The Rhine Region of Fresh Water Influence (ROFI) is a shallow frictional river plume in front of the Dutch coast. Each tidal cycle a new tidal plume front with fresh-water is released. Recently, internal gravity waves have been observed in this plume. Using a Froude number analysis, support for the internal wave generation mechanism by a tidal plume front is found. It is shown, that on averaged neap tides the density stratification is large. This results in a larger area where the internal waves can be released from the tidal plume fronts compared to spring tides. As the Rhine ROFI is located in shallow water, it is investigated what the effect of bathymetry variation is on internal waves. This is studied by extending the standard KdV model derivation to account for a variable bed. This resulted in a small correction on the propagation speed inside the KdV equation. Observations of internal waves have been used to validate the KdV model. By scaling analysis of the observed waves it is obtained that the relative wave height and relative depth balance for most of the observed events. For these events the wave period and velocity amplitude of the KdV model are well matched with the measurements. This showed that the KdV model may be used for a first estimate of internal waves in the Rhine ROFI. By developing a TGE fitting procedure, it was possible to obtain the pycnocline depth and the direction of wave propagation with only limited data available. Therefore, the parameters have been varied and the error between the TGE solution and the velocity potential obtained from the velocity measurements has been minimized. ... Read more

In this report a first assessment is made of the impact of hurricanes on Saint Martin. Two bays at the east coast of Saint Martin, Baie Orientale and Baie de L'Embouchure, are studied under the conditions of hurricane Irma and Maria, which both have passed over in September 2017. During these hurricanes the bays were exposed to large wind speeds up to 40 [m/s]. Also the bays were subject to runoff due to large rainfall. The runoff has been flowing into the bays as fresh water, but also as high saline waters. This due to the salt ponds which are located in the region.

The model has been run in Delft3D and as result large wind-setup driven circulations were obtained. These circulations caused a drop of waterlevel during Irma and an increase under Maria. The saline and fresh waters discharged during the hurricanes were mostly kept onshore and is distributed over the two basins.
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