Three-Month-Long Maintenance Work at Devil’s Gate Predicted to Have Much Less Impact on Neighborhoods Than ‘Big Dig’

Trucks brimming with sediment will once again roll through local neighborhoods near the Devil’s Gate Reservoir starting Thursday when Los Angeles County Public Works is scheduled to begin annual maintenance work lasting until December 15.

But at least one local nature advocate believes the impact on local residents will be far less “than any of the recent years have had.” 

The three-month-long annual maintenance of the reservoir immediately behind the nearly 100-year-old dam is important to reduce the buildup of sediment over time and eliminate or substantially reduce the frequency of large-scale sediment removal projects, said Steven Frasher, Public Information Officer at LA County Public Works.

The Devil’s Gate Reservoir provides flood control protection to downstream communities along the Arroyo Seco.

Over the last three years, LA County Public Works, as part of its Devil’s Gate Reservoir Restoration Project, removed 1.3 million cubic yards of sediment from the reservoir which has not been removed since 1994, to provide flood relief to the communities that have endured nearly a decade of elevated flood risk along the Arroyo Seco.

In addition to providing flood relief, the Devil’s Gate Reservoir Restoration Project has also established a permanent stormwater maintenance area that allows for the creation of 70 acres of enhanced habitat and recreational opportunities for local communities.

The controversial project has led hundreds of truck trips in and out of the Arroyo Seco daily. Known as the Big Dig, the project has come under fire by residents of Pasadena and nearby La Cañada Flintridge. It has also been assailed by the Arroyo Seco Foundation and the Pasadena Audubon Society, both of which filed a lawsuit to stop it.

This year’s annual maintenance is anticipated to remove approximately 45,000 cubic yards of sediment deposited within the reservoir, according to Frasher.

The annual maintenance work will include clearing vegetation within the reservoir basin and excavating excess sediment that washed in during the past storm season. 

Trucks that will be used  to load sediments will make roundtrips in and out of the Arroyo Seco daily from Monday through Friday, 7 a.m. to 3 p.m. Work may continue until 6 p.m, according to LA Public Works.

According to Frasher, due to the amount of sediments that accumulated in the reservoir, the maintenance work may extend into the storm season. 

A storm occurring would temporarily halt maintenance activities as time is needed for the water to recede and the reservoir to dry to enable continued work.  

Frasher said due to the large size of the reservoir, the maintenance activities may also occur simultaneously rather than in stages.  

Work is being done to ensure that native plants and local wildlife will be protected once construction commences, according to Frasher. 

“The project team is taking great care to protect the wildlife and the habitat restoration areas surrounding the reservoir. Biologists started surveys for nesting birds in the reservoir and adjacent areas in early August. Additional biological surveys will be conducted prior to the start of construction, and a construction monitor will conduct twice weekly inspections of the project site.” 

“The two strips adjacent to the east and west side slopes of the basin, the Flint Wash area and the Altadena Drain area, will be flagged and native plants within the boundaries will be protected,” said Frasher. 

Tim Brick, Managing Director at Arroyo Seco Foundation said there have been good outcomes reported as a result of the completion of the Devil’s Gate Reservoir Restoration Project. 

However he also said it will take years for Hahamongna Watershed Park to recover from the excavation activities. 

“I think the exciting thing was that there was water kept behind the dam this year until the beginning of July, which really created the opportunity for some better habitat and all of that.” 

“But it’s really going to take many years for Hahamogna to recover from the excavation program that the county has conducted.” 

Brick believes this year’s annual maintenance would have lesser impact to the neighboring areas as compared to the three-year Devil’s Gate Reservoir Restoration Project but it will continue to have an impact on the Habitat of the Hahamongna. 

“In general, the sediment maintenance program will have much less impact than any of the recent years have had.” 

“But there still will be a regular maintenance program in which they’re going to go in and destroy a large amount of a very important riparian and alluvial scrub habitat in the stream zone each year. So there’s going to be some negative impacts on the habitat of Hahamogna, but the impacts on the neighborhood are likely to be considerably less than we’ve seen in recent years.”

Brick also believes the annual maintenance program won’t affect conservation projects in the Hahamongna area. 

“I think it’ll have minimal impact on the conservation programs. The county is committed to move forward with at least one more major restoration planting. And I don’t think that this year’s program is likely to interfere with that significantly,” he said.