The first phase of a controversial four-year sediment removal project in Devil’s Gate Dam is scheduled to begin at the end of the month — a project which will result in hundreds of truck trips a day in and out of Hahamongna Watershed Park.

During this phase of the $66.6 million Devil’s Gate Dam Sediment Removal Project, vegetation will be removed from the first 50 acres behind the dam, and dirt roads will be paved over to make way for trucks entering and exiting the park from the Foothill (210) Freeway in April.

The construction will force the closure of some sections of recreational trails in the rugged foothills of Northwest Pasadena.

All told, 1.7 million cubic yards of sediment will be removed from 70 acres to help clear debris-filled spillways in the Devil’s Gate Dam.

Critics claim the traffic impacts, noise and air pollution caused by the trucks and the sediment will present a massive health hazard and impact their quality of life for years. They are joined by conservationists who say the project will decimate Hahamongna Watershed Park‘s ecosystem.

The project, dubbed “The Big Dig,” has been compared to Boston’s Big Dig, a $14.8 billion traffic tunnel project that negatively impacted area residents for 15 years.

“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. “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 20 years ago and be a slow and sustainable program.”

The county’s Public Works Department claims compromised spillways could be blocked by sediment during a major storm, causing Devil’s Gate Dam to overflow into the Arroyo Seco, which includes the Rose Bowl and Brookside Park.

In times when it’s not raining, there will be more than 400 truck trips a day into the area to collect the sediment. That is expected to continue for the next four years starting in April.

A significant amount of sediment has not been removed from Devil’s Gate since 1994, when workers hauled out 160,000 cubic yards of soil and debris.

An additional 1 million cubic yards of soil and debris were dumped into the basin by the Station fire in 2009, which burned more than 160,000 acres in Altadena, Pasadena, La Cañada Flintridge and Acton.

Devil’s Gate is the oldest dam constructed by the LA County Flood Control District, providing flood protection for the cities of Pasadena, South Pasadena, and Los Angeles.

“I’m worried about what’s going to happen when the trucks start rolling,” said local preservationist Tom Seifert. “I don’t think the community is prepared for this. The county has not been reasonable in the spirit of negotiations.”

Local residents won several battles during the fight to stop the project, including a major victory when local Supervisor Kathryn Barger scaled back the project from 2.4 million cubic yards of sediment removal over five years to 1.7 million cubic yards over four years. The motion by Barger was a compromise between the Public Works plan and a plan by Pasadena officials, which called for just 1.1 million cubic yards of mud, rocks and tree limbs to be removed.

Barger’s motion came a year after Judge James Chalfant put the project on hold and forced the county flood control district to revise the project’s environmental impact report and allow for 45 days of public review before a vote by the Los Angeles County Board of Supervisors, which must approve revisions.

Neither Barger’s motion nor Chalfant’s ruling reduced the number of truck trips into the area.

The project has also been opposed by the Glendale and La Cañada Flintridge city councils.

So far, 3,300 people have signed a local petition on opposing the project.

Hahamongna Watershed Park, located in the Arroyo Seco, is the key connecting corridor linking the San Gabriel Mountains to downtown Los Angeles, providing water, sediment, habitat and wildlife to the entire LA River system. Critics contend that the area’s rich riparian resources are too valuable to be turned into a maintenance area for county flood control workers. Critics are also worried about the potential negative environmental impacts on the Park. They claim the project would upset ecological systems in the area due to the removal of trees and vegetation in the area.

About 6,000 species of plants and animals inhabit the area where the excavation will occur, according to Altadena Town Councilmember Dorothy Wong.

“A lot of this people understand, the sediment needs to be removed, but excavating at an invasive quick way is going to wipe out the biodiversity that rarely exists,” said Wong. “They say they need to take it out because the flood will destroy Los Angeles, but it has not destroyed LA. This is a balancing act that LA is not willing to play. They are using fear to scare people.”

Local residents have long been fighting to maintain the 1,300-acre park as green space for families and hikers. Located between Altadena and Pasadena in the Upper Arroyo Seco, Hahamongna provides access to foothill trails in La Cañada Flintridge and to US Forest Service property further north, into the San Gabriel Mountains.

The park is managed by the city under guidelines laid out in the Hahamongna Watershed Park Master Plan, which calls for the city to restore, enhance and reestablish the historic native plants of the Arroyo Seco. The property, which gets its name from the Native American Tongva people who lived in the Arroyo Seco hundreds of years ago and means “flowing water, fruitful valley,” was sold to the Metropolitan Water District in 1970 for $490,000. The land was sold with a stipulation that its usage would support open space and recreational activities. In 2005, MWD sold the land back to the city for $1.2 million after the agency admitted that it had no plans for its use.

“The Big Dig is too big. It needs to be balanced. It’s so big that even the construction company [contracted by the county to do the work] is concerned,” Wong said. “The County of LA has not been managing this area. The county has not really listened to people about this. People who know the area know how special it is. We have 6,000 species that live in that area because it has not been messed with.”