Soon after workers finished building a 14-foot-wide tunnel beneath the southern stretch of the Great Highway in 1993, it became clear that the tunnel, which keeps sewage from spilling into Ocean Beach, was at risk.
San Francisco’s southern shoreline is losing ground to erosion and sea level rise, endangering not only the Lake Merced Tunnel but the lower Great Highway and beach restrooms and parking lot near Sloat Boulevard.
City officials are finally working on policy changes to address the retreating shoreline. The most ambitious plan that may be codified calls for the closure of the busy Great Highway between Sloat and Skyline boulevards, a route for commuters from areas farther south on the Peninsula.
Moving forward with the plans would mean more change for the quiet neighborhood surrounding the San Francisco Zoo, where an unusual five-story, 56-condo development is under construction at Sloat Boulevard and 47th Avenue.
On Thursday, planning commissioners will have a chance to weigh in on the proposed amendments to the Western Shoreline Area Plan before they reach the Board of Supervisors and the California Coastal Commission for approval.
“South Ocean Beach is experiencing erosion now and The City needs to move quickly to improve the beach condition and protect the wastewater infrastructure in the area,” city planner Maggie Wenger said in an email through a spokesperson.
The plans call for city officials to narrow the southern reaches of the Great Highway to two lanes before removing it entirely, pave a trail from Sloat Boulevard to Fort Funston and bury a “shoreline protection device” to guard the Lake Merced Tunnel.
Planning staff are recommending that the commission vote in favor of the plans, which pull from the 2012 Ocean Beach Master Plan led by pro-development nonprofit SPUR.
Ben Grant, an urban planner with SPUR who has headed the plan since 2009, said the policy changes are “a key step because it says everyone has signed on to this basic approach that we’re trying to create.”
“The Ocean Beach Master Plan does not have the force of law,” Grant said.
The plans also call for relocating the sandy restrooms and crumbling parking lot inland.
“The restroom is going to be beach if we give it room to be beach,” Grant said. “It’s in an area that, as the shoreline recedes and erosion continues, is going to want to become beach.”
But Grant said protecting the Lake Merced Tunnel is the “tip of the spear” because it is part of billions of dollars in wastewater infrastructure that the San Francisco Public Utilities Commission owns in the area.
The City has come under fire over the last two decades for not having a long-term plan in place to address erosion and sea level rise, instead placing boulders on the beach to curb erosion, Grant said.
“Everybody wants to get those rocks off the beach,” Grant said. “That’s really the goal of our coastal management approach, but right now they’re sort of the Band-Aid for the Lake Merced Tunnel.”
Grant also said previous efforts have focused on protecting roadways rather than the tunnel.
While it recognizes the risk, the SFPUC is not far along in the process when it comes to protecting the tunnel. The proposed plans call for the low-profile protection of the tunnel, but Chris Colwick, a SFPUC spokesperson, said the department is also considering relocating the tunnel out of the risk area.
“There is a risk and it’s something that we want to evaluate now before it becomes sort of an emergency repair,” said Colwick. “Big picture, it’s a necessary effort on behalf of The City.”
The tunnel is a critical piece of infrastructure that transports wastewater from the southwest to the Oceanside Treatment Plant, Colwick said. The tunnel also fills with rainwater and wastewater that would otherwise enter the ocean.
Meanwhile, the Department of Public Works is already working toward narrowing a portion of the Great Highway because of erosion, closing down the two southbound lanes between Sloat and Skyline boulevards.
“What we’re going to do is abandon that,” said Public Works spokesperson Rachel Gordon. “It’s called managed retreat. We’re going to pretty much abandon the road for vehicular traffic and send cars and trucks to the northbound side.”
Public Works plans to break ground on the project early next year, Gordon said.
Once the project is complete, the Recreation and Park Department plans to begin construction on the $2 million bicycle and pedestrian trail that will replace the southbound lanes.
The southern pedestrian trail currently ends at Sloat Boulevard, where the sandy parking lot sits across from the Great Highway.
“The possibility of a dedicated trail from Funston along the Great Highway all the way to the Cliff House … and beyond is awesome,” wrote Great Highway neighbor Brian Veit in a letter to planning commissioners.
Rec and Park doesn’t expect trail construction to begin until late 2018, at the earliest.
Editor’s note: This story has been updated from its original version.