Modélisation côtière appliquée aux prédictions de marée pour la réduction des sondages hydrographiques

To reduce soundings to chart datum, precise tidal predictions are necessary. Tidal models at SHOM are generally set up from interpolation of measurements. However, in Golfe du Morbihan, tide is complex, particularly tidal range varies very quickly around islands, where tidal streams are very strong. Measurements density does not allow a good representation of these variations. A hydrodynamical model has been set up with TELEMAC-2D software from Laboratoire National d'Hydraulique et d'Environnement (LNHE) of Electricite de France (EDF). The mean amplitude error of this model equals 5 cm, the mean phase difference is lower than 9 minutes. From this hydrodynamic model, a tidal model has been set up using analysis of calculated water levels. Afterwards, this tidal model has been adjusted to measurements. This tidal model provides better results than the model issued from measurements interpolation : grid points density allow to reproduce strong tidal range gradients. The mean error of this model equals 2,7 cm (standard deviation 1,7 cm).