Partial Draining of Lake Perris Should Resume, Engineers Say

To guard against the seismic instability of the Lake Perris dam, a team of independent geologists and engineers this week supported the state’s plan to partially drain the reservoir.

The state Department of Water Resources found this summer that a 7.5-magnitude earthquake in the area could damage the earthen dam and flood communities near the Riverside County recreation area.

The state already has lowered Lake Perris 23 feet below normal levels, and should drain an additional 18 inches in the next few weeks, said Sue Sims, DWR spokeswoman.

Lake Perris park Supt. Ron Krueper estimates visits to the state recreation area could drop 15% to 20% next spring and summer.

Since the draining began this summer, reducing the lake’s surface area by one-fifth, the park has closed two of its four boat launches and limited the number of vessels on the water, Krueper said.

More than 1 million people visited Lake Perris last year. Now the water resources department, which owns the dam, can begin planning for repairs to the 31-year-old structure, said Rich Sanchez, Perris Dam project manager with the department.

“This was a milestone for us in that it ... gave us a validation we needed to proceed,” Sanchez said. The state is required by law to have independent geologic experts evaluate dam safety.

Engineers will examine how to reinforce seismic weaknesses in the foundation of the 2-mile dam; solutions could include replacing unstable foundation soils or adding cement to the soil, Sanchez said. Sims could not estimate how much such a project would cost.

The lake, which holds nearly 43 billion gallons at maximum capacity, will remain lowered for at least a few years while the dam is repaired, Sanchez said.