California loses billions of gallons of stormwater

For too long, California and other states have viewed stormwater as a threat or an inconvenience, something that must be removed from cities and communities as quickly as possible.

But as traditional water sources face increasing pressure from climate change, population growth, agriculture and other factors, those unused gallons of rainwater falling onto asphalt or down rain gutters are beginning to be seen as an untapped resource that can help close the growing gap between supply and demand.

In a report released Thursday, Pacific Institute researchers determined that each year, 59.5 million acre-feet of stormwater goes uncaptured across the United States, or about 53 billion gallons per day. The amount is equivalent to 93% of water withdrawals for municipal and industrial uses in 2015, the most recent year for which data was available at the national level.

“The numbers are clear. It’s time to elevate the role of stormwater capture in the national water conversation,” said Bruk Berhanu, lead author of the report and senior researcher at the Pacific Institute, a California-based water-focused think tank.

Of the 10 states with the most “untapped potential,” California ranks ninth with approximately 2.27 million acre-feet of runoff from urban areas each year. (One acre-foot is approximately 326,000 gallons, enough water to supply up to three homes for a year.)

What's more, Los Angeles represents the urban area with the highest stormwater runoff potential in the West, ranking 19th in the country. The census-defined urban area includes Los Angeles, Long Beach and Anaheim, and experiences approximately 490,000 acre-feet of runoff each year, or approximately 437 million gallons per day.

It would be neither feasible nor desirable to capture every drop of that lost water, as some stormwater is needed for environmental use, ecological health, recreation and other purposes, Berhanu said. However, the sheer volume indicates that much more could be done and that stormwater could become an important alternative supply in communities across the country.

Texas was the state with the most untapped potential: 7.8 million acre-feet of runoff from urban areas each year. The analysis took into account the size of each urban area, as well as its historical annual precipitation, the researchers said.

The findings come at a critical time. In California and many other parts of the world, traditional water sources, including groundwater aquifers and freshwater from rivers, streams, and snowmelt, are becoming less reliable.

The Fifth National Climate Change Assessment found that the southwestern United States can expect prolonged periods of reduced precipitation in the coming years, which will be interrupted by extreme rainfall spells and flooding. The Colorado River, a water lifeline for 40 million people across the region, is expected to see its flows reduced by up to 30% by 2050.

People walk along the Laguna Beach boardwalk as stormwater falls into the Pacific Ocean in February 2019.

(Kent Nishimura / Los Angeles Times)

In response to supply shortages, urban water managers are turning to strict conservation measures and alternatives such as desalination and wastewater recycling.r to help keep faucets flowing. But stormwater is also a boon, and a growing number of cities and states are beginning to implement projects to take advantage of the rains when they come.

For years, stormwater “was seen as a problem, as a burden that had to be carried elsewhere, whereas today we see it more as a resource,” said Seth Brown, executive director of the nonprofit National Municipal. Stormwater. Alliance. “That's the big paradigm shift that's happened in the stormwater sector.”

Despite this growing interest, the report found that further stormwater absorption is hampered by a lack of comprehensive data characterizing national volumetric potential, as well as a lack of a national framework for capture, treatment and reuse of rainwater, among other barriers.

Water rights and public health codes governing use and contaminants are also challenges, Brown said. Funding can also be an obstacle because stormwater efforts often require long-term thinking and investments.

But the payoff is worth it, especially as the limitations of past unsustainable practices become clearer, he said. While stormwater likely won't replace all other supplies, it could be a key piece of a city or region's water portfolio.

“What we'll see in the future will be all of the above: water recycling, as well as stormwater capture and reuse,” Brown said. “It's going to play a pretty big role, so we should talk about it, think about it and start addressing it now.”

In California, officials are working to achieve this through a series of projects. During water year 2023, state agencies allowed more than 1.2 million acre-feet of groundwater recharge, including nearly 400,000 acre-feet that were recharged after Gov. Gavin Newsom temporarily lifted regulations to allow divert more stormwater floodwater to areas where it could seep into the ground.

The state is also moving forward with plans for a proposed tunnel that would capture and move more water from the Sacramento-San Joaquin River Delta during wet years. Had the tunnel been operational this winter, the Department of Water Resources could have captured about 481,000 acre-feet of stormwater between Jan. 1 and Feb. 22, or enough water for about 5 million people for a year, officials said.

“The recent winter storms have brought a large amount of water that has the potential to be captured and stored underground to replenish groundwater basins,” said Margaret Mohr, DWR deputy director of communications. She noted that since 2019, the state has invested more than $160 million in projects that help urban areas capture, store and reuse runoff.

“As we face a warmer, drier future caused by climate change, we will continue to see less snow cover, meaning we cannot rely as much on snow cover for future water supplies as we did in the past. past,” Mohr said. “California must continue to invest in water management strategies such as stormwater capture, groundwater recharge, and recycled water to ensure our water supply remains safe and reliable and to provide continued flood protection to communities.” .

Los Angeles is also taking steps to improve its stormwater capture capacity. In 2018, Angelenos passed Measure W, a tax aimed at capturing and cleaning more stormwater before it reaches the ocean. The program, which allocates about $280 million annually to stormwater projects, has had some success, although a recent evaluation found its progress has been slow.

The work often includes removing concrete, asphalt and other aspects of the built environment to create more opportunities for stormwater to seep into the ground, where it can recharge the aquifers that feed the city's supplies.

The program's ultimate goal is to capture 300,000 acre-feet of water per year by 2045. On average, Los Angeles County now captures and infiltrates about half that amount, according to Vision 45, a report published by the Defense Council of Natural Resources, Heal the Bay and Waterkeeper of Los Angeles last year.

Stormwater runoff on its way to the ocean fills the Los Angeles River in Vernon in March 2023.

(Brian van der Brug/Los Angeles Times)

That report provides a roadmap for a more sustainable water future in Los Angeles and includes several recommendations to improve stormwater capture. These include regional new construction projects; better use of existing projects; and the implementation of projects at the parcel and neighborhood scale.

“[E]Every year, whether we have above-average or below-average rainfall, billions of gallons of stormwater flow over paved surfaces, through the storm drain system, and into the ocean with no opportunity for infiltration because we don't yet have the infrastructure to capture it. . all the rain that falls in a single rain event,” he said.

The Pacific Institute assessment also outlines a series of recommendations to improve stormwater capture, starting with more detailed quantification of opportunities at the local, regional and state levels, as well as the creation of national guidelines.

Other recommendations include expanded funding and funding opportunities for stormwater capture; improved regional approaches and inter-agency collaboration; and reduced restrictions on how stormwater can be used. Public-private partnerships can also make a big difference, since “runoff is generated on both privately owned lands and publicly owned lands,” said Berhanu, the lead author.

That could mean rain barrels or rain gardens in front yards, or increased interest from corporations with large real estate portfolios. San Francisco, for example, now requires large new developments of 100,000 square feet or more to install on-site reuse systems, such as gray or stormwater systems, for irrigation, toilets and other non-potable uses.

“We definitely don't want to single out one particular strategy over another, but it is very clear that there must be a combination of strategies involved,” Berhanu said.

Heather Cooley, research director at the Pacific Institute, noted that stormwater capture has other benefits as well.

“Urban runoff into waterways is a major source of pollution,” he said. “Metals, nutrients, chemicals, pesticides – all kinds of things we use in our urban spaces and discharge into waterways. Therefore, not only does it help avoid impacts to downstream water supply, but it can also provide water quality benefits.”

Stormwater capture is also a key component of flood control, as channels like the Los Angeles River help prevent water from flowing into neighborhoods during heavy storms.

But all of those needs and uses could be better addressed by improving stormwater capture capabilities and ensuring more droplets are saved, the report said.

“This research shows that's a lot of water,” Cooley said. “It could be an important component of our water supply and could help close the gap between supply and demand in communities across the United States.”