The U.S. Army Corps of Engineers Sacramento District awarded a contract for the installation of a temporary pump system at Isabella Dam in Lake Isabella, California, on Sept. 28, 2023, to increase the capacity of the existing pump system and redirect seepage back into the lake.
By Oct. 2, the new system had been installed and was operational. The temporary system has currently eliminated downstream flows caused by seepage.
Henri Mulder, a geotechnical engineer with the USACE South Pacific Division who works out of the Isabella Dam Safety Modification Project Resident Office, stressed that the seepage is not a risk to the safety or structural integrity of the dam.
“All dams experience seepage,” said Mulder. “However, the elevated seepage levels we’re seeing this year are the result of record precipitation and the higher lake levels that resulted.”
The Sacramento District will continue assessing the Isabella Dam seepage to determine if more permanent changes need to be made to increase the pumping system’s capacity.
“This pump is a temporary solution,” said Mulder. “After further evaluation, we plan to install a more permanent solution within six to twelve months.”
The Sacramento District engaged in extensive pre-construction modeling of both inflows and outflows at Isabella Lake before the recent modifications to the dam, which included an improved filter and drain system. And although the current collected seepage levels exceed pre-construction estimates, the system is working as designed.
“During design, models represent our best estimates of site conditions, so there are always adjustments to be made after construction,” said Mulder. “That’s why we execute fill plans after finishing a big project like this.”
Completed in 1953, Isabella Dam is located approximately 40 miles northeast of Bakersfield. The reservoir is impounded by two earthen dams on the Kern River and Hot Springs Valley. Today, Isabella Lake and its dams reduce flood risk for Bakersfield and the surrounding region and is a primary water source for water users throughout Kern County. The Isabella Dam Safety Modification Project addresses overtopping, seismic and seepage issues identified with Isabella Lake’s main and auxiliary dams and spillways to reduce the likelihood of dam failure. Construction of the dam modifications began in 2017 with the relocation of facilities within the project footprint, and the project achieved substantial completion in 2022.
