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Okavango Delta Threatened

Plans to build a weir could cause irreversible damage

Botswana`s principal Important Bird Area (IBA), supporting huge numbers of waterbirds, and the world`s largest Ramsar site, the Okavango Delta, could be irreversibly damaged if plans to build a weir on the Okavango River in Namibia go ahead.The Namibian Power Company, NamPower, is investigating the feasibility of generating hydro-electric power by constructing a 6?8 m high weir at the Popa Falls in Namibia or slightly upstream of them. The weir would have a devastating impact by trapping sediment being transported down the Okavango River, an essential element of the ecosystem. This sediment, studies by the Okavango Research Group (ORG) have demonstrated, plays a key role in maintaining the varied and productive nature of this inland oasis. Such damage has often been reported from similar schemes in the past, such as the Kariba or Cahora Bassa Dams and their effect on the Zambezi Delta. The Okavango River brings water and sediment into the system, and these are distributed throughout the swamps by a network of channels. As Professor McCarthy, head of the ORG puts it The channels leak water, but retain the sand. As a consequence, channels have a limited life, and become less efficient in transporting water as sand accumulates, and eventually they fail and are abandoned. New channels form elsewhere in response. This constantly shifting allocation of water to different areas is important because of another interesting feature of the Delta, the high rate of water evaporation in the region, resulting in 98% of the annual floodwater being lost to the atmosphere each year, leaving the previously dissolved salts in the system. The dissolved salts locally accumulate to toxic levels, particularly on islands in the seasonal and permanent swamps. As water shifts elsewhere following channel abandonment, rain flushes out the toxic salts from affected areas, resulting in ecosystem renewal. The constant shifting of channels spreads nutrients and salts over the whole Delta McCarthy explains. Because the sandy sediment is so vital to the functioning of the ecosystem, no structure that will inhibit its movement into the Delta should ever be constructed he concluded.Currently NamPower is undertaking only a preliminary investigation into the feasibility of the scheme, but its potentially far-reaching consequences should not be underestimated. Pete Hancock, BirdLife Botswana

4th July 2014