BEACH AND NEARSHORE PROFILES AT OREGON INLET, NC: A CASE FOR EQUILIBRIUM PROFILES

A principal component analysis was used to investigate spatial and temporal variability in onshore-nearshore profiles over a three-year period on the barrier islands adjacent to Oregon Inlet, North Carolina. The objectives included summarizing Pea Island and Bodie Island profile variability as a function of: (1) distance from the inlet; (2) beach nourishment; and (3) storms.

Comparison of floating and fixed point datum methods revealed the first eigenvector on both Pea Island and Bodie Island explains 47.8% and 62.2% of the data variance, respectively. Eigenvector 1 is a gross feature expressing profile slope. A symmetrical trend of progressive profile steepening away from the inlet exists in the spatial weightings along each island. Negatively weighted, dissipative beaches occur nearest the inlet, while positively weighted, reflective profiles are located away from the inlet. The average profile slopes at 2.1 km south of Oregon Inlet on Pea Island and 1.8 km north of the inlet on Bodie Island coincide with shoreline orientation and migration rate changes, and delineate a zone of tidal inlet influence.

The temporal trend on eigenvector 1 varies between islands. The Bodie Island profiles steepened over the study period, but Pea Island displayed no trend in time. The lack of a temporal trend along Pea Island indicates that profile shape changes occur at time periods greater than the three-year study period. These low frequency profile changes indicate large-scale sediment cycling and may represent a dynamic “equilibrium” shape at each profile. This information reveals that characteristic shapes, often considered in beach nourishment design criteria, can be known and modeled, and neither the storm climate nor the total 1.7 million m³ of inlet throat and ebb-tidal delta disposal material placed on Pea Island impacted the gross profile morphology.