Monitoring and Modelling Tidal Regime Changes Following Inlet Scour

Entrance closure has been identified by the local coastal communities as one of the more important management problems for the small barrier estuaries. The paper describes analyses of water level records and a simulation model illustrating tidal and fluvial interactions with the estuarine morphology. As management tools, they may be used to identify conditions likely to lead to restriction of tidal exchange through the estuary entrance. Ten months of water level data and two morphological surveys for Lake Conjola, a typical small barrier estuary south of Sydney, Australia, are examined here. The data analysis has included determination of the principal tidal constituents and mean water level, using a rolling time window. Different typical responses of the constituents have been found to storms accompanied by high stream inflow and those accompanied by sand overwash and to gradual accretion of sand in the entrance. Fluvial, tidal and morphological data for periods following a major fluvial event, have been examined to provide data on the progression of entrance conditions from partly closed, through scoured and through partial closure by an overwash event. The relative contribution of fluvial fluxes, tidal flows and coastal storms has been evaluated. The model, which simulates the response of a simple basin to tidal forcing and fluvial inflow, provides outputs which include diagrams of tidal attenuation and entrance velocities as functions of entrance resistance and fluvial inflow. On these diagrams may be plotted trajectories showing the response to the different types of events.