Developer David Murdock's plan to make safety improvements on the Lake Sherwood dam, a prerequisite for refilling the lake and building a golf course and housing project in the mountainous Ventura County area, has won state approval, an official said Thursday.
Murdock will be required to make two structural changes to improve the dam's ability to withstand earthquakes, according to Vern Persson, who heads the engineering design unit of the state's Division of Safety of Dams.
Persson said bedrock supporting the dam will be anchored with steel rods to prevent rock layers from slipping during a temblor. A concrete buttress will also be built to support one of the spillways for the 43-foot-high dam, he said.
The dam has figured prominently in five years of wrangling between area residents and two successive owners of the lake and surrounding property who have proposed housing developments around the sparsely populated area just west of Westlake Village.
Lake Drained in 1984
The previous owner, Dayton Realty Co. of Beverly Hills, drained the 150-acre lake in May, 1984, after winning a court battle with residents who opposed the action. The company said the draining was necessary to inspect the dam, but area homeowners contended that it was unnecessary and a retaliation for their opposition to Dayton's proposal to build 1,400 homes around the lake.
Of about 120 dams in California ordered inspected in 1980 under a federally funded safety program, only Lake Sherwood was fully drained, Persson said. Although the state in 1983 ordered that the level of the lake be kept at least 10 feet below the top of the dam, "We didn't feel total draining of the lake was necessary," he said.
Because of the draining, homeowners attracted to the area by the lake have had to pull their boats onto land and endure backyard views of graded dirt.
The lake bed and 1,600 acres of surrounding land were purchased by Murdock Development Co. in October, 1984. The company's plans for refilling the lake and building 700 condominiums and houses, along with an 18-hole golf course received mixed reviews from homeowners at a public meeting last week.
Murdock representatives could not be reached for comment about the state's go-ahead for dam repairs.
No Urgent Safety Problem
The state approved an engineering and geological report, authored by civil engineering consultants hired by Murdock, that concluded there is no urgent safety problem with the dam, which was built in 1904.
However, Persson said, the structural upgrading will improve features of the dam that "could have been a risk" to residents downhill in the Westlake area of Thousand Oaks and in adjacent Westlake Village in Los Angeles County.
"We don't like to panic people about dam safety because it's a very sensitive subject," Persson said.
Computer projections indicate that the dam would survive an earthquake of 7.0 magnitude on the Richter scale along the Santa Monica-Malibu Coast fault, which comes within about 6 1/2 miles of the dam, Persson said. Officials also believe that the dam would withstand the water pressure that would result if 30 inches of rain fell on the area in a 72-hour period.
But the Lake Sherwood dam study found that the strength of its concrete falls short of most dams. Persson said that finding has prompted an additional requirement that samples of concrete be tested at five-year intervals for signs of deterioration.
Persson said several concrete cylinders removed from the dam for testing crumbled at pressures of 1,600 to 1,700 pounds per square inch. Experts expect newly built dams to handle pressures of 2,500 to 3,000 pounds per square inch, he said, and some dams can withstand up to 9,000 pounds per square inch.
He said inspectors believe the dam tests reflect poorer construction materials, not progressive weakening.
"Concrete dams normally hold up pretty well," he said.