Living Shorelines Assessment for Community Resiliency in Coastal Pennsylvania
As sea levels rise, the people along Pennsylvania’s eastern coastlines face many challenges, including the loss of tidal wetlands and the associated increase in coastal flooding (Nicholls 2004). Tidal wetlands remain a valuable buffer for rising seas levels and vital habitat for fish and wildlife (Beck et al. 2001; Knight 1997). Unfortunately, the Delaware Estuary in southeast Pennsylvania has lost >95% of its coastal marshes since colonial times (DEP 2015), and ecologically sound measures are needed to protect those that remain from erosion (horizontal loss) and/or drowning (vertical loss). Living shorelines represent an innovate measure to protect and enhance Pennsylvania’s remaining coastal wetlands, and to restore these vital habitats at locations where they were once present. The goal of this study was to identify locations that were amenable to living shoreline implementation within the coastal zone of southeast Pennsylvania and to prepare initial conceptual designs for a subset of candidate living shoreline sites. Locations for conceptual designs were selected based on feasibility of implementation and adaptive management activities, as well as pre-existing physical and biological conditions.
A two-tiered rapid assessment methodology was developed to assess potential living shoreline locations and condition. First, a desktop-based GIS analysis was employed to identify sites that were situated on public land and were classified as having, or that once had, emergent wetland land cover. A subset of the sites that were accessible and aligned with stakeholder priorities were selected for rapid in situ site assessment. A living shoreline feasibility model was developed to integrate historic trajectory, biological and physical condition, and community value, as represented through public access and educational outreach potential, metrics which were assessed at each site. Model output was used to identify site-specific goals and trajectory drivers, allowing for the selection of the appropriate living shoreline tactic at each site. The highest ranking sites were subsequently revisited for further topographic and bathymetric data collection for the development of site-specific conceptual designs.
Conceptual designs were developed for the Bartram’s Garden, Windy Point, and Paine’s Park sites. Attainable goals for Bartram’s Garden and Paine’s Park were deemed to be habitat and water quality uplift (as well as outreach). The design for both sites focused on shallow subtidal mussel pens to attenuate energy waterward of the existing shoreline, and to provide water quality uplift through the filtration of the resident bivalve population. At Windy Point, the primary goal was erosion control. Low and high marsh communities in compartmentalized locations along the existing shoreline would increase habitat values and buffer against erosion. It is important to note that before these designs can be implemented, more refined data collection is necessary to confirm modeled elevation profiles and test geotechnical support of the substrate. This study showed the value of an integrated desktop and field-based methodology to identify and prioritize potential living shoreline site locations. Further, the development of a rapid assessment living shoreline feasibility model will allow for additional sites to be evaluated in an identical manner for continued site identification and prioritization along Pennsylvania’s coastal margins.