Numerical Simulation of Near-Field Dredging Plumes: Efficiency of an Environmental Valve

Abstract

Numerical simulations of the sediment-air-water buoyant jet released through the hopper dredgers’ overflow shaft have been performed. The release of sediments into the marine environment due to skimming the excess water from the dredging vessel’s hopper can lead to increased turbidity and adverse effects on the adjacent environment. Base-case simulations have been validated using in situ field observations. Simulations have been performed using the large-eddy simulation technique, which allows including the effect of large turbulent structures on the sediment dispersion. The complex nature of the flow field poses challenges for numerical simulations, such as the presence of propeller jets and three different phases: water, sediment, and air bubbles. The model has been applied to simulate the effect of a so-called environmental valve, which reduces air inclusion. This valve has been used in the past, but its efficiency as a function of the boundary conditions was never analyzed before. It is shown in this article that this type of valve can be very effective in reducing the generated turbidity, but only under given combinations of dredging speed, sediment concentration, overflow shaft diameter and overflow-stern distance.