Longshore Sand Waves at Southampton Beach, New York: Observation and Numerical Simulation of their Movement
COASTAL ENGINEERING RESEARCH CENTER VICKSBURG MS
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This paper describes measurements and numerical simulations of the movement of eleven longshore sand waves observed at Southampton Beach, Long Island, New York. Longshore sand waves are wave-like forms that maintain identity while moving along the shore and represent a simple type of collective sediment movement or large-scale coastal behavior. These large morphologic features are created by periodic opening of a small inlet and subsequent welding of its ebb shoal to the beach. During a 16-month observation period, the longshore sand waves did not disperse during their steady migration westward in the direction of predominant wave incidence, and longer waves moved faster than those with smaller wavelengths. A numerical model of shoreline change including both standard particulate longshore sand transport and a component describing migration of a longshore sand wave is developed in which the velocity of the wave is related to the calculated longshore discharge of water. The model shows wave refraction to be an important mechanism contributing to the longevity of longshore sand waves, acting to retard the otherwise expected diffusion. Model calculations of the migration of a single longshore sand wave agree quantitatively with the observations.
- Physical and Dynamic Oceanography
- Geology, Geochemistry and Mineralogy