摘要
The river Niger is the 3rd longest river in Africa, with a stream length of 4200 km, a drainage basin of 2,170,500 km2 of which 1,500,000 km2 is an active basin, and an average discharge of about 6000 m3/s. The natural variability of its rainfall and discharge is analyzed for several major sub-basins, in the context of the West African drought which has lasted for nearly 40 years, showing two paradoxes: the increase of Sahelian runoff since the beginning of the drought due to land degradation, and the steep decrease of sudanian runoff over the same period, substantiated by the long-lasting decrease of the groundwater tables. Much information about the water resources available in the basin is collected and analysed by the NBA1, which is summarized in this paper including surface water resources, rainfall over the basin, existing and projected dams. The river Niger is deficient in dams to control water, especially in its upper and middle basins. Nigeria has many dams, including large dams, while Burkina Faso has many small dams, but there are only a few dams upstream of the river Niger in Mali/Guinea/Ivory Coast. It is therefore likely that several dams will be built in the Niger basin in the coming years, and several are in the project phase. All of these will have a large impact on the river Niger regime and the environment, especially the Fomi dam which will change significantly the river regime upstream of the inner Delta, inducing an important reduction of the flooded area, and the Tossaye dam on the Saharan border of Mali which could promote a very significant level of evaporation. It is very important before building these dams to take into account the past years variability of climate and river regime.
The river Niger is the 3rd longest river in Africa, with a stream length of 4200 km, a drainage basin of 2,170,500 km2 of which 1,500,000 km2 is an active basin, and an average discharge of about 6000 m3/s. The natural variability of its rainfall and discharge is analyzed for several major sub-basins, in the context of the West African drought which has lasted for nearly 40 years, showing two paradoxes: the increase of Sahelian runoff since the beginning of the drought due to land degradation, and the steep decrease of sudanian runoff over the same period, substantiated by the long-lasting decrease of the groundwater tables. Much information about the water resources available in the basin is collected and analysed by the NBA1, which is summarized in this paper including surface water resources, rainfall over the basin, existing and projected dams. The river Niger is deficient in dams to control water, especially in its upper and middle basins. Nigeria has many dams, including large dams, while Burkina Faso has many small dams, but there are only a few dams upstream of the river Niger in Mali/Guinea/Ivory Coast. It is therefore likely that several dams will be built in the Niger basin in the coming years, and several are in the project phase. All of these will have a large impact on the river Niger regime and the environment, especially the Fomi dam which will change significantly the river regime upstream of the inner Delta, inducing an important reduction of the flooded area, and the Tossaye dam on the Saharan border of Mali which could promote a very significant level of evaporation. It is very important before building these dams to take into account the past years variability of climate and river regime.
