https://thehill.com/changing-america/sustainability/infrastructure/3816724-heres-how-california-is-trying-to-hold-on-to-its-rainwater/

Story at a glance


  • Over the past few weeks, California has been inundated with heavy rainfall, leading to widespread flooding and power outages.  

  • Many communities already had processes in place to help capture the excess water given the severe drought the state has been experiencing.  

  •  Strategies include groundwater recharge projects and upgrading cities with low-impact development features.  

California is trying to hold on to as much of its rain water as it can even as it deals with a terrible series of storms that has led to widespread flooding, 19 deaths and more than 20,000 homes without power.  

The reason is simple: the Golden State is also experiencing a three-year drought that had left Californians short of water.  

The state has experimented with a number of ways to hold on to the rain when it comes.  

Groundwater recharge projects 

Researchers across the west are investigating and implementing groundwater recharge projects, or man-made interventions aimed at helping aquifers replenish themselves. 

“The general concept is you’ve got enough water on the surface. You’d like to put it in the ground,” explained Andrew Fisher, a professor of earth and planetary sciences at the University of California, Santa Cruz.  

Because more groundwater has been pumped out of the ground over the years than has been naturally replenished, more space is available underground to hold additional surface water.  

That space, “which is vastly greater than the sum of all of the surface storage reservoirs that exist now or could be built,” is itself a resource, said Michael Kiparsky, water program director at the Center for Law, Energy & the Environment at University of California, Berkeley School of Law.  

Projects aimed at moving surface water into those spaces include putting water in percolation basins and letting it settle into the ground or building injection wells that lead the water directly into aquifers. 

Over 340 projects have been proposed by communities in California, while the state itself has a goal of expanding average groundwater recharge by at least 500,000 acre-feet each year. One acre-foot is equivalent to an acre of land with water one foot deep, Fisher explained.  

“That’s about enough water for two California families for a year,” he added. 

The California Department of Water Resources has announced it is expediting the permitting process for projects. 

Thanks to climate change, “we have and will continue to have too much water when we don’t want it and not enough when we do, and so storage is the key,” said Kiparsky. “The fact that we’ve created this massive space underground holds the key to that problem.” 

Expanding reservoirs and improving operations   

In 2018, California approved expansion projects for the Los Vaqueros Reservoir and Pacheco Reservoir.  

Combined, the projects, along with construction of two new reservoirs, are expected to boost California’s reservoir storage by 9 percent. Construction on each expansion is not expected to begin until the late 2020s, however. 

Reservoirs are manmade lakes formed by the construction of dams in river valleys. During times of high rainfall, reservoirs collect water which is then slowly released over the following weeks and months.  

The Pacheco project will increase the reservoir’s size from 6,000 acre-feet to 141,600 acre-feet, while the Los Vaqueros project will increase the reservoir from 60,000 acre-feet to 275,000 acre-feet.  

Although new reservoirs and expansions can improve water supply flexibility, costs are high and some environmentalists have raised concerns about the projects’ impacts on local wildlife. The four projects received a total investment of nearly $2 billion from the state of California.  

In addition, existing California regulations mandate when reservoirs are allowed to fill up and by how much, as empty space in a reservoir can be crucial to collect excess water when a major storm hits. 

“The rule might say, after a big storm in January, you must release enough water so that you’re at 60 percent, or whatever the rule is,” said Fisher. “And there’s a reason for that because if you don’t empty out part of the reservoir, it is not available for the next storm. It can’t help with flood control.” 

But if no storm hits, some reservoirs may empty too soon, leading to wasted water. On the other hand, if a reservoir does not empty enough and a dam is overwhelmed, it runs the risk of flooding downstream. To avoid this, some reservoirs, including Folsom Reservoir and Lake Mendocino, are using more advanced weather prediction technologies to guide operations.  

“A lot of these dams—federal, state dams—when they were developed decades ago, the weather forecasts weren’t as good as they are now,” said Fisher.  

Using updated forecasting technology, reservoir operators can empty out water to account for excess rain if a major storm is predicted. These forecast-informed reservoir operations could also be adopted by other states in similar situations, though different weather patterns and melting snow would need to be taken into account. 

Sponge cities and low-impact development  

Permeable pavement, or a surface that allows runoff to pass through pavement and into underlying stone beds and soil, can help California and states like it preserve water, according to California Sea Grant. The grant is a collaboration with the National Oceanic and Atmospheric Administration and universities across the state.  

The resource is a type of low impact development (LID), or system that uses or mimics natural processes to manage stormwater, according to the EPA.  

In San Francisco, permeable pavement has already been installed on some streets. The city’s utilities commission has spent upwards of $60 million on grants to help fund construction of permeable pavement and rain gardens. The city is also home to bioretention planters designed to capture water along curbs. 

It’s a key development and one that many urban and suburban communities filled with asphalt, concrete, and other impervious surfaces could copy.  

“A lot of times, this green infrastructure that’s put in place can have the benefit of not only slowing down the hydromodification, but also cleaning that water out,” said Kiparsky.  

“And that allows microbes to do their magic and remove some of the contaminants that are in that kind of urban water, so you’re handling water quality as well as the hydromodification.” 

Water boards throughout the state also are advancing the effort with rain barrels and cisterns, tree preservation and rooftop gardens.  

Completed in late 2021, the East Los Angeles Sustainable Median Stormwater Capture Project aimed to collect urban and stormwater runoff from a tributary area in East Los Angeles.  

The wells constructed as part of the project are located in highway medians and help divert storm runoff into underground aquifers, adding to local water supplies. Some medians are complete with parks, where residents can walk their dogs or exercise.  

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