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Grand Canyon Monitoring and Research Center, in cooperation with SWCA Environmental Consultants, Inc.

U.S. Geological Survey
Open-File Report 2007-1195
version 1.0

Comparisons of Water Quality and Biological Variables from Colorado River Shoreline Habitats in Grand Canyon, Arizona, under Steady and Fluctuating Discharges from Glen Canyon Dam

By Barbara E. Ralston, Matthew V. Lauretta, and Theodore A. Kennedy

2007

Hydrograph showing daily mean, minimum and maximum discharge at Lees Ferry, Ariz., from August 15, 2005 to October 22, 2005. Arrows indicate dates of sample collection under fluctuating and steady releases (September 4, 2005-September 16, 2005 and September 22-October 7, 2005) (from figure 2).

Abstract

Glen Canyon Dam operations are known to affect mainstem Colorado River temperature and shoreline habitats for native fish. Options for ameliorating the impacts that operations have on young native fish include changing release volumes and/or changing the daily range of releases. Long-term alterations of operations that may produce a measurable biological response can be costly, particularly if the treatment involves reduced power generation. In September and October 2005, a series of two-week releases occurred that alternated between daily fluctuations that varied by 76 m³ s^-1 and steady releases. The purpose of these short-term experiments was to study the effect of daily operations on water quality parameters and biotic constituents (phytoplankton, macroinvertebrates, and fishes) of associated shoreline habitats. Our results indicate that measured biological and physical parameters were, in general, unaffected by flow treatments. However, results should be interpreted cautiously as time within and between treatments was likely insufficient to affect measured parameters. These results lead to the recommendation that studies like this may be more amenable to laboratory experiments first and then applied to a large-scale setting, preferably for longer duration.

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