Physical and numerical investigation of the hydrodynamic implications of aquaculture farms

Abstract

Effects of long-line mussel farms on flow structure have been studied in this paper. Experiments in a tidal basin facility on Froude scaled long-lines were used to better understand how droppers impact flows. The observations demonstrate that flow speeds within the long-line is reduced by 25–30% from ambient, and material transport to downstream droppers is significantly reduced. These results suggest that neglecting the physical barrier imposed by the aquaculture installations will result in a considerable overestimation of nutrient supply to the bivalve and thus an overestimation of carrying capacity. An existing two-dimensional depth integrated model has been refined to better predict hydrodynamics and solute transport within suspended aquaculture farms. The numerical model has been refined to include both the form drag imparted by the individual mussel droppers and the blockage effect that the suspended canopy presents. Additional turbulent kinetic energy production is incorporated into the two equation k−ɛ closure model. Data collated in the laboratory was used to calibrate and validate the numerical model. It has been demonstrated that predicted velocities and solute transport correlate well with experimental results. The numerical model was applied to a designated aquaculture site on the West Coast of Ireland, Casheen Bay. The effect of long-lines on hydrodynamics and solute transport was analysed. Flushing studies were used to study particle renewal terms in the embayment. Several flushing characteristics were calculated, including, the average residence time and the exchange per tidal cycle coefficient. The viability of using relatively simple flushing studies formulae to assess the development potential of small scale aquaculture projects is discussed.