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LA County captured enough rainfall this week to provide water to 65,600 residents for a year

While this week’s atmospheric river drenched Southern California with record-breaking rainfall, some water managers were busy capturing some of that runoff to save for dry days ahead. Others were busy fending off an environmental disaster.

Los Angeles County Public Works captured 2.7 billion gallons of stormwater as the rain fell in sheets, public information officer Liz Vazquez told CNN in an email – enough water for 65,600 residents for a year.

In all, stormwater capture facilities across Southern California snagged around 15,000 acre-feet – or around 4.9 billion gallons – for recharge into groundwater since Sunday night, according to Rebecca Kimitch, a spokesperson for Metropolitan Water District of Southern California.

One of those agencies is the Las Virgenes Municipal Water District, whose treatment plant was slammed by nearly 10 inches of rain at a rate that had officials scrambling for a workaround to prevent raw sewage from being discharged into Santa Monica Bay at Surf Rider Beach.

At the peak of the storm, the plant was taking in 38 million gallons of water a day. A typical day’s intake is more like 7.5 million gallons, but it was built to treat more than that – around 12 million gallons a day, said Mike McNutt, an LVMWD spokesperson.

What fell earlier this week was a “huge and rapid increase” in water intake, he said, which majorly strained the functionality of the plant and could have resulted in an environmental disaster.

As the water rose, staff played a bit of a shell game with its resources, sending some of the water to a balancing pond that’s typically used later in the treatment process and then pumped it back to the beginning of the plant for treatment.

Malibu Creek, where LVMWD discharges some of its recycled water, is highly protected by the Environmental Protection Agency, McNutt said, and “the staff truly averted an environmental disaster where raw sewage would have been sent downstream.”

Partially treated wastewater was on the brink of overflowing at Las Virgenes Muncipal Water District’s Tapia Water Reclamation Facility on February 4, 2024. - Las Virgenes Municipal Water District
Partially treated wastewater was on the brink of overflowing at Las Virgenes Muncipal Water District’s Tapia Water Reclamation Facility on February 4, 2024. - Las Virgenes Municipal Water District

Water managers across the West are facing the urgent need to conserve rainfall to prepare for the next drought. But many of these facilities weren’t designed for the most extreme rain events – which the region will still see, even as the overall climate gets hotter and drier.

Most facilities “are intended for low and medium-flow events – rainfall of up to 1.5 inches a day,” Kimitch said. “Flood control and safety are the primary concerns during high flow events like this.”

With the reservoirs across the state well above average for this time of the year, some like Lake Oroville and Shasta Lake have been coordinating flood control releases to make room for runoff from the soaking storms that hit the state recently, said Ryan Endean of the California Department of Water Resources.

Water in Lake Oroville, for instance, stands 116% of average. Some of what it released will run through the State Water Project to the San Luis Reservoir “where it will be captured to maintain overall water supply,” Endean said.

“These releases are necessary to provide critical flood protection for downstream communities and ensure that the reservoirs have room for storing snowmelt runoff in the spring,” Endean explained.

In Los Angeles County, the State Water Project released excess storm water from Pyramid Lake that is being “captured and stored downstream in Lake Piru by the United Conservation District for future water supply,” Endean added, explaining that the state coordinates with local water agencies “to capture and store as much water as possible from these types of releases.”

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