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New setback in plan to dredge Devil’s Gate Dam

A Los Angeles Superior Court judge has issued a ruling in a long-running dispute between environmentalists and Los Angeles County over a plan to dig out decades of accumulated sediment behind a critical flood control dam.

Judge James Chalfant ruled Tuesday afternoon that the county’s report was deficient in describing the environmental impacts of a massive dam clearance project at Devil’s Gate Dam in Pasadena. The ruling means that the Board of Supervisors’ 2104 approval of the sediment removal project was overturned, said attorney Mitchell Tsai, representing the environmental groups.

The Pasadena Audubon Society and the Arroyo Seco Foundation sued the county in 2014 to reduce the scope of the sediment removal to about half that amount and to take more time to accomplish the job. They argued the plan would result in major damage to wildlife habitat and disrupt surrounding communities with truck traffic. 

The judge found shortcomings in the county’s description of how it would mitigate damage to the habitat for birds and other wildlife in the Hahamongna Watershed Park behind the dam.

The  excavation cannot begin until the county corrects certain flaws in the project's environmental impact report. The judge's ruling requires Los Angeles County to revise the  EIR and put it before the Board of Supervisors for renewed approval, Tsai said. 

Chalfant agreed with the county on the amount of sediment that could be excavated if the project were to go forward, some 2.4 million cubic yards. The environmental groups had petitioned to limit the project to just half that amount. 

Speaking to lawyers for the environmental groups that sued, Chalfant said, "I understand you wish they had adopted a smaller project, but you don't get to say that. The county gets to say which alternative is better."

The judge asked both sides to return to court in late March to reargue an issue about whether the cumulative environmental impacts of the project were properly presented by the county.

Chalfant said he wrote his ruling more than week before the Oroville Dam in Northern California sustained major damage to its main and auxiliary spillways, raising fears of flooding downstream and triggering the evacuation of more than 200,000 people.

"The importance of flood control should be obvious to all," he said. "We should be very sensitive to dams' and spillways' ability to control water volumes."

Even if the Board of Supervisors approves a new environmental document, the sediment removal could still be at least months or longer away from starting because the county must still finish getting permits from state and federal agencies.

"Will we start digging tomorrow?" said Michelle Ouellette, an attorney representing the county. "No. It takes time to ramp up a project like this."

Devil's Gate Dam, dedicated in 1920, is the oldest of Los Angeles County's 14 flood control dams. It is so full of sediment that engineers have predicted that a series of major storms could block the dam's valves and cause flood damage to some 500 or more homes downstream along the Arroyo Seco Channel. Flooding could also close parts of the 110 freeway between Pasadena and downtown L.A.

In 2014, the L.A. County Board of Supervisors approved a plan from the county Flood Control District to excavate a large portion of the park-like area behind the dam. The plan would remove 2.4 million cubic yards of dirt over three to five years. That's enough dirt to fill the Rose Bowl more than three times over.
The groups sought to minimize damage to wildlife habitat in the Hahamongna Watershed Park, which is a large basin behind the dam. They also maintained the full project as envisioned  would result in too much traffic from dirt-hauling trucks.
Foundation executive director Tim Brick called the county's plan "the big dig." He worried the project would put as many as 400 dirt-hauling trucks a day on surrounding streets. He said the counter proposal from environmental groups would reduce that to about 100 trucks per day.
County officials say storms following the 2009 Station Fire in the San Gabriel Mountains caused more than 1 million cubic yards of sediment to flow down into the basin behind the dam. That inflow of sediment reduced the water-holding capacity of the Devil's Gate Dam to just 1.3 million cubic yards, below the 4-million-cubic-yard standard the county estimates is necessary to handle the water and debris that a big storm could send into the basin.

Click here to see a timeline of sediment buildup at Devil's Gate Dam.

Correction: Feb. 15, 2017 An earlier version of this story incorrectly stated Judge Chalfant had ruled in favor of the county. KPCC regrets the error.