The Stability of Living Shorelines - An Evaluation

This project set out to strengthen arguments that living shorelines were a viable and preferred method of erosion control along much of the Chesapeake Bay shoreline. Using statistical tests and data that describe shoreline and environmental condition along tidal shoreline, the study found that indeed marshes are frequently associated with stable shoreline and therefore recommending living shoreline treatments to manage erosion problems was a reasonable strategy that warranted strong consideration. Additional tests revealed a lower occurrence of marshes when traditional erosion control structures like bulkheads and revetments were present. This confirms these structures can permanently impact the growth of tidal marshes. Consideration of alternative treatments particularly in low energy settings is recommended. Additional statistical relationships revealed that marshes were not prolific in high energy environments, suggesting the living shoreline strategy was environmentally restricted and any model would need to account for this. Under a separate task, erosion rates were computed along shoreline where living shoreline treatments were in place. While the results could not confirm that the living shoreline treatment performed better at reducing shoreline erosion rates, there was enough evidence from the 35 sites that were analyzed to confirm that erosion could be reduced using soft stabilization techniques. Based on criteria evaluated in the aforementioned analyses, a protocol was developed to model the locations where living shoreline treatments should be considered for erosion control. Using existing GIS based databases a spatially explicit model was generated. The model was tested in the county of Northumberland, Virginia located on Virginia’s Northern Neck. The model delineated areas as suitable, unsuitable, and suitable with design restrictions. The model was validated against random field inspections and permit reviews. The results indicate strong agreement (75%) between the modeled output and the field review when considering a site suitable (inclusive of design restrictions) and unsuitable. The model had less agreement (58%) between the output and the field assessment when considering explicit treatment types for suitable areas. We attribute the discrepancy largely to the limitations associated with data availability and professional bias. Despite this, the model has enormous potential as a management tool and represents the only decision making tool currently devoted to the subject of living shorelines in this region, and one of the few nationwide. The Center for Coastal Resources Management recommends the model be run throughout the Bay where data exists, and will seek avenues for funding to begin this venture. This report as well as outreach material collected as part of this project and others within the Center for Coastal Resources Management have been posted to a new Living Shoreline Website at http://ccrm.vims.edu/livingshorelines/index.htm