Environmental impact assessment study of the new offshore dumping sites for Šventoji port in Lithuania

Transcription

1 Environmental impact assessment study of the new offshore dumping sites for Šventoji port in Lithuania Introduction Summary In 2003 Lithuanian Ministry of Transport initiated the preparation of feasibility study on possible reconstruction of small fishery port located in Šventoji, Lithuania. The results of the study justified the necessity to rebuild the port and use it mainly for the recreational boating purposes. Vision of the Šventoji port reconstruction One of the main phase of the port reconstruction is sediment dredging. It will be necessary in order to clean the eastern and western basins of the Šventoji river, form the basin and new entrance channel. According to the available results during the development of the new entrance channel and the outer harbor particular amount of dredged sediments could be used for the nearshore nourishment purposes. Another amount of dredged sediments could be dumped at sea, however currently there are no suitable places for the offshore dumping in the vicinity of the port. Proposition of new offshore dumping places should be implemented according to the Lithuanian Law on the Environmental Impact Assessment (EIA). The EIA study of the new offshore dumping sites for Šventoji port was implemented within the South Baltic programme funded ECODUMP project. The main goal of the EIA study was to propose alternative locations of new offshore dumping sites for the future disposal of sediments, planned to be dredged from the Šventoji port area. The study has summarized available data on sediment composition, geological structure of the Šventoji port basin, hydrological and hydrodynamical processes, environmental components and ongoing/planned sea use.

2 Available data on the amount of sediments to be dredged According to the preliminary calculations completed in 1989 during the design of 45 meters depth yacht port following amounts of sediments will be dredged from various parts of the Šventoji port. In the western basin 46.7 thousand. m 3 ; In the eastern basin 25.0 thousand. m 3 ; from the mouth of Šventoji river 81.4 thousand. m 3 ; from the internal navigational channel 107 thousand. m 3 ; from the outer entrance channel thousand. m 3. Total foreseen amount thousand. m 3 of sediments, which include: sludge (mud) 69 thousand. m 3 ; loam 7 thousand. m 3 ; sand thousand. m 3. Lithological types of sediments in Šventoji port basin

3 Analysed alternatives The EIA study has examined four potential places for the new offshore dumping sites. All the alternatives are located in the territorial waters of the Lithuanian part of the Baltic Sea on the southeastern slopes of KlaipėdaVentspils plateau, which is characterized by slightly hilly terrain. Four alternatives of the offshore dumping places for Šventoji port 1st dumping site in a distance of 7 km to the west from Šventoji port entrance with the depth of m. The site is selected in the coastal zone in the area of Klaip_edaVentspils plateau morainic relief in the countersunk formed by recent marine erosionaccumulation processes. 2nd dumping site in a distance of 10 km to the west from Šventoji port entrance with the depth of m. The site is located in the deep formed in the surrounding of relict derivatives.

4 3rd dumping site in a distance of 12 km to northwest from Šventoji port entrance with the depth of m. The site is in the neighborhood of west edge of morainic relief with 20m isobath. 4th dumping site in a distance of 15 km from Šventoji port entrance with the depth m. In this sea bottom area southern end of the KlaipėdaVentspils plateau borders with northern slope of the Gandsk deep. Alternative places for the disposal of sediments were selected according to the current and planned uses of the sea, environmental conditions, geologicalgeomorphological structure of the sea bottom, lithodynamic conditions, distribution of ecosystem components, composition and pollution level of the sediments in Šventoji port in order to minimize the impact on marine environment. Current and planned sea uses Selection of the location of new offshore dumping areas needs to consider other activities at sea. Following activities were analysed: navigational issues, nearshore fishery, engineering uses of the seafloor, potential oil rigs, areas of cultural importance (including wrecks), military areas (former minefields, etc.), protected areas, recreational zones. Navigation

5 Commercial fishing areas Engineering uses of the seafloor

6 Potential oil rigs Areas of cultural importance

7 Military exclusion zones Areas of biological importance

8 Reef habitats Characteristics of dredged material and behavior after the dumping Dredged sediments in each barge were considered as a mixture of sediment types with the composition and grain size described below. It was assumed that the whole amount of dumping material is discharged in each of the dumping sites described above. The whole amount of dredged sediments (79000 m3) was evenly distributed for the dumping through the period of one year using average capacity of barge equal to 700 m3. In the numerical simulations we assumed a number of three ship passages per day. Fractions, mm MUD SAND < >2 % m³ Conc Tons The potential spread of dumping material (bedload, suspended) dredged in the waters of Šventoji port for four alternative dumping sites using the 3D sediment transport model SHYFEM. Modelling involve

9 the spread of dredged sediments during disposal and after the sediments being settled with given scenario of multiple dumping events for one year. Maximum SURFACE SSC Maximum BOTTOM SSC TOTAL DEPOSITION

10 Characteristics of the disposal sites The transport of the discharged materials depends on the circulation features in the dumping site areas. Therefore general circulation patterns in the investigated areas, obtained averaging the numerical results over the oneyear long simulation were observed. Geological and geochemical characteristics of surface sediments in the alternative dumping areas were analysed according to the results of new survey.

11 Alternative Station Horizont Sediment type Concentration, mg/kg Cu Pb Zn Ni Cr Cd Hg Contamination class SD1 Pebbles 1 SD2 Pebbles SD3 05 Fine sand 1,15 2,51 20,9 4,7 5,0 <0,05 <0,01 I 2 SD4 05 Coarse sand 2,6 4, ,64 6,8 <0,05 <0,01 I 3 SD5 05 Till 16,5 10,1 64,6 25,9 34,2 0,26 0,03 Not classified SD6 08 Medium sand 0,94 3, ,22 5,85 <0,05 <0,01 I 4 SD7 05 Coarse sand 9,26 8,86 50,4 14,6 22 0,20 0,02 II SD8 08 Fine sand 2,77 4,87 19,5 4,22 13,2 <0,05 <0,01 I Analysis of bottom relief for the each dumping area was completed with the help of multibeam echosounder.

12 Alternatives summary Alternative 1 Distance, km 7.1 Depth, m Types of sediments suitable for dumping Sand, till Type of dumping Concentrated Advantages Close to the port Improving sediment balance in the nearshore Disadvantages Compensations for fishermen needed Probable impact on reef habitats Probable impact on fish migration Sand, till Concentrated Close to the port Improving sediment balance in the nearshore Close to engineering uses (cables) Compensations for fishermen needed Probable impact on reef habitats Close to the protected area Sand, till Concentrated Minimum conflicts with other sea uses Limited site capacity Probable impact on reef habitats Limited site capacity Minimum conflicts with other sea uses Sand, till, mud Mixed: concentrated/dispersive Favourable sedimentary conditions Far from the port Large capacity of the site