NUMERICAL SIMULATION OF SHORELINE CHANGE WITH LONGSHORE SAND WAVES AT GROINS

Abstract

Longshore sand waves (LSWs) are macro-morphologic features that maintain form while migrating along the shore with speeds on the order of kilometers per year. LSWs can dominate shoreline evolution by causing both apparent long-term erosion and accretion seemingly unrelated to the calculated or estimated net and gross longshore sand transport rates. This paper explores three possible mechanisms, wave asymmetry, form advection, and surf-zone contraction, hypothesized to maintain and translate LSWs. The mechanisms are implemented within the framework of a shoreline change numerical model. Simulations implementing the LSW evolution mechanisms are tested with observations made ofLSWs at Southampton, Long Island, New York. Consideration is also given to movement of LSWs at and through groins. It is concluded that fundamental questions remain on processes governing the behavior of LSWs.