Grand Canyon National Park Resources Benefit from 2008 High-Flow Experiment at Glen Canyon Dam
According to recently released research findings by the U.S. Geological Survey (USGS), resources along the Colorado River in Glen Canyon National Recreation Area and Grand Canyon National Park generally benefitted from the 2008 high-flow experiment conducted in March 2008 from Glen Canyon Dam, near Page, Ariz.
The purpose of the 60-hour high flow test experiment was to determine if water releases designed to mimic natural seasonal flooding could be used to improve downstream resources in Glen Canyon National Recreation Area and Grand Canyon National Park. USGS scientists and their cooperators undertook a wide range of physical and biological resource monitoring and research activities before, during, and after the release. Scientists sought to determine whether or not high flows could be used to rebuild Grand Canyon sandbars, create nearshore habitat for the endangered humpback chub, and benefit other resources such as archaeological sites, rainbow trout, aquatic food availability, and riverside vegetation.
The USGS has released a comprehensive fact sheet and two reports (see below) summarizing study results from the 2008 experiment. Among the key findings from these reports are:
- The 2008 experiment resulted in widespread increases in the area and volume of sandbars, expansions of camping areas, and increases in the number and size of backwater habitats (areas of low velocity flow thought to be used as rearing habitat by native fish).
- Six months after the experiment, the new sandbars had been largely eroded by typical fluctuating flow dam operations driven by electrical energy demand; however, median sandbar elevation was still slightly higher and backwater habitats still slightly more abundant than before the experiment. Although stable and relatively lower monthly volume releases are the most effective at limiting sandbar erosion, the volume of water that must be released from Glen Canyon Dam annually is determined by basin hydrology and legal requirements to deliver water from the upper to lower Colorado River Basin.
- Timing the 2008 experiment in March likely reduced successful nonnative seedling germination and created new sandbars during the spring windy season, which allowed for the greatest transport of windblown sand to archeological sites where it protects sites from weathering and erosion.
- In the Lees Ferry rainbow trout fishery, high flows reduced the New Zealand mud snail population by about 80 percent. This nonnative species is considered a nuisance species because the snails cannot be digested when eaten by trout. In contrast, midges and black flies, high-quality food items for fish, increased.
- Young rainbow trout in the Lees Ferry river reach had better survival and growth rates following the experiment, which scientist think may have resulted from improved habitat conditions and better food quality. Additionally, data show that rainbow trout did not move downstream in significant numbers as the result of the high flows.
These findings will be taken into consideration in development of a new protocol for conducting additional high-flow experiments, announced by Secretary Salazar in December 2009.