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It is estimated that 400 to 800 million tons of sediment from the Orange River was discharged from 1968 to April 2005 in this area. In comparison, it is estimated that about 400 million tons of sediment resulted from near-shore and coastal diamond mining during the same period.
The research project, titled Assessment of the Cumulative Effects of Sediment Discharges from On-Shore and Near-Shore Diamond Mining Activities on the BCLME, was one of 75 projects linked to the BCLME, which had received funding to the tune of R65 million through the United Nations Development Programme (UNDP) over the past four years. The BCLME programme aims to pave the way for the three countries of the Benguela - Angola, Namibia and South Africa - to manage the region’s valuable marine and coastal resources, and to strike a better balance between human needs and conservation issues.
The Benguela Current region is situated along the coast of southwestern Africa, stretching from east of the Cape of Good Hope in the south, northwards to Cabinda in Angola and encompassing the full extent of Namibia’s marine environment.
The BCLME programme acknowledges that nature does not heed man-made boundaries - environmental problems occur across national boundaries. As part of this programme, marine scientists and experts from Angola, South Africa and Namibia have pooled their resources for the past four years, working on numerous projects to protect the ecosystem of one of the most productive ocean areas in the world, the Benguela Current region.
CSIR sediment dynamics specialist and leader of the project on sediment discharges from diamond mining, Geoff Smith, says in recent years some diamond mining operations have resulted in the discharge of up to several million tons of tailings at a single site annually.
“Several future mining operations are planned to be of a similar scale. This study was rooted in a concern that cumulative effects, over time and space, may be severe,” Smith explains. The project area covered a section of the Namibian coastline, from the Olifants River (in the south), to Spencer Bay (in the north), and from the high-water mark extending to 40 m in depth.
Other findings included:
• Natural sediment, i.e. from the Orange River and windblown sediment tend to be fine. Most of the sediment discharged from mining, however, is medium to coarse sand. The fine sediment is mobilised by wave action and is transported rapidly, generally northward, by wind-driven and wave-driven currents. This is not the case with coarse mine sediment, which generally results in accretion. Of a total of 361 million tons of sediment (primarily sand) estimated to have been discharged from 1970 to recent years, about 294 million tons or 81% are accounted for by measured accretion of the shore and near-beach region.
• The discharge of large volumes of sand can result in long-term (years to decades) deposition on reefs, which overshadows natural trends. By 2013, an estimated total of about 3 km of rocky inter-tidal and near-shore sub-tidal smothering of reef in the demonstration areas will occur. This estimate is based on measured accretion to date and future accretion based on planned mining rates, on known reef areas. The smothered area comprises only 1-2% of the rocky shore in the Namibian part of the project area. Nevertheless, it is important to verify that the impacted shore does not constitute a unique and important habitat.
Recommendations put forward include that detailed logs should be kept of the hourly/daily rates of all sediment discharges, as well as accurate directional wave measurements and wind data in mining areas.
Consideration should be given to discharging at wave-exposed sites that will result in more rapid dispersion of sediment, as opposed to wave-sheltered sites; while discharge of selective mine tailings into mined-out areas should also be considered. (In Namibia the policy is to discharge tailings into the marine environment, unlike South Africa, where tailings are discharged into slimes dams).
The Benguela Current Commission, representing South Africa, Namibia and Angola, has recently been established and an interim agreement signed. This is hoped to result in continued, meaningful transboundary cooperation in matters relating to BCLME.
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