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Lake Powell’s storage capacity updated for first time since 1986

SALT LAKE CITY – A new report released today and compiled by the U.S. Geological Survey (USGS) in cooperation with the Bureau of Reclamation provides updated information on Lake Powell’s storage capacity. The report confirms Lake Powell has lost 4% of its potential storage capacity since 1986, when the last survey was completed, and 6.79% since 1963, when the diversion tunnels of Glen Canyon Dam closed, and the reservoir began to fill. The loss is largely due to sediments continuously transported by the Colorado and San Juan rivers settling on the reservoir bottom.

“It is vitally important we have the best-available scientific information like this report to provide a clear understanding of water availability in Lake Powell as we plan for the future,” said Assistant Secretary for Water and Science Tanya Trujillo. “The Colorado River system faces multiple challenges, including the effects of a 22-year-long drought and the increased impacts of climate change.”

Lake Powell is the reservoir behind Glen Canyon Dam. It extends from just south of the Utah-Arizona border northeast along the southern edge of Grand Staircase Escalante National Monument and is a key water storage unit in the Colorado River system, which provides water to approximately 40 million people, irrigates 5.5 million acres of agricultural land, and has the capacity to generate more than 4,200 megawatts of hydropower electricity.

Lake Powell’s storage capacity has been calculated twice before this study: pre-Glen Canyon Dam elevation-area-capacity tables were calculated from contour maps in 1963, and a reservoir-wide, range-line bathymetric survey was conducted in 1986. This most recent survey, conducted by the USGS in 2017 and 2018, indicates: 1) the total storage capacity is 25,160,000 acre-feet, 2) a decrease of 1,833,000 acre-feet or 6.79% of storage capacity from 1963 to 2018, and 3) 1,048,000 acre-feet or 4% decrease from 1986 to 2018. The average annual loss in storage capacity was approximately 33,270 acre-feet per year between 1963 and 2018.

“Conducting repeat surveys with the most up-to-date technology is critical to understanding water storage capacity in Lake Powell,” said Dan Jones, USGS scientist and co-author of the study. “The new surveys show that the rate of reservoir storage capacity loss observed between the three surveys has remained consistent.”

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.

topobathymetric digital elevation model Map

Reclamation converted the TBDEM data into a format that is useful for the management of Lake Powell and operations at Glen Canyon Dam. Those data will be incorporated into the reservoir’s databases and models for planning and operations.

The USGS Scientific Investigations Report is titled “Elevation-Area-Capacity Relationships of Lake Powell in 2018 and Estimated Loss of Storage Capacity Since 1963” and can be found on the USGS Publications Warehouse.

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Michael McGreer Mesquite, Nevada
Dr. Michael Manford McGreer is managing editor of and writes on issues that impact public policy.

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