Tunnel excavations will not affect bathing water

When dredging in the seabed, fractions of seabed material will inevitably be spilled in the water and reduce transparency in the vicinity of the dredging. However, there are two factors that have led experts to conclude that the bathing water around the Fehmarn coast will not be affected to the extent that it will impact on bathers.

First, currents in the Fehmarnbelt area generally move in a west-east going direction, i.e. parallel to the coastline. This means that only during dredging close to the shore will the sediment plumes possibly reach the northern beaches of Fehmarn.

Secondly, the FEHY study concludes that the water in Fehmarnbelt is normally unclear during high winds as a result of seabed material being naturally whirled up. Measurements carried out by FEHY in 2009 and 2010 close to the coast of Fehmarn show that the amount of re-suspended natural seabed material in the water may be up to 100 mg/l, which is significantly above the visibility limit.

Only along the coastline close to the alignment, where there are no tourist areas, can the seabed material from the dredging work reach a level that corresponds to the natural background level of approx. 10mg/. However, as the background level in itself means that the water is relatively unclear, the additional material from the dredging operations will not significantly change the water quality.

“Dredging operations for the fixed link will not intensify the natural process of re-suspension and will not adversely affect the quality of the bathing water at Fehmarn. Moreover, the proportion of re-suspended dredging material will be so limited that we don’t expect it to be visible as it will mix with the natural materials”, says Anders Bjørnshave, Environmental Manager, Femern A/S.

In cooperation with the contractor, Femern A/S will plan the dredging operations in detail so as to minimise the near-shore dredging work during the peak bathing season.

The amount of spilled material from dredging in the seabed depends on the machinery used. The spilled material will disperse into the surroundings and then be diluted as a result of three factors: the current, water mixing and the settlement of particles on the seabed. According to the studies, all sediment particles from the dredging operations in Fehmarnbelt will end in the natural settling areas in the region.