Wetland Risk
The Erosion Vulnerability Assessment (EVA) assigns a vulnerability index to all tidal wetlands mapped by the state of Maryland. The 50-year planning window, depicting the location of the shoreline in 50 years based on historic erosion rates, provides the basis for evaluating vulnerability. This rate of recession is assumed to continue providing the shoreline is not stabilized. That being the case, wetlands (i.e. polygons) that are outside the planning window have a “no risk” factor. Moderate vulnerability is assigned to wetlands that are partially or entirely within the planning window. If however, the wetland is designated by the state of Maryland as a Wetland of Special State Concern (WSSC), the index factor for a wetland partially or entirely within the planning window is elevated to “high”. These areas represent the potential loss of “critical” wetland habitat. A similar rationale is used for wetlands depicted as lines (wetlands whose area or width is too small for accurate depiction using polygons).
It is understood that surrounding features (attributes) and conditions on the landscape can modify a wetland’s vulnerability to shoreline erosion. Topography, for example will dictate if the wetland has a low sloping platform to migrate landward upon. Long-term protection of development will likely take precedent over protection of wetlands. External datasets are used to extract conditions and attributes with the ability to increase (e.g erosion control structures) or decrease (naturally maintained uplands) the survival capacity of a wetland undergoing erosion. The EVA model searches for places where vulnerable wetlands (wetlands within the 50-year planning window) are coincident with these attributes or conditions. These areas are highlighted in the interactive map tool under “Modifiers” for planning and management purposes. The attributes noted to affect a wetland’s sustainability under erosive conditions, have themselves not been assigned a risk factor.
Beach Vulnerability
The Erosion Vulnerability Assessment (EVA) assigns a vulnerability index to all beaches identified in the Comprehensive Shoreline Inventory for Maryland. The classification is based directly on the erosion rates calculated in the revised Maryland Geological Survey’s (MGS) Shoreline Changes study that used historic and current shoreline survey positions to compute change in position. As mentioned above, this study was revised for EVA to extend into smaller tributaries and to reflect the current state of shoreline hardening in the bay. The vulnerability classification applied for beaches is below:
Erosion level |
Average erosion rate |
Beach Risk |
Slight |
1 ft/yr |
Low |
Low |
3 ft/yr |
Moderate |
Moderate or High |
6 ft/yr or 11 ft/yr |
High |
Accretion, No Change or Protected (structure) |
0 ft/yr |
No Risk |
There are no identifiable modifiers used in this study that increase or decrease a beaches susceptibility to erosion. The classification applied above acknowledges the potential for structures to protect beaches. The presence of a continuous sediment supply would be required under any scenario to maintain a beach undergoing shoreline erosion. The supply of sediment can be impeded when structures are present. An analysis of this type was beyond the scope of this project.