Evaluation of turbidity generated by cutter suction and grab dredgers

Abstract

Dredging-induced sediment losses into the ambient waters at 15 sites have been evaluated by using a vessel-mounted acoustic Doppler sensor system. The loss rates per unit volume of cutter suction and grab dredging ranges 2.4-13.5 kg m-3 and 2.7-188.9 kg m-3, respectively. The loss rates largely depend on the current speed and grain composition of the dredged material. Mechanical grab dredging after crushing the bedrock covered with sediments generates markedly large release of sediments beyond about 100 kg m-3, which is presumably responsible for the rock fragments preventing the grabs from being tightly closed.