REGIONAL WAVE CLIMATE AND SHOREZONE RESPONSE (NORTH CAROLINA)

The U.S. Army Corps of Engineers, as part of the Wave Information Study, developed a 3-phase wave model with inner shelf wave statistics (Phase III) calculated every 3 hrs over a 20 yr period (1956-1975) at an along-the-coast interval of 10 naut mi. Phase III data were used to define the regional wave climate along the North Carolina coast. A matrix of 8 shorezone attributes, including storm frequency, water level, and sediment characteristics, 10 bathymetry measurements defining the inner shelf profile, and 4 measures of shorezone morphologic change was constructed with a 1 minute sampling interval. Power spectrum analysis and principal components analysis were used to determine modes of variation within the data sets.

The wave climate along the mid-Atlantic coast has periodic temporal organization. Fourteen month, annual, 6-month, 4-month, and synodic (29.5 day) cycles are present. These periodicities correspond to cycles in extratropical cyclone frequency and intensification, and shifts in mean cyclone tracks relative to the shoreline. Three statistically independent components of the wave climate are defined: overall wave energy, swell, and sea/swell (high seas with low swells). Swell waves provide 55% to 60% of the wave energy to the nearshore zone.

Four modes of inner shelf profile variation exist along the North Carolina coast. Volumetric differences are associated with wave approach angles. Regional distributions of steep inner shelf profiles are correlated with along-the-coast variations in the 20 yr wave climate, particularly wave period.

Wave climate is not correlated with shorezone response measures (rate of change and overwash distance) in most of the data set (60% to 75%). In those components where an association is described, low amplitude, short period waves are correlated with high erosion and large overwash distances.