Dredging begins on San Dieguito River channel

Dredging begins this week to open the mouth and restore tidal flushing to the San Dieguito Lagoon, near Dog Beach in Del Mar.

Bulldozers will carve a route for dump trucks to travel beneath the Camino del Mar bridge and deposit sand on the nearby beach. The final step of the process, expected in about two weeks, will be the removal of the last plug of sand at low tide to begin the water’s flow into the ocean.

The dredging is expected to produce about 16,000 cubic yards of sediment that will be spread south of the river mouth as far as 18th Street. The last time the lagoon was dredged was in 2017.

Like most lagoons along the San Diego County coast, the San Dieguito is periodically bulldozed, usually in the fall, to clear the sand that’s pushed up by waves over the summer and closes the lagoon. The opening prevents stagnation and restores the saltwater exchange that supports wetland marine life.

Southern California Edison Co. pays for the dredging at San Dieguito as part of a 2003 agreement approved by the California Coastal Commission to mitigate the environmental effects of the San Onofre Nuclear Generating Station. Independent studies showed the plant’s powerful seawater cooling system killed huge amounts of fish, kelp and other marine life.

The agreement required the four-year, $100 million restoration of the San Dieguito Lagoon completed in 2011. It’s one of two SONGS mitigation projects still monitored by the Coastal Commission, even though the nuclear power plant ceased production in 2012.

A Coastal Commission scientist said earlier this month that the San Dieguito Lagoon restoration has yet to meet its targets for wetlands restoration.

“Edison has undertaken a planting program to try to increase vegetation in the salt marsh areas,” said senior environmental scientist Kate Huckelbridge at the Commission’s Oct. 16 meeting in Chula Vista.

Last year, the utility was about 33 acres short of its required minimum of 90 acres of wetland habitat under the agreement, Huckelbridge said. Edison tilled and re-planted three areas at San Dieguito in 2017 and this year added 39,000 more plants in those same areas to increase salt marsh coverage.

Edison also is enlarging an artificial reef it built off the coast of San Clemente as part of a separate SONGS mitigation project.

The Coastal Commission is working with Edison to determine why the restoration projects have been slow to take effect, Huckelbridge said.

— Phil Diehl is a reporter for The San Diego Union-Tribune