Session E1: Hydrodynamics within a Fish Migration River Between Saline and Fresh Water

Abstract: The presentation addresses the preliminary design of a fish migration river between the saline Dutch Waddensea and the fresh water lake IJsselmeer. An important constraint is that there should be no leakage of saline water from the Waddensea to lake IJsselmeer since this lake serves a fresh water reservoir for the northern part of the Netherlands. However, the fish migration river should provide a sufficient lure stream, increased levels of fresh water odeurs, in the Waddensea allowing fish to find the entrance of the fish migration river. In addition, the tidal range within the fish migration river should preferably allow for the development of brackish inter tidal areas In our study we used a 1-dimensional hydrodynamic model (SOBEK) in combination with a 3-dimensional hydrodynamic model (Delft3D-Flow) of the fish migration river. These models compute water levels, flow velocities and salinities within a schematized fish migration river. The 1-dimensional model, due to its limited computational time, served as a “quick-scan” model allowing many iterations (scenario simulations). The 3-dimensional model, requiring much more computational effort, was only used for a small number of selected scenarios and mainly served to examine the salinity structure within the fish migration river. The mean water level in the Waddensea is higher than the mean water level in lake IJsselmeer. Therefore, without additional measures, regardless of its length a fish migration river level will result in a leakage of salt. Hence, a valve temporarily closing the migration river during flood is necessary. Main finding of our study is that, applying a valve, the fish migration river will not leak salt and will provide sufficient lure stream