Captured stormwater boosts Los Angeles County reserves

Heavy rains this winter and spring caused torrential flows down local streams and rivers, and Los Angeles County managed to capture and store a significant amount of that stormwater, officials say.

To be exact, they have trapped an estimated 295,000 acre-feet of water since last October, or 96.3 billion gallons.

That amount is enough to supply about 2.4 million people a year, nearly a quarter of the county's population.

“This year has really been a great year,” said Mark Pestrella, director of Los Angeles County Public Works.

The county, working with the Los Angeles Department of Water and Power and other agencies, was able to capture and store this amount of water thanks in part to investments totaling more than $1 billion since 2001, Pestrella said. Some of the money has gone to building dams and increasing the capacity of expansion lands, where water is sent to basins and then seeps underground into aquifers.

“Our investments are paying off,” Pestrella said.

The county has also spent more than $1 billion since 2001 removing sediment from reservoirs to ensure their water-harvesting capacity does not decline.

A large portion of the funding comes from the Los Angeles County Flood Control District, which receives revenue from property taxes.

Money for stormwater harvesting infrastructure has also come through the Clean and safe water programwhich was established after county voters approved Measure W in 2018.

Although the amount of runoff captured since October has been substantial, county facilities absorbed more water during the major storms of the previous 12 months: an estimated 626,000 acre-feet, or enough to supply approximately 5 million residents for a year.

The last two wet seasons have dumped exceptional amounts of rain, approaching the record set between 1888 and 1890.

The runoff pooled behind 14 county dams and flowed downstream onto land that recharges groundwater at 27 county-operated facilities. Much of the water collected last winter is now stored underground.

Captured rain not only increases local cities' supply, but is much cheaper than importing water from Northern California or the Colorado River.

Storm runoff that is not captured flows to the Pacific Ocean through the San Gabriel and Los Angeles rivers, as well as other waterways.

Capturing more stormwater and reducing reliance on imported water are among the top goals of Los Angeles County's water plan, which the Board of Supervisors adopted in december.

County officials developed the plan to make the region more resilient to the effects of climate change, including more severe droughts and storms expected to unleash heavier downpours. By 2045, the plan Calls for Los Angeles County to become 80% dependent on local water supply by capturing more stormwater, recycling wastewater, and boosting conservation.

“We know that, given climate volatility, we have to save every drop of water we can. So this has to continue to be a trend that we invest in,” said Lindsey P. Horvath, president of the Board of Supervisors.

Horvath said she was pleased to see the amount of rainwater captured and that the county's plan lays out a path to take advantage of downpours when they arrive.

“The more we see investments in infrastructure, the more we can capture and make a difference, and maintain that local water resource.”

Los Angeles Department of Water and Power officials said the agency captured about 99,000 acre-feet of stormwater between Oct. 15 and April 15, some of that through joint efforts with the county.

That included more than 12,200 acre-feet of stormwater flowing into the city's Tujunga Spreading Grounds, which was expanded in a project completed in 2022.

“We've really been building capacity to capture large storm flows,” said Martin Adams, director general of the DWP. “The fact that we've actually captured more is a direct result of the efforts that water agencies have made at the local level to capture that water before it reaches the ocean.”

Since 2008, the DWP has invested more than $130 million in stormwater infrastructure projects.

City officials plan to further increase the local water supply by investing in more stormwater capture as well as wastewater recycling and cleaning contaminated groundwater in the San Fernando Valley.

Projects that divert storm runoff for underground storage make economic sense, Adams said.

“If we put water in the soil, we will be more drought-resistant and more resilient,” Adams said. “We're going to have a much larger portion of the city's water supply here, under our old feet.”

Pestrella said Los Angeles County officials are working toward a goal of doubling the area's stormwater capture capacity.

Environmental advocates have supported efforts to harness more runoff, recycle water and reduce dependence on water supplies. Sacramento-San Joaquin River Delta and the depleted Colorado River reservoirs.

The amount of water captured this year represents a significant step forward, said Conner Everts, executive director of the Southern California Watershed Alliance.

“It's impressive how much more we've done now with the projects that have been underway over the last five to 10 years,” Everts said. “We need to rely more on local water supplies and we have great potential to continue to do so.”