San Rafael, CA – Santa Venetia, a low-lying community adjacent to San Francisco Bay, is susceptible to flooding from severe storms and high tides. To help reduce the risk of future incidents, which is increasing due to sea level rise, land subsidence, and deterioration of the existing flood barrier, the Marin County Flood Control and Water Conservation District is proposing a project to rebuild the levee system along Gallinas Creek.
The proposed project would rebuild the flood mitigation berm along Gallinas Creek, which was originally constructed in mid-1980s.
The neighborhood just east of the Marin County Civic Center relies on a combination of flood mitigation infrastructure including pump stations, bypass pipes and the perimeter flood barrier system. Watershed studies point to the perimeter flood barrier as the weak link in the system, making the area susceptible to flooding from high tides in the Bay. The levee between Gallinas Creek and the neighborhood was raised in the 1980s with a timber-reinforced berm (TRB) following several significant flood events. This section is located primarily on private property and has deteriorated to varying conditions and elevations.
The proposed project, estimated to cost $6 million, would rebuild the levee system along the perimeter of lower Santa Venetia to provide a 100-year level of protection with allowances for sea level rise and land subsidence. A 100-year water level has a 26% chance of occurring during a 30-year period. The barrier would be replaced within its existing footprint with a similar but taller structure that is made of composite material and embedded deeper into the levee. Areas that don’t have any barrier will see installation of a new barrier on top of their existing levee. The new barriers would be constructed of composite lumber and bring the top of berm up an average of about 12 to 18 inches. The underlying earthen levee will not be rebuilt.
In order to reconstruct the entire length of TRB, this project would permit the District to purchase easements from about 100 private parcels along the levee to ensure future maintenance access on foot by Santa Venetia Flood Control Zone 7 staff. Based on sea level rise projections and land subsidence rates, the proposed project could offer 100-year level protection until approximately 2050.
Of the $6 million estimated cost, about $5 million has been designated for this project. The designated funding includes a $3 million FEMA grant, $840,000 from the County of Marin contingent upon approval of special tax measure by Santa Venetia voters, and $1.16 million from the Zone 7 fund balance plus expected revenues over the next few years. The remaining $1 million needed to cover the project costs could be obtained through passage of a special tax on the 660 homes that would experience tidal inundation at varying depths without the barrier system. The area that contains the 660 parcels would comprise a proposed subzone 7A.
On November 17, the Marin County Flood Control and Water Conservation District Board of Supervisors will hold a public hearing to consider an all-mail ballot for consideration of a special tax measure in March 2021. The tax would be $297 per parcel per year for seven years for the 660 parcels. Approval would require a two-thirds majority by registered voters of those parcels, which would also establish a new subzone 7A.
If the special tax passes, the construction of the TRB could begin as soon as June 2021 with an estimated completion date of November 2022. For more information and resources, visit the Gallinas levee project webpage.