Stability and fate of dredged sediment.

Hopper dredgers often remove fine-grained sediment from navigation channels and release this material at disposal sites into water about 20 m deep. Such operations involving dredgers with a capacity of 703 mSUB3 were studied at two locations in the Great Lakes. Almost all of the sediment released is deposited from a thin, radally spreading, bottom surge in a ring between 50 and 160 m from the point of impact with the lake floor. The layer formed by a single discharge has a thickness of about 3 mm. The minimum radius of a deposit that is formed by sedimentation from turbidity currents is determined by the range of the surge (300 m) and the deposit cannot have side slopes greater than 0.05. These conditions control the capacity of a designated disposal area. The surface layer of the deposit is in contact with the overlying water and may be dispersed. Conditions in mined, submarine pits in New York Harbor favour the containment of dredged sediment. The side slopes and roughness of the pit floors will restrict the spread of the bottom surge. The pits act as traps for fine-grained sediments and the naturally high sedimentation rates would make net erosion of the dredged sediment deposit unlikely. (from Authors' summary)