Evaluation of criteria for predicting erosion and accretion on an estuarine sand beach, Delaware Bay, New Jersey

Predicting erosion and accretion of sand beaches in estuaries is important to managing shoreline development and identifying potential relationships b etween biological productivity and beach change. Wave, sediment and profile data, gathered over twenty-nine days on an estuarine sand beach in Delawar e Bay, New Jersey, were used to evaluate the performance of four criteria t hat predict beach erosion and accretion due to wave-induced cross-shore sed iment movement (Dean 1973; Sunamura and Horikawa 1974; Hattori and Kawamata 1980; Kraus et al. 1991). Each criterion defines a relation, between a wav e and sediment parameter, and includes a coefficient that discriminates bea ch erosion and accretion events. Relations, based on small-scale laboratory and field data, were evaluated for predicting erosion or accretion at the study site. Significant wave heights at the study site, monitored near high water, ranged from 0.08 to 0.52 m with periods of 2.4 to 12.8 s. Median gr ain sizes of sediments on the beach foreshore, gathered at low water, range d from 0.33 to 0.73 mm. All four criteria showed a clustering of erosion an d accretion events. Relations derived from small-scale laboratory data were better predictors of erosion on the profile at the field site than those d erived from field data gathered on exposed ocean environments. The planar p rofile and dominance of incident waves of low height and short period are s imilar to laboratory conditions characterized by initial planar beach slope s and monochromatic waves. Decreasing the value of the empirical coefficien t to account for the differences in the magnitude of wave energy and grain size increases the performance of the criteria tested to predict erosion of the profile.