Climate Readiness - Using Advanced Lasers and Sonar to Determine if Lake Oroville Has Lost Capacity

With California experiencing extreme swings between severe drought to torrential rain, the Department of Water Resources (DWR) wanted to see if the State Water Project's largest reservoir, Lake Oroville, had shrunk (or lost storage capacity) due to weather swings and almost six decades of service. DWR utilized the latest terrain-mapping technology to determine if there have been any changes in the lake’s volume to optimize how the reservoir is operated and ensure accuracy in estimating California’s water supply availability.

 

Lake Oroville was created in the 1960s with the construction of Oroville Dam. When Lake Oroville was filled in 1968, surveys estimated the dam impounded 3,537,577 acre-feet of water with a maximum depth of 690 feet and 167 miles of shoreline spread across the main reservoir and its three connecting Feather River forks.

 

Because decades have passed since its construction, DWR sought to assess whether sedimentation (rock and silt settling on the lakebed floor) had altered Lake Oroville's storage capacity and topography significantly. Starting with an airplane-mounted LiDAR (Light Detection and Ranging) laser system, DWR took advantage of the lake’s historically low water levels in 2021 to first map portions of the basin that would typically be under water during normal years. Then a boat outfitted with multibeam-sonar bathymetry instruments spent weeks in 2022 sending sonar pulses into the depths of Lake Oroville to map its underwater surface terrain. What resulted were highly detailed 3D topographic terrain models of the bottom of the lake, which DWR engineers used to calculate a new storage capacity of 3,424,753 acre-feet, approximately 3 percent less than previously estimated.

 

“Having updated storage capacity data allows us to operate Lake Oroville in a more efficient manner,” said John Yarbrough, DWR’s deputy director of the State Water Project. “It ensures we are providing adequate flood storage protection during winter months and accurately accounts for the state’s water supply, which is especially important as we experience climate change-driven weather extremes.”

 

With Lake Oroville’s new storage capacity data, DWR worked closely with its internal water operations team and coordinated with external partners such as the U.S. Army Corps of Engineers (USACE) to update storage capacity totals that inform water operations at statewide facilities. This information is also crucial for ongoing efforts by the USACE to update Lake Oroville’s Water Control Manual, which will allow DWR to improve its ability to retain water supply while balancing flood protection for downstream communities.

 

Compared to aerial photogrammetry surveying methods used during the construction of Oroville Dam, which mapped the terrain contours in 20-foot elevation increments, current methods were able to pinpoint with accuracy areas where sedimentation resulted in minor storage loss – primarily below 420 feet and in the far reaches of the lake’s forks.

 

“LiDAR and multibeam-sonar bathymetry are the latest technology available to map above and below water terrain surfaces accurately,” said Tony Squellati, manager for DWR’s Division of Engineering-Geomatics photogrammetry and computer mapping unit. “We were able to map Lake Oroville’s above and below water terrain with LiDAR and sonar at a density of 20 to 50 3D point measurements per square meter, which provided a high level of detail. You could even detect the old intact roadways and train tracks that were used during the dam’s construction in the ‘60s.”

 

While Lake Oroville is a primary water facility for the state, the dam performs a critical role in protecting the City of Oroville and downstream communities from floods. During the typically wet winter months (October through April), DWR maintains storage space in the reservoir to capture high inflows from storms and spring snowmelt, permitting controlled and coordinated releases from the dam. New storage capacity data will be used to ensure that water operations at Lake Oroville continue to provide required flood control protection.

 

When the warm summer months arrive, DWR transitions from performing flood control releases at Lake Oroville to capturing as much water in the reservoir as possible while still meeting water delivery and environmental requirements. DWR estimates that the new storage capacity will have negligible impacts to water allocations while still maintaining the ability to fill Lake Oroville to capacity for the benefit of water supply, recreation, hydropower production, and fish and wildlife enhancement.

 

Even with a 3 percent reduction in storage capacity, Lake Oroville remains the largest reservoir within the State Water Project and the second largest California reservoir, behind only the U.S. Bureau of Reclamation’s Lake Shasta. With 167 miles of shoreline, ample recreation opportunities, and scenic views of the valley below, the tallest dam in the United States and Lake Oroville State Recreation Area remain a premier destination for visitors of all ages while providing a most precious resource – water.

 

Note: DWR will start using Lake Oroville’s new storage capacity data for water operation calculations on Monday, July 1, 2024.