RECENT DEVELOPMENTS AND A REVIEW OF SEDIMENTATION MONITORING IN LAKE POWELL

Lake Powell is the second largest man-made reservoir in the United States and is primarily sourced by the sediment-laden Colorado and San Juan Rivers. Spanning the Utah and Arizona border, it was created in 1963 following the completion of Glen Canyon Dam. The Lake Powell hydrologic system, including its river sources and reservoir storage, are well monitored. Extensive deltas have developed at the river inlets and account for the primary loss in reservoir storage capacity, which was calculated during the planning stages of Lake Powell. Aerial surveys and high-resolution contour maps were commissioned in the 1940s to establish baseline estimates for storage potential. These maps have recently been developed into a digital elevation model (DEM), providing a topographic surface of the canyon prior to the creation of Lake Powell. To monitor storage volume loss, the U.S. Bureau of Reclamation maintained a range-line surveying program from the reservoir’s inception until 1986 when the elevation-area-capacity relationships were last calculated. Subsequent single- and multibeam sonar bathymetric surveys have intermittently been conducted, though coverage of the reservoir has not been complete. In cooperation with the U.S. Geological Survey and the Earth Resources Observation and Science Center, multibeam bathymetric and light detection and ranging (LiDAR) surveys were conducted in 2017 and 2018 to update the elevation-area-capacity relationships. Combining the bathymetry and LiDAR into a single, continuous topobathymetric dataset provides the highest resolution surface of Lake Powell since Glen Canyon was flooded. Simple DEM differencing of the most recent topobathymetry and pre-dam DEM produces a three-dimensional approximation of total sediment volume that has been deposited in Lake Powell. Interpolated surfaces, derived from the earlier range-line and sonar surveys, document intermediate steps in deposition, exhibiting delta progression and varying rates of sedimentation throughout the life of the reservoir. These datasets build a framework of timing and distribution of sedimentation throughout Lake Powell. Relating these estimates with long-term hydrologic and climatic trends in the Upper Colorado watershed will provide valuable tools for future reservoir management concerns.