High-tech flights help fight threat of sea water intrusion along coast

ByDan Ashley and Tim Didion KGO logo
Tuesday, December 20, 2022
High-tech flights help fight threat of sea water intrusion along coast
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Potential drought-fighting technology is being used to map a climate-related threat of a sea water invasion threatening wells up and down the coast.

CAPITOLA, Calif. (KGO) -- Thousands of visitors crowd the beaches around the Capitola - Santa Cruz area, without ever realizing they're standing on the front lines of an ongoing battle triggered by California's drought. The enemy? Sea water being sucked into the same wells that provide fresh drinking water to surrounding communities.

"And the physics of it are basically like, if we're pulling in sea water, how do we pump less or create a barrier, a hydraulic barrier to push it back out," says Ron Duncan, general manager of the Soquel Creek Water District.

He explains that when the water table falls low enough, wells near the coast can begin to pull in the salty sea water potentially making them unusable. To fight back, the agency is expanding a system to pump treated wastewater back into the ground. The goal is to recharge the ground water and push back the sea water.

"We have seven miles of coastline that we pump around. And so what we do is we'll pull out some of that water we inject, let some of it go out and create a hydraulic barrier, but also capture some of that as a water source," Duncan explains.

But to achieve that delicate balance, the agency needed to map where the salt water was coming in. That required peering deep beneath the waves and shoreline, with a technology we showed you here on ABC7. It's known as an airborne electromagnetic survey, and looks something like a space ship suspended from a helicopter. Pulses penetrate the ground, mapping the geology underneath.

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Earlier this year, we profiled teams from Stanford and the California Department of Water Resources that have been flying across sections of California mapping the geology. They're identifying areas, where water can flow easily into the aquifer, for future groundwater recharge programs. But Duncan says using AEM to locate salt water along the coast was a different challenge. To do that, Soquel partnered with a Danish company that had a version of the technology.

"And they flew the helicopter all day. And then they came back and landed, downloaded the data. And within 30 minutes, we were able to say it worked as far as being able to see 600 feet down into the aquifer offshore," he says.

Combining the data from the flights with other sources allowed his team to map salt water incursion along a broad area of the shoreline and prioritize sections for the groundwater recharge program.

It's a strategy that could soon get a boost up and down the coast.

"Yeah, I think so. I think we're just starting to understand how to use the data," says Katherine Dlubac, Ph.D., who runs the electromagnetic survey program for the California Department of Water Resources.

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Their team just completed a new coastal survey last month, generating data that will be shared and available to water agencies.

"To answer the questions we think we're going to have. So, where are good recharge areas, where is possible sea water intrusion?" she explains.

Essentially drawing invisible battle lines, which could help secure an already strained water supply, as the pressures from drought and climate change continue to build along our coast.

"It doesn't take a rocket scientist to see what, if we don't take action now, what's going to happen," say Soquel Creek Water District's Duncan.

While coastal sea water intrusion is a widespread issue along the coast, experts say that sea level rise could also create new problems for interior water districts in the Bay Area as well.

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