Seasonal and yearly profile changes of Delaware beaches

The continuous threat of erosion on Delaware beaches has prompted state officials to initiate a 50-year shore protection plan comprising beach nourishment projects with an overall estimated cost of {dollar}170 million. The attempts of previous studies to model the evolution of Delaware beaches based on standard longshore sediment transport formulas have not provided satisfying results due to inherent limitations of one-line models and lack of high quality data.; In this study measured data from densely spaced semi-yearly profile surveys of the beaches at North Shore, Rehoboth, Dewey and Bethany is analyzed and processed to yield seasonal and yearly erosion and accretion patterns. The correlations between profile change parameters are used to highlight the shortcomings of simple one-line models in predicting Delaware beach evolution.; A two-line model using a profile length scale ratio as a parameter is introduced to estimate the rates of longshore and cross-shore sediment transport as the inversion of the measured profile data. Both cross-shore and longshore rates are found to be of the same order of magnitude giving them equal importance for sediment transport modeling. They are correlated with wave and tide forcing mechanisms as well as local nourishment activity to gain a better understanding of their interaction. Results point out a strong seasonal dependency of the cross-shore sediment movement related to seasonal changes in the local wave climate and water surface elevation. In addition, the computed average rate of longshore transport is shown to compare favorably with known values of sediment transport rates along the Delaware Atlantic coast.