Southern Marin flood control projects inch forward

Marin flood control officials have approved $1.8 million for a half-dozen infrastructure projects in Mill Valley, Tamalpais Valley and Marin City.

The projects, approved by the Flood Zone 3 Advisory Board on Jan. 13 for its next two-year budget cycle, range from pumps to levees. The funds will pay for pre-construction planning and engineering for systems that minimize high tides and upland runoff, according to staff and consultant reports.

“We’re making progress,” said Garry Lion, board chair. “It’s kind of slow and painful, but we’re making progress getting things into their proper allocation budgets.”

For Mill Valley, the panel approved $700,000 to complete the engineering to replace the Sycamore pump station, which handles stormwater runoff. The station predates the district and is run by the Mill Valley Department of Public Works. Last year, the city awarded a $4.2 million contract for its replacement.

Two other projects concern tidal waters in the Tamalpais Junction area. The board approved $250,000 to hire real estate consultants to report on acquiring rights of way as a precursor to replacing the Cardinal Road levee with a “sheet-pile wall,” a staff report said.

“This proposed project will address seepage through the concrete wall and earthen levee from Flamingo Road to about 1,100 feet downstream along the left bank of Coyote Creek,” another county report said. The flood district estimated the levee mitigation would cost $4.2 million.

An additional $50,000 will be spent to survey sediment levels and stream banks along Coyote Creek, Nyhan Creek and Bothin Marsh, the report said. Lion said a bike path is near these lowlands that stretch inland from the northern end of Richardson Bay.

Another $60,000 will be spent to bring the Crest Marin pump station up to code and stabilize the bank of Nyhan Creek “around the outfall,” a staff report said. The district’s consultants estimated the pump station replacement would cost $5.9 million.

The final project on the flood district budget concerned one of several pending projects in Marin City. Two years ago, the district installed a temporary pump system at the wetland pond along the Highway 101 exit and Drake Avenue. The site is the only vehicle access to the neighborhood and it floods in king tides.

The pump worked during the king tides early this month, but high bay waters immediately across the highway flooded areas of northern Sausalito. The flood district approved $704,000 to prepare construction plans for a permanent pump station. Of that sum, $125,000 will be spent to automate turning on the temporary pump.

The flood district is also coordinating with state and federal agencies that are planning other flood and stormwater projects at the entrance to Marin City. Caltrans has proposed fixing an aging drainage culvert that connects the wetland pond to Richardson Bay and building a new culvert under Highway 101 to drain into Richardson Bay.

Last summer, county flood and water officials received numerous comments from Sausalito residents in floating homes at Gate 6 1/2 Road, which lies across from the wetland pond. They were concerned increasing drainage flows would negatively affect the bay bottom below their homes.

Several residents raised those concerns at the Flood Zone 3 board meeting. Lion said planners are looking at moving the proposed new culvert slightly to the north.

The flood district is also studying draining and dredging the wetland pond, which has “elevated lead and zinc, typical of freeway runoff, as well as elevated arsenic due to natural geology,” a staff report said. It noted the state has allocated $2.5 million for environmental dredging.

Terrie Green, chair of the Marin City Community Services District board, has repeatedly called on Caltrans to mitigate runoff from Highway 101 above Golden Gate Village, the county’s largest public housing project, that flows downhill into the wetland pond.

The flood district budget estimated the “total future costs” of its Marin City pond projects at $4.1 million. The estimated costs for the Marin City projects, the Cardinal Road levee mitigation and the Crest Marin pump station approach $14 million.

The district has a $19 million fund balance, a staff report said.

Lion said the district would move forward with construction when the final engineering and permitting are completed, and as more funds become available.