Numerical and Experimental Modelling of Near-Field Overflow Dredging Plumes

Turbidity plumes are an important topic in the environmental aspects of dredging. Turbid sediment plumes can cause damage when they reach environmentally sensitive areas such as coral reefs, sea grass fields and wetlands. 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 research, physical and numerical modelling are used 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 will add to the representation of the complexity of the flow. The goal of the research is to improve the predictions of dredging-induced turbidity in the planning phase. In this way, modifications of the dredging operations can be made in order to reduce the environmental impact.nrpages: 312status: publishe