The influence of entrance constriction on hydrodynamics and intertidal morphology within estuarine basins

Abstract

We investigate the influence of basin entrance constriction on current velocities, tidal asymmetry, bed shear stresses and intertidal morphology by using a numerical model developed in Delft3D. Hypsometric curves created for six sub-estuaries within Tauranga Harbour indicate a possible link between intertidal hypsometry and entrance constriction. Model results for both spring- and neap tidal cycles show that a constricted subestuary with a deep entrance channel is associated with low current velocities and bed shear stresses in the centre of the basin– conditions favourable for sediment deposition. These constricted geometries are shown to be characterized by convex intertidal equilibrium profiles. Unconstricted sub-estuary model results display an even distribution of relatively high current velocities and bed shear stresses resulting in potential for erosion throughout the estuary. The unconstricted basins in our study are mainly associated with concave intertidal equilibrium profiles. Flood dominance increases from the entrance further into the estuary for both constricted and unconstricted conditions.