Description and Summary Evaluation of Two Proposed Experimental Options for the Colorado 

River Ecosystem during Water Years 2007 – 2011 

For Consideration and Discussion by Members of the Glen Canyon Dam Technical Work Group 

at their May 24-25, 2006 Meetings 

Prepared by the Grand Canyon Monitoring and Research Center in Cooperation with Members 

of the Science Planning Ad Hoc Group through its affiliation with the Glen Canyon Dam 

Adaptive Management Work group 

May 17, 2006 

1 
SECTION I – Background on Experimental Planning 

Background: The Glen Canyon Dam (GCD) Adaptive Management Program (AMP) has been 

evaluating the Modified Low Fluctuating Flow (MLFF) regime for 10 years. Recent findings 

presented at the Glen Canyon Monitoring and Research Center’s (GCMRC) 2005 Science 

Symposium and during the recent Technical Working Groups (TWG) Knowledge Assessment 

Workshop indicate that Glen Canyon Dam flows that are different from the MLFF during certain 

times of the year are likely to move the Colorado River ecosystem (CRE) in the Grand Canyon 

closer to the stated purposes of the Glen Canyon Dam Environmental Impact Statement (EIS) 

preferred alternative, and to protect and improve the values for which Grand Canyon National 

Park and Glen Canyon National Recreation Area were established. 

Purpose: Identify a suite of flow and non-flow actions that will be implemented or tested in FY 

2007-2011. The experimental plan provides the foundation for 5-Year Monitoring and Research 

Plan and FY 2007-08 Biennial Work Plan. 

• General Goals of Each Experimental Option 

• Improve resource conditions 

• Enhance understanding (learning) of relationship between proposed action and 

target resources. 

Experimental Options Evaluated by SPG: Five experimental options were developed 

cooperatively by GCMRC and the SPG: 

1. Continue evaluating MLFF in spring/summer/ fall, with winter ramping experiments and 

Beach Habitat Building Flows (BHBF) in winter/spring. 

2. Continue evaluating MLFF in spring and summer, w/ winter ramping experiments and 

BHBF in winter/spring and stable flows in September and October. 

3. Increased fluctuating flows in summer and winter, BHBF in fall, and implementation of a 

wide-ranging suite of management actions. 

4. Seasonally adjusted steady flows throughout the year, possible spring BHBF and 

implementation of a limited suite of management actions. 

5. Seasonally adjusted steady flows implemented incrementally over a period of 6 years, 

possible spring BHBF, and implementation of a limited suite of management actions. 

 Option 1 was dropped by the SPG in favor of Options 2 and 3. A concerted effort was made 

by the SPG to combine Options 2 and 3 that evolved into SPG Option A. Option 4 was dropped 

in favor of Option 5, which became SPG Option B. Each option consists of flow and non-flow 

treatments and activities that are intended enhance understanding (learning) of relationship 

between proposed action and target resources while also benefiting CRE resources. The 

descriptions included here were based on input from SPG members and/or agreements arrived at 

during SPG meetings. The suite of treatments associated with each experimental option is 

intended to be implemented at the earliest opportunity, beginning as early as Water Year 2007. 

No-Action Alternative: The No Action Alternative would involve a continuation of the MLFF 

operation pursuant to the 1996 Record of Decision (ROD). 

2 
 Assuming a continuation of 8.23 million acre foot annual releases, the No-Action Alternative 

would consist of daily release patterns very similar to flows that have occurred during Water 

Year 2006. Daily peak flows would be highest in summer months of July and August, with 

peaks of between 17,000 and 19,000 cfs, while the lowest peak flows would occur in shoulder 

season months during spring and fall. Peak flows in winter months, such as December through 

February, also be similar to operations that occurred in WY 2006. 

 The No-Action Alternative would allow for continued monitoring and evaluation of 

experimental treatments that were implemented during Water Years 2003 through 2006, (such as 

BHBF and alternative fluctuating flows during winter). Continuing MLFF would also provide 

an additional period of time to monitor and evaluate the effects of (a) significantly warmer 

summer and fall releases from the dam in 2003-2006 and (b) a reduced population of rainbow 

trout (RBT) on humpback chub (HBC) survival and recruitment. Additional management 

actions or experiments, such as BHBF, translocation of HBC or non-native fish management 

could be undertaken under the No-Action Alternative. 

Summary Comparison of Experimental Options A and B: Major elements of SPG Options A 

and B are shown in a side-by-side comparison in Table 1.1. For purpose of description, each 

option is assumed to be implemented in association with minimum annual releases from GCD of 

8.23 million acre feet. However, either of the options could be implemented under higher (or 

lower) annual releases. 

3 
Table 1.1. Side-by-Side Comparison of Flow and Non-Flow Treatments Proposed within 

Experimental Options A and B. 

Flow/Non-Flow Treatment, 

Management Option or 

Conservation Measure 

Option A 

Enhanced Fluctuating Flows 

(10 months), in combination 

with ecologically stable 

flows (2 months), w/ 

Enriched BHBF 

(winter/spring) 

Option B 

Stable Flow Testing, initially 

in summer/fall (4 mos.), 

eventually moving toward 

Seasonally Adjusted Steady 

Flows in all months, w/ 

Enriched BHBF(winter/spring) 

Implement Expanded 

Fluctuating Flows Testing 

Yes, (all months except in 

September and October) 

None (all releases within ROD 

operating constraints) 

Stable Flows Yes, but Sep.-Oct. Only Yes, (4-12 months each year) 

Beach/Habitat-Building Flow 

(41,000 to 45,000 cfs, 1-3 

days, in spring) 

Yes, (in April following sand 

enrichment from major 

tributaries) 

Yes, (in April following sand 

enrichment from major 

tributaries & depending Native 

Fish considerations) 

Ramping Rate Studies Yes (November – August) None (ROD ramping rates) 

Tests of Exotic Fish Control, 

(Warmwater & Coldwater) 

Yes, as needed Yes, as needed 

Build & Test (Selective 

Withdrawal Structure) 

Yes Yes 

HBC Translocation Yes Depends on Further Analysis 

HBC Refuge(s) Yes Depends on Further Analysis 

HBC Population 

Augmentation Planning 

Planning efforts toward 

Implementation (as needed) 

No activities toward this action 

4 
SECTION II - Experimental Option Summary Descriptions 

DESCRIPTION OF EXPERIMENTAL OPTION A 

Introduction: SPG Option A provides for increased fluctuating flows in summer and winter, 

BHBF in winter/spring, and implementation of a wide-ranging suite of management/ 

experimental actions. Option A emphasizes achieving resource improvements using a suite of 

flow and non-flow actions: HBC conservation would be provided through exotic fish control, 

augmentation planning, translocation, Selective Withdrawal Structure (SWS) operation, annual 

steady flows (in September and October) and BHBF tests conducted under tributary enriched 

supply conditions. Increased fluctuating flows in winter and summer would be targeted at: 1) 

increasing hydropower generation during periods of high energy demand, 2) enhancing aquatic 

food base production and delivery of organic drift for potential diet to RBT an HBC, and 3) 

improving rainbow trout fishery below GCD. Option A also proposes several short-term 

experiments (such as LCR confluence ponding) to promote learning about the effects of dam 

operations on CRE resources. 

The SPG reached the following agreements with respect to the elements of Option A:

Continued Testing of Beach/Habitat-Building Flows with a New Trigger: Experimental 

BHBF would occur under a new “sediment trigger.” The trigger for the a BHBF would be: 1) 

0.5 million metric tons of sand is introduced by the Paria River and retained above RM 30; and 

2) an additional "weighted" one million metric tons of sand is delivered by the Paria River, Little 

Colorado River (LCR) or lesser tributary sources in-between. To calculate the weighted input, 

sand from the Paria River is given full value, and sand from the LCR and other sources is valued 

at 50% of the actual input. Under this new trigger, the sand supply from the LCR can be 

factored into future sediment experiments, but there is a check on implementing a BHBF test 

solely on the LCR inputs to avoid scouring eddies upstream in the Marble Canyon reach. 

 BHBFs would also be implemented subject to the following guidelines (not rules): 

• Special steady flows are not required to retain sand until the trigger is achieved 

• Adequate funding is available to research and monitor effects 

• Adequate water is available 

• BHBF tests would not result in unacceptable, adverse impacts (e.g., tamarisk 

reproduction, impact HBC, food base) 

• BHBF’s would promote ecological integrity of the CRE 

 The SPG agreed that decision guidelines for such test flows should be flexible enough to 

allow for BHBF research to occur on a frequent basis that allows potential benefits from repeated 

tests under tributary sand enriched conditions to be fully evaluated. The specific scope/objectives 

of effort would be based on a GCMRC proposal/plan for testing and implementing the BHBF 

based on new sediment trigger and BHBF guidelines. 

Stable Flow Testing: The SPG asked some fundamental questions relating to future proposals 

for testing steady flows: “What are “steady flows?” and “Is there a range of fluctuations that is 

5 
ecologically insignificant. The SPG agreed that the GCMRC would be requested to develop a 

proposal to test ecologically steady flows in September, October, and possibly November to 

improve HBC survival and recruitment. Tests would be targeted at defining an ecologically 

steady flow, the level of steady flow, and the effect of a short duration spike (e.g., 1 hr/5000 cfs) 

to benefit food base drift. Another flow element agreed upon was that the river can not drop 

below 7,000 cfs. While steady flows in August may be important to young-of-year (YoY) HBC 

in the main stem and to minimize export of sand following tributary input, they were not 

included in Option A because of adverse impacts to power generation. 

HBC Augmentation Planning will be included as an element Option A. Planning activities 

would include developing a captive brood stock/refuge population, a genetics management plan, 

a stocking plan, and identification of production/grow out facilities in preparation for possible 

need for future augmentation (as determined by Fish and Wildlife Service (FWS)). 

Augmentation planning was viewed as a prudent and needed safe guard in case of catastrophic 

loss associated with possible negative effects of the Experimental Program (e.g., SWS and the 

related potential proliferation of warm and cool water non-native fish). 

Power Costs Analysis: Western Area Power Administration (WAPA) committed to provide 

estimated power costs and methods of calculation for each option for review by the Science 

Advisors prior to the SPG/TWG meeting in May. 

Selective Withdrawal Structure: Option A includes construction of a SWS by 2011 or sooner

if possible. The goal of the SWS will be to maintain ecological integrity in the CRE, coldwater 

trout fisheries in Lees Ferry reach, and improve main stem habitat for HBC and other native 

fishes. The issue of how many units to implement to achieve desired effects (i.e., are two units 

enough?) was unresolved and presumably would be addressed in the NEPA process. 

Mechanical Removal: The scope of a the mechanical removal effort will be based on the 

GCMRC proposal/plan for developing, testing, and implementing methods for control of 

problematic non-native fishes in main stem below Lees Ferry and tributaries targeted for 

translocation/control. The GCMRC’s plan will be coordinated with Grand Canyon National 

Park’s efforts to remove brown trout from selected tributaries. Special attention is needed to 

develop public support for continuing the mechanical removal effort 

Experimental Design: Option A would be implemented using a forward titration experimental 

design in next 5-year phase with review in 2011(or when Temperature Control Device (TCD) 

becomes operational) to determine appropriate actions and experimental design for the future. 

Actions and experimental design in the later phases of experimentation will be determined by the 

response of HBC and sediment to the actions implemented in the next 5 years.

 

6 
 Option A envisions the implementation of all of the actions described in Table 2.1. Some of 

these actions are ongoing while others would be implemented as soon as feasible or following 

appropriate research and planning. The effect of the management actions described here would 

be monitored, to the extent possible, throughout the program’s implementation. Program 

implementation would be subject to change if scientific information and analysis was gathered 

that suggested an adverse effect of the program on the HBC population or other priority CRE 

resources. 

Proposed Modifications To The Modified Low Fluctuating Flow Regime 

 The Glen Canyon Dam EIS Record of Decision identified the MLFF alternative as the future 

operational regime for Glen Canyon Dam. Proposed experimental fluctuating flows associated 

with Option A, include alternative operations that allow a 2X increase in the hourly downramping rate (3,000 vs. 1,500 cfs/hr.) during the months of November through August. In 

addition, daily ranges in fluctuations are allowed to expand to 10,000 or 12,000 cfs/day versus 

the current limit of 8,000 cfs. Months that are subject to the largest increase in daily stage are 

associated with winter and summer peak energy demands. January would have a daily range of 

12,000 cfs, while July and August would have a daily range of 10,000 cfs rather than 8,000 cfs. 

Under Option A daily fluctuations would be greatest in January (5,000 to 17,000 cfs), but also 

relatively high in February (5,000 to 15,000 cfs), July, and August (both 8,000 to 18,000 cfs). In 

water years with annual volume greater than 8.25 million acre feet, release patterns consistent 

with the proposed pattern described here would be developed. 

Proposed “Mini” Flow Experiments 

 In addition to the proposed daily, weekly, and annual pattern described above, Option A 

include a number of other experiments that would be conducted including are non-native fish 

management flows (e.g., summer stranding flows) 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 adaptive management as discussed below. 

Summer Stranding Flows - The conceptual design of a summer stranding flow to control 

survival/recruitment of larval and YoY trout was proposed by Korman et al. (2005). 

 Korman et al. (2005) observed that YoY trout generally occupied the daily minimum flow 

elevation even after flows rose during the day, and thus avoided stranding when flows fluctuated. 

They noted substantial decreases in density following the early September reduction in the 

minimum daily flow from 10,000 to 5,000 in 2003 and 2004. Based on their observations and a 

review of the literature, they identified that the factors that affect the extent of stranding include 

channel morphology, substrate, fish size and age, species, time of day, exposure frequency, 

season, temperature, and the rate of stage change. The extent of stranding has been observed to 

be highest in low-angle habitats, such as Lees Ferry, with abundant cover. Small brown trout (50 

cm) have been shown to be more vulnerable to stranding than larger juveniles. Stranding rates 

tended to increase at lower water temperatures and were highest if flow reductions occurred 

during daylight hours. A decrease in the down-ramping rate from 60 cm/hr. to 10 cm/hr was 

shown to reduce stranding of brown trout YoY by 50%. 
 Based on these observations, they hypothesized that if higher flows were maintained for an 

extended period of time, young fish would eventually move to those higher elevations. Thus, an 

effective stranding flow would be one that maintained elevated flows (e.g., 15,000 cfs) for 2 or 3 

days and was followed by a very sharp drop in flows to a minimum flow level (e.g., 7,000 cfs). 

The most effective timing of such a flow would be when large numbers of YoY trout are present, 

(i.e., June, July, or August). 
Table 2.1. Experimental Program Elements Associated with Option A, 1998 to 2011.1 1Orange indicates element not impleme

implemented during a particular year. MLFF = modified low fluctuating flow alternative, BHBF = Beach/Habitat Building Flow. 2Modifications relative to ROD flows i

during weekdays, but relatively higher minimum flows on Sundays with flows never dropping as low as ROD flows on Sundays; faster downramp rates; and experiment

flows and fall flows. 3Adaptively managed to be shifted to control of warmwater nonnative species as necessary. 

Water Year 

Dominant Dam Operation Mechanical Removal

Temperature Control Device (TCD) 

Beach/Habitat Building Flow 

Humpback Chub Comprehensive Plan Research 

2003 MLFF with 

experimental fluctuating flows 

Trout removal No TCD No BHBF No activities 

2004 Same as previous Same as previous No TCD No BHBF No activities 2005 MLFF with 

experimental fluctuating flows and fall testing 

Same as previous No TCD Fall BHBF No activities 

2006 Modified MLFF 

w/Ecologically Stable Flows in September and October [see text for description]2 

Trout and possibly warmwater species removal3 

Complete Draft EIS/BO Spring BHBF 

dependent on sediment input from Paria and Little Colorado Rivers 

Research and development of augmentation approac

2007 Same as previous Same as previous Complete FEIS/BO Same as previous Same as previous 2008 Same as previous Same as previous Initiate construction Same as previous Same as previous Water Year 

Dominant Dam Operation Mechanical Removal3 

Temperature Control Device (TCD) 

Beach/Habitat Building Flow 

HBC Comprehensive Plan Research 

2009 Knowledge Assessment 

Same as previous Same as previous Continue construction Same as previous Continue research or 

begin implementation appropriate 

2010 Same as previous Same as previous TCD operations Same as previous Same as previous 2011 Same as previous Same as previous Same as previous Same as previous Same as previous 2012 Same as previous Same as previous Same as previous Same as previous Same as previous 
 Despite the expectation that a summer stranding flow could be effective in controlling trout 

numbers, and thus competition with and predation of HBC, a number of uncertainties exist that 

would be evaluated during experimentation. For instance, an observed reduction in small fish 

following a sharp drop in flows could reflect transport out of the reach rather than mortality. 

Stranding mortality of YoY fish ultimately may not affect the size of the adult population if 

survival at this life stage is not a limiting factor for the population or if compensatory 

mechanisms effectively negated the effect of increased mortality. There is also the potential for 

stranding of native fish species. These factors would be evaluated during stranding experiments. 

Ponding Flows - Ponding flows are those relatively high mainstem flows that produce a quiet 

water area near the mouth of the Little Colorado River. This ponded area gives young humpback 

chub a place to grow before they enter the harsher conditions of the main channel Colorado 

River. It has been hypothesized that this area is important to increasing the survival of young 

humpback chub. The timing of ponding flows has generally been considered for the spring. 

Although ponding flows have been provided in the past, their effectiveness has not been 

demonstrated and is considered very uncertain. Ponding flows could be considered for 

incorporation into the proposed long-term experimental program especially in high water years 

or in years when equalization releases are needed. 

Electrical Power Production Experiments - The 1996, ROD flows were intended to improve 

the status of a variety of resources in the CRE. The operational parameters of these flows were 

conservatively chosen to ensure that the anticipated benefits to these resources would be 

achieved, and operational parameters were to be reexamined and modified as appropriate 

through an adaptive management process. However, there has been very little experimentation 

directed at the operating parameters themselves. For example: would a factor of two increase in 

the down-ramp rate have a measurable and deleterious effect on sediment retention of Marble 

Canyon beaches? Does an increase in the daily variation (25 to 50 percent) produce additional 

drifting food for trout and humpback chub? Can New Zealand mud snails be reduced by a 

higher daily variation? 

 As part of Option A, short-term experimentation is proposed with operational parameters. 

This would likely include the modification of more than one operating parameter at a time since 

recent analysis show very little power benefit from the liberalization of just one parameter. 

These experiments could be conducted at any time of the year; however, they may be 

concentrated in the winter months when the most benefit to power resources might be achieved 

with little harm to other resources. 

Proposed Non-Flow Management Actions and Anticipated Effects 

Selective Withdrawal Structure -- Before Glen Canyon Dam was constructed, the seasonal cycle 

of the Colorado River included a natural warming trend in the late summer as the water 

temperature would increase from the near freezing winter temperature to approximately 29o

C. 

Since the dam was constructed, the temperature of the water released has become relatively 

steady at between 7 and 10°C because the water is drawn year round from the deep, fixed-level 
penstock intakes. Near the dam, these cold releases are tolerated by the trout fishery, but as this 

water moves downstream, it only warms to about 15.5°C which is not warm enough to allow 

humpback chub to reproduce in the mainstem of the Colorado River. Cold summertime water 

from these hypolimnetic releases can inhibit hatching and survival of eggs and larvae and it is 

believed that juvenile HBC (<50 mm TL) can experience thermal shock as they descend into the 

mainstem Colorado River from seasonally warmed tributaries. 

 Recent drought conditions have resulted in warmer releases as reservoir elevations have 

dropped. However, without a TCD, increasingly cooler release temperatures are expected. The 

Science Advisory Board has recommended a pilot program to install selective withdrawal 

structures on two of the units at Glen Canyon Dam. Option A includes implementation of this 

recommendation over the next 5 years (Table 2.1). However, because analyses indicate that 

placing temperature control devices on only two-units may not be sufficient to increase the 

temperature of the river to levels that will promote reproduction by HBC, Option A proposes that 

consideration be given to the planning and compliance work needed to construct selective 

withdrawal structures on enough units to increase water temperature below the LCR to levels 

that would improve the survival of larval and juvenile HBC. 

 Because increasing water temperatures in the mainstem Colorado River could potentially 

improve conditions for some warmwater non-native fishes that compete with or prey on HBC, 

additional experimentation would be warranted. The goal would be to determine the appropriate 

combination of cold and warmer water withdrawals needed to benefit the native endangered fish, 

while controlling benefits to warmwater non-native fishes in the system. 

Humpback Chub Augmentation Planning- Option A includes a variety of HBC augmentation 

planning activities for the FY 2007-2011 period, including developing a captive brood 

stock/refuge population, a genetics management plan, a stocking plan, and identification of 

production/grow out facilities in preparation for possible need for future augmentation (as 

determined by FWS). Establishment of a captive broodstock would provide a genetic refuge for 

humpback chub. However, releasing propagated individuals from this broodstock into the wild 

could pose biological risks such as genetic introgression, inbreeding depression, domestication, 

and a potential to decrease the effective population size of the wild population (Van Haverbeke 

and Simmonds, 2004). To mitigate a potential catastrophe and as part of developing a captive 

broodstock program, a captive broodstock management plan would be developed now, an 

adequate facility for holding fish would be identified, and a stocking plan would be developed. 

Humpback chub currently being held at Willow Beach National Fish Hatchery could serve as a 

starting point for such a program (Van Haverbeke and Simmonds, 2004). 

 In addition, consideration would be given to developing grow-out ponds, where larval or 

juvenile fish could be held in a predator-free environment until they are large enough to survive 

and be reintroduced into the CRE. The fish to be maintained in these ponds could originate from 

captive adults spawned in captivity as part of a broodstock program or could be obtained by 

capturing wild larvae or juveniles. 
Efforts to Increase the Geographical Extent of Occupied Humpback Chub Habitat in the 

Colorado River Ecosystem - In order to expand the areas inhabited by HBC and to protect the 

Grand Canyon population of HBC from potential catastrophic events in the Little Colorado 

River, it has been proposed that YoY humpback chub be translocated to other Grand Canyon 

tributaries. 

 Translocation activities were initiated in the LCR during August 2003 and August 2004, by 

capturing YoY humpback chub in the lower portion of the LCR and moving them to locations in 

the LCR upstream of Chute Falls (a natural barrier to upstream migration). Results of 

monitoring indicate that at least some of the translocated fish survived and grew well in the 

upper portion of the LCR (Sponholtz et al. 2005). This resulted in an expansion of the inhabited 

range of HBC by 4 km and there were indications during 2005, that some of the translocated fish 

were in spawning condition. It is not yet known whether offspring were produced by these fish. 

Expansion of the population above Chute Falls, while potentially beneficial, would not remove 

susceptibility of the population to a catastrophic event in the Little Colorado River. 

 Initial efforts to expand translocation activities would include research and field 

experimentation to identify candidate streams and to determine where translocated fish would be 

likely to survive. Although the goal would be to produce a fully self-sustaining HBC population 

outside the LCR, even establishing additional areas that contain fish that do not reproduce would 

result in improved protection for HBC in Grand Canyon. It is anticipated that monitoring would 

be required to evaluate the success of translocation efforts, to track the status of translocated fish, 

and to improve knowledge about the biological requirements of humpback chub. 

 Some initial work has been done to rank potential tributary sites (Stevens 2005) based on a 

variety of criteria. These criteria included the presence of barriers to fish movement, the 

abundance of non-native predators, abundance of native fish, habitat suitability (e.g., temperature 

regimes), perceived ability to remove non-natives, and jurisdictional issues. Compared to the 

LCR, which presently contains the best known available conditions for YoY humpback chub, the 

tributaries that ranked the highest were Bright Angel Creek and Shinumu Creek. 

Mechanical Removal of Non-native Fishes - The presence of non-native fishes in habitats 

occupied by HBC is considered one of the major threats to survival of HBC populations in Grand 

Canyon. In addition to implementing selected flow-related actions to reduce the numbers of 

non-native fishes in occupied areas, advocates for Option A, believe that mechanical removal 

actions should also be conducted. 

 Since January 2003, mechanical removal using electrofishing has been conducted on an 

experimental basis in the Colorado River. The current mechanical removal efforts, which are 

ongoing, target a 24-km reach of the Colorado River that extends from 8 km upstream to 16 km 

downstream of the LCR. These efforts have been primarily intended to remove rainbow and 

brown trout, which are known predators of juvenile HBC. Over 16,000 trout were removed from 

the treated reach of river during 2003 and 2004 and there are indications that the abundance of 

trout within the reach dropped by over 50% during that time (Coggins and Yard, 2005). 
 In addition to electrofishing, weirs or other fish-trapping methods could be used to remove 

trout from tributaries. This technique may be useful for controlling trout spawning in Colorado 

River tributaries by removing adult trout as they move into tributary spawning areas. In 2002, a 

feasibility study was initiated in Bright Angel Creek, a known spawning tributary used by brown 

trout, to evaluate trout capture potential using a weir. During the 64 days the weir was in use, 

423 brown trout and 188 rainbow trout, ranging in size from 210 to 620 mm, were captured 

(SWCA Environmental Consultants, 2005). This study indicated that fish-trapping methods 

could be an efficient and cost-effective way to remove non-native salmonids from native fish 

habitat and to reduce trout spawning success in tributaries. If Colorado River tributaries, such as 

Bright Angel Creek, are selected as sites for introducing translocated HBC juveniles (see above), 

such methods could be extremely valuable for reducing the numbers of non-native fishes in the 

tributaries or for controlling access by non-native fishes. 

 As part of Option A, it is proposed that mechanical removal efforts be continued as part of 

the long-term integrated experimental program, on an as-needed basis. If water temperatures 

increase as a consequence of natural conditions (e.g., low flows and low reservoir elevations) or 

because of the construction and operation of a temperature-control device, there is a possibility 

that warmwater nonnative fish species could expand to areas currently utilized by YoY HBC. To 

combat such expansions, mechanical removal efforts should be adapted, as necessary, to target 

other species, in addition to trout, that are identified as being the dominant predators and 

competitors with HBC. 
DESCRIPTION OF EXPERIMENTAL OPTION B 

 The approach used to develop Option B, was to first determine the priority resources and 

values for experimentation by using legal and policy guidance, and an analysis of status and 

trends of park values. The next step was to identify the threats that limit the abundance and 

distribution of these resources. Finally, Option B includes an experimental approach that: a) 

addresses the threats; b) tests alternative management scenarios that are scientifically credible 

and likely to succeed in reversing declines in park values; c) provide sufficient contrast and 

duration to draw reliable conclusions; and d) could be implemented in the future to meet the 

intent of the Grand Canyon Protection Act. 

Priority resources - A thorough review of legal and policy documents as well as the status and 

trends of park resources and values, it is clear that the distribution and abundance of humpback 

chub and the distribution and abundance of sediment resources are park values that have 

undergone significant declines in the CRE. An analysis of the status and trends of these 

resources suggests that the key research questions are: a) how can resource managers restore 

rearing habitat for humpback chub in the mainstem?; and b) how can resource managers 

maintain a positive mass balance of sand? 

Threats - The most significant threats to the distribution and abundance of humpback chub 

appear to be changes in water temperature, daily flow fluctuations, non-native predators, 

competitors and parasites, and range contraction. The most significant threats to the 

distribution and abundance of sediment resources appear to be the loss of mainstem sediment 

inputs, daily flow fluctuations, and flow magnitude. 

Experimental approach (WY 2007 to WY 2013) - From Water Year 2007 through WY 2013, the 

proposed Option B design tests the effects on humpback chub and sediment of equalized monthly 

volumes with ROD fluctuations (Flow A), combinations of steady and constrained fluctuating 

flows of different duration (Flows B & C), as well as seasonally-adjusted steady flows (Flow D). 

Flows B, C, and D are replicated (factorial design). 

 In addition to testing the effects of these flows on sediment abundance and distribution, and 

humpback chub abundance and distribution, Option B includes a rigorous evaluation of these 

flows on other resources, including the food base, recreation, and cultural resources. The flow 

regime included in Option B is expected to benefit theses resources (e.g. the food base as a result 

of stabilized flows, recreation as a result of increased quantity and quality of camping beaches, 

cultural resources as a result of counteracting erosion with increased aeolian transport of 

sediment). 

Additional Non-Flow Treatments - In addition to these flows, Option B, advocates for non-native 

species control as needed through WY 2013. Other non-flow management actions such as 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) are still open to risk analysis and a 

discussion of the options available to meet the perceived need. Option B does not include 
humpback chub augmentation, but does focus on taking steps to improve habitat below the dam. 

The flows associated with Option B, are summarized below in Table 2.2, and the following text. 

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

Dates Flow Monthly 

volume1

Discharge (cfs)2 BHBF3

October 2006 to July 2007 A 700 ROD fluctuations 

(7500-13,500) 

No 

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

December 2007 to July 2008 C 720 Constrained fluctuations 

(: 4000 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 

(: 4000 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 

(: 4000 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 

(: 4000 daily) 

One or more if 

triggered 

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

April 2012 1060 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 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 AGC purposes. 

3

 BHBF are 41,000 to 45,000 for 1-3 days depending on research objectives. 
April 2013 1060 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 620 Steady (10,000) No 

Flow A (Equalized monthly volumes) - This block tests the level of sediment accumulation under 

equalized monthly volumes and ROD flows. Equalizing monthly volumes eliminates months with 

high sediment export rates, maintains a higher minimum flow throughout much of the year for 

increasing food base productivity, and retains daily fluctuations for load following. These flows 

will allow testing of the hypothesis that stable near-shore habitats will support growth and 

recruitment of young humpback chub. No BHBF will occur in conjunction with these flows. 

Flow B (Short-term steady flows) - These blocks test whether four or eight months of steady 

flows are sufficient to provide humpback chub rearing habitat in the mainstem. The blocks begin 

in August when the highest numbers of young-of-year normally enter the mainstem. The steady 

flows provide a stable near-shore environment and an increase in water temperature (especially 

in backwaters). These flows will allow testing of the hypothesis that stable near-shore habitats 

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

BHBF will occur in conjunction with these flows. 

Flow C (Constrained fluctuations) - Fluctuations are constrained to reduce sediment transport 

and still allow growth in the food base while providing some fluctuations to reduce impacts on 

hydropower generation. These flows will allow testing of the hypothesis that stable near-shore 

habitats will support growth and recruitment of young humpback chub. 

 During these flows, a BHBF will occur immediately once the sediment input trigger is met. The 

trigger is met when: 1) 0.5 million metric tons of sand is introduced by the Paria River and retained above 

RM 30; and 2) an additional "weighted" one million metric tons of sand is delivered by the Paria River, 

Little Colorado River or sources in-between. To calculate the weighted input, sand from the Paria River 

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

However, a BHBF will not occur if there is a high risk of unacceptable negative impacts (this criterion 

will be quantified if possible) to young-of-year humpback chub residing in the mainstem. 

 Experimentation with limited duration "supply conditioning" fluctuating flows may occur 

before the BHBF to test whether prescribed fluctuations will more evenly distribute the sediment 

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

subsequent sediment input trigger is met during the same block of experimental flows, then 

another BHBF test will immediately occur. 

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 1.5 million metric tons of tributary supplied sand in Marble Canyon. No 

“supply conditioning” fluctuating flows will occur. 
Experimental approach (WY 2014 and beyond) - For experimentation starting in WY 2014, 

proponents of Option B, advocate a timely reassessment of the status and trends of park values, 

as well a reassessment of our knowledge of the effects of flows, temperature and non-native 

control and further testing (as needed) of both daily and seasonally variable flows, temperature 

(using a SWS), BHBFs, and non-native control in a factorial design. Based on the modeling 

results evaluated to date, Environment favors a pilot SWS with three or four units to maximize 

the duration of warm water when YoY humpback are the most vulnerable to the negative effects 

of cold water. 
SECTION III 

Estimated Impact Of Option A And B On The Colorado River Ecosystem 

 The two experimental options described above were evaluated by the GCMRC staff and 

cooperating scientists relative to their operational flow elements and predicted influence on: 1) 

downstream water temperature, 2) suspended-sand transport, 3) hydropower economics, 4) river 

stage variation, 5) stability of shoreline habitats, 6) productivity of the food web, 7) drift, 8) 

recreational camping and 9) potential for wind-blown sand to mitigate erosion of cultural sites 

located above the active fluctuating zone (5,000 to 25,000 cfs). 

 Throughout the experimental planning process, attempts were made to use best-methods and 

simulation capabilities to predict how key resources would be influenced by the various 

experimental operations being proposed. Although quantitative estimates were attempted for 

Options A and B, with respect to suspended-sand transport in March 2006, the estimated costs 

and benefits to hydropower associated with Option A were derived from a projected annual 

hydrograph that was significantly different than the one used to estimate the sediment transport 

values. Because the economic benefit estimated for Option A was associated with an annual 

hydrograph that was not similar to data for Option A, comparisons of the two experimental 

options are presented here in only a very general way. 

Estimate of Influence on Downstream Water Temperatures 

Flow Patterns - The reduced peak fluctuating flows associated with Option B results in lower 

flow velocities for water released from Glen Canyon Dam, and therefore promotes more 

downstream temperature increases in late summer and fall months than flows associated with 

Option A. In addition, stable flows in summer months, such as August, associated with Option 

B, promote increased warming in late summer months when dam releases tend to be at their 

annual warmest. Summer flows under Option A are not stable until September, October, and 

possibly November so Option B tends to provide more potential for both downstream warming 

and stability in late summer when young-of-year native fish could be flushed from the Little 

Colorado River into the main channel habitats by summer spates. Near-shore aquatic habitats, 

such as backwaters are thought to warm most efficiently under more stable flows, while 

fluctuating flows tend to disrupt warming by diurnal filling and draining the water in them. 

Selective Withdrawal Structure - Estimating effectiveness of Selective Withdrawal 

Structure operation has been recently undertaken by Reclamation. On the basis of the 

simulations run for historical hydrology for Water Years 1992 through 1994, release 

temperatures from Glen Canyon Dam appear vary from about 7 to approximately 22 degrees 

Celsius annually under the proposed SWS design. The degree to which release temperatures are 

elevated also appears to vary relative to hydrology and storage conditions in Lake Powell, as 

well as the total number of units (2 vs. 4 vs. 6 vs. 8 of 8) that are retrofitted with external intake 

structures at the dam. While all of the simulations for these historic hydrologic conditions 

achieve a release temperature of 15 degree Celsius with a minimum of two of the eight units 

operated with SWS, the duration over which that temperature can be sustained can be expanded 

under certain hydrologic conditions through addition of SWS’s on all eight units (WY 1994 
simulation). Under the hydrologic conditions of WY 1993, little if any increase duration of 

warming was associated with simulated releases between 2 and 8 SWS’s. Operation of a 

variable number of SWS’s in combination with either diurnally varied or stable release patterns 

also influences the degree to which dam releases are additionally warmed at water moves 

downstream through the ecosystem. 

Estimate for Suspended-Sand Transport 

 Option A - On the basis of recent sand-transport data collected below Glen Canyon Dam, 

sediment scientists (S. Wright and D. Topping, personal communication) estimate that the 

operational releases associated with Option A would result in a relative, moderate increase in 

suspended-sand transport compared to Record-of-Decision operations that have occurred under 

8.23 MAF annual releases since 2000. Although sand transport would be elevated during winter 

and summer months, when experimental fluctuating flows were enhanced, sand transport would 

also be reduced in the months of September and October, under “ecologically” stable flows. The 

net, overall influence of the combined operations is predicted to increase annual sand transport, 

but not dramatically when compared with ROD operations. While tributary sand inputs would 

likely accumulate in the main channel during fall months with ecologically stable flows 

associated with Option A, recent monitoring data suggest that average to below average sand 

inputs would be quickly exported downstream during peaking operations in summer and winter 

under Option A. Elevated sand transport of newly input sand supplies during November through 

December fluctuating flows could possibly help in distributing new sand deposits on the bed of 

the main channel more evenly downstream throughout reaches, such as lower Marble Canyon 

and Eastern Grand Canyon prior to High-Flow testing after December when sediment triggers 

are met. This concept must be field tested, as the idea of a more uniform sand bar restoration 

response following tributary sand inputs and a limited period of fluctuating flows with daily 

peaks between 14,000 and 16,000 cfs, is a hypothesis. 

 Option B - On the basis of recent sand-transport data collected below Glen Canyon Dam, 

sediment scientists (S. Wright and D. Topping, personal communication) estimate that the 

operational releases associated with Option B would result in a substantial reduction in 

suspended-sand transport during the initial year (Flows A) of Option B, and an even greater 

reduction in sand-transport for years in which seasonally-adjusted steady flows (Flows D) occur, 

compared to ROD operations that have occurred under 8.23 MAF annual releases since 2000. 

Monitoring data collected since 1999 suggest that tributary sand supplies would likely 

accumulate within the main channel under Option B experimental operations in all months of the 

year. Accumulation of annual tributary sand inputs prior to implementation of BHBF’s was an 

original strategy identified in the 1995 final EIS on Glen Canyon Dam operations for restoring 

sand bars and related habitats. 

Relative Estimates for Costs and Benefits to Hydropower 

 Option A - On the basis of some very preliminary economic modeling conducted by Western 

Area Power Administration, an attempt is made here to characterize the relative costs and 

benefits to the hydropower resources, with respect to the Colorado River basin fund. Only 

general, relative comparisons are presented here for the costs and benefits of Options A and B. 
For purposes of simple comparative analysis, the benefit to the hydropower resource associated 

with Option A is defined as +X. The estimated costs to hydropower associated with Option B 

will be therefore described as –nX. 

 Relative to the ROD, operations associated with Option A are thought to provide benefit to 

hydropower by reducing the extent to which the Colorado River basin fund must currently be 

used to purchase replacement power to meet customer need. This benefit is associated with the 

ability to more optimally follow customer demand throughout the day during high-demand 

months associated with winter and summer. 

 The annual benefit to hydropower under Option A of +X is somewhat limited by the 

proposal to release “ecologically” stable flows during the months of September and October 

during each experimental year. The benefit to hydropower during the remaining ten months of 

the year is derived from the ability to test an hourly downramp rate that is twice as large as what 

is normally allowed under the ROD (3,000 cfs/hr vs. 1,500 cfs/hr), in combination with the 

ability to exceed the daily range of the ROD by 25 to 50 percent in months of peak energy 

demand (ranges of 10,000 to 12,000 cfs in some winter and summer months). 

 Option B - Proposed experimental operations associated with Option B impose additional 

costs to the hydropower resource by increasing the need to use the Colorado River basin fund to 

purchase replacement power during months when flows are steady or when fluctuating 

operations are constrained beyond what the ROD would normally allow to meet customer energy 

demand. 

 An estimate of the increased replacement power costs associated with the initial years of 

implementing Option B (Flows A and B) are approximately -3X, or three times greater than the 

benefit associated with Option A, with respect to reduced impact to the Colorado River basin 

fund. An estimate of the increased replacement power cost estimates associated with the final 

years of implementing Option B when flows are held stable throughout the year (Flows D), are 

approximately -6X, or six times larger than the estimated economic benefit associated with 

Option A, with respect to increasing replacement power costs and impact to the Colorado River 

basin fund. These relative cost/benefit assessments do not include the influence of BHBF 

releases. 

Estimate for the Increased Daily Stage Variation 

 Option A - Estimates were made for the additional difference in daily minimum river stage 

that would occur as a result of summer (August) operations associated with Option A versus 

daily lows that would occur under the Record-of-Decision diurnal operations. Comparison of 

Option A and ROD flows indicates that the difference in stage for daily flows in late summer 

would be increased by 1.7 to 2.6 feet, depending on river width and river mile. Implications of 

increased daily variations in stage associated with Option A are somewhat uncertain with respect 

to influence on native fishes. Such increased fluctuating daily range may increase drifting 

organic matter, but the operation may be limiting in the overall primary and secondary 

productivity of the ecosystem. 
Option B - has periods of fluctuations that result in daily stage variations that are typical of ROD 

operations in shoulder-season months (6,000 cfs) during implementation of Flows A, under 8.23 

MAF releases. A decrease in the variation of daily stage to 4,000 cfs per day occurs toward the 

end of Flows A and throughout Flows B and C. Otherwise, Option B mandates flows that are 

stable in all other periods except for times that BHBF’s occur. 

Stability of Shoreline Habitats 

 Option A – experimental operations in this alternative provide for “ecologically” steady 

flows each year, but only during the months of September and October. During these fall 

months, stage varies by about 2,000 cfs per day. 

 Option B - Flows associated with Option B provide for stable shoreline habitats 4 out of 12 

months a year when Flows A occur, with additional stable flow months being progressively 

added as the experimental option is continued through Flows B and C. Ultimately, during Flows 

D, all flows are stable, except during short periods in the spring when BHBFs are released 

following sediment input triggers. Overall, Option B experimental operations provide for greater 

shoreline habitat stability through time and initially result in more stable shoreline habitats 

throughout the ecosystem during late summer and fall months (August through November) 

compared to stage changes that occur under Option A (ecologically stable flows in September 

and October, only). 

Productivity Associated with the Aquatic Food Web 

 Option A has wider-ranging daily changes in stage during winter and summer months 

compared to either the ROD or Option B, but limits daily low stages in summer to 7,000 cfs. 

Increased fluctuations may result in lower aquatic productivity as compared to option B. The 

limits on daily low stages in summer (7000 cfs) may mitigate some of these impacts. 

 Option B - Although some uncertainties remain in this area of resource response, generally, it 

is estimated that more stable flows should result in greater overall productivity below the dam. 

A more constant submerged environment allows more aquatic macrophytes to establish and 

grow. Hence, Option B is predicted to result in increased food base initially under limited 

fluctuations from spring through July and stable flows in August into fall. Large operational 

changes from August to September are avoided. Option B operations would presumably result 

in increasingly greater aquatic productivity as flow stability is increased throughout spring, 

summer and fall seasons. Conversely, relatively less aquatic productivity would be derived from 

implementation of operations associated with Option A where fluctuations are larger than ROD 

in July and August. 

Transport of Drifting Organics 

 Option A – for a given level of productivity, fluctuating flows are likely to promote more 

drifting organic matter from upstream to downstream than will typically occur under more stable 

flows. However, the overall, long-term abundance of drifting material downstream is most likely 
limited by the overall productivity. For organic material to be present in the drift it must first be 

produced. 

 Option B – has more limited fluctuations than in Option There remains uncertainty about 

what the overall influence of Options A and B would be compared with ROD operations. While 

implementation of either of the experimental options would provide new opportunities to resolve 

this uncertainty. 

Recreational Camping Areas 

 Option A - wider daily ranges in fluctuating flows during summer and winter months will 

generally reduce the area of sand bars that are available for camping (above the daily peak flow 

stage for any given amount of sand bar abundance throughout the ecosystem). 

 Option B - provides more limited daily ranges and will therefore result in larger camping 

areas being available for recreational uses. 

Cultural sites and terrestrial vegetation associated with sand deposits 

 Minimizing the extent to which daily flows vary with respect to stage may allow for larger 

portions of near-shore sand bars to remain desiccated throughout the year. 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. Sandy, near-shore habitats 

along the river that are subjected to repeated wetting and drying are often the sites of 

colonization and establishment of terrestrial vegetation, both native and non-native. 

Colonization of new plants in these near-shore settings may help stabilize sand deposits, but may 

also reduce the degree to which wind can redistribute sand upslope to higher locations where 

cultural preservation sites are eroding. 

 Option A – with wider daily stage changes, more area of any given sand bar will tend to be 

inundated and wetted more frequently. The wet areas of the sand bar may be exposed to 

influence of blowing wind during the part of each day when the river stage is at its minimum, but 

the potential for sand grains to be windblown will be limited compared to similar exposure of the 

sand bar under dry conditions. 

 Option B – more highly constrained fluctuating flow operations provide more stable flow 

conditions than either those of Option A or the ROD, and therefore may result in more windtransported sand (for any given shoreline sand bar abundance) being carried into cultural sites if 

sand deposits are abundant nearby at lower elevation (presumably, maintained by successful 

restoration and maintenance influences of period BHBF implementation under enriched sandsupply conditions).