Marin City slated to receive portable flood pumps

The Marin County Public Works Department hopes to complete a $2.5 million project by mid-winter that will ease, but not eradicate, the flooding problem in Marin City.

The project calls for the purchase of two portable pumps and the installation of 1,400 feet of pipes to transport rainwater more quickly to Marin City Pond, a 3-acre detention basin next to the Gateway Shopping Center.

“The pumps won’t solve the problem;” said Rosemarie Gaglione, the county’s public works director, “but they’re going to improve it very much.”

Gaglione said that because of the topography in Marin City, a major storm is not required for flooding to occur there. She noted that the area has flooded at least once every year since she joined the county three years ago.

In instances where flooding occurs during relatively mild storms, Gaglione said, “These pumps are going to make a very big difference.”

She added, however, “If you’re talking about a very large storm, then they’re not going to be able to keep up.”

The project is just one of several Marin City flood remediation efforts in the works. The Marin City watershed is a relatively steep and bowl-shaped area encircled by a ridge. Water flows downhill through residential areas into a series of storm drains that feed into Marin City Pond.

Because Marin City is near Richardson Bay, the chance of flooding increases during high tides. When tides rise, it becomes more difficult to move water from Marin City Pond into the bay via a culvert that passes under Highway 101. A gate that connects the pond to the bay has to be lowered during high tides to prevent water from the bay from flowing into the pond.

Flooding in Marin City typically affects Donahue Street and impedes access to the Highway 101 ramps, restricting mobility for residents and visitors who must wait until the stormwater drains to Richardson Bay.

Most recently, flooding caused a complete closure of Donahue Street in 2021. The road also was closed because of flooding in 2014, and there have been several other instances where a partial restriction of traffic lanes interfered with access.

The county has awarded a $1.37 million contract to GSW Construction Inc. of San Francisco to complete the underground component of the new project, which will also include the creation of two concrete boxes, known as sumps, for gathering the water. The sumps will be connected by new pipes to an existing storm drainage system that runs along Donahue Street. Construction could begin as early as August.

The work will take place on weekdays during daytime hours and involve traffic control measures. Some lane closures might be required, so traffic delays could occur. Access will be maintained, however, for Gateway Shopping Center businesses and emergency service vehicles.

The portable pumps will be purchased at the end of construction and are expected to be operational by mid-winter.

Gaglione said the portable pumps are only an interim solution. The departments has plans for the creation of a permanent, more powerful pump station at the pond, a floodwall and multiple storm drain upgrades.

The department has already secured $884,000 from the Federal Emergency Management Agency for this larger project’s design, permitting and environmental analysis. Public works plans to apply for another FEMA grant to cover the estimated $12 million cost of construction. Gaglione said that since the county already received a design grant from FEMA, there is a strong likelihood the agency will fund the larger project.

The $2.5 million for the portable pump project is coming from $10 million in state funds secured by Sen. Mike McGuire, a Democrat from Sonoma County who represents Marin, as part of an amendment to the 2022 state budget.

The Transportation Authority of Marin, which was named as the agency to administer and distribute the $10 million, has allocated $4.15 million of it to other projects. TAM has assigned $400,000 to the permanent pump station project and $750,000 for the construction of a permanent floodwall, which will replace a temporary floodwall installed in 2015. This new floodwall will require some wetlands mitigation. TAM also also reserved $3 million for the removal of sediment from the Marin City Pond.

“There’s a desire in the community to dredge the pond to make it more aesthetically pleasing and enhance the environment by putting in more wetland marshes,” said Tracy Clay, an engineer with the Marin County Flood Control and Water Conservation District.

In addition to all these projects, the flood control district is overseeing the creation of a new stormwater plan for Marin City. The San Francisco engineering firm Schaaf & Wheeler is being paid $784,000 to develop the plan, with more than $312,000 earmarked for community outreach. Earlier this month, county staff reviewed the results of an in-person and online survey conducted in June. More than 200 respondents gave report-card style grades to more than 20 prospective projects.

“We’re asking them what’s most important to you,” Clay said. “It’s about people’s personal preferences. Once we have that, then the engineers and the scientists will make a determination about what project components are best able to achieve these goals.”

A final stormwater plan is expected to be completed by fall. Clay said the next step will be to figure out how to fund it. She said none of the $10 million secured by McGuire is available.