The California Coastal Commission recently approved a $175-million project that will protect San Francisco’s Ocean Beach as well as key parts of the city's wastewater infrastructure imperiled by climate-induced erosion of the coastal bluffs.
The Ocean Beach Climate Change Adaptation Project approved on Nov. 14 includes a 3,200-ft-long buried seawall at Ocean Beach to protect the sewer system infrastructure, which includes the city’s Lake Merced Tunnel and a nearby recycled water facility.
“These long-term improvements will protect the vital wastewater infrastructure at risk,” Anna Roche, San Francisco Public Utilities Commission project manager, said in a statement. “But equally important, this project offers an opportunity for the city to drastically improve public use and accessibility along the coast south of Sloat Boulevard.”
Once the seawall is completed the dunes and related habitats will be restored. Maintaining the restored beach and the seawall will cost approximately $1 million annually, according to the commission. Relocating the wastewater infrastructure would cost $1.6 billion, according to San Francisco Water Power Sewer.
The San Francisco Public Utilities Commission's proposal calls for rerouting Great Highway away from the narrowest part of the beach, building a more than 1-mile-long multi-use public trail with views of the Pacific Ocean where the highway currently runs and a beach nourishment project that features new sand as the shoreline gets widened 78 feet.
Additional elements involve maximizing open space and public recreational access in the area through habitat restoration. A Coastal Development Permit for the project was approved in November.
Construction on the project is expected to start in late 2027.
Coastal erosion on Ocean Beach has severely impacted road and water infrastructure.
Photo courtesy California Coastal Commission
The commission report's on the Ocean Beach project says that shoreline erosion is threatening the most seaward component of the commission’s combined sewer system, the Lake Merced Tunnel, a 14-ft-diamter pipe located under the Great Highway. “With rising sea levels and more intense storms, erosion is only expected to get worse,” the report details,” which amplifies the urgency to protect critical coastal infrastructure, habitats and the beach itself.”
The Great Highway was originally constructed in 1929 and has been modified many times since, including during the 1993 construction of the tunnel pipeline that combines stormwater/wastewater flow and overflow storage.
As part of its overflow function, the tunnel holds untreated combined stormwater and wastewater flows during periods when the Oceanside Water Pollution Control Plan is unable to treat the quantity of influx, such as during major storm events. If the tunnel’s capacity ever fills, excess water heads to the Pacific Ocean via a pipe that runs 3.5 miles offshore.
In addition to mitigating erosion impacts, the new project will protect the tunnel with armoring.
Rerouting Great Highway away from the beach between Sloat and Skyline boulevards includes improvements to two intersections while other needs include rerouting a bus layover and turn-around area and reconfiguring the San Francisco Zoo parking entrance. The highway’s move also features a new beach access stairway and outlooks, public restrooms and 60 parking spaces at the south end of the project replacing the current 30 nearby that will get eliminated with the changes.
Habitat restoration includes removing revetments and debris previously used to reduce erosion, reshaping the bluff to increase accessibility to open space, new native vegetation planting and sand replenishment.
