Inlet Morpho-Dynamics During a Storm Event Inferred from Tidal Records: A Case Study Of The Brunswick River, NSW, Australia

A 24.5h moving window is used to analyse storm effects on the tidal dynamics. Compared to earlier studies using window lengths varying between 2h (for tsunami analysis) to 14 days for tidal inlet analysis, the present method provides good resolution of variations of hydraulic efficiency during storms or floods. The importance of de-trending before carrying out the harmonics analysis has been studied and it was found to be highly important. De-trending involved removing the 24.5h mean before harmonic analysis. The main results are the morphodynamic timescale Tmorph and the varying response functions F1 and F2 of the diurnal and semi-diurnal tidal constituents through a storm event at the Brunswick River, Australia. Tmorph is inferred from time series of primary semi-diurnal gain G2(t)= |F2| with an exp(-t/Tmorph) curve fit. The results show only insignificant morphological change. Thus, the changes in tidal response for this medium sized catchment are mainly due to hydraulic effects. These include the influence of river flow Qf via the non-linear friction term and increased estuary surface area during the flood. The traces of both F1(t) and F2(t) in the complex plane show an equilibrium before the storm, dynamic change during the storm and relaxation mimicked by exp(-t/Tmorph) after the storm.