Los Angeles County Says Massive Sediment Removal Project is About to Begin in Devil’s Gate Reservoir

Published : Friday, October 5, 2018 | 4:25 PM

A controversial four-year effort to increase flood protection for communities downstream of Devil’s Gate Dam and restore habitat within the Hahamongna Arroyo Seco Watershed will begin later this month, County officials announced Friday afternoon.

With all state and federal environmental permits finally in place, Los Angeles County Public Works will begin the process of removing 1.7 million cubic yards of sediment from the reservoir immediately behind the nearly 100-year-old dam.

According to the announcement, the Devil’s Gate Reservoir Restoration Project “will establish a permanent stormwater maintenance area that allows for the creation of 70 acres of enhanced habitat and recreational opportunities for local communities.”

The area was designated as Hahamongna Watershed Park by the City 25 years ago, honoring the area’s native origins.

The final project, approved in November 2017 by the Los Angeles County Board of Supervisors, was developed over a period of nine years with considerable input and resistance from environmental groups and local residents.

The County’s original proposal, following the November 2014 release of its environmental impact report, was to remove nearly 2.4 million cubic yards of accumulated material.

However, the County’s initial environmental impact report was rejected by Superior Court Judge until a smaller, 1.7 million cubic yard project was ultimately authorized by the Board in November of 2017 on a motion by 5th District Los Angeles County Supervisor Kathryn Barger.

Members of the Arroyo Seco Foundation brought a lawsuit against the LA County Flood Control District in 2016 as the District sought approval to dig out millions of cubic yards of sediment behind the dam to remove a threat that heavy rainstorms could inundate the dam and flood homes along the Arroyo Seco Channel.

The project had been on hold since being halted by Superior Court Judge James Chalfant in March of 2017, prior to Barger’s compromise motion.

“This modified approach prioritizes safety, addresses environmental concerns and mitigates disruption for our local residents,” Barger said in a statement following the decision last year.

While cautiously optimistic following the compromise decision, local Hahamongna activists are not happy with the project moving forward.

“The County Flood Control District’s sediment and habitat removal program is going to be devastating to Hahamongna, the most precious environmental zone in our region,” said Arroyo Seco Foundation Managing Director Tim Brick.

Continued Brick, “The Arroyo Seco Foundation and the Pasadena Audubon Society have tried through a bitterly-fought lawsuit to reduce the negative aspects of the County’s program. We know that a sediment removal program is needed, but it should have begun twenty years ago and be a slow and sustainable program.”

The first phase of the project includes what County officials call “the enhancement” of more than 70 acres of wildlife habitat surrounding the project area. Invasive plant species will be replaced with healthy, native habitat, and slopes within the basin will be recontoured to provide increased opportunities for wildlife foraging and to encourage species diversity within the restoration area.

The second phase, due to begin in late October or in early November, will include the construction of new access roads within the reservoir that will enable haul trucks to avoid residential areas during sediment removal.

This phase also includes the removal of 51 acres of vegetation that County officials said had “taken a foothold” within the reservoir in recent years.

Actual sediment removal is expected to begin in April 2019.

During construction, some sections of recreational trail will be closed temporarily for public safety. Signs will be posted weeks in advance of the work, to inform hikers of the scheduled closures.

Los Angeles County Public Works Community liaison and project manager Brittany Barker has been designated as the point of contact for local officials and the community. She can be reached during business hours at (626) 458-4971.

There is also a 24-hour hotline available at (800) 675-HELP (4357).

Visit the project website at devilsgateproject.com for more information.