Encinitas tracking El Niño’s impact on beaches

It’s an inescapable reality: El Niño stripped away a lot of sand from local beaches this winter, leaving chattering cobblestones in its wake.

Wide beaches protect infrastructure and attract beachgoers. So it begs the question — how much sand was lost? And will it return?

To find answers, a city of Encinitas employee and intern teamed up with Scripps Institution of Oceanography to operate a Mobile Beach ERosion Monitoring (MoBERM) wagon to monitor sand levels at Moonlight Beach and Cardiff State Beach. MoBERM was invented by Timu Gallien at Scripps Institution of Oceanography and was funded by the California Coastal Conservancy and USC Sea Grant.

Since October, they’ve tracked changes in beach area, revealing how tides and waves affect sand movement. Long term, city data will help Encinitas determine when and where to conduct beach replenishments, which involve piping offshore or coastal lagoon sand onto beaches.

Demonstrating how sand levels are recorded, intern Sean Lee recently pulled the survey wagon north along the water’s edge at Moonlight Beach, occasionally navigating around towels and curious beachgoers.

He then dragged the wagon along the high tide mark, followed by three bisecting lines. Every half-second, survey equipment on the wagon plotted a GPS point.

“With those GPS points, we can find out the exact coordinates, and then how the beach’s elevation is changing and the beach’s width,” Lee said, noting he’s out there capturing data at least once a week.

Monitoring sand is nothing new. But the survey equipment in recent years has gotten smaller and very precise — within two centimeters of accuracy, according to Katherine Weldon, the city’s shoreline preservation manager.

“We got an accurate read on El Niño for the first time, which is unique,” Weldon said. She added the city will continue to collect data for the foreseeable future.

El Niño is known for large and frequent winter swells, speeding up coastal erosion that’s normal at San Diego beaches in the winter. Initial city numbers point to El Niño’s impact locally this winter: Moonlight Beach lost 340.79 square meters of sand from December to January and then another 906.72 square meters of sand from January to February.

“We saw the shoreline recede a lot during months where there was a combination of huge storms and high tides,” Weldon said.

From February to March, however, beaches gained back 300.15 square meters of sand. Weldon said the initial data will be converted to show sand movement in terms of cubic yards, a more accurate measure.

Sand will keep returning to beaches in the coming months, as is typical in the spring and summer. The city will record just how much comes back, though it’s possible that a significant chunk could be permanently washed offshore.

Cities are working to combat coastal erosion, which is exacerbated by inland dams trapping sediment that would otherwise flow to beaches, rising sea levels and bluff seawalls that cut off a natural supply of sand.

Encinitas has a project in the works that would regularly pour offshore sand on beaches over 50 years, and sand-level data will help the city fine-tune this and other nourishment plans.

“If we have data showing a stretch of beach has plenty of sand, we could hold off on nourishing it for a while or put less sand than originally planned,” Weldon said.

She added: “It’s taking a scientific approach to beach replenishment.”

The data will also shed light on sand transportation patterns over time, so beach replenishment sand could be strategically placed to best protect erosion hotspots or vulnerable infrastructure.

Scripps Institution of Oceanography provided the sand-tracking equipment, in exchange for Encinitas collecting data. Encinitas’ data will supplement existing Scripps research, and more local entities could contribute data down the line.

Bob Guza, a research scientist with Scripps, said it’s critical to track sand in light of so much money being spent on nourishment plans.

“In order to make these hard choices on which beaches receive sand, we have to have know if and how long the sand will stay there,” Guza said.

It’s something he’s been studying for quite some time. Notably, Guza and a team closely monitored a regional SANDAG replenishment project that deposited sand in 2011, including in Cardiff.

Their observations strongly suggest that some of the 2011 sand stuck around this winter in Cardiff, according to Guza, who added that it “significantly protected” Coast Highway 101 from flooding.

“It’s not only a question of the economic impact, because if Highway 101 is closed, you can’t get emergency vehicles past,” he said.

By contrast, he said Torrey Pines State Beach wasn’t replenished in 2011, and it’s in worse shape than beaches that were nourished. Guza noted current sand levels at Torrey Pines are the lowest that Scripps has recorded since it began monitoring there in 2001.

Guza said quite a bit of replenishment sand often washes away permanently after a few years, but added if people want healthy beaches, coastlines have to be regularly maintained like roads. However, he cautioned that leaders must also consider the price tag and environmental impacts of nourishments.

“It’s a complicated equation to consider,” Guza said.

Guza said sand-surveying technology is much less expensive, simpler and smaller than it was just a few years ago, paving the way for Encinitas and other local entities to contribute to Scripps’ sand research.

“Instead of taking three people to set up, one person can do it holding what looks like a kiddie wagon,” he said.

He added: “It’s something that’s very useful because we can’t be everywhere.”

This article was updated with Weldon's comment that the initial data will be converted to show sand movement in terms of cubic yards, a more accurate measure.

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