Storm-generated variations in nearshore beach topography

A series of nearshore beach profile measurements from the Outer Banks of North Carolina spanning a four-month period have been examined for temporal variations in nearshore topography. Principal component analysis of the profile data indicates that most of the variation in nearshore topography occurs in four principal modes, two quasiseasonal and two subseasonal. The first principal component, or eigenvector, corresponds to a bar-berm function. The second, to a terrace function. Combined, the first two vectors explain 76.3% of the total variance. The third and fourth components, representing subseasonal modes, are a ridge and runnel and a storm bar function, respectively. Both occur in direct response to storm wave activity. Although the bar-berm and terrace modes of profile variation have been previously identified using principal component analysis techniques, the subsequent modes have not. The ridge and runnel function accounts for 10.6% of total profile variability and the storm bar function accounts for 5.0%. ?? 1985.