Large-Eddy simulations of a sediment-laden Buoyant jet resulting from Dredgers using overflow

Turbidity plumes are an important topic in the environmental aspects of dredging. The main source of turbidity while employing Trailer Suction Hopper Dredgers is the release of excess water through the overflow shaft. In order to minimise environmental impacts of turbidity in early stages of planning as well as during project execution, turbidity prediction tools are necessary. To this end, numerical modelling tools are the most effective in the prediction of the sea currents and sediment dispersion. The near field plume dynamics below and directly behind the sailing hopper dredgers has always been the weakest link in these predictions, since accurate input of the vertical and horizontal distributions of sediment at the source location are paramount to obtain reliable results at the environmentally sensitive areas further away. In this paper, a Computational Fluid Dynamics model is presented as a tool to determine the three-dimensional flows of water, sediment and air bubbles directly after release from the overflow shaft. A full dredger hull geometry and an actuator disk accounting for propeller action add to the representation of the complexity of the flow. It is shown that the model can reproduce two different cases of overflow plumes measured in the field with fair accuracy.