GCMRC - Research - Information on High Flow Releases, Nov 2004

Information on High Flow Releases, Nov 2004

GCMRC Press Release

Charles G. Groat
Director of the U.S. Geological Survey
Addressing press conference at the Glen Canyon Visitor's Center, Sunday November 21st, 2004.
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U.S. Geological Survey Ready to Evaluate the Effects of Possible High Flow Releases from Glen Canyon Dam

In anticipation of a possible experimental high flow release from Glen Canyon Dam, the U.S. Geological Survey (USGS), Grand Canyon Monitoring and Research Center is collaborating with investigators from the Arizona Department of Fish and Game, the Fish and Wildlife Service, the National Park Service, Northern Arizona University and other cooperators to prepare a suite of scientific experiments designed to evaluate the effect of the experimental high flows on natural resources in and near the Colorado River in the Grand Canyon. If conducted, the test flow will consist of a maximum release of 41,000 cubic feet per second of water from Lake Powell through the dam and into the Colorado River for a period of 60 hours on or around November 22nd.

The results of the scientific investigations described herein will be used to evaluate the use of high flows as a management action for the preservation and restoration natural resources in the Colorado River below Glen Canyon Dam. These investigations will additionally contribute substantially to our understanding of the effect of high flows on natural resources so that we may better understand the relationship between the operations of the Glen Canyon Dam and the natural environment.

The ecosystem surrounding the Colorado River below Glen Canyon Dam has been significantly altered since the dam was completed in 1963. Of particular concern is the reduced amount of sediment available for building beaches below the dam and the recovery of one of the rivers indigenous fish species - the endangered humpback chub. Beaches are also important as a foundation for terrestrial habitat adjacent to the river and recreational rafters and hikers who camp on them. Sediment is also important for in place preservation of archaeological sites and other cultural resources. Most sediment entering the Grand Canyon now arrives via Paria River inputs below the dam. Scientific experiments planned for the event will focus on sediment, native fish, and food for aquatic animals.

Research will be supported by pre- and post-release remote sensing to determine the fate of beaches and sediment in the system. Aerial photography will be complemented by channel bed mapping and sediment classification using sophisticated multibeam sonar. Subsequent remote sensing efforts around Memorial Day and 18 months post-flood will track changes in the system over time.

USGS scientists will focus their investigations on sediment resources, specifically, how much of it moves through the Grand Canyon during the high flow event, and how much is retained in the form of beaches or channel deposits. Shoreline beaches will be measured using a combination of conventional survey equipment and airborne Light Detection and Ranging (LiDAR) equipment. LiDAR is a relatively new surveying technology that can deliver highly accurate topography from aircraft flying thousands of feet above the ground in remote locations. Sediment suspended in the water will also be measured using a combination of water sampling and a laser based technology. A major portion of research is focused on the well-being of native fish. The humpback chub, an endangered species, is one of four remaining native fish in the Grand Canyon. USGS scientists will be monitoring how the high flow releases affect the survival of a population of young humpback chub in the Grand Canyon near the confluence of the Little Colorado River.

Non-native rainbow trout are an important resource for anglers in the first 15 miles below Glen Canyon to Lees Ferry. Surveys of relative abundance of trout were recently completed by the Arizona Department of Fish and Game. Surveys will be repeated in mid-December to determine the effect of flows on trout populations and trout diet.

Another endangered species, the Kanab ambersnail will be the focus of an experiment to determine if their habitat can be protected from experimental floods. Vegetation occupied by snails in the zone to be inundated will be removed by hand, stacked on pallets and moved above the flood. After the high flow ends, vegetation will be relocated to the flood zone and growth hormones will be applied to plants to encourage re-establishment of snail habitat.

The aquatic foodbase is important for all species living in the river. A fundamental component of the foodbase is drift or the floating array of invertebrates, algae and other bits and pieces of raw material carried down the river as a result of the natural erosion of the channel and surrounding landscape. Drift provides a source of energy and carbon to higher organisms, including fish. Drift samples will be taken below the Little Colorado River to determine changes in the foodbase before, during and after the flood. Pre- and post-flood surveys of algae and aquatic vegetation beds, an important part of the foodbase, will also be conducted in the Lees Ferry reach.

Another part of an overall experiment to test the effect of flow and non-flow actions that enhance and restore natural resources in the canyon involves the removal of non-native fish from a critical habitat for the endangered humpback chub near the confluence with the Little Colorado River. While unrelated to flows, this research effort will continue in concert with the overall research design.

If successful, these research and monitoring activities will allow management actions to protect and enhance natural and cultural resources in the Grand Canyon.