Using Lidar to Measure Reservoir Storage

Elevation-Area-Capacity Relationships of LakePowell in 2018 and Estimated Loss of Storage Capacity Since 1963

Scientific Investigations Report 2022-5017
Water Resources Mission Area
Prepared in cooperation with the Bureau of Reclamation

For a while now, we’ve been waiting for LIDAR, light detection and ranging technology, to bring us the elusive self-driving car. Unfortunately, it always seem to be 5 years out. However, I read with amazement about a team of scientists from South America and the United Kingdom who used helicopter-mounted lidar to peer below the rainforest foliage and get a view of the remains of structures below the trees discovering villages that are hundreds of years old and had been swallowed by the jungle.

Now, scientists are finding many other uses for Lidar. The U.S. Geological Survey (USGS) , in cooperation with the Bureau of Reclamation (Reclamation), surveyed Lake Powell between fall 2017 and spring 2018 topographic light detection and ranging (lidar) data (land elevation) and multibeam bathymetry (bed elevation of a water body to calculate the capacity of Lake Powell, the second largest reservoir in the nation.

Lake Powell is located on the Colorado River across the Utah– Arizona border and was created in 1963 by the completion of the Glen Canyon Dam. Nearly 200 miles of the Colorado River was flooded upstream from the dam creating the reservoir/lake. In the United States only Lake Mead, which is approximately 300 miles downstream on the Colorado River is larger.

Though the instrumental record of the Upper Colorado River Basin is robust, with daily stream gage monitoring going back decades, only two studies have estimated the Lake Powell storage capacity. The original, pre-Glen Canyon Dam elevation-area-capacity tables (Bureau of Reclamation, 1963) that were calculated from contour maps and a reservoir-wide, range-line bathymetric survey that was completed 25 years post-impoundment in 1986 (Ferrari, 1988). Both studies utilized the best-available technology at the time but lacked the precision of current surveying methods.

Lake Powell has continuously trapped sediment from the sediment-laden Colorado and San Juan Rivers at the river deltas, diminishing the storage capacity at the highest elevations of the reservoir. During the most recent survey of Lake Powell, USGS scientists used high-resolution multibeam bathymetry and lidar to create the equivalent of an underwater topographic map of the reservoir. The data were then combined to create a topobathymetric digital elevation model (TBDEM), a continuous representation of submerged bathymetry and subaerial topography.

Just as the land above the water has its highs and lows, so too does the land beneath the water’s surface. Those features are known as bathymetry. In a reservoir the build-up of sediment slowly over time reduces the capacity of to the reservoir – how much water it can hold.

The lidar topographic data were acquired during a 2-day airborne survey on April 2 and April 3, 2018, and completed by The Atlantic Group, LLC they found that the total storage capacity of Lake Powell is now 25,160,000 acre-feet. This is a decrease of 1,833,000 acre-feet or 6.79% of storage capacity from 1963 to 2018. The average annual loss in storage capacity was approximately 33,270 acre-feet per year between 1963 and 2018.

Locally, the Occoquan Reservoir in an urbanized area has suffered a 15% loss of capacity associated with accelerated siltation over a shorter period of time.