Fluid dynamics of dredging

Abstract

Centrifugal pumps are used for pumping slurry from the dredge cutter head or drag head located in front of the suction pipe inlet to the final placement site or dredge hopper. Cavitation is an important phenomenon that must be avoided on the suction side of the pump that is quantified by the net positive suction head. The settling velocity is important for determining whether the sediment settles to the bottom of the pipeline. There is a critical velocity for the slurry in the pipeline that must be maintained such that the dredged sediment remains in suspension and minimizes contact with the pipe wall to keep friction losses at a minimum. Friction losses and minor losses are calculated and input to the energy equation to determine the system head curve over a range of flow rates. The system head curve and pump head characteristic curve are used to evaluate the dredge pump head and flow requirements needed to satisfactorily transport the dredged sediment to the placement location. A submerged ladder pump is installed on the ladder or drag arm to avoid cavitation, and booster pumps are added along the discharge pipe to ensure the transport of slurry over long distances greater than a mile or 1.6 kilometers.