ENCINITAS, Calif. – The city of Encinitas used some giant scissors to cut a giant ribbon, to celebrate some giant piles of sand on Cardiff State Beach.
Sometimes giant piles of sand are just sand. But these piles are not. They’re engineered “living dunes” that have been five years in the making. And they’re part of an ongoing effort to save Cardiff from rising sea levels.
These super dunes may even provide a roadmap for saving other beaches that are susceptible to climate change, up and down California’s coast.
Erosion, Erosion, Erosion
When it comes to California’s beaches, erosion is normal. Our coastal landscapes are meant to change. However, rising sea levels and intense storms have exacerbated the dangers of erosion, and the fact that we’ve built homes and infrastructure right up against it means that it’s a huge concern.
In many places, we fight against erosion by “nourishing” beaches, which means adding a bunch of sand to increase their size, like at Zuma Beach in Malibu. We sometimes also line the beaches with giant rocks, especially along roads, the hope being that those rocks will absorb some of the energy put out by the powerful ocean, thus saving the infrastructure behind them.
That’s what officials were doing at Cardiff for years, in an effort to protect the beach and North Coast Highway 101, but it wasn’t working.
“[Cardiff] was already experiencing flooding during extreme high tide events and during extreme storms,” said Jayme Timberlake, Coastal Zone Program Administrator for the City of Encinitas.
Any sand that they used to nourish the beach was quickly washed away, shrinking its usable area. And the rocks that they used to protect the 101 were just being thrown up onto it.
“It did cause a lot of issues with access, access to the highway itself. The highway is pretty critical for daily commuters,” said Timberlake.
Recognizing that the problem wasn’t going to get any better as sea levels rose, the city decided to act, and over the course of five years designed and built a “living shoreline.”
While the process is similar to beach nourishment in that it uses a lot of sand, it’s completely different in that it’s meticulously engineered, offers tiers of protection and is designed to last a long time.
Like a Sandy Layer Cake
Beneath the piles of sand are rocks, or cobble, that are stacked at specific angles, and increase in size the further you get from the water. They’re buried about ten feet deep and are sitting on top of a thick fabric that’s designed to keep them from sinking.
“There’s science backing cobble at being pretty effective at shoreline protection. It stacks up more steeply and higher as waves attack it,” said Brian Leslie, Senior Coastal Scientist with GHD, a firm that the city contracted with on the project. “It’s … like this first line of defense for the dune, so the dune doesn’t get eroded right away when we start to get these big waves and tides.”
The city installed sand fences and planted native vegetation on top of the mounds to stop them from blowing away. There’s also the added benefit of building natural habitat for the adorable snowy plovers.
“This is a coastal strand that was formerly … a dune system, so it’s bringing back what used to be here and it’s meant to be a permanent feature,” said Leslie.
The dunes will erode so they’ll require nourishing, though it’s unclear how often.
A Big Experiment
“The Cardiff project is very unique. Nobody has really tried that before in California,” said Nick Sadrpour, Science, Research & Policy Specialist at the University of Southern California’s Sea Grant Program. “This burgeoning idea of living shorelines, of working with nature, of mimicking nature, is really exciting from a coastal resilience perspective.”
Cardiff, though, is a big experiment.
Researchers from the SCRIPPS Institution of Oceanography and UCLA, as well as government groups like the California Coastal Commission and the State Coastal Conservancy, will all be keeping tabs on what goes on there.
They’ll be watching for changes in the growth and slope of the dunes, as well as the movement of cobble and sand migration.
“Success is the stabilization of the dunes,” said Timberlake. “While we try to discern the next steps in adapting to sea level rise, and to these larger sea level rise projections.”
If all goes well, similar projects could pop up all along the coast. However, they won’t be workable for every location, and it’s not like the project was exactly cheap.
These dunes cost between 2.5 to 3 million dollars, according to Timberlake.
And even if the dunes are successful, both Timberlake and Leslie acknowledge that they may only last 20 to 30 years before rising sea levels make them impractical, at least at Cardiff.
“Once we get to the three feet and over [range], it’s going to be tough to keep a dune system here,” said Leslie. “It’s a problem now and that problem’s going to get worse over time.”
California could lose roughly half of its beaches by 2100, according to the United States Geological Survey.
“After 30 years, we haven’t quite identified what we’re going to do yet,” said Timberlake. “It basically bought us some further time to devise plans for that area.”