Quantification of hydrodynamic changes induced by an offshore mussel aquaculture farm using COHERENS (Part 2)

The goal of this numerical study is the quantification of hydrodynamic changes (especially sea currents) induced by an offshore aquaculture farm similar to that of the industrial project “Westdiep Sea Farm”. To do that, a parameterization of the impact of longlines and droppers on hydrodynamics has been included in the 3D COHERENS hydrodynamic model and the impact of several configurations of the aquaculture farm on currents and bottom shear stress has been estimated in a simplified test case. In this previous internship project, a numerical study to quantify the impacts of an offshore aquaculture farm on hydrodynamics processes has been performed. To do so, a new module has been developed in the COHERENS model to compute the drag forces exerted by the droppers and then this module has been applied on a simplified case study, i.e. a modest farm with up to 40 longlines of 104 droppers and located in a straight open channel of 500 m width and 2 km length. The simulations show that, in all configurations tested, the presence of droppers significantly changes the hydrodynamics of the channel. Particularly, analysis of the bottom shear stress variations allowed to conclude that the presence of a modest offshore aquaculture farm could modify the erosion/sedimentation pattern around the farm, leading, for example, to a risk of destabilization of the neighbouring sandbanks, which would justify the implementation of an environmental monitoring program. Nevertheless, this previous work remains a preliminary study and many simplifications have been applied in order to obtain results in the given time. This second work (Part 2) will allow to refine the physics of the test channel in order to make it more realistic and to obtain results more faithful to the hydrodynamic reality in the North Sea. In this report, different sensitivity studies will be carried out mainly for the first phase of the project. Several metrics will be illustrated. Then, comparisons between the different phases will be made.

Report

This report was written as a continuation of a report produced during an end-of-master internship at RBINS.