Hydrodynamics and sediment transport offshore of the downdrift beach and southern ebb shoal of Indian River Inlet, DE

Abstract

The Indian River Inlet (IRI) is a stabilized inlet located on the southeast coast of Delaware, USA and connects the Atlantic Ocean to the Indian River and Rehoboth bays. Long-term and large-scale net alongshore wave-driven sediment transport is form south to north in this portion of the coastline. The downdrift (north) beach of IRI suffers from severe and persistent erosion due to the interruption of the alongshore transport from the jetties. A sand bypassing system is present, but high erosion rates have persisted over the past decade even though bypassing rates have increased. The inability to successfully combat this erosion is attributed to the lack of understanding of the forcing mechanisms in the area. The goals of this study are to understand and quantify the littoral processes offshore of the downdrift beach and southern ebb shoal. Average wave conditions were quantified as short period, locally generated wind waves and several wave focal points were discovered along the downdrift beach. Nearshore currents patterns displayed interesting variability based on tidal phase and offshore mean wave direction. A divergence area was discovered and currents were found to flow opposite of the large-scale transport in certain areas along the downdrift beach. A large sediment transport rate to the south was estimate and may be linked to the persistent erosion. Also, the southern ebb shoal displayed a dissipative effect on approaching wave energy flux and current variability over the shoal appeared to be related to tidal phase.