This page highlights the San Anselmo, CA High Water Mark (HWM) Project which took place on December 13, 2014. See more High Water Mark case studies.
Community Profile: The Town of San Anselmo, CA, is a small community located north of San Francisco, CA, in Marin County. The town (population of 12,336) is built on a floodplain and is located in the Ross Valley Watershed, a 28-square-mile area which includes 44 miles of stream channels, one of which, San Anselmo Creek, flows through San Anselmo’s downtown area.
Flood History: San Anselmo Creek periodically floods during rain events. According to past records, heavy rains have caused the San Anselmo creek to flood up to 4 feet. Major floods of record were in 1925, 1940, 1963, 1982, and 2005, with the worst storm of record in 1982.
During these flooding events, San Anselmo Creek will overflow and saturate the main avenue, Francis Drake Boulevard. In fact, flooding is prevalent enough that the town has a Dropcam focused on downtown businesses.
Planned Flood Risk Mitigation
In order to reverse the effects of flooding, the Town is working closely with the Marin County Flood Control and Water Conservation District in implementing a flood control plan known as the Capital Improvement Plan (CIP). To further protect home and business owners, mortgaged houses and buildings within the 100-year flood plain are required to have flood insurance.
The Town of San Anselmo, CA, has developed a three-part plan to both reduce water flow and/or capacity in the town, as well as help mitigate the rising costs of flood insurance. First, the community will, in conjunction with their CIP, remove a building in the floodplain, lower a baseball field so it can act as a retention basin, and make construction adjustments to bridges along San Anselmo Creek. The intent is to remove homes and buildings from the floodplain. In an effort to mitigate the cost of flood insurance, the Town of San Anselmo has also applied to become part of the Community Rating System (CRS).
With their history of flooding, the Town of San Anselmo wanted to raise flood risk awareness and promote mitigation projects to help reduce flood water flow during peak storm events. The community leveraged the HWM Initiative as a way to publically announce future projects and gain support for mitigation projects. The community’s intent is to bring long-term protection to homes and citizens.
HWM Project Activities
The Town of San Anselmo hosted a HWM Launch Event on Saturday, December 13, 2014, to give the public information about the local watershed, flooding history, and the Flood Protection & Watershed Program. The HWM Launch Event was coordinated to coincide with a local pancake breakfast at the local fire station in an effort to both attract and keep local residents interested and engaged in the event. Partner Federal agencies and many local organizations manned tables outside the fire station. In advance of the event, five HWM signs we erected along downtown San Anselmo, indicating the height of historic floods.
San Anselmo’s town hydrologist, Gerhard Epke, worked directly with FEMA Region IX to organize the event. Mr. Epke coordinated the design, development, and placement of HWM, signs as well as the coordination and organization of the HWM Launch Event. FEMA Region IX worked closely with the community to support the effort. Both the USACE and the NOAA NWS provided outreach support and participated in the event.
The event was attended by many local, Regional, and State stakeholders, including
- Jared Huffman (Congressman, D-CA);
- Sean Condry (San Anselmo Public Works Director);
- Katie Rice (Marin County Supervisor);
- Ross Valley Watershed Association representatives;
- Flood Zone 9 Advisory Board members;
- Marin County Storm Water Pollution Prevention Program representatives; and
- Assemblyman Levine's Office
Mitigation Action Update
The HWM Launch Event served as a reminder to residents about past flooding, but also allowed the Community Public Works Director and others to talk about the impacts of flooding and the importance of the mitigation projects the town was undertaking. To date, the Town of San Anselmo applied for the CRS program and is awaiting their CRS designation. Other updates include the following:
- The Flood Control District has been reanalyzing its site selection criteria for detention basins in the Ross Valley watershed.
- The community is releasing an RFQ for Environmental Assessment of Memorial Park Detention Basin (part of the Flood Control Program).
- The community is preparing to update their local Hazard Mitigation Plan.
- The community is leveraging the CRS Program for Public Information (PPI) outreach program to assess flood insurance rates and helping homeowners prepare for April 1 increases through obtaining elevation certificates and revising their storm water ordinance to limit creation of impervious surfaces.
Resulting Media Coverage
The HWM Launch Event drew significant media coverage by local news channels and newspapers. For clips from the event visit:
- Flood control discussed as San Anselmo unveils high water mark signs – Marin News
- Flood Protection Open House Dec. 13 – The Ross Valley Reporter
- Open House Held Saturday December 13th, 2014 – Ross Valley Flood Protection and Watershed Program website