Tidal dynamics of the south-west lagoon of New Caledonia: observations and 2D numerical modelling

The purpose of this paper is to determine, with the aid of a two-dimensional model, the depth-averaged tidal stream in the south-west lagoon of New Caledonia. A description based on field data is given first. Coastal sea level and open-sea data (bottom pressure, currents) are harmonically and spectrally analysed. The first-order dynamics of this lagoon are dominated by semi-diurnal tides. Except for the passes, diurnal tides and currents are weak, only the two tidal harmonics M 2 and S 2 are subsequently investigated. A numerical model is used to provide a coherent and dense picture of the tidal dynamics of M 2 and S 2 and their variability. The validity of the model is assessed by comparing its results with measured sea level and current data. Amplitudes and phase-lags of the M 2 tide increase from south to north. M 2 currents are maximum in the south and in the passes. S 2 amplitudes increase from south to north but slower than M 2 . S 2 phases spread from north-west to south-east. Using model results, the long-term movement of the water mass due to tidal influence is estimated by calculating the residual Lagrangian velocity.