The state Department of Water Resources has begun using laser and sonar technology to measure reservoir capacity and has found that Lake Oroville, the State Water Resources Project’s largest reservoir, has been shrinking since its creation in 1960.
In 2021, DWR used an airplane-mounted laser pulse to map parts of the basin’s topography that were not submerged at the time because the lake’s water level was historically low. Then, in 2022, a boat sent sonar pulses into Lake Oroville to map the underwater topography. Engineers calculated that the reservoir’s capacity was 3% less than previous estimates, more than 100,000 acre-feet less.
“You can also see the old road and railroad tracks that remain in place that were used when the dam was built in the 1960s,” Tony Squellati, manager of the photogrammetry and computer mapping division for DWR’s Engineering and Geographic Information Division, said in a news release.
The change in the lake’s volume is likely due to sediment, such as rocks and silt, that has accumulated on the lake bottom over the 60 years since the Oroville Dam was built, as well as extreme weather events, such as droughts and rains. The Bureau of Water Resources began using the new data on storage capacity on Monday to help with water operations calculations.
California reservoir levels continue to reach record highs, with nearly every major reservoir above its historical average after a record winter storm in 2023 nearly brought the state out of drought. Lake Oroville is at 95% of its historical average and is currently at 121% of its historical average. It was nearly above 100% in May for the second straight year, according to DWR data.
Folsom Lake is in the 80th percentile, or 114% of its historical average, Lake Shasta is at 113% and Lake New Melones is at 133%. All three reservoirs are operated by the federal government’s Central Valley Project.
Lake Oroville drains the Feather and Sacramento Rivers into the Sacramento-San Joaquin Delta, providing water for millions of Californians. Some of the water is diverted into the South Bay waterways, which serve Alameda and Santa Clara counties, while the rest flows into the Central Valley farmland and Southern California cities.
Oroville Dam opened in 1968 and, at 770 feet, is the tallest dam in the U.S. Located just northeast of the Oroville city limits, water from the dam’s main spillway flows into the Feather River.
The dam was at the center of a crisis in 2017 when torrential rains damaged the main spillway, and more than 180,000 residents downstream from the dam in Butte, Sutter and Yuba counties were ordered to evacuate after diverted water threatened to breach the dam’s emergency spillway.
Extensive repairs costing more than $630 million followed, and state water officials released water from the newly rebuilt spillway for the first time in April 2019. A forensics team determined that the crisis was the result of “long-standing systemic failings” by both state water officials and federal regulators, writing in a nearly 600-page report that design flaws were exacerbated by years of inadequate repair work.
The Department of Water Resources said repairs and improvements made in 2017 and 2018 brought the dam up to “state-of-the-art” standards.
