Sediment dynamics surrounding a flood tidal delta adjacent to reclamation and a dredged turning basin

Abstract

Field measurements of tidal current velocities are used to infer sediment transport characteristics in the lower section of a large, tidally dominated estuarine system at Whangarei Harbour, New Zealand. Recent (2002) developments at the harbour entrance included a 32.6 ha intertidal reclamation and a 31.8 ha dredged turning basin. Residual distance vectors indicate that the postdevelopment, large-scale pattern of sediment transport dynamics remains consistent. Minor, localised modification of transport potentials has been observed immediately adjacent to the developments, however. These modifications include a slight realignment of current flows near the reclamation wall and some leakage from a previously identified transport loop near the dredged basin. The potential for scour is identified along the eastern margin of the dredged basin, which could act to remove material moving downslope into the basin from its western edge. These data are consistent with numerical model results that predicted minimal consequences resulting from the developments. Lower harbour sediment dynamics are consistent with established patterns for tide-dominated inlets, with separation of the channel into areas of ebb and flood dominance, and typical transport patterns over the flood tidal delta. Broad-scale inlet geomorphology has been maintained, which is consistent with other dredged tidedominated inlets.