Sea-level rise is coming, but when and how much?
The consensus is that sea-level rise will occur in Southern California, but how much and when are questions that complicate developing mitigation plans.
Encinitas, a city of almost 60,000, 25 miles north of San Diego, is trying to get a grip on those questions to deliver a Coastal Vulnerability and Resiliency Plan. If only they had a crystal ball.
It is impossible to foresee the future 50 to 100 years from now, and that makes planning for eventualities that far in advance a crap shoot. So you do it incrementally.
“If I knew the future of climatic events — when’s the next tsunami going to hit Crescent City—put how much sea-level rise is there going to be by 2100 in that category — I wouldn’t be a professor at Scripps,” said Bob Guza, professor emeritus for the Integrative Oceanography Division at Scripps Institution of Oceanography. “I could make a fortune in the insurance industry.”
He went on to say that he expects there to be one to six feet of sea-level rise in the area by 2100. “It could be more than that,” he said. “I don’t think it will be less.”
That’s why the city is putting plans into place — incremental ones with pauses to see that works and what unintended consequences may crop up.
One of the main actions is to protect Highway 101, which could be washed out during a major water event.
“We have a living shoreline project,” said Katherine Weldon, shoreline program administrator for the city. “That is where riprap [loose stone used to armor shorelines] was put in in the 1920s to protect Highway 101. We’ll put in more riprap then put sand on top of that.”
She said it’s a quasi-green project in that the birds will benefit, and it will help protect the highway as well.
“We also have the opportunity to do ‘opportunistic beach fill projects,’ where we put sand in four locations in our city and track how the sand moves and where it goes,” Weldon said.
Then there’s a 50-year Army Corps of Engineers adaptation project that looked at different ways to protect the shoreline. It was determined that the best path forward was beach nourishment, bringing in sand from outside the city and placing it strategically on the beach every five years. The key to something like that, Guza said, is close monitoring to see where the sand ends up eventually.
“What could go wrong, the worst that could happen is that it can get washed away, right? Not quite true,” he said, pointing to a beach nourishment project where the sand didn’t just wash away but ended up moving south and clogging the Tijuana River.
“So you need to know something like that. There are a lot of methods that we’re not really confident in how they will work. There are ideas that you can make a living beach that will hold the sand in place. These might work in the short term.”
But looking out 50 to 100 years? “I think that’s awful far out to plan,” Guza said. “The planning that we’re doing should be directed to 10, 20, 30 years out and done incrementally. Incremental defenses and learning from these projects as we go, so as they get bigger, we have a better clue on what the heck we’re doing.”
Since the city is 100 percent built out and there is no political will for a managed retreat of properties. “Maybe there will be a big El Nino in 2040 in Southern California and that will raise awareness, but until then it’s fruitless to talk about massive retreat and things like that on the West Coast because it’s not politically feasible,” Guza said.
But more seawalls need to be built, and staircases too. “No doubt we’re going to build more seawalls to protect cliffs,” Guza said. “This is happening as we speak; more cliffs are getting armor. I think it’s also important to know what the consequences of armory are. It stops erosion, but that cuts the sand off from the beach.”
And Weldon said during a major flood event, the rising tide will destroy staircases. “It’s one product nobody has talked about, fixing the staircases, which could be a ton of money. Be prepared for that because it’s what happens with high tide.”