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Colorado River/Grand Canyon Focus of Science Meeting
Released: 4/23/2001

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communication
119 National Center
Reston, VA 20192
Pat Jorgenson 1-click interview
Phone: 650-329-4011

Editors: Print reporters and television news crews are encouraged to drop in on the proceedings and interview presenting scientists, during the breaks. A public affairs specialist will be there to assist.

The effect of low flows of the Colorado River, last summer, on fish, sand distribution, power production, recreation and other aspects of the river environment will be the focus of a Grand Canyon Science Symposium, April 26 and 27, at the Little America Hotel Conference Center in Flagstaff, Ariz. The symposium, which is free and open to interested members of the public, is sponsored by the Grand Canyon Monitoring Research Center, a program of the U.S. Geological Survey.

The focus of this year’s symposium is the effects of a controlled, experimental low flow of 8,000 cubic feet per second (cfs) downriver from Glen Canyon Dam, from June through September, 2000, followed by a four-day spike of 30,000 cfs, in late September.

Slide-illustrated talks, on topics from the importance of the size of sand grains, disruption of the aquatic food chain and the economic value of recreation on the river, will be presented from 8 a.m. to 5 p.m., Thursday, April 26, and from 8 a.m. to noon, Friday, April 27. Posters that explain many of the projects that are being used to gather data on the Colorado River in the Grand Canyon, will be on display in the conference center from 7 to 9 p.m., April 26.

Among the presentations are:

Effects of a Low, Steady Summer Flow on Native Fishes – Short-term monitoring and periodic sampling of fish populations show possible main-channel spawning by flannelmouth suckers, bluehead suckers and humpback chub, but no similar expansion of non-native fish, except for fathead minnows. A four-day spike in the flow, to 30,000 cfs in September, had a significant negative effect on non-native species, but a lesser effect on native fish.

Economic Impact of Low Flow on Electrical Power Production – The controlled low flows of the summer of 2000 altered the pattern of water released through the power plant at Glen Canyon Dam. Because the electrical power from Glen Canyon is sold by the Western Area Power Administration to several western states, variations in release schedules need to be carefully planned and monitored.

Main-Channel and Near-Shore Warming of the River, Under Steady Low Flows – As releases from Glen Canyon Dam were reduced to 8000 cfs on June 1, 2000, water temperatures at downstream locations immediately increased and remained high throughout most of June, July and August and recorded the highest temperatures for these stations during the last decade. The average monthly temperature of 19 degrees Celsius (67 degrees Fahrenheit) at the Diamond Creek station was about double the temperature there in 1997, when flow levels were steady and high.

Growth of Exotic and Native Plants in Near-Shore Habitats During the Summer 2000 Low, Steady Flow – Monthly inspection of vegetation at six sites between Lees Ferry and Bright Angel Creek show a small but significant increase in the densities of native plants, followed by a modest decline, following the September spike flow. Seed-propagated non-natives, such as Tamarix, showed a much more rapid increase during the summer, but also a much larger decrease in densities, resulting from the fall spike. The authors of this study conclude that the experimental low flows created lasting near-shore habitat for larval fish, but encouraged the growth of plants that impact other resources, especially recreation.

Sediment Delivery and Distribution Prior to and During the Low-Flow Experiment – Prior to construction of Glen Canyon Dam, substantial amounts of sand accumulated in the two-mile stretch between Lees Ferry and the Grand Canyon only when flows were lower than about 9000 cfs, usually between July and March. The first releases from Lake Powell in 1965 scoured an estimated 16 million metric tons of fine sediment from the river’s bed and banks on the Lees Ferry/Grand Canyon reach, and the only time that the supply would be enhanced was during occasional large tributary floods. The amount of suspended sediment in the water, as measured at the Grand Canyon gage, miles below Glen Canyon Dam, was the coarsest and most depleted during June 2000 than at any other time since such record keeping began. Side-scan sonar that was used to produce images of the bottom and sides of the riverbed during the low-flow experiment and immediately following the September spike, shows pebbles and cobbles dominating the mid portions of the river, while sand deposits were limited to the margins of the channel. Overall, scientists say, there were no extreme changes in the amount of sediment removed or deposited on the two-mile stretch of river.

The Economic Impacts of the Low-Flow Experiment on River Recreation – While the low flows of summer 2000 seemed to benefit private anglers and boaters, they reportedly were responsible for fewer whitewater thrills and more accidents for commercial river runners. Five of nine boat-grounding incidents resulted in removal of passengers from rafts and in some cases, resulted in termination of the river trip. Accident rates during the low-flow period were highest for motorized rafts, which constitute 75 percent of all recreational boating on the river. Conversely, angling concessionaires benefited slightly from the improved fishing conditions during the low flows, but reported a loss of $30,000 during the spike flows.

The Grand Canyon Monitoring and Research Center (GCMRC) studies the effects of the operation of Glen Canyon Dam on downstream resources within the Glen Canyon National Recreation Area and Grand Canyon National Park. The GCMRC’s scientific activities contribute to meeting the statutory requirements placed on the Secretary of the Interior by Congress via the 1992 Grand Canyon Protection Act, the 1995 Glen Canyon Dam Environmental Impact Statement, and the 1996 Record of Decision. The scientific activities are performed by both in-house and external research experts, often in collaborative effort. The GCMRC annually extends a formal Solicitation for Cooperative Agreement Proposals (see below) to solicit additional research. Research results are used to refine the conceptual model of the impacts of differing dam operations on the Colorado riverine ecosystem. The GCMRC presents The State of Natural and Cultural Resources in the Colorado River Ecosystem Report (SCORE report) on a semi-annual basis.

Offices of the GCMRC are located at 2255 N. Gemini Drive, Room 341, Flagstaff, AZ 86001, telephone 520-556-7094, where it maintains a research library that is open to the public, as well as scientific researchers. The chief scientist at the GCMRC is Dr. Barry Gold. The Center maintains a website at http://www.gcmrc.gov.

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