U.S. Department of the Interior

U.S. Geological Survey

Science Activities Associated with Proposed 2008 

High-Flow Experiment at Glen Canyon Dam

A sandbar along the left shore of the Colorado River near river mile 30 shortly before (top) and 

shortly after (bottom) the November 2004 high-flow experiment. People and boats indicate scale.

Grand Canyon National Park lies 

approximately 15 miles downriver 

from Glen Canyon Dam, which was built 

on the Colorado River just south of the 

Arizona-Utah border. Because the dam 

stops most sediment moving downstream, 

its presence has resulted in erosion and 

shrinkage of river sandbars in Grand 

Canyon. Fewer and smaller sandbars 

mean smaller camping beaches for 

visitors to use, continued erosion of 

cultural sites, and possibly less habitat 

for native fish, including the endangered 

humpback chub.

In an effort to restore sandbars and 

related habitat and to comply with its 

responsibilities under the Grand Canyon 

Protection Act, the Department of the 

Interior has proposed a high-flow release 

of water from Glen Canyon Dam in March 

2008. The U.S. Geological Survey’s (USGS) 

Grand Canyon Monitoring and Research 

Center is responsible for coordinating 

research associated with the proposed 

experiment. The proposed studies are 

designed to evaluate the feasibility of 

using such high flows to improve a range 

of Grand Canyon resources.

Background

Before Glen Canyon Dam was 

built, spring snowmelt swelled the 

Colorado River, contributing to the 

river’s natural flood cycle and transporting large quantities of sand that created 

and maintained Grand Canyon sandbars. 

Now most of the river’s sediment is 

trapped behind the dam. The 2008 highflow experiment is designed to simulate, 

to some degree, the natural sand-carrying activity of the pre-dam Colorado 

River by moving sand that has entered 

the system from tributaries below the 

dam up and onto sandbars. 

Two similar tests were conducted in 

1996 and 2004. In the 1996 event, scientists learned that tributary-supplied sand 

does not accumulate on the riverbed over 

multiyear periods under typical dam 

operations. In fact, the 1996 high flow 

actually resulted in a net reduction in 

overall sandbar size. This finding led to 

the second high-flow test in 2004, when 

relatively large quantities of new sand 

had entered the system from tributaries 

below the dam. 

The 2004 experiment resulted in 

an increase of total sandbar area and volume in the upper half of Marble Canyon 

(see photos), but farther downstream, 

where sand was less abundant, sandbars 

eroded. Scientists concluded that more 

sand than was available during the 2004 

high flow will be required to achieve 

increases in total sandbar area and 

volume throughout all of Marble and 

Grand Canyons. The proposed 2008 

experiment and accompanying studies 

will build upon the lessons learned from 

these two previous tests.

The Proposed 2008 High-Flow Experiment 

and Associated Research

The proposed 2008 experiment will 

be different from the two previous tests 

in several important ways. In November 

2007, sand supplies in the main channel 

of the Colorado River were approximately three times larger than in 2004, 

a result of flooding on the Paria River, 

which enters the Colorado just downstream from Glen Canyon Dam. Such an 

abundance of sand occurs, on average, 

only once a decade. A second important 

difference is that the high flow will be 

followed by normal dam operations. This 

experiment will thus help determine if 

new sand deposits can be retained under 

normal operations.

 Research associated with the 2008 

experiment (listed in the table) will focus 

on a wide range of questions, not just 

whether high-flow releases are capable of 

rebuilding and maintaining sandbars over 

time. Do such releases have the ability 

Fact Sheet 2008–3011

February 2008
to create advantages for native fish? Is it 

possible that high flows can temporarily displace nonnative fishes? Can they 

build and maintain backwater habitats 

that possibly offer growth advantages to 

humpback chub and other native fishes? 

Can new sand deposits help protect cultural sites? Will increased sand carried by 

the wind from restored sandbars reduce 

erosion and increase the preservation 

potential at archaeological sites? What 

effects do high-flow experiments have on 

riverside vegetation, on rainbow trout, on 

the aquatic food base that supports native 

and nonnative fishes, and on Lake Powell 

water quality?

A comprehensive synthesis of the 

results of all of the experimental studies 

conducted in association with a possible 

2008 experiment and previous high-flow 

tests is planned. Additionally, the data 

gathered in the proposed 2008 experiment 

will inform the continued development

of a sediment transport model for the 

Colorado River. The improved model will 

help determine the optimum frequency, 

timing, duration, and magnitude of future 

high-flow releases.

Collaboration

The 2008 high-flow experiment 

and associated research activities will 

be undertaken cooperatively by scientists and resource managers from the 

Department of the Interior’s Bureau of 

Reclamation (Reclamation), National 

Park Service, U.S. Fish and Wildlife 

Service (USFWS), and U.S. Geological 

Survey (USGS). State and university 

partners will also provide assistance.

Reclamation operates the Glen 

Canyon Dam and will conduct the 

release. In compliance with the Endangered Species Act (ESA), Reclamation 

has prepared a biological assessment 

that evaluates the impact of the proposed experimental operations on listed 

species. In response, the USFWS is 

preparing a biological opinion that will 

provide ESA compliance for both the 

2008 experiment and other experimental flow operations from the dam for the 

next 5 years. Reclamation has prepared 

an environmental assessment, which is 

is available to the public for comment. 

The National Park Service is working with other agency partners to carry 

out an outreach plan for the public, 

especially river runners and backcountry users, about safety concerns during 

the proposed high flows. A decision 

by the Department of the Interior on 

performing the high-flow experiment is 

anticipated in late February 2008, with 

plans to conduct the test in early 

March 2008. 

The science activities associated 

with the proposed experiment were 

developed with the guidance of the Glen 

Canyon Dam Adaptive Management 

Program, a Federal initiative designed 

to assist the Secretary of the Interior in 

protecting resources downstream of Glen 

Canyon Dam. The program includes a 

wide range of stakeholders, including 

Native American tribes, Colorado River 

Basin States, environmental and recreation groups, power customers, and State 

and Federal agencies.

The most current and additional 

information about the proposed high-flow 

experiment may be found by visiting 

www.gcmrc.gov.

For more Information contact:

John Hamill

U.S. Geological Survey

Southwest Biological Science Center

Grand Canyon Monitoring and

Research Center

Flagstaff, Arizona 

Telephone: 928-556-7364

Email: jhamill@usgs.gov

http://www.gcmrc.gov

Experimental 

study 

Description 

1.A. Sand budgeting Data will be collected to determine the amount of sediment available in the system and its availability for restoring 

sandbars and camping beaches, patterns of erosion and deposition, and changes in sediment grain size. 

1B. Eddy-sandbar 

studies 

Data will be collected on the evolution of specific eddy sandbars before, during, and after a high flow. These 

data will be used to improve the predictive capabilities of the existing sediment model and determine the 

optimal peak flows of future high-flow experiments. 

1.C. Response of 

sandbars and select 

cultural sites 

Data will be collected to determine whether (1) sandbars throughout the Colorado River ecosystem gain or lose 

sand as the result of a sand-enriched high flow, (2) new sand can offset gully erosion, and (3) enlarged sandbars 

provide source material for the windborne transport of sand upslope into archaeological sites. 

1.D. Backwater habitats Measure backwater habitats and sample them for fish in spring and fall to evaluate (1) how backwaters formed 

by a high flow change over time and (2) how fish, particularly humpback chub, use backwaters. 

2. Riparian vegetation 

studies 

Document changes in riparian vegetation following a high flow to determine if disturbances influence 

the success of nonnative species. 

3. Food availability Data will be collected to determine how high-flow experiments affect the quantity and quality of food 

available to invertebrates and, ultimately, fish. 

4.A. Redds (fish-nest) 

study 

Data will be collected to determine how high-flow experiments affect spawning and survival of earlylife stages of rainbow trout in Lees Ferry. 

4.B. Movement study Data will be collected to determine if high-flow experiments displace rainbow trout from Lees Ferry and 

if displacement varies by fish length. 

5. Lake Powell Data will be collected to determine if a high flow results in higher nutrient releases and changes in the 

reservoir’s hypolimnion. 

6. Kanab ambersnail Kanab ambersnail habitat at Vaseys Paradise will be moved to minimize impacts to an endangered species. 

7. Synthesis of 

knowledge 

Data and knowledge gained as the result of the high-flows test will be synthesized in an attempt to 

address strategic science questions required to improve management. 

Experimental studies associated with the proposed 2008 high-flow experiment.