Glen Canyon Dam Adaptive Management Program Administrative History

ABSTRACT: This book is a response to the USGS’s call for a research design that could be used as a framework for prioritizing cultural resources in the Colorado River ecosystem below Glen Canyon Dam. Changing River includes summaries of current environmental conditions and previous research and brings together diverse archaeological opinions about Grand Canyon’s human story. It then presents a theoretical basis for using a landscape approach to organize future research efforts in the canyon. The research presented here explores the geophysical, paleoclimatic, and biological parameters that have shaped the canyon landscape and influenced choices made by humans as they attempted to adapt to this ecosystem. It then focuses on the distribution of cultural materials and patterns using several archaeological approaches, and investigates natural and cultural realms as mutually reinforcing and interacting components of an integrated ecosystem to which humans have applied meaning and value over time.

Between 1999 and 2005, drought in the western United States led to a >44 m fall in the level of Lake Powell (Arizona-Utah), the nation's second-largest reservoir. River discharges to the reservoir were halved, yet the rivers still incised the tops of deltas left exposed along the rim of the reservoir by the lake-level fall. Erosion of the deltas enriched the rivers in sediment such that upon entering the reservoir they discharged plunging subaqueous gravity flows, one of which was imaged acoustically. Repeat bathymetric surveys of the reservoir show that the gravity flows overtopped rockfalls and formed small subaqueous fans, locally raising sediment accumulation rates 10–100-fold. The timing of deep-basin deposition differed regionally across the reservoir with respect to lake-level change. Total mass of sediment transferred from the lake perimeter to its bottom equates to ~22 yr of river input.