Wave propagation under influence of currents

Wave propagation under influence of currents

Gautier, C.
Van der Westhuysen, A.

Rijkswaterstaat

SBW

2010-11-19

The present study aims to assess the prediction of wave penetration into tidal inlets under ambient current in SWAN. The performance of SWAN in the modelling of wave-current interaction was studied for two field cases, namely Port Phillip Bay Heads, Australia, and the Amelander Zeegat in the Dutch Wadden Sea. In-situ wave observations were available for both field situations. In addition, the Amelander Zeegat field case includes recently obtained marine (X-band) radar fields of a number of variables over the tidal inlet. The ambient current was shown to have a significant effect on the wave parameters. The addition of enhanced current-induced whitecapping using the expression of Deltares (2010b) has an important, but comparatively smaller impact, which is mainly seen in the significant wave height and mean period. In the Port Phillip Bay field case, which features near-idealised swell and wind sea conditions, the enhanced dissipation term clearly reduces Hmo during ebb, for which negative current gradients are found, improving the agreement with observations. For slack and flood, which feature positive or small negative current gradients, generally small impacts on wave height were found. By contrast, in the Amelander Zeegat, reductions in Hmo were found during ebb, but also for slack and flood, since negative gradients in the current field were found during all tidal phases. Although the results for Hmo improved with the application of the enhanced currentinduced dissipation, T m-1 ,O remains underestimated in the Amelander Zeegat field case. The optimal value for the proportionality coefficient Cds3 in the enhanced current-induced dissipation term has not been found yet. For some situations Cds3 = 0.8 is better, for others Cds3 = 1.6, suggesting that the parameterisation of Deltares (2010b) should be further refined. Therefore, calibration for specific situations is recommended at present. Comparison of SWAN results with the spatial fields processed from the radar observations has given valuable insight into the spatial performance of SWAN. Furthermore, qualitative agreement has been found between the observed wave lengths and computed values.

radar
wave current interaction
SWAN
wave prediction

TLJ6000

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Deltares

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