Environmentalists to sue county over Devil's Gate Dam sediment

Environmental groups are planning to file a lawsuit against Los Angeles County on Wednesday over its plans to remove sediment behind the Devil’s Gate Dam in Pasadena.

The Arroyo Seco Foundation and the Pasadena Audubon Society are scheduled to announce the lawsuit at a press conference near the dam on Wednesday morning.

The groups takes issue with plans to remove more than 2.4 million cubic yards of sediment that has built up over decades.

Tim Brick, managing director of the Arroyo Seco Foundation, said that the large scope of the project would bring in overwhelming truck traffic and pollution and would damage important habitat for wildlife and recreation.

Over time the site has become a popular destination for outdoor enthusiasts as more vegetation has grown on the dirt and mud deposited there during rainstorms. 

Brick estimates that the excavation would bring more than 400 truckloads into the area each day. 

“They really didn’t examine better alternatives that could’ve accomplished the same goal of flood protection but done it in a much less destructive way,” Brick said.

The Los Angeles County Board of Supervisors approved the final Environmental Impact Report for the county’s plan in November.

Brick supports an alternative plan provided by a sediment working group approved by the City of Pasadena. That plan calls for a 1.1 million cubic yard removal, with ongoing sediment removal as needed.

Brick said he’s concerned that the county’s plan might not adequately address ongoing sedimentation in the basin.

“Part of our fear is that we’re just going to be back here 20 years from now with the same kind of massive program rather than an ongoing program,” Brick said.

Brick said one of the goals of the lawsuit is to work with the county to develop a stream restoration and management program as part of the excavation.

An official with the county Department of Public Works said that the size of the approved project affords protections for downstream communities in Pasadena and South Pasadena.

“That whole community has evolved over the last hundred years with the dam in place, expecting a certain level of flood protection,” said Gary Hildebrand, who manages the county Flood Control District. “With the smaller quantity of sediment removed that’s being proposed by the working group, you wouldn’t be providing the same level of flood protection to the downstream communities.”

Hildebrand said that the county considered historical accumulation when developing its excavation plan. He said that more than a million cubic yards of sediment entered the basin in the year after the 2009 Station Fire.

He said that amount is comparable to the 1.1 million cubic yards opponents say they would like to see removed.

“One event can take up that capacity, and then the question is how much remaining capacity you have in the reservoir for future sediment deposition,” Hildebrand said.