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Mapping How an El Niño Winter Could Create Massive Flooding in Pasadena

As if California's ever persistent drought wasn't enough to worry about, the potential for an El Niño-fueled rainy season has some people in Pasadena prepping for the possibility of massive flooding, reports KPCC. The problem all stems from the reservoir that flows up to the Devil's Gate Dam in Pasadena—over the years, debris and sediment has built up, choking off release valves and water release gates. In addition to the normal buildup, the Station Fire in 2009 sent exponentially more debris into the dam, further hindering its effectiveness. This has Los Angeles County Flood Control officials concerned that a series of big enough storms could overwhelm the dam and send floodwaters crashing through the affluent Aroyo Seco neighborhood and beyond. A report compiled by the LA County Flood Control shows that a big enough storm could send water flowing two to 10 feet above the walls of the Arroyo Seco Channel. Flooding could even stretch onto the 110 Freeway.

LA County flood officials have wanted to clear the debris for years. In 2014, the Los Angeles County Board of Supervisors approved a five-year plan to clean 2.4 million cubic yards of sediment out of the dam site to alleviate flood risk. Work was halted, however, when Pasadena residents concerned about pollution and construction noise opposed the project. The nonprofit Arroyo Seco Foundation sued the city over the sediment removal plan—they prefer the Pasadena City Council's plan that scales back the amount of sediment removed by half and spreads the project out over several more years. No progress will be made on either sediment project until the lawsuit is settled, likely after the El Niño rainy season.

Tim Brick, managing director of the Arroyo Seco Foundation believes the threat is exaggerated and not worth the hassle to the neighborhood from hundreds of trucks hauling out sediment. The foundation prefers a "sensible slow program" that will "minimize the impacts." Meanwhile, homeowners in the rich Aroyo Seco area are dealing with the flood information, some hearing about it for the first time.

Others know of the risk, but have little recourse should they become victim of a flood. The federal government does not require the purchase of flood insurance for houses in the area because the county classifies the flood danger as being "temporary" because their impending plans to remove the sediment would solve the problem, the same plans that have been frozen by lawsuits until well after the heavy rains have fallen. —Jeff Wattenhofer


·El Niño: Hundreds of homes could flood along Arroyo Seco Channel in biggest storm [KPCC]
·L.A. County supervisors OK debris clearance for Devil's Gate Dam [LA Times]
·Final Arroyo Seco Channel Hydraulic Analysis [LA County Flood Report]
·Watch the Enormous El Niño Growing in the Pacific Right Now [Curbed LA]