Digital Coast

Issue

Salt marshes provide excellent protection from storm surge and storm waves generated during extreme wind events. However, changes in sea level and impacts from human activities can weaken or fragment shoreline marshes, making shoreline habitats in coastal bays and estuaries more vulnerable to wave energy. Coastal managers need information to help them understand the link between waves and their effects on the protective estuarine environment.

Process

The Wave Exposure Model (WEMo) was used to understand the link between marsh distribution and wave energy generated by extreme winds in Carteret County, North Carolina, from 2007 to 2009. Marsh coverage maps were created from aerial imagery and used to randomly select marsh vegetation sites. The width of the marsh was calculated for each site, and wave energy was estimated using the WEMo model. Sites were divided into five zones ranging from high to low wave energy, and marsh occurrence and width versus wave energy was plotted.

Impact

Shorelines with naturally high wave energy are more vulnerable to extreme events because of reduced marsh protection. The marsh coverage maps are being used for restoration projects in these high wave energy areas, where considering the anticipated landscape pattern (narrow fringing marshes) of restored salt marshes is necessary for the best project design.

Width of randomly selected salt marshes in southern Core Sound and Back Sound, NC as a function of representative wave energy (RWE; Joules m^-1)

Frequency of occurrence of randomly selected salt marshes in southern Core Sound and Back Sound, NC as a function of representative wave energy class (RWE; Joules m^-1)