ASR - A Global Partner for the Sustainable Management of Coastal and Marine Resources

Mossel Bay

Location: Mossel Bay, South Africa

Type of Project: Numerical Modelling, Aquaculture

Client: Irvin and Johnson Limited

ASR Projects- Mossel Bay

(Left to Right) Dispersion and dilution of nitrate in typical low, average and high energy conditions at Mossel Bay.

Project Overview:

ASR Limited was commissioned on behalf of Irvin & Johnson Limited, to quantify the hydrodynamics of Mossel Bay and to investigate the dispersion of water-borne pollutants from a proposed caged-fish farm.

Project Outcomes:

To perform this investigation, ASR first conducted a field data campaign to collect relevant site specific data on wave heights and currents. This data was used to calibrate a numerical model which was then be used to make predictive assessments of pollutant dispersion patterns. Analysis of the data indicated that surface water current circulation in Mossel Bay is dominated by winds and tides.

As part of the study, ASR also had to determine the quantity and composition of the fish waste produced from the farm. This required an accounting of the mass of fish present in the cages and then determining the amount of waste produced per kilogram of food provided.

The study modelled the dispersion of nutrients from a fully operational fish farm for a range of wave and wind conditions. By using the worst case scenario of a fully stocked fish farm, the modelling results could be scaled down for the fish farm operations under less intensive conditions. The nutrient dispersion was modelled for low, average and high energy conditions as well as for the conditions measured during the instrument deployment.

The study results indicated that the hydrodynamics around the proposed fish farm were likely to be sufficient to disperse the dissolved waste from the fish cages.

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