Attachment 2.

Frequently Asked Questions & Answers

(March 15, 2002 Version)

January – July

NATIVE FISH

Q: I understand there is little direct evidence of predation by non-natives on HBC: If this is 

correct, why is the focus by GCMRC on non-native fish?

A: Although, there is considerable uncertainty regarding the causal mechanism for the decline in 

adult HBC abundance, the predation / competition hypothesis has a higher likelihood than other 

mechanisms (disease/parasitism, hydrology, food-limitations, habitat degradation, etc.) for 

explaining the decline. In addition, this is a testable hypothesis using management flow 

prescriptions. Finally, it is plausible that the predation / competition hypothesis could overwhelm 

any benefits derived from management flow prescriptions intended to provide beneficial habitat 

conditions. 

There is considerable circumstantial evidence that would suggest that predation could be 

influencing survivorship of YOY HBC. Specifically,

1. There is direct evidence of predation by trout, primarily BNT (8-10%); however, there is 

evidence of lower predation by RBT (1-0.5%) (Valdez and Ryel 1995; Rowell 2001). 

2. The positive expansion in trout abundance system-wide in the Colorado River mainstem 

3. The highest proportion of fish in the LCR inflow area are composed of trout.

4. The composition of trout, in the LCR-inflow reach, consist of 97% RBT, and 3% BNT.

5. There has been a 4-6 fold increase in relative trout abundance in the last 7 yr.

6. Assuming Valdez and Ryel (1995) mouth-gape analysis is correct, the size-class of 

vulnerable fish to predation is the same size-class that fails to recruit into the adult HBC 

population.

7. Assuming that these estimates are correct and taking into account the local distribution and 

change in abundance since 1990-1993, estimated annual consumption of HBC-YOY should 

have increased.

a. Annual consumption of HBC corrected for recent change in relative abundance

i. Rainbow trout = 1990-1993: 227,760 2001: >1,000,000

ii. Brown trout = 1990-1993: 32,850 2001: 120,000

Alternately, using population estimates for just the LCR area would suggest that RBT occur in 

densities of approximately 10,000 fish/mile. If the region encompassing the first 5 miles around 

the LCR inflow represents the only part of the HBC population that successfully recruits back to 

the source population, and only 1% of the trout in this area prey on HBC, and HBC are only 

vulnerable during the year for a limited 3-month period (90d), and only 1-fish is consumed per 

predatory trout per day, then a conservative estimate would be 45,000 HBC consumed. This 

compares to an estimated annual recruitment of 10,000 – 20,000 HBC to the LCR population in 

recent years.

A final reason, given the uncertainty associated with the competition predation hypothesis is that 

from a biological and sediment resource perspective this is a low risk experiment, with testable 

hypotheses.
2

Q: -How does load-following benefit native fish?

-How is it low-risk to disadvantage non-natives and not affect native fish?

A: GCMRC believes the benefits to native fish will accrue indirectly through a reduction in 

predation/competition by non-native fish, primarily salmonids in the LCR reach. The model 

developed by Dave Speas and Carl Walters provides support for load-following to negatively 

impact RBT by interfering with and disrupting spawning activity as well as reducing the 

recruitment of young fish. The working assumption is that non-native fish overwhelm any 

benefits to native fish from management flows that improve habitat conditions.

Load-following destabilizes or reduces the permanence of near shoreline habitat. Conceptually, 

YOY for most species of fish are found along the lentic edge of the river, occupying habitat that 

maximizes feeding opportunities while decreasing risk from predation. When there is a change 

in stage fish must move laterally while following the vertical change in water edge. Repeated 

movement by fish and increased distance traveled, results in lateral and longitudinal displacement 

that increases the likelihood for predation. The greater the magnitude in change and rate the 

greater the effect.

Load-following can equally affect both non-native and natives fishes. There are thought to be few 

HBC in the mainstem during the time of the year that load-following would occur and therefore, 

HBC will not be negatively affected. However, the hypothesis being tested is that the current 

abundance of nonnative fish has created a predator/competitor load that is too excessive. It is the 

abundance of predators that has overwhe lmed survivorship of YOY along shoreline. The intent 

behind this flow prescription is to disadvantage non-natives rather then benefit native fish. This 

experiment would test alternate hypotheses whether or not YOY survivorship is habitat limited or 

is predator limited.

Q: If you won’t benefit native fish in the fall, why do you go to steady flows?

A: There are a number of hypotheses to test:

Ho: Turbidity reducing predation 

• This hypothesis, that turbidity reduces predation by visual sight feeders is considered 

hierarchically second to the reduction in predator loads.

Ho: Potential benefit to native fish from more stable near shore habitat.

• GCMRC has stated that the greatest number of YOY HBC enter the mainstem during fall 

monsoon events, therefore there is also the potential for stable flows following these 

events to provide warmer and more suitable habitat conditions for these fish during the 

fall. GCMRC should evaluate the downstream warming potential and the increase in 

suitable habitat of these mainstem conditions during the Sept – Nov time period.

• Expect this potential benefit may be overcome by non-native interactions.

Ho: Lower flows result in the retention of a more natural sediment mix and higher mainstem 

sediment concentrations for bar building in January. The more natural mix of sediment 

(fines through sand) will result in better bar stability and also affect nutrient cycling
3

Q: Is there any response of HBC to ROD flow changes? Do we know if there are changes in 

the LCR that may be the cause and that will be ignored by this effort?

A: We are beginning to look at the LCR hydrology record. One would expect to see changes in 

LCR hydrology due to development in the watershed resulting in groundwater depletion, surface 

water retention, and changes runoff patterns in response to paved areas, among others. It is not 

clear if we will be able to correlate these with changes in HBC. The working hypothesis is that 

predation and competition from non-natives will overwhelm habitat effects. This hypothesis also 

assumes that some portion of the LCR population recruited from fish which spent part of their 

early life history in the mainstem and that this portion of the recruitment is being negatively 

affected by non-native fishes.

There are othe r hypotheses that might explain the decline in abundance of HBC. Although there 

is considerable uncertainty around all of these alternate hypotheses. Not all of the hypotheses are 

experimentally testable to explain the causal nature of the recent decline of HBC. For this 

reason, we are suggesting an experiment to reduce predators in the mainstem because it is a 

practical and low risk treatment. However, if we were to implement such an experiment it does 

not imply that the current effort monitoring the species of concern would be discontinued, or that 

alternate mechanisms or factors that might be also contributing to the decline would be ignored, 

unconsidered or omitted from the present monitoring.

Q: Can we test the warming hypothesis for October – December when YOY might emerge in 

mainstem? 

A: Cooling is as probable as warming during this period. A temperature monitoring effort as part of 

the monitoring and research activities that accompanies this experiment is warranted.

Q: A published paper shows drift out of LCR in May/June, will this be affected by the proposed 

flows?

A: The paper by Robinson et al. is based on one year of data. It was for 1992, a high flood year for 

LCR. There may be problems in the accuracy and representative sampling, i.e. annual variation. 

The data wasn't correlated with any mechanistic parameters. Other data have documented HBC 

YOY in main channel during fall with decreasing abundance moving toward winter presumably 

due to predation, cold temperatures, downstream movement, or a combination of these.

Q: It seems like running high fluctuating flows to impact population around LCR has a 

potential negative impact on the whole system?

A: This is true and intended to be so for salmonid spawning, recruitment, and food base, in the Lees 

Ferry reach. However this negative becomes a potential positive for native fish downstream of 

Lees Ferry. HBC are at a very low abundance or non-existent in the LCR reach at this time either 

due to downstream transport or predation, therefore no impact on native fish is expected during this 

time. April stabilization optimizes the recovery of the foodbase because of light regime etc. Food 

may not be limiting downstream in any regard.

Q: What is the potential of confusing impact of fall low steady flows vs. fluctuating flows on 

native fish? 
4

A: Fluctuating flows are not believed to have any direct impact on native fish. Fall low steady flows 

may have secondary benefits to native fish through improved habitat conditions IF non-native 

predation is reduced first. We may have difficulty in the long term assigning cause and effect 

relationships to these two factors. However the best science data and intuition suggest that HBC 

may be better off as a result of these experiments.

Q: Will 1 year of experimentation allow you to see an effect on native vs. non-native fish 

interactions? 

A: Not likely. Repeated experiments over several years would improve the probability of detecting an 

effect. The strength of treatment will be related to the number of years the experiment is repeated 

as well as the magnitude of the flow fluctuations. Effects on native fish will be more difficult to 

detect than effects on non-natives, which will only be measurable after several years. Changes in 

non-native predator abundance may detectable within 2 years. Prefer 2 to 3 years of 

experimentation.

Q: Are we applying too many treatments to measure this effect on the fish community? 

A: From a biological perspective the core experiment is an annual flow regime, repeated over time, 

not seasonal elements of the annual hydrograph . There may be confounding effects if we consider 

predator removal in BAC and the LCR along with the flow experiment. The tradeoff is not doing 

enough to improve HBC.

NON-NATIVES

Q: Would load-following confound measuring impacts of Brown Trout removal in Bright 

Angel?

A: Load-following is designed to be a more systematic treatment. One year of load following vs. 

one-year of Brown Trout evaluations are very different. Having both would enhance the 

potential effort.

The hypothesis that is being tested is whether or not predation is limiting YOY HBC recruitment. 

Whether we have multiple treatments that are each reducing predator loads does not affect the 

overall nature of the test. For the test, it is not what reduces trout more effectively (flows, 

tributary treatments, mechanical removal), but whether the reduction of trout abundance by some 

means has an effect on YOY HBC recruitment? Depending on the ultimate test response (which 

remains unknown), a titration approach could be implemented that would allow for a measure of 

efficiency of one method over the use of an alternate method.

Q: Are the wheels in motion to do Brown Trout removal this Fall?

A: Grand Canyon National Park is supportive but the resources (staff and funding) are not there to 

do it this Fall.

Q: Could you move the load-following period to February to address the possible public 

concern of stranding adult trout?
5

A: This can be considered. One is not sure if it will have the same effect of reducing non-native 

spawning. Using slower down ramp strategies as well could reduce stranding of adults. 

Q: Could you reduce concentrations of rainbow trout around the LCR by some other 

mechanism besides high fluctuating flows? 

A: While GCMRC is considering a mechanical removal effort around the LCR this would be intended 

primarily to better understand predation and have a secondary benefit of removal in a limited area. 

This would not be as systemic an effect as flows would be. Feasible removal estimates for 2-4 

electro-fishing trips are from 8-15% of the adult population in the LCR reach. Flows could reduce 

individual year classes by 50%. These efforts should be complementary. Objectives could not be 

accomplished by mechanical removal alone. Monitoring will allow us to determine the added 

benefit of LCR efforts.

Q: Are the high fluctuating flows “fishable”? 

A: Yes, depending on the ramping rates. Notification will need to be provided at the ramp to 

minimize the safety hazard from swift changes in stage.

Q: Can you achieve the same desired downstream effects on non-native fish with lower 

fluctuating flows?

A: Probably not. There is a historical negative correlation between RBT recruitment and the degree of 

annual flow fluctuation. Experimental data suggest lower egg hatchability and fry survival under 

high fluctuating flows. The further one goes toward approaching recent ROD operations the less 

effective fluctuating flows are likely to be. 

Q: Is there a problem if one were to shift the high fluctuating flows a month or two (i.e., begin in 

March instead of January)? 

A: Spawning and emergence of RBT is spread over at least a six-month period. Moving the flows to 

later would miss the peak of both of these phenomena and reduce the effectiveness of the 

experiment. To increase the effectiveness, these flows should occur for 6 months rather than the 

three being proposed.

Q: If you fluctuate from 5,000 – 25,000 cfs, will you kill adult trout through stranding, perhaps 

several hundred a day until spawning season ends?

A: Stranding will probably occur but that mortality during this time of year will be minimal, likely an 

order of magnitude less than hundreds. If the estimate of a hundred fish per day over 15 miles for 

three months were accurate, this would represent up to 5% of the adult population. 

Q: Do we know the location of standing pools for adult rainbow trout?

A: These locations are documented in GCES reports and are known to the Lees Ferry trout guides. 

There are approximately 5-6 areas where stranding will be most prevalent. These locations are 

known and can be monitored by the guides and AGFD and adult trout can be monitored if needed.
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Q: Could AGFD reduce non-native fish through changes in fish regulation?

A: It is unlikely that regulation would have the desired affect.

Q: Can there be more analysis to fine tune the January – March hypothesis regarding stagerelationships and timing with respect to interrupting spawning and maximize reduction in 

success of redds?

A: Data exists that could be used to analyze the amount of wetted area available at different flow 

stages but it won’t really represent the amount of destabilization that occurs from high fluctuating 

flows. Historical data does suggest that pre-Rod fluctuations were effective at reducing the 

abundance of non-native fish.

Q: Is it the fluctuating flows that are intended to reduce non-native fish? 

A: Yes, through a combination of disrupting spawning activity and success as well as reducing 

survival and recruitment of young salmonids.

Q: Will the proposed high fluctuating flows reduce non-native fish above and below Lees Ferry 

equally? 

A: Probably not. This response will be proportional to non-native fish abundance, which decreases 

downstream. There is also an unknown contribution from tributary spawning downstream, which 

will not be affected by these flows. Furthermore there will be some attenuation of the amplitude of 

fluctuations as one proceeds downstream. This argues for more rather than less fluctuation in 

discharges in order to achieve the desired effect in the LCR reach.

Q: Given that the guides believe Lees Ferry population abundance is beginning to decline, are 

the high fluctuating flows needed? The Lees Ferry Guides have reported seeing a 40% 

decrease in last 6-18 months in catch rates. 

A: The observations of the Lees ferry Guides have not been corroborated by AGFD electrofishing 

data. Some new data may be available by the AMWG meeting and will be reviewed as it becomes 

available. Provisional field observations from downstream monitoring also show no equivalent 

decrease. Preliminary trip data from AGFD & GCMRC will be refined prior to AMWG to verify 

this and current Lees Ferry abundance.

Q: Are there different ways you could disrupt the spawning than what you’ve shown? 

A: There are possibilities but nothing very feasible-sediment augmentation, more extreme flow 

fluctuations, extended flow reductions (steady low, e.g. 3000cfs flows).

SEDIMENT
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Q: Could you use a HMF to conserve sediment instead of low steady flows or low loadfollowing flows?

A: You might potentially store some sand and possibly some limited amount of finer sediment 

within eddies, but the total sand conservation achieved would be far less than if the entire channel 

bed was available for storage of fines under the 10,000 cfs or less flow alternative. A comparison 

of results from the 1996 BHBF, and the 1997, 31,500 cfs spike flow provide some valuable 

insights on this matter. One important concept to keep in mind is that the total potential storage 

for sand within eddies is only a small fraction of what can be stored within the main channel, 

under flow conditions that limit downstream transport.

Eddy-sand bars studied following the November 1997, spike flow (under relatively sedimentsupply enriched conditions), showed a much finer grain-size distribution than bars created by the 

1996 BHBF (under relatively greater sediment-depleted conditions). The 1997 eddy deposits 

were relatively cohesive compared with the 1996 deposits, and were much darker in color, 

suggesting some higher content of organics. Unfortunately, the average thickness of most of the 

1997 deposits was on the order of 10-20 cm, or relatively thin compared with bar thickness 

measured after the 1996 BHBF. One preliminary conclusion derived from the 1997, sediment 

experiment was that the 31,500 cfs spike flow produced a “stage-limited” response, and that 

thicker and larger bars might have been deposited in November 1997, had the stage been 

increased to above peak power plant levels. Flows preceding the November 1997 test were not 

as low as those being proposed for future experiments, yet there was still evidence to suggest that 

at least some portion of the summer sediment inputs remained in the channel by the time the high 

flow occurred.

Q: Are there other options for sediment conservation in September-December? Options might 

include HMFs or steady 8,000 -10,000 cfs flows? Load-following between 5000-9000 cfs? 

Would the conceptual model or Wiele efforts help sort this out?

A: The conceptual model is not predictive in the sense that we can calculate the expected outcome 

of an experiment, but it may have utility in comparing the results of several options for portions 

of the proposed hydrograph.

Wiele’s bar-evolution modeling simulations indicate that bars are most effectively deposited 

when a combination of high suspended-sediment concentrations and high-stage conditions occur 

simultaneously. Limiting downstream transport of newly input fine sediment until the release of 

a controlled flood is the most probable means of achieving both of the above conditions, if 

releasing a controlled flood during or immediately after tributary inputs is not a viable option. 

The conceptual model’s sediment dynamic sub-model is based on the same basic premise: when 

abundant sand supply is available, then it will get mobilized by a high-flow release and the result 

will be an increase in sand storage at high stage elevations.

Q: Given that the motion focuses on sediment, how does the low load-following benefit the 

sediment?

A: The winter load following component of the experiment is not intended to benefit the sediment 

resource. However, there may be some advantage derived from the winter load-following with 

respect to modifying the newly formed bar morphologies.
8

Q: Will the load-following erode the recently deposited sediment from the BHBF? What 

sediment-related hypotheses does the load-following test?

A: Any operation following the BHBF will result in reworking of the newly deposited sand bars. 

This bar reworking can be viewed as “erosion,” but there is no way to avoid it. The basic 

question remains as to what operation will export the least volume of sand downstream for any 

range of antecedent sand-storage conditions? A secondary consideration concerns how the 

operations that follow the BHBF will affect the morphology of the new bars with respect to 

ecosystem value. A few hypotheses might be considered:

Ho: Winter load-following does not result in a increased export of stored sediment.

Ho: Winter load-following does not modify new eddy bars in a manner that makes them more 

stable of greater resource value.

Ho: Winter load-following does not achieve eddy bar morphologies that allow for greater access 

to recreational users.

Q: If you go to the low load-following proposed, can you test the up- and down-ramp rates and 

their effects? 

A: Addressing the sediment-transport dynamic issues related to ramping rates is a difficult challenge 

that requires very high-resolution data sets, or a very sophisticated numerical predictive 

capability. GCMRC has been examining an optically-based technique (LISST) for measuring 

suspended sediment. Results to date look promising. We will know by summer if we can use 

this approach to examine changes on up- and down-ramp rates. In the event that LISST 

technologies prove adequate for monitoring suspended-sediment transport in the Colorado River 

ecosystem, then these methods will be used for evaluating issues of ramping rates and 

relationships to sand resources, etc. Researchers at University of Arizona have studied issues of 

ramping rates and their impacts on the dynamics of sand bars previously. These EIS results can 

be reviewed again, and additional numerical simulations can be run and evaluated, pending 

approval by managers and on the basis of funding availability.

INTEGRATION

Q: What dose “RPA flows” in the AMWG motion refer to? 

A: RPA flows suggest the need for experimentation to benefit native fishes, which is consistent with 

this proposal.

Q: Are the purposes responsive to the motion?

Materials describe two purposes: (1) sediment, and (2) benefits native fish. I thought the 

motion was primarily about sediment.

A: The point of the motion was primarily to test the sediment Ad hoc group’s second 

recommendation, but GCMRC interpreted the motion as a sediment conservation experiment 

within the framework of benefiting native fish.
9

Q: Is the GCMRC draft proposal in concert with the RPA?

A: Yes. As per the FWS RPA, the draft proposal identifies the need for the development of 

experimental flows to test, or the implementation of alternate flows as specified in the 

Biological Opinion of GCD. One such flow was the 2000-LSSF experiment (SWCA 2000) 

that used a holistic hydrograph that was intended to produce habitat improvements that would 

benefit HBC, rather than a mechanistic approach specifically applied to a life history 

component. The approach here is more discrete and testable than the former flow scenario.

Q: Why isn’t this a program of flows?

A: Given that the motion asks for a proposal to be brought back to the AMWG in April for 

WY 2002-2003, this is intended to be an element of a program of flows. It is clear from the 

conference call that there are a number of alternative ideas for experimental flows. This is the 

flow GCMRC recommends the AMP try first, with the understanding that this single year’s flow 

would fit into an overall program of flows.

Q: Integrated Ecosystem Experiment: I recommend that the experiment should be less 

ambitious and should simply test the sediment paradigm. The experiment should be within 

Law of the River and the ROD. We do have to get through July and August with meeting 

power supplies.

A: The AMP is intended to use an ecosystem-science approach in testing the effects of dam 

operations. It also recognizes that the Endangered Species Act mandates that the Department of 

the Interior take action to protect these species. At the January AMWG meeting, GCMRC 

presented data that indicated sediment resources and HBC are not responding to the ROD as 

anticipated in the EIS. It would be irresponsible for GCMRC to make a recommendation to the 

AMWG for an experimental flow that does not take an ecosystem science approach and that does 

not address the resources of concern. It is our belief that the flows proposed in the February 8 

(Version 1.1) draft are within that portion of the ROD that allows for experimentation, if ROD 

flows are not achieving the intended benefits. GCMRC also believes that after the AOP process 

considers the experimental flow request and determines WY 2003 monthly volumes, the 

proposed flows are in compliance with the current interpretation of the Law of the River as all of 

the flow elements that are proposed for testing could be implemented, following appropriate 

compliance, within the current interpretation of the Law of the River.

WATER FLOW ISSUES

Q: How can you conduct low steady flows or low load-following flows? Don’t they violate the 

AOP?

A: The concerns expressed about monthly volumes and the AOP process are important ones. 

Annual release volumes are defined by statute and resulting operating criteria. Monthly release 

volumes are determined to meet annual requirements, support firm power generation 

commitments, and address the combined risks of powerplant bypasses, and over- and underrelease of annual volumes. The GCPA did not alter the water development philosophy of the 

previous 1956 and 1968 Acts; thus, the financial integrity of the Basin Fund is of great concern to 

the States. As the AOP is developed each year, consideration is given to all the factors listed in 
10

the 1970 Operating Criteria, which include environmental concerns. The issue raised on the Feb. 

8 conference call was not so much that the monthly volumes cannot be adjusted, but rather that 

the process of developing those monthly volumes must remain consistent with the water 

development and financial goals of previous Acts. If monthly volumes need to be adjusted from 

the typical decision making process in order to conduct an experiment, this issue would need to 

be addressed during the preparation of the 2003 AOP.

Q: If this is an 8.23 MAF year, July and August would be 800,000 Acre Feet and September, 

October, and November would be low volume months. How can you conduct the flows you 

describe, given these potential volumes?

A: The proposed hydrograph shows both the end of the 2002 water year (expected to be 8.23 maf) 

and the entire 2003 water year (expected to be about 10 maf). No adjustment to the 2002 water 

year hydrograph is proposed, with the possible exception of reacting to fall tributary inputs. 

Thus, July and August of the 2002 water year are expected to be about 800,000 af months, and 

GCMRC will monitor the effects of ROD releases during this year as part of a “baseline” data 

collection to determine the effects of ROD operations. 

The reaction to fall tributary inputs is to recommend either a reduction to low steady releases 

(below 10,000 cfs) to conserve sediment inputs in the main channel or low fluctuating flows 

(5,000 – 10,000 cfs) to conserve sediment inputs in the eddies, or lastly the release of a HMF.

Q: Could UC and LC talk about a way to work this out if deliveries are lower and water 

volumes need to be shifted for this experiment, especially since releases from Mead 

wouldn’t be affected?

A: This can be done as long as the Compact and the specific annual release requirements contained 

in the 1970 Operating Criteria can’t be violated.

Q: If FY 2002 is an 8.23 MAF year and one needs to take information from Summer of 2000 

and compare it to ROD flows in 2001 and 2002, do you have the baseline data collection for 

that comparison?

A: A similar level of effort for monitoring downstream native and non-native fish has continued 

since the LSSF flows of 2000. Seining at a lower level of effort is continuing. The integrated 

sediment data is continuing to be collected. Reduced efforts on downstream temperature is 

ongoing. The level of resolution and many of the specific studies intended to answer specific 

effects of the LSSF treatment have not been continued. Once a set of experimental flows is 

established and the hypotheses to be tested are articulated, GCMRC will need to review the 

power of the existing monitoring activities.

Q: What reservoir elevation do we need to be at to use the spillways?

A: By January 2003, Lake Powell storage elevation needs to be at 3657 feet to have 14,000 cfs of 

flow in either of the spillways. This level of discharge is needed for the spillway to function in a 

safe manner. For January 2003, the lake level is projected to be 3648 feet. As a result, there 

seems to be little hope that the BHBF proposed for January 2003 could exceed 45,000 cfs.
11

Q: December is a high power demand month, is it possible to do fluctuating flows up to 15,000 

cfs. What would this do to sediment storage for a January BHBF?

A: Load following between 9,000 and 15,000 cfs during December 2002, is certainly one of the 

possibilities being evaluated following summer/fall sediment inputs. If the sediment inputs 

occurred in September, and the flows were released to 10,000 cfs or less through November, then 

there would be less downstream transport during the proposed December load following than if 

normal operations occurred throughout the September through December period. The impact on 

downstream transport of newly input sand during the December operations is most easily 

evaluated by reviewing figure 2, included in the Rubin et al. memorandum of August 2000.

Assuming: 1) that at least 500,000 tons of sand entered the main channel from the Paria River in 

September 2002, 2) that flows were immediately reduced to 10,000 cfs or less from the time of 

the input until December 1st, and 3) that the average flow for December 2002, was about 12,000 

cfs – figure 2 suggests that about one-half of the newly input sediment introduced in September 

2002, would be transported downstream in about 45 to 250 days, once December’s operations 

started. Likewise, if we assume that the proposed BHBF occurred at the start of January 2003, 

then there is reason to believe with some certainty that less than one-half of the September 

sediment input would be exported downstream before the January BHBF was released.

Q: If sediment is stored in the eddies in an HMF, why do you go to monthly low flows? 

A: The HMF approach foregoes hypotheses related to storing the fuller range of sediment 

components and the turbidity effects. Also, there is only a limited volume of sand that can be 

stored in the eddies and it is much less than the volume of fine-sediment that can be stored in the 

channel bed throughout the entire river channel. Results of the November 1997, sediment 

experiment (31,500 cfs) indicated that sand storage increased within eddies, but that this increase 

in storage was very limited compared to the volume of sand that might have been conserved had 

a higher flow been released that would have taken advantage of higher-elevation storage 

locations along shorelines. There is no basis at this time for concluding that the potential eddystorage volume within the ecosystem is sufficient to sustain sand-bar maintenance long term. In 

light of this, the most conservative scientific experimental approach is to conduct the flow 

experiment that has the greatest likelihood of optimizing sediment conservation and sand-bar 

restoration/maintenance. Doing less optimal sediment treatments in the future may very well be 

justified during periods when reduced-flow operations are not possible, or on the basis of new 

findings that indicate that the fullest range of channel storage is not required for long-term sand 

bar sustainability.

Q: Why not test a BHBF in Fall?

A: This is viewed as outside the current interpretation of the Law of the River.

Q: Concerned that load-following is outside the ROD? Do we have compliance for fluctuating 

flows that violate daily ranges and proposed upramp rates?

A: GCMRC believes that this would be covered as an experiment under the ROD. We do need to 

check into compliance.
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Q: I want to ask you to look at trade -off in fine sediment losses through a two-stage approach:

-HMF followed by a BHBF and the benefit of doing low load-following during winter-peak 

demand

A: Because we don’t have a very robust numerical predictive capability, with respect to sediment 

dynamics in this system, the best way of quantifying these differences is by conducting the 

proposed experiment, and then comparing the results to those of the proposed alternatives. The 

next best way is by using empirically derived methods for estimating sediment transport, such as 

the method shown in figure 2, of the Rubin et al. (2000) memorandum.

Q: There are non-ROD elements in Figure 1, load-following, low Fall releases, could include 

BHBF outside ROD period and HMF outside the ROD. Recommends two Figures: an 

ideal hydrograph and one that balances legal/policy trade -offs.

A: Given the provision in the ROD that calls for experiments if the resources are not responding as 

expected to the ROD flows, no elements of the proposed flows are thought to be outside the 

ROD. GCMRC and the TWG should review this more thoroughly.

Q: Why is a fall BHBF outside Law of the River?

A: The current interpretation of the Law of the River would prevent a BHBF from occurring for 

other than dam safety purposes. The triggering criteria developed to address that provide a 

window between January to July for conducting BHBFs.

Q: What’s next? When will the public be informed?

A: This is the conceptual phase. The questions and concerns we heard today will be used to refine 

what we bring to the TWG in February. The TWG will provide an opportunity for public input. 

Following the TWG, a recommendation will be forwarded to the AMWG. We assume that 

detailed design work with scientists and detailed public impact will occur following that and final 

approval will be obtained in July? GCMRC and the AGFD held a preliminary meeting with the 

Fishing Guides at Lees Ferry on February 12 to provide the same conceptual material that was 

presented on February 8 and invite their input.

Q: How much money do we have for this?

A: The experimental flow fund will contain about $1 million by January 2003. Any remaining 

funding needs will be sought as an appropriation request or through reprioritizing AMP activities.

Q: Can we consider 5,000 – 9,000 cfs flows in lieu of steady 8,000 cfs flows for September –

December? Would low fluctuations in fall be as optimal as flat flows?

A: Mike will provide assessment, HBC is thought to be more positive with stable flow-this period 

represents time of greatest historical near shore habitat loss according to recent analysis by 

Korman, rainbow trout might be more negative with fluctuation but probably minor this time of 

year, What about turbidity-Ted?? Sediment Loss??

Q: What is the total cost impact on hydropower of the proposed experimental hydrographs?

A: WAPA will provide.
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Q: Are the proposed experimental hydrographs a departure from the ROD, given the proposed 

range of daily fluctuations?

A: The ROD allows for experimentation if there is evidence that the preferred alternative is not 

achieving the intended benefits. The high fluctuating flows are being proposed under the 

experimentation allowed by the ROD.

Q: Can this or any hydrograph even be implemented since the AOP process is the mechanism 

for adjusting monthly volumes and proposing monthly volumes?

A: To be provided

Q: Will the falling limb of the hydrograph following the BHBF going right into high fluctuating 

flows allow us to test benefit of BHBF?

A: A few days of steady flows following the BHBF, as in 1996, for monitoring may be required

Q: Would a stepped-down hydrograph following BHBF to accomplish progressive reworking of 

the sediment deposits produce an eddy profile that is more stable and friendly to people using 

the river?

A: [To be added]

Q: Can the duration of the BHBF be limited based on real time tracking of sediment transport 

so one could propose 2-5 days and truncate the BHBF based on real-time data regarding 

sediment transport and beach building?

A: 

Q: Should the BHBF peaks be higher in stage?

A: One may want to test a higher magnitude BHBF but the hydrology under which this experiment is 

being proposed won’t allow it. There is also value in repeating the magnitude of the 1996 BHBF 

and only changing duration.

Q: How much water will bypass the power plant during a BHBF?

A: To be added by BOR

Q: Can one predict the ratio of sediment stored -to- sediment exported from a BHBF? Is there 

an optimum BHBF level that yields maximum storage with limited export?

A: To be added
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Q: What is the purpose of the 5,000 cfs low flow?

A: To provide a stable minimum foodbase level but with flow levels fluctuating enough above that to 

disrupt spawning and survival/recruitment of non-natives.

Q: Is the trigger for a BHBF the same if the sediment inputs are in the fall as compared to 

January?

A: Yes.

Q: Is compliance in place to conduct these flows or is additional compliance needed?

A: Compliance will be required.