The maps below illustrate the elevation of Dhigh, or the 'first line of defense,' along the South Atlantic and Gulf coasts. Extensive spatial variability in elevation can be observed. Darker red shades indicate relatively low elevations and a corresponding high vulnerability to overwash and inundation. Lighter red shades indicate high, well-developed dunes and relatively low vulnerability to overtopping and net coastal change. (See Storm Impact Scale for more background.)
Map of dune elevation for coastal North Carolina. On the left side of the map are histograms showing the distribution of these 'first line of defense' elevations, one for northern North Carolina and one for southern North Carolina.
Graph of the elevations of the dune crest and the dune base along Cape Hatteras National Seashore. The gap in data near the top of the graph corresponds with the position of Oregon Inlet. Note the spatial variability along the coast. Lower first line of defense elevations (red) are vulnerable to overwash and inundation regimes. Coasts with lower dune base elevations (blue) are vulnerable to the collision regime and dune retreat. The dune elevation map to the right of the graph covers the same stretch of the Cape Hatteras National Seashore and the vertical scale of dune elevation corresponds to the North Carolina map.
Map of dune elevation for coastal South Carolina and Georgia. On the either side of the map are histograms showing the distribution of these 'first line of defense' elevations, one for South Carolina and one for Georgia. An additional plot of cross-sections produced from gridded lidar data illustrates differences in vulnerability along Cumberland Island National Seashore (see bottom right hand corner of map). The first line of defense elevation of the red cross-section is nearly 6 meters below the elevation of the dark green cross-section.
Map of the 'first line of defense' elevations for the eastern coast of Florida. On the left of the map are histograms showing the distribution of these elevations, one for northeastern Florida, one for east central Florida, and one for southeastern Florida.
Northern Gulf of Mexico
Map of Dhigh, elevations for the barrier islands in the northern Gulf of Mexico (Louisiana, Mississippi, Alabama, and Florida's Panhandle). Low elevations, less than 2 m, make Louisiana's barrier beaches vulnerable to extreme coastal change during hurricanes.
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