Ecological risks of the hydrotechnical buildings in the region of the straits of Estonia, the Baltic Sea: two case studies

摘要

Two case studies are analysed in the shallow marine area of West Estonia, consisting of a zone of straits, the islands and the semi-enclosed sub-basins. First, possible environmental risks and ecological developments in relation to the plans to build a fixed road link (a bridge with sections of the dam) across the Suur Strait from the Estonian mainland to the biggest island of the West Estonian Archipelago. Second, to make openings into the existing road dam, by which the Vaike Strait has been closed for about 100 years; local eutrophication and sediment displacement is already evident. 2D hydrodynamic and forced oscillation water exchange models are used for simulations and the future prospects are discussed. It was found that the Suur Strait link project affects the water and nutrient exchange in the study area. The ventilation of the Vaeinameri sub-basin will be decreased by about 10-20% and the acceleration of eutrophication processes could appear in certain places. As the economic possibilities of Estonia only enable the cheapest building options, no compensatory dredging and rehabilitation programs are allowed. The planned holes in the Vaike Strait dam have a very decent positive ecological effect: it is very hard to restore the past situation.