Abstract
Tidal inlets which link a tidal basin to the sea via a constricted entrance are common on the south-east Australian coast. Closure, or even significant constriction, raises water levels but restricts tidal range within the basin, while open entrances provide regular and significant tidal exchange with the ocean. A rapid assessment procedure with minimal data requirements has been shown to be informative for monitoring and a useful component of any Decision Support System set up as part of a management structure. Such a system is presented in this paper. It is based on one permanent water level gauge inside the inlet plus the use of a simple, first-order hydrodynamic model to relate the tide range, mean water level and river flow to the inlet cross sectional area. The method is tested against data from the
 Snowy River Estuary in south-eastern Australia but would be suitable over a range of estuaries. In addition, the framework presented can also provide a mechanism to explore conditions over the range of expected data, thus allowing better selection of model schematization and runs in estuarine systems where the use of 2 or 3D modeling can be justified.
Highlights
Tidal inlets which link a barrier estuary to the sea via a constricted entrance are common on the south-east Australian coast
The model gives the equilibrium solutions under the given tidal and river flow conditions, and does not directly simulate the transition of the estuary from one state to another. Instead it may be used by the estuary manager to observe the likely trajectory of the entrance condition in response to changes in the main forcing parameters
While monitoring of entrance condition in small barrier estuaries with minimal fluvial inputs can be readily achieved through the interrogation and data transformation of tide gauge water level records, this is not achievable in estuaries with greater catchment flows
Summary
Tidal inlets which link a barrier estuary to the sea via a constricted entrance are common on the south-east Australian coast. The Lake Conjola case illustrates the case of a small barrier estuary where a digital water level record at 15 minute sample rate is available from a gauge located approximately half way along the inlet channel to the lake This provided a reliable data set over a number of decades. For the Lake Conjola DST, the tidal amplitude is found by tidal analysis of the record from the estuary, using a moving window following the method of Hinwood and McLean (2001) and the same procedure is proposed as a generally applicable technique In this analysis, a time window is chosen and the water level data within the window are analysed to determine the amplitude and phase of the leading tidal constituents. The computed amplitude and phase constants have been plotted in figure 3 against the date of the central day within the 14-day window, using the Julian day as the measure of time
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