The effects of irrigation dams on water supply in Ghana

2014

English

Dams are constructed to even-out floods and droughts. This involves storing water when there is more than enough and using it when there is less than enough. The largest dams in the world (the Three Gorges dam (22.5 GW) in China, Itaipu dam (14 GW) in Brazil and Guri Dam (10 GW) in Venezuela) have been built for hydropower generation. Considering dams with a reservoir capacity of over 1 billion m3, Africa counts 54 of such dams with a total reservoir capacity of about 726 billion m3. Of these dams, 20 are multipurpose dams, mainly used for both hydroelectricity and irrigation, 22 are used mainly for hydroelectricity and 12 mainly for irrigation. In Ghana, the Akosombo, Kpong and Bui dams with a combined reservoir capacity of 162 billion m3 are the largest hydropower facilities but Kpong and Bui also have irrigation purposes covering 3,000 and 5,000 ha of land respectively. Some lake shore irrigation activities also take place on the shores of the Akosombo lake. In addition, there are many other large, medium and small dams serving the purposes of irrigation and other multiple uses in Ghana. The largest irrigation dam in Ghana is located at Tono in the Upper East Region, with a capacity of about 93 million m3 at full supply level. Irrigation dams in Ghana have been used mainly in rice and vegetable production. There are over 380 small to medium reservoirs in the three northern regions with surface areas averaging at 6 – 20 ha. Recently, commercial irrigation activities have sprung up where such water facilities are used for growing fruits and other horticultural crops for export, thus generating jobs and income in crop production. The embankment and catchment protection has been a major problem regarding the management of the dams and reservoirs in Ghana. Larger dams can be disruptive to the surrounding ecosystem, both upstream and downstream. In northern Ghana especially, the problem of reservoir siltation limits the benefits from the reservoirs. In the Upper East Region, crocodiles which are considered sacred and protected animals, live in about 27 reservoirs and often make burrows in the dam walls, thus weakening such structures and making them vulnerable to failure during floods. Structural failures also occur due to poor design and construction. For Ghana, nearly 9.44 million animals in 2010 would have consumed up to 22 million m3 of water. This should be equivalent to the maximum safe storage of the Bontanga reservoir in the Northern Region of Ghana. Irrigation dams in Ghana have served purposes other than irrigation and the need for multiple considerations in design cannot be over-emphasised.

Agodzo, S. K.; Obuobie, E.; Braimah, C. A.