When it rains in California, millions of gallons of water runs down city streets, into storm drains and out to the Pacific Ocean. But with the state in its fourth year of drought, it can鈥檛 afford to waste that resource. Some cities are capturing that rain by soaking it up like a sponge. Could this be California鈥檚 next big 鈥渦ntapped鈥� water supply?
It鈥檚 a busy morning in a San Fernando Valley neighborhood. On Elmer Avenue people are hopping in their cars and garbage trucks are making their rounds. Look to the northeast, you can see mountains.
"Those are the mountains where it all starts," says Eileen Alduenda with the . "Those are the San Gabriel Mountains. The historic watershed had water moving through those mountains and straight down Elmer Avenue into the Paseo.鈥�
The Paseo is an alley at the end of the street. She and ecologist Chris Solek know a lot about how water moves through this valley when it rains.
鈥淭he watershed is still there but what鈥檚 changed is the surface has become completely impervious,"says Solek.
Decades ago homes were built, roads were paved and now 40 acres of concrete funnel water down this one block of Elmer Avenue. So when it rains, the street becomes a stream and it floods.
鈥淪o all the water is coming down on a hard surface because it has nowhere to go and in a natural system it has the chance to slow down, spread out and sink in.鈥�
It becomes groundwater, which the city and the rest of the state desperately need in a drought. But urban areas in California have spent decades engineering a landscape to send water away as quickly as possible.
Five years ago, Elmer Avenue became LA鈥檚 first residential test site to instead treat water as a scarce resource that should be captured.
鈥淭his is where it all starts at Elmer Avenue,鈥� says Solek as he takes me to what he calls the upstream end of the avenue and points to what looks like a typical storm drain in the sidewalk. But what鈥檚 underneath makes all the difference.
鈥淭ypically catch basins are concrete so the water just runoffs, directly into the storm drain system and it goes to the ocean," says Solek. "In this case a soft bottom allows water to percolate, to infiltrate the soil and augment that groundwater.鈥�
Colorful drought tolerant plants line the sidewalks of Elmer Avenue. But it isn鈥檛 just pretty landscaping. These are bioswales - 鈥渄itches鈥� 鈥� engineered to slow down water so it soaks into the ground to mimic a natural landscape.
Under Elmer Avenue there's more - an engineered system that allows water to filter through layers of soil.
鈥淪o when they did the Elmer Avenue project they had to excavate and open up the street and actually put these things into the ground and then repave the street,鈥� says Solek.
Permeable driveways also help sponge up water. Chris Solek says in two years, the street was able to capture enough water to supply up to 66 households daily. That鈥檚 32 acre feet. The Elmer Avenue pilot project helped spark a similar project just a few miles away.
鈥淪o this is our traditional greenstreet project,鈥� says Art Castro, a civil engineer with Los Angeles Department of Water and Power. He鈥檚 on a Woodman Avenue median, a bioswale that鈥檚 collecting rainwater from the surrounding 120 acres.
鈥淭he whole thing is 3500 feet long, three-quarters of a mile and this captures roughly 55 acre feet a year,鈥� says Castro.
Castro is a big proponent of stormwater capture, but he says the highest hurdle is cost. The Elmer Avenue project cost $2.5 million. Woodman cost $3 million. But Castro says LADWP needs to capture much more stormwater, either to survive a drought or deal with a future of more intense storms. There鈥檚 a nearly
鈥淲e鈥檙e going to have 16,000 acre feet per year, that鈥檚 roughly 80,000 homes per year that we could potentially supply,鈥� he says.
Two-hundred million dollars is available in last year鈥檚 water bond to get large and small projects off the ground. A found that capturing stormwater in San Francisco and Southern California alone could provide up to 600,000 acre feet of water a year, enough to supply about 1.2 million households.
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