Bani River
The Bani River is the principal tributary of the Niger River in Mali.<ref>Bani means "little river" in Mande languages. Template:Citation.</ref> The river is formed from the confluence of the Template:Ill and Bagoé rivers some Template:Convert east of Bamako and it merges with the Niger near Mopti. Its length is about Template:Convert.
Geography
The Bani River has three main tributaries: the Baoulé that rises near Odienné in Côte d'Ivoire and passes just south of Bougouni, the Bagoé River that rises near Boundiali in Côte d'Ivoire and the Banifing-Lotio that drains the region around Sikasso. The drainage basin upstream of Douna has an area of Template:Convert, 85% of which lies in southern Mali and 15% in northern Côte d'Ivoire.
The annual rainfall varies across the catchment basin with the southern area in Côte d'Ivoire receiving Template:Convert a year while the northern area around Douna<ref name=douna /> receiving only Template:Convert.Template:SfnTemplate:SfnTemplate:Sfn For the period 1965-1995 the average annual rainfall for the basin was Template:Convert.Template:Sfn The rainfall is seasonal with most of the rain falling between May and October. The maximum rainfall occurs in August.
The discharge of the Bani River is also highly seasonal, with the maximum flow occurring at the end of September and very little flow between February and June. The river enters the Inland Niger Delta north of San and after the annual rains the river floods (the French word crue is sometimes used) and covers the floodplain.
There is a significant inter-annual variation in the rainfall and, as a consequence, in the quantity of water flowing in the river. The drought that started at the beginning of the 1970s led to a very large reduction in the flow and up to the present time the volumes are still much lower than those observed in the 1950s and 1960s. The reduction in the flow of the river was much greater than the reduction in the rainfall. The average rainfall for 1981-1989 was 20% less than for 1961-1970 while the discharge of the river was reduced by 75%. The effect of the reduced rainfall was less extreme for other tributaries of the Niger. Over the same period the catchment basin of the Upper Niger suffered a similar 20% reduction in rainfall but the readings at the Koulikoro gauge station were only reduced to 50% of the earlier values.Template:Sfn Because of the accumulated groundwater deficit, even in a year with high rainfall, the discharge of the Bani River is less than in the wet decades of the 1950s and 1960s.Template:Sfn
Talo Dam
In 2006 the Talo Dam was constructed to irrigate parts of the floodplain to the south of the river near the town of San. Prior to the construction of the dam, these areas were only fully flooded in very wet years, the most recent of which occurred in 1967. The dam is located Template:Convert west of San, Template:Convert downstream of Douna and Template:Convert upstream of Djenné.<ref>The dam is located at Template:Coord.</ref> The dam acts as a weir in that water can flow over the top of the retaining wall. The construction of the dam was highly controversial.Template:Sfn The environmental impact assessment commissioned by the African Development Bank<ref>Template:Citation</ref> was criticised for not fully taking into account the hydrological impact downstream of the dam.Template:Sfn
The retaining wall is Template:Convert high and Template:Convert in length, creating a reservoir with a capacity to retain Template:Convert of water. This volume represents 1.3% of the average annual discharge of the river (over the period 1952-2002 the average discharge was Template:Convert.<ref>A flow of Template:Convert corresponds to Template:Convert per year. Template:Convert is equivalent to Template:Convert/y</ref><ref name=dnh>Template:Citation</ref> A downstream flow of Template:Convert can be maintained during the dry season by opening a sluice gate. From the published information it is unclear how much of the total discharge will be diverted for irrigation and, of the diverted water, how much will drain back into the river. The downstream effect of the dam will be to delay the arrival of the annual flood and to reduce its intensity.
Djenné Dam
In May 2009 the African Development Bank approved funding for an irrigation dam/weir to be built on the Bani near Soala, a village situated Template:Convert south of Djenné.<ref>The village of Saola is located on the left back of the Bani at Template:Coord</ref><ref>Template:Citation</ref> The dam is one element in a 6-year US$66 million program that also includes the building of a dam on the Sankarani River near Kourouba and the extension of the area irrigated by the Talo dam. The proposed Djenné dam will retain Template:Convert of water, significantly more than the Talo dam.<ref>Template:Citation</ref> It will allow the "controlled flooding" of 14,000 ha of the Pondori floodplain (on the left bank of the river to the south of Djenné) to allow the cultivation of rice and the irrigation of an additional 5000 ha for growing 'floating grass' (Echinochloa stagnina know locally as bourgou) for animal feed.
The effects of the dams on the flooding of the Inland Niger Delta downstream of Mopti are expected to be modest,Template:Sfn as the discharge of the Bani is only one third of that of the Niger: for the period 1952-2002 the average flow at Douna was Template:Convert compared with Template:Convert for the Niger at Koulikoro.<ref name=dnh/>
Notes
References
- Template:Citation.
- Template:Citation. Pages 30–31 contain a table dated 2003 prepared by J.R. Patenaude, giving values for the water flow in an average year (assumed to be 125 m3/s or 3.9 km3/y).
- Template:Citation.
- Template:Citation.
- Template:Citation.
- Template:Citation. Also published in French with the title "Le Niger: une Artère vitale. Gestion efficace de l’eau dans le bassin du Haut Niger".