Monday, June 9, 2008

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Challawa Dam

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The Challawa Dam in Kano State, Nigeria, was built to control flooding caused by seasonal and variable rainfall and to support irrigation. It also supplies water to Kano, Nigeria’s third-largest city with a population of seven million. The Challawa River feeds into the Hadejia River, which then flows into the Hadejia-Nguru wetlands. Local rainfall peaks in August, with a subsequent dry season lasting from November to April. This rainfall pattern makes water levels in the Hadejia-Nguru wetlands highly seasonal.

The Challawa Dam has tamed highly seasonal downstream flooding at the expense of the Hadejia-Nguru wetlands. The combined effect of drought and the dam reduced the extent of seasonally flooded land from 300 000 hectares in the 1960s to between 70 000 and 100 000 hectares in recent years. Such severe reduction of the annual flooding extent has put the wetlands at risk and reduced the economic and environmental benefits they provide, including agriculture, cattle, fuelwood, fish, shallow aquifer recharge, and habitat for migratory and local bird species.

The economic impact of the Challawa Dam (and the Tiga Dam further upstream) has also been negative, eventually incurring millions of dollars more in losses than were yielded in benefits. In addition, while flood control was among the intended benefits of the dam, heavy rains often cause serious flooding above the dam.
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