Las Vegas Review-Journal (Sunday)
New data helps manage Socal’s shrinking beaches
Decision-makers learn where to replenish sand
Millions of dollars are being spent to add sand to Southern California beaches — but a new study suggests technology can give a better understanding of how sand moves, offering data decision-makers could use in planning how to fix the eroding coastline.
A new paper published recently by University of California, Irvine researchers in Coastal Engineering Journal analyzed beaches between Long Beach and La Jolla, offering new data and methods that can be used to figure out the most vulnerable areas of coastline and whether those beaches are suitable for the mega, costly projects often turned toward for trying to replenish and retain sand.
The study comes as coastal cities across the state are grappling with eroding beaches, due in part to human development that has impacted natural sand supply but also rising sea levels and climate change.
Because shrinking sand impacts everything from recreation, public access, infrastructure and the economy, decision-makers are searching for solutions — historically, major sand replenishment projects have moved at a snail’s pace, taking years and even decades to get through permitting and secure government funding.
“I’m really excited to have the resources that help, potentially, inform these decisions,” said Daniel Kahl, UCI researcher and lead author of the paper. “It can help us inform where nourishments will be most beneficial and where they won’t be the best.”
The researchers used satellite imagery dating back nearly 20 years and wave data from that same period from the Scripps Institution of Oceanography in San Diego to analyze “longshore transport,” which is wave-driven movement of sand along the coast, the pathway that shows which direction sand will be redistributed.
Their paper also analyzed “divergence of drift,” which shows whether sand will accumulate or diminish, based on the movements of sand.
“This method characterizes a process that can help us understand which areas of the beach are susceptible for erosion, but also where beaches might grow if given enough sand,” Kahl said.
Determining ‘feeder’ beaches
The new information could help decision-makers better understand whether areas are “feeder” beaches that contribute to other coastal communities or whether sand stays put.
“It’s more complex than we previously thought,” Kahl said. “Maybe there’s more ideal locations for nourishments based on these sediment pathways we see. And there’s areas where sand won’t accumulate, and maybe that’s not the best location (for a replenishment) and other sites should be considered.”
“The data essentially shows: Where do we get the most bang for our buck when it comes to placing sand on the coast,” said Brett Sanders, UCI civil and environmental engineering professor and co-author of the published paper.
The data showed, for example, that the Surfside beach along Orange County’s northern coast, is an area that suffers from severe erosion — a well-known fact and why the U.S. Army Corps of Engineers is spearheading a $23 million project now underway to dredge and place 1.1 million cubic yards of sand there. It’s a project done periodically since the 1960s.
The project is thought to have regional benefit, with currents expected to spread sand nearly 12 miles to Newport Beach — but the latest data shows that may not be the case, the researchers said.
Sand typically stops in Huntington Beach, part of the reason those beaches have continued to grow over the years at a rate of about 3 feet each year, Sanders said. And sand in West Newport, in turn, travels up the coast to Huntington Beach.
So maybe Newport Beach officials reconsider if it’s worth paying into the pot for that large replenishment project, Sanders said. “This is critical from a management perspective, because it tells us which communities along the coast need to work together on plans to manage the coast.”
Their research also validates the importance of sand retention structures in Newport Beach — groin jetties built in the 1960s to trap sand — and the city’s regular, ongoing efforts to nourish beaches with sand from the Newport Harbor and the Santa Ana River, Sanders said.
San Clemente is a prime candidate for sand replenishment, with the material wanting to stick around, based on the models.
The problem San Clemente currently faces, however, is getting the sand. A $14 million project more than two decades in the making was put on hold a few weeks ago when the dredger ran into trouble sucking up rocks instead of sand at an Oceanside borrow site, with no definitive answer on when that project may get back on track.