PROPOSED LONG-TERM EXPERIMENTAL PROGRAM OF FLOWS 

AND MANAGEMENT ACTIONS IN THE COLORADO RIVER 

BELOW GLEN CANYON DAM

submitted by 

Western Area Power Administration, Arizona Game and Fish Department, 

and the Federation of Fly Fishers 

January 2006 

1 INTRODUCTION

 Western Area Power Administration (Western), Arizona Game and Fish Department 

(AGFD), and the Federation of Fly Fishers (FFF) have recently proposed that an integrated set of 

flow and non-flow actions be pursued as the long-term experimental program below Glen 

Canyon Dam. The purpose of this proposed integrated program is to provide a set of benefits to a 

variety of resources including the: 

• Grand Canyon population of the humpback chub (Gila cypha); 

• Sediment resources (conservation) in the Grand Canyon critical reach over the long-term; 

• Aquatic food base; 

• Value of the power resource; and 

• Lees Ferry trout fishery. 

Although all of these resources are expected to benefit from the proposed integrated program, the 

primary focus is on the humpback chub. This program capitalizes on the information gathered to 

date on the status and trajectory of the humpback chub population, flows thought to benefit that 

population and the resources on which it depends, and non-flow management actions that would 

be effective in controlling nonnative predators and competitors of chub. 

 Several flow experiments have been tested since the ROD, including beach-habitat 

building flows (BHBF) (1996, 2004), habitat maintenance flows (1997, 2000), low steady 

summer flows (2000), winter fluctuations (2003–2005), and near steady flows (2005). Except for 

these relatively short-term experimental releases, modifications to the modified low fluctuating 

flows (MLFF) of the ROD have not been discussed or recommended by the Adaptive 

Management Program (AMP) committees or planned by the U.S. Bureau of Reclamation 

(Reclamation). However, recent findings presented at the Glen Canyon Monitoring and Research 

Center (GCMRC) Science Symposium and during the recent Technical Working Groups (TWG) 

Knowledge Assessment Workshop, indicate that Glen Canyon flows different from the MLFF 

during certain times of the year are likely to move the Colorado River ecosystem in the Grand 

Canyon closer to the stated purposes of the Glen Canyon Dam EIS preferred alternative, and to 

protect and improve the values for which Grand Canyon National Park and Glen Canyon 

National Recreation Area were established. 
Table 1. Experimental Program Elements 1998 to 2011.1

Water Year 

Dominant Dam 

Operation

Mechanical 

Removal

Temperature 

Control Device 

(TCD) 

Beach/Habitat 

Building Flow 

Humpback Chub 

Comprehensive 

Plan Research 

1998 MLFF with habitat 

maintenance flow 

No removal No TCD No BHBF No activities 

1999 MLFF only No removal No TCD No BHBF No activities 2000 MLFF with low 

summer steady flows 

and habitat 

maintenance flow 

No removal No TCD No BHBF No activities 

2001 MLFF only No removal No TCD No BHBF No activities 2002 Same as previous No removal No TCD No BHBF No activities 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 [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 

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 
Table 1 (Cont.) 

Water Year 

Dominant Dam 

Operation

Mechanical 

Removal3 

Temperature 

Control Device 

(TCD) 

Beach/Habitat 

Building Flow 

HBC 

Comprehensive 

Plan Research 

2009 Same as previous Same as previous Continue 

construction 

Same as previous Continue research 

begin 

implementation if 

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 2013 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 = modi

alternative, BHBF = beach/habitat building flow. 

2 Modifications relative to ROD flows include lower minimum flows during weekdays, but relatively higher minimum flows on 

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. 
Proposed Long-Term Experimental Program 4 January 2006 

 Our proposal envisions the implementation of all of the actions described here (Table 1). 

Some of these actions are ongoing while others could be initiated almost immediately. Finally, 

others would require some research and planning before they could be implemented. We propose 

that these management actions be implemented as simultaneously as feasible, and that the 

integrated set of actions continue until the Grand Canyon population of humpback chub is 

considered self sustaining and that the number of chubs is sufficiently above the established 

recovery goal population size that discontinuing one or more of these management actions would 

be considered an acceptable experimental risk. 

 The effect on humpback chub of the management actions described here would be 

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

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

that suggested an adverse effect of the program on the humpback chub population. 

2 PROPOSED EXPERIMENTAL FLOWS AND ANTICIPATED EFFECTS 

2.1 PROPOSED MODIFICATIONS TO THE MODIFIED LOW FLUCTUATING 

FLOW REGIME 

 The Glen Canyon Dam EIS Record of Decision (ROD) identified the Modified Low 

Fluctuating Flow (MLFF) alternative as the future operational regime for Glen Canyon Dam. In 

keeping with the adaptive management of that facility, we have proposed a modification to the 

MLFF that would benefit the humpback chub by controlling nonnative fish and improving the 

aquatic food base while providing some benefit to the power resource 

 The overall pattern of proposed flows and ROD flows in an 8.25 million acre feet water 

year is shown in Figure 1. Under our proposal, 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 shown here would be developed. 

 As compared to ROD flows, minimum flows during the week would be lower in January, 

February, and March and in June, July, and August. Proposed maximum flows would be about 

the same as ROD maxima, but slightly higher in February, March, and April and July, August, 

and September, and slightly lower in January and June. 

 One of the main purposes of the proposed modification of flows is to improve the state of 

the food base in the Colorado River ecosystem. Presumably, this can be accomplished by 

providing higher minimum flows during the summer. During the summer, when the food base is 

more susceptible to the effects of exposure, flows under our proposal would not drop below 

7,000 cfs. An examination of the graphs provided (Appendix A) compares the proposal with 

ROD flows for a typical week day for each summer month. A close examination will reveal that 

the minimum weekday flows under the ROD are actually higher during the summer months than 

the proposed flows. However, these graphs do not show possible flow patterns on Sundays. 
Proposed Long-Term Experimental Program 5 January 2006 

Figure 1. Proposed Glen Canyon Dam and ROD Releases from October through 

September. 

 Western's scheduled demand for electrical power is significantly less on Sunday. Sunday 

is considered an “off peak” time period, just like nighttime hours during the week. Western can 

take advantage of the flexibility under the ROD to save water on Sunday. This is done by 

reducing the peak flows on Saturday to something less than the ROD allows. With a lower 

Saturday peak, Western can now reduce flows on Sunday to 5,000 cfs during the 7 PM to 7 AM 

nighttime hours. Under the ROD, an 8,000 cfs minimum is required during the remaining 

daytime hours. This is referred to as "stepping down into Sunday". Western often uses this 

method to plan the week. In fact, Western and Reclamation have had discussions with the fishing 

guides about this practice over the years and has sometimes agreed to limit its use voluntarily 

depending on the state of the trout population at Lee Ferry. 

 Under our proposal, Western would agree to suspend this practice altogether in order to 

provide Sunday minimum flows that do not differ from the weekday minimum flows (i.e., 7,000 

to 8,000 cfs depending on the summer month). The proposed flows therefore, commit to a higher 

minimum flow throughout the summer season as compared to the minimum flow that would 

occur during nighttime hours under the ROD. 

 In addition to differences in maximum and minimum flows, the proposed flow regime 

differs from ROD flows in the on-peak duration (generally longer in the proposed regime as 

compared to ROD flows; Figure 2) and the downramp rate (slightly greater in the proposed 

regime; Figure 2). 

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

October November December January February March April May June July August September

Release (cfs)

Proposed Flows ROD Flows
Proposed Long-Term Experimental Program 6 January 2006 

Figure 3. Proposed Hourly Pattern of Releases for a Weekday in January. 

 During the winters of 2003, 2004, and 2005, daily fluctuations between 5,000 and 

20,000 cfs were implemented in an attempt to reduce the recruitment of rainbow trout in the 

main channel, and also to reduce competition and predation of trout species on humpback chub. 

These fluctuations were intended to reduce survival of trout eggs and young. As an incidental 

benefit, they were intended to increase the average size and health of trout in the Lees Ferry 

fishery by reducing recruitment and density, and thus lowering competition. 

 Evidence presented by Korman at the 2005 GCMRC Science Symposium (Korman et al. 

2005a), suggests that recently there may be little mainstem spawning and recruitment of rainbow 

trout downstream of the Paria River, the area the AMP wants to manage for native fishes. 

Korman also speculated that the Lees Ferry population serves as the source of the trout that occur 

near the Little Colorado River. If the Lees Ferry reach is the source of the fish that prey on and 

compete with humpback chub at and downstream of the Little Colorado River, control of the 

Lees Ferry population using dam operations could provide an important benefit for humpback 

chub. 

 The fluctuations tested did not strand or increase mortality of many adult fish, but it did 

reduce reproductive success by affecting the thermal regime at some redds (Korman et al. 

2005b). Fluctuating flows are also thought to have disoriented and stranded some larval and 

juvenile fish. Given the possible link between the Lees Ferry trout production and trout 

abundance in mainstem habitat of the humpback chub, continued implementation of fluctuating 

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

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 of Day

Release (cfs)

Proposed Operation ROD Operation

13 Hours @ 16964 CFS 15 Hours @ 17000 

4 Hours @ 5000 CFS

5 Hours @ 8964 CFS
Proposed Long-Term Experimental Program 7 January 2006 

flows appears to be warranted. Because another of the AMP goals is to maintain a healthy sport 

fishery at Lees Ferry, the overall effect of fluctuations on the quality of the trout fishery should 

be evaluated during the study period. 

 Proposed maximum daily flows would be less than those tested in 2003 through 2005, 

however, proposed minimum daily flows from January through March would be the same (i.e., 

5,000 cfs; Figure 1 and 3). Because Korman et al. (2005b) determined that the majority of redds 

occurred at elevations below the 8,000 cfs flow, the proposed flow regime should effectively 

expose redds and adversely effect reproductive success. Because most spawning occurs in midMarch (Korman et al. 2005b), fluctuations at this time of the year are expected to have the 

greatest impact on reproductive success of trout. The effectiveness of the proposed winter 

fluctuation pattern would be tested and compared to the results of Korman et al. (2005b).

 Helwig and Leibfried (Appendix B) reviewed the literature regarding the aquatic food 

base in the Colorado River below Glen Canyon Dam and the effects of flow magnitude and 

fluctuating flows on standing crop and drift. Their evaluation suggests that increased flows can 

increase standing crop of the food base and that fluctuations can induce drift, thus increasing the 

availability of food to fish. However, they also identified uncertainties associated with the 

specifics of these relationships that could be evaluated in a long-term experimental program. 

2.2 OTHER FLOW EXPERIMENTS 

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

proposed experimental flow regime would include a number of other experiments that would be 

used to refine operations to perform specific tasks. Included are nonnative fish management 

flows (e.g., summer stranding flows), fall steady flows to benefit young humpback chub, 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, but are discussed below. 

Summer Stranding Flows 

 The conceptual design of a summer stranding flow to control young-of-the-year (YOY) 

trout was proposed by Korman et al. (2005) based on observations made during their study of the 

effects of winter fluctuating flows and on the scientific literature. Stranding flows would target 

trout, specifically larvae and juveniles. 

 Korman et al. (2005b) 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. 
Proposed Long-Term Experimental Program 8 January 2006 

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, but avoidance of impacts to other resources should also be a consideration. 

Thus, a stranding flow in the period of June, July, or August should be considered. 

 Despite the expectation that a summer stranding flow could be effective in controlling 

trout numbers, and thus competition with and predation of humpback chub, a number of 

uncertainties exist that should 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 can be evaluated during stranding 

experiments. 

Fall Flows 

 Monsoonal rains flush juvenile humpback chub from the Little Colorado River into the 

colder Colorado River, where presumably there is higher mortality. To offset this impact, it has 

been suggested that, after heavy runoff in the Little Colorado River, Glen Canyon Dam releases 

should be steady to reduce impacts to juveniles that enter the mainstem until these juvenile fish 

have grown large enough to increase overwinter survival. These flows could be steady or nearly 

steady, and are currently being considered for September and October. This operational pattern 

could become an important component of an overall dam release strategy if it is shown to benefit 

young humpback chub and ultimately contribute to recovery. 

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. 
Proposed Long-Term Experimental Program 9 January 2006 

Electrical Power Production Experiments 

 ROD flows were intended to improve the status of a set of natural resources in the 

Colorado River Ecosystem. 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 an increase in the downramp rate have a 

measurable and deleterious effect on sediment retention of Marble Canyon beaches? Does an 

increase in the daily variation produce additional drifting food for trout and humpback chub? 

Can New Zealand mud snails be reduced by a higher daily variation? Korman et al. (2005) 

reviewed the literature on the effects of ramp rate on stranding and determined that 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%. The downramp rate tested during 2003 through 2005 was approximately 

15 cm/hr. 

 We propose short-term experimentation with operational parameters. This likely includes 

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. 

2.2 PROPOSED NON-FLOW MANAGEMENT ACTIONS AND ANTICIPATED 

EFFECTS 

Temperature Control Device 

 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 humpback chub (<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, future increases in reservoir elevations predicted in the latest 

24-month study (Reclamation 2005) will result in increasingly cooler release temperatures and 

potentially harmful effects on humpback chub. It is essential that planning for these cooler 

release temperatures proceed and that the original plans for installation and operation of a TCD 
Proposed Long-Term Experimental Program 10 January 2006 

be put back on track. The Science Advisory Board has recommended a pilot program to install 

temperature control devices on two of the units at Glen Canyon Dam. We propose that this 

recommendation be implemented over the next few years (Table 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 humpback chub, 

we propose that consideration be given to the planning and compliance work needed to construct 

temperature control devices on enough units to increase water temperature below the Little 

Colorado River to levels that would improve the survival of larval and juvenile humpback chub. 

 Because increasing water temperatures in the mainstem Colorado River could potentially 

improve conditions for some warmwater nonnative fishes that compete with or prey on 

humpback chub, additional experimentation could 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 nonnative fishes in the system. 

Continued Efforts toward Humpback Chub Augmentation 

 The status of the humpback chub population in the Colorado River ecosystem could 

potentially be improved through artificial augmentation methods (i.e., stocking). We propose that 

a stocking program be developed and continued until the population of humpback chub in the 

Colorado River ecosystem becomes self-sustaining. 

 Establishment of a captive broodstock could provide a genetic refugium 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 genetic effective population size of the wild population (Van Haverbeke 

and Simmonds 2004). As part of developing a captive broodstock program, a captive broodstock 

management plan should be developed, an adequate facility for holding fish should be identified, 

and a formal stocking plan should be developed. The 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 should 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 Colorado River ecosystem. 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. A recent idea is that grow-out ponds 

could be constructed at the mouth of the Little Colorado River or the mouth of the Paria River. 

Efforts to Increase the Geographical Extent of Occupied Humpback Chub Habitat in the 

Colorado River Ecosystem 

 In order to expand the areas inhabited by humpback chub and to protect the Grand 

Canyon population of humpback chub from potential catastrophic events in the Little Colorado 
Proposed Long-Term Experimental Program 11 January 2006 

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

tributaries. 

 Translocation activities were initiated in the Little Colorado River during August 2003 

and August 2004 by capturing YOY humpback chub in the lower portion of the Little Colorado 

River and moving them to locations in the Little Colorado River upstream of Chute Falls 

(a natural barrier). Results of monitoring indicate that at least some of the translocated fish 

survived and grew well in the upper portion of the Little Colorado River (Sponholtz et al. 2005). 

This resulted in an expansion of the inhabited range of humpback chub 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 humpback chub 

population outside the Little Colorado River, even establishing additional areas that contain fish 

that do not reproduce would result in improved protection for humpback chub 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 nonnative predators, abundance of native fish, habitat suitability (e.g., temperature 

regimes), perceived ability to remove nonnatives, and jurisdictional issues. Compared to the 

Little Colorado River, 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 Nonnative Fishes 

 The presence of nonnative fishes in habitats occupied by humpback chub is considered 

one of the major threats to survival of humpback chub populations in Grand Canyon. In addition 

to implementing selected flow-related actions to reduce the numbers of nonnative fishes in 

occupied areas, we 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 Little Colorado River. These efforts have been primarily intended to remove 

rainbow and brown trout, which are known predators of juvenile humpback chub. Over 16,000 

trout were removed from the treated reach of river during 2003 and 2004 and there are 
Proposed Long-Term Experimental Program 12 January 2006 

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 

humpback chub juveniles (see above), such methods could be extremely valuable for reducing 

the numbers of nonnative fishes in the tributaries or for controlling access by nonnative fishes. 

 We propose that mechanical removal efforts be continued as part of the long-term 

integrated experimental program. 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 humpback chub. 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 

humpback chub. 

3 REFERENCES 

Coggins, L., and M. Yard. 2005. Update on 2003 and 2004 Mechanical Removal of Non-Native 

Fishes from the Colorado River. Presentation to the Technical Working Group, May. Available 

at http://www.usbr.gov/uc/rm/amp/twg/mtgs/05may18/documents/Attach_10.pdf. 

Korman, J., M. Kaplinski, J.E. Hazel, III, T.S. Melis. 2005a. Effects of the 2003/2004 

Experimental Increase in Daily Flow Fluctuations from Glen Canyon Dam on the Early Life 

History Stages of Rainbow Trout. Presentation at the Grand Canyon Monitoring and Research 

Center Science Symposium, Tempe, Arizona, October. Available at http://www.gcmrc.gov/ 

news_info/outreach/symposiums/2005/files/day02/08-09_josh_korman_score_05.pdf. 

Korman, J., M. Kaplinski, J.E. Hazel, III, 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, Cooperative Agreement No: 04WRAG0006, 

Modification No. 002. Grand Canyon Monitoring and Research Center, Flagstaff, Arizona, June. 

Sponholtz, P., D. Stone, and J. David. 2005. Monitoring for Humpback Chub (Gila cypha) above 

Chute Falls, Little Colorado River. Presentation to the Glen Canyon Dam Adaptive Management 
Proposed Long-Term Experimental Program 13 January 2006 

Work Group, August. Available at http://www.usbr.gov/uc/rm/amp/amwg/mtgs/05aug30/ 

documents/Attach_004.pdf 

Stevens, L. 2005. Humpback Chub Translocation in Grand Canyon: Background, Feasibility, 

Experimental Design, and Compliance Considerations. Presentation to the Glen Canyon Dam 

Adaptive Management Work Group, November. Available at http://www.usbr.gov/uc/ 

rm/amp/twg/mtgs/05nov29/Attach_06a.pdf. 

SWCA Environmental Consultants. 2005. Feasibility Study to Determine the Efficacy of Using a 

Weir in Bright Angel Creek to Capture Brown Trout. Final report to the Grand Canyon Science 

Center, Grand Canyon National Park, Grand Canyon, Arizona, November. Available at 

http://www.usbr.gov/uc/rm/amp/twg/mtgs/05nov29/Attach_06b.pdf. 

U.S. Bureau of Reclamation (Reclamation). 2005. Twenty-Four Month Study—Lake Powell. 

Available at http://www.usbr.gov/uc/water/crsp/studies/crsp_gc.txt. 

Van Haverbeke, D.R., and R.L. Simmonds, Jr. 2004. The Feasibility of Developing a Program to 

Augment the Population of Humpback Chub (Gila cypha) in Grand Canyon. Report No.

USFWS-AZFRO-FL-03-007, U.S. Fish and Wildlife Service, Arizona Fishery Resources Office, 

Flagstaff, Arizona, July. 
Proposed Long-Term Experimental Program 14 January 2006 

APPENDIX A 

REPRESENTATIVE WEEKDAY FLOWS DURING AN 

8.25 MILLION ACRE FEET WATER YEAR 












Proposed Long-Term Experimental Program 27 January 2006 

APPENDIX B 

EVALUATION OF THE EFFECTS OF PROPOSED FLOWS ON THE AQUATIC FOOD 

BASE 
Proposed Long-Term Experimental Program 28 January 2006 

DRAFT REVIEW

FOOD BASE RESTORATION FLOWS 

BELOW GLEN CANYON DAM 

Submitted to 

WESTERN AREA POWER ADMINISTRATION 

P.O. Box 11606 

Salt Lake City, Utah 84147-0606 

(801) 524-5493 

Submitted by 

Kara Hilwig and Bill Leibfried 

SWCA ENVIRONMENTAL CONSULTANTS 

114 N. San Francisco St., Suite 100 

Flagstaff, Arizona 86001 

(928) 774-5500 

www.swca.com 

SWCA Project No.10827-091 

January 24, 2006 
INTRODUCTION

Western Area Power Administration has proposed changes in dam operations for WY 2006. 

This document is a preliminary review of the literature pertaining to the effects of flow regimes 

on the aquatic food base at Lee’s Ferry. 

AQUATIC FOOD BASE

The food base in any aquatic system is an important factor that has direct impacts on fish 

community dynamics including abundance, reproduction and recruitment, condition, and even 

distribution. Primary production, such as algal growth, is often the driving force for aquatic food 

bases. Algal growth provides food and cover for aquatic invertebrates that are consumed by fish. 

The aquatic food base in the Colorado River ecosystem (CRE) was studied extensively from the 

early 1980s to 2001. Kennedy and Gloss (2005), with the support of studies such as Leibfried 

and Blinn 1987, Maddux et al. 1988, Usher and Blinn 1990, Shannon et al. 1994, Valdez and 

Ryel 1995, Valdez and Carothers 1998 and others, describe two distinct food webs in the CRE. 

The natural components of the food base in the CRE have changed with the construction and 

operation of Glen Canyon Dam (Stone 1964). Primary production at Lee’s Ferry is driven by 

Cladophora glomerata (a long filamentous green algae), which is fed upon by chironomids and 

simuliids (aquatic insect larvae) and Gammarus lacustris (a shrimp-like amphipod) that was 

stocked to augment the trout food base. Studies indicate abundance of the above aquatic 

invertebrates in the CRE is generally proportional to the abundance of Cladophora. Trout and 

humpback chub can be generally classified as drift feeders and much of their diet consists of 

food items that have been suspended and are drifting in the water column (Valdez and Ryel 

1995). Drift in the CRE is generally classified of as freely floating aquatic invertebrates and 

Cladophora that are then considered available to fish for consumption. 

FOOD PREFERENCES

The major characteristics of the fish food base in the Colorado River below Glen Canyon Dam 

have been summarized as: 

• The primary food items found in trout stomachs collected at Lee’s Ferry were 

Cladophora, Gammarus and chironomids (McKinney and Speas 2001, Carothers and 

Minckley 1981); 

• Gammarus and chironomid abundance increases with abundance of Cladophora

(Leibfried and Blinn 1987); 

• Gammarus prefers Cladophora as habitat and feeds on diatoms attached to the filaments 

(Shannon et. al 1994); 

• Humpback chub feed on invertebrates approximately in proportion to their availability in 

the drift (Valdez and Ryel 1995). 
Thus, the diatom community contained within filaments of Cladophora provides food resources 

for Gammarus and other invertebrates, which when present in the drift are fed upon by trout and 

humpback chub. 

DRIFT

In reviewing the research that has been done on the impacts of fluctuating flows on the quantity 

of invertebrates in the drift in the CRE the following conclusions can be drawn: 

• Cladophora quantities in drift samples increase with downstream distance (Valdez and 

Ryel 1995). 

• Invertebrate quantities in drift samples decrease with downstream distance (Valdez and 

Ryel 1995, Leibfried and Blinn 1987). 

• Seasonality of drift is not clear (Leibfried and Blinn 1987, Blinn et al. 1994, Shannon et 

al. 1996, McKinney et al. 1999). 

• Drift is low during steady flows and higher during fluctuating flows (Leibfried and Blinn 

1987). 

• Drift of Gammarus increases on the ascending limb of the hydrograph (Leibfried and 

Blinn 1987). 

• Drift of Gammarus increases on the descending limb of the hydrograph (McKinney et al. 

1999, Valdez and Ryel 1995). 

• Ramp rate has no effect on the amount of drift dislodged (Shannon et al. 1996). 

• Increased flow following periods of low flow and the ascending and descending ramp 

rates determined drift rates (Leibfried and Blinn 1987). 

• Drift was greatest when initial flow was below approximately 5,000–8,000 cfs and was 

increased to approximately13,000 to 18,000 cfs. Higher flow rates of the same magnitude 

of change did not appear to result in higher drift rates (extrapolated from Leibfried and 

Blinn 1987). 

Thus, invertebrate quantities in the drift are increased during fluctuating flows; however, 

magnitude of flows and fluctuations, seasonality of fluctuations, and ramp rates that induce 

optimal drift of invertebrates are not clear. 

STANDING CROP

In order for drifting organisms to contribute to the food base of fishes, there must be sufficient 

standing crop of algae and invertebrates to contribute to drift. In reviewing the research on 

factors that determine the standing crop of Cladophora and aquatic invertebrates in the CRE, the 

following conclusions can be made: 

• Growth and abundance of Cladophora is determined by light and nutrient availability, 

water temperature, and grazing pressure (Litchman et al. 2003). 
• Phosphorus may be limiting to Cladophora . 

• Daily fluctuations of 5,000–20,000 cfs (WHAT UNIT?) result in a significant reduction 

of Cladophora (Usher et al. 1987) due to desiccation of exposed algal mats. 

• Standing crop of Cladophora increases with increasing depth (Usher et al. 1987). 

• Standing crop of Cladophora decreases with distance downstream (Usher et al. 1987). 

• One time desiccation is less detrimental than repeated desiccation (Usher et al. 1987). 

• Fluctuating flows may effect Cladophora abundance and diatom community structure 

(Usher et al 1987 and 1988). 

• Nutrient stress can increase Cladophora fragmentation, thereby increasing drift but 

decreasing diatom abundance (due to less available substrate) for Gammarus (Usher et al. 

1987). 

• With increased water velocity, diatom communities would shift from loosely attached 

species to more closely attached communities thus impacting Gammarus grazing (Usher 

et al. 1987). 

• Standing crop of invertebrates was significantly greater during summer steady flows 

when compared to standing crop during winter fluctuating flows (Leibfried and Blinn 

1987). 

• Invertebrate standing crop was reduced from 2,517 individuals per square meter in a 

permanently wetted sample to 772 in the zone of fluctuation during October and from 

992 individuals per square meter to 44 in December (Leibfried and Blinn 1987). 

• Daily fluctuations in flow reduce the standing crop of Cladophora (Usher et al. 1988). 

• Exposure greater than 12 hours results in loss of Cladophora during fluctuating flows 

(Usher et al. 1988). 

• Four hours of exposure duration freezing conditions as well as hot, dry and breezy 

conditions ) results in greatest loss of Cladophora during fluctuating flows. (Usher et al. 

1988). 

• In 1985, standing crop was greatest during somewhat steady winter-spring high flows 

(25,000 cfs) as compared to fluctuating winter flows (3,500–18,000; extrapolated from 

Leibfried and Blinn 1987 and Valdez and Ryel 1995). 

• Recovery of snail density after desiccation is rapid (1 week) but aquatic insect density 

requires greater than 4 months to recover (Blinn et al. 1995). 

In summary, fluctuating flows have negative impacts to Cladophora survival and invertebrate 

abundance during exposure times four hours in freezing or hot windy conditions. Steady flows 

may increase standing crop of Cladophora and invertebrates especially during spring and 

summer months when days are longest and invertebrates are likely reproducing. The effect of 

fluctuating flows on food web dynamics, which determine food base abundance, is not clear. 
CURRENT CONDITIONS

Knowledge of current standing crop conditions is important to determine how fluctuating flows 

induce optimal invertebrate drift. 

• Standing crop measurements have not been conducted since 2001 (Shannon et. al 2001). 

• Phytobenthos composition may be changing in the Lee’s Ferry area with a decrease in 

Cladophora abundance and subsequent decrease in Gammarus abundance (Rogers et al. 

2003). 

Standing crop measurements of invertebrates and phytobenthos have been conducted by several 

researchers since 1964. A comparative investigation of current standing crop density and 

composition to that recorded during previous studies, when combined with flow regimes over 

time, may provide some insight into the impacts flow regimes on standing crops. 

UNCERTAINTIES

As with any ecological system, variables other than those being studied may impact standing 

crop and drift dynamics and result in uncertainties regarding what most influences the 

invertebrate community at CRE. Specific factors requiring further investigation that may be 

contributing to standing crop and drift dynamics are discussed below. 

• Current standing crop conditions and impacts of current ROD flows and recent BHBF to 

standing crop are unknown. 

• Threshold velocity magnitudes and fluctuations that will sustain food base standing crop 

and drift are unknown. 

• The quantity of standing crop and drift abundance of greatest benefit to fish is unknown. 

• Effects of New Zealand mudsnail on standing crop and invertebrate density are unknown. 

• Effects of low oxygen and increased temperatures on Cladophora and invertebrate 

density are unknown. 

• Utility of drift or Fine Particulate Organic Matter (FPOM) to fish below Lee’s Ferry is 

unknown. 

• Changes in standing crop estimates among all previous standing crop studies relative to 

flow conditions during those studies have not been investigated. 

Isolating the impacts of fluctuating flows on food base standing crop and drift dynamics is 

difficult. The impact of current ROD flows on the food base is unknown and should be 

measured before the implementation of new experimental flow regimes. 
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discharge for lotic communities. Journal of North American Benthological Society 

14:233–248. 

Carothers, S.W. and W.L. Minckley. 1981. A study of fishes, aquatic invertebrates and aquatic 

plants of the Colorado River and selected tributaries from Lee’s Ferry to Separation 

Rapids. Final Report to Water and Power Resources Services, Contract No. 7-07-30-

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