A contested plan to build an underground seawall to protect a critical stormwater tunnel along the coast of South Ocean Beach in San Francisco was given conditional approval by the California Coastal Commission last week.
Several commissioners said they had reservations about the proposal from the San Francisco Public Utilities Commission that involves building an underground armoring wall and artificial dunes, building up the beach and bluffs by manually replacing sand, and constructing recreational amenities along the Great Highway extension between Sloat and Skyline Boulevards.
One commissioner said the Coastal Commission was stuck between a rock and a hard place in considering the approval, which its own staff said would not be recommended under the California Coastal Act. But, as the staff report and presentation also noted, not approving protections for the stormwater tunnel would create even more risk to the coastal ecosystem than moving forward with the $175 million armoring plan.
The Lake Merced Tunnel serves as transport, storage and overflow tunnel for the Westside Pump Station treatment plant and a wastewater treatment plant, the Oceanside Water Pollution Control Plant, that serves the city’s west side and treats about a third of the city’s wastewater, according to the Coastal Commission staff report.
The tunnel and water treatment plants are threatened by coastal erosion and sea level rise.
Criticism and backing
The Lake Merced Tunnel was completed in 1993 and protecting it from coastal threats has been a long-running effort. The city built the tunnel without Coastal Commission approval and then promised to work with the U.S. Army Corps of Engineers to protect it from ocean intrusion without installing armoring by replenishing or “renourishing” the sand at the south end of Ocean Beach, which is being naturally eroded.
Armoring can protect inland infrastructure from the effects of erosion, but it is avoided because, according to the Coastal Commission, “shoreline armoring can have a variety of negative impacts on coastal resources, including adverse effects on sand supply, public access, coastal views, natural landforms, and overall shoreline beach dynamics on and off site, ultimately resulting in the loss of beaches.”
But when the city’s sand renourishing plan was deemed not feasible by the Corps of Engineers in the 1990s, the city installed armoring without Coastal Commission permission. It was later granted emergency, temporary permits, as maintenance was needed in 2010 and 2011, but further extensions were denied in 2015. The city was ordered to come up with a long-term plan by this past July.
The Coastal Commission’s allowances for such armoring projects are usually reserved for structures that were built before the passage of the Coastal Act of 1976, but the commission decided the immediate need to protect the tunnel and treatment plants outweighed the negative impacts.
The project will involve installing a 3,200-foot-long wall made up of 3-foot diameter concrete pilings that will be buried up to 30 feet underground and extend up to 15-20 feet above the beach. Those will be capped by a 3-foot-thick top layer of a mixture of cement, sand and sediment and then covered with another 4 feet of sand as part of engineered bluffs.
The overall work also calls for building a multi-use recreation trail, a bathroom at Sloat Boulevard, a parking lot at Skyline Boulevard, staircases to the beach and an access road for city vehicles.
The SFPUC project drew opposition from the Surfrider Foundation, researchers at the University of California, Berkeley and the University of California, Santa Cruz, and some residents, who spoke during the public comment period at the Coastal Commission’s meeting in San Francisco.
They pointed to the project’s reliance on constantly replenishing sand on the beach, the effects of the underground wall — the buried portion of which will be permanent–and the very goal of protecting the tunnel in its current location rather than moving it further inland.
Chase Davenport, a researcher at U.C. Santa Cruz and founder of the Ocean Beach Institute, a climate research initiative, said during the Coastal Commission’s public comment period that he thought the rate of sand displacement would be a greater challenge than the staff report, and project, anticipated.
“We are concerned the project’s shortsighted sediment plan will require much more sediment than anticipated, and that the sediment will be far more expensive than anticipated, potentially leaving us with an exposed seawall and no long-term plan for renourishing it,” he said.
Those thoughts were echoed throughout the public comment period.
Support for the armoring plan
The Coastal Commission report said sand replenishment could cost as much as $200 million alone.
But the armoring solution was favored by the nonprofit policy research group San Francisco Bay Area Planning and Urban Research Association, known as SPUR, which created an Ocean Beach Master Plan to guide a comprehensive management plan for Ocean Beach.
The Master Plan said relocating the Lake Merced Tunnel wasn’t feasible without also relocating the treatment plants, which wouldn’t happen any time soon. It therefore supported protecting the tunnel in place.
Ben Grant, who wrote the master plan, also spoke during the comment period and called the SFPUC project a good plan.
The project was ultimately unanimously approved by the Coastal Commission with conditions, including a five-year plan to monitoring the rate of sand replenishment and an ultimate reauthorization period of 25 years from the infrastructure’s construction, which is expected to be completed in 2031.
That means the project’s permit will again come before the Coastal Commission for reauthorization in 2056.
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