Abstract by author:
The major impacts of mining on the physical environment are identified to be: (a) Direct disturbance of sediments caused by excavation, (b) Increased turbidity, (c) Seabed smothering, (d) Changed particle-size distribution of mined areas due to the selective entrainment of fine sediment fractions
Furthermore, numerical modelling of the tailings plume indicate the following: (a) A tailings discharge at sub-surface depths and at pressure will greatly increase the rate at which the sediment settles to the sea floor, whereas disposal discharge above the sea surface will lead to a slower rate of settling. Sub-surface tailings disposal will consequently limit the extent of the mixing zone (area of impact) as well as limit the area affected by the tailings disposal. (b) The maximum concentration of total suspended solids (Turbidity) reached in the upper water column will be between 50-100 mg/1. Close to the sea floor maximum concentrations are predicted to vary between 1, 000 to 10, 000 mg/1. (c) During mining, the sediment plume mixing zone, defined as the area with a concentration of suspended solids of more than 10 mg/1, is predicted to be less than 300 x 300 m. (d) During normal current conditions, the gravel and sand fractions will settle within 60 m of the point of disposal. The silt and clay fractions will, to a greater extent, be carried away from the mined areas
The findings of the dissertation indicate that marine diamond mining should not have a major impact on the physical environment, though it is acknowledged that further work needs to be done in order to properly assess the significance of the impacts that are identified. The dissertation recommends an environmental monitoring programme, and ways of optimising the management of the mining operation so as to cause the least damage possible. By following these recommendations, the impacts of the mining operations will be kept to a minimum, whilst valuable environmental data will be obtained that can help improve the understanding of these impacts
