Laguna Beach cannot control storms, but flooding can be reduced and measures can be taken to better prepare residents and businesses for the next deluge, according to a task force report.
With a presentation at Tuesday’s City Council meeting, the Laguna Canyon Flood Task Force culminated eight months of reviewing floods in the canyon and considering ways to shore up the city’s defense against the next deluge.
“A recent study revealed that the ocean-facing slopes of Laguna have only about 7 inches of topsoil overlaying steep, impermeable rock,” task force Chairman Eric Jessen told the council. “Even with vegetation holding the topsoil in place, heavy rains saturate the soil within two hours. Then the run-off starts to come our way.
“Where there is development in the flood plains, damage occurs. We’ve seen this many times at Aliso Creek Inn & Golf Course, and in downtown Laguna.”
But the city can mitigate some of that.
“We can reduce the flooding downtown by more than 30% simply by enlarging a short segment of the storm drain under Coast Highway from its current 800-cubic-feet-per-second capacity to match the upstream conduit capacity of 1,050 [cubic-feet-per-second],” he said. “By any standard, 30% is a huge reduction.”
The project would involve interrupting highway traffic and requires the approval from the California Department of Transportation, which has jurisdiction over the highway. In July, the flood task force recommended the city begin immediate negotiations with Caltrans to include that channel segment in a city project to repair the reach from the ocean to Beach Street, which is scheduled to skip the highway.
But there is concern that including this proposal would delay the city’s project, scheduled to start in the fall of 2012.
The task force also recommended installing high-tech devices to monitor rising water in Laguna and El Toro creeks and establishing neighborhood flood-watch programs.
Among the task force’s recommendations to be done sooner rather than later: the annual removal of debris along Laguna creek, removing privately owned encroachments and stored items that dam the flow, and requiring businesses to keep floodgates on-site and install them when notified.
As for long-term measures, the task force considered a previous proposal to enlarge the channel under Broadway and Ocean Avenue, but failed to find the necessary funding source.
Less expensive and disruptive proposals include some channel modifications along the creek.
The task force also considered the construction of large retention basins in the canyon, but it would take 320 5-foot deep basins — which altogether would be three times larger than Emerald Bay — to protect the canyon from a 100-year storm.
However, modifications can be made to the existing retention basin just up El Toro Road, which could factor into downstream measures, Jessen said.
“One thing is for certain, as long as storms come in off the Pacific and as long as Laguna is surrounded by hills, there is going to be flooding from time to time,” Jessen said. “The measures we’ve recommended in the report will help people deal with flooding, maybe even attenuate it and help protect lives and property. But we will never eliminate the storms.”
Councilwoman Verna Rollinger, who co-sponsored the task force with Councilman Kelly Boyd, said the goal was to make flooding less hazardous in the canyon and downtown. She praised task force members Jessen, Bob Borthwick, William Lawson, Carl Nelson, Norm Grossman, Karl Koski, Charles Quilter II, Louis Longi and Susan Hamil for their outstanding contribution to the city.
She also thanked Barbara Metzgar for editing the report, Public Works Director Steve May and City Manager John Pietig for their services.
City staff will make a status report on implementation of the task force recommendation in February.