Effect of off-shore sand dredging on turbidity

Dredging activities carried out in a 30 miles offshore sand pit have been monitored under the INTERREG Beachmed-E EuDREP project (www.beachmed.it) in order to establish the relevance of turbidity production during these kind of works. A run with suction of 4'000 tons of sand, removed from a mine 2.5 m thick, 34 m deep, covered by 30 cm of silt, was monitored by several instruments. During the monitoring, two weak currents co-existed at different depths and with different directions. Produced turbidity, simulated by a 3D finite element model, was well below expectations. Material settled down after approximately 2 hours and it was seen to diffuse for approx. 800 m. Concentration was smaller in the submerged part of the water column than on the surface. No significant deposit of silt in the areas around the pit was observed.