Climate Change and the Management of Natural Systems in Cameroon

9. Climate Change and Management of Physical Barriers in Riverine Systems

191 Chapter Nine Climate Change and Management of Physical Barriers in Riverine Systems Summary The construction of large dams on riverine systems is a subject of great controversy. Environmental effects have been well documented. The basic point at issue is whether their benefits outweigh their environmental and social costs. This chapter makes an assessment of the human-related physical barriers constructed on riverine systems in Cameroon and identifies the conflicting resource development and management goals which may arise in the face of increasing global warming and the use of dams for development purposes. It reviews the ecological implications of dams and man-made lakes and establishes how dams can conflict with measures to enhance the resistance and resilience of riverine ecosystems to climate change. The chapter finally concludes that there is a needed change in paradigm to the use of a series of smaller dams on rivers. These could provide most of the benefits at lower investment cost, greatly reduce social costs and environmental costs, and enhance the adaptations of riverine ecosystems to global warming. Key Words: Dams, man-made lakes, ecological effects, ecosystem connectivity, aquatic life, aquatic habitats, sustainable management. Introduction Far back into history, man has undertaken the modification of rivers mainly to ensure ready and reliable availability of water. Rivers and streams have been dammed to store water, sometimes for single use but increasingly for multi-purpose development projects. It has been estimated that there are about 10,000 artificial lakes with surface area exceeding 1,000 km2 , scattered round the world. In addition, millions of small rivers and streams have been dammed and there are so many small impoundments that it is almost impossible to gauge their numbers (Obeng, 1979). 192 In Africa these dams play an important role in rural water supply for domestic and agricultural use. There are more than 20,000 small dams in the Central African Republic, about 12,000 in the Nyanza Province of Kenya, and many in Northern Ghana, Sudan, Nigeria and Uganda. Such small impoundments are also a common feature of China, and in India almost all major and minor rivers have dams on them. Cameroon has also constructed several dams. The chapter assesses the human-related physical barriers and alterations to hydrology as a basis for resolving development and resource conservation conflicts with increasing human water demand and global warming. It reviews the environmental implications of dams and man-made lakes as opposed to natural water bodies and identifies the scope for building the resistance and resilience of aquatic systems in the management of these structures with increasing global warming. Dams and Reservoirs Hydro-electric power in Cameroon is obtained from water. The largest power station is built at Edea on the Sanaga River fall where a dam 1600 metres high has been built to hold back water. It is the third largest dam in West Africa, the first two being Kainji on the Niger River in Nigeria and Akosombo on the Volta River in Ghana. These two stations each generate 750,000 kilowatts, while Edea between 150,000 to 250,000 kilowatts (Ngwa, 1979). To generate electricity, a dam is built across a river on top of the fall. Below the fall, a power house in which a large turbine and electric generators are installed. Water is directed through huge steel pipes from the reservoir above, behind the dam down into the power house, where it falls into the blades of the turbine, causing them to rotate. This turns the electric generators and so produces electricity (Figure 1). The speed at which the turbine revolves is dependent on the height of the fall, and the amount of water in the fall and the amount of water in the reservoir. This means that the level of water in the reservoir must be kept high and constant so that there is no drop in the amount of electricity produced. It is for this reason that two additional dams – the Mbakaou and the Bamendjin dams were built on the Djerem and Nun Rivers, to increase the water in the Edea station during the dry season. The capacity of the Mbakaou dam is 2.9 milliard cubic 193 metres of water while that of the Bamendjin is 1.8 milliard cubic metres of water (Ngwa, 1979). See Figure 1. Figure 2 presents the Bamendjin dam. It is 245 m long and 17 m high and is built on the...