CA Coastal Commission approves massive seawall to protect SF's Ocean Beach against erosion

SAN FRANCISCO (KGO) -- The California Coastal Commission approved a plan to build a massive seawall to protect San Francisco's Ocean Beach against erosion on Thursday.

In addition to the seawall, there would be a seaside trail, parking lot, and other features.

It would all happen right by the Great Highway, which voters recently agreed to permanently close to cars to create a recreational area.

Supporters say it's a critical plan that would transform San Francisco's Ocean Beach and protect the area from erosion and rising sea levels.

RELATED: SF residents divided over Measure K to permanently close portion of Great Highway to cars

The $175 million project would shore up a wastewater treatment plant and a sewage tunnel on the southern end of Ocean Beach.

"It's the Lake Merced Tunnel. It's large enough you could drive a truck through it. Its 14-foot diameter tunnel, it carries storm water and sewage from that side of the city to the oceanside treatment plant," said Anna Roche, senior project manager of the SFPUC.

The SF Public Utilities Commission says that really critical infrastructure is at risk of failing and its plan would protect it.

"If it fails, that means we could be spilling sewage onto the beach and hundreds of thousands of residents would not be able to flush their toilet," Roche said.

MORE: Should SF's Great Highway permanently close to cars? Here's what both sides say on Prop K

Many people agree it's important to protect the city's aging infrastructure, but they don't think a large seawall is the way to do it.

The Surfrider Foundation says it would be the biggest seawall they've ever seen along the California coast.

"It's huge. It's huge," said Jennifer Savage with the Surfrider Foundation. "3,000 feet long, up to 120 feet wide, 35 feet deep."

As part of the city's plan, the seawall would then be covered with tons of sand. Opponents argue that sand would be washed away with time and would need to be replenished.

MORE: Tensions rising over proposition that would close part of San Francisco's Great Highway

The Surfrider Foundation says there are other solutions, including relocating the sewage treatment plant or building a smaller seawall.

"You could have a lower seawall. You could have a more complete dune ecosystem," Savage said.

Chase Davenport is a coastal scientist and a surfer.

ABC7 News originally talked to him about Proposition K, which permanently closes the great highway to vehicle traffic.

MORE: Debate over changes to San Francisco's Great Highway intensify with Prop K

Davenport supports that. But he doesn't agree with a big seawall going up.

"As a surfer, I'm opposed to it. As a scientist, I'm opposed to it," Davenport said.

"It's going to eliminate a lot of our beach. Even if the plan works like they say it would, it's going to require an unbelievable amount of sand to cover the seawall. We don't have that sand, (then) our beach starts to disappear," Davenport said.

On Thursday, the SFPUC reacted to their plan passing.

"I'm super excited, because we've been working on this for a long time. I think it's the right move for San Francisco," Roche said.