County Delivers Upbeat Report on Devils Gate Dam Sediment Project

Project managers from the L.A. County Department of Public Works delivered an upbeat report Monday on the controversial Devil’s Gate Dam Sediment Removal Project, first conceived in 2019.

The report was presented during a Joint Special Meeting of the City of Pasadena and Los Angeles County.  

“This was a pretty contentious project, but we brought the community into the discussion in terms of how we could address the concerns of both the Pasadena-Altadena side as well as the La-Canada Flintridge side. And it was a win-win,” L.A. County Fifth District Supervisor Kathryn Barger told the Council.

Barger represents Pasadena on the L.A. County Board of Supervisors.

“This,” she continued,  “is the template now for what we use whenever we’re doing projects as it relates to clean trucks, which I think is exciting because this was the first project at this size where we did it. Now that we’ve put the natural habitat in there, if you hike it, it is incredible.”

Devil’s Gate Project Manager Keith Hala of Los Angeles County Public Works explained to the Council that Devil’s Gate is one of 14 major dams that the County Flood Control District oversees.

Beginning with a history of the project, Hala explained that the 2009 Station Fire burned a majority of the nearby Hahamongna watershed. 

“And as a result of that there was concern that all the debris flow would come down, impact the dam and prevent us from being able to provide flood control,” he said. 

The County then developed a plan to remove 1.3 million cubic yards of built-up sediment that could reduce the dam’s effectiveness, equal to  “about three Rose Bowls worth of debris.”

Hala also confirmed that the final project was finished a  year ahead of time, and that the County configured the reservoir to continue with annual cleanouts. From September to October, reported Hala, County crews removed 25,000 cubic yards of sediment “and effectively restored capacity to the dam to ensure flood flood control for downstream residents.”

“Our goal,” continued Hala, “is to not have to go back and do these big cleanouts again. Our goal is to go in and go in and remove just a small amount each year so that we’re impacting the residents less and less each year. I believe last year we were only there for about six weeks, which, in comparison to the main project, was about five months of impact. So we really reduced how long we were in this reservoir.” 

The County also reconfigured the southeast entrance that formerly served as the County vehicle entrance, converting it to a pedestrian-only entrance.

 As part of the cleanout project, the County is also currently restoring over 70 acres of habitat in and around the area, said Hala. 

According to Hala’s presentation, the County has installed 33,000 native plants, and planted over 200 oak tree acorns. 

Hala added that the new planting have been meeting or exceeding expectations and  “now we just move into our maintenance phase.” 

The area has also seen the return of at least a few federally protected bird species to the area, he said..  

Hala also emphasized that a number of other changes have been implemented based on discussions with local residents. 

“Dust mitigation is a pretty big priority for us,” said Hala, and also explained that the same exits and entrances will be used, but that trucks would use “white noise” backup systems instead of beeps, so as not to disturb residents and nearby schools. 

The County is also designing and constructing a new, nature-friendly entrance to Hahamongna Park, said Hala, with final design plans due to be completed in early 2024, and construction in late 2024.