Tropical Storm Hilary dumped about 3.18 inches of rain on Palm Springs on Sunday, making it one of the wettest days on record for the city. While a few inches of rainfall may not sound like a lot, it adds up to millions of gallons of water flooding neighborhood streets and clogging vital roads in and out of the city.

And when those floodwaters recede, where does all of that water go?

Lorraine Garcia, communication manager with the Coachella Valley Water District (which is responsible for regional stormwater protection in the area stretching from the Whitewater River to the Salton Sea), knows that it’s a simple question with a complex answer.

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The stormwater protection system in the valley is built to funnel huge amounts of fast-moving floodwaters into the 18 stormwater protection channels, Garcia explained, the largest of which is the 50-mile Coachella Valley Stormwater Channel that locals often think of as “the wash.”

For many, seeing millions of gallons of rainwater whisked away from the valley floor to the Salton Sea seems like poor water management. But the stormwater protection system is doing exactly what it was designed to do, Garcia said.

“Our number one goal is to safely move water through the protection channels and away from homes, people and properties,” she said.

Flooded streets like this one on East Palm Canyon Drive were a common site Sunday as Tropical Storm Hilary hit the Coachella Valley.

Garcia added that it’s extremely difficult to capture water that’s moving as fast as it was on Sunday.

Earlier this year, when the water district was monitoring the rate of snowmelt combined with imported Colorado River water, Garcia said water moving through the Coachella Valley Stormwater Channel flowed up to 50 cubic feet per second, or about 370 gallons per second.

On Sunday around 11 p.m., speed gauges at one site along the stormwater channel measured the water flowing at about 21,100 cubic feet per second, or about 158,000 gallons per second.

“When there are storms like what we had over the weekend, the water is moving too fast for it to sit there and absorb back into the ground,” Garcia said.

Because the Coachella Valley sits atop a massive groundwater basin covering about 440 square miles, if it were to rain a little bit over a week, the water would have time to seep back into the ground. Even then, Garcia said it’s impossible to measure how much water is actually captured in situations like that.

Now, California is no longer in dire drought conditions, thanks to the dozen atmospheric river storms that swept through the state over the winter. In response, CVWD and other valley water districts have lifted emergency water conservation measures.

Still, scientists warn of “climate whiplash” due to climate change, which makes extreme droughts and extreme floods more common, and urge for water conservation despite higher-than-average rain and snowfall.

This chart from monitoring equipment shows the spike in water levels as stormwater traveled through Tahquitz Creek the past seven days.

Snowmelt from the surrounding mountains and annual stormwater is also not enough to replenish the groundwater used by the Coachella Valley. Instead, CVWD and the Desert Water Agency jointly operate replenishment facilities that get their water from the State Water Project and the Colorado River to keep the groundwater supply stable.

Garcia said that other parts of California could do a better job of water storage during large storms. It’s estimated about 24 trillion gallons of water fell on the state during this winter’s storms, but few urban areas were able to capture the water. Los Angeles County only captured about 20% of the runoff from those storms.

“We need support from the public in order to build the infrastructure needed to capture the water,” she said. “It costs a lot of money.”

As columnists and experts have pointed out, it’s often hard to worry about drought when it’s flooding, and vice versa. 

Here in the Coachella Valley, however, we’re doing okay, Garcia said.

“We store as much as we can in our groundwater,” she said, “whether it’s imported water, snowmelt or rain.”


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