Instability of Sandbars in Grand Canyon

Abstract

The Glen Canyon Dam, located in the northeastern corner of Arizona, is operated to satisfy peak power demands of neighboring states. The discharge regime of the dam is such that the river stage in the Colorado River downstream of the dam varies diurnally as much as 4 m in some sections. It is alleged that these fluctuations of the river stage are responsible for the destruction of sandbars and, as a result, the loss of the extant biomass and the reduction of recreational facilities. In this paper, an analysis is developed to determine the equilibrium slope below which slope failures (mass wasting, bank failures) due to seepage of bank‐stored water would be unlikely. The sediments enclosed by the equilibrium seepage slope (range 11°–14° for the sediments downstream of the Glen Canyon Dam) and the maximum slope angle (range from 26° to 32°) is subjected to ongoing aggradation and erosion. Field data from ground surveys support the analysis described in this paper.