Barrier island migration and onshore sediment transport, southwestern Delaware Bay, Delaware, U.S.A.

Abstract

A detailed sediment budget for part of a rapidly migrating (3 m yr −1) barrier system of southwestern Delaware Bay demonstrates that longshore drift and other principal sources of sediment are insufficient to balance the sediment budget during 1926–1981. Changes in bathymetry from 1964 to 1984 indicate that erosion is occurring in shallow areas outside the surf zone. If approximately half of the sediment eroded offshore is transported onto the beach, the sediment budget balances. These results suggest that sand and gravel is supplied to the barriers of the study area from offshore. Several processes probably combine to carry sediment landwards. Tidal currents are weak, and probably rarely entrain sediment without the assistance of waves. Once entrained, sediment may be carried onshore by the combined influence of dominant ebb-tidal currents and frequent northwest winds. This process is probably also aided by a residual onshore shear stress associated with 2nd-order Stokes waves.