The possible effect of re-opening of the Väike Strait (Baltic Sea): results of high-resolution modelling

In recent decades, the ecological condition is said to be deteriorating in the area of the Väike Strait in the West Estonian Archipelago. The strait has been closed by a 3 km-long road dam since 1896 and according to widespread opinion, as no water exchange between the Gulf of Riga and the Väinameri Sea occurs through this strait, the existence of the dam should be the main reason for those adverse changes. The main aims of the study are to analyse the past changes in the Väike Strait area, and to decide whether re-opening of the strait by constructing some bridged openings can improve the situation. The possible influence of holes were analysed by the means of high-resolution (size of the grid 200 m) twodimensional hydrodynamic modelling. Renewal times of water masses were calculated. The results on water and matter exchange suggested that the planned holes probably have a very small positive effect. The water exchange, depending on the scenario, increased only by about 6–12%, and yet in the zones nearby the dam. Most of the past changes have probably occurred either due to natural or of larger scale causes, such as isostatic land uplift, natural sedimentation and overall eutrophication of the sea. They cannot be turned back merely by constructing the openings, or even by entirely re-opening the strait.