Determination of the sediment source flux from dredging by CFD simulations

---

Lynyrd de Wit, Bram Bliek, Cees van Rhee

Friday 3 july 2015

11:15 - 11:30h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 15B. Sediment - Transport

---

The environmental impact of dredging works depends on the frequency, duration and intensity of the stresses like turbidity and sedimentation caused by dredging and on the resilience of an ecosystem. Turbidity and sedimentation depend on the amount of sediment spilled from a dredger and on the sediment spill mixing and settling behaviour. 3D CFD (computational fluid dynamics) simulations are used to simulate the near field mixing and deposition of TSHD (trailing suction hopper dredger) overflow sediment plumes near and under the TSHD keel. Near field mixing influences the source flux of sediment available for dispersion towards areas at kilometres from the dredging site. In this paper, simulations of TSHD overflow plumes are compared with field measurements of TSHD overflow plumes. The CFD model is able to reproduce the plume descend towards the bed, plume suspended sediment concentration and plume flux in a satisfactory way. For a detailed and accurate determination of the far field source flux of suspended sediment from a TSHD, measurements or detailed near field CFD simulations are necessary. But in this paper results of a parameter study are summarised which can be used to get a reasonable estimate of the far field source flux of suspended sediment from a TSHD without the computational burden of heavy near field CFD simulations. Finally, the CFD model is used to test the efficiency of adjustments to the TSHD overflow outflow to minimise the environmental impact.