Managing sand along the Colorado River to protect cultural sites downstream of Glen Canyon Dam

Abstract

The construction of Glen Canyon Dam in northern Arizona has greatly reduced the supply of sand to the Colorado River corridor through Glen Canyon National Recreation Area and Grand Canyon National Park, hereafter referred to as Glen Canyon and Grand Canyon, respectively. This deficit has strongly affected the natural sediment cycle in this iconic landscape and has lowered the availability of windblown (aeolian) river sand that previously shielded hundreds of unique prehistoric and historic cultural sites. U.S. Geological Survey scientists and their cooperators have conducted a range of studies to assess whether, and under what circumstances, river-derived sand can still reach and protect these sites under current dam operations. Results indicate that most cultural sites hosted in river-derived sand have an elevated risk of erosion that threatens their long-term preservation. However, repeated high-water releases from the dam following downstream tributary inputs of sand to the Colorado River, combined with riparian vegetation removal, could offset some of the erosion caused by wind and precipitation-driven hillslope runoff at some locales. These findings are helping managers conserve limited sand resources to preserve river-corridor cultural sites while still meeting the growing demands for hydropower and water in the Southwestern United States.