Short- and long-term responses of beach fills determined by EOF analysis

Topographic data from three different beach nourishment projects were analy zed using empirical orthogonal functions (EOFs) to determine the response o f the fills at different time and space scales. The studied nourishments we re undertaken at Ocean City, Md., Silver Strand, Calif., and Sylt, Germany, encompassing different nourishment schemes, forcing conditions, and genera l beach properties. Time series of measured beach topographies were used as input data in the EOF analysis, which produced maps describing the dominan t spatial patterns in the data. These patterns displayed the effect of the fills, severe storms, and natural morphological features such as shore-atta ched shoals and rhythmic features. The evolution in time of the eigenvector s showed that the perturbation of the natural conditions typically caused b y a fill disappears after about 1 year, provided that the material is avail able for cross-shore adjustment by the normal wave climate. If the fill mat erial is placed high up on the beach, a series of severe storms may be need ed to adjust the topography back to its natural state.