Santa Monica Bay Low Flow Diversion Phase Coming in Under Budget

The next phase of work for a Proposition O low-flow diversion project along Santa Monica Bay will prompt some lane closures along the Pacific Coast Highway in Pacific Palisades next fall.

Members of the Pacific Palisades Community Council heard from a project engineer on March 28 that it's coming in under budget. The next package of work for Santa Monica Bay low flow diversion upgrades requires completing a remaining 900-foot alignment near the PCH and "micro-drilling" will be required, according to project engineer Andy Flores.

In November 2004, city voters passed the Proposition O clean water bond, authorizing $500 million of general obligation bonds for projects to protect public health by cleaning up pollution in L.A.'s rivers, lakes and beaches. Several projects have been occurring along the PCH leading to Temescal Canyon Road have been underway to remove bacteria and other pollutants from urban runoff and keep them from reaching Will Rogers State Beach and the adjacent coastal waters.

The interceptors and diversions will reroute the run-off into the city's sewer system.

"It will improve the beneficial use of Santa Monica Bay, reduce beach closure incidents, improve public health and the marine aquatic environment," Flores said.

Flores said the second phase of the project will require temporary lane closures on the PCH from south of Entrada Drive to the Annenberg Beach House, and the 12-month construction project is expected to start sometime this fall.

Flores said that Caltrans tentatively plans to announce these PCH-related closures as the project dates get closer:

• On the morning peak hours between 6 and 10 a.m. two northbound and three southbound lanes will need to be provided, as well as prohibit the left turn ingress and egress at driveways.
• On the evening peak hours between 3 and 7 p.m. three northbound and two southbound lanes will need to be provided while prohibiting left turn ingress and egress at driveways.
• During off peak hours between 10 a.m. and 3 p.m. and 7 p.m. and 6 a.m., two northbound and southbound lanes will need to be provided, as well as a 10-foot center buffer lane. Openings for left-hand turn access to driveways will need to be provided.

Flores added they will need to do the "shoring," also known as the open trench method, using metal piles to hold up the soil during the pipe's installation.

"The only other way to build this is core drill the entire 800 length and pour a large concrete wall," he said. "Under the PCH we don’t have nice homogenous soil. There’s a lot of substructure and sewer lines, so we extensively mapped and we did a lot of potholing. Once we realized we had a problem, things changed."

The diversion pipes will eventually connect to Santa Monica's running north-south with the PCH.

"We have a 39-inch pipe that's continuous south to north," Flores said. "We’re adding a second parallel system."

For more information on this and other Prop O projects, visit the website.

The large Temescal Canyon stormwater improvement project nearby has been halted since last month's tragic trench collapse.

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