Tidal characteristics in Bass Strait, south-east Australia

Abstract

We used a two-dimensional, barotropic, numerical model to examine the complex behaviour of the tides in Bass Strait. Bass Strait, located in south-east Australia between the Australian continent and Tasmania, has the appropriate dimensions to create a half-wave tidal resonance for the M2 tides. The M2 tidal wave (amplitude < 0.4 m) enters the strait from both strait openings, increasing the M2 tidal amplitude towards the central northern Tasmanian coast to a maximum of ∼1.1 m. The tidal phases and current ellipses in the strait showed the M2 tides resembled a half-wavelength resonance in a curved, open basin. The semidiurnal, S2, and diurnal, K1 and O1, tidal amplitudes were comparatively small (<0.2 m), progressive in nature and mostly constant through the strait. The model simulations revealed that when only open boundary tidal (OBT) forcing was included in the model, the model over predicted the M2 amplitudes by ∼10–15% in the strait's central region; when OBT and direct gravitational tidal (DGT) forcing were included, the model accurately reproduced the observed tidal amplitudes. DGT forcing was used to generate resonantly amplified M2 tides (amplitudes of 0.1–0.3 m) locally, with destructive interference between the OBT-forced and DGT-forced tides occurring in the centre of the strait. The model simulations also revealed that storm systems propagating west to east attenuated the M2 tidal amplitudes in the strait. The greatest decrease in the tidal amplitudes occurred along the central northern Tasmanian coast and was attributed to tide surge interaction and resonance behaviour in the strait.