Modelling Dynamic Plume Behaviour
Type:
Presented during:
CEDA Dredging Days 2021
Authors:
J. Gundlach, A. Zorndt, J. Visscher, and T. Schlurmann
Abstract
One of today's major challenges for governmental authorities is the designation of disposal areas in maintenance dredging operations including an assessment of turbidity-induced processes in the designated dumping site. Regional prediction of turbidity and advection of turbid plumes are typically based on numerical far field models. For process-based representation, far field models may also be coupled with near field models.
This study presents a simple near field model for mimicking involved processes and estimating the dynamic plume behavior of disposed material.
Regularly applied far field models for coastal or estuarine environments, such as Delft 3D, Telemac or UNTRIM, are only poorly capable to model the involved processes and effects of sediment disposal by means of directly placing the dredged material on the seafloor. A more accurate approach follows the integration of the unique sediment distribution including the dumping and spreading of material in the water column in order to adequately obtain a process-based simulation of disposed material. One of the most applied state-of-the-art models considering these processes is the Short Term FATE (STFATE) model, developed by the USACoE in the 1970s and further elaborated in the 1990s. By adapting the methods and equations of STFATE, the present study develops a modification and implementation of a near field model in Matlab. This modeling approach divides the dynamic plume behavior into two phases: First, the descent in the water column, where mass, momentum, buoyancy, solids and vorticity are conserved. Second, the impact of the sediment plume on the bottom, where its motion is approximated according to the conservation of energy. With the start of passive plume behavior, the model is terminated and provides sediment concentrations for the water column and the amount of solids at the bottom either settled or in suspension.
The developed Matlab model simulates the near field behavior of disposed fine sediments and may provide input for an implementation in far field models.
Keywords: Sediment Disposal, Dynamic Plume Modeling, Matlab.