Applying a Coastal Vulnerability Index to San Mateo County: Implications for Shoreline Management

Climate change will cause increased coastal erosion and flooding along vulnerable shorelines and, therefore, to assess risk along the coastline and bayline of San Mateo County, a coastal vulnerability index (CVI) was used. San Mateo County is on a peninsula between the Pacific Ocean and San Francisco Bay, and therefore has both bay and ocean shorelines. The CVI measured physical parameters such as beach width, distance to 20 meter isobath, distance of vegetation behind the back beach, dune width and percentage rocky outcrop in order to produce relative vulnerabilities along both ocean and bay shorelines. Results found significant differences between overall vulnerabilities of the coastside and the bayside, which are important because governing bodies that manage San Mateo County are responsible for decision making on both sides. For example, when assessing distance to the 20 meter isobath, the coastside has several sites where it is very close to the shoreline, whereas the 20 meter isobath does not exist on the bayside because San Francisco Bay is very shallow adjacent to San Mateo County. The ramifications of this is that the bayside could be less vulnerable to storm powered wave damage compared to the coastside but is more vulnerable to flooding from sea level rise. Other findings revealed that the lack of sand dunes and beaches on the bayside will make the bayside more vulnerable to damage from wind waves, sea level rise or king tide events. San Mateo County does not have many areas with a high percentage of rocky outcrop on either bayside or coastside. This suggests that the San Mateo shoreline as a whole is vulnerable to waves since they will be breaking on weaker shore geology. Vulnerabilities are also compared with media coverage of property loss following recent storms with challenges faced by governing bodies identified.