San Francisquito Creek Baylands: Landscape Change Metrics Analysis

Major Findings
Over the past 150 years, lower San Francisquito Creek and the adjacent baylands have been modified for the sake of land reclamation and flood control. This study focused on developing an understanding of the magnitude of habitat change since the mid-19th century through comparisons of key historical and contemporary landscape-scale habitat features, as well as several key landscape metrics that relate to ecological functions and landscape resilience. The major findings from the analyses conducted for this study are as follows:
• Historically, the San Francisquito Creek Baylands included a mosaic of habitat types, including an extensive tidal marsh plain with salt pannes and an expansive tidal channel network, a broad bay flat, and a relatively wide contiguous low-gradient tidal-terrestrial transition zone.
• Since the late 19th century, a combination of land reclamation and the inland migration of the shoreline has resulted in a 55% decrease in tidal marsh area, a 67% decrease in total tidal channel length, a 40% reduction in channel flat area, a 20% increase in bay flat area, and a 95% decrease in tidal-terrestrial transition zone length.
• Land reclamation has also resulted in the creation of new features that did not exist in the area historically including tidal lagoons, non-tidal open water features, and non-tidal wetlands.
 

Recommendations
The findings from this study provide insight into the drivers for and magnitude of habitat change within the San Francisquito Creek Baylands, and can therefore help inform climate-resilient approaches for regaining some of the lost landscape features and ecological functions. Specific management recommendations developed from the study findings are as follows:
• The dramatic decrease in tidal marsh area and associated tidal channel length since the mid-1800s make tidal marsh restoration a high priority. To make restored areas sustainable over the long-term, restoration should include reestablishing regular tidal inundation as well as reestablishing a connection with San Francisquito Creek and the delivery of freshwater and fine sediment. Restoration efforts should focus on large contiguous areas with minimal infrastructure and should ideally be done sometime over the next decade to ensure the restored areas will have a chance of surviving the sharp increase in the rate of sea level rise that is predicted to occur around 2030 (Goals Update 2015).
• Similarly, the dramatic decrease in the tidal-terrestrial transition zone makes it a high priority for any restoration vision for this area. The transition zone provides distinct ecological services and marsh migration space, and is in need of restoration throughout the South Bay. Since most of the upland land along the historical tidal-terrestrial transition zone is currently developed, near-term restoration efforts should focus on creating transition zone habitats on the bayside of flood risk management levees (Goals Update 2015).
• The landscape metrics used in this study (tidal habitat area, tidal channel length, and tidal-terrestrial interface length) can be used to help design resilient landscape restoration and adaptation strategies around the mouth of San Francisquito Creek. Specifically, the metrics can be used to assess the long-term ecological benefit associated with various processes-based restoration approaches (i.e., approaches that create habitat features and establish physical processes required for habitat resilience). Additional useful landscape metrics are being developed as part of the Resilient Silicon Valley project (see Robinson et al. 2015).