Hydrodynamic Partitioning of a Mixed Energy Tidal Inlet

The inlet modeling system, developed by the U.S. Army Corps of Engineers Coastal Inlets Research Program, was used to investigate the intermittent movement of sediment throughout the Shinnecock Inlet ebb shoal complex. Circulation, sediment transport, and morphology change were calculated by a two-dimensional finite-difference model that was coupled with a steady state finite-difference model based on the wave action balance equation for computation of wave-driven currents. The inlet modeling system, forced with various combinations of incident waves and tide, was applied to three configurations of Shinnecock Inlet (13 August 1997, 28 May 1998, and 3 July 2000) to determine the distribution of hydrodynamic forces and investigate the dominant pattern of morphology change. This pattern was previously identified through principal component analysis of five scanning hydrographic operational airborne LIDAR (light detection and ranging) system surveys of Shinnecock Inlet from June 21, 1994, to July 3, 2000. The numerical simulations suggested these dominant variations in morphology could be generated through the integration of tidal transport, wave transport, and sediment movement associated with the deflection of the ebb jet by longshore currents. The ebb jet generated sand waves within the interior of the ebb shoal and supplied sediment to the most seaward regions of the system. Longshore currents induced by incident waves from the east and west quadrants redirected the tidal transport, resulting in a supply of sediment to the bypass and attachment bars. During less energetic incident wave conditions, both tide and wave patterns of transport coexisted and interacted, resulting in a broad range of morphologic features. As wave energy increased, the tidal transport pattern was overshadowed and morphology change was concentrated along the western barrier and bypass bars.