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Flood risks in the Coachella Valley

The Coachella Valley maintains its desert status by receiving, on average, less than 5 inches of rain a year. While rain isn’t common around the Palm Springs area, that doesn’t mean it’s citizens are strangers to flood waters.

The most recent flood occurred on September 9th when a monsoonal thunderstorm turned a Palm Springs neighborhood into a rapid river.

After nearly a six year drought, a forecast of rain is welcomed across much of the Golden State but the desert is much more selective on the type of storm it can handle.

Alex Tardy, Warning Coordinator Meteorologist for the National Weather Service in San Diego, describes, “The Winter storms are bad. The subtropical moisture of a dying hurricane
scenario, those are bad too but they tend to rain more 12-18 hours. They’re more spread out. It’s these individual thunderstorms… you put one on a mountain side and on a desert that’s not used to rain and water just rushes down rapidly”.

“Think about how the ground is sloped around you and what that means if there is a heavy rain event,” says David Wilson, Engineering Manager at Coachella Valley Water District. To assist in directing where the storm water flows he describes the infrastructure, “We have tributary channels that come through all the urbanized areas and receive the flows coming out of the mountains and convey those flows down to the Whitewater River or the Coachella Valley Storm Water
Channel and out to the Salton Sea”.

The geographic setup plays a large role in the type of weather the Coachella Valley experiences. The large mountains surrounding the valley, up to almost 11,000′, can both inhibit as well as enhance weather events.

“They (the mountains) can take a storm off the Pacific with heavy rain and on the other
side of the mountain just completely evaporate, remove it where it might even be sunny while it’s pouring rain on the other side,” notes Tardy.

Development and infrastructure also play a role in how much rain an area can handle.

“Through most of the developed area it’s all mostly on blow sand which used to be more pervious and now we’ve got these streets, these rooftops and there’s less area to absorb the rainfall,” explains Wilson.

Tesfaye Demissie, a Senior Storm Water Engineer with Coachella Valley Water District, breaks down the details, “The rate of absorption throughout the Coachella Valley varies depending on where you are at. Up in the mountains it’s almost nothing and as you head out into the foothills or valley floor it increases so based on our data we think it’s about 2 feet per day absorption rate in the more pervious locations”.

Another monsoonal storm that affected many valley residents was in September 8th, 2014.

La Quinta’s Interim City Engineer, Bryan McKinney, remembers, “Well I had just arrived here at work and it started raining really heavily and it probably lasted an hour, hour and a half. The streets flooded over the top of the curb and into the grass area”.

It was this storm that prompted the city to hire consultants to plan for future flood events.

McKinney continued, “These drainage studies we’re doing, the focus of that is to provide one travel lane for emergency vehicles even on a 150-250 year storm. There’s agreements in place now that certain pumps will be turned off, other pumps will be utilized to lower these lake levels and provide additional capacity for some of the street drainage, so that should help alleviate some of those issues we’ve been experiencing also”.

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