Drifter study of circulation near Indian River Inlet, DE

Abstract

Current patterns were investigated to the north of the stabilized lower-mesotidal Indian River Inlet located on the Delaware Atlantic Coast with Lagrangian drifter measurements and numerical model simulations. A suite of GPS-tracked current-following drifters were deployed north of the Indian River Inlet, near the site of severe and chronic downdrift erosion and numerous sediment nourishments. Over four field experiments drifters measured flow patterns to the north of the Indian River Inlet, collectively spanning the semi-diurnal tidal cycle. Current patterns sufficiently before or after flow reversal within the inlet were found to vary with tidal phase. Hydrodynamics near the inlet were simulated during drifter field experiments and the Eulerian current meter deployments of a previous study using a 2D dynamically coupled Delft3D-FLOW and DELFT3D-WAVE model of the Delaware Atlantic Coast and Delaware Bay. Simulation water levels, velocities, significant wave heights, peak periods, and wave directions were validated with data collected near the inlet, yielding validations of mean Willmott score 0.54 ± 0.25. Simulated flow patterns were assessed through qualitative comparison with observed drifter tracks to indicate reasonable agreement in the falling tide and conditional agreement during the middle of the rising tide. Numerical simulations indicated that tidal forcing dominates current patterns over the study area. Accurate bathymetry was also determined to be important to hydrodynamic predictions in the area.