Environmental assessment of controversial bridge over Øresund
Anne Berit Bjørken
Excavating the Øresund seabed will ensure that the planned Øresund Bridge will not have undesirable environmental consequences in the Baltic, believes Torkild Carstens, chief scientist at SINTEF NHL.
Two years ago, Carstens was appointed as one of two environmental controllers to the Øresund Consortium which is to build the controversial rail and road link between Denmark and Sweden. The professor has won acceptance for many of his proposals, which will help to ensure an adequate flow of water to the Baltic with as little interference as possible from the Øresund project. But even Carstens' proposals are controversial, because they will affect certain aspects of the Øresund environment.
Water to the Baltic
The Øresund Bridge is very controversial. Its opponents claim that the bridge piers, landfills and an artificial island will reduce water exchange in the Baltic Sea. This will reduce the flow of salt and oxygen-rich water and threaten Baltic cod stocks."My task has been to evaluate all the environmental impact assessments of the bridge project. The most important thing is to ensure that the bridge does not affect conditions in the Baltic, and that it does not lead to unnecessary changes in Øresund," says Carstens, who is also a professor at the Dept. of Hydraulic Engineering at NTH.
When Carstens was called in, the design of the bridge was such that it would have reduced the flow of water through the Sound by 2.5%. Pressure from the two environmental controllers brought about a long series of numerical analyses of the bridge project. These have led to extensive changes in the design, which will produce a reduction in water flow of only 0.5%. This will be compensated for by dredging in order to reduce the reduction to zero.
Torkild Carstens of SINTEF NHL is environmental consultant to the Øresund Consortium.
Major consequences
"A 2.5% reduction in flow-through may sound like a minor change, but in the Baltic even small systematic changes can have important consequences. The current is dependent on low-pressure passages. The waters of the Kattegat have a higher salinity and are therefore heavier than those of the Baltic. When the flow goes from the Kattegat, the salty water sinks beneath the surface layers in the Baltic and ensures good water exchange, while the fresher surface water runs out into the Kattegat. The salty water is essential for the survival of the Baltic cod stocks. If the flow is reduced, the supply of oxygen-rich salty water will also be reduced."The most important changes are that the landfill on the Danish side will be modified, and that the artificial island that is to be built will be relocated, so that it will lie just behind the natural island of Saltholmen. The bridge-builders also suggest making the Sound deeper by making compensatory excavations on each side of the island, and that the bridge piers should be given a better shape than was originally planned. Deepening the seabed by the bridge will maintain the natural rate of water exchange in the Baltic, but it may have unfortunate local environmental consequences. Opponents fear that among other things, the sediments spilled by the excavations will destroy mussel banks and patches of eelgrass, on which both fish and birds graze.
The bridge with Europe that has caused dissension even in the Swedish Parliament.
Hesitant Swedes
The Øresund Bridge has caused a great deal of trouble in Parliament and the Government in Sweden. The Swedes are hesitating to give clearance to build the bridge because of the strength of the opposition to the project. As long as three years ago Sweden and Denmark agreed to link up their two countries by means of a bridge over Øresund. The Danes have already demolished dozens of houses and spent nearly a billion kroner on the motorway between Copenhagen and Kastrup. They are threatening to sue the Swedes if the bridge is not built this time. The Øresund Bridge will be about 16 km long, and will cost some 12 billion kroner from coast to coast. Such a link between Sweden and Denmark across Øresund would fulfil a 100-year-old dream of joining up Sweden with the rest of Europe.In the middle of Øresund lies Saltholmen. But the bridge cannot pass over it because the island is protected by the EU on account of its rich bird-life. The bridge-builders have decided that in its place, an artificial island will be constructed in the Sound. Now the scientists, led by Carstens, have proposed relocating this island to just behind Saltholmen, because there it would present least of an obstacle to the water flow. The problem, however, is that this would affect the Saltholmen birds, which graze just at this spot behind the holm. For this reason, the proposal is being opposed by biologists.
"If, as a friend of the environment, I were to choose the best alternative for Øresund, I would advise against building a bridge over the Sound, and suggest tunnels instead. However, the governments of the two countries have decided that there is to be a rail and road link between their countries, and how much it can cost. A bridge will certainly be least expensive, and my task is to help ensure that a bridge is as environmentally friendly as possible," says Carstens.
The Swedish Water Court's latest demand, made in May 1994, for more precise calculations, is an expression of SwedenΔs inability to act decisively in this matter.