Estimating wave tolerance of Spartina alterniflora in coastal Alabama

The initial establishment and survival of a salt marsh is regulated by a variety of factors, including salinity, sediment type, elevation, nutrient levels, and wave climate. Despite the obvious importance of wave climate on the existence or nonexistence of wetlands along shorelines of water bodies, there are currently few methods for its evaluation at wetland locations. This study used an existing wind-wave hindcast method to estimate wave climate at sites with and without Spartina alterniflora along the shoreline in coastal Alabama. The sites with vegetation along the shoreline had lower wave levels than nearby sites without vegetation. Other sites with eroding stands of vegetation had wave levels intermediate between the no-vegetation and vegetation sites. The upper limit of wave energy for (noneroding) salt marsh existence was a median significant wave height of about H = 0.1 meter and a corresponding 80 percentile (less than this level 80% of the time) significant wave height of H = 0.2 meter. Sites with less wave energy had vegetation along the shoreline. The results indicate that wave height frequency distribution based on wind-wave modeling hindcasts is an appropriate methodology for wave climate evaluation at wetland sites. The results can be used to minimize the size of breakwaters used in constructed wetlands.