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Arroyo Seco Foundation

News of the Arroyo


Sediment to be cleared from Devil's Gate Dam in preparation for El Niño rainfall


County officials plan to remove approximately 1,000 cubic yards of sediment from the front of the dam.




September 3, 2015 - The County Flood Control District is getting ready for winter storms by moving 1,000 cubic yards of sediment from the dam over to Johnson Field, but questions remain about how to develop an ongoing, sustainable dam management program that will provide flood protection and protect the rare environment in Hahamongna Watershed Park and the surrounding neighborhoods. -


Sara Cardine,


La Cañada Valley Sun


Devil's Gate Dam -- The water below Devil's Gate Dam in the Hahamogna Watershed is long gone, leaving behind cracked earth and hearty plants that are wilting in the sun in La Cañada Flintridge on Tuesday, August 5, 2014.
(Tim Berger / Staff Photographer / September 3, 2015)

The sediment-laden Devil's Gate Dam reservoir will likely weather the strong El Niño storms forecast for fall and winter and should be ready for a five-year sediment removal project scheduled to start this spring, county Public Works officials reported.

In preparation for heavy rains predicted by weather forecasters, the Los Angeles County Flood Control District plans to remove approximately 1,000 cubic yards of sediment, in addition to dead tree branches and other vegetation, from the area immediately in front of the dam. That work is scheduled to begin this month, according to Gary Hildebrand, the department's deputy director.

"All of our dams, including Devil's Gate, are designed to handle the sediment and storm runoff that come from the watersheds that feed to them," said Hildebrand, estimating the basin above Devil's Gate has about 1.3 million cubic yards of capacity left.

"When we talk about El Niño, yes, there's a concern about larger amounts of rainfall, but a lot of it is going to depend on the nature of the storm events that come in through the season," he added.

The county Public Works Department is currently seeking permits from state and federal agencies that will allow for the removal of 2.4 million cubic yards of sediment that has filled the basin near the Hahamongna Watershed since the 2009 Station fire and the heavy rains that followed.

"This is a large project, so a lot of the permitting process can be lengthy," Hildebrand said.

The total cost of the haul — including an environmental impact report, mitigation plans and subsequent habitat restoration — has been estimated at roughly $65 million.

Hildebrand said once approvals from the U.S. Army Corps of Engineers, California Department Fish and Wildlife and State Water Resources Control Board have been obtained, which may happen by the end of this year, crews will be able to prepare the area for the longer-term project.

Meanwhile, members of the nonprofit Arroyo Seco Foundation and the Pasadena Audubon Society say the debris basin above Devil's Gate would be in a much better position to handle intense El Niño rains had Public Works initiated a more moderate sediment removal sooner.

"We've been advocating steps should have been taken years ago to restore capacity at the dam that's been eaten up by sediment," said Tim Brick, managing director for the Arroyo Seco Foundation. "The time to get ready for a flood is five or 10 years before the flood happens."

In December, the two conservation groups sued the county over the potential negative impacts the haul, as planned, would have on local habitats. Their chief complaint is that a more moderate, longer-term plan recommended by the Pasadena City Council was largely ignored and should be reconsidered.

Laura Garrett, conservation chair for the Pasadena Audubon Society, said Tuesday there are several still outstanding concerns about how local wildlife, including the endangered bird Least Bell's Vireo, could be harmed or displaced by such a large-scale haul.

The litigants are scheduled to appear in court in late October to determine a trial date, according to attorney Mitchell Tsai, who represents the conservationists. In the meantime, the Department of Public Works is free to continue the sediment removal plan that was approved by the Los Angeles County Board of Supervisors in November.

Hildebrand assured residents hauling would not take place until after the rainy season, and that officials would closely monitor the area throughout fall and winter.

"We're fully aware of the current condition of the reservoir now and as we move through the storm season," he said.




Arroyo Seco Foundation, 570 W. Avenue 26 #450, Los Angeles, CA 90065-1011
PO Box 91622, Pasadena, CA 91109-1622 (323) 405-7326