San Diego County’s Imperial Beach is already experiencing coastal flooding thanks to a warming climate pushing sea levels up.
But the problems don’t stop at the coast for the working-class community of 26,000 — rising sea levels are also moving the water issues inland.
The future that faces a low-lying town next to the U.S.-Mexico border was in full view in the winter of 2019.
A Pacific storm relentlessly pummeled the shore with 10-to-15-foot waves. At the same time, an unusually large tide boosted sea levels more than a foot above normal high tides. Add in a storm surge, and the result was predictable.
Seacoast Drive, a street that runs along the beach with dozens of condominiums, got drenched as waves washed over the rip-rap designed to protect the homes.
“High tide events — you couple that with rain events, and you pretty much have created the perfect storm for a situation like these particular houses,” said Julia Fielder, a researcher at San Diego’s Scripps Institution of Oceanography.
Fielder is a physical oceanographer, and has tracked sea levels along the Imperial Beach shore for years.
“Where you’re going to get flooding from the coast, you’re going to get flooding from inland, and it all sort of combines to make everything wet,” Fielder said.
Fast-forward to the present and waves are washing over Seacoast Drive’s coastal armaments on regular sunny days with normal 6-foot-high tides. And the rising water is making its presence felt inland, far away from the shore.
“These things are really heavy,” said Chris Helmer of the Imperial Beach Public Works Department as he lifted a manhole cover off a storm drain. “There you go.”
Almost half of Imperial Beach’s stormwater finds its way here at the edge of the Tijuana Estuary on the western edge of the town.
“Looking down here, you actually see the water coming up in our storm drain system,” Helmer said.
The pipe is full of water on a clear sunny day. So, when rains come, the water has nowhere to go but onto the streets.
San Diego State University (SDSU) Researchers are looking into the situation as an effort to help the community craft a coping strategy. This includes a study of the local groundwater table.
“Most studies so far are focusing on sea level impacts on the coastline,” said Hassan Davani, a water resources engineer at SDSU. “But now you have this whole urban system with most things underground and now you need to deal with it because groundwater is rising.”
The main issue with seawater being pushed inland is that it is heavier than freshwater. So, when the two collide, seawater pushes the underground freshwater table up.
“Rising sea level is happening, and now we can show it is actually more urgent than we were thinking about— because previous studies focus on the coastline and only above the ground interaction,” Davani said. “So the issue of compound (flooding) when a typical rain can cause flooding, that’s the one we expect to get worse.”
And it doesn't help that the city’s stormwater infrastructure is aging.
“We know every pipe has a crack, and once the soil is saturated it finds its way — it infiltrates into the pipe,” Davani said. “So then if we can conserve rainwater in any way, if we can do rainwater harvesting, it's kind of helping indirectly.”
The idea is to have the entire community, every home and apartment, add rain barrels to take pressure off the aging stormwater system. But getting buy-in from every property owner in the city is far from assured.
“Here’s the problem, and here is part of the solution,” said Jennifer Galey, from the Solana Center for Environmental Innovation.
She sells rain barrels and thinks getting complete buy-in from the community is unrealistic. “It’s part of the solution, getting these rain barrels,” Galey said.
That leaves the city with some difficult choices. Low-cost solutions like rain barrels seem attractive, but the city may have to spend money on expensive storm drain repairs to keep rising groundwater out of the pipes.
With street flooding already happening far away from the beach, the pressure for a solution increases as the sea level rises.
“Imperial Beach is almost like a canary in a coal mine in terms of understanding what the future will hold,” said Fielder. “In terms of sea level rise, but also in terms of adaptation.”
She said other cities will look at the community to understand how officials cope with the impacts linked to a changing climate.
But understanding the problem is actually the easy part. The hard part will be finding solutions that don’t bankrupt the city’s treasury.
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