Environmental impact of port construction: Port of Sillamae case study (Gulf of Finlad, Baltic Sea)

摘要

The aim of the study was to assess and map the location and status of environmentally sensitive areas (valuable marine habitats) near the Port of Sillamae, and to assess the potential impacts from the dredging and disposal operations on the local marine ecology (especially on valuable habitats). The observations and field measurements were carried out there since the time when the dumping site of radioactive substances from the former uranium enrichment plant at Sillamae was in use. The rate of erosion of the narrow separating dam of the dumping site and the velocities of accumulation of shore sediment were assessed in this study. The monitoring of seashore dynamics in recent years has been focused on an area east of the port. While being an attractive recreation area for the local people, that area is characterized by active natural processes. Repetitive measurements are carried out with the aim of monitoring the impact of the port on shore processes, particularly on increasing erosion of the shores. The most recent investigations since 2004 have not revealed any direct impact of the port facilities on shore dynamics. At the same time, changes caused by extremely strong storms of January 2005 or of winter 2006-2007 are evident. Over the last 30 years, the average freezing date has shifted from December to January and ice break-up begins earlier. As a result, the ice-free period, when wave action can freely access the coast, gets gradually longer, and it happens mainly on account of more stormy autumn and winter months. Dredging and disposal operations may have either direct (removal or burial) or/and indirect effects (enhanced turbidity and sedimentation rates, and changes in hydrographic regime) on benthic invertebrates. Thus, the magnitude and direction of the effects depend on the processes involved. The data obtained before, during and after dredging and disposal revealed the re-establishment of directly affected communities following a year after the cessation of disturbance. The results of special monitoring program concluded that the environmental impact of the dredging operations on the benthic communities was minimal to moderate. Using the results of hydrodynamic modeling of the area at the Port of Sillamae, the behavior of suspended sediment plumes from dredging and disposal of concrete material was modeled using FRESCO high resolution, σcoordinate, non-hydrostatic, baroclinic model system. Wind waves are calculated by narrow directional approximation model and the turbulent mixing based on the k-ω turbulence closer model. Numerical experiments have been performed for four nested marine basins with different space resolution. In the highest resolution nested domain the horizontal grid size was approximately 1/10 of nautical miles. Modeling results included spatial information on suspended sediment concentrations and sedimentation rates.