Public urged to help decide fixes for Ocean Beach erosion problem
by Thomas K. Pendergast
A century from now, the fate of Ocean Beach might be traced back to a recent public meeting held at the San Francisco Zoo.
It was there, on Jan. 15, that those putting together the Ocean Beach Master Plan held a workshop for the community, to participate in the genesis of an overall strategy for dealing with numerous challenges that the beach would face in the next 100 years.
"The idea of the Ocean Beach Master Plan is to work with all the different agencies, federal, state and local," said Benjamin Grant, program manager at the San Francisco Planning and Urban Research Association (SPUR). "And to work with the different communities that are affected and the different issues advocates are involved in, to really think long-term about Ocean Beach so that we can establish a framework for making decisions over the long haul, about erosion, about infrastructure, about Ocean Beach as one of the city's magnificent open spaces."
The complicated politics and jurisdictional thicket that must be dealt with in the master plan are easily matched by the complexities of nature. The ocean is trying to compensate losing about 200 yards of sand to humans at the north end of the peninsula by taking chunks off the bluffs to the south.
For now, at the southern end of the beach a temporary fix consisting of large rocks and concrete "armoring" protects the Fort Funston bluffs from further erosion, plus the Great Highway that sits on them. Yet, this temporary measure just buys some time. There is discussion about moving the roadway.
Even more difficult is the question of how to deal with the Lake Merced sewer pipe, an old-school combination raw sewage pipe and storm drain, that runs deep underground directly beneath the Great Highway.
"The main thing we're trying to do today is to listen to the public and to welcome people to share their ideas with us," Grant explained. "We're presenting a lot of background information insofar as we've been able to understand it. What we want to do today is get feedback from the public on whether we're even coming close to getting it right. We're not here to tell people how it is. We're here to say: 'Well this is what we think so far. What do you think?'"
What some experts have been thinking about is the sewer pipe problem.
"It's the tip of the iceberg, as it were. It's the piece of the infrastructure that's the most imminently threatened by erosion and has been the thing that's precipitated the recent emergency armoring. I know that's an issue that's hot on many people's minds," said landscape engineer James H. Streeter. "So we're definitely thinking about that, working with the Public Utilities Commission on trying to figure out what's possible in terms of the long-term vision for infrastructure."
Streeter works for AECOM, a consulting company advising the planners.
He noted that the erosion issue could not be fully appreciated without considering the overall dynamics of ocean currents and the impact of human activity along the entire Pacific shoreline of the Bay Area.
"Outside the Golden Gate Bridge there's a huge sandbar, which is a naturally occurring thing but in order for the really big ships to get to Oakland there needs to be a ship channel which is always dredged through that sandbar," he explained. "That sand material mixes with the water and gets washed to shore. Because more sand is introduced into this coastal dynamic system it means there's more sand to be washed onto Ocean Beach."
That is, north of about Noriega Street. The loose sand from the dredging has added about two hundred feet to the shoreline during the last century.
"At Sloat some of the tides go north, which are the ones carrying the sand. Below Sloat the tides then go southward with no sand and that causes scouring of the beach, which basically creates a lot of erosion," Streeter said.
Bob Battalio is a civil engineer who works for ESA-PWA, a coastal engineering and consulting firm also involved in the master plan.
"What I realize is that what's really vulnerable is our beach because if you assume that infrastructure is so valuable and costly to reconfigure, you want to maintain it in its present form as long as you can, and yet you have sea level rise, which will move the shore landward. The most likely thing to happen would be that the pipes stay where they are, the shore moves landward and the beach gets narrow. Instead of infrastructure vulnerability, we're really talking about beach vulnerability and then also the roadways."
"I have not seen a detailed vulnerability analysis for the sewer infrastructure. I think that's something that should be done," he said. "That detailed analysis would allow us to answer those questions to a greater certainty.
"The pipes are actually fairly low in elevation, so it's possible that you could get erosion over the top of the pipes, especially the ones south of Sloat. It might not adversely affect the pipe itself because the pipes are reinforced concrete and they have some strength. The one south of Sloat is actually below the beach elevation. It's down pretty low."
He noted that the sewer pipe was tunneled through the material that makes up the Fort Funston bluffs.
"It's a little harder. It's not just loose sand. It's not really clear what the threshold of damage to the pipe is and how close the surface of the beach needs to get or whether or not the damage requires that waves hit it."
The US Army Corps of Engineers, who are responsible for dredging the sand bar for the shipping lane, has another idea of what to do next.
"We can provide beach-quality sand from our dredging project and we actually are most of the way through a planning document to construct a vegetated sand dune along the portion south of Sloat to Fort Funston bluffs, where all the emergency revetment has been placed" said Peter Mull, a project manager for the Corps who's advising the master planners.
"So, you'd bury that rock in the sand dune, like existed in the '90s, vegetate that and it would be a sacrificial dune. So that sand then would provide sand resources. As wave energy increases that sand would be pulled off shore to help nourish the sand bars,' he said.
Mull estimated the dredging could supply the newly vegetated beach with about 300,000 cubic yards of sand each year. The other choice, he said, was to move the sewage tunnel at an estimated cost of $140 million.
"This is the beginning of the conversation. It's by no means the end," Grant said.
More workshops are planned for around May and late summer. For more information or to be added to a mailing list of future meetings, send an e-mail to [email protected].