Construction crews have finished emergency work on a damaged underground drainage channel that caused a crater-size sinkhole on a golf course and threatened to undermine Pacific Coast Highway.
Although the emergency work has been completed, the sinkhole filled and the threat to the highway abated, a county official said Wednesday that repair work to the large, underground channel will continue for several weeks. And officials remain mystified as to what caused the problems.
"We are still unable to pin down a cause or sequence that led to the ultimate failures," said Jim Miller, chief of flood control design for the county. "Some thought that it is potentially related to the earthquake earlier this year. That has some merit, but we don't know how we'd prove it."
The hole near the 13th green at the Links at Monarch Beach appeared Feb. 21, and several days later workers traced it to a leaky underground drainage channel that carries runoff from Salt Creek to the ocean. Evidently, the aged, underground, 14-foot-high channel began to leak and a portion of it washed away, which ultimately caused the ground above it to fail, creating an 80-foot-long hole on the golf course.
Part of the problem was that the oldest section of the underground channel was built in 1932, when Pacific Coast Highway was constructed through South County, and later attached to a newer section built in 1973, officials said. The leaks occurred near the juncture of the two sections, officials said.
Miller said the emergency work cost the county and the California Department of Transportation, which are sharing the expenses, between $60,000 and $70,000. It could cost the county an additional $200,000 to finish its share of repairs. Caltrans' portion of the repair work will take two months and cost an estimated $350,000, spokesman Albert Miranda said.
The major portion of the repair work includes replacing the floor of the channel, which runs directly beneath the highway, Miller said. A new concrete floor will be anchored to the walls of the channel, Miller said.