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The Lake Chad basin

The Lake Chad basin, located in Northern Central Africa, covers almost 8% of the continent and spreads over seven countries (Map 3 and Table 16).

Table 16: Lake Chad basin: areas and rainfall by country

About 20% of the total area of the Lake Chad basin, or 427500 km², is called the Conventional Basin (42% in Chad, 28% in Niger, 21% in Nigeria and 9% in Cameroon), which is under the mandate of the Lake Chad Basin Commission. This commission was created in 1964 by the four member states with the objective of ensuring the most rational use of water, land and other natural resources and to coordinate regional development.

Rivers and discharges

Lake Chad is a terminal depression with the seven basin countries grouped around it, of which four are in direct contact with the lake: Nigeria, Niger, Chad and Cameroon.

In Nigeria, two sub-basins drain into the lake:

• the Yedseram/Ngadda sub-basin to the south;
• the Hadejia/Jama'are-Komadougou/Yobe sub-basin to the north.

The Yedseram River and its tributaries rise in the Mandara hills and it 'loses' most of its water while flowing northwards through a 7-km-wide flood plain. Further downstream, together with the Ngadda River it forms an 80-km² swamp and does not maintain a definable water course to the lake.

The Komadougou/Yobe River is the border between Nigeria and Niger over the last 300 km. Upstream of the confluence of the Hadejia and Jama'are rivers the Hadejia-Nguru wetlands (fadamas) start. These cover a total area of about 6000 km² and a water surface area of about 2000 km², but dam construction and increasing water abstraction for irrigation purposes upstream since the 1980s contribute to the fact that large areas of the floodplains are becoming increasingly drier [172]. All rivers crossing this area lose flow as a result of evaporation and evapotranspiration and infiltration to recharge the groundwater. The inflow varies between 1 and 1.8 km /year, the outflow between 0.6 and 0.7 km /year. When the inflow is more than 2 km³/year, the outflow gradually increases to 1.2 km³/year. Upstream the peak flow is at the end of August and rises and falls rapidly reflecting the sporadic nature of heavy rainfalls and the largely impermeable strata. Downstream the peak flow is in January. The flow into Lake Chad is about 0.5 km³/year. In Niger, in addition to the border Komadougou/Yobe River, there are the Koramas in the south of the country close to the border with Nigeria. These are seasonal rivers and their flow does not reach Lake Chad.

In the north, far away from Lake Chad, is Algeria. The country possesses few renewable water resources. To the east is Sudan with Wadi Kaya and Wadi Azum, both seasonal wadis with spate flows that originate on the western slopes of the Jebel Marra. Their alluvial aquifers could deliver about 0.08 km /year of water of excellent quality [30].

To the south is the Central African Republic, a humid country with enormous water resources. The sources of the Chari-Logone Rivers are located in the Central African Republic and the quantity of water leaving the country to Chad was about 33 km³/year in the period before the 1970s, but fell to 17 km³/year during the 1980s [29].

The amount of water crossing the border from Cameroon to Chad varies between 3 and 7 km/year. More to the north, the Logone River forms the border between Cameroon and Chad until N'Djamena where it flows together with the Chari River which then continues north to the lake. These rivers have a tropical regime with a single flood occurring at the end of the rainy season, which lasts from August to November. They are characterized by irregular inter-annual flows and by their large water 'losses', estimated at about 5 km³/year, due to flooding of the adjacent Ya�r� lowlands in Chad and Cameroon. The largest area flooded covers about 8000 km² and is used for pasture, fishing, flooded rice production and flood recession cropping. In order to expand the Ya�r� area, two sites for regulatory dams have been identified on upstream branches of the Logone in Cameroon and Chad. However, this would be to the detriment of water uses for hydro-electric power generation and for irrigation outside these Ya�r� lowlands [86].

The rivers outside the Chari-Logone basin in Chad have flash floods during heavy rains and negligible flows the rest of the time, like the Batha River. This regime seriously limits irrigation development.

The Chari-Logone rivers, with 38.5 km³/year, contribute for about 95% of the total inflow into Lake Chad. In recent history the area of Lake Chad has varied between 3000 and 25000 km², with a variation in its level of over 8 metres and a variation in volume of between 20 and 100 km³. The total inflow in recent times has varied between 7 km³/year (1984/85) and 54 km³/year (1955/56) [40]. Due to the lowering of the lake level, ideas have been put forward to replenish the lake with water from the Congo/Zaire basin through the construction of a 2400 km-long canal, but for the time being this is impractical on technical, economic and political grounds [86].

Irrigation potential and water requirements

In Nigeria, the planned irrigation under the existing water management works is estimated at 185000 ha, of which only about 32000 ha have been completed and irrigated. The total identified potential has been evaluated at 356000 ha. However, even the complete development of the first 185000 ha would already create water shortages. In addition, Nigeria plans the development of 146000 ha of fadamas, of which 20000 ha in the upper part, 27000 ha in the middle part and 99000 ha in the lower part [172].

In Niger the irrigation potential in the Koramas sub-basin has been estimated at 8000 ha, in the downstream Kadougou/Yobe river valley and around the lake at 40000 ha [167]. In the northern part of the country there are some oases, but no information on them is available.

The irrigation potential in the Algerian part of the basin is estimated to be 0 ha [*]. The irrigation potential in Sudan is about 4000 ha [30].

The irrigation potential for the whole of the Central African Republic is estimated at 1.9 million ha, but no details are available on location [17]. About one-third of the country is situated in the Lake Chad basin, the remaining two-thirds being in the Congo/Zaire basin. A first approximation of the part of the potential in the Lake Chad basin is estimated at 500000 ha [*]. This would require 8.25 km³/year of water, which is about one-quarter to a half of the total quantity of water leaving the country to Chad, depending on the period of reference.

For Chad, the irrigation potential has been estimated as follows [21a]:

Table 17: Irrigation potential and water requirements in the Lake Chad basin in Chad

In addition, there are an estimated 90000 ha of oases in the Saharian zone, but most probably to be irrigated by non-renewable groundwater [85].

The irrigation potential for Cameroon is estimated at about 100000 ha in the Lake Chad basin [*]

Table 18 summarizes the figures for the whole of the Lake Chad basin and for the Conventional Basin.

Table 18: Lake Chad basin: irrigation potential and water requirements, result of the country studies

At present, out of a potential of over 1.1 million hectares in the Conventional Basin fewer than 100000 ha are actually irrigated. However, due to the lowering of the level of Lake Chad in recent history, every new irrigation development has to be studied very carefully. Already in 1980 the maximum development was estimated at fewer than 400000 ha by a UNDP-financed study [38]. The recently prepared master plan for the Conventional Basin proposes to concentrate future developments on small-scale projects.

Taking into consideration the above aspects, the total potential for the whole of the Lake Chad basin is presented in Table 19.

Table 19: Lake Chad basin: irrigation potential, water requirements and areas under irrigation, result of the basin study

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