BRIEFING MEMORANDUM 

Date: January 20, 2011 

To: GCDAMP - Technical Workgroup 

From: John Hamill, Chief and Ted Melis, Deputy Chief, both at USGS Grand Canyon 

Monitoring and Research Center; (o) 928-556-7364 or (c) 928-607-5253 

SUBJECT: Summary of upcoming U.S. Geological Survey Circular 1366 on the results of three 

high-flow experiments released from Glen Canyon Dam, Arizona 

BACKGROUND 

Three high-flow experiments (HFEs) were conducted by the U.S. Department of the Interior at 

Glen Canyon Dam, Arizona, in March 1996, November 2004, and March 2008. These experiments, 

also known as artificial or controlled floods, were scheduled releases of water from Glen Canyon 

Dam above powerplant capacity that were designed to mimic some aspects of pre-dam Colorado 

River seasonal flooding. The goal of these experiments was to determine whether high flows could 

be used to benefit important physical and biological resources in Glen Canyon National Recreation 

Area and Grand Canyon National Park that are being adversely affected by the operation of the 

dam. Examples of these downstream resources include native species, such as the endangered 

humpback chub (Gila cypha), sandbar habitats, cultural sites, and recreational resources. The report 

summarizes and synthesizes the extensive body of results published since 1996 and outlines a 

possible strategy for initiating future HFEs. 

FINDINGS 

Sediment and Sandbars 

Five key sediment conclusions have important implications for designing future HFEs: 

1. HFEs effectively build sandbars by transferring sand from the riverbed to sandbars either by 

eroding existing low-elevation sandbars or by using tributary-supplied sand. 

2. HFEs conducted soon after tributary flooding accompanied by sand enrichment are 

effective at increasing sandbar area and volume and less likely to result in the erosion of lowelevation parts of sandbars. 

3. Sandbars are rebuilt relative quickly (hours to a few days) under sand-enriched conditions 

but then also tend to erode quickly over days to months following an HFE. 

4. Monitoring data show that sandbars erode more quickly as release volumes and daily 

fluctuations increase; the rate of erosion is reduced when tributary sand production occurs 

following sandbar building. 

5. From February 1996 and October 2008 many of the sandbars at long term study sites in 

Grand Canyon experienced slight increases in size (both area and volume) over that period 

despite ongoing erosion of the deposits. This increase occurred during a period of variable 

basin hydrology which included 6 years of above annual minimum releases and 7 years of 

minimum annual releases. 

 

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Biological Resources 

Four biological conclusions have important implications for designing future HFEs: 

1. On the basis of 2008 HFE research, spring-timed HFEs have the potential to significantly 

increase the size of the rainbow trout population in the Lees Ferry reach and downstream 

areas being managed for native fish. 

2. Increases in the rainbow trout population associated with the March 2008 HFE appear to 

have been the result of improvements in spawning/rearing habitat and increased availability 

of better quality food that improved the survival of juvenile trout. 

3. The large increases of rainbow trout numbers documented in the river reach near the Little 

Colorado River confluence may adversely affect the endangered humpback chub, because 

rainbow trout are known predators of young chub and compete with native fish for limited 

food and habitat. 

4. HFEs resulted in no measurable direct impact, positive or negative, to humpback chub 

populations, possibly because of the short duration of the HFE (2-1/2 to 7 days). 

 

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A SCIENCE-BASED STRATEGY FOR FUTURE HIGH-FLOW EXPERIMENTATION 

Key Questions 

1. Can sandbar building during HFEs exceed sandbar erosion during periods between HFEs, 

such that sandbar size can be increased and maintained over several years? 

2. Does the seasonal timing of HFEs influence the rainbow trout response?

Strategy 

• An adaptive management approach would be most effective for assessing the key questions 

above. The diverse objectives of river managers means that potential impacts to other 

downstream resources must also be carefully considered. 

• With only 6-10 percent of the pre-dam sand supply still entering Grand Canyon National 

Park from the Paria and Little Colorado Rivers, rebuilding and maintaining sandbars 

systemwide requires repeated HFEs following typical tributary floods that occur annually. 

This is true for two reasons: (1) typical dam operations do not allow multiyear 

accumulation of tributary sand inputs to occur in the river channel, and (2) new sandbars 

are eroded to some extent by typical dam releases following each HFE. 

• Paria River flooding is the primary source of new sediment inputs; flooding primarily 

occurs from mid-summer through early fall; therefore, ideally, HFEs would be timed for 

mid-October or November. Because the Paria River more rarely experiences winter 

flooding, resulting in an HFE in mid-March to April under this strategy, about two-thirds of 

future HFEs would occur during the fall. The Little Colorado River also delivers important 

new sand supplies, and those inputs can also be considered by managers annually as criteria 

for the next HFE are evaluated relative to the river’s sand accounting (see attached figure). 

• If future flow experiments are strategically timed to follow a variety of tributary floods and 

HFE hydrographs are appropriately designed (peak magnitudes and durations) to match the 

volume of new sand annually delivered to the river, scientists hypothesize that it may be 

possible to enlarge and maintain sandbars through time. 

 

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Addressing Uncertainty 

Although the strategy suggested above is made on the basis of monitoring data and published 

results, uncertainties exist about its ability to maximize future sandbar building and how HFEs will 

affect other resources over the long term. It is thus critical that long-term monitoring of the 

effects of HFEs be conducted and the results evaluated to adapt this strategy to changing 

conditions. 

• If monitoring under the suggested triggering strategy indicates that sandbars continue to 

erode or cannot be rebuilt and sustained at a desired level, then managers may choose other 

experimental options, such as further constraining dam releases, augmenting sand supply to 

Grand Canyon from sources in Lake Powell, or both. 

• Tracking the status and response of the aquatic food web and fish populations to HFEs is 

critical. 

Although the proposed strategy does not guarantee success, sandbar trends without HFEs are one 

of the few outcomes that sediment researchers can predict with absolute certainty: without HFEs, 

sandbar size will decrease through time. 

 

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FIGURE CAPTION - Historical USGS data on Paria and Little Colorado River flow and 

sand delivery to the Colorado River (as measured and modeled tributary stations below the 

dam) supports the proposed fall and spring strategy for releasing future high-flow 

experiments (HFEs) from Glen Canyon Dam that are intended to maximize rebuilding and 

maintenance of sandbars. Diamonds = Paria River and Squares = Little Colorado River 

data. 

 

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Completed and In-Review 2008 High-Flow Experiment Scientific Reports 

(All available at http://www.gcmrc.gov, excepting four currently still pending final USGS 

approval)

The 24 reports listed below (20 final and 4 still considered to be “in review” under USGS 

Fundamental Science Practices) are referenced to the individual research project numbers 

(Projects 1–7 and associated post-HFE monitoring data) and activities described in the December 

2007 Science Plan for a March 2008 High-Flow Experiment, as recommended by AMWG in 

January 2008 and approved by the U.S. Department of the Interior for implementation in 

February 2008. An upcoming USGS circular intended to summarize and synthesize all HFE 

results for three flow experiments with peak flows exceeding GCD powerplant capacity (those 

released in 1996, 2004, and 2008) is anticipated by early 2011 in fulfillment of Project 7 

(Synthesis of knowledge). 

PROJECT 1—SEDIMENT, ARCHAEOLOGICAL SITES, AND BACKWATERS

Project 1.A—Sand budgeting 

Topping, D.J., Rubin, D.M., Grams, P.E., Griffiths, R.E., Sabol, T.A., Voichick, N., Tusso, R.B., 

Vanaman, K.M., and McDonald, R.R., 2010, Sediment transport during three controlled-flood 

experiments on the Colorado River downstream from Glen Canyon Dam, with implications for 

eddy-sandbar deposition in Grand Canyon National Park: U.S. Geological Survey Open-File 

Report 2010-1128, 111 p., at http://pubs.usgs.gov/of/2010/1128/. 

Project 1.B—Eddy sandbar studies 

Wright, S.A., and Kaplinski, M., in press, Flow structures and sandbar dynamics in pool-rapid 

units during a controlled flood, Colorado River, Arizona: Journal of Geophysical ResearchEarth Surface. 

Logan, B., Nelson, J., McDonald, R., and Wright, S., 2010, Mechanics and modeling of flow 

sediment transport and morphologic change in riverine lateral separation zones, in Hydrology 

and sedimentation for a changing future; existing and emerging issues (Joint Federal 

Interagency Conference 2010—Federal Interagency Hydrologic Modeling, 4th, and Federal 

Interagency Sedimentation, 9th), Las Vegas, Nev., June 27- July 1, Proceedings: v. ISBN: 978-

0-9779007-3-2, CD-ROM. 

Project 1.C—Response of sandbars and select cultural sites 

Hazel, J.E., Jr., Grams, P.E., Schmidt, J.C., and Kaplinski, M., 2010, Sandbar response in Marble 

and Grand Canyons, Arizona, following the 2008 high-flow experiment on the Colorado 

River: U.S. Geological Survey Scientific Investigations Report 2010-5015, 52 p., at 

http://pubs.usgs.gov/sir/2010/5015/. 

Rubin, D.M., Topping, D.J., Chezar, H., Hazel, J.E., Schmidt, J.C., Breedlove, M., Melis, T.S., 

and Grams, P.E., 2010, 20,000 grain-size observations from the bed of the Colorado River and 

implications for sediment transport through Grand Canyon, in Hydrology and sedimentation 

for a changing future; existing and emerging issues (Joint Federal Interagency Conference 

2010—Federal Interagency Hydrologic Modeling, 4th, and Federal Interagency Sedimentation, 

9th), Las Vegas, Nev., June 27- July 1, Proceedings: v. ISBN: 978-0-9779007-3-2, CD-ROM. 

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Draut, A.E., Topping, D.J., Rubin, D.M., Wright, S.A., and Schmidt, J.C., 2010b, Grain-size 

evolution in suspended sediment and deposits from the 2004 and 2008 controlled-flood 

experiments in the Marble and Grand Canyons, Arizona, in Hydrology and sedimentation for a 

changing future; existing and emerging issues (Joint Federal Interagency Conference 2010—

Federal Interagency Hydrologic Modeling, 4th, and Federal Interagency Sedimentation, 9th), 

Las Vegas, Nev., June 27- July 1, Proceedings: v. ISBN: 978-0-9779007-3-2, CD-ROM. 

Draut, A.E., Sondossi, H.A., Hazel, J.E., Jr., Andrews, T., Fairley, H.C., Brown, C.R., and 

Vanaman, K.M., 2009, 2008 Weather and aeolian sand-transport data from the Colorado River 

corridor, Grand Canyon, Arizona: U.S. Geological Survey Open-File Report 2009-1190, 98 p., 

at http://pubs.usgs.gov/of/2009/1190/of2009-1190.pdf. 

Draut, A.E., Hazel, J.E., Jr., Fairley, H.C., and Brown, C.R., 2010a, Aeolian reworking of 

sandbars from the March 2008 Glen Canyon Dam high-flow experiment in Grand Canyon, in 

Melis, T.S., Hamill, J.F., Bennett, G.E., Coggins, L.G., Jr., Grams, P.E., Kennedy, T.A., 

Kubly, D.M., and Ralston, B.E., eds., Proceedings of the Colorado River Basin Science and 

Resource Management Symposium, November 18-20, 2008, Scottsdale, Arizona: U.S. 

Geological Survey Scientific Investigations Report 2010-5135, 325-331 p., at 

http://pubs.usgs.gov/sir/2010/5135/. 

Project 1.D—Biological and physical aspects of backwater habitats 

Grams, P.E., Hazel, J.E., Schmidt, J.C., Kaplinski, M., Wright, S.A., Topping, D.J., and Melis, 

T.S., 2010a, Geomorphic response of sandbars to the March 2008 high-flow experiment on the 

Colorado River downstream from Glen Canyon Dam, in Hydrology and sedimentation for a 

changing future; existing and emerging issues (Joint Federal Interagency Conference 2010--

Federal Interagency Hydrologic Modeling, 4th, and Federal Interagency Sedimentation, 9th), 

Las Vegas, Nev., June 27- July 1, Proceedings: v. ISBN: 978-0-9779007-3-2, CD-ROM. 

Grams, P.E., Schmidt, J.C., and Andersen, M.E., 2010b, 2008 high-flow experiment at Glen 

Canyon Dam—morphologic response of eddy-deposited sandbars and associated aquatic 

backwater habitats along the Colorado River in Grand Canyon National Park: U.S. Geological 

Survey Open-File Report 2010-1032, 73 p., at http://pubs.usgs.gov/of/2010/1032/. 

Behn, K.E., Kennedy, T.A., and Hall, R.O., Jr., 2010, Basal resources in backwaters of the 

Colorado River below Glen Canyon Dam—effects of discharge regimes and comparison with 

mainstem depositional environments: U.S. Geological Survey Open-File Report 2010-1075, 25 

p., at http://pubs.usgs.gov/of/2010/1075/of2010-1075.pdf. (This report is not directly tied to 

HFE reporting, however, the report’s findings relate to Projects 1.D and 3.) 

PROJECT 2—RIPARIAN VEGETATION

Ralston, B.E., 2010, Riparian vegetation response to the March 2008 short-duration, high-flow 

experiment—implications of timing and frequency of flood disturbance on nonnative plant 

establishment along the Colorado River below Glen Canyon Dam: U.S. Geological Survey 

Open-File Report 2010-1022, 30 p., at http://pubs.usgs.gov/of/2010/1022/. 

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PROJECT 3—AQUATIC FOOD BASE

Rosi-Marshall, E.J., Kennedy, T.A., Kincaid, D.W., Cross, W.F., Kelly, H.A.W., Behn, K.A., 

White, T., Hall, R.O., Jr., and Baxter, C.V., 2010, Short-term effects of the 2008 high-flow 

experiment on macroinvertebrates in the Colorado River below Glen Canyon Dam, Arizona: 

U.S. Geological Survey Open-File Report 2010-1031, 28 p., at 

http://pubs.usgs.gov/of/2010/1031/. 

PROJECT 4—RAINBOW TROUT

Project 4.A—Redds study 

Korman, J., Kaplinski, M., and Melis, T.S., 2010, Effects of high-flow experiments from Glen 

Canyon Dam on abundance, growth, and survival rates of early life stages of rainbow trout in 

the Lees Ferry reach of the Colorado River: U.S. Geological Survey Open-File Report 2010-

1034, 31 p. http://pubs.usgs.gov/of/2010/1034/. 

Korman, J., Kaplinski, M. and T.S. Melis. In press, Effects of fluctuation flows and a controlled 

flood on incubation success and early survival rates and growth of age-0 rainbow trout in a 

large regulated river, Transactions of the American Fisheries Society. 

Korman, J. and Melis, T.S., 2011, The Effects of Glen Canyon Dam Operations on Early Life 

Stages of Rainbow Trout in the Colorado River, U.S. Geological Survey Fact Sheet, FS-2011-

3002, 4 p. 

Project 4.B—Movement study 

Hilwig, K.D., and Makinster, A.S., 2010, Evaluating effects of a high-flow event on rainbow 

trout movement in Glen and Marble Canyons, Arizona, by using acoustic telemetry and 

relative abundance measures, in Melis, T.S., Hamill, J.F., Bennett, G.E., Coggins, L.G., Jr., 

Grams, P.E., Kennedy, T.A., Kubly, D.M., and Ralston, B.E., eds., Proceedings of the 

Colorado River Basin Science and Resource Management Symposium, November 18-20, 

2008, Scottsdale, Arizona: U.S. Geological Survey Scientific Investigations Report 2010-5135, 

219-225 p., at http://pubs.usgs.gov/sir/2010/5135/. 

Makinster, A.S., Persons, W.R., Avery, L.A. and Bunch, A.J., 2010, Colorado River fish 

monitoring in Grand Canyon, Arizona—2000 to 2009 summary: U.S. Geological Survey 

Open-File Report 2010–1246, 26 p. 

PROJECT 5—LAKE POWELL QUALITY OF WATER

Vernieu, W.S., Effects of the 2008 high-flow experiment on water quality in Lake Powell and 

Glen Canyon Dam releases, Utah-Arizona: U.S. Geological Survey Open-File Report 2010–

1159. 

PROJECT 6—KANAB AMBERSNAIL CONSERVATION MEASURES 

Sorensen, J.A., Kanab Ambersnail habitat mitigation for the 2008 high flow experiment—

August 2009 draft cooperator report from Arizona Game and Fish Department: Phoenix, 

Arizona Game and Fish Department. 

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PROJECT 7—SYNTHESIS OF KNOWLEDGE

Melis, T.S., Topping, D.J., Grams, P.E., Rubin, D.M., Wright, S.A., Draut, A.E., Hazel, J.E., Jr., 

Ralston, B.E., Kennedy, T.A., Rosi-Marshall, E., Korman, J., Hilwig, K.D., and Schmit, L.M., 

2010, 2008 High-flow experiment at Glen Canyon Dam benefits Colorado River resources in 

Grand Canyon National Park: U.S. Geological Survey Fact Sheet 2010-3009, 4 p., at 

http://pubs.usgs.gov/fs/2010/3009/. 

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Pending 2008 High-Flow Experiment Reports and Related Reports 

Anticipated to be USGS Approved before February 1, 2011

Cross, W.F., Baxter, C.V., Donner, K.C., Rosi-Marshall, E.J., Kennedy, T.A., Hall, Jr., R.O., 

Wellard-Kelly, H.A. and Rogers, R.S., in review, Ecosystem ecology meets adaptive 

management: food web response to a controlled flood on the Colorado River, Glen Canyon, 

Ecological Applications. 

Grand Canyon Monitoring and Research Center (five chapters with multiple authors), in review, 

The effects of three Glen Canyon Dam high-flow experiments on the Grand Canyon 

ecosystem: U.S. Geological Survey Circular. 

Makinster, A.S., L.A. Avery, and W.R. Persons. in review. Status of the Lees ferry rainbow trout 

fishery: U.S. Geological Survey Open File Report 2010-xxxx. 

Melis, T.S., Korman, J. and Kennedy, T.A. in review, Abiotic & Biotic Responses of the 

Colorado River to the March 2008 and Two Earlier Controlled Flood Experiments at Glen 

Canyon Dam, Arizona, USA, River Research and Applications.