LAKE POWELL — The Bureau of Reclamation last week revised its data on the amount of water stored in Lake Powell, with a new, lower tally taking into account a 4% drop in the reservoir’s total available capacity between 1986 and 2018 due to sedimentation.

Bureau data on the reservoir’s water-storage volume showed a loss of 443,000 acre-feet between June 30 and July 1 — a 6% drop in storage from 6.87 million acre-feet (which is 28.28% of live storage based on 1986 data) to 6.43 million (26.46% of full).  

The cause was a recalculation of water stored based on a Bureau of Reclamation and U.S.Geological Survey study released in March — the first such analysis in more than 30 years — about Lake Powell’s loss of storage capacity due to the amount of sediment that the Colorado River and other tributaries deposit into the reservoir. The study was based on data about sediment in the lake collected in 2017 and 2018.

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“After inputting the new data on July 1, 2022, storage values at the current elevation were updated, resulting in a decrease of 443,000 acre-feet,“ bureau officials wrote in an email. 

The Bureau of Reclamation has performed two prior sediment surveys: pre-impoundment (before the construction of the dam — up to 1963) and in 1986. 

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