Environmental impact associated with the dumping of dredged material at sea. A study for the limassol port extension works

The construction of major marine works is frequently associated with the need to relocate large quantities of material. Relocation at sea is associated with a number of environmental impacts. For non-contaminated silty/clay material main environmental effects include blanketing of the sea bed and increase in turbidity, or reduction in the clarity of water. Blanketing of the sea bed has a harmful effect on the marine life whose ability to recolonise the new material is doubtful. The importance of marine life can be evaluated in relation to the number of species and specimens living on the sea bed. Measurements reveal that there is a reduction in the number of species with increase in depth. The dumped material that covers the sea bed, and therefore affects adversely the marine life, has less impact the greater the water depth. The increase in turbidity, associated with the suspended soil material in the water, although temporary, it nevertheless has a potential impact on the tourist industry. Places which are popular with tourists because of the clarity of their waters, might have adverse publicity if the turbidity increases to noticeable levels. Turbidity levels depend on the current direction and speed, the rate of mixing (dispersion coefficient), the size and density of the dumped material and the method of dredging and disposal. Predictions of expected turbidity levels can not therefore be made with accuracy or great confidence if the above parameters are not well known. Sensitivity analyses can however be made in order to predict the range of values of the expected turbidity levels. The impact on marine life and the increase of turbidity can be reduced by dumping the dredged material in deep water and at great distance from bathing beaches. This measure is associated with adverse financial implications. The optimum relocation site is one at which the total cost of both the environmental damage and the relocation cost is minimum.