El Nino storms, decreased sand levels cause of erosion
Where’s the sand? Those who walk the beach along La Jolla Shores and a few other La Jolla beaches in recent months have noticed an increase in rocks and stones along the shore.
Just past the ends of Kellogg Park, residents have reported severe sand erosion, the likes of which they’ve never seen before. While scientists say erosion happens every winter, this year has other factors making the situation more noticeable.
“I walk on the beach with friends at least once a week and we’ve been doing that for years,” said Shores resident Susan Tschirn. “It’s part of enjoying the Shores. But in the last few months, the sand has eroded and these rocks appeared, and part of the beach is gone. I’ve never seen it like this, ever.”
Terry Krazewski, owner of Ocean Girl beach apparel, echoed Tschirn’s concerns. “There are so many rocks in that area and I don’t recall ever seeing that many there,” she said. “Were these rocks always there or did they appear abruptly? And from where?”
La Jolla Light reached out to Scripps Institution of Oceanography coastal oceanographer Scott Jenkins for some answers. He said there is an annual cycle of sand movement; it drifts offshore during the winter and returns during the summer. However, this year, there are unique factors in place affecting the cycle.
“The sand is always in motion; it’s a movable thing. You know that when you pick it up and it slips through your fingers,” Jenkins said. “(Sand erosion) happens every year, but in some years the changes are more severe. This year, there are a lot of moving parts.”
One of those moving parts, as many have suspected, is the El Nino storm. “Every time there is a strong El Nino year, such as what we are having now, there will be a lot of beach erosion,” he said. “It’s happened a number of times.”
This year, coupled with the increased intensity of erosion beyond what occurs every winter, is a decrease in sand replacement, he said.
“Beaches will lose sand in the winter,” he said. “It goes to sand bars and marine canyons, and some of it comes back in the summer, but not all of it gets through.” This is true particularly in La Jolla Shores, where the underwater canyons are located; here sand loss is not unusual.
“But for us to have stable beaches, we need new sand and where does it come from?” Jenkins continued. “We have several big rivers nearby that can replace the sand at the beach (by flowing to the ocean and bringing sand with it), but many have dams on them … so not a lot of new sand gets to the ocean to replace the sand that gets lost.” While there is typically a rate of loss and a rate of replacement, “The supply of new sand hasn’t been keeping up with the loss of sand,” he added.
Another source of new sand is La Jolla’s coastal bluffs, which are actually ancient beaches lifted by tectonic activity over the centuries, but Jenkins said sea walls and other infrastructure on these bluffs has slowed the rate of new sand getting to the beach.
“We’ve cut off our two sources of new sand,” he said. “There are rocks underneath our sandy beaches that are just now getting exposed.”
Despite all the outlying factors this year, Jenkins said some of the sand is expected to return this summer.
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