Virginia Institute of Marine Science
Living shorelines represent a shoreline management option that combines various erosion control methodologies and/or structures while at the same time restoring or preserving natural shoreline vegetation communities. A common living shoreline design in Chesapeake Bay includes a low offshore rock sill to absorb wave energy with an emergent wetland landward of the sill to enhance erosion control, provide critical habitat, and improve water quality condition. This study is part of a larger, ongoing project to (1) evaluate erosion control effectiveness and the sustainability of offshore sill and fringing marsh design and structure, (2) evaluate ecological services (e.g., habitat value, water quality remediation) provided by the various components of the living shoreline design, and (3) develop design criteria that may enhance services provided by living shoreline designs in low and moderate energy environments. This project measures the performance of sills in Chesapeake Bay in support of developing design guidance. In particular, it assesses how the windows (or gaps/vents) in some sills affect their value for shore protection and water quality. The approach utilizes both field data collection (e.g., site assessment and survey, water quality data collection) and hydrodynamic modeling methodology. Two sites, varying in construction design and age, were assessed at St. Mary’s City, Maryland on the St. Mary’s River (Figure 1-1). Site 1 is part of a larger project and has about 1,000 feet of shoreline with a gapped sill that was built in 2002 (Figure 1-2). Site 2, a 1,000 feet non-gapped sill, was built in 1998 and is adjacent to Site 1 (Figure 1-2). Previous data exists for Site 1, which includes the implemented construction plan and the as-built survey. Both sites were surveyed to provide the present dimensions of the sill systems. Modeling methodology was used to assess residence time and age of water that flushes through sill structures and associated fringing wetland along part of Site 1. Also analyzed was the impact of several different window configurations and dimensions on beach shape and shore protection as well as the site substrate and vegetation characteristics, surface water and groundwater quality, and nekton.
Shoreline Management, Shoreline Protection, Maryland
This project was funded, in part, by the Department of Environmental Quality's Coastal Resources Management Program through Grant #NA06NOS4190241, Task 94.04 of the National Oceanic and Atmospheric Administration, Office of Ocean and Coastal Resource Management, under the Coastal Zone Management Act of 1972, as amended.
Hardaway, C., Reay, W. G., Shen, J., Lerberg, S., Milligan, D., Wilcox, C. A., & O'Brien, K. P. (2007) Performance of Sills: St. Mary’s City, St. Mary’s River, Maryland. Virginia Institute of Marine Science, College of William and Mary. https://doi.org/10.21220/V5VH9Q