Tuesday, June 10, 2008

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Lake Al Wahda

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The second-largest dam in Africa and the largest in Morocco, Al Wahda Dam has a capacity of 9 714 million m3. Located in the Gharb Plain, the dam was built in 1996 to reduce devastating flooding along the Ouergha River, provide water for irrigation, and generate hydroelectricity.

Since completion of the dam, flooding has decreased by 90 per cent, potential irrigation has increased by about 110 000 ha, and hydroelectricity production has reached approximately 400 Gwh per year. The electricity produced by the dam allows the Moroccan government to avoid burning 140 000 metric tonnes of fossil fuels per year, thereby reducing greenhouse gases released into the atmosphere.

However, natural and human-caused erosion is filling the dam with silt and threatens its long term sustainability. It is estimated that the reservoir loses 60 million m3 of capacity each year to siltation. In addition, these sediments trapped in the reservoir do not reach the coastal estuary, which has altered the balance of siltation and erosion along the coast in favour of erosion. Another potential threat to the dam's future viability is suggested by climate and hydrological modeling, which predicts that a 1° Celsius increase in average air temperature between 2000 and 2020 might reduce runoff to the Al Wahda Dam by 10 per cent.

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