7423 - Laserfiche WebLink

Home Browse Search

Flood Releases Cause Damage To Beaches And Terrestrial Resources I I I I I I I I I I I I I I I I I I I The GeES Determined That operation Of Glen Canyon Dam, Through Control Of Flows In The Colorado River, Bas Substantial Adverse Effects On Downstream Bnvironmental And Recreational Resources Construction of the dam and subsequent regulation of river flows has changed downstream resources in many ways. Some of these changes, such as the increase in riparian vegetation, the development of an exceptional trout fishery, and the extended white-water boating season are beneficial. However, two aspects of current operations, flood releases and fluctuating releases, were found to have negative impacts on downstream re- i t sources. Impacts were assessed by comparing current \-.,\~").~,,,~\,operat~ons, w~ich include ~loods and fluctuations, . to j .~ ~ operat~ons wh~ch would avo~d flood releases and wh~ch would convert fluctuating releases to steady releases. A flood release is defined as a discharge greater than the maximum powerplant release of 31,500 cubic feet per second (cfs). During floods, substantial quantities of riparian vegetation are scoured away, drowned, or buried by redeposited sand. As a result of the flood releases of 1983, vegetation loss in some areas reached 50 percent, and 95 percent of the marshes and 75 percent of the nests of some riparian bird species were destroyed. Because the dam cuts off the main pre-dam source of sediment to the river downstream, frequent flood releases of sediment-free water cause significant and irreversible degradation of the environment by eroding a substantial portion of the sand deposits. These de- posits provide substrate for streamside vegetation and wildlife habitat, and are highly valued as campsites by white-water boaters. Significant loss of sand beaches would reduce by approximately 50 percent the recreation benefits (not commercial revenues) associated with white-water boating.