Short- and Long-Term Responses of Beach Fills Determined by EOF Analysis

Abstract

Topographic data from three different beach nourishment projects were analyzed using empirical orthogonal functions (EOFs) to determine the response of the fills at different time and space scales. The studied nourishments were undertaken at Ocean City, Md., Silver Strand, Calif., and Sylt, Germany, encompassing different nourishment schemes, forcing conditions, and general beach properties. Time series of measured beach topographies were used as input data in the EOF analysis, which produced maps describing the dominant spatial patterns in the data. These patterns displayed the effect of the fills, severe storms, and natural morphological features such as shore-attached shoals and rhythmic features. The evolution in time of the eigenvectors showed that the perturbation of the natural conditions typically caused by a fill disappears after about 1 year, provided that the material is available for cross-shore adjustment by the normal wave climate. If the fill material is placed high up on the beach, a series of severe storms may be needed to adjust the topography back to its natural state.