Swathes of California have seen atmospheric rivers dump heavy rains since the end of December, with storms forecast to bring 75 trillion litres more over the next two weeks. The deluge is a problem – severe flooding has wreaked havoc on the San Francisco Bay Area and led to at least six deaths.
But it could also offer some respite to a state in the throes of a severe water crisis driven by megadrought and overuse.
While some of the stormwater will top up California’s severely depleted reservoirs and aquifers, much of it will flow off pavement and farmland into rivers and drainage systems to be carried out to sea. Several projects are testing efforts to capture more of that water before it is lost.
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“Historically, we’ve viewed stormwater as a nuisance,” says at the University of California, Santa Cruz. “The approach that a lot of places have taken is to get it off the landscape as quickly as possible.”
The water crisis in the western US is changing that thinking. Across California, water managers and researchers are focusing on “managed aquifer recharge” in an effort to capture as much stormwater as possible and get it underground.
The approach has been around for decades, but it wasn’t a priority when water could be imported from elsewhere and deficits could be made up by pumping groundwater, says at Stanford University in California. “The day of reckoning hadn’t come yet,” he says.
It has now. Climate change has reduced snowpack – the state’s largest store of water – and a drying Colorado River offers less water to import. A recent found California’s heavily irrigated Central valley has lost around 2 cubic kilometres of groundwater to unsustainable pumping each year since 1961.
The crisis has spurred a hunt for other sources of water, including capturing more of the flow from California’s increasingly intense but brief storms. Last year, California governor Gavin Newsom issued an order streamlining the permitting process for aquifer recharge and other water conservation projects.
“People are serious about this,” says , a water consultant working on a project in Central valley to pump stormwater from an underused canal into wells. He says a single well can add around 1 million litres of water per day to the aquifer below it during the right conditions. Other projects have skipped wells to flood fields outside the growing season or flood crops that can tolerate the water.
In the Bay Area, the Alameda County Water District maintains a series of inflatable rubber dams that can divert stormwater flowing in creeks into gravel quarries where it seeps down into the groundwater basin.
“We’re sipping off of those big flows,” says Fisher, who has a test project diverting stormwater running off hillsides into a basin in the Pajaro valley near Santa Cruz. “We’re taking a fraction of that water, we’re slowing it down and we’re getting it to locations where it can get into the ground.”
There are growing efforts to capture more stormwater in more urban areas as well. Luthy points to two parks under construction in and that double as aquifer recharge sites. A from the Los Angeles Department of Water and Power found the city could feasibly capture enough stormwater to supply roughly a quarter of its water by 2035.
It has been done before. Orange County, California, has had one of the most sophisticated urban water reclamation systems in place for decades. Rain that falls over about 5000 square kilometres collects in a reservoir, and is then diverted to a system of ponds where it percolates underground.
Over the past decade, an average of 17 per cent of the water for the county’s 2.5 million people has come from this system, says at the Orange County Water District. Even more has come from wastewater that is treated, then pumped back underground through a system of wells.
There are many obstacles to expanding recharge projects, from securing water rights and land to dealing with contamination, which can be a problem with urban and agricultural runoff. But “we’re looking at stormwater differently in the 21st century”, says Luthy.
In all, 340 local recharge projects have been proposed in the state, according to a by California state water agencies. If all were built, they could store around 570 billion litres of water in a wet year.
That wouldn’t be enough to close California’s water deficit and reverse the effects of the ongoing megadrought, but “there’s enough water to justify the effort”, says Fisher.
