Stormwater capture in Los Angeles hits new high

Local water supply strategy for LA gains momentum

As Angelenos experience more extreme weather patterns, stormwater capture is stepping into the spotlight as a viable, and valuable, source of local water for Los Angeles.

Between October 1, 2022 and April 4, 2023 the Los Angeles Department of Water & Power (DWP) reported capturing an impressive 108,570 acre-feet of stormwater. That’s roughly 20% of the city’s entire water use for a year.

For perspective, LA’s current average annual capture is in the ballpark of 60,000–80,000 acre-feet, and the City has a goal of 150,000 acre-feet of stormwater capture per year by 2035. The 2022–2023 water year was also impressive for rain; LA County Public Works reported it to be the seventh-highest rainfall season in the past 150 years.

From the Mono Basin perspective, between April 1, 2023 and March 31, 2024 DWP is allowed to divert 4,500 acre-feet of water from Mono Lake’s tributary streams, which it began exporting in late January. Starting in April 2024, due to the higher lake level, DWP will be allowed, but not required, to export 16,000 acre-feet from the Mono Basin. This makes DWP’s 108,570 acre-feet of Los Angeles stormwater capture exceptionally valuable.

According to Los Angeles Waterkeeper, currently only about 20% of stormwater gets captured. While there are real obstacles to bringing full-scale stormwater capture to fruition, the potential to increase the amount of water captured, and reduce need for imported water from Mono Lake and the Owens Valley, is high. Expanded facilities will capture more stormwater, even in years of average rainfall.

City planners have been working to fund and implement stormwater capture systems for years—2004’s Proposition O helped fund DWP’s Stormwater Capture Parks Program for nine projects in existing City parks, and 2018’s Measure W aimed tax revenue at increasing local water supply through more effective stormwater capture, water recycling, and conservation. DWP’s Stormwater Management Plan, the 2020 DWP Urban Water Management Plan, and LA’s Green New Deal all include the goal of capturing 150,000 acre-feet per year by 2035.

Large-scale stormwater capture takes the form of spreading grounds, often engineered into green spaces such as parks and wetlands. Small-scale stormwater capture, in the form of rain gardens, rain barrels, and permeable pavers, can be done by individuals. In addition to stormwater capture, these efforts can also alleviate local flooding, improve water quality, improve local parks, provide social and economic benefits, and reduce urban heating.

With the people of Los Angeles calling for a more sustainable, local water supply, and DWP making significant progress in that direction, it becomes increasingly easy for Los Angeles to thrive with less diverted water from the Mono Basin.

This post was also published as an article in the Winter & Spring 2024 Mono Lake Newsletter. Top photo courtesy of the Green New Deal.