workshop could not determine whether the increased 

flow variations characteristic of this option, relative to BASE operations, would have a negative or 
38

positive impact on adult flannelmouth sucker. The knowledge assessment workshop participants 

concluded that increased flow fluctuations described in this option would decrease mainstem spawning, 

incubation, and rearing by flannelmouth sucker. This conclusion was coded with a moderate level of 

certainty. Increased flow variability, especially during the summer and fall, when the numbers of young 

flannelmouth sucker entering the mainstem increases, would likely have a negative impact; winter high 

flows likely would have less of a negative impact, at least in the near term. 

Option A Variation: This option would be expected to have similar impacts to resources as in Option A, 

above. The increased ramping rates described by Option A Variation have the potential for greater habitat 

disturbance and physical displacement of young fishes than Option A or BASE operations. 

Option B: The knowledge assessment workshop participants could not determine the impacts that 

increased flow variability would have on adult flannelmouth sucker. The reduced fluctuations described 

in this option would be expected to have a neutral to beneficial impact on mainstem spawning and 

incubation by this species. The knowledge assessment concluded that steady flows and reduced variation 

in monthly volume, as are described by this option, would favor young flannelmouth sucker in nearshore 

habitats by increasing habitat persistence. The knowledge assessment participants were very certain that 

low summer steady flows would have a positive effect on nearshore rearing by flannelmouth sucker. 

Option C: The knowledge assessment workshop does not provide sufficient guidance to evaluate the 

impacts of the variable flows described in this option on adult flannelmouth sucker. Because the spring 

flows described by this option are relatively consistent with BASE operations, and because most 

flannelmouth sucker spawning is in tributary streams, this option would not be expected to impact 

flannelmouth sucker differently than BASE operations for much of the year. 

The steadier fall flows described in this option would, according to knowledge assessment participants, be 

expected to provide benefits to young flannelmouth sucker in nearshore habitats during September and 

October. The increased winter flows described in Option C would not be predicted to have much impact 

on young flannelmouth sucker because smaller numbers of this age class are in the system at that time of 

the year, though this might change if there were a large increase in the density of this age class of 

flannelmouth sucker. Because this species evolved in a system with occasional floods, it would be 

reasonable to predict that at least some of the young fish would survive high winter flows. 

Rainbow Trout 

Options 

BASE Operations: Electrofishing catch rates (catch per unit effort) for rainbow trout in Glen Canyon 

have been decreasing since 2001, decreasing by more than one half from 2005 to 2006. Factors 

contributing to the decline may include high fish density leading to heavy competition for resources, very 

low oxygen levels in water released from the dam in the fall of 2005, and/or the introduction of New 

Zealand mudsnails. [Very low oxygen levels, less than 5 mg/l, were observed in the Glen Canyon Dam 

releases in November 2005 (W. Vernieu, unpublished data, 2005), a physical parameter value that would 

be expected to reduce survivorship of aquatic organisms]. Fisheries management theory (e.g., Griffith, 

1999; Moyle and Cech 2004) would predict that when competition for available resources among rainbow 

trout, or other fish species, becomes so great that the population decreases, then condition (a measure of 

relative weight compared to length) of remaining fish may be expected to increase. The mean condition 

factor for rainbow trout in the Lees Ferry reach increased in 2006 compared to 2004 and 2005 (Hunt and 

others, 2006), and three distinct year classes were captured during the June 2006 electrofishing (the most 
39

recent survey for which data are available, but a cause-and-effect relationship for the 2006 Lees Ferry 

trout population observations has not been established. 

In general, the flow fluctuations implemented under BASE operations encouraged natural reproduction of 

rainbow trout (Gloss and Coggins, 2005), though redd counts in 2006 decreased to about 10% of that 

observed in 2005, so recent spawning success by rainbow trout in Glen Canyon decreased. Individual 

survivorship among remaining larvae experienced greater rates of survival compared to previous years, as 

counts of young rainbow trout were about 30% of that observed in 2005 despite the much lower redd 

count in 2006 (J. Korman, unpublished data, 2006). 

The abundance of rainbow trout decreases with distance from Glen Canyon Dam. This longitudinal 

change in fish abundance is likely a function of environmental conditions including increasing turbidity 

of the river with increasing distance from the dam. Data collected during 2003–6 demonstrate that the 

nonnative fish mechanical removal project dramatically decreased trout abundance around the confluence 

of the Little Colorado and Colorado Rivers. This decrease in abundance was coupled with a decrease in 

the condition of trout. The abundance of trout in the Marble Canyon reach of the Colorado River is less 

than in the Glen Canyon reach. Relative abundance indices indicate a riverwide decrease in the rainbow 

trout population starting in 1999 that persists through 2006. Currently, the abundance of rainbow trout in 

the Marble Canyon reach has decreased by two thirds since 2000. The knowledge assessment reached few 

conclusions about what factors most affect this fish population. 

Available information suggests that rainbow trout do not spawn in Marble Canyon, at least at any regular 

frequency. Catches of mostly larger size classes of rainbow trout in this river reach support this 

conclusion (J. Korman, unpublished data, 2006). Substrates in this reach are thought to be too coarse to 

provide for consistent rainbow trout spawning. Available information suggests that the rainbow trout 

present in this reach are spawned upstream in Glen Canyon, but this assertion should be subjected to 

additional investigation. 

Option A: The increased flow fluctuations proposed in this option are expected to have a negative impact 

on the numbers of adult rainbow trout in Glen Canyon, according to the option proponents and the 

knowledge assessment workshop conclusions. Korman and others (2005b) concluded that 5,000–20,000 

cfs fluctuations had only minor negative impacts on trout egg survival. In response to lower cohort 

numbers, surviving adults are expected to have less competition for resources and therefore to have 

improved condition (Moyle and Cech, 2004) under this flow scenario, an expectation supported, but not 

proven, by observations in 2006. 

The increased DSV that are characteristic of Option A would be expected to have a negative impact on 

the adult rainbow trout population in Marble Canyon. Proponents of this option state that the increased 

winter fluctuations described would reduce nearshore rearing success by rainbow trout in Glen Canyon by 

decreasing habitat stability, a contention supported by the knowledge assessment workshop conclusions 

and Korman and others (2005b). Fewer rainbow trout in the system would be expected to lead to reduced 

competition with associated higher condition factors in the remaining fish. 

Although limited numbers of rainbow trout exist in Marble Canyon, the knowledge assessment concluded 

that increased flow variations, as described by this option, would not affect the very limited amount of 

spawning of rainbow trout in Marble Canyon, but did expect that increased flow fluctuations would have 

a negative impact on young-of-year and juvenile nearshore rearing in Marble Canyon through habitat 

destabilization. 
40

Option A Variation: The impacts of Option A on Glen Canyon rainbow trout would be magnified by 

Option A Variation. The increased ramping rates described in the latter would have greater potential for 

habitat disturbance and depression of overall population numbers. 

Option B: Relative to the BASE operations, Option B proposes reduced flow variability. The decreased 

flow variations would be expected to increase habitat stability in Glen Canyon and thereby have a 

positive effect on mainstem spawning and incubation of rainbow trout in this reach. Greater flow stability 

would reduce risk of loss of redds and eggs due to desiccation or lethal temperatures. If survivorship 

increases dramatically, the resulting condition of survivors may decrease in the face of increased 

competition for resources. However, this option may also be expected to yield more annual primary 

production and higher numbers of invertebrates that may allow the system to support a larger population 

of rainbow trout above Lees Ferry. 

Because the knowledge assessment concluded that increased fluctuations would have a negative impact 

on the Marble Canyon rainbow trout population, it is reasonable to conclude that reduced fluctuations 

would have a neutral to positive impact on this fish population. 

The conclusion of the knowledge assessment that increased fluctuations would not affect rainbow trout 

spawning in Marble Canyon suggests that the decreased flows described in this option would have limited 

or no impact. 

Option C: The reduced fall flow variability, relative to BASE operations, described in Option C can be 

expected to have a positive impact on adult rainbow trout in Glen Canyon, according to the knowledge 

assessment participants. Reduced displacement would likely accompany these flows increasing the 

potential for survivorship. 

The increased ramping rates proposed in this option may have a destabilizing effect on nearshore habitats 

and therefore would reduce nearshore rearing success of rainbow trout. The increased flow fluctuations 

described by this option during the winter months might have some limited negative effect on whatever 

small numbers of rainbow trout that may spawn in Marble Canyon. The steady flows proposed for 

September and October by this option might displace relatively fewer of these fish, resulting in an overall 

neutral impact from flow Option C to rainbow trout. 

Invasive Fish: Coldwater and Warmwater Species 

Options 

BASE Operations: The GCDAMP recently concluded a 4-year experiment (2003–6) to remove rainbow 

trout and other nonnative fishes from the reach of the Colorado River near the mouth of the Little 

Colorado River, the tributary where humpback chub are known to spawn. This experiment was very 

successful at removing rainbow trout, the species with the largest presence in this reach. Ongoing 

monitoring will assess whether this removal had the desired effect of increasing the survivorship of 

humpback chub. Because the temperature of water released from Glen Canyon has been above average 

since 2002, warmwater nonnative fish species may have increased with a concomitant negative impact on 

native fishes. Small numbers of warmwater nonnative fishes are currently captured in the course of other 

fish monitoring efforts, especially in the lowest reaches of the Colorado River in Grand Canyon. The 

GCDAMP has embarked on efforts to investigate the threats posed by warmwater nonnatives and 
41

methods that may be helpful in controlling these species. This effort will conclude with preparation of a 

plan to control both warmwater and coldwater nonnative fishes. 

Option A: The proponents of this option anticipate that spawning success of rainbow trout in Glen 

Canyon will be reduced, thereby reducing the numbers of this species that will require removal in the 

future. The knowledge assessment participants concluded higher fluctuations would likely have a 

negative effect on both cold water and warmwater nonnative fishes because of the likelihood that these 

flows would displace nonnative species that are not adapted to the Colorado River, where flooding was 

historically common. 

Option A Variation: The displacement and habitat disruption expected by the flow variation proposed 

for Option A would also be expected in this option. The increased ramping rates of this option might 

magnify these effects. 

Option B: The reduced fluctuations and increased minimum flows proposed in Option B would likely 

have positive impacts on the aquatic food base, thereby increasing food availability for both native and 

nonnative fishes, warmwater and coldwater species alike. Steadier flows would reduce physical 

displacement of fishes. If this allowed nonnative species to increase, they would be expected to compete 

with and prey on the native species. If the reduced fluctuations described in this option allowed native 

fishes to increase at the expense of nonnatives, the outcome anticipated in the knowledge assessment 

workshop, the natives would benefit. It would be most conservative to predict a net neutral impact on 

nonnatives as a result of this option because both natives and nonnatives would benefit from greater 

habitat stability and increased food supply. 

Option C: This option departs from BASE operations by implementing higher winter fluctuations, which 

the knowledge assessment participants predicted would have negative impacts on nonnative fishes 

through physical displacement. This option also differs from BASE operations by promoting lower 

September and October flows, which could be expected to favor both native and nonnative fishes because 

of reduced displacement. Because of these two contrasting effects, this option can be expected to have a 

net neutral effect with respect to nonnative fish populations. 

Disease and Asian Tapeworm 

Options 

BASE Operations: The introduced intestinal fish parasite Asian tapeworm is currently known to infect 

humpback chub and other native fishes in Grand Canyon. This parasite likely entered this system in 

common carp. A large-scale parasite study is under way to further investigate Asian tapeworm and other 

parasite infection rates. Results of this study are expected to become available in Federal fiscal years 2007 

and 2008. 

Because of its prevalence in western North America, whirling disease, which infects trout species, could 

become a concern, but to date has not been detected in trout in Grand Canyon. 

The knowledge assessment concluded that the effect of temperature on these two parasites was the only 

impact that could be predicted with any certainly. The effects of other possible system modifications, 

including increased or decreased DSV on these parasites are not well known. 
42

Part 3. Terrestrial Biological Resources 

Executive Summary 

Terrestrial biological resources evaluated with respect to the flow options being considered include 

riparian vegetation segregated by surface elevations (<25,000 cfs surface elevation, 25,000–45,000 cfs, 

and >45,000 cfs) and two endangered terrestrial animal species: the southwestern willow flycatcher 

(Empidonax traillii extimus) and Kanab ambersnail (Succineidae: Oxyloma haydeni kanabensis). Riparian 

vegetation located below the 25,000 cfs surface elevation will be most directly affected by the flow 

options being considered. Effects on vegetation in this zone for options A, A Variation, and C may 

include an expansion of marsh vegetation (cover and diversity) in association with increased winter and 

summer fluctuations. Option B and BASE operations may maintain marsh vegetation at current levels or 

marsh area may decline with reduced inundation levels. Under Option B, vegetation would advance 

shoreward with possible drying of vegetation along the upper edge of the 25,000 cfs surface elevation. 

Woody riparian vegetation between 25,000 cfs and 45,000 cfs is expected to become denser under options 

A, A Variation, and possibly Option C, but is likely to change little under BASE operations. These same 

plants may decline under Option B because of reduced inundation levels and possibly reduced ground 

water availability associated with reduced fluctuations and steady flows. Seasonal changes in water 

availability would likely manifest itself in compositional shifts in zones below 45,000 cfs. 

 

Beach/habitat-building flows largely affect vegetation up to and slightly above 45,000 cfs surface 

elevation through scour, burial, and temporary delivery of water. Timing of a BHBF after early April may 

increase salt cedar (Tamarix ramosissima) establishment and spread, particularly when associated with 

Option B. Results associated with an ill-timed BHBF could include channel narrowing because of 

shoreward expansion of vegetation largely affected by a BHBF in combination with Option B. 

Endangered southwestern willow flycatcher and Kanab ambersnail are most affected by magnitude and 

timing of BHBFs. Conservation measures associated with snail habitat, which involve temporary removal 

of vegetation during flooding and subsequent replacement, appear to be a successful in alleviating habitat 

loss at Vaseys Paradise. The potential introduction of New Zealand mud snails (NZM) to the spring area 

during a high flow may be a concern, but how the potential introduction of NZM may affect ambersnails 

and their habitat is unknown. Willow flycatcher habitat is most likely affected by late season (June–

August) BHBFs, specifically for fledglings that may be shaken from their nest. These potential effects are 

applicable to BASE operations and all experimental options. 

 

Riparian Vegetation: Stage Elevation of Base Flow to 25,000 cfs (marsh and obligate 

riparian vegetation) 

Operations 

BASE Operations: Vegetation occupying areas between base flow and the 25,000 cfs surface elevation 

is directly affected by dam operations (Stevens and others, 1995, p. 1032; Kearsley, 2006, p. 183–185; 

Melis and others 2006b, p. 37). Marsh vegetation occupies low-lying, fine-grained habitats often 

associated with upper pools of return current channels and bar platforms, although it can also be found 

along channel margins (Stevens and others, 1995, p. 1032). It is the most dynamic area within the riparian 
43

zone and an area that is more susceptible to nonnative species introduction and expansion. A primary 

factor that makes this area susceptible to nonnative introductions is its daily exposure to disturbance and 

its close proximity to water during the growing season (April–September). Fluctuations transport seeds 

and allow species introductions within this zone through subsequent germination. Sediment redistribution 

under MLFF appears to consist largely of removal of sediment above base flow and deposition of 

sediment into eddies below 8,000 cfs (Melis and others, 2006b, p.10). Observations indicate that marsh 

vegetation has decreased in area with implementation of MLFF (Stevens and others, 1995, p. 1033), 

Vegetation response to a BHBF was studied under sediment-starved conditions in 1996 (Kearsley and 

Ayers, 1999; Stevens and others, 2001; Melis and others, 2006, p. 38). Vegetation response to a BHBF 

conducted under sediment-enriched conditions has yet to be studied in detail. In 1996, vegetative cover 

changed significantly immediately following the BHBF as a result of burial, reworking, and subsequent 

vegetative growth, but species composition was little affected (Kearsley and Ayers, 1999). The direction 

of change was dependent on the zone evaluated. Marshes increased in number and extent following the 

high flow, but these increases were not statistically significant. Substrate grain size was more 

homogeneous following the high-flow event and was largely devoid of seeds (Kearsley and Ayers 1998). 

In general, high flows would likely result in some reworking of return channel/marsh sites. High flows 

are likely to deliver large amounts of dissolved and particulate nitrogen and phosphorus to these areas, 

which would probably benefit riparian vegetation (Melis and others, 2006b, p. 38). 

Option A: Relaxation of flow operations in summer months would result in an expansion of marsh 

vegetation in the summer because of an increased area of daily inundation (Stevens and others, 1995, p. 

1033). These flows may also increase species diversity and cover within this zone as a result of greater 

water availability during the growing season. Greater fluctuations during winter months may affect water 

availability in soil seed banks and result in an increase in seedling density within the zone and for areas 

located above the area of daily inundation (Kearsley and Ayers, 1998, p. 20). Seed banks may include 

exotic herbaceous perennials such as pepperweed (Lepidium latifolium) or other weedy species that grow 

well in soils that are less saturated as would occur under a fluctuating flow discharge (Laubhan and 

Shaffer, 2006). Seed banks below the 25,000 cfs zone that are subject to daily disturbance are likely to be 

exported and the total number of seeds should be lower in the zone. Areas with woody phreatophytes that 

can expand clonally and by seed germination (salt cedar Tamarix ramosissima, arrowweed Pluchea 

sericea, seepwillow Baccharis emoryi, coyote willow Salix exigua, cheat grass Bromus spp.) may expand 

with increased inundation levels (Stevens and Ayers, 1993, p.7; Stevens and others, 1995, p. 1030). 

Increased vegetation density and area within this zone could increase the density of terrestrial plant 

arthropods densities. Terrestrial arthropods are a food source for both terrestrial and aquatic species (Yard 

and others, 2004). 

Option A Variation: Effects of Option A Variation are likely similar to Option A. 

Option B: The reduced fluctuations and stable flows that are entailed in this option would provide a 

stable shoreline for shoreward plant species colonization and expansion in this zone. Plant movement 

toward the channel would occur as plants forage for water (Hutchings and deKroon, 1994), and drying out 

and dying of plants, and subsequent replacement by plants more tolerant of drier condition, at the upper 

end of the zone would also be expected (Porter, 2002). The density of nonnative plants such as saltcedar 

is likely to expand along the shoreline (Melis and others 2006b, pp. 38–39). Peppergrass, another invasive 

species, may also expand in this zone (Laubhan and Shaffer, 2006). 
44

If BHBFs are timed after March and early April, then the incidence of salt cedar seed transport and 

subsequent establishment increases. The long-term effect of shoreward expansion of woody vegetation in 

the absence of disturbance could include channel narrowing (Graf, 1978). 

Pepperweed may expand into the open spaces of the upper end of this zone through rhizomatous growth, 

if it is present prior to the implementation of this option (Laubhan and Shaffer, 2006). The open sand that 

becomes available through reduced fluctuations provides an open niche for occupation by both native and 

exotic plant species. 

Expansion of vegetated area within this zone could increase terrestrial plant arthropod densities. 

Terrestrial arthropods are a food source for both terrestrial and aquatic species (Yard and others, 2004). 

Stabilized shorelines will also provide habitat to shoreline terrestrial invertebrates that are less abundant 

under fluctuating flows (Lightfoot and others, 2006, p. 71). Increases in shoreline vegetation associated 

with this option will increase habitat complexity and may benefit riparian breeding birds (Holmes and 

others, 2005). 

Option C: The continuation of fluctuating flows with stable flows in the fall would have a slightly 

dampened effect on marsh vegetation compared to Option A. Vegetation is not expected to expand 

shoreward appreciably, as in Option B, but it may become more dense and increase in diversity since 

more water will be available prior to the growing season, similar to Option A. The composition of the 

vegetation in this zone may be different than those encountered under BASE operations or Option B 

because the timing and volume of available water shifts slightly, possibly favoring spring and early 

summer species (Bermuda grass Cynodon dactylon, sedges, salt cedar) over later flowering species 

(seepwillow, reedgrass). 

A BHBF would have similar affects on plants in this zone as those described for BASE operations. If a 

BHBF was timed later in the spring then this option might benefit salt cedar germination over native 

species (Stevens, 1986). 

 

Riparian Vegetation: Stage Elevation 25,000–45,000 cfs (facultative herbaceous and 

woody riparian vegetation) 

Options 

BASE Operations: Riparian vegetation located between 25,000 cfs and 45,000 cfs surface elevations is 

indirectly affected by MLFF operations. However, plants located above this surface elevation are affected 

more by amounts of local precipitation. Stevens and Ayers (1993) recorded the effect of surface elevation 

on growth and water stress of salt cedar and coyote willow. Coyote willow exhibited a negative response 

to stage elevation and a positive response to higher discharges. Under BASE operations, compared to dam 

operations before 1991, salt cedar should be maintaining or expanding in area while the opposite would 

be true for coyote willow (Stevens and Ayers, 1993). 

During the 1996 BHBF, understory cover was eliminated in this zone, largely through burial (Kearsley 

and Ayers, 1999), and total cover in this zone significantly decreased. Six months after the BHBF cover 

values were not significantly different than those values recorded prior to the BHBF (Kearsley and Ayers, 

1999). Recovery from burial was by species that could withstand burial and included native species such 

as coyote willow and introduced species such as salt cedar (Kearsley and Ayers, 1999; Stevens and 

others, 2001). Seedling germination within this zone following a BHBF would be depended on depth of 
45

burial and local precipitation that followed. A seed bank study associated with the 1996 BHBF showed 

reduced numbers of seeds and seedlings after the BHBF suggesting that burial or scour evacuated seeds 

and aggraded sand was primarily sterile (Kearsley and Ayers, 1998). Seeds that are located near the 

surface in this zone and that are removed by a BHBF may temporarily affect seed predators and higher 

trophic levels. Timing of the BHBF as it affects foraging by higher trophic levels requires consideration: 

later season BHBFs may affect riparian bird foraging and subsequent nesting success if these resources 

are depleted in May, June, and July. 

Option A: Relaxation of fluctuations would increase the area of inundation, expand the area of available 

ground water and differentially affect plants located above 25,000 cfs. Woody riparian vegetation would 

increase in density (Kearsley, 2006; Melis and others, 2006b p. 37), and clonal species (arrowweed, 

coyote willow, seepwillow) would expand with increased water availability. It is unknown which species 

(natives vs. nonnatives) would benefit from long-term availability of water to this zone, though species 

that flower later in the season (seepwillow) may benefit over early season species (salt cedar). Nonnative 

perennial herbs (peppergrass, camelthorn Alhagi maurorum) that span this zone and the previous zone 

may also expand locally and downstream. The area of potential expansion would likely be below 35,000 

cfs surface elevation. 

A BHBF would deliver water to vegetation above daily fluctuations, remove and bury ground litter and 

possibly mechanically scour seeds (mesquite Prosopis glandulosa) for subsequent germination. This may 

results in increased areas occupied by mesquite, a species associated with predam vegetation. The same 

consequences mentioned above about time of year for BHBFs and potential tamarisk expansion are 

possible under this option. As for BASE operations, seeds that are located near the surface in this zone 

and that are removed by a BHBF may temporarily affect seed predators (arthropods and birds) and higher 

trophic levels. Timing of the BHBF as it affects foraging by higher trophic levels requires consideration: 

later season BHBFs may affect riparian bird foraging and subsequent nesting success if these resources 

are depleted in May, June, and July. 

Option A Variation: Similar to the responses predicted for Option A. 

Option B: Reduced fluctuations would reduce the area of inundation and ground water availability and 

would affect vegetation differentially depending on a species water requirements (Taiz and Zeiger, 1991). 

Salt cedar is better adapted to withstand water stress than other riparian species (coyote willow) (Stevens 

and Ayers, 1993) and may have higher survival relative to other species. Vegetative growth would 

generally be reduced because of decreases in available ground water. Vegetation expansion could be 

slower than under other experimental options, which may be a benefit to campsite area. However, 

vegetation might migrate shoreward following the shoreward movement that would be observed below 

the 25,000-cfs zone. 

A BHBF would deliver water to vegetation above the zone of daily fluctuations, remove and bury ground 

litter, and possibly mechanically scour seeds for subsequent germination. Establishment of seedlings 

located at higher stage elevations may be less likely than under other options being considered. Litter 

accumulation, a potentially important source of carbon for the aquatic ecosystem, within this zone may be 

reduced as a result of lower productivity. The same consequences mentioned above about time of year for 

BHBFs and potential tamarisk expansion is possible under this option. 

Option C: The continuation of fluctuating flows with stable flows in the fall would have a similar to 

slightly greater affect on vegetation within the prescribed surface elevation relative to BASE operations 

or a slightly dampened response when compared with option A. Vegetation would be expected to expand 
46

in area and foliar density (Kearsley, 2006) but not to the extent that might be observed under Option A. 

Just as in the previous zone (<25,000 cfs) species composition may change. The increased winter 

fluctuations and slightly reduced summer fluctuations may benefit early season herbaceous and woody 

perennial species like salt cedar more than later season species. Changes in species composition and litter 

fall accumulation under this option and other options should be monitored and evaluated for ecosystem 

implications. 

A BHBF would deliver water to vegetation above the zone of daily fluctuations, remove and bury ground 

litter, and possibly mechanically scour seeds for subsequent germination. Establishment of seedlings 

located at higher stage elevations may occur at a rate similar to BASE operations and Option A. The same 

consequences mentioned above about time of year for BHBFs and potential tamarisk expansion is 

possible under this option. 
47

Riparian Vegetation: Stage Elevation Above 45,000 cfs (facultative woody riparian 

vegetation and relict predam riparian vegetation) 

Options 

BASE Operations: Vegetation occupying areas above the 45,000 cfs surface elevation is affected more 

by local precipitation than by daily operations (Kearsley, 2006, p. 183–185; Melis and others, 2006, p. 

37). Ground water accessible to species with taproots sustains established plants, but seeds that require 

scour for germination, like mesquite, do not readily germinate at this elevation. Bunch grasses (Aristida 

purpurea, three awn) and annual species (Bromus rigidus) are affected by local precipitation. A BHBF 

would deliver water to vegetation above the zone of daily fluctuations, but litter above 45,000 cfs would 

not be removed or buried by a BHBF. A flow that exceeds 1260 cms (45,000 cfs) may be beneficial to the 

predam high water zone, but this statement is associated with some uncertainty (Melis and others, 2006b, 

p. 37). A lack of high flows has limited recruitment in the predam high water zone (Anderson and 

Ruffner, 1988). 

Option A: Vegetation occupying areas above the 45,000-cfs surface elevation is affected more by local 

precipitation than by daily operations (Kearsley, 2006, p. 183–185; Melis and others, 2006b, p. 37). 

Ground water accessible to species with taproots sustains established plants, but seeds that require scour 

for germination, like mesquite, do not readily germinate at this elevation. Bunch grasses (Aristida 

purpurea, three awn) and annual species (Bromus rigidus) are affected by local precipitation. A BHBF 

would deliver water to vegetation above the zone of daily fluctuations, but litter above 45,000 cfs would 

not be removed or buried by a BHBF. A flow that exceeds 45,000 cfs may be beneficial to the predam 

high water zone, but this statement is associated with some uncertainty (Melis and others, 2006b, p. 37). 

A lack of high flows has limited recruitment in the predam high water zone (Anderson and Ruffner, 

1988). 

Option A Variation: Similar to Option A. 

Option B: Vegetation occupying areas above the 45,000 cfs surface elevation is affected more by local 

precipitation than by daily operations (Kearsley, 2006, p. 183–185; Melis and others, 2006b, p. 37). 

Ground water accessible to species with taproots sustains established plants, but seeds that require scour 

for germination, like mesquite, do not readily germinate at this elevation. Bunch grasses (Aristida 

purpurea, three awn) and annual species (Bromus rigidus) are affected by local precipitation. A BHBF 

would deliver water to vegetation above the zone of daily fluctuations, but litter above 45,000 cfs would 

not be removed or buried by a BHBF. A flow that exceeds 45,000 cfs may be beneficial to the predam 

high water zone, but this statement is associated with some uncertainty (Melis and others, 2006b, p. 37). 

A lack of high flows has limited recruitment in the predam high water zone (Anderson and Ruffner, 

1988). 

Option C: Vegetation occupying areas above the 45,000 cfs surface elevation is affected more by local 

precipitation than by daily operations (Kearsley, 2006, p. 183–185; Melis and others, 2006, p. 37). 

Ground water accessible to species with taproots sustains established plants, but seeds that require scour 

for germination, like mesquite, do not readily germinate at this elevation. Bunch grasses (Aristida 

purpurea, three awn) and annual species (Bromus rigidus) are affected by local precipitation. A BHBF 

would deliver water to vegetation above the zone of daily fluctuations, but litter above 45,000 cfs would 

not be removed or buried by a BHBF. A flow that exceeds 45,000 cfs may be beneficial to the predam 

high water zone, but this statement is associated with some uncertainty (Melis and others, 2006b, p. 37). 
48

A lack of high flows has limited recruitment in the predam high water zone (Anderson and Ruffner, 

1988). 

Wildlife Resource Linkages 

 

Two wildlife resources of concern are the southwestern willow flycatcher and Kanab ambersnail. Both 

are impacted by high flows (Melis and others, 2006b, p. 39). The impacts to southwestern willow 

flycatchers are associated with inundation of rearing habitats located in the upper riparian zone (located 

above 35,000 cfs) and possibly foraging habitats within the fluctuation zone (8,000–20,000 cfs). The 

latter is more uncertain. The willow flycatcher is a riparian breeding bird that has nested along the river 

corridor since 1963 and possibly before the dam (Sogge and others, 1997; Holmes and others, 2005). 

Their nests are usually found in tamarisk trees, at heights well above inundation levels (Sogge and others, 

1997; Stevens and others, 2001). The timing and magnitude of high flows are the most important 

variables that might impact willow flycatchers. If flows exceed 1,274 cms (45,000 cfs), and occurred 

during the breeding season or into the period when young birds fledge (May–August or September), then 

this species could be affected with some certainty. Stevens and others (2001) reported nominal impacts 

associated with the March 1996 high flow including reduction in groundcover and branches located lower 

than 0.6 m. The high flows did not reach nest trees. Stevens and others (2001) speculated that the high 

flows might have had an impact on foraging habitat (i.e., marsh areas), but Holmes and others (2005) 

point out that studies that make these linkages directly are not available. 

 

The habitat of Kanab ambersnail at Vaseys Paradise is affected by the discharge of the spring and river 

stage elevations. Spring discharge influences available wetted area above river stage elevation, while river 

stage determines how far down the slope vegetation can become established. The available wetted area 

and amount of moisture influences plant composition, which in turn influences snail distribution (Stevens 

and others, 1997b; 1998; Meretsky and Wegner, 2000). High flows that occur with low frequency may 

temporarily reduce snail habitat for several years (Stevens and others, 2001). However these impacts may 

be alleviated through temporary removal and replacement of vegetation. A conservation effort associated 

with the 2004 BHBF involved temporary removal and replacement of habitat and appears to have promise 

for the conservation of this species (Cox and others, 2005). High flows that transport New Zealand 

mudsnails into habitats occupied by Kanab ambersnail may be of some concern because of to resource 

competition between these snail species, but this is unknown. 

 

 

Part 4. Recreation and Cultural Resources 

Executive Summary 

Effects of flows on recreation and cultural resources are multi-dimensional. Studies that evaluate the 

trade-offs between attributes that are important for maintaining a high-quality recreational experience or 

maintaining cultural site integrity are very limited, therefore the multi-dimensional effects of flows on 

recreation and cultural resources are difficult to quantify. Nonetheless, the available data on flow impacts 

to single attribute components are fairly robust in some areas, allowing for a general evaluation of the 

four proposed experimental options in relation to the BASE operations (MLFF). In general, Option B 

appears to have the most potentially beneficial outcomes for recreation in terms of maintaining campable 

area, maintaining the types and volumes of flows that are preferred by most recreational boaters and 

anglers, and increasing safety, navigability, and the overall quality of recreational experience. In terms of 

cultural resources, Option B also offers the best possibility of restoring and maintaining sandbars at both 

lower and higher elevations, and it would allow the most dry sand to be available during optimal times of 
49

year for redistribution to the higher elevation old high water zone within the CRE where most 

archaeological sites occur. Option C offers a less optimal experimental approach for maintaining 

campable area and a high-quality recreation experience, while Options A and A Variation appear to have 

mostly negative impacts in terms of both recreation and cultural resources. The one area in which Options 

A and A Variation may be superior to the others is in terms of reducing potential pathogen loads near 

campsites; the higher daily ranges and steeper ramping rates throughout the year will constantly rework 

the shoreline sediments and thereby potentially maintain more optimal sanitary conditions in the vicinity 

of campsites. 

Strategic Science Questions 

3-6. What GCD operations (ramping rates, daily flow range, etc.) maximize trout fishing 

opportunities and catchability? 

3-7. How do dam controlled flows affect visitors’ recreational experiences, and what is/are the 

optimal flows for maintaining a high quality recreational experience in the CRE? 

3-8.What are the drivers for recreational experiences in the CRE, and how important are flows 

relative to other drivers in shaping recreational experience outcomes? 

3-9. How do varying flows positively or negatively affect campsite attributes that are important to 

visitor experience? 

3-11. How do varying flows positively or negatively affect visitor safety, health, and navigability of 

the rapids? 

2-1. Do dam controlled flows increase or decrease rates of erosion at arch sites and TCP sites, and if 

so, how? 

2-3. If flows contribute to arch site/TCP erosion, what are the optimal flows for minimizing impacts 

to these cultural resources? 

 2-7. Are dam controlled flows affecting TCPs and other tribally-valued resources in the CRE, and 

if so, in what respects are they being affected, and are those effects considered positive or negative by 

the tribes who value these resources? 

Angling Opportunity, Quality, and Access 

Options 

Option A: The Option A flow regime, which is characterized by increased fluctuations, both in terms of 

higher daily ranges at least 5 out of 7 months (more often under most probable and wet scenarios) and 

higher downramping rates throughout the year, is expected to reduce angling opportunities, quality, and 

access. 

Increasing the daily flow to above approximately15,000 cfs significantly reduces the number of angling 

locations, while increases in the daily maximum and range in flows, as well as decreases in the daily 

minimum flow, will increase the distance between the areas where adult fish are holding and angler 
50

access points. Both of these factors decrease angling opportunity and access, especially for shore-based 

anglers. 

In the past, AMWG stakeholders have advocated for increased winter fluctuations based on the 

hypothesis that high winter fluctuations may benefit the Glen Canyon trout fishery by reducing spawning 

and the survival of trout redds, thereby reducing trout numbers and intraspecies competition and 

ultimately improving trout condition. Recent observations by the Arizona Game and Fish Department 

(Hunt and others, 2006) indicate an increase in the average condition of Lees Ferry rainbow trout in 2006 

compared to the same value in 2004 and 2005. However, a number of biotic and abiotic factors besides 

wider winter fluctuations were at work in 2005 and 2006, so a direct cause-and-effect relationship 

between improved trout condition and wider winter fluctuations has not been established that explains 

these observations. Greater fluctuations in DSV may increase food availability by increasing drifting 

organic debris, assuming that primary productivity has been successful in preceding months; however, the 

work of Korman and others (2005b) also showed decreased growth in young-of-year rainbow trout with 

higher DSV that could offset potential benefits of higher drift levels. Questions that remain to be 

answered through experimentation concern whether increase drift of organic debris is sustainable on a 

long term basis under higher fluctuating flows and whether increased drift translates into improved 

fishing quality. 

Two different social science studies (Bishop and others, 1987; Stewart and others, 2000) conclude that 

increased fluctuations do not improve angling opportunity, quality, or access. These studies relied on 

statistically reliable social science survey methods to determine angler preference for certain types of 

flows. In both studies, most anglers expressed preference for constant flows over fluctuating flows. 

Changes in flow (rising or falling water) were considered an important attribute of an excellent fishing 

experience for slightly more than half of all anglers, but rising or falling water ranked behind several 

other attributes that were considered more important for an excellent trip, such as “good weather” and 

“low water” (Stewart and others 2000, p.40). In the Bishop and others (1987, p.124–127) study, anglers 

were specifically asked to consider the likelihood that fluctuating flows promoted more drift, and 

therefore improved feeding behavior, when making their assessment of flow preferences. Even when 

presented with this information on the potential benefits of increased drift for angling quality, the 

majority of respondents preferred stable flows over fluctuating flows. Dissatisfaction with fluctuating 

flows among anglers generally increased as flow volumes increased (Bishop and others 1987, p. 132). 

In both studies, anglers expressed a strong preference for flows in the 10,000–15,000 cfs range. As flow 

levels increased above 15,000 cfs, angler satisfaction ratings decreased ((Bishop and others 1987, p. 132–

133; Stewart and others, 2000, p.44–45.) At flows of 20,000 cfs and 25,000 cfs, the percentage of anglers 

characterizing these flows as “very unsatisfactory” was 19% and 39%, respectively (or 36% and 56% 

when “very unsatisfactory” and “somewhat” unsatisfactory responses were combined), compared with 

6% “very unsatisfactory” responses for flows in the 15,000 cfs range (Stewart and others, 2000, p. 193.) 

The percentage of unsatisfactory responses continued increasing as flows increased above the 25,000-cfs 

flow level. Conversely, one third of all respondents (33%) applied the “very satisfactory” rating to flows 

in the 15,000 cfs range, whereas 17% rated flows in the 20,000 cfs range as “very satisfactory” and only 

5% of anglers rated flows of 25,000 cfs as “very satisfactory”(Stewart and others, 2000, p. 193.) Under 

the 8.23 MAF annual release scenario, flows at or above 25,000 cfs are more frequent under Option A 

than under MLFF, and this also holds true for the most probable and wet hydrologic scenarios, (although 

the differences between frequency of high flows eventually disappears in the wettest of the wet years, 

when steady high flows at or above 25,000 cfs are required under all the options.) 
51

Anglers also expressed preference for moderate (10,000–15,000 cfs) and moderately low (7,500–10,000 

cfs) flows over lower (<7,500 cfs) flows. In the Stewart study (2000, p. 193), 39% of anglers rated flows 

of 7,500 cfs as very or somewhat satisfactory, 38% rated 7,500 cfs as “neutral” (neither satisfactory nor 

unsatisfactory), and less than a quarter (24%) rated this flow level as somewhat or very unsatisfactory. As 

flow levels decreased below 7,500 cfs, anglers expressed increasing dissatisfaction (e.g., 40% rated flows 

of 5,000 cfs as somewhat or very unsatisfactory, 50% rated flows of 4,000 cfs as somewhat/very 

unsatisfactory, 54% were very or somewhat unsatisfied with 3,000 cfs, and 56% somewhat to very 

unsatisfied with 2,000 cfs). According to the Bishop and others (1987), the increasing dissatisfaction with 

lower flows has to do with increasing difficulty of boat access upriver and increasing potential for 

equipment (motor/prop) damage as flows decreased, rather than with concerns about decreasing drift or 

fish catchability (Bishop and others, 1987, p. 116). In fact, about half the respondents in the Bishop study 

(1987, p. 117) believed that chances of catching fish increased with lower flows, but only up to a certain 

point (10,000 cfs). Flows lower than 10,000 cfs were viewed progressively less favorably by the majority 

of respondents (Bishop and others, 1987, p. 133). Given that under the 8.23 MAF annual release scenario, 

Option A includes more frequent lower minimum flows than BASE operations (more flows less than 

7,000 cfs), this aspect of the flow regime is also interpreted as having a negative impact on angler 

opportunity, quality, and access. 

Option A Variation: Under Option A Variation, the assessment of effects to angler opportunity, quality, 

and access are generally similar to those described under Option A; although, the negative repercussions 

are potentially somewhat greater because of wider fluctuations, increased downramping rates, and more 

frequent lower minimum flows relative to both BASE operations (MLFF) and Option A.

Option B: The effects of steady flows and equalized monthly volumes are projected to have a mostly 

beneficial effect on angler opportunity, quality, and access. These predictions are supported by both 

empirical evidence and data collected from statistically reliable social science surveys of Lees Ferry 

anglers; although, they are countered to a certain degree by information collected during the 2005 

knowledge assessment workshop (Melis and others, 2006b). 

According to participants in the 2005 knowledge assessment workshop (Melis and others, 2006b), steady 

flows will reduce the availability of drifting organic debris and hence, will reduce the catchability of 

trout. Additionally, lower steady flows during summer are likely to promote the establishment of seedling 

tamarisk trees along the shoreline and on low elevation sandbars, and these seedlings may temporarily 

hinder fishing activity following a return to higher flows. These predictions from the knowledge 

assessment workshop are based exclusively on anecdotal observations, and have not been verified 

through independent, peer-reviewed studies. On the other hand, participants in the 2005 knowledge 

assessment workshop also concluded that stabilizing monthly volumes would likely result in a more 

stable food supply for rainbow trout in the Glen Canyon reach and likely improvement in angling 

opportunity and access due to a decrease in distance between the bank and the areas where fish are 

feeding. The potential for increased growth in trout under stable flows is also supported by the work of 

Korman and others (2005b, p. v) who found a 25% increase in otolith ring width that correlated with 

periods of Sunday steady flows. 

The knowledge assessment predictions of steady flow impacts need to be balanced in relation to previous 

findings by Bishop and others (1987) and Stewart and others (2000). In both of these studies, which were 

based on statistically reliable social science survey methods to determine angler preference for certain 

types of flows, anglers expressed preference for moderate (10,000–15,000 cfs) and moderately low 

(7,500–10,000 cfs) stable flows over lower (<7,500 cfs), higher (>15,000 cfs), or fluctuating flows. In 

both the Bishop and others (1987) and Stewart and others (2000) studies, anglers expressed a strong 
52

preference for flows in the 10,000–15,000 cfs range. As flow levels increased above 15,000 cfs, angler 

satisfaction ratings decreased, with the highest levels of dissatisfaction correlated with the highest flows. 

Anglers also expressed a preference for steady flows over fluctuating flows. This preference was 

maintained even when respondents were reminded that higher fluctuations promoted drift, which could 

increase catchability of the fish. Thus, although there may be a reduction in drift under Option B, the 

available social science data does not support the view that steady flows would have a negative impact on 

angler opportunity or quality. 

Option C: Increased daily ranges in winter months and increased downramping rates in November 

through July are hypothesized to reduce angling opportunities, quality and access. Increasing the daily 

flow to above approximately 15,000 cfs significantly reduces the number of angling locations, while 

increases in the daily maximum and range in flows, or a decrease in the daily minimum flow, will 

increase the distance between the areas where adult fish are holding and anglers access points (Melis and 

others, 2006b.) This increase in distance leads to the conclusion that there will be reduced angling 

opportunity and catchability under Option C. Although winter fluctuations are hypothesized to benefit the 

trout fishery by reducing trout spawning success and thereby ultimately improving trout condition 

through reduced competition, this relationship has not been demonstrated through recent evaluations of 

the 2003–5 winter fluctuating flow experiment (Korman and others, 2005b). The 2005 knowledge 

assessment workshop and the study by Korman and others (2005b) found that the destabilizing impact of 

higher fluctuating flows on trout rearing habitat and trout growth rates counteracted some of the 

hypothesized benefits to the sport fishery (Melis and others, 2006b.) 

The assessment that wider fluctuations are detrimental to angling opportunity, quality, and access is 

supported by two different studies (Bishop and others, 1987; Stewart and others, 2000) that relied on 

statistically reliable social science survey methods to determine angler preference for certain types of 

flows. In both studies, most anglers expressed preference for constant flows over fluctuating flows. 

Changes in flow (rising or falling water) were considered an important attribute of an excellent fishing 

experience for slightly more than half of all anglers, but rising or falling water ranked behind several 

other attributes that were considered more important for an excellent trip, such as “good weather” and 

“low water” (Bishop and others 1987, p.114). In the Bishop and others (1987) study, anglers were 

specifically asked to consider the likelihood that fluctuating flows promoted more drift and therefore 

improved feeding behavior, when making their assessment of flow preferences, yet even when presented 

with this information, the majority of respondents preferred moderate (15,000–10,000 cfs) to moderately 

low (10,000–7,500 cfs) stable flows over fluctuating flows (Bishop and others,1987, p.123–127.) 

Fluctuating flows were also perceived to be more problematic at higher flows (at or above 25,000 cfs) 

than at lower volume flows (Bishop and others,1987, p.132.) 

According to participants in the 2005 knowledge assessment, low steady flows in September and October 

will reduce the availability of drift and hence, Option C flows are hypothesized to reduce trout 

catchability. This negative assessment must be qualified, however, based on previous findings by Bishop 

and others (1987) and Stewart and others (2000). As noted above, most anglers expressed preference for 

stable flows over fluctuating flows. This preference was maintained even when respondents were 

reminded that higher fluctuations promoted drift, which could increase catchability of the fish. Thus, 

although there may be a reduction in drift with steady flows in the fall, the available social science data 

do not support the view that these flows would have a negative impact on angler opportunity or quality. 

Effects of Beach/Habitat-Building Flows on Angling Opportunity, Quality, and Access 
53

BHBFs are included as an element of all four experimental options, as well as BASE operations, and in 

all instances, BHBFs are considered to have a negative impact on angling opportunity, quality, and access 

(Bishop and others, 1987, p.129; Stewart and others 2000, p. 193.) This negative outcome is because high 

flows eliminate angling opportunities during the high-flow event and may result in reductions in food 

availability for weeks to months following the high-flow event. However, reduction in food availability 

depends on the timing of the flood in relation to antecedent food base conditions and season; floods 

occurring in the fall or winter months are more likely to have longer term effects than those that occur in 

the spring or early summer, when conditions are better for algae growth and faster recovery. 

The negative effects of BHBFs on angling experience are documented in two different social science 

studies (Bishop and others, 1987; Stewart and others, 2000) that relied on statistically reliable samples 

and survey methods to determine angler preference for certain types of flows. In both studies, high flows 

(flows of 25,000 cfs or more) were considered by the majority of anglers to be “somewhat” or “very 

unsatisfactory,” with the percentage of “very unsatisfactory” responses increasing steadily as flow levels 

increased (Bishop and others, 1987, p.129; Stewart and others, 2000, p. 193.) The highest levels of 

dissatisfaction correlated with the highest flows. At flows of 40,000 cfs, 50,000 cfs, and 60,000 cfs, the 

percentage of anglers characterizing these flows as “very unsatisfactory” was 65%, 69%, and 71%, 

respectively (or 72%, 74%, and 74% when “very unsatisfactory” and “somewhat unsatisfactory” 

responses were combined, respectively). 

Campsites (campable area availability) 

Options 

BASE Operations: As documented by Kaplinski and others (2005) in the 2005 The State of the Colorado 

River Ecosystem in Grand Canyon (SCORE) report (Gloss and others, 2005) campable area above 25,000 

cfs has diminished under MLFF at the rate of about 15% per year. These findings are congruent with 

findings of Topping and others (2003) that flows above ~9,000–10,000 cfs promote transport of sediment 

out of the system. The only deviation from the general downward trend in campable area occurred 

following the beach/habitat-building flows in 1996 and 2004, leading Kaplinski and others (2005) to 

conclude that “provided that enough sediment is available for deposition, high-flow events are the only 

mechanism by which sandbars used as campsites above the 25,000-cfs stage elevation can be built and 

maintained.”

Option A: The effects of increased daily fluctuations on sediment transport and sandbars are reasonably 

well known from sandbar measurement data collected sporadically during the 1980s and early 1990s 

(Beus and Avery, 1992; Kaplinski and others, 2005), as well as from recently and historically compiled 

sediment transport data (Topping and others, 2000a, 2000b, 2003, 2006). It is well established that 

increased fluctuations will result in higher sediment transport rates, with sediment derived primarily from 

eddy storage complexes, the primary setting of most campsites in the CRE. However, as discussed by 

Beus and Avery (1992) responses of sandbars to higher fluctuating flow regimes are complex, highly 

variable, and dependent on antecedent conditions. The work of Beus and Avery (1992, chapters 6 and 10) 

suggests that under sediment-enriched conditions, short-duration higher flows or higher fluctuating flows 

could potentially result in aggradation of some sandbars, while others would either continue to erode, or 

show minimal measurable change. Under sediment depleted conditions, however, fluctuating flows will 

generally increase the rate of erosion of sandbars. 
54

Given the wider fluctuating flows proposed under Option A and the known relationship to increased rates 

of sediment export under fluctuations, Option A will likely translate into smaller camping beaches over 

time, even if BHBFs occur whenever a sediment trigger is met. However, this hypothesis requires future 

testing. Given what is known today about sandbar responses under highly fluctuating flow regimes, the 

prediction is that campable area would continue to decline under Option A, although perhaps at a 

somewhat reduced rate relative to BASE operations, provided that BHBFs are implemented more 

frequently under sediment-enriched conditions. When these predicted outcomes are couple with the 

proposed higher fluctuations in summer, however, which effectively prohibit camping in areas below the 

highest flow level (which under Option A would be up to 19,000 cfs in summer under the minimum 

release scenario and 25,000 to 33,000 cfs under the wet scenario), campable area throughout the system 

would likely be reduced compared with BASE operations that have less extreme fluctuations, lower daily 

maximums, and generally higher daily minimums. 

Option A Variation: Under Option A Variation, the assessment of effects to campsites is generally 

similar to Option A; although, the reduction of campable area is likely to be somewhat greater than 

Option A because of the wider fluctuations occurring during more months of the year and the increase in 

downramping rates during November through March.

Option B: Sustained low flows below 9,000–10,000 cfs are known with certainty to constrain the amount 

of sediment transported out of the system to negligible amounts (Topping and others, 2003). As 

documented by Wright and others (2005), Schmidt and others (in review), Hazel and others (2006), and 

Topping and others (2006), new tributary sand inputs are conserved and will accumulate in the main 

channel at stable flows of 8,000 cfs (based on results of summer 2000 low summer steady flow test) and 

under fluctuating flows ranging between 5,000 and 10,000 cfs (based on monitoring sand transport during 

the fall of 2004 before the November 2004 high-flow test). Thus, a stable flow regime that constrains 

flows to around 10,000 cfs much of the time and reduces fluctuations is likely to promote sediment 

retention and slow the rate of campable area decline. In addition, sustained low flows would expose more 

campable area on a sustained basis, increasing the amount of campable area exposed at lower elevations 

(Hazel and others, 2001). However, over time, without occasional higher flows (BHBFs), sustained low 

steady flows could result in decreases to the size and volume of sandbars above the low-flow level 

because of the cumulative effects of repeated cut bank failures and the consequent redistribution of higher 

elevation sediment to lower elevations (at or slightly below the level of the highest flows). In other words, 

unless low steady flows are accompanied by occasional periods of higher flows or periodic BHBFs (as is 

proposed under Option B), the conserved sand would, over time, likely end up being stored in the river 

system below a level that is beneficial for use by campers. 

In general, under all hydrologic scenarios, the flow pattern proposed under Option B appears to benefit 

campsite availability, particularly in the highest-use recreational seasons (summer). However, one 

drawback of stabilizing flows in summer is that low steady flows would permit tamarisk and other 

vegetation to encroach on sandbars (Porter and Kearsley, 2001; Porter, 2002), which could eventually 

offset any gains resulting from greater bar exposure at lower elevations. On the other hand, drying out and 

dying of some plants and replacement by more drought-tolerant species at the edges of the riparian zone, 

as observed in 2000 by Porter ( 2002) could potentially open up additional areas for camping. 

Unfortunately, measured information that would allow us to quantify rates of vegetation encroachment 

and/or loss on sandbars under steady (or any other) flows, is lacking, so the overall impact of vegetation 

changes on campable area is unknown. 

Option C: Option C includes a couple of months of stable flows in September and October, higher daily 

ranges in winter months, and steeper downramping rates in November through July compared to BASE 
55

operations. As previously noted, Topping and others’ (2003) analysis of historical sediment transport data 

shows that sediment retention will occur at flows below 9,000–10,000 cfs. Therefore, it is reasonably 

certain that low, stable fall flows will reduce the rate of transport of sediment compared with the more 

variable flows of typical BASE operations, or even higher fluctuating regimes. On the other hand, higher 

fluctuating flows are known to increase the rate of sediment export out of the system (Topping and others 

2000a, 2000b, 2006; Rubin and others, 2002), so higher fluctuations in the winter–spring months will 

likely translate into smaller camping beaches over time, even with occasional sediment-triggered BHBFs 

coupled with fall steady flows. Considering these factors in combination, the effect on campable area 

from the Option C flow regime compared with BASE operations is uncertain but is most likely to result in 

a continuing reduction of campable area over time, though possibly at a slightly reduced rate compared to 

BASE operations. Once again, this assessment is predicated on the assumption that BHBFs would be 

implemented under sediment-enriched conditions more frequently than in the past, and that BHBF 

implementation under these conditions is in fact sustainable over multiyear time scales. 
56

Effects of Beach/Habitat-Building Flows on Campable Area 

BHBFs are an important element of all four experimental options, as well as BASE operations. BASE 

operations include hydrologically triggered BHBFs, while the four experimental options include 

sediment-triggered BHBFs. Sediment-triggered BHBFs are likely to result in aggradation of many 

sandbars and increased sand deposits at higher elevations, with consequent increases in campable area, 

provided that the floods occur under sufficiently sediment-enriched conditions. Sandbar responses will 

not be uniform throughout the ecosystem, but overall, BHBFs occurring under sediment-enriched 

conditions are likely to have a positive impact on campable area, BHBFs that occur in the spring (Option 

B), that are preceded by an extended period of lower, steady flows (Option B and potentially Option C) 

and that are not immediately followed by high fluctuating flows (as proposed in Options A, A Variation, 

and potentially Option C) are likely to increase campable area the most and for the longest period of time. 

Quality of Water and Human Health 

There is a high degree of uncertainty about effects of the four experimental options on water quality and 

human health. This uncertainty is due to a shortage of basic research on how dam operations affect human 

health in the CRE. 

Options 

Option A: The relatively higher flow volumes and higher fluctuations proposed in summer and winter 

compared to BASE operations, will promote recirculation of nearshore sediments (Melis and others, 

2005), therefore the prediction is that Option A flows would decrease concentrations of human pathogens 

in the water, especially in the shoreline zones near popular campsites, thereby likely reducing the threat of 

waterborne pathogens on human health. 

Option A Variation: As with Option A, the relatively higher flow volumes and higher fluctuations 

proposed throughout most of the year, as compared with BASE operations, will promote recirculation of 

nearshore sediments (Melis and others, 2006b), therefore the prediction is that Option A Variation would 

decrease concentrations of human pathogens in the water, especially in the shoreline zones near popular 

campsites, thereby likely reducing the threat of waterborne pathogens on human health. 

Option B: With lower, more stable flows throughout most years, and the accompanying increases in 

nearshore temperatures under the 8.23 MAF annual release hydrologic scenario, concentrations of human 

pathogens in the water, especially in the shoreline zones near popular campsites, are likely to increase, 

thereby increasing risks to human health (Melis and others, 2006b). 

Option C: The relatively high-flow volumes and fluctuations in winter and moderate fluctuations in 

summer will promote recirculation of nearshore sediments, therefore the prediction is that these flows 

would decrease concentrations of human pathogens in the water, especially in the shoreline zones near 

popular campsites, thereby likely benefiting human health (Melis and others, 2006b). 

Effects of Beach/Habitat-Building Flows on Water Quality and Human Health 

In the short term, BHBFs may stir up concentrations of bacteria and temporarily cause a deterioration in 

water quality from the standpoint of visitor health. After flood waters subside, however, a reduction in 

concentrations of pathogens near campsites is expected. 
57
58

Visitor Safety and Rafting Navigability 

While there is considerable anecdotal information concerning the effects of very low (<7,000 cfs) and 

very high (>33,000 cfs) flows on navigability, relatively little peer-reviewed research is available on these 

topics; therefore, considerable uncertainty surrounds the effects of flows on navigability and safety. Given 

the shortage of peer-reviewed studies that specifically address the effects of flows on navigability, effects 

to this important aspect of visitor experience must be considered somewhat uncertain. 

Options 

Option A: Highly fluctuating flows are predicted to increase safety risks somewhat and decrease 

navigability, although actual data supporting this conclusion are very limited (Brown and Hahn-O’Neill, 

1987). At flows above the 31,500-cfs range and below 9,000 cfs, Brown and Hahn-O’Neill documented 

an elevated risk of having a safety-related incident, compared with flows in the 9,000 to 31,500-cfs range, 

which were rated as the safest flows by Brown and Hahn-O’Neill (1987, p.45). Fluctuations make rapids 

less predictable and boats more vulnerable to stranding as flows decrease more rapidly than currently 

allowed under BASE operations, although no existing studies unequivocally demonstrate an increased 

risk to boaters from fluctuating flows (Brown and Hahn-O’Neill, 1987, p.45). As noted in the 2005 

knowledge assessment (Melis and others, 2006b), some boaters maintain that fluctuations can improve 

navigability by increasing the available options for running rapids under varying flows. There is anecdotal 

information suggesting that steeper ramping rates may increase safety risks for anglers, but it is unclear 

whether the perceived increased risks to anglers would be substantiated upon further study. 

There is a high degree of certainty that lower flows (<9,000 cfs) increase the probability of boats hitting 

rocks, sustaining equipment damage (especially to motors), and getting stranded in rapids (Brown and 

Hahn-O’Neill, 1987), and under Option A, very low flows (<7,000 cfs) would occur more often and for 

longer duration than currently occur under BASE operations. The potential benefits to navigability that 

come with the moderately high daily maximums in winter and summer under the 8.23 MAF annual 

release scenario are likely to be offset by the effects of higher fluctuations and lower minimum flows 

under the same scenario. As hydrology becomes wetter, flows become higher and eventually stable, 

topping out at a steady 33,000 cfs in the summertime under the wettest hydrology. This flow level is one 

of the most dangerous for boaters, according the Brown and Hahn-O’Neill study. 

Option A Variation: Under Option A Variation, effects to navigability and safety are generally similar to 

Option A, although safety risks may be slightly greater than Option A due to the wider fluctuations 

occurring during more months of the year and the increase in downramping rates during November 

through March.

Option B: Effects of sustained steady flows on safety and navigability are considered to be positive 

because the stage at which flows would be constrained under Option B are considered to be safer than 

higher or lower volume flows (Brown and Hahn-O’Neill, 1987) and the river on average would be 

slightly slower (particularly during 8.23 MAF annual release years), and runs in the rapids would be more 

predictable, in comparison to BASE operations, during the high-use seasons. Previous studies (Bishop 

and others, 1987) documented that moderate, stable flows of 10,000 to 15,000 cfs were generally 

preferred by whitewater boaters, and flows in the range of 9,000 to 31,500 cfs are the safest for boaters 

(Brown and Hahn, 1987, p. 45), compared with both higher and lower flows. In the absence of 

fluctuations, and with the volumes being proposed under this experiment, the technical difficulty of most 

rapids would be reduced relative to higher, lower, or highly fluctuating flows, hence improving 

navigability and safety. 
59

 

Option C: Effects of Option C on safety are uncertain, but likely would be positive in some respects and 

negative in others. The potential benefits to navigability that come with the relatively high daily 

maximums are offset by the higher fluctuations associated with winter ramping rate experiments, as 

higher fluctuations make rapids less predictable and boats more vulnerable to stranding when flows 

decrease more rapidly than under normal BASE operations. The fall steady flow regime may also affect 

navigability in a negative way, as many rapids become more challenging with lower volume (<9,000 cfs) 

flows. Note that there is relatively little difference between Option C and Option A under the wet 

hydrology scenario, when flow volumes in summer peak at a steady 33,000 cfs under both options. As 

noted above, the study by Brown and Hahn-O’Neill in 1987 found flows above the 31,500 cfs level to be 

the most dangerous for recreational boaters, and in a separate study, Jalbert (1996, p. 16) concluded that 

more accidents were likely to occur under flows of 31,500–33,000 cfs than at 45,000 cfs. 

 

Effects of Beach/Habitat-Building Flows on Visitor Safety and Rafting Navigability 

BHBFs are an important element of all four experimental options, as well as BASE operations, and in all 

instances, the impact of sediment-triggered BHBFs on visitor safety and navigability is considered to be 

neutral. The effects of high flows above powerplant capacity on navigability and safety are not well 

documented in the peer-reviewed literature, but anecdotal information and several in-house National Park 

Service studies that have not yet been subject to peer review (Jalbert, 1996, 2001) suggest that higher 

flows improve the navigability of most rapids by covering rocks that would otherwise be exposed and by 

creating more channels for boaters to chose from as they navigate downstream. Also, Webb’s work 

(1999) shows that BHBFs can clear channels of rock debris accumulations, which generally, but not 

always, creates easier passage for boats after flows diminish. 

Several “in-house” studies have been undertaken by the National Park Service to evaluate effects of high 

flows at or above powerplant capacity on safety (e.g., Brown and Hahn-O’Neill, 1987; Jalbert, 1996.) The 

results of the 1996 study are somewhat difficult to evaluate because the study was relatively short term, 

the sampling strategy was not random, the study did not take into account nonflow factors such as boater 

experience, and the results were not subject to rigorous independent peer review. In addition, various 

studies have evaluated boaters’ perceptions of risk at high flows (e.g., Bishop and others, 1987; Shelby 

and others, 1992; Stewart and others, 2000), but the findings from these studies have not been 

independently evaluated through actual monitoring of safety incidents during non-experimental flow 

events. Based on a comparison of data from 1987, when flows in the low 30,000-cfs range were common, 

with incident data collected during the 1996 BHBF, Jalbert (1996, p. 16) concluded that more accidents 

were likely to occur under flows of 31,500–33,000 than at 45,000 cfs. The 1996 National Park Service 

study concluded that despite observing a slight increase in boat flips and unintentional swims at a couple 

of rapids during the 1996 BFBH, the overall numbers of incidents at 45,000 cfs were not significantly 

different from those reported during non-experimental flow conditions (Jalbert, 1996.) Studies 

specifically designed to evaluate safety issues at a variety of different flows are needed to substantiate 

these conclusions. 

 

Recreational Experience Quality (including access to attraction sites) 

Options 

BASE Operations: The consensus of experienced Grand Canyon boaters is that BASE operations 

(MLFF) noticeably improved the recreational experience in the CRE for whitewater recreationists relative 
60

to the pre-EIS period (historical dam operations from 1963 through 1991). This improvement was largely 

due to the reduction in daily range and ramping rates of daily fluctuations and the constraining of flow 

volumes (lower highs and higher lows) compared to pre-EIS conditions; therefore, a flow regime that 

moves toward further reduction in daily fluctuations is likely to be perceived more positively by a 

majority of experienced Grand Canyon boaters than one that moves in the opposite direction. Effects of 

BASE operations on angler experience are less clear cut, although the documented flow preferences of 

anglers (Bishop and others, 1987; Stewart and others, 2000) indicate a preference for BASE operations 

over the more variable and extreme pre-EIS fluctuating flow conditions. 

Option A: The pattern of higher fluctuating flows (higher daily ranges and steeper downramping rates) 

proposed by Option A is contrary to the documented preferences of most boaters and many anglers 

(Bishop and others, 1987; Stewart and others, 2000). Minimum flows would be lower than historical 

BASE operations under this alternative, and more highly fluctuating flows are proposed throughout most 

of the year. All of these flow elements are perceived to have negative impacts to recreational experience, 

based on the results of social science surveys of boaters and angler preferences by Bishop and others 

(1987) and Stewart and others (2000). 

In terms of access to attraction sites, a somewhat negative effect is predicted due to the increased 

fluctuations in both summer and winter, which make boat mooring near attraction sites unpredictable. 

This impact is likely to be felt more by private boaters and commercial guides (the people who manage 

the boats) than by commercial passengers. 

Given that many factors contribute to recreational experience quality besides flows, it is currently difficult 

to assess how Option A would ultimately affect overall recreational experience quality, but when one 

considers the likely impact of the proposed operating regime under Option A, with its wider fluctuations 

and steeper downramping rates, a decrease in the quality of the both angling and whitewater boating 

recreation experience quality is predicted. 

Option A Variation: The effects to recreational experience quality of Option A Variation are generally 

similar to those of Option A, although likely somewhat more pronounced (and negative), due to wider 

fluctuations occurring during more months of the year and an increase in downramping rates during 

November through March, as compared with Option A.

Option B: When one considers the flows alone, the proposed Option B operating regime is likely to have 

an overall positive effect on recreational boating experience and a mixed effect on angling opportunity 

and quality, because Option B proposes flows that are most consistent with the documented preferences 

of the majority of whitewater rafters and anglers. 

Based on anecdotal accounts and limited social science survey data, a generally positive effect on access 

to attraction sites is predicted under Option B, due to the predictable nature of equalized volumes and 

stable flows. With stable flows, boaters will spend less time dealing with changing mooring conditions 

and therefore have more time and a potentially more enjoyable experience visiting attraction sites. In 

addition, the warmer nearshore water temperatures that would likely accompany stable summer and early 

fall flows is considered to be a beneficial effect by many boaters (Stewart and others, 2000; Jonas and 

Stewart, 2002). The effects of warmer water and stable flows may benefit trout condition as well, but only 

up to a certain degree (~°16 C). 

Many factors besides flows contribute to recreational experience quality, and the trade-offs associated 

with specific flows have never been thoroughly evaluated, so an accurate assessment of how this 
61

proposed experiment would ultimately affect overall recreational quality is difficult to predict without 

collecting more data that specifically evaluates trade-offs among the various attributes contributing to the 

overall quality of recreational experiences in the CRE. However, when one considers the flows alone, the 

proposed operating regime under Option B is likely to have a positive effect on both angling and 

whitewater boating experience quality, in comparison to BASE operations. 

Option C: The proposed operating regime of Option C is likely to have a mixed effect on both angling 

opportunity and whitewater boating experience quality. The pattern of fluctuating flows proposed for 

winter in Option C is contrary to the documented preferences of most boaters and many anglers (Bishop 

and others, 1987; Stewart and others, 2000). In addition, flows lower than 10,000 cfs are generally not 

preferred by most boaters, so implementing two months of low fall steady flows may negatively impact 

the boating experience. On the other hand, the warmer water that would likely accompany lower fall 

steady flows may counteract some of the negative aspects of the fall flow regime. 

In terms of access to attraction sites, effects of Option C are both negative and positive, due to the 

counteracting effects of winter fluctuations and fall stable flows. The negative effects of increased 

fluctuating flows are likely to impact private boaters primarily, as few if any commercial trips would be 

on the water in the winter months when the highest fluctuations are proposed, while the beneficial effects 

of fall stable flows on attraction site access would be experienced by both private and commercial 

boaters. 

As noted above, many factors besides flows contribute to recreational experience quality, so it is difficult 

to precisely assess how Option C would ultimately affect overall recreational quality without undertaking 

additional focused studies. Based on currently available data, there is likely to be very little difference in 

terms of overall recreational experience quality in comparison to BASE operations. 

Effects of Beach/Habitat-Building Flows on Recreational Experience Quality (including access to 

attraction sites) 

BHBFs are an important element of all four experimental options, as well as BASE operations, and in all 

instances, the impact of sediment-triggered BHBFs on the whitewater recreational experience is 

considered to be mostly positive, with certain caveats. Impacts to the angler experience (discussed 

elsewhere) are considered to be largely negative. 

As noted previously, studies by the National Park Service have evaluated the effects of high flows at or 

above powerplant capacity on visitor safety, an important component of visitor experience. The 1996 

National Park Service study found no significant difference in numbers of incidents resulting in injury or 

death (Jalbert, 1996.) Studies by Bishop and others (1987) and Stewart and others (2000) specifically 

evaluated the effects of different flows on recreational experience, and these studies concluded that for 

both boaters and anglers, moderate flows of 10,000 to 20,000 cfs were preferred over higher flowers; 

however, Jalbert (1996) found that most boaters who were interviewed during the 1996 BHBF were 

excited to be running on the high experimental flows, and some deliberately scheduled their trip to 

maximize time spent on the high flow. The results of the Jalbert study, which were not subject to 

independent peer review, plus additional anecdotal information from river guides, indicates that flows 

over 40,000 cfs are perceived as both positive and negative by different user groups, with boaters with 

more experience generally having a more positive perception of the high-flow experience than the less 

experienced boaters. This issue warrants a future focused study. 
62

The effects of high flows at or above powerplant capacity on access to attraction sites is not well 

documented, but anecdotal information suggests that it would have neither a generally positive nor 

negative effect. At specific attraction sites, pulling over and parking boats may be easier or more difficult, 

but available anecdotal information does not indicate a dominant trend in one direction or another. 

Some additional likely positive benefits of BHBFs that relate to the overall quality of the recreation 

rafting experience include increased numbers and sizes of camping beaches and improved sanitary 

conditions near camps. 

Archaeological Sites and Traditional Cultural Properties (TCPs) 

Effects of flows on archaeological sites are evaluated primarily in terms of the degree to which sediment 

would be deposited and retained at higher elevations, either via direct deposit from high flows or via 

indirect redeposition by aeolian transport from lower elevation sandbars to eroding terrace surfaces where 

most archaeological sites occur. 

Options 

Option A: Effects to cultural resources are uncertain but likely would have negative implications for 

archaeological site stability and TCP integrity relative to BASE operations, even with the likely beneficial 

effects of sediment-enriched BHBFs. This is due to the higher sediment transport rates that would 

accompany wider fluctuating flows and steeper downramp rates, and the fact that the sandy, nearshore 

deposits would be subjected to frequent, repeated inundation and therefore would not be available for 

redistribution to higher elevations via wind transport. 

Option A Variation: The effects to archaeological sites and traditional cultural properties from Option A 

Variation are generally similar to those of Option A, although perhaps slightly more pronounced (and 

negative), due to wider fluctuations occurring during more months of the year and an increase in 

downramping rates during November through March, as compared with Option A.

Option B: Effects to cultural resources are uncertain but possibly positive due to greater sediment 

retention with stable flows and more flows that are consistently less than 10,000 cfs during large portions 

of each year. Minimizing the extent to which daily flows vary with respect to stage may allow for larger 

portions of nearshore sandbars to remain desiccated throughout the year, permitting the dry sand to be 

redistributed beyond the zone of inundation. Once sand deposits are dried out and remain dry, wind 

transport of sand and silt may occur in directions that transport fine sediment upslope in to cultural site 

preservation areas. Unresolved uncertainties relate to effects of vegetation encroachment on open sand 

areas under stable flows and the sustainability of repeated BHBFs over time. 

Option C: Effects to cultural resources are uncertain but probably neutral relative to BASE operations, or 

perhaps slightly positive, due to implementation of sediment-enriched BHBFs coupled with greater 

sediment retention with low stable flows in the fall; however, the sediment conservation effects of fall 

steady flows may be largely offset by the higher sediment transport rates accompanying the wider 

fluctuations in winter relative to BASE operations. 

Effects to TCPs from Options A through C are uncertain, due to lack of specific data about TCP locations 

and specific qualities of TCPs that are being affected by flows. With regards to effects to native plants (a 

major interest of several Native American tribes), short duration BHBFs may benefit native vegetation in 

the higher terrestrial zones by temporarily elevating ground water levels and by increasing disturbance to 
63

the vegetation, which has the potential to encourage regeneration of many new high-water zone and old 

high-water zone native species. 

Effects of Beach/Habitat-Building Flows on Archaeological Sites and Traditional Cultural Properties 

BHBFs under sediment-enriched conditions are an important element of all four experimental options, as 

well as BASE operations, and in all instances, the impact of sediment-triggered BHBFs on archaeological 

sites and TCPs are considered to be mostly positive, although this assessment requires verification 

through additional research and monitoring. A number of short-term studies undertaken to evaluate the 

effects of the 1996 experimental flood on historical properties within the CRE, and on the basis of a few 

site-specific studies, the conclusion was that there was either no effect, no adverse effect, or potentially 

beneficial effects from the BHBF (Balsom and Larralde, 1996.) In the future, effects of BHBFs should be 

evaluate for a sample population of sites, in order to more fully characterize BHBF effects to 

archaeological sites on a systemwide basis. 

 

The effects of flows above powerplant capacity on sandbars and high elevation sediment supply is 

relatively well documented (Webb and others, 1999; Kaplinski and others, 2005; Hazel and others, 2006). 

BHBFs appear to be the only mechanism available for restoring large volumes of sand to elevations 

above the highest level of normal dam operations, and restoring the sand supply at higher elevations 

within the CRE is probably the only flow-based action that can significantly alter the downward trajectory 

of archaeological site integrity in the CRE. BHBFs have been shown to increase higher elevation sandbar 

areas systemwide, at least on a temporary basis (Hazel and others, 1999, 2006; Kaplinski and others, 

2005b), and these sandbars can potentially serve as sources for sediment to be redistributed across 

archaeological site areas by wind, provided that subsequent flows do not rapidly erode the newly built 

sandbars (as was the case in the winter–spring of 2004–5.) BHBFs have also been demonstrated to 

deposit sand in arroyo mouths up to the highest flow level (Yeatts, 1997; Hazel and others, 2000), thereby 

temporarily reducing the gradient of arroyos and potentially slowing rates of down cutting in the lower 

reaches of the drainage. Once again, however, more focused studies are needed to quantify the long-term 

effects of BHBFs on cultural resources in the CRE. 

Part 5: Hydropower Resources 

(Please see table 3.2 and appendix E, this report, for details on methods and assumptions.) 
64

Summary Table 

Table 3.2. Summary comparison of flow-related resource effects estimated for four options under 

consideration by the Glen Canyon Dam Adaptive Management Program compared to BASE operations 

(modified low fluctuating flow). The table provides, where possible, the potential effects of each option on 

individual resources are ranked 1 (most) through 4 (least) where possible. 

 Option A Option A Variation Option B Option C 

Fine-sediment 

Storage 

 

Fine-sediment 

storage (all flows up 

to 45,000 cfs) 

(3) Potential increase 

over BASE with 

BHBF effects, 

however, the relaxed 

constraints on 

fluctuating flows 

increase sand export 

and may offset BHBF 

influences 

(4) Potential increase 

over BASE with BHBF 

effects, however, these 

most relaxed constraints 

on fluctuating flows 

increase sand export 

and may offset BHBF 

influences 

(1) Overall, provides 

greatest potential 

increase in sand 

conservation over 

BASE with BHBF 

effects, and sand 

habitats might be 

more stable following 

BHBFs 

(2) Potential increase 

over BASE with BHBF 

effects, fall stable flows 

help limit sand export, 

but relaxed constraints 

on fluctuating flows 

might offset reduced 

sand export during 

stable flow months 

Water 

Temperatures 

 

Water Temperatures 

(mainstem) 

(based on numerical 

modeling) 

No significant change 

over BASE without 

temperature control 

device (TCD) 

No significant change 

over BASE without 

TCD 

No significant change 

over BASE without 

TCD 

No significant change 

over BASE without 

TCD 

Water Temperatures 

(nearshore) 

(based on existing 

data and state-ofknowledge) 

(3.5) No significant 

change over BASE 

without TCD 

(3.5) No significant 

change over BASE 

without TCD 

(1) Greatest potential 

increase overall – see 

text for potential 

range of increase 

(2) Potential increase in 

Aug (when stable flows 

triggered), Sep – Oct; 

otherwise no significant 

change over BASE 

without TCD 

Diurnal Stage 

Variations (DSV) 

Downstream 

Increase in DSV over 

BASE in winter (Dec 

– Feb and summer 

(Jul – Aug) 

Increase in DSV over 

BASE in all months 

except Apr – May 

Decrease in DSV 

over BASE in all 

months 

Increase in DSV over 

BASE in winter (Dec – 

Feb) and decrease in 

Sep – Oct (steady) 

Aquatic food base 

Aquatic Food Base 

(Glen) 

(3) Decrease relative 

to BASE from Dec. 

through Feb. and July 

through Aug 

(4) Decrease relative to 

BASE for all months 

except April and May 

(1) Increase relative 

to BASE in 74 of 84 

months 

(2) Decrease relative to 

BASE from Dec. 

through Feb. 

Aquatic Food Base 

(Grand) 

(3) Decrease relative 

to BASE from Dec. 

through Feb. and July 

through Aug 

(4) Decrease relative to 

BASE for all months 

except April and May 

(1) Increase relative 

to BASE in 74 of 84 

months 

(2) Decrease relative to 

BASE from Dec. 

through Feb. 

Adult Fish 

Populations 

 

Adult Population 

(HBC) 

Uncertain Uncertain Uncertain Uncertain 

Adult Population 

(FMS) 

Uncertain Uncertain Uncertain Uncertain 

Adult Population 

(RBT #’s in Glen) 

(3) Potential decrease (4) Potential decrease (1) Potential increase (2) Potential increase 
65

Adult Population 

(RBT size in Glen) 

(2) Potential increase (1) Potential increase (4) Potential decrease (3) Potential decrease 

Mainstem 

spawning and 

incubation 

 

Mainstem Spawning 

& Incubation 

(HBC) 

(3) Potential decrease (4) Potential decrease (1) Potential increase (2) Potential increase 

Mainstem Spawning 

& Incubation (FMS) 

(3) Potential decrease (4) Potential decrease (1) Potential increase (2) Potential increase 

Mainstem Spawning 

& Incubation (RBT 

- Glen) 

Potential decrease (no 

ranking: value 

dependent) 

Potential decrease 

(most) (no ranking: 

value dependent) 

Potential increase (no 

ranking: value 

dependent) 

Potential increase (no 

ranking: value 

dependent) 

Mainstem Spawning 

& Incubation (RBT 

- Marble) 

No change No change No change No change 

YOY/Juvenile 

nearshore rearing 

 

YOY/Juvenile 

Nearshore Rearing 

(HBC) 

(3) Potential decrease (4) Potential decrease (1) Potential increase (2) Potential increase 

YOY/Juvenile 

Nearshore Rearing 

(FMS) 

(3) Potential decrease (4) Potential decrease (1) Potential increase (2) Potential increase 

YOY/Juvenile 

Nearshore Rearing 

(RBT - Glen) 

Potential decrease 

(no rank: value 

dependent) 

Potential decrease (no 

ranking: value 

dependent) 

Potential increase (no 

ranking: value 

dependent) 

Potential increase (no 

ranking: value 

dependent) 

YOY/Juvenile 

Nearshore Rearing 

(RBT - Marble) 

No change No change No change No change 

Invasive Fish 

Species (cold water 

species; 

downstream) 

(2) Potential decrease (1) Potential decrease (4) Potential increase (3) Potential increase 

Invasive Fish 

Species (warm 

species) 

(1.5) No change (1.5) No change (4) Potential increase (3) Potential increase 

Disease (Asian 

Tapeworm) 

No change No change No change No change 

Disease (Whirling 

Disease) 

No change No change No change No change 

Terrestrial Riparian 

Resources 

 

Marsh and obligate 

riparian vegetation 

(below 25,000 cfs) 

Potential increase of 

marsh vegetation 

Potential increase of 

marsh vegetation 

Marsh vegetation 

maintained or 

decreased; vegetation 

advancing shoreward 

 Marsh vegetation 

maintained or 

decreased 

Lower Riparian 

Habitat (24,000 to 

45,000 cfs) 

Increased dense 

woody vegetation 

Increased dense woody 

vegetation 

Woody vegetation 

maintained or 

decreased; vegetation 

advancing shoreward 

Increased dense woody 

vegetation, but less than 

Options A and A 

Variation 

Upper Riparian 

Habitat (45,000 to 

60,000 cfs) 

No change; 

vegetation most 

affected by 

precipitation 

No change; vegetation 

most affected by 

precipitation 

BHBFs after April 

could spread tamarisk 

shoreward 

No change; vegetation 

most affected by 

precipitation 
66

Recreational 

Resources 

 

Angling 

opportunity, quality, 

and access 

(3) Potential decrease (4) Potential decrease (1) Potential increase 

(improved fishability) 

(2) Potential increase 

Campsites (3) Potential decrease 

over base, even with 

BHBF effects 

(4) Potential decrease 

over BASE, even with 

BHBF effects 

(1) Greatest potential 

increase over base 

with BHBF effects 

(2) Potential increase 

over base with BHBF 

effects 

Human Health (1.5) Potential 

decrease in pathogen 

concentrations near 

camps over BASE 

(1.5) Potential decrease 

in pathogen 

concentrations near 

camps over BASE 

(4) Greatest potential 

increase in pathogen 

concentrations near 

camps overall 

(3) Potential increase in 

pathogens in September 

(and August when 

stable flows are 

triggered), otherwise 

potential decrease over 

BASE 

Visitor 

Safety/Rafting 

Navigability 

Potential reduction Potential reduction Potential 

improvement 

No net change 

Recreational 

Experience 

Potential reduction Potential reduction Potential 

improvement 

No net change 

Cultural Resources 

Archeological Site 

Preservation 

(3) Potential increase 

over base with BHBF 

effects 

(4) Potential increase 

over base with BHBF 

effects 

(1) Greatest potential 

increase over base 

with BHBF effects 

 

(2) Potential increase 

over base with BHBF 

effects 

Traditional Cultural 

Property 

Conservation 

Unknown Unknown Unknown Unknown 

Hydropower 

Resources 

 

Increased 

Hydropower LoadFollowing Capacity 

(2) Yes, capacity is 

increased (see 

Appendix E for 

details) 

(1) Yes, greatest 

increase in capacity (see 

Appendix E for details) 

(4) No, greatest 

decrease in capacity 

(see Appendix E for 

details) 

(3) No, capacity is 

decreased (see 

Appendix E for details) 

Decreased 

Hydropower 

Replacement Costs 

(2) Yes, costs are 

decreased (see 

Appendix E for 

details) 

(1) Yes, greatest 

decrease in costs (see 

Appendix E for details) 

(4) No, greatest 

increase in costs (see 

Appendix E for 

details) 

(3) No, costs are 

increased (see 

Appendix E for details) 
67

Chapter 4: Estimated Effects of Proposed Nonflow 

Actions on Downstream Resources 

Temperature Control Device 

Part 1. Physical Resources 

 

Downstream Water Temperatures 

Because all four experimental options include the use of a temperature control device (TCD) starting in 

water year 2012, the effects of the TCD are primarily evaluated with respect to BASE operations, which 

do not use a TCD. However, because the TCD affects release temperatures for all options, it may also 

affect the differences between the options since the amount of downstream warming is dependent on the 

release temperature. 

Main Channel 

The numerical modeling detailed in appendix D can be used to evaluate the effects of the TCD by 

analyzing the last 5 years of the simulation period (i.e., the period when the TCD is in operation). 

Example model results are shown below. 

9

10

11

12

13

14

15

16

Release RM31 RM65 RM127 RM225

Average mainstem water

temperature over last 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

6

8

10

12

14

16

18

20

22

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

Average mainstem water

temperature over last 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

Figure 4.1 Average mainstem water temperatures at 5 locations (left) and average monthly 

temperatures at river mile 65 (right) for the last 5 years of the simulation period (i.e. period 

with TCD) for most probable hydrologic scenario. 

The effects of the TCD are clearly evident in figure 4.1 where it is seen that all options have significantly 

warmer water throughout the system as compared to BASE operations. The warming is greatest in the 

summer months and typically negligible in the winter. 
68

Nearshore Environments 

Because nearshore environments are connected to the mainstem, increased mainstem temperatures are 

expected to translate to similar increases in nearshore temperatures. Stable flows during months when 

release temperatures are cooler than air temperatures (i.e., months when downstream warming is 

expected) are still expected to promote warmer nearshore environments (particularly backwaters). 

However, because the TCD will tend to bring the mainstem and nearshore temperatures closer to 

equilibrium with the atmosphere, the impacts of stable flows on nearshore temperatures will tend to be 

reduced. Mainstem modeling results indicate that downstream warming is expected to continue to occur 

in spring, summer, and fall months with the TCD in operation. 

Options 

Option A: Main channel temperatures are expected to be significantly warmer than would be present as 

the result of BASE operations during spring, summer, and fall. Because nearshore environments are 

connected to a warmer mainstem they are expected to be warmer as well. 

Option A Variation: Same as Option A. 

Option B: Same as Option A. 

Option C: Same as Option A. 

Downstream Water Temperature Summary 

A TCD is expected to significantly increase mainstem and nearshore temperatures throughout the system 

for all options during the spring, summer, and fall. Because release temperatures are increased, the 

differences between the options, in terms of mainstem and nearshore temperatures, tend to be reduced 

because the differences are driven by downstream warming and downstream warming is less when release 

temperatures are warmer. Thus, the ranking of the options presented in chapter 3 is expected to hold with 

a TCD in operation, with the differences between the options being reduced from the no-TCD case. 

Part 2. Aquatic and Fisheries Resources 

Executive Summary 

The addition of a TCD would increase water temperatures, which would generally be a benefit to native 

and nonnative aquatic organisms. The primary benefits of increased water temperatures would be 

increased annual aquatic primary production and invertebrate production and increased metabolic rates 

for native and nonnative fishes, which are likely to result in increased growth rates, especially in the 

presence of increased food (vegetation and invertebrates) availability. 

Increased mainstem temperatures, the goal of the implementation and operation of a TCD were generally 

thought by the knowledge assessment participants to be of benefit to fishes, native and nonnative. 

Operation of the TCD may also increase the numbers and persistence of Asian tapeworm. The only 
69

resources for which the knowledge assessment did not draw conclusions in response to a TCD were: 

rearing of young rainbow trout in Marble Canyon, the adult rainbow trout in Marble Canyon, and adult 

humpback chub. The proponents of all options being considered recognize that a TCD may benefit both 

desired and undesired species, in both desired and undesired locations, and so support research and 

development of methods to control species where and when it is necessary to benefit native fishes. The 

Science Advisors have also concluded that while there are risks to operation of a TCD, the potential 

benefits to native organisms render the risk acceptable. The results of the knowledge assessment 

workshop support the implementation of a TCD to benefit many resources, including the Grand Canyon 

food base, and mainstem spawning and rearing by humpback chub and other native fish. 

Aquatic Food Base: Glen Canyon and Grand Canyon 

Options 

Option A: Installation of a TCD will have a positive effect on the aquatic food base in both Glen and 

Grand Canyon by increasing growth rates of both algae and invertebrates (Melis and others, 2006b). 

Although the instantaneous benthic biomass of algae and invertebrates may not increase with installation 

of a TCD, more algae and invertebrate biomass will be produced annually because of faster growth rates 

in warmer water. 

Option A Variation: Installation of a TCD will have a positive effect on the aquatic food base in both 

Glen and Grand Canyon by increasing growth rates of both algae and invertebrates (Melis and others, 

2006b). Although the instantaneous benthic biomass of algae and invertebrates may not increase with 

installation of a TCD, more algae and invertebrate biomass will be produced annually because of faster 

growth rates in warmer water. 

Option B: Installation of a TCD will have a positive effect on the aquatic food base in both Glen and 

Grand Canyon by increasing growth rates of both algae and invertebrates (Melis and others, 2006b). 

Although the instantaneous benthic biomass of algae and invertebrates may not increase with installation 

of a TCD, more algae and invertebrate biomass will be produced annually because of faster growth rates 

in warmer water. 

Option C: Installation of a TCD will have a positive effect on the aquatic food base in both Glen and 

Grand Canyon by increasing growth rates of both algae and invertebrates (Melis and others, 2006b). 

Although the instantaneous benthic biomass of algae and invertebrates may not increase with installation 

of a TCD, more algae and invertebrate biomass will be produced annually because of faster growth rates 

in warmer water. 

Fish 

Humpback Chub 

Adults: Participants in the knowledge assessment workshop could not conclude whether or not the TCD 

would result in a net benefit to adult humpback chub because of potentially conflicting results. The value 

of the TCD for adult humpback chub, described in all options being considered, requires additional 

assessment. The increase of mainstem water temperatures has been thought to be a benefit to adult 

humpback chub by many authors, including Hamman (1982), Valdez and Ryel (1995), and Clarkson and 
70

Childs (2000), among others, by promoting survival, growth, and maturation as a result of increased 

metabolic rates. However, if warmer water temperatures had the predicted effects of increasing nonnative 

warmwater fishes and/or Asian tapeworm, then the net effects on adult humpback chub could be neutral. 

Managers responsible for operating a TCD will likely want to maintain the option of reducing or 

eliminating the use of the TCD in some years, thereby using cooler water temperatures to help control the 

proliferation of nonnative fishes and Asian tapeworm. Modeling of mainstem water temperatures suggests 

that when basin hydrology is higher the maximum water temperature released even with operation of the 

TCD will be less than in years with lower flows, which is expected to result in less than optimum water 

temperatures for both native and nonnative fishes in high-flow years. The net influence of these various 

factors requires additional investigation. 

Mainstem Spawning and Incubation: Warming mainstem temperatures resulting from a TCD were 

thought by the knowledge assessment participants to be of benefit to mainstem spawning and incubation 

by humpback chub. Adult humpback chub could be expected to grow and mature more quickly in a 

warmer environment, thereby increasing gamete maturation. Available literature (e.g., Hamman, 1982; 

Clarkson and Childs, 2000) suggests increased survival of humpback chub eggs in warmer water 

temperatures. All four options being considered would be expected to have a positive effect on this 

resource area because of their support for the installation and operation of a TCD. However, this benefit 

could be negated if predatory nonnative fishes increased, thereby increasing loss of eggs and larvae to 

predators. 

Young-of-year and Juvenile Nearshore Rearing: The knowledge assessment workshop participants 

found that warmer mainstem temperatures would have a positive effect on nearshore rearing by 

humpback chub through increased metabolism leading to increased growth and survival. All options 

being considered therefore offer positive benefits to this resource area due to their inclusion of a TCD. 

However, if nonnative predatory fishes increase in response to warmer water temperatures, predation on 

young life stages of native fishes could increase, potentially negating the benefits to natives. 

Other Native Fish 

Adults: Flannelmouth sucker was the native fish species other than humpback chub considered during the 

knowledge assessment workshop. This species was thought to generally benefit from TCD operation. 

Increased mainstem temperatures may be expected to increase growth and maturation rates of 

flannelmouth sucker through increasing food supply, increased metabolic rates, and increased ability to 

avoid predation through improved swimming capacity (Ward and others, 2002). Proponents of all options 

support the TCD and therefore may all be expected to provide benefits to flannelmouth sucker adults. If 

warmer water temperatures also benefit predatory nonnative fishes, these benefits could be reduced or 

lost. 

Mainstem Spawning and Incubation: The knowledge assessment workshop participants found that 

warmer mainstem temperatures would have a positive effect on nearshore rearing by native fishes through 

increased metabolism leading to increased survival and growth. All options being considered therefore 

offer positive benefits to this resource area due to their inclusion of a TCD. If warmer water temperatures 

also benefit predatory nonnative fishes, these benefits could be reduced or lost. 

Rainbow Trout 
71

Numbers and Condition in Glen Canyon: Colorado River temperatures in Glen Canyon are generally 

near the bottom of the ideal range for rainbow trout. Therefore, if water temperatures were increased 

through the operation of a TCD, metabolic rates for adult rainbow trout would likely increase, leading to 

increased growth rates (Moyle and Cech, 2004). Because sunlight is not limiting in Glen Canyon (Yard 

and others, 2005), the warmer temperatures produced from TCD operation would be expected to increase 

annual primary productivity, thereby increasing food availability for rainbow trout. The TCD supported 

by all options would be expected to benefit this resource. 

Mainstem Spawning and Incubation: The knowledge assessment workshop participants thought that 

mainstem warming of the Colorado River would not have a measurable effect, positive or negative, on 

mainstem spawning by rainbow trout in Glen Canyon. While metabolic rates would increase, dissolved 

oxygen decreases with increasing temperature, a critical physical parameter for developing fish eggs. 

Therefore, all options are neutral with respect to this resource area. 

Invasive Fish Species (coldwater and warmwater species) 

Because the knowledge assessment workshop participants found that warmer mainstem temperatures 

would result in improved conditions and therefore increased survival of both coldwater and warmwater 

nonnative fishes, all options being considered offer benefits to this resource area due to their inclusion of 

a TCD. Because these species compete with and/or prey upon native fishes, increases in nonnative fishes 

increase risks to native fishes. 

Disease and Asian Tapeworm 

Because the knowledge assessment workshop participants found that warmer mainstem temperatures 

would increase the survival, growth, (Oskinis, 1994) and infection rates of Asian tapeworm and whirling 

disease (were it present), all options being considered may be expected to increase these parasites due to 

the warmer release temperatures resulting from the operation of a TCD. Because Asian tapeworm infects 

native fishes, it may be assumed that this would increase morbidity and mortality of native fishes. 

Part 3. Terrestrial Biological Resources 

Executive Summary 

The effect of warmer temperature on riparian habitat is largely unknown for vegetation in the CRE. The 

zone most likely to be affected by warmer temperatures under all flow options is the zone most proximal 

to the river (base flow to 25,000 cfs). Potential changes could include expansion of salt cedar or other 

nonnative species adapted to warmer temperatures following a late season BHBF; Option B may promote 

this possibility the most. All vegetation is expected to grow more extensively with warmer water and 

nutrient exchange rates between the land and water would likely increase, which may be a benefit to the 

ecosystem. Changes in the terrestrial flora would likely accompany a change in invertebrate density and 

diversity which may also benefit terrestrial and aquatic systems. 

Riparian Vegetation: Stage Elevation to 25,000 cfs (Marsh and obligate riparian 

vegetation) 
72

Options 

BASE Operations: The effect of warmer temperature on riparian habitat is largely unknown for 

vegetation below the 45,000-cfs stage elevation in the CRE (Melis and others, 2006b, p. 37). Studies in 

the Walker River Delta in Nevada (Young and others, 2004) indicate that tamarisk germinates throughout 

a range of seed bed temperatures (0–40°C). These temperatures may be constant or vary diurnally. 

Optimal germination was diurnal with 16 hours of 10°C and 8 hrs of 20°C. Germination was variable by 

seed lots. A similar response was noted for coyote willow (Salix exigua) a species native to the CRE 

(Young and Clement, 2003). Other factors contributing to the uncertainty include physiological responses 

associated with germination and clonal growth of wetland and riparian species (Farnsworth and 

Meyerson, 2003; Güsewell and others, 2003). 

Option A: Vegetative growth rates would likely increase under a warmer regime, resulting in denser 

marsh and riparian vegetation within the fluctuation zone. Besides temperature, nutrient concentrations in 

water also come into play and would likely differentially affect native and nonnative species found in the 

fluctuation and lower riparian zones (Biondini, 2001; Farnsworth and Meyerson, 2003; Güsewell and 

others, 2003). This effect would likely be more pronounced in the fluctuation zone that is also subject to 

daily disturbance. These changes could cascade up the trophic food web by changing invertebrate 

composition and types of plant species that provide nearshore cover for aquatic species. 

Option A Variation: Vegetation response to this option would be very similar to the response described 

for Option A. 

Option B: Nonnative species may grow more rapidly under warmer water conditions, particularly 

following a BHBF that may redistribute silts and clays and provide open areas for colonization. 

Option C: The responses by riparian vegetation to warmer water conditions under Option C would likely 

be similar to those observed for the BASE operations and Option A. Vegetative growth rates would likely 

increase under a warmer regime, resulting in denser marsh and riparian vegetation within the fluctuation 

zone. Besides temperature, nutrient concentrations in water also come into play and would likely 

differentially affect native and nonnative species found in the fluctuation and lower riparian zones 

(Biondini, 2001; Farnsworth and Meyerson, 2003; Güsewell and others, 2003). This effect would likely 

be more pronounced in the fluctuation zone that is also subject to daily disturbance. These changes could 

cascade up the trophic food web by changing invertebrate composition and types of plant species that 

provide nearshore cover for aquatic species. 

Wildlife Resource Linkages 

Southwestern willow flycatcher would likely benefit from the increased invertebrate densities that would 

accompany vegetation growth associated with warmer water temperatures. Kanab ambersnail may be 

little affected by the TCD because the majority of snails appear to occupy habitat above the 25,000-cfs 

elevation. 

Part 4. Assessment of Effects to Recreation and Cultural Resources 

Executive Summary 
73

An increase in water temperature through implementation of a TCD will likely benefit both angling and 

whitewater recreation for a variety of reasons (bigger trout, more enjoyable swimming opportunities, 

safer conditions for recreationists); although, the potential impacts of increased pathogen loads on both 

fish and humans remain highly uncertain and could potentially negate some of the beneficial effects of 

warming the water. There are also uncertainties regarding how warmer water may effect the trout 

population as warmwater species increase and potentially compete with the trout for a limited food 

supply.

Angling Opportunity, Quality, and Access 

In addition to improving the water temperature from the standpoint of wading anglers, increased water 

temperature is predicted to increase the size and abundance of rainbow trout in Glen Canyon up to about 

16° C. Therefore, implementation of a TCD is likely to result in benefits to the trout fishery, unless 

temperatures significantly exceed 16° C for extended periods of time or parasites and pathogens 

counteract the beneficial effects to primary productivity (food base) and trout growth from warming (see 

the food base section for specific references on the expected relationships between water temperature and 

aquatic productivity). Increased temperature will also increase metabolic demand and the consequent 

increase in feeding rate may improve “catchability.” Possible negative impacts include increased diseases, 

such as whirling disease, or increased competition from warmwater nonnatives in a food-limited 

environment.

Quality of Water and Human Health 

An increase in waterborne pathogens is likely to occur with warmer water temperatures. During the 2000 

low summer steady flow experiment, river guides and private boaters experienced a notable increase in 

incidents of waterborne viral infections among passengers and crew, adding further anecdotal support to 

the notion that warmer flows are not conducive to maintaining optimal human health conditions. 

Visitor Safety 

Hypothermia and heart attacks due to thermal shock are some of the greatest risks to boaters and anglers 

who come out of their boats in the CRE (Meyers and others, 1999, p. 37). Under normal dam release 

temperatures of 7–12°C, people can lose muscle control in a matter of minutes and may lose 

consciousness in less than 10 minutes. This reality forces potential rescuers to take additional risks in 

their attempts to get swimmers out of the water as quickly as possible. Although no specific studies have 

been done in the CRE to document the relationships between water temperature and safety incidents, the 

well-known and well-documented hypothermia risks associated with typical dam release temperatures 

(Meyers and others, 1999, p. 37) leaves little room for doubt that warmer water would significantly 

reduce safety risks associated with Colorado River recreation. 

Recreational Experience Quality 

Studies documenting the relationship between water temperature and recreational experience are lacking, 

but anecdotal information, plus some social science survey data, indicate that warmer water would likely 

improve the boating and angling experience because warmer water would allow visitors to enjoy being in 

the water and getting soaked in the rapids, and both anglers and whitewater boaters are less likely to die 

from hypothermia-related issues if they inadvertently fall out of their boats. Anecdotal information 

suggests that most visitors currently manage to enjoy their recreation experience in spite of the very cold 

water temperatures. The Stewart and others (2000, p. 161) study found that a small majority of 
74

commercial passengers (53%) did not believe that their trip would have been any more enjoyable with 

warmer water, but a slightly larger majority of private boaters and river commercial guides shared the 

opposite opinion (i.e., 57% of private boaters and 58% of commercial guides felt that warmer water 

would have improved their overall experience.) The trade-offs associated with different aspects of visitor 

experience affected by warmer water (i.e., improved “swimmability” versus possible increase in viral or 

bacterial infections) have never been studied and remain unknown.

There is certainty that warmer temperatures decrease water viscosity, allowing fine sediment to settle out 

faster, and thereby reducing the suspension of sediment in the water column and the amount of sediment 

available for downstream transport (Lane and others, 1949; Hubbell and Ali, 1961; ASCE, 1975). In 

theory, warmer water reduces the amount of sediment transported from sandbar deposits (S. Wright, 

personal comm., 2006), and therefore could have a slightly beneficial effect for recreation by increasing 

the longevity of sandy deposits used as camping beaches. 

Nonnative Fish Control 

Part 1. Aquatic and Fisheries Resources 

Executive Summary 

The only effect of nonnative control that the knowledge assessment participants thought predictable with 

certainty was the negative effect on populations of coldwater nonnatives in response to their removal. 

This is consistent with the data available in 2006 that indicate that over 90% of the rainbow trout 

population previously present in the reach of the Colorado River near the mouth of the Little Colorado 

River has been removed by the four year GCDAMP effort. The knowledge assessment participants 

concluded that mechanical removal of warmwater nonnatives would have negative impacts on that 

population. The adult humpback chub population has stabilized beginning in about 2000, and has 

remained so through 2005 (the most recent year for which data are available; Melis and others 2006a), 

suggesting that mechanical removal focused on coldwater species has not hurt the humpback chub 

population. Continued monitoring is needed to fully assess whether the mechanical removal effort 

benefits the native fish population. 

All of the options being considered include control of nonnative fish populations, as needed. All of the 

options, therefore, may be expected to have a neutral to positive effect on the native fishes from 

implementation of nonnative control actions, as needed, especially for early life stages. 

Aquatic Food Base: Glen Canyon and Grand Canyon 

Options 

All Options: Nonnative fish control might benefit native fishes by affecting the amount of food available 

for native fishes or by affecting native fishes’ ability to effectively feed. Competition between native and 

nonnative fishes for food or feeding arenas has not been demonstrated in the CRE. However, if 

competition for food is occurring between native and nonnative fishes, then nonnative fish removal has 

the potential to increase the amount of food available for native fishes. If native and nonnative fishes are 
75

competing for feeding arenas (e.g., areas of slower water such as eddy fences that are in close proximity 

to faster water), then removal of nonnative fishes might make it easier for native fishes to effectively feed. 
76

Fish 

Humpback Chub: Adults 

Option A: The increased flows and daily fluctuations described in this option would not, in the absence 

of a TCD, be expected to raise water temperatures, and higher flow variations may displace nonnative 

fishes (Li and Moyle 1999), so threats to native fish by nonnative warmwater species would likely be 

limited under this option. The knowledge assessment did not have sufficient information to judge whether 

or not mechanical removal of nonnatives was of benefit to adult humpback chub. Proponents of this 

option suggest, consistent with the knowledge assessment, that the increasing flows described would limit 

the rainbow trout population, which would reduce the need for active control of this species. 

Option B: This option may implement conditions that are favorable for warmwater nonnatives by 

reducing displacement by high flows. Efforts to control warmwater species are indicated by this 

information and are supported by the proponents of this option, but benefits to adult humpback chub are 

uncertain. 

Option C: The departures from BASE operations proposed in Option C suggest that rainbow trout 

population numbers might be slightly reduced and warmwater species might benefit slightly from the 

Option C flows. Efforts to control nonnative species are indicated by this information and are supported 

by the Option C proponents, but benefits to adult humpback chub are uncertain. 

Humpback Chub: Mainstem Spawning and Incubation 

Removal of nonnative fishes was generally thought by the knowledge assessment workshop participants 

to have positive effect on mainstem spawning and incubation of humpback chub; although, additional 

investigation is needed. All options support this action, as needed, and so all offer some positive impacts 

to this resource area. 

Humpback Chub: Young-of-Year and Juvenile Rearing 

The knowledge assessment concluded that young humpback chub rearing in nearshore habitats benefited 

from nonnative control efforts by reducing predation and competition; although, this conclusion needs 

additional investigation. All options, because they propose nonnative control as needed, would be 

expected to provide a benefit to this resource. 

Other Natives 

Adults: The knowledge assessment workshop did not have sufficient information to conclude whether or 

not nonnative control would benefit adult flannelmouth sucker. However, it is logical to think that 

reduced competition and/or predation could be beneficial to native species.

Mainstem Spawning and Incubation: Removal of nonnative fishes was generally thought by the 

knowledge assessment workshop participants to have positive effect on mainstem spawning and 

incubation of flannelmouth sucker; although, additional investigation is needed. All options support this 

action, as needed, and so all offer some positive impacts to this resource area.
77

Young-of-Year and Juvenile Rearing: The knowledge assessment concluded that young flannelmouth 

sucker rearing in nearshore habitats benefited from nonnative control efforts through reduction of 

competition and predation; although, this conclusion needs additional investigation. All options, because 

they propose nonnative control as needed, would be expected to provide a benefit to this resource.

Rainbow Trout 

Numbers and condition in Glen Canyon: Removal of rainbow trout in Marble Canyon has a negative 

impact on that species in that reach, but the impact of this removal on the Glen Canyon rainbow trout 

population has not been determined.

Invasive Fish Species (Coldwater and Warmwater) 

The knowledge assessment workshop participants concluded that removal of rainbow trout had had a 

negative effect on that species, consistent with the study objectives and design. They also concluded that 

they did not have enough information to conclude whether or not a similar effect would be observed on 

warmwater species. Because all options include nonnative control, they would all have similar effects on 

these resources. 

Part 2. Assessment of Effects to Recreation and Cultural Resources 

Executive Summary 

There are localized negative impacts to angling opportunity and quality from removal of trout from 

tributaries and selected reaches of the river, and trout removal has been identified by several Native 

American tribes as a negative impact to TCP values in the CRE. Impacts to recreation experience are 

undocumented and therefore unknown, but are likely to be minimal for whitewater recreationists and 

negative for trout anglers who fish the reaches below Less Ferry. 

Angling Opportunity, Quality, and, Access 

Mechanical removal of rainbow trout in Marble Canyon has been shown to significantly reduce the 

population of trout in this section of the river, and the extent of the reduction can be quantified (GCMRC, 

unpublished data). Thus, for the relatively few anglers who frequent Marble Canyon, the impact of trout 

removal is expected to be negative. However, mechanical removal of rainbow trout in lower Marble 

Canyon or near the mouth of the Little Colorado River is not believed to significantly affect the trout 

population in Glen Canyon where most angling is currently concentrated due to the hypothesized “site 

fidelity” of these fish; this hypothesis has not been formally tested though, so effects of trout removal on 

the Glen Canyon reach are considered to be uncertain. Removal of brown trout from tributary creeks in 

Grand Canyon would have a negative impact on angling opportunity and quality in those specific 

tributaries, as well as in the mainstem. The effect of reducing the abundance of warmwater nonnative 

fishes on the population of rainbow trout is currently unknown. Removal of rainbow trout in Glen Canyon 

could potentially benefit the sport fishery, when fish numbers and/or condition warrant a reduction in 

population size to increase condition of the remaining population. 
78

Recreational Experience Quality (including access to attraction sites) 

 

Aside from the hypothesized effects to angling opportunity and quality discussed above, the effects of 

mechanical trout removal (or mechanical removal of nonnative species in general) on visitor experience is 

a subject of continuing speculation, but one for which no actual data are currently available. During the 

2005 knowledge assessment workshop, several participants expressed the opinion that there were 

increased risks to visitors because of the use of electricity in the water near shorelines and camps, and 

there were concerns about potential negative impacts to the wilderness-like experience; however, other 

workshop participants argued that these risks and impacts were mitigated through public outreach and 

education, and therefore, recreational experience was not adversely effected by this activity. No data 

relevant are currently available to resolve these debates, and further evaluation of this issue is probably 

warranted. 

Traditional Cultural Properties 

The killing of trout and other life forms in the vicinity of the mouth of the Little Colorado River has been 

identified by Native American tribes (Hopi and Navajo) as an issue of concern and a potentially 

detrimental impact to traditional cultural property values associated with this area. The Grand Canyon. as 

a whole, has been identified as a TCP by most of the tribes involved with the Glen Canyon Dam Adaptive 

Management Program, so mechanical removal in other parts of the CRE could also potentially be viewed 

as having a negative impact by the tribes. Trout removal does not directly affect the physical integrity of 

archaeological sites, many of which are also considered to be TCPs by Native American tribes, but there 

is some (slight) potential of impacts to archaeological sites from onshore base camp activities associated 

with the trout removal project; however, on shore impacts can and largely have been mitigated through 

educational outreach efforts to the cooperators who engage in this work. 

Translocation of Humpback Chub 

Part 1. Aquatic and Fisheries Resources 

Executive Summary 

The translocation of humpback chub above Chute Falls in the Little Colorado River has, as of 2006, been 

shown to be successful in that the translocated fish have survived well and have spawned. This suggests 

that this species may be amenable to physical relocation, and that therefore the translocation may be 

expected to add numbers to the overall adult humpback chub population in Grand Canyon; although, 

long-term monitoring has not been conducted to confirm this assumption. The spawning success of the 

population above Chute Falls, and the small number of emigrants to this population from below Chute 

Falls, suggests that translocated populations in other tributaries might begin to reproduce and contribute 

to future generations. 

Translocation and any associated reproduction of humpback chub confound the assessment of impacts of 

various natural and man-made conditions on humpback chub because population increases or decreases 

cannot be ascribed to only one factor. The stabilization of the humpback chub population in Grand 

Canyon (Melis and others 2006a) suggests that this population is not in a critical situation at this time and 

so more dramatic management actions, such as translocation, may be premature if scientists and managers 
79

are to be given sufficient time to determine single or limited numbers of factors affecting the size of the 

humpback chub population. The knowledge assessment was inconclusive regarding the effects of 

translocation. 

The options offer a distinct contrast with regard to this action. Options A and A Variation call for 

continued translocation and Option B does not favor translocation. The proponents of Option C only 

favor translocation if it can be shown to not confound an overall experiment and assessment, which 

remains to be shown as of October 2006. 

Fish 

Humpback Chub: Adults 

Option A: Although it is impossible to evaluate and compare absolute numbers from this vantage point in 

time, the humpback chub moved to Colorado River tributaries other than the Little Colorado River and 

surviving there might compensate for humpback chub not produced or lost after hatching under this 

option due to other effects, such as displacement. 

Option A Variation: Although it is impossible to evaluate and compare absolute numbers from this 

vantage point in time, the humpback chub moved to Colorado River tributaries other than the Little 

Colorado River and surviving there might compensate for humpback chub not produced or lost after 

hatching under this option due to other effects, such as displacement. 

Option B: Any potential benefits to the humpback chub population that might be realized by additional 

translocations would not be demonstrated if this option is adopted. By not expending resources on 

translocation, there would presumably be more resources available for conservation and management 

actions in Grand Canyon aimed at improving the existing population and its habitat. 

Option C: This option would refrain from implementing this action until its potential impact on an 

experimental design and impact assessment are known with greater certainty; although, Option C 

proponents favor consideration of translocation, they do not advocate immediate implementation. 

Humpback Chub: Mainstem Spawning and Incubation 

Option A: Translocation of humpback chub above Chute Falls on the Little Colorado River may have 

already played some minor role in supporting the overall Grand Canyon population of this species 

through the production of small numbers of young in the translocated population. If translocations to 

other tributaries were similarly successful, or more so, more humpback chub might be expected in the 

mainstem. The presence of additional humpback chub in the mainstem would only be expected to lead to 

increased spawning and incubation if other habitat parameters were conducive to these activities. The 

increased flow fluctuations proposed in Option A are not expected to contribute to increases in mainstem 

spawning and incubation, whether from humpback chub naturally present or present because of humanmediated translocation. 

Option A Variation: Translocation of humpback chub above Chute Falls on the Little Colorado River 

may have already played some minor role in supporting the overall Grand Canyon population of this 

species through the production of small numbers of young in the translocated population. If translocations 

to other tributaries were similarly successful, or more so, more humpback chub might be expected in the 
80

mainstem. The presence of additional humpback chub in the mainstem would only be expected to lead to 

increased spawning and incubation if other habitat parameters were conducive to these activities. The 

increased flow fluctuations proposed in Option A are not expected to contribute to increases in mainstem 

spawning and incubation, whether from humpback chub naturally present or present because of humanmediated translocation. 

Option B: This option does not support translocation, so no effect of translocation can be evaluated. 

Option C: Because this option only supports translocation under specific conditions it may not be 

implemented, reducing any chance that translocation would affect mainstem spawning and incubation 

under implementation of this option. 

Other Native Fish: Adults 

Translocation of humpback chub above Chute Falls of the Little Colorado River and to other tributaries 

would not be expected to impact other native species, given the current population sizes. If translocation 

were to result in very dramatic increases of the number of humpback chub in the Colorado River, then 

there might be some issues of increased competition between native fish species, but that potential seems 

very remote from the vantage point of 2006. Because these species evolved together, it is unlikely that 

there would be competition that would result in the decline of one species to the detriment of another. 

Other Native Fish: Mainstem Spawning and Incubation 

 

The small numbers of all native fishes in the Colorado River in Grand Canyon in 2006 suggest that it is 

unlikely that any humpback chub translocation will affect mainstem spawning and incubation of natives 

other than humpback chub under any of the options being considered. Physical factors are more likely 

than translocation of one species to have effects on mainstem spawning and incubation. Humpback chub 

and other native fish species evolved together in the Colorado River and so would be assumed to have 

developed strategies for coexistence. 

Invasive Fish Species (Coldwater and Warmwater) 

All options being considered support control of nonnative fishes, as needed, to benefit native fishes. If 

humpback chub were physically relocated or propagated and released, actions supported primarily under 

Options A and A Variation, they could provide some resource competition to nonnative fishes. The 

translocated humpback chub population would have to increase to a relatively high number before this 

effect could be measurable. In the near term, impacts to nonnative fishes from translocated humpback 

chub would likely be very minimal. 

Part 2. Assessment of Effects to Recreation and Cultural Resources 

Executive Summary 

Depending on where translocations occur, there could be some negative impacts to recreational 

experience and Native American TCPs from translocation of the endangered humpback chub. For 

example, translocation into a tributary canyon such as Shinumo Creek could potentially result in 

decreased access for recreational use (if human use is subsequently found to have negative impacts to fish 
81

habitat or water quality or otherwise conflicts with sustaining this species in its new habitat). More 

intrusions of fish biologists and resource managers and their associated mechanized gear in an area that is 

being managed for a wilderness-type experience could also have potentially negative impacts for 

recreation experience. Furthermore, translocations in the Little Colorado River gorge or in other 

tributaries of Grand Canyon could potentially result in impacts to as yet unidentified Native American 

traditional cultural properties because of increased incidental use of these areas, either as a direct result of 

the research and monitoring activities associated with the translocation effort or as a result of increased 

publicity about the area that would inevitably accompany a successful translocation program. 

 
82

Humpback Chub Refuge, Propagation, and Genetics 

Management Planning 

Part 1. Aquatic and Fisheries Resources 

Executive Summary 

The GCDAMP Humpback Chub Ad-hoc Group (HBCAHG), has identified catastrophic loss as an 

important threat to the Grand Canyon humpback chub population. This threat is also identified in the 

2002 Recovery Goals promulgated by the U.S. Fish and Wildlife Service (In 2006, a court ordered this 

version of recovery goals set aside and also ordered that the goals be revised in 2007.). This threat has 

been the primary motivation for the development of plans to establish one or more refuge populations of 

humpback chub outside of Grand Canyon. A small stock of humpback chub has been established at 

Willow Beach National Fish Hatchery, Arizona, on the Colorado River below Hoover Dam. 

The GCDAMP Humpback Chub Ad-hoc Group, with support from the TWG and AMWG, has contracted 

for the preparation of a genetics management plan for humpback chub that includes planning for refuge 

populations and approaches to propagation and augmentation; although, the HBCAHC does not propose 

augmentation of the wild population at this time. Options A, A Variation, and C support the planning for 

a refuge, propagation, and augmentation, but they do not call for immediate augmentation. Option B 

proponents do not favor such actions based on the premise that such efforts divert resources from 

protection and improvement of the wild population and their habitat. 

The knowledge assessment was inconclusive regarding the effects of humpback chub augmentation. 

Humpback Chub 

BASE Operations: The GCDAMP has contracted for the preparation of a genetics management plan for 

humpback chub. Some segments of the plan should be ready for review during 2007, with the final plan 

scheduled for completion and submittal in December 2007. 

Option A: A humpback chub refuge helps address the concern over the potential for catastrophic loss of 

large numbers of humpback chub by maintaining a population outside of Grand Canyon that could be 

used as brood stock, if required. This option supports the establishment of a refuge as insurance against 

large-scale loss. 

The planned humpback chub genetics management plan meets the prescription in this option for planning 

to be conducted toward augmentation, as this plan is an important precursor to augmentation of the wild 

population. If there were losses of humpback chub due to any of the flow elements of this option, 

augmentation with wild fish could help maintain the size of the Grand Canyon humpback chub 

population. 

Option A Variation: Same as Option A 

Option B: The proponents of Option B are concerned that energy and resources expended outside of 

Grand Canyon on humpback chub protection may be unwise uses of resources. For this reason, Option B 
83

proponents offer only tentative support for the concept of establishing a humpback chub refuge outside of 

Grand Canyon. 

The proponents of this option are concerned that any moves towards propagation and/or augmentation of 

the wild humpback chub population divert energies and resources from protection and improvement of 

the natural habitat and wild population. For this reason Option B proponents do not propose propagation, 

augmentation, or planning for augmentation. 

Option C: Same as Option A 

Summary Table 

Table 4.2. Summary comparison of nonflow-related resource effects estimated for four options under 

consideration by the Glen Canyon Dam Adaptive Management Program compared to BASE operations 

(modified low fluctuating flow). The table provides, where possible, the potential effects of each option on 

individual resources are ranked 1 (most) through 4 (least) where possible. 

 Option A Option A Variation Option B Option C 

TEMPERATURE 

CONTROL 

DEVICE 

 

Water temperature 

Water Temperatures 

(mainstem) 

(based on numerical 

modeling) 

Increase over BASE 

by about 4 – 5 oC in 

summer/fall, on 

average 

Increase over BASE 

by about 4 – 5 oC in 

summer/fall, on 

average 

Increase over BASE 

by about 4 – 5 oC in 

summer/fall, on 

average 

Increase over BASE by 

about 4 – 5 oC in 

summer/fall, on 

average 

Water Temperatures 

(nearshore) 

(based on existing data 

and state-ofknowledge) 

Increase over BASE 

similar to mainstem 

Increase over BASE 

similar to mainstem 

Increase over BASE 

similar to mainstem 

plus enhanced 

warming nearshore 

most of the year 

Increase over BASE 

similar to mainstem 

plus enhanced warming 

nearshore in Sep – Oct 

Fine-sediment 

storage 

 

Fine-sediment storage Potential increase; 

significant 

uncertainty in 

magnitude 

Potential increase; 

significant 

uncertainty in 

magnitude 

Potential increase; 

significant 

uncertainty in 

magnitude 

Potential increase; 

significant uncertainty 

in magnitude 

Aquatic food base 

Aquatic Food Base 

(Glen Canyon) 

Annual productivity 

likely increases 

Annual productivity 

likely increases 

Annual productivity 

likely increases 

Annual productivity 

likely increases 

Aquatic Food Base 

(Grand Canyon) 

Annual productivity 

likely increases 

Annual productivity 

likely increases 

Annual productivity 

likely increases 

Annual productivity 

likely increases 

Adult fish 

populations 

 

Adult Population 

(HBC) 

May increase May increase May increase May increase 

Other Natives May increase May increase May increase May increase 

Adult Population (RBT 

#’s in Glen Canyon) 

Likely decreases Likely decreases Likely increases Likely increases 
84

Adult Population (RBT 

size in Glen Canyon) 

Likely increases Likely increases Likely decreases Likely decreases 

Mainstem spawning 

and incubation 

 

Mainstem Spawning & 

Incubation (HBC) 

Increased spawning 

success likely 

Increased spawning 

success likely 

Increased spawning 

success likely 

Increased spawning 

success likely 

Other natives Increased spawning 

success likely 

Increased spawning 

success likely 

Increased spawning 

success likely 

Increased spawning 

success likely 

Mainstem Spawning & 

Incubation (RBT – 

Glen Canyon) 

Increased spawning 

success likely 

Increased spawning 

success likely 

Increased spawning 

success likely 

Increased spawning 

success likely 

YOY/Juvenile 

nearshore rearing 

 

YOY/Juvenile 

Nearshore Rearing 

(HBC) 

Increased rearing 

success likely 

Increased rearing 

success likely 

Increased rearing 

success likely (threats 

from predation could 

increase) 

Increased rearing 

success likely (threats 

from predation could 

increase) 

YOY/Juvenile 

Nearshore Rearing 

(Other natives) 

Increased rearing 

success likely 

Increased rearing 

success likely 

Increased rearing 

success likely (threats 

from predation could 

increase) 

Increased rearing 

success likely (threats 

from predation could 

increase) 

YOY/Juvenile 

Nearshore Rearing 

(RBT – Glen Canyon) 

Increased potential 

for rearing success 

Increased potential 

for rearing success 

Increased potential 

for rearing success 

Increased potential for 

rearing success 

Invasive Fish Species 

(coldwater species 

downstream) 

Increased potential 

for rearing success 

Increased potential 

for rearing success 

Increased potential 

for rearing success 

Increased potential for 

rearing success 

Invasive Fish Species 

(warmwater species) 

Increased potential 

for rearing success 

Increased potential 

for rearing success 

Increased potential 

for rearing success 

Increased potential for 

rearing success 

Disease (Asian 

Tapeworm) 

Infestation may 

increase 

Infestation may 

increase 

Infestation may 

increase 

Infestation may 

increase 

Disease (Whirling 

Disease) 

No change No change No change No change 

Terrestrial riparian 

resources 

 

Marsh and obligate 

riparian vegetation 

(below 25,000 cfs) 

May increase, but 

unknown 

May increase, but 

unknown 

May increase, but 

unknown 

May increase, but 

unknown 

Lower Riparian 

Habitat (25,000 to 

45,000 cfs) 

No effect expected, 

but unknown 

No effect expected, 

but unknown 

No effect expected, 

but unknown 

No effect expected, but 

unknown 

Upper Riparian Habitat 

(45,000 to 60,000 cfs) 

No effect expected No effect expected No effect expected No effect expected 

Recreational 

Resources 

 

Angling opportunity, 

quality, and access 

Likely improves Likely improves Likely improves Likely improves 

Quality of water and 

human health 

Possibly deteriorates Possibly deteriorates Likely deteriorates Possibly deteriorates 

Visitor Safety Improves Improves Improves Improves 

Recreational 

Experience Quality 

Likely improves Likely improves Likely improves Likely improves 

DOWNSTREAM 

NONNATIVE FISH 

CONTROL

 

Aquatic food base 

Aquatic Food Base No change No change No change No change 
85

(Glen Canyon) 

Aquatic Food Base 

(Grand Canyon) 

May increase May increase May increase May increase 

Adult Fish 

Populations 

 

Adult Population 

(HBC) 

Unknown Unknown Unknown Unknown 

Other Natives Unknown Unknown Unknown Unknown 

Adult Population (RBT 

#’s in Glen canyon) 

Unknown Unknown Unknown Unknown 

Adult Population (RBT 

size in Glen Canyon) 

Unknown Unknown Unknown Unknown 

Mainstem spawning 

and incubation 

 

Mainstem Spawning & 

Incubation (HBC) 

Likely increases Likely increases Likely increases Likely increases 

Other natives Likely increases Likely increases Likely increases Likely increases 

Mainstem Spawning & 

Incubation (RBT – 

Glen Canyon) 

Unknown Unknown Unknown Unknown 

YOY/Juvenile 

nearshore rearing 

 

YOY/Juvenile 

Nearshore Rearing 

(HBC) 

Likely increases Likely increases Likely increases Likely increases 

YOY/Juvenile 

Nearshore Rearing 

(Other natives) 

Likely increases Likely increases Likely increases Likely increases 

YOY/Juvenile 

Nearshore Rearing 

(RBT - Glen) 

Unknown Unknown Unknown Unknown 

Invasive Fish Species 

(cold water species 

downstream) 

Decreases Decreases Decreases Decreases 

Invasive Fish Species 

(warm species) 

Decreases Decreases Decreases Decreases 

Recreational 

Resources 

 

Angling opportunity, 

quality, and access 

Decreases Decreases Decreases Decreases 

Recreational 

Experience Quality 

Decreases angling 

opportunity; possible 

impact to wilderness 

experience values 

Decreases angling 

opportunity; possible 

impact to wilderness 

experience values 

Decreases angling; 

possible impact to 

wilderness experience 

values opportunity 

Decreases angling; 

possible impact to 

wilderness experience 

values opportunity 

Traditional cultural 

properties 

Potentially 

detrimental 

Potentially 

detrimental 

Potentially 

detrimental 

Potentially detrimental 

TRANSLOCATION 

OF HUMPBACK 

CHUB

 

Adult HBC Likely increase Likely increase Same as BASE Likely increase, if 

implemented 
86

Adult; Other natives Unknown Unknown Same as BASE Unknown 

Mainstem spawning 

and incubation - HBC 

Unknown Unknown Same as BASE May improve if 

implemented 

Invasive fish species – 

coldwater 

Decrease Decrease Same as BASE May decrease if 

implemented 

Angling opportunity, 

quality, and access 

Likely no impact Likely no impact Same as BASE Likely no impact 

Traditional cultural 

properties 

Potentially 

detrimental 

Potentially 

detrimental 

Potentially 

detrimental 

Potentially detrimental 

HUMPBACK CHUB 

REFUGE,

PROPAGATION, AND 

GENETICS 

MANAGEMENT 

PLANNING

 

HBC Increased security Increased security Same as BASE Increased security 
87

Chapter 5: Evaluation of Proposed Experimental 

Designs 

Introduction 

A fundamental tenet of adaptive management is “learning by doing,” or using science to determine the 

cause-and-effect relationship among natural events, anthropogenic change, and/or experimental 

treatments in relation to desired resource conditions. This tenet is reflected in the specific approach to 

adaptive management that is articulated in the Glen Canyon Dam Adaptive Management Program 

(GCDAMP) Strategic Plan, which is as follows: 

1. Models are developed to reveal the potential effects of policies, activities, or practices that are being 

considered for implementation; 

2. Questions are formulated as testable hypotheses regarding the expected responses or linkages of the 

Colorado River ecosystem to dam operations and other management actions; 

3. Experiments are conducted to test hypotheses and answer questions; 

4. Management activities reveal, through monitoring and evaluation of results, the accuracy or 

completeness of the earlier predictions; and 

5. New knowledge and information produced through experimentation are incorporated into 

management discussions and recommendations to the Secretary of the Interior. 

As defined in the GCDAMP strategic science plan and monitoring and research plan, long-term 

experimental activities are a suite of flow and nonflow treatments and/or management actions designed to 

improve the condition of target resources (e.g., humpback chub, cultural sites, sandbars, etc.) and,

through monitoring and research, improve the understanding the relationship between 

treatments/management actions and target resources. Designing experiments that yield statistically valid 

results is a major challenge in the Colorado River ecosystem (CRE) where variability is high and 

unpredictable owing to a variety of factors such as changing basin hydrology and water quality, climate 

change, and introductions of nonnative species. However, a properly designed experimental program 

implemented over a long time frame is more likely to yield more definitive information on the 

relationship between specific actions and the condition of target resources. 

Chapters 3 and 4 address the likely effect of the experimental options on the condition of target resources 

in the CRE. The purpose of this section is to evaluate the general strengths and weaknesses of each option 

with respect to their likelihood to yield information that will improve the understanding the relationship 

between proposed treatments/management actions and target resources. The strengths and weaknesses of 

the proposed experimental design or approach associated for each option are evaluated relative to the 

amount of learning that is likely to occur under each of the proposed options. 

 

 
88

Option A and Option A Variation Experimental Design 

The approach employed by Options A and A Variation is referred to as a reverse titration, meaning that a 

suite of management actions or experiments are implemented as soon as feasible to achieve resource 

benefits. Table 5.1 illustrates the timing for implementation of various actions over time. Resource 

response would be evaluated through ongoing monitoring programs. Then, following an assessment, 

treatments will be systematically removed one at a time under continued monitoring until benefits are 

observed to diminish (learning by undoing). Under Options A and A Variation, the priority goal is to 

achieve positive resource responses for a number of resources, but especially hydropower, rainbow trout, 

and humpback chub; understanding the relationship between actions and resource responses is a 

secondary priority. The option includes several so called mini experiments to better understand the fate of 

young humpback chub in the mainstem, use of BHBFs to conserve sand resources, and use of fluctuating 

flows to suppress trout reproduction. The purpose of the mini experiments is to determine the 

effectiveness of these actions, before being implemented as management actions. 

Strengths 

 

1. Tests implementation of a suite of actions on overall resource responses, including: 

a. Wider flow fluctuations with associated hydropower generation benefits 

b. Steeper ramping rates with associated hydropower generation benefits 

c. Minimum flows to protect food base 

d. Implementation of a temperature control device (TCD) to elevate mainstem water 

temperatures and promote humpback chub spawning and recruitment 

e. Nonnative fish management to reduce predation on and competition with native fishes 

f. Translocation of humpback chub to other tributaries in the Grand Canyon to provide 

insurance against population loss 

Weaknesses 

1. The approach presumes, contrary to conclusions contained in the knowledge assessment report, 

that the actions needed to achieve GCDAMP goals are known 

2. The approach of simultaneously implementing multiple management actions or “mini 

experiments” will greatly confound the ability to assess the effectiveness of specific management 

or experimental actions for achieving a desired resource response 

3. Implementing a new flow regime and other actions at this time will confound the assessment of 

the effects of elevated water temperatures and reduced trout populations on native and nonnative 

fishes under BASE operations. 

4. The option provides for no testing of steady flows to protect/restore downstream resources 

5. There is no basis in the literature for the reverse titration concept. GCMRC is unaware of how the 

effects of removing an action could be evaluated statistically. 

 

Option B Experimental Design 

The Option B experimental approach is referred to as a factorial research design where several treatments 

would be systematically implemented over a 7-year period and then replicated under different hydrologic 

conditions for an additional 7 years. The factorial approach is intended to provide the greatest possible 

degree of statistical rigor under large-scale field experimental conditions while limiting confounding 
89

effects. Option B is aimed primarily at testing the effects of steady flows and increased water 

temperatures in combination with several other treatments (BHBF, nonnative fish control) on target 

resources. Table 2.1 illustrates Option B’s proposed plan for implementing steady/fluctuating flows and 

BHBFs over time. Specification of how nonnative fish control and implementation/operation of a TCD 

will be factored into the design is not provided.

Strengths 

1. Incrementally tests the effects of progressively longer periods of stable flows (habitat stability) 

and increased water temperatures in combination with other treatments (nonnative fish 

management, BHBF, etc) on target resources (humpback chub, camping beaches, archeological 

sites, food base, etc). Option B includes implementation of a TCD. 

2. The proposed design provides for testing under two hydrologic scenarios (i.e., replication of the 

experiment over period of 14 years). 

3. Provides a robust test of the effects of steady flows (habitat stability) on target resources 

(humpback chub, camping beaches, food base, etc) by implementing progressively longer periods 

of stable flows 

Weaknesses 

1. Natural factors may confound the results of the experiment 

2. Implementing a new flow regime at this time will confound the ongoing assessment of the effects 

of elevated water temperatures and mechanically reduced trout populations on native and non 

native fishes. 

3. The option does not include testing of the effects of wider fluctuating flows on hydropower 

resources and downstream resources 

4. Length (2 years) and timing of steady flow increments may not be sufficient to evaluate the 

effectiveness on target resources, particularly if hydrologic conditions vary significantly between 

years. 

5. Specification of how non native fish control and implementation/operation of a TCD will be 

factored into the experimental design is not provided. 

Option C Experimental Design 

Option C proposes implementation of various treatments over three 5-year phases. The experimental 

approach is referred to as a forward titration whereby new treatments would be added incrementally to 

improve knowledge of the relationships among treatments and the resources affected by those treatments. 

For example, steady flows in September and October would be implemented in segment 1, a TCD in 

segment 2, and an August steady flow trigger to benefit young humpback chub in segment 3, if needed. 

The services of a biostatistician would be employed to identify more specifically how this design would 

actually be implemented. None of the treatments proposed under option C are consider “management 

actions” in recognition of the large degree of uncertainty associated with the effects of most actions as 

identified in the 2005 knowledge assessment. Option C specifically incorporates assessments, and 

adaptation at 5 year intervals, of relevant findings of a new The State of the Colorado River Ecosystem in 

Grand Canyon (SCORE) report and knowledge assessment. Option C does not support mini experiments 

until they are analyzed for their confounding effects on the main experiment. 
90

 
91

Strengths 

1. Tests implementation of a series of treatments to improve knowledge of the relationships among 

treatments and the resources affected by those actions, including: 

a. September/October steady flows to provide habitat stability and benefit humpback chub 

b. Possible August steady flow trigger to benefit HBC recruitment 

c. Wider fluctuations December to February to benefit hydropower 

d. Relaxed ramping rates in 9 months to benefit hydropower 

e. BHBFs to conserve sand resources. 

f. Implementation of a TCD to elevate mainstem water temperatures and promote HBC 

spawning and recruitment 

g. Nonnative fish management to minimize competition/predation with native fish 

2. Includes a formal review at 5 year interval based on updated SCORE report and knowledge 

assessment 

3. Limits implementation of treatments and mini experiments that may confound the results of the 

experiment (e.g., translocation) 

Weaknesses 

1. Natural factors may confound the results of the experiments 

2. Implementing a new flow regime at this time will confound the ongoing assessment of the effects 

of elevated water temperatures and reduced trout populations on native and non native fishes. 

3. Specific details on implementation of various treatments using the forward titration design are not 

provided. The scientific/statistical basis for forward titration concept is unclear. 
92

Table 5.1 Experimental program elements under Options A and A Variation from 2007 to 2016, with prior 

treatments shown for 201 through 20061

.

Water 

Year 

Dominant 

Dam 

Operation

Mechanical 

Removal

Temperature 

Control 

Device 

(TCD) 

Beach/Habitat 

Building Flow 

Humpback 

Chub 

Comprehensive 

Plan Research 

Humpback 

Chub 

Comprehensive 

Plan Habitat 

2001 MLFF only No removal No TCD No BHBF No activities No activities 

2002 Same as 

previous 

No removal No TCD No BHBF No activities No activities 

2003 MLFF with 

experimental 

fluctuating 

flows 

Trout 

removal 

No TCD No BHBF No activities No activities 

2004 Same as 

previous 

Same as 

previous 

No TCD No BHBF No activities No activities 

2005 MLFF with 

experimental 

fluctuating 

flows and 

fall testing 

Same as 

previous 

No TCD Fall BHBF No activities No activities 

2006 Modified 

MLFF [see 

text for 

description]2 

Trout and 

possibly 

warmwater 

species 

removal3 

Complete 

Draft EIS/BO 

Fall BHBF 

dependent on 

sediment input 

from Paria and 

Little Colorado 

Rivers 

Research and 

development of 

augmentation 

approach 

Expansion of 

humpback chub 

habitat (e.g., 

translocation to 

Colorado River 

tributaries) 

2007 Same as 

previous 

Same as 

previous 

Complete 

FEIS/BO 

Same as 

previous 

Same as 

previous 

Same as 

previous 

2008 Same as 

previous 

Same as 

previous 

Initiate 

construction 

Same as 

previous 

Same as 

previous 

Same as 

previous 

2009 Same as 

previous 

Same as 

previous 

Continue 

construction 

Same as 

previous 

Continue 

research or 

begin 

implementation 

if appropriate 

Same as 

previous 

2010 Same as 

previous 

Same as 

previous 

TCD 

operations 

Same as 

previous 

Same as 

previous 

Same as 

previous 

2011-

2016 

Same as 

previous 

Same as 

previous 

Same as 

previous 

Same as 

previous 

Same as 

previous 

Same as 

previous 

1

 Orange indicates element not implemented, green indicates element is implemented during a particular year. MLFF = modified low 

fluctuating flow alternative, BHBF = beach/habitat building flow. 2

 Modifications relative to ROD flows include lower minimum flows during weekdays, but relatively higher minimum flows on Sundays with 

flows never dropping as low as ROD flows on Sundays; faster downramp rates; and experimentation with summer stranding flows and fall 

flows. 3

 Adaptively managed to be shifted to control of warmwater nonnative species as necessary. 
93

Chapter 6: Scientific “Take Home” Points for 

Selecting an Experimental Option 

Given the information presented in the first five chapters of this report, it is clear that the selection of an 

experimental option and an experimental design is not simple. Decision makers must make their choice in 

the face of scientific uncertainty, and the need to balance scientific learning against potential resource 

benefit, while also considering cost and legal and policy concerns. Additionally, a great deal rests on this 

decision: How will Glen Canyon Dam be operated for the next 5 to 20 years? Given the scientific 

expertise of the Grand Canyon Monitoring and Research (GCMRC), and the fact that it has not advanced 

one of its own experimental option alternatives, GCMRC has the ability and responsibility to provide 

decision makers with some important insights and recommendations relevant to the selection of an 

experimental option. 

The complexity, and associated uncertainty, confronted when attempting to evaluate the net outcome of 

any one of the proposed experimental option makes it difficult for scientists to recommend one of the four 

options over the others. Additional confounding influences, such as climate change, only magnify the 

uncertainty. The need for experimentation comes when predictions cannot be made within bounds of 

acceptable risk and uncertainty, yet knowledge is still required to support decisions. As the Colorado 

River ecosystem continues to integrate all of the forces acting on it, one important goal of the science 

providers is to fully integrate efforts to study experimental treatments that managers have at their 

disposal, such as artificial floods or a temperature control device. One element of the science program that 

can foster such integration during and between treatments is a well integrated monitoring program that is 

linked with ongoing conceptual modeling and research. The foundations for both of these have been 

established within the adaptive management program over the last decade. 

The primary “take home” points that GCMRC developed in the course of preparing this document are 

related to sound ecosystem science practices. GCMRC’s recommendations are also informed by its 

extensive experience with the research that has been undertaken over the past decade for the Colorado 

River ecosystem. Ultimately, selecting an experimental approach is tied to one or more value baseddecisions; however, GCMRC provides the following recommendations with the intention of providing a 

few scientific insights. 

1. Complete the Current Experiment 

GCMRC recommends that managers continue implementing the modified low fluctuating flow 

(MLFF) regime for at least another 2–4 years. Such a strategy will provide scientists with the time 

and data required to fully evaluate the biological responses tied to experimental treatments 

(mechanical removal of nonnatives) and natural variability (water temperature) imposed on the 

river ecosystem during 2003 through 2006. 

Following years of heated public debate concerning the operation of Glen Canyon Dam, the 1996 Record 

of Decision selected the MLFF regime as a means of permitting “recovery and long-term sustainability of 

downstream resources while limiting hydropower capacity and flexibility only to the extent necessary to a 

achieve recovery and long-term sustainability.” Based on data that has been gathered and analyzed by 

GCMRC to date it is unclear whether MLFF has achieved this goal. The State of the Colorado River 

Ecosystem in Grand Canyon (SCORE; Gloss and others, 2005) report provided a 10-year progress report 
94

that suggested that several of the predictions contained in the final environmental impact statement (final 

EIS) had not yet been realized. However, the report also identified several issues that remained 

unresolved. One issue was whether sediment conservation goals could be realized using beach/habitatbuilding flows (BHBF) under tributary enriched sand supply conditions and continued MLFF operations. 

This issue will only be resolved through additional BHBF testing under MLFF operating regime. 

The evaluation of MLFF as it relates to humpback chub conservation is still a work in progress. For 

example, data published since the SCORE report was finalized indicate that the humpback chub 

population has stabilized over the past 4 years at about 5,500 adult fish. These findings are in sharp 

contrast to the SCORE report finding and suggest that it may be possible to support a self-sustaining 

population of humpback chub in the Grand Canyon under a MLFF regime. A major experiment was 

completed in 2006 in which over 90% of the trout population in the vicinity of the Little Colorado River 

was removed mechanically. In addition, beginning in 2002, water temperatures in the Colorado River 

have undergone significant warming owing to drought conditions which results in warmer releases from 

Glen Canyon Dam. Within the next 2–4 years, the effects of these actions on humpback chub recruitment 

will become evident based on the results of ongoing monitoring programs. Changing to an alternative 

flow regime will provide a potentially confounding influence on the scientific interpretation of the effects 

of mechanical removal and natural warming under the MLFF regime. 

2. Evaluate Experiments Relative to Managers’ Future Desired 

Conditions 

Members of the Adaptive Management Work Group recently asked: “What is the Best Flow 

Regime?” Presumably, the best operating regime for Glen Canyon Dam would be one that best 

meets all of the management objectives for both upstream and downstream resources, but this 

question cannot be answered by scientists unless managers provide clearly defined resource 

response conditions that are both measurable and attainable. 

Managers are responsible for deciding objectives for desired future resource conditions. Scientists can 

provide managers with a range of viable alternatives for trying to achieve the desired downstream 

conditions, but the performance measures must be clearly identified and associated with measurable 

responses. Most important of all, the objectives must be achievable within this highly altered ecosystem. 

Adaptive Management identifies all management policies as experiments owing to uncertainty in 

ecosystem response. To be meaningful to resource managers, a dam operating regime worthy of the effort 

expended for scientific evaluation must have potential for benefiting downstream resources while also 

maintaining other pre-existing resources or values. To address GCDAMP managers’ needs it seems most 

responsive that evaluations focus on potential resource benefits that are documented to occur under a 

fluctuating flow regime (presumably, the MLFF since it was selected as the preferred alternative). Future 

evaluations should therefore be made in conjunction with a flow regime that can be implemented long 

term under the natural range of hydrologic flow conditions that occur in the upper Colorado River Basin 

and within the physical and legal dam operating criteria that constrain managers. If desired future 

conditions are defined, but cannot be achieved under MLFF or alternative fluctuating flows, then either 

new flow constraints need to be considered (e.g., stable flow testing) or nonflow alternatives for 

achieving downstream resource objectives will require consideration, such as sediment augmentation 

strategies for sustainable sandbar restoration. Unfortunately, a full evaluation of the MLFF regime is not 

yet completed, particularly with respect to biological responses.
95

3. Implement and Scientifically Test a Temperature Control Device 

Whatever experimental option is selected, the GCMRC maintains that it should include a science 

strategy for resolving the issue of temperature as a limiting factor in humpback chub life history. 

The rationale for such testing is tied to a need to better understand early humpback chub life 

history in the main channel, as well as potential influences on recreational safety, primary and 

secondary productivity in the food web, etc. 

All of the four experimental options include construction and testing of a temperature control device 

(TCD) with two or more units at Glen Canyon Dam. The GCMRC cannot predict the ultimate ecosystem 

response to implementation of a TCD at Glen Canyon Dam, but if such a device were available for 

testing, then it could illuminate questions about the role of cold water in limiting the early life survival of 

native fishes. The Science Advisors echoed the need for such testing in 2003, as did the participants in the 

2005 knowledge assessment workshop. Simulation results for a two-unit TCD presented in chapter 4 

indicate that such a device will likely result in significantly warmer temperatures in the main channel 

below Glen Canyon Dam, especially during periods of minimal annual releases. The TCD simulation 

provides a sharp contrast compared to flow-only strategies. 

Recommendations forwarded by the Science Advisors in their 2003 report should be considered carefully 

as a TCD science plan is developed and implemented. This would include proceeding cautiously with 

tests and with anticipation that warmer water may result in undesired benefits to warmwater adapted 

nonnative fishes, parasites, and diseases. The GCMRC recommends that testing should be conducted 

under a flexible design which allows the device to be turned on and off on basis of findings and results 

related to fishery responses. Research and development of a program aimed at warmwater, nonnative 

fishes control is strongly advised by scientists. Both in terms of cost and ecosystem risk, scientists have 

identified this experimental element as one that requires perhaps the greatest level of planning, model 

support, and statistical rigor. 

4. Continue Testing of Sand-Enriched BHBFs 

Resolving whether or not tributary sand-enriched beach/habitat-building flows achieve sediment 

conservation should be a high priority. Testing should be continued under recommendations by 

sediment scientists as opportunities of tributary sand enrichment occur. 

Because managers have identified a priority need to know more about the loss of sediment in the 

Colorado River ecosystem and implications associated with ongoing erosion of sand habitats, the 

GCMRC recommends that testing of BHBFs under tributary-enriched sand supplies should proceed as 

opportunities occur. This recommendation was also made during summer 2006 by the protocol evaluation 

panel on sediment resources (SEDS-PEPIII; Wohl and others, 2006, written communication). In addition, 

the high costs identified in a recent draft report on the feasibility of sediment augmentation from upstream 

sources to the Colorado River ecosystem (Randle and others, in review), suggest that all feasible flow 

strategies for sandbar restoration and maintenance using downstream tributary sand supplies need to be 

evaluated before importing additional sediment is considered. 

5. Consider the Role of Hydrologic Variability and Dam Operating Constraints 
96

Variation in natural hydrology of the upper Colorado River Basin and its further expression 

through physically constrained dam operations may “mask” the influence of flows associated with 

all of the proposed experimental options being currently considered. 

While the differences between operations may be clear during years with minimal release volumes, these 

differences may be greatly reduced when annual release volumes increase because of wetter basin 

hydrology. The response of some or all downstream resources may actually be affected more by variation 

in basin hydrology and dam operating constraints than by the releases under any specific dam operating 

regime over decade-long timescales. One example of the possible influence of natural variability is 

presently occurring with respect to elevated water temperatures released from the dam. The influence of 

the drought that has decreased storage in Lake Powell since 2000 may be more of a significant treatment 

effect than MLFF or nonnative removal effects during the 2003–6 experiment. 

 

6. Attempt to Limit Confounding Variables 

To the degree that it is possible, GCMRC recommends that treatments (flow and nonflow) be 

isolated from one another to promote learning about causative responses to dam operations and 

other treatments. The GCMRC recommends taking a disciplined and structured approach to 

implementing new treatments.

Learning is an inherent part of the adaptive management strategy; one that is considered to have value to 

resource managers, especially if lessons about resource responses are transferable to other ecosystem 

settings. The challenge for learning is already great enough when scientist attempt to evaluate treatment 

responses under “field condition” experiments. Adding to the complexity through implementation of a 

“kitchen sink” approach, which has been referred to as “the fool’s gamble” by Carl Walters, can lead to 

unexplained responses that may also be opposite to the desired resource benefit direction. Such dramatic 

experimentation is especially risky when the objects of the experiment are finite natural resources such as 

sediment or fish. Experiments that are designed with the goal of obtaining statistically rigorous results 

may require additional time and cost, but such results may also provide longer-lasting benefits to natural 

and cultural resources and those who manage those resources. 

7. Approach Stable Flow Tests Logically 

General evidence suggests that a more stable flow regime may benefit a variety of GCDAMP 

resources (i.e., humpback chub, rainbow trout, sand bars, food base, etc.); however, further testing 

is recommended to determine if such perceptions are in fact reality. 

If increased recruitment of chub is not detected in the next several years, then it might be reasonable to 

conclude that testing of stable flows is the next logical flow treatment to implement for evaluation. Stable 

flows that are implemented prior to complete evaluation of chub response to the 2003–6 experimental 

treatment and natural variability in temperature may result in confounding of the evaluation while also 

resulting in unnecessary costs. If the “future desired conditions” for downstream resources of the 

Colorado River ecosystem can be achieved under the modified low fluctuating flow regime, then stable 

flow testing is presumably unnecessary. 

8. Continue Model Development to Support Management Decision Making 
97

Use of modeling can help eliminate false starts and blind paths for experimental evaluation. Flow, 

temperature, and sediment transport are prime areas where modeling has already provided 

planning-support benefits and as such should continue to be explored, defined, and supported 

regardless of which experimental option is recommended next.

To the extent possible, existing and future numerical models for the Colorado River ecosystem should be 

developed and tested by both scientists and managers. The flow and temperature models for the system 

have already been integrated and have allowed for the inclusion of decade-long evaluations of various 

experimental flow scenarios with and without a temperature control device in this report. Such simulation 

results provide new perspectives to both managers and scientists about the range of options available to 

manage temperatures in this river ecosystem. 

The science recommendations outlined above cannot ensure absolute learning about cause-and-effect 

relationships among dam operations and downstream resource responses. Likewise, such 

recommendations cannot guarantee that resource benefits will be achieved below Glen Canyon Dam. 

However, taking an approach that attempts to build on the previous knowledge gained over the nearly two 

decades of available monitoring and research data may be the most effective strategy available to the Glen 

Canyon Dam Adaptive Management Program. 

Building on learning about sediment conservation options derived from the 1996 and 2004 BHBF tests 

can presumably occur at the same rate that tributaries provide new sand supplies below the dam, but only 

if the tests are conducted in response to new sand deliveries. In the realm of fishery biology, learning may 

build on the data collected before, during, and after the significant period of 1999 through 2010, when the 

adult humpback chub population began to stabilize and the period of warmest dam releases in over 30 

years commenced in parallel with the application of nonnative fish control. Only time and additional 

monitoring and modeling results will provide the basis for evaluating the outcome of this significant 

experiment. Such an evaluation may be best constrained by continuing the MLFF operation for the next 

few years as a means of providing continuity in understanding the influence of both flows, nonflow 

treatments and natural variability under a backdrop of the preferred alternative operating regime. 
98

References Cited 

Anderson, L.S. and Ruffner, G.A., 1988, Effects of the post-Glen Canyon Dam flow regime in the old 

high water zone plant community along the Colorado River in Grand Canyon: Glen Canyon 

Environmental Studies executive summaries of technical reports. NTIS no PB-183505/AS. 

ASCE, 1975, Sedimentation Engineering, Vanoni, V.A., ed., New York. 

Bagstad, K.J., Stromberg, J.C., and Lite, S.J., 2005, Response of herbaceous riparian plants to rain and 

flooding on the San Pedro River, Arizona, USA, Wetlands, v. 25, p. 210–223. 

Balsom, J. R. and Larralde, S., eds, 1996, Mitigation and monitoring of cultural resources in response to 

the experimental habitat building flow in Glen and Grand Canyons, spring 1996: Salt Lake City, 

Bureau of Reclamation, Upper Colorado Region. 

Benke, A. C., Hall, C. A. S., Hawkins, C. P., Lowe-McConnel, R. H., Stanford, J. A., Suberkropp, K., and 

Ward, J. V., 1988, Bioenergetic considerations in the analysis of stream ecosystems, Journal of 

the North American Benthological Society, v. 7, p. 480–502. 

Beus, Stanley S. and Avery, Charles C., 1992, The influence of variable discharge regimes on Colorado 

River sand bars below Glen Canyon Dam: final report, Northern Arizona University, Flagstaff, 

AZ 

Biodini, M., 2001, A three-dimensional spatial model for plant competition in a heterogeneous soil 

environment, Ecological Modeling, v. 142. p. 189–225. 

Bishop, R., Boyle, K., Welsh, M., Baumgartner, R., and Rathburn, P., 1987, Glen Canyon Dam releases 

and downstream recreation: an analysis of user preferences and economic values. Glen Canyon 

Environmental Studies Report No. 27/87, NTIS No. PB88-183546/AS, p.319–326 

Blinn, D. W., Shannon, J. P., Stevens, L. E. and Carder, J. P., 1995, Consequences of fluctuating 

discharge for lotic communities. Journal of the North American Benthological Society, v. 14, p. 

233–248. 

Brown, C. and Hahn-O’Neill, M. G., 1987, The effects of flows in the Colorado River on reported and 

observed boating accidents in Grand Canyon: Final report to the Bureau of Reclamation, Glen 

Canyon Environmental Studies Program, Flagstaff. 

Clarkson, R.W. and Childs, M.R., 2000, Temperature effects of hypolimnial-release dams on early life 

stages of Colorado River Basin Big-River Fishes. Copiea, v. 2000, no. 2, p. 402–412. 

Cox, D., Lutz, C., and Nelson, C., 2005, Beach/habitat building and status of endangered Kanab 

ambersnail. Abstract Grand Canyon Monitoring and Research Center 5th Biennial Science 

Symposium, Tempe, AZ. 

Estades, C.F., 2001, The effect of breeding-habitat patch size on bird density, Landscape Ecology, v. 16, 

p. 161–173. 
99

Farnsworth, E.J., and Meyerson, L.A., 2003, Comparative ecophysiology of four wetland plant species 

along a continuum of invasiveness, Wetlands, v. 23, p.750–762. 

Gloss, S.P., and Coggins, L.C., Jr., 2005, Fishes of Grand Canyon, Pages 33–56 in Gloss, S.P., Lovich, 

J.E., and Melis, T.S., eds. The State of the Colorado River Ecosystem in Grand Canyon: U.S. 

Geological Survey Circular 1282, 220 p. 

Graf, W.L. 1978. Fluvial adjustments to the spread of tamarisk in the Colorado Plateau region, Geological 

Society of America Bulletin, v. 89, p. 1491–1501. 

Graf, J.B., 1995, Measured and predicted velocity and longitudinal dispersion at steady and unsteady 

flow, Colorado River, Glen Canyon Dam to Lake Mead, Water Resources Bulletin, v. 31, p. 265–

281. 

Griffith, J.S., 1999, Coldwater streams, in Kohler, C.C., and Hubert, W.A., eds, Inland fisheries 

management in North America (second edition): American Fisheries Society, Bethesda, 

Maryland, p. 481–504. 

Güsewell, S., Bollens, U., Ryser, P. and Klötzli, F., 2003, Contrasting effects of nitrogen, phosphorus and 

water regime on first- and second-year growth of 16 wetland plant species, Functional Ecology , 

v.17, p. 754–765. 

Hamman, R.L. 1982. Spawning and culture of humpback chub: Progressive Fish Culturist, v. 44, no. 4, p. 

213–216. 

Hazel, J., Kaplinski,,M., Parnell, R., and Manone, M., 2001, Monitoring the effects of the spring 2000 

habitat maintenance flow on Colorado River ecosystem sandbars: fact sheet prepared for U.S. 

Geological Survey Grand Canyon Monitoring and Research Center, Flagstaff. 

Hazel, J.E., Jr., Topping, D.J., Schmidt, J.C., and Kaplinski, M., 2006, Influence of a dam on finesediment storage in a canyon river, Journal of Geophysical Research, Earth Surface, v. 111, 

F01025, doi:10.1029/2004JF000193, 2006, 16 p. 

Hoffnagle, T.L., 1996, Changes in water quality parameters and fish usage of backwaters during 

fluctuating vs. short-term steady flows in the Colorado River, Grand Canyon: report prepared for 

Glen Canyon Environmental Studies by Arizona Game and Fish Department. 31 pp. 

Holmes, J.A., Spence, J.R., and Sogge, M.K., 2005, Birds of the Colorado River in Grand Canyon: a 

synthesis of status, trends and dam operation effects in Gloss, S.P., J.E. Lovich, T.S. Melis eds., 

The state of the Colorado River ecosystem in Grand Canyon: a report of the Grand Canyon 

Monitoring and Research Center, U.S. Geological Survey Circular 1282. p.123–138. 

Hubbell, D.W. and Ali, K.A., 1961, Qualitative effects of temperature on flow phenomena in alluvial 

channels: in short papers in the Geologic and Hydrologic Sciences, Articles 293–435, Geological 

Survey Research 1961, U.S. Geological Survey Professional Paper 424-D, p D21–D23. 

Hunt, T., Ward, D.L., and Rogers, R.S., 2006, Lees Ferry long-term trout monitoring: 2006 trip report 

(Trip LF20060626): Arizona Game and Fish Department, Flagstaff, Arizona, 8 p. 
100

Huryn, A. D., and Wallace, J. B., 2000, Life history and production of stream insects: Annual Review of 

Entomology, v. 45, p. 83–110. 

Hutching, M.J. and deKroon, H., 1994, Foraging in plants: the role of morphological plasticity in resource 

acquisition, Advances in Ecological Research, v. 25, p.159–238. 

Jalbert, L., 1996, The effects of the 1996 beach/habitat building flows on observed and reported boating 

accidents on the Colorado River in Grand Canyon National Park: final report submitted to Glen 

Canyon Environmental Studies Office, Flagstaff, AZ. 

Jalbert, L., 2001, The effects of low steady summer flows on whitewater boating safety in Grand Canyon 

National Park: paper presented at Glen Canyon Dam Adaptive Management Program Colorado 

River Ecosystem Science Symposium, April 2001, Flagstaff. 

Jobson, H. E., and Schoellhamer, D. H., 1993, User’s manual for a Branched Lagrangian Transport 

Model: U.S. Geological Survey Water Resources Investigations Report 87• 4163, 80 p. 

 

Jobson, H. E., 1997, Enhancements to the Branched Lagrangian Transport Modeling system: U.S. 

Geological Survey Water-Resources Investigations Report 97• 4050, 56 p. 

Jonas, L.M. and Stewart, W.P., 2002, An overview of various impacts to Grand Canyon River 

experiences, with a focus on intergroup encounters, flow levels, and the 2000 low summer steady 

flow experiment, Electronic Access: 

http://gcmrc.gov\library\reports\cultural\Recreation\Encounters_finalreport.pdf 

Kaplinski, Matt, Behan, Jeff, Hazel, Joseph E., Manone, Mark, and Parnell, Roderic, 2005a, Evaluation of 

campsite studies in the Colorado River ecosystem: analysis and recommendations for long term 

monitoring, Cooperative agreement OOPG400255, 0001, 57 p. 

Kaplinski, M, Behan, J., Hazel, J.E., Parnell, R.A. and Fairley, H.C., 2005b, Recreational values and 

campsites in the Colorado River ecosystem, Chapter 12, in Gloss, S.P., Lovich, J.E. and Melis, 

T.S., eds, The state of the Colorado River ecosystem in Grand Canyon: a report of the Grand 

Canyon Monitoring and Research Center: U.S. Geological Survey Circular No.1282, p. 193–205. 

Kaplinski, M., 2006, Near shore water temperature data: August 12 to November 14, 2005, data delivery 

report prepared for Grand Canyon Monitoring and Research Center by Namtek, Inc. 

Kearsley, L.H. and Quartoroli, R., 1997, Effects of a beach/habitat building flow on campsites in Grand 

Canyon: Final report of Applied Technology Associates for the Glen Canyon Environmental 

Studies Program. 18 p. 

Kearsley and Ayers, 1998, Terrestrial vegetation work for 1997 steady low and high flows: final report to 

Grand Canyon Monitoring and Research Center, Flagstaff, AZ 86001. Cooperative Agreement 

No. 1425-97-FC-40-20850. 29pp + appendices. 

Kearsley, M.J.C., 2006, Vegetation dynamics. In Kearsley, M.J.C. ed., Inventory and monitoring of 

terrestrial riparian resources in the Colorado River corridor of Grand Canyon: an integrative 

approach, report from Northern Arizona University submitted to Grand Canyon Monitoring and 

Research Center, U.S. Geological Survey, Flagstaff, Arizona. 262 p. 
101

Kearsley, M.J.C, and Ayers, T.J., 1999, Riparian vegetation responses: snatching defeat from the jaws of 

victory and vice versa, in Webb, R.H., Schmidt, J.C., Marzolf, G.R., and Valdez, R.A., eds., The 

Controlled Flood in Grand Canyon: Washington, D.C., American Geophysical Union, 

Geophysical Monograph series, v. 110, p 309–327. 

Korman, J., Kaplinski, M, and J. Buszowski, 2005a, Effects of air and mainstem water temperatures, 

hydraulic isolation, and fluctuating flows from Glen Canyon Dam on water temperatures in near 

shore and backwater environments in the Colorado River in Grand Canyon: draft report prepared 

by Ecometric Research for GCMRC. 

Korman, J., Kaplinski, M., Hazel, J.E., and T.S. Melis, 2005b, Effects of the experimental fluctuating 

flows from Glen Canyon Dam in 2003 and 2004 on the early life history stages of rainbow trout 

in the Colorado River: final report, prepared for GCMRC by Ecometric Research. 

Lane, E.W., Carlson, E.J., and Hanson, O.S., 1949. Low Temperature Increases Sediment Transportation 

in Colorado River, Civil Engineering, ASCE, v. 19, No. 9, p. 45–46. 

Laubhan, M.K. and Shaffer, T.L., 2006, Seed germination of Cirsium arvense and Lepidium latifolium: 

implications for management of montane wetlands, Wetlands, v. 26, p. 69–78. 

Li, H.W., and Moyle, P.B., 1999, Management of introduced fishes, in Kohler, C.C., and Hubert, W.A., 

eds., Inland fisheries management in North America (second edition): American Fisheries 

Society, Bethesda, Maryland, p. 345–374. 

Lightfoot, D.C., Brantley, S.L., Cobb, N.S., and Delph, R.J., 2006, Arthropods. In Kearsley, M.J.C. ed, 

Inventory and monitoring of terrestrial riparian resources in the Colorado River corridor of Grand 

Canyon: an integrative approach, report from Northern Arizona University submitted to Grand 

Canyon Monitoring and Research Center, U.S. Geological Survey, Flagstaff, Arizona. 262 p. 

Magirl, C.S., in press, Bedrock-controlled fluvial geomorphology and the hydraulics of rapids on the 

Colorado River: The University of Arizona, Tucson, Ph.D. dissertation. 

Marsh, P.C., 1985, Effect of incubation temperature on survival of embryos of native Colorado River 

fishes. Southwest Naturalist, v. 30, p. 129–140. 

Melis, T.S., Martell, S.J.D., Coggins, L.G., Pine, W.E. and Andersen, M.E., 2006a, Adaptive 

management of the Colorado River Ecosystem below Glen Canyon Dam, Arizona: using science 

and modeling to resolve uncertainty in river management, proceedings of the American Water 

Resources Association Specialty Conference on Adaptive Management and Water Infrastructure, 

June 26–28, 2006, Missoula, MT, 6 p. 

Melis, T.S., Wright, S.A., Ralston, B.E., Fairley, H.C., Kennedy, T.A., Andersen, M.E., Coggins, L.G. Jr., 

and Korman, J., 2006b, 2005 Knowledge assessment of the effects of Glen Canyon Dam on the 

Colorado River ecosystem: an experimental planning support document, U.S. Geological Survey, 

Flagstaff, Arizona 86001, 82p. 

Meretsky, V.J., and Wegner, D.L., 2000, Kanab ambersnail at Vaseys Paradise, Grand Canyon National 

Park, 1998–1999 monitoring and research: final report, SCWA, Inc. Electronic Access: 

http://www.gcmrc.gov/library/reports/biological/terrestrial/KAS/Meretsky2000.pdf
102

Mills, G. S., Dunning, J. B, and Bates, J. M, 1991, The relationship between breeding bird density and 

vegetation volume, Wilson Bulletin, v. 103, p. 468–479. 

Moyle, P.B., and Cech, J.J., Jr., 2004, Fishes: an introduction to ichthyology (fifth edition): Prentice Hall, 

Upper Saddle River, New Jersey. 

Myers, T. M, Becker, C.C., and Stevens, L. E., 1999, Fateful journey: injury and death on Colorado River 

trips in Grand Canyon. Red Lake Books, Flagstaff. 

Oskinis, V, 1994, Temperature and development of Bothriocephalus acheilognathi Yamaguti, 1934 

(Cestoda) in laboratory conditions: Ekologija v4, p. 40–42. 

Porter, Marianne E. and Kearsley, Mike, 2001, The response of Tamarix to experimental flows in Grand 

Canyon, Hydrology and Water Resources in Arizona and the Southwest, v. 31, p. 45–50. 

Porter, M.E., 2002, Riparian vegetation responses to contrasting managed flows of the Colorado River in 

Grand Canyon, Arizona: Masters thesis, Northern Arizona University, Flagstaff, Arizona, 33 p + 

figs. 

Price. P. W., 1984, Insect ecology, Second edition, John Wiley & Sons, New York, p. 387–574. 

Rubin, D.M. and Topping, D.J., 2001, Quantifying the relative importance of flow regulation and grainsize regulation of suspended-sediment transport (•), and tracking changes in bed-sediment grain 

size (•). Water Resources Research, v. 37, p.133–146. 

Rubin, D.M., Topping, D.J., Schmidt, J.C., Hazel, J., Kaplinski, K., and Melis, T.S., 2002, Recent 

sediment studies refute Glen Canyon Dam hypothesis: EOS, Trans., American Geophysical 

Union, v. 83, n. 25, p. 273, 277–278. 

Schmidt, J.C., Topping, D.J., Grams, P.E., and Hazel, J.E., Jr., 2004, System-wide changes in the 

distribution of fine sediment in the Colorado River corridor between Glen Canyon Dam and 

Bright Angel Creek, Arizona: final report submitted to the U.S. Geological Survey Grand Canyon 

Monitoring and Research Center, Flagstaff, AZ. 

Shelby, B., Brown, T., and Baumgartner, R., 1992, Effects of streamflows on river trips on the Colorado 

River in Grand Canyon, Arizona, Rivers, v. 3, p. 199–201. 

Sogge, M., Felley, D., and Wotawa, M., 1998, Riparian bird community ecology in the Grand Canyon, 

final report: U.S. Geological Survey, Colorado Plateau Field Station report, 57 p. 

Sogge, M., Tibbitts, T.J., and Petterson, J. 1997. Status and breeding ecology of the southwestern willow 

flycatcher in the Grand Canyon: Western Birds, v. 28, p. 142–157. 

Stevens, L. E., Protiva, F.R., Kubly, D.M., Meretsky, V.J., and Petterson, J.R., 1997b, The ecology of 

Kanab ambersnail (Succineidae: Oxyloma haydeni kanabensis, Pilsbry 1948) at Vaseys Paradise, 

Grand Canyon, Arizona: report to Grand Canyon Monitoring and Research Center, Department of 

Interior, Flagstaff, Arizona, U.S.A. 
103

Stevens, L.E. and Waring, G.L., 1986, Effects of post-dam flooding in riparian substrates, vegetation and 

invertebrate populations in the Colorado River corridor in Grand Canyon, Arizona, NTIS 

publication 19, 175 p. 

Stevens, L.E., and Ayers, T.J., 1993, The impacts of Glen Canyon Dam on riparian vegetation and soil 

stability in the Colorado River corridor, Grand Canyon, Arizona: 1992 final report, submitted to 

National Park Service, Cooperative Studies Unit, Northern Arizona University, Flagstaff, AZ 

86001, p.7–1 to 7–9. 

Stevens, L.E., Ayers, T.J., Bennett, J.B, Christensen, K., Kearsley, M.J.C., Meretsky, V.J., Phillips, A.M., 

III, Parnell, R.A., Spence, J., Sogge, M.K., Springer, A.E., Wegner, D.L., 2001, Planned flooding 

and Colorado River riparian trade-offs downstream from Glen Canyon Dam, Arizona: Ecological 

Applications, v. 11, p. 701–710. 

Stevens, L.E., Schmidt, J.C., Ayers, T.J., and Brown, B.T. 1995. Flow regulation, geomorphology, and 

Colorado River marsh development in the Grand Canyon, Arizona: Ecological Applications, v. 5, 

p. 1025–1039. 

Stevens, L.E., Meretsky, V.J., Nelson, C.B., and Sorenson, J.A., 1998, The endangered Kanab ambersnail 

at Vasey’s Paradise, Grand Canyon, Arizona: 1997 annual monitoring report, prepared from 

Grand Canyon Monitoring and Research Center. Electronic Access: 

http://www.gcmrc.gov/library/reports/biological/terrestrial/KAS/Stevens1998.pdf

Stewart, W., Larkin, K., Orland, B., Anderson, D., Manning, R., Cole, D., Taylor, J., and Tomar, N., 

2000, Preferences of recreation user groups of the Colorado River in Grand Canyon: final report 

submitted to U.S. Geological Survey Grand Canyon Monitoring and Research Center, Flagstaff. 

Stone, D.M., and Gorman, O.T., 2006, Ontogenesis of endangered humpback chub (Gila cypha) in the 

Little Colorado River, Arizona, American Midland Naturalist, v. 155, p. 123–135. 

Taiz, L. and Zeiger, E., 1991, Plant Physiology, Benjamin/Cummings Publishing Company, p. 249–264. 

Topping, D.J., Rubin, D.M., and Vierra, Jr., L.E., 2000a, Colorado River sediment transport: pt. 1: natural 

sediment supply limitation and the influence of Glen Canyon Dam: Water Resources Research, v. 

36, p.515–542. 

Topping, D.J., Rubin, D.M., Nelson, J.M., Kinzel, P.J and Corson, I.C., 2000b, Colorado River sediment 

transport: pt. 2. Systematic bed-elevation and grain-size effects of sand supply limitation. Water 

Resources Research, v. 36 p. 543–570. 

Topping, D.J., Schmidt, J.C., Vierra, L.E. Jr., 2003, Computation and analysis of the instantaneousdischarge for the Colorado River at Lees Ferry, Arizona: May 8 1921, through September 30, 

2000. U. S. Geological Survey Professional Paper 1677. 

Topping, D.J., Rubin, D.M., Schmidt, J.C., Hazel, J.E., Jr., Melis, T.S., Wright, S.A., Kaplinski, M., 

Draut, A.E., and Breedlove, M.J., 2006, Comparison of sediment-transport and bar-response 

results from the 1996 and 2004 controlled-flood experiments on the Colorado River in Grand 

Canyon: CD-ROM Proceedings of the 8th Federal Inter-Agency Sedimentation Conference, 

Reno, Nevada, April 2–6, 2006, ISBN 0-9779007-1-1. 
104

Topping, D.J., Rubin, D., Schmidt, J., Hazel, J., Melis, T., Wright, S., Kaplinski, M., Draut, A., 

Breedlove, M., 2006, Comparison of sediment-transport and bar response results from the 1996 

and 2004 controlled-flood experiments on the Colorado River in Grand Canyon, in Proceedings 

of the 8th Federal Interagency Sedimentation Conference, April 2–6, 2006, Reno, NV, 8 p. 

Trammell, M., Valdez, R., Carothers, S., and Ryel, R., 2002, Effects of a low steady summer flow 

experiment on native fishes of the Colorado River in Grand Canyon, Arizona, report prepared for 

GCMRC by SWCA, Inc. 

U.S. Geological Survey, 2006, Grand Canyon population of humpback chub stabilizing, U.S. Geological 

Survey Fact Sheet 2006-3190. 

Valdez, R.A., and Ryel, R.J., 1995, Life history and ecology of humpback chub (Gila cypha) in the 

Colorado River, Grand Canyon, Arizona. Final report to the Bureau of Reclamation, Salt Lake 

City, Utah, Contract No. 0-CS-40-09110. BIO/WEST Report No. TR-250-08. BIO/WEST, Inc., 

Logan, Utah. 

Valdez, R.A., S. W. Carothers, M. E. Douglas, M. Douglas, R.J. Ryel, K.R. Bestgen, and D.L. Wegner, 

2000, Research and implementation plan for establishing a second population of humpback chub 

in Grand Canyon: Report to Grand Canyon Monitoring and Research Center, Flagstaff, AZ, 

SWCA, Inc., Flagstaff, AZ. 

Vernieu, W.S., Hueftle, S.J., and Gloss, S.P., 2005. Water Quality in Lake Powell and the Colorado 

River, in Gloss, S.P., Lovich, J.E., and Melis, T.S., eds, The state of the Colorado River 

ecosystem in Grand Canyon: a report of the Grand Canyon Monitoring and Research Center, U.S. 

Geological Survey Circular 1282, p. 69–85. 

Ward, D.L., Maughan, O.E., Bonar, S.A., and Matter, W.J., 2002, Effects of temperature, fish length, and 

exercise on swimming performance of age-0 flannelmouth sucker: Transactions of the American 

Fisheries Society, v. 131, p. 492–497. 

Waring, G.L., 1995, Current and historical riparian vegetation trends in Grand Canyon, using multitemporal remote sensing analysis of GIS sites: final report, National Park Service, 24 p. 

Webb, R. H., Schmidt, J.C., Marzolf, G.R., and Valdez, R.A., eds., 1999, The Controlled Flood in Grand 

Canyon. American Geophysical Union, Washington, D.C., Geophysical Monograph Series, 

v.110, 367p. 

Wiele, S. M., and Smith J. D., 1996, A reach-averaged model of diurnal discharge wave propagation 

down the Colorado River through the Grand Canyon. Water Resources Research, v. 32, No. 5, p. 

1375•1386. 

Wiele, S. M., and Griffin, E. R., 1997, Modifications to one-dimensional model of unsteady flow in the 

Colorado River through the Grand Canyon, Arizona: U.S. Geological Survey Water-Resources 

Investigations Report 97•4046, 17 p. 

Wright, S.A., Melis, T.S., Topping, D.J., and Rubin, D.M., 2005, Influence of Glen Canyon Dam 

operations on downstream sand resources of the Colorado River in Grand Canyon, in Gloss, S.P., 
105

Lovich, J.E., and Melis, T.S., eds., The state of the Colorado River ecosystem in Grand Canyon: 

U.S. Geological Survey Circular 1282, p. 17–31. 

Yard, H.K., Van Riper III, C., Brown, B.T., and Kearsley, M.J., 2004, Diets of insectivorous birds along 

the Colorado River in Grand Canyon, Arizona. The Condor, v. 106, p. 106–115. 

Yard, M.D., Bennett, G.E., Mietz, S.N., Coggins, L.G., Jr., Stevens, L.E., Hueftle, S., and Blinn, D.W., 

2005, Influence of topographic complexity on solar insolation estimates for the Colorado River, 

Grand Canyon, AZ. Ecological Modelling, v. 183, p. 157–172. 

Yeatts, Michael, 1997, High elevation sand retention following the 1996 spike flow. Hopi Cultural 

Preservation Office. Report prepared for Grand Canyon Monitoring and Research Center, dated 

December 1997. 15 p. Electronic Access: 

http://www.gcmrc.gov/library/reports/cultural/Hopi/Yeatts1997.pdf

Young, J.A., and Clements, C.D., 2003, Seed germination of willow species from a desert riparian 

system, J. Range Manage, v. 56, p. 496–500. 

Young, J.A., Clements, C.D. and Harmon, D., 2004, Germination of seeds of Tamarix ramosissima, J. 

Range Manage, v. 57, p. 475–481. 
106

Appendix A: Methods for Determining Flows 

Development of Monthly Lake Powell Inflow and Release Sequences for the Assessment of 

Experimental Options 

Overview 

The Science Planning Group (SPG) was charged with completing an assessment of long-term 

experimental flow proposals for the operation of Glen Canyon Dam. Three long-term 

experimental flow proposals are being evaluated. These proposals are labeled: Option A, Option 

B, and Option C. Additionally, a fourth option, a variation of Option A, is also being analyzed.1

The SPG concluded that the proposals needed to be analyzed under a broad range of hydrologic 

scenarios. The agreed upon methodology was to study the effects under three 10-year hydrologic 

sequences: a dry sequence (90 percent exceedance), a most probable sequence (50 percent 

exceedance), and a wet sequence (10 percent exceedance). 

The monthly release volumes for the three options were developed by the SPG under the 

assumption of an 8.23 million acre-feet (maf) water year release from Lake Powell. While over 

the past 6 years (2001 through 2006 inclusive) this has been the actual water year release from 

Lake Powell, studies using the Colorado River Simulation System (CRSS) model reveal that 

future releases will likely be greater than the 8.23 maf objective in approximately 50 percent of 

the years. 

The CRSS model was used to develop the inflow and release sequences for the dry, most 

probable, and wet sequences. Input to the CRSS model includes monthly natural flow and 

current and future water demands throughout the Colorado River Basin. The Bureau of 

Reclamation (Reclamation) currently has 99 years of natural flow data (1906–2004) for use as 

input data. Colorado River reservoirs in the CRSS model behave according to policy rules that 

are created using RiverWare software. 

Several methods are available for ascertaining the range of possible future inflows. In the 

Colorado River, a particular technique (called the Indexed Sequential Method) has been used 

since the early 1980s and involves a series of simulations, each applying a different future inflow 

sequence (USBR, 1985: Ouarda, and others, 1997). Each future inflow sequence is generated 

from the historical natural flow record by “cycling” through the record. For example, the first 

simulation assumes that the inflow for the 2007 through 2016 period will be the 1906 through 

1915 historical record, the second simulation assumes the inflow for 2007 through 2016 will be 

the 1907 through 1916 historical record, and so on. As the method progresses, the historical 

record is assumed to “wrap-around” (i.e., after 2004, the record reverts back to 1906, yielding a 

possible 99 different inflow sequences). The result of the Indexed Sequential Method is a set of 

99 separate simulations referred to as “traces.” This enables an evaluation of proposed criteria 

over a broad range of possible future hydrologic conditions. Evaluations can utilize all 99 traces 

 

1

 These proposals are described in detail elsewhere in this assessment. 
107

with statistical techniques, or alternatively, a set of analogues (a set of model traces) can be used 

to represent a range of future hydrologic conditions. 

Development of the Dry, Most Probable, and Wet Sequences 

A CRSS model run was performed on July 25, 2006. The initialization date for the model run 

was January 1, 2007. The initial conditions (storage in Colorado River reservoirs) used in the 

simulation were those values as predicted from Reclamation’s July 2006 24-month study. The 

model was run for 19 years (2007 through 2025). A total of 99 traces were generated. 

The policy rules in the CRSS model run were those consistent with Reclamation’s “no action” 

rule set as of July 2007. It is important to note that an National Environmental Policy Act 

(NEPA) process which in part addresses the operation of Glen Canyon Dam is currently 

underway. A Draft Environmental Impact Statement (EIS), Lower Colorado River Basin 

Shortage Guidelines and Coordinated Management Strategies for Lake Powell and Lake Mead

(Shortage EIS), is being prepared and contains alternatives which propose coordinated operations 

between Lake Powell and Lake Mead under low reservoir storage conditions. A possible 

outcome of the Shortage EIS is the implementation of operations at Lake Powell that deviate 

from no action. The draft Shortage EIS is scheduled to be released in February 2007. The final 

Shortage EIS is expected to be released in September 2007 with a Record of Decision completed 

in December 2007. Implementation of a coordinated operating strategy through this NEPA 

process could modify future annual release volumes from Lake Powell. 

Lake Powell operations under the no action rule set in CRSS follow the Criteria for Coordinated 

Long-Range Operation of Colorado River Reservoirs. The objective to maintain a minimum 

release of 8.23 maf governs the operation when Lake Powell storage is lower than storage at 

Lake Mead or Upper Basin storage is below 602(a) storage.2 Storage equalization releases 

(releases greater than 8.23 maf/year) are made to equalize storage between Lake Powell and 

Lake Mead on September 30, when Lake Powell is projected to be greater than storage in Lake 

Mead and Upper Basin storage is greater than 602(a) storage. Additionally, when Lake Powell 

fills, Lake Powell is operated under a spill avoidance strategy, whereby water is released in the 

January through June time frame to allow a July fill without the unnecessary spillage of water. 

Three analogues (three model traces) representing the minimum probable (90 percent 

exceedance), most probable (50 percent exceedance), and maximum probable (10 percent 

exceedance) derived from the 99-trace CRSS simulation form the hydrologic basis for this 

assessment. 

To develop the dry, most probable, and wet sequences, the average 10-year Lake Powell inflow 

volume from 2007 through 2016 (ten years) was calculated for all 99 traces. This average 10-

year inflow ranged for a low of 7.70 maf to a high of 13.92 maf. The mean ten-year Lake Powell 

inflow for all 99 model traces was 10.26 maf.3

 The 10-year volumes were ranked. The dry, most 

 

2

 For further information on 602(a) storage, refer to Adoption of an Interim 602(a) Storage Guideline Final 

Environmental Assessment (March 2004) at http://www.usbr.gov/uc/library/envdocs/ea/pdfs/EA_602a.pdf. 3

 Simulated average inflow is less than the historical average inflow due to increasing water demands in the Upper 

Basin. 
108

probable, and wet sequences were selected from the 90th, 50th, and 10th exceedance percentiles, 

respectively. The three selected analogues are displayed in Table A-1. 

Table A-1 

Dry, Most Probable, and Wet Lake Powell Inflow Sequences 

 Dry Sequence Most Probable 

Sequence 

Wet 

Sequence 

Exceedance Percentile 90 % 50 % 10 % 

CRSS Numeric Trace Trace 55 Trace 31 Trace 5 

Analogue Period 1961–1970 1937–1946 1911–1920 

Average Powell WY Inflow 8.56 maf 9.77 maf 12.8 maf 

Plots of Lake Powell water year inflow for 10 years for the three hydrologic conditions (dry, 

most probable, and wet) are displayed in Figures A-1, A-2, and A-3. 

Dry Sequence (Trace 55) Inflow in AF

0

2,000,000

4,000,000

6,000,000

8,000,000

10,000,000

12,000,000

14,000,000

16,000,000

18,000,000

20,000,000

2007200820092010201120122013201420152016

Figure A-1 

Lake Powell Water Year Inflow for 2007 Through 2016 Under the Dry Sequence 
109

Most Probable Sequence (Trace 31) Inflow in AF

0

2,000,000

4,000,000

6,000,000

8,000,000

10,000,000

12,000,000

14,000,000

16,000,000

18,000,000

20,000,000

2007200820092010201120122013201420152016

Figure A-2 

Lake Powell Water Year Inflow for 2007 Through 2016 Under the Most Probable Sequence

Wet Sequence (Trace 5) Inflow in AF 

0

2,000,000

4,000,000

6,000,000

8,000,000

10,000,000

12,000,000

14,000,000

16,000,000

18,000,000

20,000,000

2007200820092010201120122013201420152016

Figure A-3 

Lake Powell Water Year Inflow for 2007 Through 2016 Under the Wet Sequence 

Note that in all three sequences there is high degree of variability. The most probable sequence is 

a mix of average, above average, and below average inflow years. In the dry sequence, there are 

two years with above average inflow. In the wet sequence, 5 of the 10 years have average inflow, 

4 have near average inflow, and one year has below average inflow. 
110

After defining the three sequences, release data for Lake Powell for the 10-year period were 

extracted from CRSS output. The summation of these data for the three sequences, by water 

year, is displayed in Table A-2. 

Table A-2 

Lake Powell Water Year Release for 2007 Through 2016 Under the 

Dry, Most Probable, and Wet Sequences 

 

Water Year 

Release 

Dry 

Sequence 

Most Probable 

Sequence 

Wet 

Sequence 

2007 8.23 maf 8.23 maf 8.23 maf 

2008 8.23 maf 9.72 maf 11.43 maf 

2009 8.23 maf 8.23 maf 8.89 maf 

2010 8.23 maf 8.23 maf 13.23 maf 

2011 8.23 maf 8.23 maf 9.59 maf 

2012 8.23 maf 11.96 maf 11.37 maf 

2013 8.23 maf 8.61 maf 14.11 maf 

2014 8.23 maf 9.71 maf 10.74 maf 

2015 8.23 maf 8.38 maf 8.72 maf 

2016 8.23 maf 8.23 maf 14.96 maf 

Under the dry sequence, there are no years in the next 10-year period where storage equalization 

releases would be required. Under the dry sequence, simulated releases from Lake Powell are 

8.23 maf each year for the period 1907–1916. 

Under the most probable sequence, inflow is sufficient enough that in half of the years storage 

equalization releases (releases greater than 8.23 maf) would be required. It is likely that over the 

next ten years, there will be a number of years with releases greater than 8.23 maf.

Under the wet sequence, releases greater than 8.23 maf would occur in all but the first year. 

Under this sequence, Lake Powell would fill in the years 2012, 2013, 2014, and 2016. 

Monthly Release Volumes from Lake Powell 

The assessment evaluates proposed changes in monthly release volumes in addition to proposed 

modifications to the Glen Canyon Operating Criteria (developed from the 1996 Glen Canyon 

Dam Operations EIS Record of Decision). 

The monthly release volumes from CRSS for the dry, most probable, and wet sequences for the 

10-year period 2007 through 2016 form the “base case” for this assessment. 

The no action rule set in CRSS contains a default monthly release pattern for years when the 

annual target release is 8.23 maf. This pattern is shown in Table A-3 with monthly release 

volumes listed in thousand acre-feet (kaf). 
111

Table A-3 

CRSS (Base Case) Monthly Releases Under an 8.23 maf Water Year 

Month 

Base Case 

Monthly Release (kaf) 

(8.23 maf water years) 

October 600 

November 600 

December 800 

January 800 

February 600 

March 600 

April 600 

May 600 

June 650 

July 850 

August 900 

September 630 

For Option A (and the variation of Option A), monthly releases are equivalent with the above 

table in an 8.23 maf release year. The proponents of Option A deferred to Reclamation to 

produce monthly release volumes. The emphasis of Option A (and its variation) is on modified 

powerplant operations within the month. The monthly releases for Option A (and the variation) 

are identical to the base case in this assessment not only in 8.23 maf release years, but for all 

years regardless of whether the operation is controlled by the minimum release objective or 

equalization. 

The monthly release pattern for Options B and C, as mentioned earlier, is based on an 8.23 maf 

water year release. The monthly release patterns differ from the base case in Options B and C.4

In addition, the monthly pattern in Option B changes from year to year. A challenge in the 

development of monthly releases for Options B and C was the patterning of monthly releases in 

years controlled by equalization, and to also assure that the total water year release is the same 

for all options for any given year. 

In years when Glen Canyon’s operation is controlled by equalization, post processing of the 

output data for Options B and C was performed to assure that the annual release did not deviate 

from the base case, and that the objective to equalize storage between Lakes Powell and Mead on 

September 30 was satisfied when Glen Canyon operations were controlled by equalization. 

The CRSS model contains methods for distributing releases greater than 8.23 maf required for 

equalization. The CRSS mimics the actual operation of Lake Powell. In actual operations, inflow 

projections, Lake Powell storage, and upstream storage are factored to determine when to 

schedule equalization releases. In the CRSS model, a simulated forecast (which contains error 

and uncertainty terms reflecting historical forecast errors) is used in conjunction with projected 

 

4

 The monthly release pattern for Options B and C are described elsewhere in this assessment. 
112

operation of reservoirs above Lake Powell to forecast September 30 storage at Lake Powell. The 

CRSS model also projects September 30 storage at Lake Mead. Equalization releases, releases 

greater than 8.23 maf, are scheduled when Upper Basin Storage is greater than 602(a) storage 

and when Lake Powell storage would end up greater than storage in Lake Mead should the 

minimum objective release be maintained. 

The CRSS model begins scheduling equalization releases as early as January. In actual 

operations, January is when the first water supply inflow forecast is disseminated by the National 

Weather Service. Similarly, in CRSS, January is the first month when a simulated inflow 

forecast is developed. In CRSS, equalization releases are scheduled when the simulated forecast 

in combination with projected storage at Lakes Powell and Mead shows that releases greater than 

8.23 maf are required. CRSS determines the volume greater than 8.23 maf required for release 

and distributes this volume evenly across the months between the current month and September. 

For example, in January if the model determines that 900 kaf of equalization release is required 

(for a total water year release of 9.13 maf), an additional 100 kaf of water is scheduled in each of 

the nine months from January through September. In examining CRSS output, however, one 

never sees an even distribution of equalization across the months. That is because in the 

subsequent time step (the next month), the simulated inflow forecast changes (just as actual 

inflow forecasts change on a month-by-month basis). To follow up from the example before, one 

could potentially see a January that required 900 kaf of equalization release, but in the next 

model time step (February), the forecast could change requiring greater or lesser amounts of 

equalization release. The model would then adjust releases accordingly. The model output 

reflects uncertainty in water supply. This is consistent with actual operations where water supply 

forecasts are rarely static throughout the water year. 

There was some discussion among the SPG as to how to pattern equalization releases in Options 

B and C. Proponents of these respective options discussed the benefit of scheduling equalization 

releases in the January through June time period, such that equalization releases in late summer 

and September were minimized. Such a qualitative adjustment is problematic for this assessment 

for a couple of reasons: (1) Inflow projections continue to shift in the late spring and summer 

months. Shifting equalization releases to the January through June time period while summer and 

September releases remain similar or equal to the 8.23 maf release monthly volume would result 

in not meeting the objective to equalize storage between Lakes Powell and Mead on September 

30. In some years, Lake Powell would end up higher than Lake Mead with the reverse in others.5

(2) CRSS scheduling for equalization releases does not optimize for the Glen Canyon Operating 

Criteria or power operations. There are times, for instance, when CRSS increases a June volume 

due to equalization. CRSS might schedule an extra 145 kaf to increase the monthly release from 

650 to 795 kaf for the month. In actual operations, if the monthly volume was getting close to 

800 kaf, some equalization release would be shifted from one month to another such that 800 kaf 

months (where the daily range of low to high flows increases from 6,000 cubic feet per second to 

8,000 cubic feet per second) were achieved. If equalization releases were qualitatively adjusted 

in Options B and C, it follows that Option A equalization releases should also be adjusted from 

CRSS output. 

 

5

 This is not likely an acceptable outcome given current diminished reservoir storage in Lake Powell and Lake 

Mead. 
113

The resolution for handling equalization volumes in this assessment was to not deviate from the 

manner in which the CRSS model schedules equalization releases. For Option A, monthly 

releases are exactly as they are produced from CRSS. For Options B and C, a post processing 

method, “the CRSS Distribution Method,” was used to adjust monthly releases in equalization 

years. This method calculates the differential between the 8.23 maf monthly release and the 

CRSS produced equalization monthly release for the base case on a month-by-month basis. This 

differential for each month is then added to the 8.23 maf monthly release for Options B and C. In 

this way, the annual volumes remained the same for all options, and the monthly patterning of 

water for equalization is consistent across all of the options. 

An example of the CRSS Distribution Method for year 2013 under the most probable sequence is 

shown in Table A-4. In this year, there is a small amount of equalization release required (a total 

of 382 kaf). Additionally in this example, CRSS keeps changing direction as to whether 

equalization is necessary as the model simulates on a month-by-month basis throughout the year. 

Table A-4 

Example of CRSS Distribution Method in 2013 

WY 

2013 

Month 

8.23 maf 

Base Case 

Rel (kaf) 

CRSS 

Rel (kaf) 

Delta 8.23 maf 

Opt B 

Rel (kaf) 

Adjusted 

Option B

Rel (kaf)

8.23 maf 

Option C 

Rel (kaf) 

Adjusted 

Option C

Rel (kaf)

Oct 600 600 0 615 615 500 500 

Nov 600 600 0 595 595 650 650 

Dec 800 800 0 615 615 800 800 

Jan 800 983 183 615 798 800 983 

Feb 600 698 98 555 653 675 773 

Mar 600 571 -30 615 585 650 620 

Apr 600 656 56 1101 1157 625 681 

May 600 549 -51 861 810 625 574 

Jun 650 595 -55 833 778 725 670 

Jul 850 812 -37 615 578 825 788 

Aug 900 1045 145 615 760 800 945 

Sep 630 703 73 595 668 555 628 

Total 8230 8612 382 8230 8612 8230 8612 

Column “Delta” in the table is the difference between the 8.23 monthly pattern for the base case 

and CRSS output for the base case which includes adjustments for equalization. Note that some 

of the months have negative deltas. In the above example, equalization releases begin to be 

scheduled in January. In March, however, the model generates a lower inflow forecast whereby 

the model reverts to targeting an 8.23 maf release year. The only way to do this is to reduce 

releases below the 8.23 monthly pattern, because additional water has already been released in 

January and February. 

The important point elucidated in the table is that monthly releases are adjusted in Options B and 

C to preserve the same uncertainty in forecasts as in the base case using the CRSS Distribution 
114

Method. The volume in the “delta” column is added to the 8.23 monthly release in both Options 

B and C. This also preserves equal water year releases for all the options in all water years. 

Figure A-4 shows monthly releases (for the most probable and dry sequence) for Option A. 

These monthly releases are derived directly from the CRSS model output and are also equivalent 

to the base case. Figures A-5 and A-6 depict monthly releases under Options B, and C. Monthly 

volumes in years requiring equalization were developed using the CRSS Distribution Method in 

Options B and C. Monthly releases for the dry sequence are also shown in Figures A-5 and A-6 

to provide a reference for what releases would be in Option B and Option C under an 8.23 maf 

release year. Equalization releases are required in 2008, 2012, 2013, 2014, and 2015 under the 

most probable sequence. Releases in the following three figures are shown as average monthly 

flow in cubic feet per second (cfs). Note the varying patterns under which these equalization 

releases are made. The patterns reflect changing inflow forecasts within each of these years. 

Option A / Base Case - G.C. Monthly Releases (average flow in cfs)

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

Oct-06

Feb-07

Jun-07

Oct-07

Feb-08

Jun-08

Oct-08

Feb-09

Jun-09

Oct-09

Feb-10

Jun-10

Oct-10

Feb-11

Jun-11

Oct-11

Feb-12

Jun-12

Oct-12

Feb-13

Jun-13

Oct-13

Feb-14

Jun-14

Oct-14

Feb-15

Jun-15

Oct-15

Feb-16

Jun-16

Most Probable Scenario

Dry Scenario

Figure A-4 

Lake Powell Monthly Releases for the Dry and Most Probable Sequence for Option A 
115

Option B (GCT) G.C. Monthly Releases (average flow in cfs)

CRSS Distribution Method

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

Oct-06

Feb-07

Jun-07

Oct-07

Feb-08

Jun-08

Oct-08

Feb-09

Jun-09

Oct-09

Feb-10

Jun-10

Oct-10

Feb-11

Jun-11

Oct-11

Feb-12

Jun-12

Oct-12

Feb-13

Jun-13

Oct-13

Feb-14

Jun-14

Oct-14

Feb-15

Jun-15

Oct-15

Feb-16

Jun-16

Most Probable Scenario

Dry Scenario

Figure A-5 

Lake Powell Monthly Releases for the Dry and Most Probable Sequence for Option B 

Equalization Volumes Developed With the CRSS Distribution Method 

Option C (DOI) G.C. Monthly Releases (average flow in cfs)

CRSS Distribution Method

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

Oct-06

Feb-07

Jun-07

Oct-07

Feb-08

Jun-08

Oct-08

Feb-09

Jun-09

Oct-09

Feb-10

Jun-10

Oct-10

Feb-11

Jun-11

Oct-11

Feb-12

Jun-12

Oct-12

Feb-13

Jun-13

Oct-13

Feb-14

Jun-14

Oct-14

Feb-15

Jun-15

Oct-15

Feb-16

Jun-16

Most Probable Scenario

Dry Scenario

Figure A-6 

Lake Powell Monthly Releases for the Dry and Most Probable Sequence for Option C 

Equalization Volumes Developed With the CRSS Distribution Method 
116

It should also be noted that there will always be a difference between model simulations and 

actual operations. In actual operations, operational experience as well as other relevant factors 

not incorporated in the CRSS model are used. For instance, in the example of the simulation in 

2013, shown in Table A-4 on page 8, releases were slightly below 600 kaf in three months 

(March, May, and June) under the base case. In actual practice, these release may have been 

maintained at 600 kaf. Actual equalization releases under an implementation of Options B or C 

would also likely have additional factors considered. For consistency in this assessment, the 

CRSS Distribution Method provides a valid method for comparing the various options. 

Beach/Habitat Building Flows (BHBFs) Monthly Release Volumes from Lake Powell 

A separate data set was developed to assess the effects of BHBFs (rather than use 10-year 

sequences for dry, most probable, and wet hydrologic conditions). Monthly volumes for BHBFs 

were developed for one year with two separate water year release volumes (an 8.23 maf release 

year and a 9.678 maf release year [an equalization year]). The year for analysis of the BHBFs 

was 2008. 

Monthly volumes were developed for all three options for 2008 for three different BHBF events 

for both the 8.23 maf and 9.678 maf6

 release years. BHBFs were scheduled in either November, 

January, or March. An additional 200 kaf was added to the monthly release for months with 

BHBFs. 

 

6

 The 9.678 maf release year was not an analogue. It was obtained by averaging the releases in the five years where 

there were equalization releases in the most probable sequence (years 2008, 2012, 2013, 2014, and 2015). 
117

Table A-5 shows the monthly release distribution for a November BHBF for all three options 

under an 8.23 maf release year. For BHBFs in January and March, 200 kaf was added to January 

or March (instead of November) with the other monthly volumes remaining the same as listed in 

Table A-5. 

Table A-5 

BHBF Monthly Release Volumes in a 8.23 maf Year 

WY 

2008 

Month 

Option A 

8.23 maf 

Release 

(kaf) 

Option 

A 

change 

(kaf) 

Option B

8.23 maf 

Release 

(kaf) 

Option B

change 

(kaf) 

Option C

8.23 maf 

Release 

(kaf) 

Option C 

change 

(kaf) 

Oct 600 0 615 0 500 0 

Nov 800 200 795 200 850 200 

Dec 800 0 738 0 800 0 

Jan 800 0 738 0 800 0 

Feb 600 0 690 0 675 0 

Mar 600 0 738 0 650 0 

Apr 600 0 715 0 625 0 

May 600 0 738 0 625 0 

Jun 600 -50 715 0 600 -125 

Jul 800 -50 738 0 800 -25 

Aug 800 -100 515 -100 800 0 

Sep 630 0 495 -100 505 -50 

Total 8230 0 8230 0 8230 0 
118

The monthly release distribution for a 9.678 maf release year with a November BHBF is shown 

in Table A-6. In the 9.678 maf release year, 50 kaf was taken out of the final four months of the 

water year (June through September) for all of the options. Distributions for January and March 

BHBFs were the same as shown above except that the added 200 kaf was added to January or 

March instead of November. 

Table A-6 

BHBF Monthly Release Volumes in a 9.678 maf Year 

WY 

2008 

Month 

Option A 

9.678 maf 

Release 

(kaf) 

Option 

A 

change 

(kaf) 

Option B 

9.678 maf 

Release 

(kaf) 

Option 

B 

change 

(kaf) 

Option C 

9.678 maf 

Release 

(kaf) 

Option C 

change 

(kaf) 

Oct 600 0 615 0 500 0 

Nov 800 200 795 200 850 200 

Dec 800 0 738 0 800 0 

Jan 906 0 844 0 906 0 

Feb 721 0 811 0 796 0 

Mar 619 0 757 0 669 0 

Apr 645 0 760 0 670 0 

May 635 0 773 0 660 0 

Jun 695 -50 760 -50 770 -50 

Jul 1058 -50 946 -50 1033 -50 

Aug 1244 -50 959 -50 1144 -50 

Sep 955 -50 920 -50 880 -50 

Total 9678 0 9678 0 9678 0 
119

Appendix B: Flow Variations 

Summary of Hydrograph Parameters for Base and Options A, A Variation, B, and C – The 

following section summarizes basic differences in flows between the base case and the four 

experimental options, based on analysis of the 10-year hourly release hydrographs provided by 

Western Area Power Administration (WAPA). There are three sub-sections, one for each 

hydrologic scenario: minimum releases, most probable, and wet. For the minimum release 

hydrologic scenario all 10 years contain releases of 8.23 million acre-feet (MAF) annual water 

year volume; the most probable hydrology has 5 water years above 8.23 MAF and the wet 

hydrologic scenario has 9 water years above 8.23 MAF (see Fig. 1.1 below). 

7

8

9

10

11

12

13

14

15

16

200620072008200920102011201220132014201520162017

Annual Volume (million acre-feet)

Minimum release hydrology

Most probable hydrology

Wet hydrology

Figure 1.1 Annual water year release volumes for the three hydrologic scenarios. 

Minimum Release Hydrology

Because the minimum release hydrology scenario contains the same annual release volume in 

every water year, the basic parameters can be easily summarized in a single table for each 

experimental option. To this end, Tables 1.2 – 1.6 contain the volume, minimum and maximum 

daily flows (weekday operations), daily range, and ramping rates for each month, for each 

experimental option. The basic differences between each option and the base, for 8.23 MAF 

water years, are summarized below. 

Option A – Monthly volumes are unchanged from the base. In summer (Jul – Aug) and winter 

(Dec – Feb) seasons, the daily low flow is reduced and the daily peak flow is increased such that 

the daily range in flow is expanded. In Dec – Jan, the daily range is expanded from 8,000 cfs to 

12,000 cfs, in Feb it is expanded from 6,000 cfs to 10,000 cfs, and in Jul – Aug it is expanded 

from 8,000 cfs to 10,000 cfs. In all other months, the daily low, peak, and range are identical to 

base values. The downramp rates are increased from 1,500 cfs/hr to 3,000 cfs/hr in all months; 

upramp rates are unchanged from base. 
120

Option A Variation – This option is similar to Option A. Differences are as follows: 1) 

increased downramp rates (to 4,000 cfs/hr) in Nov – Mar, 2) expanded daily range (from 6,000 

cfs to 8,000 cfs) in Oct, Nov, Mar, Jun, and Sep (expanded ranges not fully realized under 

minimum hydrology in Jun and Sep). Daily minimum and maximum flow are contained in Table 

1.4. 

Option B – Because this option is significantly different from options A, A Variation, and C in 

design, a table of monthly flow parameters strictly comparable to the other options cannot be 

developed, nor can the option be directly compared, month by month, to the base case. Option B 

consists of several blocks with variable levels of steady flows. The original plan was for seven 

years; to make it a 10-year plan, 3 years of ROD MLFF were added to the end of this option. 

Block 1, constituting the first 10 months starting in Oct 2006, consists of equalized monthly 

volumes of moderate fluctuating flows (700,000 acre-feet months, 4,000 cfs daily range). Block 

2, encompassing the next 2 years, consists of 4 month stretches of steady flow (10,000 cfs) in 

late summer/fall (Aug – Nov) and 8 month stretches of moderate fluctuations the rest of the year. 

Block 3, encompassing the next 2 years, extends the steady flows to 8 months (Aug – Mar, also 

at 10,000 cfs) with 4 months of fluctuating flows with higher monthly volumes than the previous 

block (in order to maintain the same annual release volume). Block 4, encompassing the next 2 

years, contains steady flows year-round with monthly volumes adjusted seasonally such that 

summer, fall, and winter (Jul – Mar) are the lowest volumes with increased volume in the spring. 

All fluctuating flow blocks employ ramping rates consistent with ROD MLFF. See Table 1.4 for 

details. 

Option C – Monthly volumes are different from the base in 10 of 12 months (unchanged in only 

Dec – Jan). The volumes are lower in steady flow months (Sep – Oct) and summer (Jul – Aug) 

with the difference being made up with slightly higher volumes in Nov and Feb – Jun. Steady, 

low volume flows occur in Sep – Oct, and potentially in Aug based on triggering criteria in the 

last 5 years of the experiment. The daily low is reduced and daily peak increased in Dec – Feb 

such that the daily range is expanded from 8,000 cfs to 12,000 cfs in Dec – Jan and from 6,000 

cfs to 10,000 cfs in Feb. In months where the volume has been increased, the daily low and peak 

are both increased while maintaining the same daily range as the base. The downramp rate is 

increased to 3,000 cfs/hr in 9 months (Nov – Jul) while remaining at 1,500 cfs/hr in Aug (Sep – 

Oct are steady flows). All fluctuating flow months retain the ROD MLFF upramp rates. 
121

Table 1.2 Base (ROD MLFF) for minimum release hydrology water years 

Monthly 

volume 

(1000 acft)

Daily Low 

Flow (cfs)

Daily Peak 

Flow (cfs)

Daily Range 

(cfs)

Upramp/ 

Downramp 

(cfs/hr)

Oct 600 6000 12000 6000 4000/1500 

Nov 600 6000 12000 6000 4000/1500 

Dec 800 8500 16500 8000 4000/1500 

Jan 800 8500 16500 8000 4000/1500 

Feb 600 7000 13000 6000 4000/1500 

Mar 600 6000 12000 6000 4000/1500 

Apr 600 6500 12500 6000 4000/1500 

May 600 6000 12000 6000 4000/1500 

Jun 650 7500 13500 6000 4000/1500 

Jul 850 9000 17000 8000 4000/1500 

Aug 900 10000 18000 8000 4000/1500 

Sep 630 7000 13000 6000 4000/1500 

Table 1.3 Option A for minimum release hydrology water years 

Monthly 

volume 

(1000 acft)

Daily Low 

Flow (cfs)

Daily Peak 

Flow (cfs)

Daily Range 

(cfs)

Upramp/ 

Downramp 

(cfs/hr)

Oct 600 6000 12000 6000 4000/3000 

Nov 600 6000 12000 6000 4000/3000

Dec 800 6000 18000 12000 4000/3000

Jan 800 6000 18000 12000 4000/3000

Feb 600 5000 15000 10000 4000/3000

Mar 600 6000 12000 6000 4000/3000

Apr 600 6500 12500 6000 4000/3000

May 600 6000 12000 6000 4000/3000

Jun 650 7500 13500 6000 4000/3000

Jul 850 8000 18000 10000 4000/3000

Aug 900 9000 19000 10000 4000/3000

Sep 630 7000 13000 6000 4000/3000

Blue highlights indicate differences from base (ROD MLFF) 
122

Table 1.4 Option A Variation for minimum release hydrology water years 

Monthly 

volume 

(1000 acft)

Daily Low 

Flow (cfs)

Daily Peak 

Flow (cfs)

Daily Range 

(cfs)

Upramp/ 

Downramp 

(cfs/hr)

Oct 600 5000 13000 8000 4000/3000 

Nov 600 5000 13000 8000 4000/4000

Dec 800 5500 17500 12000 4000/4000

Jan 800 6000 18000 12000 4000/4000

Feb 600 5000 15000 10000 4000/4000

Mar 600 5000 13000 8000 4000/4000

Apr 600 6500 12500 6000 4000/3000

May 600 7000 12000 50001 4000/3000

Jun 650 7000 14000 70002 4000/3000

Jul 850 8000 18000 10000 4000/3000

Aug 900 9000 19000 10000 4000/3000

Sep 630 7000 13000 60002 4000/3000

Blue highlights indicate differences from base (ROD MLFF) 

1

 Maximum 6,000 cfs during wetter years 

2

 Maximum 8,000 cfs during wetter years 
123

Table 1.5 Option B for minimum release hydrologic scenario 

 Months 

Monthly 

volume 

(1000 acft) 

Daily 

Low 

Flow 

(cfs)

Daily 

Peak 

Flow 

(cfs)

Daily 

Range 

(cfs)

Upramp/ 

Downramp 

(cfs/hr)

1st block is 10 months of ROD/MLFF with equalized monthly volumes 

Block 1 

(10 months) 

Oct 06 – Jul 07 

all 700 8000 14000 6000 4000/1500 

2nd block is two years with 4 months of steady, 8 months fluctuating each year 

Block 2 Aug – Nov 600 10000 10000 ~ 0 ~ 0 

(2 years) 

Aug 07 – Jul 09 Dec – Jul 730 9500 13500 4000 4000/1500 

3rd block is two years with 8 months of steady, 4 months of fluctuating each year 

Block 3 Aug – Mar 600 10000 10000 ~ 0 ~ 0 

(2 years) 

Aug 09 – Jul 11 Apr – Jul 850 11500 15500 4000 4000/1500 

4th block is two years of year-round steady flow, seasonally adjusted 

Jul – Mar 600 10000 10000 ~ 0 ~ 0 

Apr 1090 18300 18300 ~ 0 ~ 0 

May 860 14000 14000 ~ 0 ~ 0 

Block 4 

(2 years, 2 mo) 

Aug 11 – Sep 

13 Jun 830 14000 14000 ~ 0 ~ 0 

5th block is three years of ROD/MLFF equivalent to Base 

Block 5 

(3 years) 

Oct 13 – Sep 16 

All years equivalent to Base scenario 
124

Table 1.6 Option C for minimum release hydrology water years 

Monthly 

volume 

(1000 acft)

Daily Low 

Flow (cfs)

Daily Peak 

Flow (cfs)

Daily Range 

(cfs)

Upramp/ 

Downramp 

(cfs/hr)

Oct 500 8100 8100 ~ 0 ~ 0 

Nov 650 7000 13000 6000 4000/3000 

Dec 800 6000 18000 12000 4000/3000

Jan 800 6000 18000 12000 4000/3000

Feb 675 6000 16000 10000 4000/3000

Mar 650 7000 13000 6000 4000/3000

Apr 625 7000 13000 6000 4000/3000

May 625 6500 12500 6000 4000/3000

Jun 725 8500 14500 6000 4000/3000

Jul 825 9000 17000 8000 4000/3000

Aug (no 

trigger) 800 8500 16500 8000 4000/1500 

Aug 

(trigger) 800 13100 13100 ~ 0 ~ 0 

Sep 550 9300 9300 ~ 0 ~ 0 

Blue highlights indicate differences from base (ROD MLFF) 

Most Probable Hydrology

Annual water year release volumes exceed 8.23 MAF in 5 out of 10 years for the most probable 

hydrology. During these years, the monthly volumes and daily patterns become dependent on 

current lake levels (Powell and Mead, if equalization is needed) and forecasted inflow volumes 

to Lake Powell which begin to be available on January 1st of each year. The general pattern is for 

monthly volumes to begin to increase (compared to minimum releases) in January and to be 

greatest in the summer, though significant variation can occur depending on lake levels, 

forecasts, and measured Upper Basin runoff. This general pattern and variability are shown in 

Fig. 1.2. 
125

400

600

800

1,000

1,200

1,400

1,600

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

Monthly volume (thousand acre-feet)

Minimum (8.23 MAF)

2008 (9.7 MAF)

2012 (11.9 MAF)

2013 (8.6 MAF)

2014 (9.7 MAF)

2015 (8.4 MAF)

Figure 1.2 Monthly volume patterns (base) for a minimum release year and 5 years of most 

probable hydrology where annual water year volumes exceed 8.23 MAF. 

In order to represent the range of release parameters for the most probable hydrology, tables 

similar to those for the minimum release hydrology were developed for water year 2012. This 

water year has the highest annual volume (11.9 MAF) as well as the highest volume in every 

month for the most probable hydrology. Tables 1.6 – 1.10 contain this information. 

The pattern of change from the minimum hydrology for the base and options A, A Variaion, and 

C are very similar. Monthly volumes begin to increase when forecasts become available on 

January 1st (for all most probable years, volumes in Oct – Dec are equivalent to minimum release 

years). In some years, monthly volumes decrease in the spring to be equivalent to minimum 

years, while in other years (such as 2012), volumes remain elevated above minimum releases 

through the spring. Summer volumes are always greater than minimum releases for annual 

volumes greater than 8.23 MAF. In terms of daily release patterns, increased monthly volumes 

result in increased daily lows and peaks with the same ramping rates and daily range linked to 

the monthly volume (as for minimum release hydrology), until monthly volumes exceed about 

1.5 MAF at which point releases become steady. This is illustrated in Tables 1.6 – 1.8 and 1.10 

where increased volumes, lows, and peaks are seen in Jan – Jun along with increased daily 

ranges (from 6000 to 8000 cfs) in months when volumes are increased to greater than 0.8 MAF. 

In Jul – Sep, when monthly releases reach 1.5 MAF, steady flow releases of 25,000 cfs are 

implemented. 

Option B is more difficult to summarize by selecting a single year because it contains 2-year 

blocks of different operations such that selecting a single year cannot represent the overall 

changes from the minimum release hydrology. For this option, all 10 years must be analyzed 

(excluding the last 3 years which are equivalent to the base). Table 1.8 contains the same 

summary information as Table 1.4 with additions detailing differences from minimum release 

hydrology. Block 1 remains unchanged because WY 2007 is an 8.23 MAF year. Block 2 (4 

months steady, 8 months fluctuating) contains increased volume in Jun – Sep 2008; during these 
126

months, daily lows and peaks are increased with daily range and ramping rates maintained for 

fluctuating months. Block 3 (8 months steady, 4 months fluctuating) remains unchanged because 

water years 2009–11 are 8.23 MAF. Block 4 (all steady flows) contains increased volumes in 11 

out of 24 months, mostly in WY 2012; when volumes are increased, the steady flow is simply 

increased to pass the required monthly volume. 

Table 1.6 Base scenario (ROD MLFF) for most probable WY 2012 (11.9 MAF) 

Monthly 

volume 

(1000 acft)

Daily Low 

Flow (cfs)

Daily Peak 

Flow (cfs)

Daily Range 

(cfs)

Upramp/ 

Downramp 

(cfs/hr)

Oct 600 6000 12000 6000 4000/1500 

Nov 600 6000 12000 6000 4000/1500 

Dec 800 8500 16500 8000 4000/1500 

Jan 970 11500 19500 8000 4000/1500 

Feb 900 11500 19500 8000 4000/1500 

Mar 770 9000 15000 6000 4000/1500 

Apr 810 9500 17500 8000 4000/1500 

May 880 10000 18000 8000 4000/1500 

Jun 1120 15000 23000 8000 4000/1500 

Jul 1470 25000 25000 ~ 0 ~ 0

Aug 1540 25000 25000 ~ 0 ~ 0

Sep 1490 25000 25000 ~ 0 ~ 0

Blue highlight indicates difference from 8.23 MAF years 

Table 1.7 Option A for most probable WY 2012 (11.9 MAF) 

Monthly 

volume 

(1000 acft)

Daily Low 

Flow (cfs)

Daily Peak 

Flow (cfs)

Daily Range 

(cfs)

Upramp/ 

Downramp 

(cfs/hr)

Oct 600 6000 12000 6000 4000/3000 

Nov 600 6000 12000 6000 4000/3000 

Dec 800 6000 18000 12000 4000/3000 

Jan 970 9000 21000 12000 4000/3000 

Feb 900 10000 20000 10000 4000/3000 

Mar 770 9000 15000 6000 4000/3000 

Apr 810 9500 17500 8000 4000/3000 

May 880 10000 18000 8000 4000/3000 

Jun 1120 15000 23000 8000 4000/3000 

Jul 1470 25000 25000 ~ 0 ~ 0

Aug 1540 25000 25000 ~ 0 ~ 0

Sep 1490 25000 25000 ~ 0 ~ 0

Blue highlight indicates difference from 8.23 MAF years 
127

Table 1.8 Option A Variation for most probable WY 2012 (11.9 MAF) 

Monthly 

volume 

(1000 acft)Daily Low 

Flow (cfs)

Daily Peak 

Flow (cfs)

Daily Range 

(cfs)

Upramp/ 

Downramp 

(cfs/hr)

Oct 600 5000 13000 8000 4000/3000 

Nov 600 5000 13000 8000 4000/4000 

Dec 800 5500 17500 12000 4000/4000 

Jan 970 9000 21000 12000 4000/4000 

Feb 900 10000 20000 10000 4000/4000 

Mar 770 8000 16000 8000 4000/4000 

Apr 810 9500 17500 8000 4000/3000 

May 880 10000 18000 8000 4000/3000 

Jun 1120 14500 22500 8000 4000/3000 

Jul 1470 25000 25000 ~ 0 ~ 0

Aug 1540 25000 25000 ~ 0 ~ 0

Sep 1490 25000 25000 ~ 0 ~ 0

Blue highlight indicates difference from 8.23 MAF years 

Table 1.9 Option B for most probable hydrologic scenario 

 Months 

Monthly 

volume 

(1000 

ac-ft) 

Daily 

Low 

Flow 

(cfs)

Daily 

Peak 

Flow 

(cfs)

Daily 

Range 

(cfs)

Upramp/ 

Downramp 

(cfs/hr)

1st block is 10 months of ROD/MLFF with equalized monthly volumes 

Block 1 

(10 months) 

Oct 06 – Jul 07 

all 700 8000 14000 6000 4000/1500 

2nd block is two years with 4 months of steady, 8 months fluctuating each year 

Aug – Nov 07 600 10000 10000 ~ 0 ~ 0 

Dec 07–May 08 730 9500 13500 4000 4000/1500 

Jun 08 820 11500 15500 4000 4000/1500 

Jul 08 1160 16500 20500 4000 4000/1500 

Aug 08 1160 18800 18800 ~ 0 ~ 0 

Sep 08 1010 17000 17000 ~ 0 ~ 0 

Oct – Nov 08 600 10000 10000 ~ 0 ~ 0 

Block 2 

(2 years) 

Aug 07 – Jul 09 

Dec 08 – Jul 09 730 9500 13500 4000 4000/1500 
128

3rd block is two years with 8 months of steady, 4 months of fluctuating each year 

Block 3 Aug – Mar 600 10000 10000 ~ 0 ~ 0 

(2 years) 

Aug 09 – Jul 11 Apr – Jul 850 11500 15500 4000 4000/1500 

4th block is two years of year-round steady flow, seasonally adjusted 

Jul – Dec 11 600 10000 10000 ~ 0 ~ 0 

Jan 12 790 13000 13000 ~ 0 ~ 0 

Feb 12 880 15300 15300 ~ 0 ~ 0 

Mar 12 780 12700 12700 ~ 0 ~ 0 

Apr 12 1290 22000 22000 ~ 0 ~ 0 

May 12 1130 18500 18500 ~ 0 ~ 0 

Jun 12 1300 22000 22000 ~ 0 ~ 0 

Jul 12 1240 20300 20300 ~ 0 ~ 0 

Aug 12 1250 20400 20400 ~ 0 ~ 0 

Sep 12 1450 24500 24500 ~ 0 ~ 0 

Oct – Dec 12 600 10000 10000 ~ 0 ~ 0 

Jan 13 800 13000 13000 ~ 0 ~ 0 

Feb – Mar 13 600 10000 10000 ~ 0 ~ 0 

Apr 13 1150 19500 19500 ~ 0 ~ 0 

May 13 860 14000 14000 ~ 0 ~ 0 

Block 4 

(2 years, 2 mo) 

Aug 11 – Sep 

13 

Jun 13 830 14000 14000 ~ 0 ~ 0 

5th block is three years of ROD/MLFF equivalent to Base 

Block 5 

(3 years) 

Oct 13 – Sep 16 

All years equivalent to Base scenario 

Blue highlight indicates difference from minimum release hydrology scenario 
129

Table 1.10 Option C for most probable WY 2012 (11.9 MAF) 

Monthly 

volume 

(1000 acft)

Daily Low 

Flow (cfs)

Daily Peak 

Flow (cfs)

Daily Range 

(cfs)

Upramp/ 

Downramp 

(cfs/hr)

Oct 500 8100 8100 ~ 0 ~ 0 

Nov 650 7000 13000 6000 4000/3000 

Dec 800 6000 18000 12000 4000/3000 

Jan 970 9000 21000 12000 4000/3000 

Feb 980 11500 21500 10000 4000/3000 

Mar 820 9000 17000 8000 4000/3000 

Apr 830 10000 18000 8000 4000/3000 

May 900 10000 18000 8000 4000/3000 

Jun 1200 16000 24000 8000 4000/3000 

Jul 1440 25000 25000 ~ 0 ~ 0 

Aug (no 

trigger) 1440 25000 25000 ~ 0 ~ 0 

Aug 

(trigger) 1440 23000 23000 ~ 0 ~ 0 

Sep 1400 24000 24000 ~ 0 ~ 0 

Blue highlight indicates difference from 8.23 MAF years 

Wet Hydrology

Annual water year release volumes exceed 8.23 MAF in 9 out of 10 years for the wet hydrology. 

As with the most probable hydrology, monthly volumes and daily patterns become dependent on 

lake levels and forecasted inflow volumes during these years. There is even greater variability in 

monthly volume patterns for the wet hydrology, as shown in Fig. 1.3 below. 

400

600

800

1,000

1,200

1,400

1,600

1,800

2,000

2,200

2,400

2,600

2,800

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

Monthly volume (thousand acre-feet)

Minimum (8.23 MAF) 2008 (11.4 MAF)

2009 (8.9 MAF) 2010 (13.2 MAF)

2011 (9.6 MAF) 2012 (11.4 MAF)

2013 (14.1 MAF) 2014 (10.7 MAF)

2015 (8.7 MAF) 2016 (15.0 MAF)

Figure 1.3 Monthly volume patterns (base) for a minimum release year and 9 years of wet 

hydrology where annual water year volumes exceed 8.23 MAF. 
130

As for the most probable hydrology, tables have been developed for the highest volume water 

year (2016, 15.0 MAF) for the base and SPG options A, A Variation, and C. Tables 1.11 – 1.14 

contain this information. The basic difference from minimum releases are the same as those 

detailed for WY 2012 of the most probable hydrology, except that summer volumes in wet WY 

2016 are higher such that in Jun – Jul the releases are steady and at or above powerplant capacity 

(33,000 cfs). Another significant difference between wet and most probable hydrology is that 

wet monthly volumes in Oct – Dec of WYs 2014 and 2015 exceed minimum releases; volumes 

never exceed minimums in these months during most probable. These higher volume releases in 

Oct – Dec occur only during nearly full reservoir conditions in order to meet January 1 target of 

3,684 feet (16 feet from full pool) at Lake Powell. 

No similar table has been developed for option B wet hydrology, simply because of the sheer 

size of the table that would be required to convey all of the differences from the minimum 

release hydrology. Monthly volumes follow generally the same pattern as for the other options 

when annual volumes exceed 8.23 MAF. Because option B contains a prevalence of steady 

flows, most often when monthly volumes are increased the steady flow is simply increased 

accordingly to pass the required volume. During fluctuating months, daily lows and peaks are 

increased while maintaining ramping rates and daily ranges up to 1.5 MAF at which point steady 

flows ensue (same as other options). For the first 7 years of wet hydrology for this option, 

monthly volumes exceed the minimum releases in about 55% of months, typically in Jan – Sep. 

Table 1.11 Base scenario (ROD MLFF) for wet WY 2016 (15.0 MAF) 

Monthly 

volume 

(1000 acft)

Daily Low 

Flow (cfs)

Daily Peak 

Flow (cfs)

Daily Range 

(cfs)

Upramp/ 

Downramp 

(cfs/hr)

Oct 600 6000 12000 6000 4000/1500 

Nov 600 6500 12500 6000 4000/1500 

Dec 800 8500 16500 8000 4000/1500 

Jan 1040 13000 21000 8000 4000/1500 

Feb 1040 14000 22000 8000 4000/1500 

Mar 890 10500 18500 8000 4000/1500 

Apr 1210 16000 24000 8000 4000/1500 

May 1400 21000 25000 4000 4000/1500 

Jun 2670 45000 45000 ~ 0 ~ 0

Jul 2030 33000 25000 ~ 0 ~ 0

Aug 1510 25000 25000 ~ 0 ~ 0

Sep 1160 15500 23500 8000 4000/1500 

Blue highlight indicates difference from 8.23 MAF years 
131

Table 1.12 Option A for wet WY 2016 (15.0 MAF) 

Monthly 

volume 

(1000 acft)

Daily Low 

Flow (cfs)

Daily Peak 

Flow (cfs)

Daily Range 

(cfs)

Upramp/ 

Downramp 

(cfs/hr)

Oct 600 6000 12000 6000 4000/3000 

Nov 600 6000 12000 6000 4000/3000 

Dec 800 6000 18000 12000 4000/3000 

Jan 1040 10000 22000 12000 4000/3000 

Feb 1040 13000 23000 10000 4000/3000 

Mar 900 10000 18000 8000 4000/3000 

Apr 1210 16000 24000 8000 4000/3000 

May 1400 21000 25000 4000 4000/3000 

Jun 2670 45000 45000 ~ 0 ~ 0

Jul 2030 33000 33000 ~ 0 ~ 0

Aug 1510 25000 25000 ~ 0 ~ 0

Sep 1160 15000 23000 ~ 0 ~ 0

Blue highlight indicates difference from 8.23 MAF years 

Table 1.13 Option A Variation for wet WY 2016 (15.0 MAF) 

Monthly 

volume 

(1000 acft)Daily Low 

Flow (cfs)

Daily Peak 

Flow (cfs)

Daily Range 

(cfs)

Upramp/ 

Downramp 

(cfs/hr)

Oct 600 5000 13000 8000 4000/3000 

Nov 600 5000 13000 8000 4000/4000 

Dec 800 5500 17500 12000 4000/4000 

Jan 1040 10000 22000 12000 4000/4000 

Feb 1040 12500 22500 10000 4000/4000 

Mar 900 10500 18500 8000 4000/4000 

Apr 1210 16000 24000 8000 4000/3000 

May 1400 21000 25000 4000 4000/3000 

Jun 2670 45000 45000 ~ 0 ~ 0

Jul 2030 33000 33000 ~ 0 ~ 0

Aug 1510 25000 25000 ~ 0 ~ 0

Sep 1160 15000 23000 8000 4000/3000 

Blue highlight indicates difference from 8.23 MAF years 
132

Table 1.14 Option C for wet WY 2016 (15.0 MAF) 

Monthly 

volume 

(1000 acft)

Daily Low 

Flow (cfs)

Daily Peak 

Flow (cfs)

Daily Range 

(cfs)

Upramp/ 

Downramp 

(cfs/hr)

Oct 500 8100 8100 ~ 0 ~ 0 

Nov 650 7000 13000 6000 4000/3000 

Dec 800 6000 18000 12000 4000/3000 

Jan 1040 10000 22000 12000 4000/3000 

Feb 1110 14000 24000 10000 4000/3000 

Mar 950 11000 19000 8000 4000/3000 

Apr 1240 16500 24500 8000 4000/3000 

May 1500 25000 25000 ~ 0 ~ 0

Jun 2740 45000 45000 ~ 0 ~ 0

Jul 2020 33000 33000 ~ 0 ~ 0 

Aug (no 

trigger) 1410 25000 25000 ~ 0 ~ 0 

Aug 

(trigger) 1410 25000 25000 ~ 0 ~ 0 

Sep 1080 18000 18000 ~ 0 ~ 0 

Blue highlight indicates difference from 8.23 MAF years 
133

APPENDIX C: Glen Canyon Dam Release 

Temperature Modeling 

We used a reservoir hydrodynamic model to analyze the five SPG scenarios (BASE, A, A 

Variation, B and C) for Lake Powell. The calibrated model provided release water temperature 

for each of the scenarios. The model we used was U.S. Army Corps of Engineers' (USACE) CEQUAL-W2 (W2; Cole and Wells 2000). 

Background Information on the Model

The W2 model is a two dimensional, longitudinal/vertical hydrodynamic and water quality 

model. Because the model assumes lateral homogeneity, it was best suited for relatively long and 

narrow waterbodies like Lake Powell (Cole 2003). The water in the model was routed through a 

computational grid of cells that represent a waterbody. Each cell was a completely mixed reactor 

for each time step. Time steps vary from seconds to minutes depending on the volume of water 

to be routed in each step. Therefore, this type of modeling is very computer time consuming. The 

bathymetry file for Lake Powell is also extremely complex, which further increases the 

computation time for each run. 

The Lake Powell W2 bathymetry had 9 branches, 90 segments, and 97 layers. All layers are 1.75 

meters thick. The branches represent the following channels and/or bays (Figure 1): 

• Main (Colorado River) channel 

• Bullfrog Bay 

• Escalante River channel 

• San Juan River channel 

• Rock Creek Bay 

• Last Chance Bay 

• Warm Creek Bay 

• Navajo Canyon 

• Wahweap Bay 
134

Figure C.1: Lake Powell Bathymetry: A) branches; B) cross section of a segment; and C) 

reservoir side profile. 

Our model used historical meteorological, hydrological and physicochemical data from the 

period 1990–2005 for calibration. This was the only period that contained all empirical data 

required by the model, including hourly meteorology, river flows, and reservoir water 

temperatures. This period captures a wide range of reservoir elevations, from full pool to the 

lowest elevation since the filling of Lake Powell in 1980. 

The model was calibrated to reservoir profiles and release temperatures over a16 year time 

period (1990–2005). The model reproduces most of the variables within error ranges of less than 

5% over the entire reservoir and period. Figures C.2–C.6 illustrate model calibration of 

temperature profiles at different locations and time of year in the reservoir. 

A 

C 

B 
135

Figure C.2: Lake Powell, Wahweap 2003 Temperature Calibration Profiles 

Figure C.3: Lake Powell, Wahweap 2004 Temperature Calibration Profiles 
136

Figure C.4: Lake Powell, Oak Canyon 2003–2004 Temperature Calibration Profiles 

Figure C.5: Lake Powell, Escalante Confluence 2003–2004 Temperature Calibration 

Profiles 
137

Figure C.6: Lake Powell, Cha Canyon 2003–2004 Temperature Calibration Profiles 

The mean error of the calibrated release temperature was 0.4°C as shown on Figure C.7. 
138

Figure C.7: Glen Canyon Dam Discharge Temperature Calibration 

SPG Model Scenario Assumptions

We used this calibrated model to analyze the SPG scenarios with three hydrology traces (wet, 

most probable, dry) from the Colorado River Simulation System (CRSS) model. We matched 

historic meteorological data to go with the three CRSS hydrology traces and it was based on the 

inflow volume of each year. Therefore the inflow water temperatures into Lake Powell were the 

same as the year we selected the meteorological data. 

We also assumed (1) the TCD would be operating 2 units out of a potential 8 units on a yearround basis, (2) the BASE scenario had no TCD operation, (3) the other four experimental 

options contained TCD operation in the last 5 years of the10- year period, (4) each of the 2 TCD 

had a capacity to release 4,000 cfs, (4) reservoir elevations within which the TCD could be active 

were between 3,700–3,520 ft , (5) a 30-ft submergence above each TCD intake was set to avoid 

surface vortex formation, as required for the protection of turbine runners, and (6) when reservoir 

elevations dropped below 3,520 ft, releases were made from the original penstock outlets at 

elevation 3,476 ft. 
139

References 

Cole, T., and S. Wells. 2000. CE-QUAL-W2: a two-dimensional, 

laterally averaged, hydrodynamic and water quality model, version 3.1. 

User Manual, Instruction Report EL-02-1 submitted to U.S. Army Corps of 

Engineers, Washington DC. 

Cole, T., and S. Wells. 2003 (Revised). CE-QUAL-W2: a two-dimensional, 

laterally averaged, hydrodynamic and water quality model, version 3.1. 

User Manual, Instruction Report EL-02-1 submitted to U.S. Army Corps of 

Engineers, Washington DC. 
140

Appendix D: Mainstem Temperature Modeling 

A.1 INTRODUCTION 

Water temperature is one of the most important drivers of biological productivity in the Colorado 

River ecosystem (CRE). Temperature influences all biological and chemical reactions and is one 

of the primary controls on the productivity of the aquatic food base and the success of native 

fishes within the CRE. Native fish species, including humpback chub, evolved in a seasonally 

warm and turbid riverine environment. The temperature regime of that environment has been 

drastically altered by the closure of Glen Canyon Dam (GCD).

 

The closure of GCD transformed a seasonally warm river into a consistently cold river owing to 

the hypolimnetic releases associated with the penstock withdrawal structures. Prior to dam 

closure, mean water temperature at Lees Ferry was 14°C, ranging from 0°C to 27°C. From 

1973–2003, GCD release temperatures averaged 9.3°C, with fluctuations between 7°C and 12°C. 

Since 2003, GCD release temperatures have warmed considerably as a result of a substantial 

water level drop in Lake Powell. In July of 2005, mean daily release temperatures reached 

13.6°C and a maximum release temperature of 16.3°C in October, 2005 (Vernieu and others, 

2005). However, release temperatures in 2006 have trended towards colder releases similar to 

those of 2003 (Bill Vernieu, personal communication, 2006). Regardless of the impacts of future 

climate and hydrological conditions on GCD release temperatures, the temperature regime of the 

Colorado River below GCD will likely remain markedly different from predam patterns under 

the current operating schedule. 

A.2 PURPOSE AND SCOPE 

The objective of this experimental options assessment is to evaluate four long-term experimental 

flow options with respect to desired downstream water temperature regimes thought to be most 

beneficial to native biological resources, including native fish and the aquatic food base, 

identified in the GCDAMP ecosystem goals. For a summary of the experimental options refer to 

chapter 2 and appendix B. 

We applied our recently developed mainstem water temperature model to simulate the fate of 

flow releases stipulated in the four experimental flow options. These simulations provide a 

quantitative comparison of the effects of variable flow regimes and release temperatures on the 

fate of the mainstem thermal environment, complementing the current state of knowledge. This 

appendix summarizes the calibration, validation and application of the unsteady transport model 

used in the mainstem temperature simulations. 
141

A.3 METHODS 

Mainstem water temperatures were simulated for BASE operations and each experimental option 

using a sequence of numerical models. First, monthly volumes were estimated for the 10-year 

period for BASE operations and all options using the BoR Colorado River Simulation System 

(CRSS) model (see appendix A for documentation). Hourly time series of dam releases were 

then generated by WAPA using CRSS monthly volumes as input into the GT-Max model (see 

appendix E for documentation). BoR then used these hourly flows to estimate GCD release 

temperatures using the CE-QUAL-W2 water quality model, including the operation of 2 units on 

a proposed Temperature Control Device (TCD) for WY 2012–16 for all four experimental 

options (BASE operations were not modeled) as described in section A.3.1 below. The 

downstream mainstem water temperature simulations were then conducted using the WAPA 

generated hourly flow releases and the BoR generated release temperatures as upstream 

boundary conditions for downstream temperature model (described in section A.3.2 below). 

A.3.1 Lake Powell 

Lake Powell hydrodynamic and water temperature modeling was conducted by BoR Salt Lake 

City staff. The methods and results are presented separately in appendix C. 

A.3.2 Downstream from Glen Canyon Dam - Mainstem 

An unsteady, one-dimensional water temperature model was developed for the 240-mile 

Colorado River (CR) mainstem reach from GCD (RM -15.6) to the Diamond Creek confluence 

(RM 226). The model employs the unsteady-flow model (UNSTEADY) of Wiele and Smith 

(1996) and Wiele and Griffin (1997) to simulate mainstem hydrodynamics and the enhanced 

Branched Lagrangian Transport Model (BLTM) of Jobson and Schoellhamer (1993) and Jobson 

(1997), to simulate water temperature dynamics. UNSTEADY is a reach-averaged model of 

diurnal discharge wave propagation developed specifically for the CR through the Grand Canyon 

(GC) and has been successfully utilized in a number of research applications in the GC. The 

BLTM model solves the one-dimensional advective dispersion equation by using a Lagrangian 

reference frame in which the computational nodes move with the flow. The BLTM model has 

found wide use throughout the U. S. Geological Survey (USGS) and elsewhere to simulate the 

fate and transport of conservative and non-conservative water quality constituents. Model 

development consisted of linking the flow and transport models and calibration and validation 

using data from the Grand Canyon Monitoring and Research Center mainstem temperature 

monitoring program. 

A.3.2.1 Calibration and Validation 

The model was calibrated and validated for two separate time periods (calibration - calendar year 

(CY) 2000; validation – CY 2005) at an hourly time step. CY 2000 was selected for calibration 
142

because it encompassed a wide range of discharge patterns (Low Summer Steady Flow 

experiment and peak discharges above 30,000 cfs) and also contained consistent water 

temperature records at the majority of the mainstem monitoring sites. CY 2005 was selected for 

validation because it had the highest GCD release temperatures ever recorded as well as 

alternating blocks of steady and fluctuating fall flows. 

The data requirements to successfully run the UNSTEADY and BLTM models were as follows. 

Hourly measurements of discharge and release temperatures at GCD were used as the upstream 

boundary conditions. UNSTEADY-generated parameters at equally spaced computational nodes, 

including discharge, top width, and cross-sectional area, were used as hydrodynamic inputs into 

the BLTM model. Longitudinal dispersion coefficients derived by Graf (1995) using dye tracer 

methods were implemented at corresponding computational nodes. The BLTM model uses 

equilibrium temperatures to calculate the energy exchange between the atmosphere and the water 

surface. This approach utilized meteorological data from the Page, AZ cooperative weather 

station including daily maximum and minimum air temperature, the times of occurrence of these 

temperatures, and average daily wind speed to calculate equilibrium temperatures. 

Hourly water temperature data from 6 mainstem sites was used to compare model predictions to 

observed temperatures. The model was then calibrated to these 6 sites by systematically 

adjusting the mass-transfer and free convection parameters within BLTM's wind function to 

minimize the root mean square error (RMSE) of the predictions. The model was further refined 

by adjusting the calculated equilibrium temperatures on a seasonal basis to provide a better fit to 

the observed data. The model was then validated for CY 2005 without further adjustment of the 

calibration parameters. Summary statistics are provided in table A.1 for both the calibration and 

validation periods at 6 river locations. The RMSEs for the calibration and validation time periods 

are comparable to each other, indicating the model is not overly sensitive to the calibration 

parameters, and typically less than 1oC, increasing downstream as expected. 
143

Table A.1. Error terms for predicted vs. observed water temperatures at 6 monitoring locations 

for 2000 and 2005. ME = mean error, MAE = mean absolute error, and RMSE = root mean 

square error. 

Site 2000 - Calibration 2005 - Validation 

ME (°C) MAE (°C) RMSE (°C) ME (°C) MAE (°C) RMSE (°C) 

RM 0 -0.02 0.25 0.32 -0.08 0.21 0.27 

RM 30 0.16 0.25 0.33 -0.23 0.34 0.44 

RM 61 0.24 0.38 0.48 -0.23 0.41 0.53 

RM 87 0.53 0.60 0.73 -0.03 0.46 0.57 

RM 166 0.70 0.84 0.98 0.07 0.59 0.72 

RM 226 1.12 1.16 1.21 0.38 0.70 0.86 

A.3.2.2 Applications, Results, and Discussion 

Model simulations were performed for mainstem water temperatures over the 10-year period for 

each of the experimental options (including BASE operations) and hydrologic scenarios. BASE 

operations, four experimental options, and three hydrologic scenarios for each option resulted in 

15 total simulations. 

The effects of the temperature control device (TCD), 2 units out of 8 possible, which is a 

component of all experimental options (but not BASE operations), were evaluated by analyzing 

the first 5 and last 5 years of the simulation period separately, since the TCD comes online for all 

options halfway through the 10-year period. In this way, the experimental options can be 

compared to BASE operations (and each other) during these separate 5-year periods, but 

comparisons across the periods are not appropriate because of hydrologic and meteorological 

differences. We compare model simulation results for the first 5 years to evaluate differences 

between BASE operations and options (without a TCD), and use the last 5 years to evaluate the 

effects of the TCD. 

Several metrics were computed to compare BASE operations and experimental options. For each 

5-year period, we computed the average temperature and the percentage of time the temperatures 

exceed 16 oC for 5 mainstem locations: at the dam and river miles 31, 65, 127, and 225 (termed 

Release, RM31, RM65, RM127, and RM225, respectively, in the plots below). The 16 oC 

threshold was chosen because it is thought to have significance for mainstem native fish 

spawning (Hamman, 1982; Marsh, 1985). The locations were chosen to bracket the model 
144

domain (Release and RM225) and coincide with known congregations of humpback chub 

(RM31, RM65, and RM127). 

The model simulation results are presented in a series of plots below. Each figure contains nine 

plots in a 3-by-3 matrix, with results from the first 5 years in the left column and the last 5 years 

in the right column. Results for minimum release hydrology (8.23 maf) are in the top row, most 

probable hydrology in the middle row, and wet hydrology in the bottom row. Figure A.1 shows 

average temperatures and figure A.2 shows the percentage of time the temperature exceeded 

16oC, for all five mainstem locations. Figures A.3 and A.4 contain the same information for a 

single site, RM65, broken down on a monthly basis in order to evaluate seasonal variability. 
145

9

10

11

12

13

14

15

16

Release RM31 RM65 RM127 RM225

Average mainstem water

temperature over first 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

9

10

11

12

13

14

15

16

Release RM31 RM65 RM127 RM225

Average mainstem water

temperature over last 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

9

10

11

12

13

14

15

16

Release RM31 RM65 RM127 RM225

Average mainstem water

temperature over first 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

9

10

11

12

13

14

15

16

Release RM31 RM65 RM127 RM225

Average mainstem water

temperature over last 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

9

10

11

12

13

14

15

16

Release RM31 RM65 RM127 RM225

Average mainstem water

temperature over first 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

9

10

11

12

13

14

15

16

Release RM31 RM65 RM127 RM225

Average mainstem water

temperature over last 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

Figure A.1 Average mainstem water temperatures at 5 locations for the first 5 years (left column) and last 5 

years (right column) of the simulation period for minimum release (top row), most probable (middle 

row), and wet (bottom row) hydrology. 
146

0

10

20

30

40

50

60

70

80

90

100

Release RM31 RM65 RM127 RM225

Percent of time over first 5 years that 

mainstem water temperature exceeds 16 o

C

Base

Option A

Option A variation

Option B

Option C

0

10

20

30

40

50

60

70

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Release RM31 RM65 RM127 RM225

Percent of time over last 5 years that 

mainstem water temperature exceeds 16 o

C

Base

Option A

Option A variation

Option B

Option C

0

10

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40

50

60

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Release RM31 RM65 RM127 RM225

Percent of time over first 5 years that 

mainstem water temperature exceeds 16 o

C

Base

Option A

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Option B

Option C

0

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Release RM31 RM65 RM127 RM225

Percent of time over last 5 years that 

mainstem water temperature exceeds 16 o

C

Base

Option A

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Option B

Option C

0

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Release RM31 RM65 RM127 RM225

Percent of time over first 5 years that 

mainstem water temperature exceeds 16 o

C

Base

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Option B

Option C

0

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80

90

100

Release RM31 RM65 RM127 RM225

Percent of time over last 5 years that 

mainstem water temperature exceeds 16 o

C

Base

Option A

Option A variation

Option B

Option C

Figure A.2 Percentage of time mainstem water temperatures exceed 16 oC at 5 locations for the first 5 years (left 

column) and last 5 years (right column) of the simulation period for minimum release (top row), 

most probable (middle row), and wet hydrology (bottom row). 
147

6

8

10

12

14

16

18

20

22

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

Average mainstem water

temperature over first 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

6

8

10

12

14

16

18

20

22

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

Average mainstem water

temperature over last 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

6

8

10

12

14

16

18

20

22

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

Average mainstem water

temperature over first 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

6

8

10

12

14

16

18

20

22

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

Average mainstem water

temperature over last 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

6

8

10

12

14

16

18

20

22

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

Average mainstem water

temperature over first 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

6

8

10

12

14

16

18

20

22

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

Average mainstem water

temperature over last 5 years ( oC)

Base

Option A

Option A variation

Option B

Option C

Figure A.3 Average mainstem water temperatures, by month, at RM65 for the first 5 years (left column) and last 

5 years (right column) of the simulation period for minimum release (top row), most probable 

(middle row), and wet hydrology (bottom row). 
148

0

10

20

30

40

50

60

70

80

90

100

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

Percent of time over first 5 years that 

mainstem water temperature exceeds 16 o

C

Base

Option A

Option A variation

Option B

Option C

0

10

20

30

40

50

60

70

80

90

100

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

Percent of time over last 5 years that 

mainstem water temperature exceeds 16 o

C

Base

Option A

Option A variation

Option B

Option C

0

10

20

30

40

50

60

70

80

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

Percent of time over first 5 years that 

mainstem water temperature exceeds 16 o

C

Base

Option A

Option A variation

Option B

Option C

0

10

20

30

40

50

60

70

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

Percent of time over last 5 years that 

mainstem water temperature exceeds 16 o

C

Base

Option A

Option A variation

Option B

Option C

0

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20

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

Percent of time over first 5 years that 

mainstem water temperature exceeds 16 o

C

Base

Option A

Option A variation

Option B

Option C

0

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

Percent of time over last 5 years that 

mainstem water temperature exceeds 16 o

C

Base

Option A

Option A variation

Option B

Option C

Figure A.4 Percentage of time mainstem water temperatures exceed 16oC, by month, at RM65 for the first 5 

years (left column) and last 5 years (right column) of the simulation period for minimum release (top 

row), most probable (middle row), and wet hydrology (bottom row). 

Examination of the plots contained in figures A.1 – A.4 reveals that the 2-unit TCD and 

hydrologic conditions tend to have greater influences on mainstem water temperatures than the 

experimental options. In all of the plots, the simulated temperatures for the experimental options 

tend to group closely together; differences from BASE operations are apparent during the last 5 

years (due to TCD); differences across the board for all options are apparent when the hydrology 

changes. These results do not come as a surprise given the dye studies of Graf (1995) who 

showed that steady and fluctuating flows of the same overall release volume result in nearly 
149

equivalent water velocities, which are a primary control on downstream mainstem temperatures 

because mean velocity determines the time available for water to warm (or cool) through surface 

heat exchange with the atmosphere. The results indicate that the differences between the options, 

in terms of monthly volumes, are not significant enough for the model to resolve the differences 

in water temperature, given the uncertainty in the calculations. 

In order to evaluate the experimental options in comparison to the TCD and the hydrology, we 

computed the range in average water temperatures between the options for first 5 years (no TCD) 

and last 5 years (TCD) for the most probable hydrology, as well as the range in average water 

temperatures between the three hydrologic scenarios for the base case over all 10 years. The 

range is defined as the difference between the maximum average temperature and minimum 

average temperature. For example, if all options result in the exact same average temperature at a 

given location then the range is zero, or if all hydrologic scenarios result in the same average 

temperature then the range is zero. By performing these calculations, it’s possible to isolate the 

effects of the experimental options (range over options, first 5 years), the effects of the TCD 

(range over options, last 5 years), and the effects of hydrology (range over hydrologic scenarios, 

base case, all 10 years). The results of these calculations, averaged over the three hydrologic 

scenarios, are presented in figure A.5. 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Release RM31 RM65 RM127 RM225

Range in mainstem water temperatures ( oC)

Between all options without TCD

Between all options with TCD

Between hydrologic scenarios

0

1

2

3

4

5

6

7

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

Range in mainstem water temperatures at RM65 ( oC)

Between all options without TCD

Between all options with TCD

Between hydrologic scenarios

Figure A.5 Ranges in average mainstem water temperatures for 5 mainstem locations (left) and at RM65 (right). 

Red lines are the ranges between options (including BASE operations) for the first 5 years and thus 

show the maximum differences between the various options. Blue lines are the ranges between 

options for the last 5 years and thus show the average effect of the TCD. These ranges are both based 

on the most probable hydrology. Green lines are the ranges between the three hydrologic scenarios 

for BASE operations, over the entire 10 years (no TCD), and thus illustrate the effects of hydrology. 

The results shown in figure A.5 provide a good summary of the model simulation results. First, 

focusing on the first 5 years where the TCD is not in operation (red lines), it is seen that the 

differences between the experimental options are, on average, less than 0.6 oC at all 5 mainstem 

sites, and almost always less than 1oC at RM65 for all months. Given the calibration results 

presented in section A.3.2.1, it must be concluded that differences between the experimental 

options are almost exclusively within the uncertainty of the model calculations. A potential 

exception to this conclusion is apparent in May and June, where the differences between options 

can exceed 1oC at RM65 because of the high volume spring releases proposed in Option B which 

inhibit downstream warming during this time of year. Even these differences, however, are quite 
150

small in comparison to the range in temperatures realized through operation of the TCD (blue 

lines in figure A.5). For example, at RM65, the TCD leads to about 5 oC of warming (over the 

base case) during the summer and fall months such that temperatures exceed 16oC during these 

months nearly 100% of the time for the minimum release hydrologic scenario. Finally, figure 

A.5 also indicates that differences between the experimental options are typically less than 

differences between the hydrologic scenarios, which result from changes in release temperatures 

due to Lake Powell elevations and decreased downstream warming in summer due to high 

volume releases. 

References

Graf, J. B., 1995. Measured and predicted velocity and longitudinal dispersion at steady and 

unsteady flow, Colorado River, Glen Canyon Dam to Lake Mead. American Water 

Resources Association, Water Resources Bulletin, 31(2), pp. 265–281. 

Hamman, R. L., 1982. Spawning and culture of humpback chub. Progressive Fish-Culturist, 

44(4), pp. 213–216 

Jobson, H. E., and Schoellhamer, D. H., 1993. User’s manual for a Branched Lagrangian 

Transport Model: U.S. Geological Survey Water Resources Investigations Report 87-

4163, 80 p. 

 

Jobson, H. E., 1997. Enhancements to the Branched Lagrangian Transport Modeling system: 

U.S. Geological Survey Water-Resources Investigations Report 97-4050, 56 p. 

Marsh, P.C., 1985. Effect of incubation temperature on survival of embryos of native Colorado 

River fishes. Southwest Naturalist, v. 30, pp. 129–140. 

Vernieu, W.S., Hueftle, S.J., and Gloss, S.P., 2005. Water Quality in Lake Powell and the 

Colorado River, in The State of the Colorado River Ecosystem in Grand Canyon: A 

Report of the Grand Canyon Monitoring and Research Center, S.P. Gloss, J.E. Lovich, 

and T.S. Melis, editors, U.S. Geological Survey Circular 1282, pp. 69–85. 

Wiele, S. M., and Smith J. D., 1996. A reach-averaged model of diurnal discharge wave 

propagation down the Colorado River through the Grand Canyon. Water Resources 

Research, 32(5), pp. 1375–1386. 

Wiele, S. M., and Griffin, E. R., 1997. Modifications to one-dimensional model of unsteady flow 

in the Colorado River through the Grand Canyon, Arizona: U.S. Geological Survey 

Water-Resources Investigations Report 97-4046, 17 p. 

 

 
151

APPENDIX E: Economic Analysis 

Economic Analysis of Power System 

Impacts of Glen Canyon Dam Long-Term 

Experimental Options 

October 27, 2006 

S. Clayton Palmer, Sam Loftin, Heather Patno 

Western Area Power Administration 

Colorado River Storage Project Management Center 

 Prepared for the Grand Canyon Monitoring and Research Center 

Abstract 

This report is prepared for the Grand Canyon Monitoring 

and Research Center (GCMRC) to be included with other 

evaluations of four proposed GCD options on biological 

and physical resources. This report analyzes the economic 

impact of the four GCD options on electrical power 

production at Glen Canyon Dam (GCD). The GT Max 

model is used to simulate the operation of GCD. The model 

is respecified to include the GCD operating parameters for 

four options. The results are compared and an economic 

value is attributed to these results. The economic impact of 

the options over the ten-year study period is reported in net 

present value and levelized annual dollars. 
152

Economic Analysis of Power System Impacts of Glen Canyon Dam Long-Term 

Experimental Proposals1

Introduction

The Glen Canyon Adaptive Management Work Group (AMWG) directed the Technical 

Work Group (TWG) to recommend options for a long-term plan for experimentation and 

improvement of downstream resources. The TWG and Grand Canyon Monitoring and 

Research Center (GCMRC) formed a Science Planning Group (SPG) to initiate this task. 

The SPG considered options for further consideration by the Technical Work Group 

(TWG) that include proposed releases from Glen Canyon Dam (GCD) and non-flow 

actions. This report will provide a cursory evaluation of the economic impact of these 

options from changes in GCD operations 

This report is prepared for the Grand Canyon Monitoring and Research Center (GCMRC) 

to be included with other evaluations of the proposed GCD options on biological and 

physical resources. Taken together, the information from GCMRC will assist the TWG 

and AMWG in understanding, evaluating and developing recommendations related to the 

proposed options. 

Purpose:

The purpose of this study is to identify the economic impacts on GCD’s power generation 

from proposed long-term operational changes. 

 

1

 Prepared by S. Clayton Palmer, Sam Loftin and Heather Patno. Western Area Power Administration, 

CRSP - MC 
153

Economic Studies:

This report should be read as an economic analysis – the effect on the regional economy 

from a change in GCD operations. This requires that the authors estimate the change in 

resource use: the addition of generating resources that would have to be brought on line 

by those customers who have long-term firm electric service contracts from the Salt Lake 

Integrated Projects (SLCA/IP)2

, as a result of those options that decrease on-peak GCD 

electrical energy generation. For any option in which on-peak electrical energy is greater 

than the base scenario, the economic impact, or the change in resource use, is the 

postponement of construction of new generating capacity required to meet growing 

electrical demand. 

Study Limitations 

Given the time constraints imposed on this study, simplifying assumptions had to be 

made to reduce the time and effort necessary to provide an analysis. Notwithstanding the 

constraints, however, the authors believe the results are sufficient for the stated purposes. 

The simplifying assumptions are explained below. Other assumptions are described later 

in the document. 

Simplifying Assumptions

 This analysis is limited to CRSP long-term firm electric service customers only. 

While other regional utilities buy and trade with customers who contract for 

CRSP resources, this analysis is simplified by assuming that those affected by 

changed operations at GCD are CRSP customers. 

 

2

 The federal hydroelectric resources that are marketed under the title SLCA/IP comprise the power 

resources of the Colorado River Storage Project. For this report, CRSP power resources will be used to 

refer to the electrical power of the SLCA/IP. 
154

 The supply and demand for electrical capacity and energy are assumed to be 

roughly equal in the market within the Western U.S. region. This means that the 

utilities’ reserve capacity margins are equal to or below the standard margins that 

are used for capacity expansion planning purposes. 

 The analysis assumes that Western passes through impacts due to changed 

operations at GCD to its customers. As an example, if an option results in a 

decrease in GCD marketable capacity, Western expeditiously reduces its 

commitment of capacity to its CRSP customers in proportion to the reduction of 

GCD marketable capacity. 

 With respect to the construction of new electrical generating capacity, if needed 

as a result of a proposed option, this construction takes place immediately and 

only to the extent required. This assumption can be considered reasonable if one 

considers that utilities who are planning new construction construct in “blocks” – 

building more than is immediately required. The utility hopes to sell that which is 

needed above native load to others at the average cost of the new facility. If a 

proposed option reduces GCD marketable capacity, the constructing utility will 

have to devote a larger portion of its new generation construction to meeting 

native load. Thus, construction and purchase plans are assumed to be altered in 

accordance with the impact on marketable capacity of a proposed option. In 

capacity cost calculations, on the advice of it’s power customers, Western has 

assumed that new generation would be either simple-cycle or combined-cycle 

natural gas powerplants, with prices provided by customers that have recently 

constructed such generation. 
155

In this regard, in order to improve the accuracy of the cost of capacity 

replacement, a capacity expansion model would have to be developed. Also, 

specific data would need to be gathered on CRSP customer demand growth and 

existing production facilities 

 For options that result in an increase in marketable capacity, the generation and 

sales assumptions are immediately postponed in direct proportion to the change of 

marketable GCD capacity in response to impact of a proposed option. 

 With respect to the value of electrical energy, the assumption is made that a 

proposed option which results in a reduction of on-peak energy means an increase 

in the production of off-peak energy, since water released through GCD is the 

same regardless of the pattern of release. In any event, the on-peak and off-peak 

electrical energy production is calculated under each option because on-peak 

generation is more valuable than off-peak. 

 Drop v. No Drop: The operational constraints specified by the ROD provide 

some flexibility for Western’s operation to meet its contractual obligations. One 

method that Western has used to increase the water available to generate electrical 

power during on-peak hours during weekdays is to reduce generation during the 

entire day on Sundays. By holding Saturday maximum generation to less than 

weekday maximum generation, Western can further decrease generation (down to 

ROD minimums, for example) during Sundays without violating the maximumdaily-change constraint. This is referred to by Western as “stepping down into 

Sunday” or as a Sunday “Drop”. This type of operation depends on the relative 

difference between weekday and Sunday prices, as it may not make financial 

sense to increase off-peak purchases on Sunday in order to reduce on-peak 
156

purchases during the week. The other type of operation is where Western 

maintains a nearly constant minimum off-peak generation during all days of the 

week, which we refer to as “no Sunday drop” operations. Since there are two 

rather different methods of operation, the analysis has been simplified by using 

only “no drop” operations in the baseline cases. References to the baseline 

through this document and in tables in the results section will be to the “no-drop” 

baseline. 

 Emergency operation of GCD as allowed by the GCD ROD, the GCD operating 

criteria and the Interagency Agreement between Reclamation and Western will 

not be included3

. We presumed that each scheduled GCD release and the 

consequential electrical energy generation is not altered “real time”. 

 We assume that modifications to the operation of the powerplant at GCD translate 

into changed purchase and construction plans for SLCA/IP customers and that the 

new resource “mix” results in additional or lesser expense to the customer utility. 

Never the less, we make no attempt to analyze the possible reduction in electrical 

consumption that results from retail or end use customers through the price 

elasticity of demand. This is beyond the scope of this report. 

The GT MAX Model

The GT MAX Model was developed by Argonne National Laboratory (ANL) under 

contract to the CRSP-MC’s Environmental and Resource Planning Division. The model 

is a computer simulation of weekly operations of all or part of the entire physical 

 

3

 Cite MOU, Reclamation & Western 
157

SLCA/IP, depending upon the user’s preference. Various weeks may be put together to 

produce annual or seasonal data. The model identifies the solution that meets hourly 

demand requirements at minimum cost, subject to a list of restrictions imposed upon it. 

Restrictions include how much water is allowed through GCD over a defined period, 

flow requirements at Flaming Gorge powerplant, or a mandate that no power be sold on 

the spot market for less than an agreed-upon price. 

GT MAX utilizes its objective function to maximize the value of water released through 

the turbines. GT Max minimizes the price paid for each hour of supplemental electrical 

generation available. Supplemental electrical generation is the generation above 

Western’s contractual obligation. GTmax’s objective function is: 

 n m 

min Σ Σ PijXij 

 i=1 j=1 

Where: Xij is the purchase of the ith megawatt of supplemental electrical power 

during the jth hour. 

Pij is the price paid (or sales price) of electrical power of the ith megawatt in the 

jth hour. 

Pursuit of the objective function is subject to a variety of constraints: 1) the water 

available for release through a given SLCA/IP powerplant during a week, 2) restrictions 

on the operation of a powerplant, 3) the technical capabilities of each powerplant, and 4) 

environmental limitations or targets that restrict the operation of the powerplants. The 

model minimizes the objective function subject to these constraints over a specified 

period of time. When actual historic input data are used, the GT MAX Model mimics 

real world SLCA/IP operations. 
158

The GT MAX’s projections do not precisely match actual powerplant operations because 

the computer model has nearly perfect information at all times while SLCA/IP operators 

do not. Operators are also constrained by other, non-modeled, physical constraints, i.e., 

power outages, scheduled maintenance, etc., while the GT MAX is not. 

The user-supplied operating restrictions incorporated into the model include minimum 

and maximum flows, hourly and daily ramping constraints,4 and minimum and maximum 

reservoir water elevations. The GT MAX Model simulates powerplant operations on an 

hourly time step over weekly periods. The model output contains 168 hourly data points 

of powerplant water release and generation. 

Normally, GT MAX is run as a simulation model with all of the larger SLCA/IP units 

simultaneously. For this SPG options analysis, GCD was modeled in isolation. This is so 

the economic impacts of changing GCD operating parameters could be estimated in 

isolation. The GT MAX is capable of, and often does, modify hourly generation at one or 

more of the SLCA/IP powerplants in response to a change at one of the units. The output 

of the GT MAX is hourly generation values for all hours of a week for one week in each 

month. 

Identification of Model Inputs that Constrain the GT Max Objective Function 

Common to All Cases 

The GCMRC described the options in order for the authors 5

 to accurately model the 

GCD options. This is the information we used to develop the operating parameters for 

 

4

 Ramping refers to the increase or decrease in the volume of water flowing through an individual 

powerplant over a specified period of time. 
159

each of the options. In order to produce detailed GCD release patterns, in some cases, 

more information was required than was provided by GCMRC. Additional information 

sometimes was requested from the sponsors. The sponsors, in most cases, participated in 

conference calls between GCMRC and the authors in order to accurately model the GCD 

options. 

Input 1—Water Available for Release through a given SLCA/IP Powerplant throughout

the Week

GT-Max utilizes a weekly volume release in acre feet (AF) from each powerplant. The 

weekly volume is calculated by equally distributing a monthly volume (AF) on a daily 

basis and then summing the days in a week. GT-Max then distributes volume hourly 

throughout the week to optimize energy from water released. 

In order to begin the economic impact of the GCD options, as inputs to the GT Max 

model, annual release volumes were needed for each hydrological condition for each year 

modeled. In addition, a monthly distribution of this annual release volume was required 

for each year and each option. The annual release volumes and the monthly distribution 

of these volumes for the base scenario were provided by Reclamation. Reclamation 

developed this information using the CRSS model. An explanation of this model and the 

development of annual release data and monthly distributions for the current effort are 

included as Appendix 1 of this report6

. 

The following table displays the GCD release as modeled by CRSS for three hydrologic 

sequences. These values are used for each of the proposed options. Additionally, the 

 5

 Draft Evaluation of GCD Options, GCMRC, June ___ 2006 
160

monthly distributions in tabular and graphic format for each year and hydrological 

condition are included at the end of the report. Notice that there are 10-years of release 

data for each hydrological condition. 

TABLE 1 

Annual GCD Release for Three Hydrological Conditions 

Water Year 

Release 

Lower Decile 

(Dry Scenario) 

Most Probable Upper Decile 

(Wet Scenario) 

2007 8.23 maf 8.23 maf 8.23 maf 

2008 8.23 maf 9.72 maf 11.43 maf 

2009 8.23 maf 8.23 maf 8.89 maf 

2010 8.23 maf 8.23 maf 13.23 maf 

2011 8.23 maf 8.23 maf 9.59 maf 

2012 8.23 maf 11.96 maf 11.37 maf 

2013 8.23 maf 8.61 maf 14.11 maf 

2014 8.23 maf 9.71 maf 10.74 maf 

2015 8.23 maf 8.38 maf 8.72 maf 

2016 8.23 maf 8.23 maf 14.96 maf 

Inputs 2—Restrictions on the Operation of a Powerplant

Water/Power Conversion Factor

Hydraulic head or the measurement of potential energy available to convert water to 

energy effects the amount of power produced with the water available. Each powerplant 

has a specific regression curve associated with it based on historical energy produced at 

different hydraulic heads. This water-to-power conversion ratio is imported into GT-Max 

and used to estimate energy production at current hydraulic head. 

 6 Development of Monthly Lake Powell Inflow and Release Sequences for the Assessment 

of Experimental Options T. Ryan, USBR, October, 2006
161

Hydraulic Head

Reclamation produces a 24-month study using its hydrologic model RiverWare. The 24-

month study reports 12 months of actual power release, bypass release, end of month 

(EOM) storage capacity and fore bay (reservoir elevation), along with reporting the 

predicted values for the next 12 months. The reservoir elevation is used as a measure of 

hydraulic head. When operations are assumed that differ from the historical or predicted 

patterned release, the release volume is added or subtracted from the EOM storage and 

CRSS model runs correlate the new release pattern and storage to EOM reservoir 

elevations. The reservoir elevation ultimately agrees at the end of any year during the 

ten-year study period. 

Development of CRSP Customer Demand/Load Data

Load calculations are estimated using the previous year’s actual customer load scheduled 

with Western. The monthly load is broken down into Sunday/Holiday, Saturday and 

Weekday 24-hour load profiles that are then reconstructed into a new monthly profile for 

the month to be studied. The new monthly load schedule is revised to meet the maximum 

capacity and energy allocations and minimum capacity take of that new month. Energy 

allocations were reduced in 2004 in consultation with power customers in response to the 

drought conditions at that time. As part of that agreement to reduce allocations, they 

have been increasing to pre-specified levels each year since 2004 with the maximum 

level to be reached in WY2009 and held constant thereafter. In this analysis, these 

intermediate energy allocation levels were used in calculating the customer loads in 

WY2007 and 2008 with the maximum level being used in 2009 through 2016. Figure 1 is 

a graphical representation of CRSP customer load for three 24-hour periods. These data 
162

are taken from December, 2005 and are illustrative of the load data collected as GT MAX 

model input values. 

Figure 1 

Illustration of Daily SLCA/IP Customer Load Pattern

December WY2006 (Calender 2005) Load

0

200

400

600

800

1000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hour

Generation (MW h)

Week Sat Sun

In addition to the input data, one needs to prepare the data for model use and specify how 

the GT MAX model will be used and how GT MAX output data will be aggregated in 

order to make appropriate comparisons. The latter is referred to as the post processing of 

the modeled data. 

Spot Market Prices

A simple price pattern in the spot market node of the model input includes $2 on-peak 

and $1 off-peak. Sensitivity analysis of the spot market node showed that the objective 

function in the model responds only to incremental differences in prices. When actual 

prices were included in the model the resulting pattern did not differ from output 
163

produced when the simple price pattern was used. Sunday generation patterns as a result 

of the simple price pattern appear flatter than Western’s normal representative schedule. 

Spot market transmission costs of $1 were added on Sunday and $0.01 on Saturday in 

order to reflect Western’s schedule during those times. The resultant pattern on Sunday 

and Saturday did follow the demand schedule input, but at a reduced generation pattern 

compared with the weekday schedule. 

Input 3—Technical Capabilities of Each Powerplant

Glen Canyon Dam 

GCD has a powerplant with an operating capacity of 1,300 MW. The GCD is currently 

operated in conformance with the operating criteria established in February 24, 19977

. 

These criteria limit such operating parameters as the maximum release (under normal 

hydrological conditions), minimum release, the maximum change in release that can take 

place from one hour to the next (up ramps and down ramps) and the maximum total 

change in release in a 24-hour period. There are other requirements and limitations on the 

operation of the GCD described in these criteria and related documents that are not part 

of this modeling effort. Mostly, these relate to the operation of the GCD under emergency 

conditions. 

Other Major CRSP Powerplants Included in the Base Scenario Modeling

The following are brief descriptions of the other CRSP powerplants and the assumptions 

used in the GT MAX modeling for all scenarios. 

 

7

 Operating Criteria for Glen Canyon Dam In accordance with the Grand Canyon Protection Act of 1992, 

February 24, 1997. 
164

 Flaming Gorge Dam contains a powerplant with a nameplate capacity of 150 

MW. It is operated within operating criteria established in 1978 and in 

conformance with a biological opinion completed in 2005. For modeling 

purposes, the Flaming Gorge powerplant was assumed to operate under a steady 

flow operation. Monthly water volumes used for the 10 year study period were 

provided by Reclamation. 

 Aspinall Units consists of three powerplants: Blue Mesa, Morrow Point and 

Crystal. Combined they total a nameplate capacity of 283 MW. Monthly water 

release data for these three powerplants over the ten year study period were 

provided by Reclamation. Operating parameters used for the modeling for this 

analysis are unrestricted for Blue Mesa and Morrow Point. For Crystal, we limited 

operation to a constant flow. 

 Fontenelle Dam houses a powerplant that has a nameplate capacity of 11 MW. 

Monthly water release data was provided by Reclamation. 

 The Collbran project consists of two powerplants called Upper and Lower 

Molina. Together they have a nameplate capacity of 12 MW. Monthly release 

data was provided by Reclamation. For modeling purposes, we assume that they 

operate at a constant rate during on-peak hours and have a zero release during offpeak hours. 

Input 4—Environmental Limitations or Targets that Restrict the Operation of the 

Powerplants 
165

Development of a Base Scenario:

The Base Scenario represents the current operation of GCD as required by the Record of 

Decision (ROD) of the GCD EIS and the subsequent GCD Operating Criteria adopted in 

February, 1997. 

The ROD was the result of an extensive evaluation of the historic operation of GCD. 

Several analyses were completed and summarized in the GCD operations EIS – including 

an economic analysis. The economic analysis and an evaluation of methods were 

reported in three volumes8

. 

Most importantly, this analysis is an attempt to add to the economic analysis completed 

and summarized in the GCD EIS. The current analysis is a much “slimmed down” 

approach. However, we attempt to estimate the opportunity cost, or economic impact of 

modified restrictions on the operating criteria at GCD9

. The power system economic 

impact of the implementation of the Modified Low Fluctuating Flow (MLFF) in the EIS 

was estimated to be $44.2 million dollars in levelized, net present value (1991 $). The 

method used to estimate this figure as the economic impact was referred to as “Annual 

Economic Cost”. The assumptions used by the authors in this report are, within the 

limited scope and effort of this analysis, an attempt to duplicate this method. 

 8

 U.S. Bureau of Reclamation, October, 1993 Power System Impacts of Potential Changes in Glen 

Canyon Power Plant Operations 

____________, July, 1995, Power System Impacts of Potential Changes in glen Canyon Power Plant 

Operations, Phase III, Final Report 

____________, February, 1990, Evaluation of Methods to Estimate Power System Impacts of 

Potential Changes in Glen Canyon Powerplant Operations 

9

 In the above reports, the analysis that best corresponds to the analysis in this report is referred to as 

federal economic impacts 
166

The MLFF and the national economic impact of $44.2 million annually is therefore the 

base scenario for this economic analysis. Therefore the impacts described in this report 

for each of the GCD options (whether positive or negative) would be in addition to the 

impact of the MLFF. 

To be complete, the MLFF must be modeled under more than one hydrological condition 

since these conditions in the Colorado River basin are quite variable. 

To develop a base scenario, the following input data is required: 

1. annual volumes of GCD release for the 10 year study period, 

2. a distribution of monthly water volumes throughout the year, 

3. properly described GCD operational constraints, 

The annual release volumes, along with the monthly distributions were developed by 

Reclamation for every month of each ten-year hydrological period. This procedure is 

described in the GT Max modeling section and further detailed in Appendix 1. Monthly 

release volumes are consistent in all 8.23 million acre feet (maf) years. When 

equalization occurs and hydrological considerations necessitate releases greater than 8.23 

maf, monthly release volumes differ (Figure 2). 
167

Figure 2 

Monthly Release Volumes for Base Hydrology in the 10%, 50% and 90% Exceedance 

Categories

480680880

1,0801,2801,4801,680

Date Jan-07 May-07 Sep-07 Jan-08 May-08 Sep-08 Jan-09 May-09 Sep-09 Jan-10 May-10 Sep-10 Jan-11 May-11 Sep-11 Jan-12 May-12 Sep-12 Jan-13 May-13 Sep-13 Jan-14 May-14 Sep-14 Jan-15 May-15 Sep-15 Jan

Date

Release (kAF)

Base 10% Base 50% Base 90%
168

The operating criteria for GCD complies with the ROD constraints (Table 2). 

TABLE 210 

Glen Canyon Base Scenario Operational 

Constraints 

Month 

Max Daily 

Change 

UP/DOWN 

Min 

Release¥

Max 

Release 

Hourly 

Upramp 

Hourly 

Downramp 

10 ROD* 5 25 4 1.5 

11 ROD* 5 25 4 1.5 

12 ROD* 5 25 4 1.5 

1 ROD* 5 25 4 1.5 

2 ROD* 5 25 4 1.5 

3 ROD* 5 25 4 1.5 

4 ROD* 5 25 4 1.5 

5 ROD* 5 25 4 1.5 

6 ROD* 5 25 4 1.5 

7 ROD* 5 25 4 1.5 

8 ROD* 5 25 4 1.5 

9 ROD* 5 25 4 1.5 

*ROD constraints limit maximum daily change up and down to: 5,000 

cfs/day if month < 600,000 AF; 6,000 cfs/day if month >= 600,000 AF and < 

800,000 AF; 8,000 cfs/day if month >= 800,000 AF. 

¥

Minimum releases between 7 am and 7 pm are 8,000 cfs and drop to 5,000 

cfs during all other hours. Minimum release constraints indicate minimum 

releases below 8,000 cfs. 

Development of Alternatives

Four alternatives were presented for analysis. These four alternatives are: SPG A, A 

Variation, SPG B and SPG C. SPG A and A Variation (A’) utilize base case monthly 

release patterns. SPG B and C requested monthly release patterns that differ from the 

MLFF. In all hydrological scenarios 8.23 maf years remain the same for the base case, 

SPG A and A Variation. SPG C alters the MLFF 8.23 maf pattern, but the monthly 

release pattern does retain the altered 8.23 maf pattern in all years. SPG B has a tiered 
169

option that requires water release volumes to change over a seven year period. Years in 

which hydrological inflows necessitate releases greater than 8.23 maf do not retain 

similar patterns. GCD equalization constraints drive monthly releases according to 

hydrological inflows. A comparison of SPG A, A’, SPG B and SPG C in graph display 

appears below (Figures 3, 4, 5). Tabular representation of monthly releases is included as 

Attachment 1. 

 10 Operation of Glen Canyon Dam, Final Environmental Impact Statement, March 1995, U.S. Department 

of Interior, Bureau of Reclamation 
170

FIGURE 3 – Wet Case 

10% Exceedance Monthly Release Volumes

480580680780880980

1,0801,180

Oct-06 Feb-07 Jun-07 Oct-07 Feb-08 Jun-08 Oct-08 Feb-09 Jun-09 Oct-09 Feb-10 Jun-10 Oct-10 Feb-11 Jun-11 Oct-11 Feb-12 Jun-12 Oct-12 Feb-13 Jun-13 Oct-13 Feb-14 Jun-14 Oct-14 Feb

Date

Release (kAF)

Base, SPG A, A' 10% SPG B 10% SPG C 10%
171

FIGURE 4 Most Probable Case 

50% Exceedance Monthly Release Volumes

480680880

1,0801,2801,4801,680

Oct-06 Feb-07 Jun-07 Oct-07 Feb-08 Jun-08 Oct-08 Feb-09 Jun-09 Oct-09 Feb-10 Jun-10 Oct-10 Feb-11 Jun-11 Oct-11 Feb-12 Jun-12 Oct-12 Feb-13 Jun-13 Oct-13 Feb-14 Jun-14 Oct-14 Feb

Date

Release (kAF)

Base, SPG A, A' 50% SPG B 50% SPG C 50%
172

FIGURE 5 Dry Case 

90% Exceedance Monthly Release Volumes

480730980

1,2301,4801,7301,9802,2302,4802,730

Oct-06 Feb-07 Jun-07 Oct-07 Feb-08 Jun-08 Oct-08 Feb-09 Jun-09 Oct-09 Feb-10 Jun-10 Oct-10 Feb-11 Jun-11 Oct-11 Feb-12 Jun-12 Oct-12 Feb-13 Jun-13 Oct-13 Feb-14 Jun-14 Oct-14 Feb-1

Date

Release (kAF)

Base, SPG A, A' 90% SPG B 90% SPG C 90%
173

In order to understand the constraints that are used as inputs for the GT MAX model for 

each of the GCD options, the operational constraints for each of the options are included 

below as Table 3 

TABLE 3 

Glen Canyon SPG A Operational Constraints 

Glen Canyon SPG B Years 1-3 Operational 

Constraints 

Month 

Max Daily 

Change 

UP/DOWN 

Min 

Release¥

Max 

Release 

Hourly 

Upramp 

Hourly 

Downramp Month 

Max Daily 

Change 

UP/DOWN 

Min 

Release¥

Max 

Release 

Hourly 

Upramp 

Hourly 

Downramp 

10 ROD* 5 25 4 3 10 0.01 5 25 4 1.5 

11 ROD* 5 25 4 3 11 0.01 5 25 4 1.5 

12 12 5 25 4 3 12 4 5 25 4 1.5 

1 12 5 25 4 3 1 4 5 25 4 1.5 

2 10 5 25 4 3 2 4 5 25 4 1.5 

3 ROD* 5 25 4 3 3 4 5 25 4 1.5 

4 ROD* 5 25 4 3 4 4 5 25 4 1.5 

5 ROD* 7 25 4 3 5 4 5 25 4 1.5 

6 ROD* 7 25 4 3 6 4 5 25 4 1.5 

7 10 7 25 4 3 7 4 5 25 4 1.5 

8 10 7 25 4 3 8 0.01 5 25 4 1.5 

9 ROD* 7 25 4 3 9 0.01 5 25 4 1.5 

*ROD constraints limit maximum daily change up and down to: 5,000 

cfs/day if month < 600,000 AF; 6,000 cfs/day if month >= 600,000 AF and < 

800,000 AF; 8,000 cfs/day if month >= 800,000 AF. ¥

Minimum releases between 7 am and 7 pm are 8,000 cfs and drop to 5,000 

cfs during all other hours. Minimum release constraints indicate minimum 

releases below 8,000 cfs. 

 

Glen Canyon SPG A Variation Operational 

Constraints 

Glen Canyon SPG B Years 4 & 5 Operational 

Constraints 

Month 

Max Daily 

Change 

UP/DOWN 

Min 

Release¥

Max 

Release 

Hourly 

Upramp 

Hourly 

Downramp Month 

Max Daily 

Change 

UP/DOWN 

Min 

Release¥

Max 

Release 

Hourly 

Upramp 

Hourly 

Downramp 

10 8 5 25 4 3 10 0.1 5 25 4 1.5

11 8 5 25 4 4 11 0.1 5 25 4 1.5

12 12 5 25 4 4 12 0.1 5 25 4 1.5

1 12 5 25 4 4 1 0.1 5 25 4 1.5

2 10 5 25 4 4 2 0.1 5 25 4 1.5

3 8 5 25 4 4 3 0.1 5 25 4 1.5

4 ROD* 5 25 4 3 4 4 5 25 4 1.5

5 ROD* 7 25 4 3 5 4 5 25 4 1.5
174

6 ROD* 7 25 4 3 6 4 5 25 4 1.5

7 10 7 25 4 3 7 4 5 25 4 1.5

8 10 7 25 4 3 8 0.1 5 25 4 1.5

9 ROD* 7 25 4 3 9 0.1 5 25 4 1.5

 

Glen Canyon SPG C Operational Constraints 

Glen Canyon SPG B Years 6 & 7 Operational 

Constraints 

Month 

Max Daily 

Change 

UP/DOWN 

Min 

Release¥

Max 

Release 

Hourly 

Upramp 

Hourly 

Downramp Month 

Max Daily 

Change 

UP/DOWN 

Min 

Release¥

Max 

Release 

Hourly 

Upramp 

Hourly 

Downramp 

10 0.01 5 25 4 1.5 10 0.1 5 25 4 1.5

11 ROD* 5 25 4 3 11 0.1 5 25 4 1.5

12 12 5 25 4 3 12 0.1 5 25 4 1.5

1 12 5 25 4 3 1 0.1 5 25 4 1.5

2 10 5 25 4 3 2 0.1 5 25 4 1.5

3 ROD* 5 25 4 3 3 0.1 5 25 4 1.5

4 ROD* 5 25 4 3 4 0.1 5 25 4 1.5

5 ROD* 7 25 4 3 5 0.1 5 25 4 1.5

6 ROD* 7 25 4 3 6 0.1 5 25 4 1.5

7 ROD* 7 25 4 3 7 0.1 5 25 4 1.5

8 ROD* 7 25 4 1.5 8 0.1 5 25 4 1.5

9 0.01 7 25 4 1.5 9 0.1 5 25 4 1.5

 

 

Glen Canyon SPG B Years 7-10 Operational 

Constraints 

 Month 

Max Daily 

Change 

UP/DOWN 

Min 

Release¥

Max 

Release 

Hourly 

Upramp 

Hourly 

Downramp 

 10 ROD* 5 25 4 1.5 

 11 ROD* 5 25 4 1.5 

 12 ROD* 5 25 4 1.5 

 1 ROD* 5 25 4 1.5 

 2 ROD* 5 25 4 1.5 

 3 ROD* 5 25 4 1.5 

 4 ROD* 5 25 4 1.5 

 5 ROD* 5 25 4 1.5 

 6 ROD* 5 25 4 1.5 

 7 ROD* 5 25 4 1.5 

 8 ROD* 5 25 4 1.5 

 9 ROD* 5 25 4 1.5 
175

Post-Processing of GT MAX Modeled Output 

As stated above, the GT MAX model output is a data set of a week (168 values) of hourly 

electrical generation, in megawatts, for the week modeled. One representative week is 

modeled for each month in a given year. A total of ten years are modeled. These ten years 

of data are the GT MAX outputs for each of three hydrological conditions. Due to the 

large amount of data generated, post-production of these data is necessary to formulate an 

understanding and a context. 

Extending the weekly runs to the entire year

Each representative week of generation modeled by GT MAX is turned into a month of 

generation by replicating the typical week four times, plus a fractional portion of a week 

determined according on the particular month. This is done for all twelve months when 

exporting the GT MAX modeled outputs into a spreadsheet. The resulting spreadsheet 

contains hourly energy production for an entire year (8760 hours) of study for a particular 

hydrological condition and scenario. The entire study data base consists of a set of these 

spreadsheets comprising the ten year study period, for each scenario, and for the three 

hydrological conditions. For ease of modeling and post processing, in each of the ten 

future years studied the first day of the Water Year begins on a Sunday, thereby 

simplifying the task of keeping track of the weekdays, Saturdays, and Sundays for the 10 

year study period. 

For the base scenario, the data consists only of hourly generation amounts. No dollar 

values are applied. 
176

Losses and Project Use

Hourly hydro generation was reduced by subtracting project use estimates and system 

losses to obtain the net hourly generation available to meet customer scheduled load. 

Project use loads were calculated using the same values that determine monthly AHP 

(available hydropower), and are based on recent energy schedules of those loads as 

recorded by the CRSP MC scheduling office. System losses were calculated at 7.81 

percent of the hourly hydro generation, the same value as used in other modeling. 

Load Following Capacity

In addition to the production of electrical energy, the GCD powerplant produces 

electrical generating capacity. Electrical energy and capacity are related but separate 

electrical products. Typically, wholesale buyers of electricity purchase two products: 

capacity and energy. These two products respectively represent the construction and 

operating costs of production. 

For the base scenario, the difference between GCD minimum generation and maximum 

generation within a month was used to determine the amount of capacity for the month. 

For example, if the GT MAX minimum hourly GCD output for December, 2008 for the 

dry hydrological condition is 300 MW (Sunday at 5 AM) and the maximum hourly GCD 

output for this month is 650 MW (Wednesday at 4 PM), then the determination of GCD 

capacity for that month is 350 MW. This is the “load following” capacity of GCD in this 

month. The “load following” GCD capacity is calculated and compared to the “total 

capacity” of GCD because it better represents the contractual relationship between 

changes in the GCD operation and the resulting impact on CRSP customers. 
177

Comparison of Options vs. Base Scenario 

For each GCD option the GT MAX is run with all of the SLCA/IP powerplants included 

in the model run. GCD generation is then extracted and put into the base case 

spreadsheet. This is done so that the impact of the option being considered is calculated 

from only the changes at the GCD powerplant. The SCLA/IP powerplants retain base 

case generation values. 

Once a spreadsheet is prepared that includes the GT MAX modeled output from GCD 

with the base scenario GT MAX output from the other CRSP units, the hourly CRSP 

generation numbers for the base scenario are compared to each hourly CRSP generation 

of an option. Each option is compared separately. 

When an hourly electrical generation value for the base scenario is compared to the same 

hour for an option, the difference will either be positive or negative. A positive difference 

means that there is that much more electrical energy produced at GCD in that hour for 

that option as compared to the base scenario. A negative difference means the opposite. 

 The difference was then multiplied by an energy price to calculate an hourly cost of 

energy purchases from or sales to the spot market. Energy costs were summed for an 

entire month and added together to get a total cost or revenue per month. 
178

The monthly load following capacity is averaged over a year. This “yearly average, loadfollowing capacity” is the relevant capacity statistic and will be compared to the same 

statistic for each option in order to calculate the capacity impacts of the options. 

Accounting for Impacts on Capacity among the GCD Options

In order to fully assess the economic impact on GCD electrical power production, the 

difference in marketable capacity between the baseline case and an option was calculated 

using a yearly average capacity value. Then, a capacity price was determined and the 

estimated change in marketable capacity was multiplied by the capacity price. This was 

then added to the estimate for economic impact of an option using energy prices alone. 

The total impact is then calculated. 

Total of Estimated Loss/Gain

The total economic impact of an option, as compared to the baseline is the addition of the 

change in the purchases and sales and the change in marketable capacity. These are 

summed to get the total impact. A preferred way to look at this, however, is to represent 

a range of possible economic impacts with the purchase/sales change being the lower end 

of an economic impact for an option. The purchase/sales change added to the value of 

loss/gain in capacity represents the upper range of possible economic impact of an option 

as compared to the baseline. 

Prior to describing the method of comparing the impact of the GCD options against the 

base scenario, it is worth noting those variables that are held constant between the base 
179

scenario and any of the GCD options. We attempt to keep all of the model inputs constant 

unless the values of these inputs are expressly changed by a GCD option. The following 

are held constant: SLCA/IP customer hourly demand, hourly purchase prices, the 

operating parameters of the other CRSP power units and capacity replacement cost. 

As the results of our analysis are described below, it is worth reiterating that these 

impacts are scored against a baseline that is a regulated electrical power generator. That 

is, GCD is regulated through restrictions on operating parameters put in place in 1997. 

Comparison Method

The hourly generation values are compared to the matching hourly values of the change 

case. The differences for each hour are the variables used to assess the impact of a GCD 

option. Therefore, only the differences (or the delta) are used. This way, a comparison of 

the base scenario with any of the four GCD options is a comparison of differences. 

The database that results from this comparison is in hourly generation value differences. 

These hourly differences are multiplied by the avoided cost or replacement cost. 

Selection of hourly avoided cost

For this economic analysis, the authors attempt to estimate the value of electrical 

generating resources that would need to be added to existing construction plans or that 

would be avoided. Whether constructed or avoided depends on the direction of the 

impact. These costs will be of two types: electrical energy and electrical capacity. As we 
180

stated at the outset of this paper, electrical energy and capacity are separate electrical 

products. Therefore, we identified energy prices and capacity prices separately. 

Electrical Energy is Valued Hourly

Wholesale electrical market participants frequently make spot market trades on an hourly 

basis, sometimes referred to as hour- ahead or real time purchases. Hour-ahead energy 

prices increase and decrease each hour to track changes in generation and system load in 

a given area over a given time period. Hourly values therefore, better represents the 

opportunity cost of using electrical energy to serve the utility’s native load as compared 

to a static price for defined on-peak and off-peak periods. 

Pricing assumptions for electrical energy values were: futures prices for energy at the 

Palo Verde trading hub for October 2006 through September 2007 as reported by Prebon 

Energy in the July, 2006 time frame11. The on-peak and off-peak price was used for all 

purchases during a given month depending on the time of the purchase. Table 4 shows 

the spot market prices used. 

 

11 Prebon Energy of Jersey City, NJ provides power marketers, utilities, producers, risk managers and 

institutions with a single comprehensive source for price information and liquidity in a broad and 

expanding range of energy markets including, coal, natural gas, oil and power. See 

http://www.prebonenergy.com/index.aspx. Prebon is one of several entities Western has access to that 

report wholesale prices at western US trading hubs. 
181

Table 4 

Spot 

Market 

Prices 

 Onpeak Offpeak 

October $ 58.39 $ 48.33 

November $ 70.25 $ 58.14 

December $ 81.31 $ 67.29 

January $ 78.68 $ 65.11 

February $ 78.75 $ 65.17 

March $ 77.01 $ 63.73 

April $ 51.44 $ 42.57 

May $ 50.25 $ 41.59 

June $ 50.74 $ 41.99 

July $ 82.24 $ 68.06 

August $ 83.00 $ 68.69 

September $ 83.91 $ 69.44 

Monthly on-peak and off-peak prices were translated into hourly energy prices by scaling 

them according customer demand. Figure 1 of this report shows a representation of 

SLCA/IP customer demand by hour for an illustrative day in December. Hourly customer 

demand information for each month was used as a surrogate for system load to create an 

index – each hour being scaled up or down in proportion to the load in that hour. The 

monthly future’s price was modified according to this index so that the average of the 

hourly prices over the period was the same as the monthly futures price. Even though 

2007 future’s prices are used, these prices remain constant for the 10-year study period. 

They are not escalated to account for inflation - this is a “real” number analysis. 

This method allows for the representation of hourly values. Historic hourly values are a 

matter of record, but we choose to construct hourly data on the value of electrical energy 

based on the market’s best estimate of future prices. This avoids the problem that, in a 

volatile energy market, past conditions are often unrepresentative of future conditions, as 

well as avoiding the problem of missing or anomalous hourly historical values. 
182

Using this set of hourly prices for a month, we multiplied the difference in electrical 

energy generation each hour by the hourly price to yield the dollar impact for that hour. 

We then summed the hourly “deltas” over the month. This was done for each month of 

the year and this process was repeated for each year of the ten-year study. 

Results 

Table 5 shows the electrical energy impact by year for each of the four options as 

compact to the base scenario. These are shown for each of the three hydrological 

conditions. A negative impact (as compared to the base case) is shown in red and in 

parentheses. Positive impacts are shown in black.
183

TABLE 5 

Impact of GCD options on the value of energy production - compared with the b

(Net of sales/purchases, 2006 $) 

Dry Hydro 2007 2008 2009 2010 2011 2012 2013 2014 Base Case $ - - $ - $ - $ - $ - $ - $ - $ A 2,658,214 1,973,837 2,166,098 1,784,279 (638,044) 2,032,725 1,963,606 1,885,246 

A Var 3,431,464 2,565,203 3,004,804 2,594,068 126,990 2,738,880 2,710,709 2,646,086 B (5,306,724) (10,047,447) (9,223,666) (13,640,087) (15,334,711) (18,243,064) (18,179,461) 982,107 

C 811,678 (693,130) (260,768) (895,798) (2,048,943) (408,833) (405,699) (961,595) 

MP Hydro 2007 2008 2009 2010 2011 2012 2013 2014 Base Case $ - - $ - $ - $ - $ - $ - $ - $ 

A 870,781 440,492 2,274,493 2,163,843 2,588,848 1,892,990 2,367,489 430,699 

A Var 1,618,909 1,309,967 3,119,687 2,952,387 3,275,465 2,794,987 3,567,623 1,266,560 B (8,833,558) (10,940,178) (10,159,789) (15,381,093) (14,577,983) (17,674,643) (20,203,360) (1,317,689) 

C (208,773) (1,317,279) (411,933) (675,850) 755,772 (340,902) (152,932) (1,586,277) 

Wet Hydro 2007 2008 2009 2010 2011 2012 2013 2014 Base Case $ - - $ - $ - $ - $ - $ - $ - $ 

A 2,098,646 1,880,026 2,486,511 1,519,587 2,862,172 2,285,072 2,960,105 2,099,602 

A Var 2,186,059 2,487,221 3,308,227 1,866,228 3,365,282 2,167,203 2,788,933 2,838,941 B (8,357,907) (8,980,300) (9,665,265) (13,347,437) (16,108,922) (21,022,289) (20,688,428) 37,310 

C $ 1,212,620 1,006,602 $ (136,670) $ (66,466) $ (632,779) $ (1,439,541) $ 1,748,008 $ (755,747) $ 
184

Table 6 is a 10-year average of the results from Table 5. The average impact of the four 

options is recorded in this table. Remember that these are impacts of electrical energy 

production only (capacity analysis will come later). It is also important to note that these 

data are the outcomes of a real analysis: there is no “inflation factor” used. 

TABLE 6 

Energy impacts, 10 Year Average 

Base Case $0

A $1,788,351

A Variation $2,530,737

B ($8,890,011)

C ($646,441)

Base Case $0

A $1,768,588

A Variation $2,626,779

B ($9,938,133)

C ($616,904)

Base Case $0

A $2,241,854

A Variation $2,682,336

B ($9,830,691)

C $114,636

Dry Hydro

M P Hydro

Wet Hydro

Capacity Impacts of the GCD Options

In addition to the generation of electrical energy, GCD also provides electrical capacity 

through contractual arrangements between Western Area Power Administration and the 

SLCA/IP customers. 
185

In order to assess the impact of an option against the base scenario, we calculated load 

following capacity for an option in the same way that we performed this calculation for 

the base scenario. As the reader will recall from our description of the base scenario, we 

took the GCD minimum and maximum generation for each week (representing a month) 

from the GT MAX model output as a representation of the “load following” capacity for 

the month. The monthly data are averaged over a year to yield a yearly average. The 

relevant comparison is therefore between the base scenario 12-month average capacities 

for a year against the same calculation for a GCD option. 

Table 7 records the “load following” capacity impacts, by year, of the GCD options as 

against the base scenario in megawatts. A GCD Option which results in a reduction in 

load-following capacity is shown in red and is parenthetical. A GCD option which results 

in an increase in load-following capacity as compared to the base scenario is shown in 

black. 

Table 8 shows the dollar impact of the GCD options regarding load-following capacity. 

Table 6 is derived from the capacity impacts recorded in Table 5. The GCD capacity 

impacts are multiplied by the replacement cost for capacity. Again, Table 6 is a record of 

“differences” only; “deltas” when compared to the base scenario. 
186

Determination of Capacity Values

For this analysis, capacity is valued at the replacement cost identified by some SLCA/IP 

customer utilities who have recently constructed facilities which provide load following 

capacity12. These customer data were collected in order to get information regarding the 

construction cost per megawatt of a recently built facility that provides electrical services 

similar to the GCD powerplant. 

For Table 8, economic impacts are presented in 2006 dollars. Red numbers in parentheses 

are reductions in economic value. Black numbers are gains in economic value.

 

12 SRP & TriState: capacity construction cost for a load following/peaking facility recently constructed in 

Arizona. 
187

TABLE 7 

Impact of GCD Options on Load Following Capacity – Compared to the Base S

Dry Hydro 2007 2008 2009 2010 2011 2012 2013 2014 2Base Case - - - - - - - - 

 

A 40 37 38 37 31 38 38 36 A Var 56 56 60 54 49 60 57 53 B (57) (126) (130) (155) (154) (214) (201) 39 

C (6) 21 (4) (1) 0 10 (4) (3) 

MP Hydro 2007 2008 2009 2010 2011 2012 2013 2014 Base Case - - - - - - - - 

 

A 44 48 34 41 33 23 38 40 A Var 60 71 57 62 55 43 66 57 B (130) (133) (144) (178) (185) (224) (232) 8 

C 0 42 (6) (1) (11) 80 (5) (6) Wet Hydro 2007 2008 2009 2010 2011 2012 2013 2014 Base Case - - - - - - - - 

 

A 33 29 36 30 20 36 63 42 A Var 33 43 41 2 27 49 54 24 B (142) (152) (142) (226) (237) (290) (196) 0

C (12) 55 (1) (28) (32) 14 63 (19) 
188

TABLE 8 

Load Following Capacity Dollar Difference Compared to the Base Ca

(2006 $) 

Dry Base

2007 2008 2009 2010 2011 2012 2013 

Base Case $0 $0 $0 $0 $0 $0 $0 A 3,208,803 2,957,005 3,019,745 2,931,286 2,509,444 3,062,295 3,076,772 2,85A Var 4,474,209 4,484,716 4,766,447 4,299,626 3,906,664 4,822,448 4,542,151 4,25B (4,549,786) (10,079,619) (10,371,797) (12,384,994) (12,303,554) (17,108,416) (16,108,811) 3,10C (447,024) 1,654,463 (291,390) (52,670) 1,669 809,276 (353,303) (20MP Base

2007 2008 2009 2010 2011 2012 2013 

Base Case $0 $0 $0 $0 $0 $0 $0 A 3,541,658 3,833,383 2,750,002 3,243,249 2,604,754 1,847,852 3,024,815 3,17A Var 4,813,007 5,705,233 4,549,188 4,929,035 4,406,651 3,424,000 5,271,135 4,54B (10,390,317) (10,640,324) (11,504,269) (14,216,585) (14,793,460) (17,925,884) (18,565,923) 65C 39,334 3,383,465 (493,853) (50,959) (895,040) 6,366,806 (419,826) (49Wet Base

2007 2008 2009 2010 2011 2012 2013 

Base Case $0 $0 $0 $0 $0 $0 $0 A 2,625,337 2,318,695 2,845,591 2,381,462 1,636,459 2,910,560 5,070,309 3,38A Var 2,625,337 3,420,095 3,298,432 216,404 2,198,121 3,911,060 4,357,609 1,92B (11,395,548) (12,131,571) (11,375,438) (18,061,776) (18,985,453) (23,172,316) (15,694,985) C (930,597) 4,402,511 (119,273) (2,248,784) (2,538,933) 1,091,040 5,079,772 (1,54
189

Table 9, below, provides information regarding the 10-year average of capacity impacts 

for the four options as compared to the base scenario. 

TABLE 9 

Average Capacity Impact of Options 

Average Average

(MW) ($)

Base Case - $0

A 36.78 $2,942,703

A Variation 55.67 $4,453,643

B (99.74) ($7,979,114)

C 4.185 334,785 $ 

Average Average

(MW) ($)

Base Case 0.00 $0

A 39.02 $3,121,775

A Variation 61.31 $4,904,693

B (122.61) ($9,808,478)

C 13.249 1,059,921 $ 

Average Average

(MW) ($)

Base Case 0.00 $0

A 36.68 $2,934,240

A Variation 41.93 $3,354,317

B (138.51) ($11,081,031)

C 12.506 1,000,514 $ 

Wet Base

Dry Base

MP Base

In order to calculate the total economic impact of the GCD options, the energy and 

capacity impacts are summed together. 
190

Table 10 

Total Economic Impact of Options Compared to Base Scenario 

(2006 $)

Dry Hydro 2007 2008 2009 2010 2011 2012 2013 2014 Base Case $ - - $ - $ - $ - $ - $ - $ - $ A 5,867,016 4,930,842 5,185,843 4,715,565 1,871,401 5,095,020 5,040,379 4,743,738 

A Var 7,905,672 7,049,919 7,771,251 6,893,694 4,033,654 7,561,328 7,252,860 6,901,945 B (9,856,510) (20,127,066) (19,595,463) (26,025,082) (27,638,265) (35,351,480) (34,288,272) 4,089,069 

C 364,655 961,333 (552,158) (948,469) (2,047,274) 400,443 (759,002) (1,168,691) 

MP Hydro 2007 2008 2009 2010 2011 2012 2013 2014 Base Case $ - - $ - $ - $ - $ - $ - $ - $ 

A 4,412,439 4,273,875 5,024,495 5,407,091 5,193,603 3,740,842 5,392,305 3,605,041 

A Var 6,431,916 7,015,201 7,668,875 7,881,422 7,682,115 6,218,986 8,838,758 5,808,509 B (19,223,875) (21,580,502) (21,664,058) (29,597,678) (29,371,442) (35,600,528) (38,769,283) (659,563) C (169,439) 2,066,186 (905,786) (726,809) (139,268) 6,025,904 (572,758) (2,084,024) 

Wet Hydro 2007 2008 2009 2010 2011 2012 2013 2014 Base Case $ - - $ - $ - $ - $ - $ - $ - $ 

A 4,723,983 4,198,721 5,332,102 3,901,050 4,498,631 5,195,632 8,030,414 5,489,128 

A Var 4,811,396 5,907,316 6,606,659 2,082,631 5,563,403 6,078,264 7,146,542 4,762,836 B (19,753,455) (21,111,871) (21,040,704) (31,409,213) (35,094,375) (44,194,605) ($36,383,413) 39,768 

C 76,006 5,615,131 (255,943) (2,315,250) (3,171,712) (348,501) 6,827,780 (2,303,451) 
191

An evaluation of the economic impact apart from the issue of hydraulic head indicates that 

option “A Variation” lies consistently above “A” indicating its increased economic value 

(Figure 6) Options “A Variation” and “A” consistently lie above the base scenario, 

indicating that they provide added economic benefits in terms of electrical power production. 

GCD option “C” vacillates between a positive and negative impact. If no August trigger is 

applied to option “C” then the impact for the option is strongly tied to hydrology and 

hydraulic head as compared to the base case. GCD option “B” reduces economic benefit and 

lies significantly below the other options in most years. However, in years 2014 – 2016, 

GCD option “B” returns to “ROD” operations. 
192

FIGURE 6 

Economic Impact by Year: Dry Hydrology

($40,000,000)($35,000,000)($30,000,000)($25,000,000)($20,000,000)($15,000,000)($10,000,000)

($5,000,000)

$0

$5,000,000

$10,000,000$15,000,000

2007 2008 2009 2010 2011 2012 2013 2014 20

Impact ($)

SPG-A A Variation SPG-B SPG-C
193

FIGURE 7 

10% Exceedance

8230 8230 8230 8230 8230 8230 8230 8230 8230 

8200870092009700

102001070011200117001220012700132001370014200

2007 Total 2008 Total 2009 Total 2010 Total 2011 Total 2012 Total 2013 Total 2014 Total 2015 Total 

Water Year

MAF Release

2008 2009 2010 2011 2012 2013 2014 2015 201

WY MAF Release Elevation
194

A comparison of the graphical representation of the total economic impact by year for the four GCD 

options in the dry hydrological (10% exceedance) category against the elevation and water release 

illustrates the impact of hydraulic head on turbine efficiency. In the dry hydrological condition all 

releases are 8.23 maf. However, between 2010 and 2012 the reservoir elevation magnitude reaches 40 

feet in difference between years. This impacts both total energy and capacity differences. A 

comparison between the graphs shows the magnitude of the total economic impact corresponding with 

the elevation curve (Figures 6 and 7 above). Further analysis shows the impact of hydraulic head on 

capacity (Figures 8 and 9). The hourly hydrograph produced in the base case for the month of 

November in years 2011 and 2012 releases the same amount of water and is scheduled nearly the same 

way. The hydrograph for 2011 decreases releases on Sunday (Figure 8). Although the water released is 

the same, the generation produced from the water does not compare (Figure 9).

FIGURE 8* 

GTMax Release Pattern

6000

7000

8000

9000

10000

11000

12000

13000

November November November November November November November November November

Month

Release (cfs)

2011 ROD Release 2012 ROD Release
195

FIGURE 9** 

A visual analysis of the most probable condition shows that the total economic impact for all scenarios 

in 2012 tend to converge toward each other (Figure 10 below). This can be explained by both the large 

annual water release in order to equalize in that year and the increased reservoir elevation in 2012 

(Figure 11). Years in which large quantities of water volume are released converge together. Once 

monthly volumes necessitate the evacuation of water above the maximum ROD constraint of 25,000 cfs, 

all scenarios release water without fluctuation consistently throughout the day at the level required to 

evacuate the monthly volume. At that point operational constraints between the options no longer 

appear because all scenarios releases high-volume, flat flows on a consistent basis. The phenomena 

appears again with wet hydrological scenarios (Figures 12 and 13). 

GTMax Generation Pattern

170

220

270

320

370

420

470

November November November November November November November November November

Month

Generation (MW)

2011 Generation 2012 Generation
196

Figure 10 

Economic Impact by Year: Most Probable Hydrology

($50,000,000)($40,000,000)($30,000,000)($20,000,000)($10,000,000)

$0

$10,000,000$20,000,000

2,007 2,008 2,009 2,010 2,011 2,012 2,013 2,014 2

Impact ($)

SPG-A A Variation SPG-B SPG-C
197

FIGURE 11 

50% Exceedance

8230

9723

8230 8230 8230

11969

8616

9719

8380

8200870092009700

102001070011200117001220012700132001370014200

2007 Total 2008 Total 2009 Total 2010 Total 2011 Total 2012 Total 2013 Total 2014 Total 2015 Total 

Water Year

MAF Release

2008 2009 2010 2011 2012 2013 2014 2015 2016

WY MAF Release Elevation
198

FIGURE 12 

Economic Impact by Year: Wet Hydrology

($50,000,000)($40,000,000)($30,000,000)($20,000,000)($10,000,000)

$0

$10,000,000$20,000,000

2,007 2,008 2,009 2,010 2,011 2,012 2,013 2,014 

Impact ($)

SPG-A A Variation SPG-B SPG-C
199

FIGURE 13 

90% Exceedance

8230

11439

8893

13229

9594

11372

13912

10745

8731

1

8200870092009700

102001070011200117001220012700132001370014200

2007 Total 2008 Total 2009 Total 2010 Total 2011 Total 2012 Total 2013 Total 2014 Total 2015 Total 201

Water Year

Million Acre Feet (maf) Release

2008 2009 2010 2011 2012 2013 2014 2015 2016

WY MAF Release Elevation
200

10-Year Average Calculations

The analysis presented in Table 8 and in Figure 2 are the estimated economic impacts by 

year for the four options relative to the base scenario. Note that GCD Option B is the only 

option in which operational criteria is modified from one year to the next. The other 

options have differing impacts in each year of a hydrological condition because the water 

release targets change from one year to the next – even within a hydrological condition. 

From these yearly data, these summary statistics are calculated: 10-year average, net

present value, annualized (levelized) net present value and expected values. Table 11 

records the 10-year average of each of the four options by hydrological condition. 
201

TABLE 11 

Total Economic Impact – 10 Year Average 

(2006 $) 

Base Case $ - 

A $4,731,054

A Variation $6,984,380

B ($24,697,448)

C ($311,656)

Base Case $ - 

A $4,890,363

A Variation $7,531,472

B ($27,972,481)

C $443,016

Base Case $ - 

A $5,176,093

A Variation $6,036,653

B ($29,855,377)

C $1,145,150

Dry Hydro

Most Probable Hydro

Wet Hydro

The Net Present Value of GCD Options

The conversion of annual dollar values over period of study to a lump sum present worth 

or present value is a standard calculation. It is a standard method for evaluating 

competing long-term projects when applied to capital budgeting. In the present case, the 

net present value of the GCD options over the ten year study period is calculated. The 

methods used here are in accord with the economic analysis guidelines followed by 

federal agencies; specifically, Western Area Power Administration13. The net present 

values of each option are recorded in Table 12 by hydrological condition. 
202

The present analysis is “inflation free”. That is, no attempt has been made to adjust the 

costs or prices used in future years of the study period by inflation rates. Therefore, this 

analysis presents dollar values in real terms14. 

The discount rate used for the net present value calculations is the discount rate published 

by the U.S. Office of Management and Budget (OMB) for the use of federal agencies 

undertaking real dollar analysis during the year 200615. The discount rate specified by 

OMB is 2.7 %. This rate is consistent with other contemporary recommendations for a 

real discount rate16. 

As shown in Table 12, the economic impact of the various GCD options varies by 

hydrological condition – even within an alternative. However, a consistent pattern 

emerges. Options A and A Variation consistently provide economic benefit over the 

range of hydrological conditions. A Variation delivers about a $20 million dollar benefit 

above Option A in the dry and most probable hydrological cases but are almost identical 

in the wet case. Option C carries a negative economic impact over the three hydrological 

conditions. Option B also carries a negative economic impact over the three hydrological 

conditions and the impact is between four and six times higher in magnitude than Option 

C. 

 13 Economic Analysis Guidelines, Western Area Power Administration, September, 1987, Golden, 

Colorado 

14 Real numbers - such as real wages, real interest rates, or nominal gross domestic product - are corrected 

for the effects of inflation. The nominal value is measured in the currency unit at that date. 

15 Office of Management and Budget (OMB), FRN, January, 2006 

16 Internet reference: real discount rates are between 1.8% and 2.5%. 
203

TABLE 12 

Net Present Value (2006 $) 

(d = 2.7, n = 10) 

Base case $ -

A $41,060,893

A Variation $60,553,426

B ($149,556,188)

C ($2,659,034)

Base case $ -

A $42,180,802

A Variation $64,939,986

B ($175,327,485)

C $3,862,269

Base case $ -

A $44,562,271

A Variation $51,572,570

B ($185,582,611)

C $9,454,159

DRY Hydrology

Most Probable

WET

Expected Value of the GCD Options

Since the hydrological conditions have a known probability, one can calculate the 

expected value of the economic impact of the GCD options. Expected value is a standard 

statistical method of describing the central tendency of a set of occurrences outcomes or 

events. The calculation is completed by multiplying each outcome by its probability of 

occurrence. 

Reclamation’s hydrological conditions were developed through modeling efforts that 
204

provide information on the probability of occurrence. The “WET” condition is the “upper 

decile” of a set of numbers generated by the RiverWare model. The “DRY” condition is 

the “lower decile” of this same set of numbers. Therefore, these two conditions occur 

with a probability of 0.10. This leaves the “most probable” hydrological condition: the 

median value of the numbers generated by the RiverWare model, with a probability of 

occurrence of 0.80. 

Table 13 reports the expected value calculations for the four GCD options. The numbers 

reported in Table 13 are the expected value of the net present value of economic impacts 

of the four GDC options. These numbers are summary statistics in that they present a 

“lump sum” economic impact of the four GCD options, where the impacts are further 

“weighted” by the probability of occurrence. Table 13 therefore represents “the bottom 

line” regarding the impacts in this report. 

TABLE 13 

Expected Value of 

Net Present Value 

(2006 $) 

(Calculated from Table 12) 

Base case $ -

A $42,306,958

A Variation $63,164,588

B ($173,775,868)

C $3,769,328
205

Figure 14 provides a visual representation of the data from Table 13. In Figure 14, the 

center line represents the base scenario. The economic impact of the four GCD options is 

represented by bars that stem in either a negative or positive way from the base scenario. 

FIGURE 14 

Net Present Value, Total Economic Impact 

(millions of 2006 $) 

($200.00) ($150.00) ($100.00) ($50.00) $0.00 $50.00 $100.00

A

A Variation

B 

C

Previous Studies Using this Method:

Similar modeling methods have been used by the authors and others in the past to 

estimate the economic impact of proposed changes in CRSP unit operations. An 

evaluation of the Low Steady Summer Flow (LSSF) experiment conducted in the spring 

and summer of 2000 used a similar modeling process17. Also, an evaluation of the 1992 

biological opinion (BO) on the operation of Flaming Gorge Dam was completed to 
206

establish cost share amounts for the long-term funding of the Upper Colorado 

Endangered Fish Recovery Program (UC-RIP)18. 

 17 Palmer, S.C. and C. Burbidge, 2004, “Financial Effect on Western and its Customers of the Low Summer 

Steady Flow Experiment at Glen Canyon Dam”, 2004, Grand Canyon Monitoring and Research Center, 

USGS publication 

18 Palmer, S.C., and T. LaRue, “The Financial Impacts to Western and Its Customers of the 1992 Biological 

Opinion on the Operation of Flaming Gorge Dam”, 1999, prepared in support of proposed Federal longterm funding legislation for the Upper Colorado and San Juan recovery implementation programs. 
207

References 

T. Ryan, USBR, October, 2006 Development of Monthly Lake Powell Inflow and 

Release Sequences for the Assessment of Experimental Options 

Palmer, S.C. and C. Burbidge, 2004, “Financial Effect on Western and its Customers 

of the Low Summer Steady Flow Experiment at Glen Canyon Dam”, 2004, Grand 

Canyon Monitoring and Research Center, USGS publication

Palmer, S.C., and T. LaRue, “The Financial Impacts to Western and Its Customers of 

the 1992 Biological Opinion on the Operation of Flaming Gorge Dam”, 1999, 

prepared in support of proposed Federal long-term funding legislation for the Upper 

Colorado and San Juan recovery implementation programs. 

U.S. Bureau of Reclamation, February, 1990, Evaluation of Methods to Estimate 

Power System Impacts of Potential Changes in Glen Canyon Powerplant Operations 

____________, October, 1993 Power System Impacts of Potential Changes in Glen 

Canyon Power Plant Operations 

____________, March, 1995, Operation of Glen Canyon Dam Final Environmental 

Impact Statement 

_____________, July, 1995, Power System Impacts of Potential Changes in Glen 

Canyon Power Plant Operations, Phase III, Final Report 

_____________, March 1995 Operation of Glen Canyon Dam, Final Environmental 

Impact Statement, , U.S. Department of Interior, Bureau of Reclamation

_____________, February 24, 1997, Operating Criteria for Glen Canyon Dam In 

accordance with the Grand Canyon Protection Act of 1992,. 

Western Area Power Administration, September, 1987, Economic Analysis 

Guidelines, Golden, Colorado 
208

Additional Related Economic Analyses

1. Annualized Present Value

Another standard method of presenting net present value information is to 

levelize the lump sum net present value data into annualized information. Table 

14 reports the results of these calculations. In this table, the data are presented 

by hydrological category. As with previous tables, negative economic impacts are 

in red, economic benefits are in black. These levelized values are probably more 

useful for GCD options A, A Variation and C. This is because the annualization of 

a net present value number for Option B tends to mask the progressive nature of 

this option. Option B progresses over seven years toward a greater number of 

months of restricted GCD operation and then ends with three years in which the 

GCD operation is unchanged from the Record of Decision. 
209

Table 14 

Annualized Present Value of GCD Options 

($2006) 

Base case

A $4,740,182

A Variation $6,990,453

B ($17,265,176)

C ($306,966)

Base case

A $4,869,467

A Variation $7,496,850

B ($20,240,285)

C $445,871

Base case

A $5,144,391

A Variation $5,953,679

B ($21,424,165)

C $1,091,414

DRY

Most Probable

WET

Expected Value of Annualized Net Present Value

As with the net present value information (Table 12), the expected value of the 

annualized data is calculated. These calculations are presented in Table 15. Again, the 

weighting is in accord with the probabilities articulated by Reclamation – upper and 

lower deciles for the wet and dry, the remainder for the most probable case. 
210

Table 15 

Expected Value of 

Annualized Net Present Value 

($2006) 

(Calculated from Table 14) 

Base Case $ - 

A $4,884,031

A Variation $7,291,893

B ($20,061,163)

C $435,142

2. BHBF CASES

All of the GCD Options include Beach/Habitat Building Flows (BHBF) as GCD 

experimentation. The Grand Canyon Monitoring and Research Center (GCMRC), has not 

prepared a science plan for the further evaluation of BHBFs. Therefore, the GCMRC 

determined that the economic evaluation of BHBFs would be modeled separately. 

Western and Reclamation prepared a base scenario under the most probable hydrological 

condition for a single illustrative year. This base-case year is one in which the GCD 

release is 9.7 million acre feet (maf). This number is the average of all most probable 

years that are above the minimum release amount of 8.23 maf. Western and Reclamation 

prepared a monthly distribution of this release for each of the four options. 

It was necessary to create a base scenario for each of the options so that the economic 

impact of the BHBF experiment would not be tainted by the change from the MLFF to 

the option. In other words a base scenario needed to be prepared for Option B so that the 
211

economic impact of a BHBF within Option B would not also include the effect of moving 

from the Option B flows back to the MLFF operations. The same was needed for Option 

C. 

The monthly GCD release volumes for each of the four options where used as input 

values to the GT MAX model to produce hourly generation values for a base scenario for 

each option. 

The second step was to redistribute the base scenario water volumes over the year to 

those monthly water volumes that would accommodate a BHBF for each of the four GCD 

options. These new monthly water volumes were then used as inputs in the GT MAX 

model to produce hourly generation values. The base scenario hourly generation values 

were then compared to the change case hourly generation values for each option. 

Once the generation differences between the base cases and the change cases were 

calculated, the differences were multiplied by the relevant electrical power prices. These 

prices are the same as those used elsewhere in this analysis. They are hourly values and 

intended to represent the opportunity costs of adding or reducing GCD electrical power 

production for each hour. 

Tables 16, 17, and 18 report the results, by month of the economic impact of the 

inclusion of a BHBF for each option. Red numbers indicate months in which the 

economic impact of GCD electrical production is reduced. Black numbers indicate 

months of economic benefit. The totals for this illustrative year are also included. There 
212

is not a significant difference in the economic impact of a BHBF among the options – 

once the impact of an option is held constant, the BHBF has roughly the same impact in 

every option. 

These tables report three time periods for each option; a fall BHBF, a winter BHBF and a 

Spring BHBF. These are reflective of the fact the GCMRC is currently pursuing further 

scientific information to indicate the best timing for BHBF. Currently, these three time 

periods are being considered. They are not additive: a BHBF within an option is 

presumed to occur once in a year – timing not yet determined. 

If a BHBF is assumed in a particular year for a particular option, the economic impact of 

the BHBF for each of options would be added to economic impact of the option in the 

year in which a BHBF is conducted. 
213

Table 16 

Option A: 

BHBF CASES 

Most Probable Hydrological Conditions 

Option A BHBF Cases: Net Purchase/Sales 

Compared to Base Case 

 

January March November 

October $0 $0 $0 

November $0 $0 $2,380,384 

December $0 $0 ($102,143)

January $2,272,793 $0 ($115,635)

February ($88,246) $0 ($87,745)

March ($75,151) $2,546,367 ($75,151)

April ($49,709) ($49,709) ($49,709)

May ($44,406) ($44,693) ($44,406)

June ($999,581) ($999,581) ($999,295)

July ($1,589,279) ($1,589,279) ($1,589,279)

August ($1,491,067) ($1,491,067) ($1,491,067)

September ($1,588,250) ($1,588,250) ($1,588,250)

Total ($3,652,897) ($3,216,212) ($3,762,297)
214

Table 17 

Option B: 

BHBF CASES 

BHBF Cases: Net Purchase/Sales Compared to Base Case

(2006 $) 

 

January March November 

October $291 $291 $291 

November ($4,879) ($4,879) $2,590,652 

December ($5,236) ($5,236) ($96,373)

January $2,657,987 ($8,019) ($110,577)

February ($101,750) ($5,930) ($101,750)

March ($92,713) $2,597,127 ($92,713)

April ($62,264) ($62,264) ($61,954)

May ($57,795) ($57,795) ($57,795)

June ($1,001,405) ($1,001,707) ($1,001,405)

July ($1,612,868) ($1,613,475) ($1,612,868)

August ($1,594,559) ($1,595,162) ($1,594,559)

September ($1,590,302) ($1,590,302) ($1,589,710)

Total ($3,465,494) ($3,347,351) ($3,728,762)

Table 18 

Option C: 

BHBF CASES 

BHBF Cases: Net Purchase/Sales Compared to Base Case

January March November 

October $218 $218 $218 

November ($5,164) ($5,164) $2,273,350 

December ($7,471) ($7,471) ($109,024)

January $2,267,243 ($8,944) ($123,940)

February ($103,150) ($5,991) ($103,150)

March ($85,946) $3,084,946 ($85,558)

April ($54,919) ($55,183) ($54,919)

May ($50,123) ($50,123) ($50,123)

June ($1,173,504) ($1,173,504) ($1,173,201)

July ($1,619,439) ($1,619,439) ($1,618,780)

August ($1,598,815) ($1,598,815) ($1,598,815)

September ($1,589,589) ($1,589,589) ($1,589,589)

Total ($4,020,657) ($3,029,058) ($4,233,530)
215

3. GCD Option C: “No August Triggers” Included in the GT MAX 

Model

GCD Option C includes “August triggers”. The idea is that, related to the flushing of 

larval and/or juvenile humpback chub into the main stem of the Colorado River in the 

Grand Canyon as a result of monsoonal activity, the flows from GCD would be steadied. 

The criteria for an August trigger have not been established. This presents a modeling 

dilemma; because of the uncertainty regarding whether to model August with or without 

these triggers. In order to assess the economic impact of GCD Option C and to deal with 

the uncertainty of triggers that remain undetermined, the GCMRC and the Option C 

proponents requested that another set of model runs and analyses be conducted in which 

GCD Option C includes “August “triggers”. This means that the operating criteria for the 

month of August is that the target volume of water will be released as a steady flow. 

The economic analysis presented in the previous tables did not include August triggers 

for any of the Augusts for GCD Option C. To the degree that GCD Option C has Augusts 

that “trigger” and others that don’t, the economic analysis presented above is an 

understatement of the economic impacts of GCD Option C. One can bracket the possible 

economic impact of GCD Option C by comparing the “with August trigger” and the 

“without August trigger” analysis. The “without trigger” would be the smallest estimated 

economic impact for GCD Option C. The “with trigger” would be the greatest estimated 

economic impact for GCD Option C. 
216

The following tables: Tables 19, 20, 21 & 22 present the economic impact of GCD 

Option C where this option is modeled an analyzed with August triggers. Table 19 

presents the total economic impact by year and by hydrological condition for GCD 

Option C with no August triggers. Table 20 reports the 10 year average of economic 

impacts of GCD Option C with August triggers. Table 21 reports the net present value of 

GCD Option C without August triggers by hydrological condition in 2006 dollars. Table 

22 is the net present value weighted by the probability of hydrological events: the 

expected value of the impact of Option C with August triggers. 

The results of the reanalysis of GCD Option C are illustrative. The impact of GCD 

Option C with August triggers is significantly different from the effect of Option C 

without August triggers. 
217

TABLE 19 

Option C: With August Triggers – by Year 

(2006 $) 

Dry Hydro 2007 2008 2009 2010 2011 2012 2013 w/ Trigger ($2,381,420) ($4,385,635) ($3,593,263) ($3,450,375) ($4,857,877) ($5,512,370) ($3,807,788) ($3,950MP Hydro 2007 2008 2009 2010 2011 2012 2013 w/ Trigger ($3,046,051) ($4,003,605) ($4,262,862) ($3,825,038) ($4,747,643) $1,228,826 ($4,326,318) ($5,02

Wet Hydro 2007 2008 2009 2010 2011 2012 2013 w/ Trigger ($2,903,652) $29,897 ($3,467,358) ($3,695,538) ($5,968,443) ($5,784,044) $3,372,967 ($4,885
218

TABLE 20 

Option C: With August Triggers – Total Economic Impact – 10 Year 

Average 

(2006 $) 

Dry Hydrology

w/ Trigger ($4,004,111)

Most Probable 

Hydrology

w/ Trigger ($3,660,830)

Wet Hydrology

w/ Trigger ($2,992,834) 

TABLE 21 

Option C: With August Triggers 

Net Present Value 

(2006 $) 

C: w/ Trigger ($34,752,282)

C: w/ Trigger ($31,573,597)

C: w/ Trigger ($25,754,612)

Dry Hydrology

Most Probable Hydrology

Wet Hydrology

TABLE 22 

Option C: With August Triggers 

Expected Value of Net Present Value 

(2006 $) 

C: w/ August T ($31,309,567)