Mullally Debris Basin

L.A. County Public Works crews remove debris from the Mullally debris basin at the end of Manistee Drive in the Paradise Valley neighborhood in La Canada Flintridge in 2010. Officials are planning a drainage tunnel from the basin to Pickens Canyon. (Raul Roa / Staff Photographer / December 28, 2010)

Nearly three years after the Mullally debris basin overflowed, leading to heavy property destruction in the Paradise Valley neighborhood, a plan to run a drainage tunnel from the basin to Pickens Canyon is getting off the ground. Construction is set to begin in summer 2013, according to county officials.

At a presentation to the La Cañada Flintridge City Council Monday night, project manager Grace Yu described the plan to construct a drainage tunnel 7 feet in diameter and 15 to 20 feet underground. The tunnel will run from the Mullally basin near the top of Ocean View Boulevard to nearby Pickens Canyon in order to prevent the basin from filling with debris and overflowing, as happened in 2010. During an early-morning rainstorm on Feb. 6 of that year, a massive boulder clogged Mullally. Rivers of mud and debris left behind by the Station fire the previous August overtook homes and destroyed vehicles in the area.

Mullally currently drains southward, in the mountainous terrain that abuts a series of cul de sacs, off the east side of Ocean View.

Yu said the goal of the $1.2-million project, which is being funded by the L.A. County Flood Control District, is to leave the basin and surrounding streets looking just the same as before.

“Before and after, from outside, isn't changing at all,” she said. “It's just in the subsurface.”

After last Thursday's brief storm the debris basin was totally empty, but storm season officially started this week, noted Chris Stone, assistant deputy director of the county Public Works' Water Resource Division.

“We're not out of woods from the Station fire yet, and we still feel Mullally debris basin is undersized,” said Stone.

Construction on the proposed drainage tunnel, which will run directly under Manistee Drive at a 5% slope, is expected to start in May to July next year and take 50 working days. Digging a jacking pit for the tunnel's excavation will take place in the month prior to the main project.

Yu said that construction will be staggered so residents on Manistee will have daily access to their homes.

Stone said that he and Yu would be presenting more detailed information and answering residents' questions at a meeting with the Paradise Valley Homeowner's Association at 7 p.m. on Nov. 1 in City Hall.

Chamber of Commerce President Pat Anderson, whose Manistee Drive home sustained severe mudflow damage when Mullally overflowed, said that the neighborhood had been anxiously awaiting this project, and was happy to see it moving forward.

“It's a great plan, it's long overdue. I, for one, am very anxious to see the plan get to the point where there's actually a shovel in the ground,” she said.

Anderson said that last week's rainfall had been a reminder of how vulnerable the neighborhood remains to a heavy storm season.

“We got a dose of it last week, as everyone knows, so for those of us who are still rebuilding our homes, it's always a very scary experience,” she said.

Anderson said that she thought the tunnel project has widespread support from the neighborhood, despite what promises to be significant construction impacts, because it will improve safety throughout the entire Paradise Valley area.

“I haven't spoken to anybody who is opposed to it, because everyone, in one way or another, is going to benefit from this,” she said. “The engineering plans are done, the funds are available to provide funding for the project, so it's a matter of taking the next steps, which the county are doing as fast as they can.”