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The Congo/Zaire River basin

This basin is the largest river basin of Africa, covering over 12% of the continent. It extends over nine countries and the largest area is in Zaire (Map 7 and Table 35). It is one of the most humid basins of Africa.

Rivers and discharges

Its sources farthest away from the mouth are located in Zambia, one draining to Lake Tanganyika, estimated at 2 km³/year, and one to Lake Mweru, where the flow at the outlet is estimated at over 41 km³/year. No information is available about the sources originating in Tanzania and flowing into Lake Tanganyika. The flows in Burundi drain mainly into Lake

Table 35: The Congo/Zaire River basin: areas and rainfall by country

Tanganyika and those in Rwanda into Lake Kivu, which is connected with Lake Tanganyika through the Rusizi border river between Zaire, Rwanda and Burundi.

In the north about two-thirds of the Central African Republic lie within the Congo/Zaire basin. It is a humid country, with many sources flowing into the Oubangui River, a major tributary of the Congo/Zaire River and forming the border between the Central African Republic and Zaire. At Bangui, its discharge is estimated at over 126 km³/year. The tributaries originating within Cameroon flow either to the Central African Republic in the east or to Congo in the south, where the discharge of the Sangha River at the border is over 52 km³/year. The Oubangui tributary forms the border between Congo and Zaire, then flows into the Congo/Zaire River which continues to be the border until the far south-west where it enters Zaire. Many other tributaries originate in Congo.

To the south is Angola, where the Kasai River, another major tributary, originates together with many other smaller tributaries.

Zaire has a very dense hydrographic system (Figure 6). The discharge of the Congo/Zaire River reaching Kinshasa and Brazzaville is about 1269 km³/year, which is equal to 32% of the renewable water resources for the whole of Africa. The river then continues to the south-west and forms the border between Angola and Zaire before flowing into the sea.

Irrigation potential and water requirements

It is difficult to find reliable estimates of the irrigation potential of the very humid countries, like Zaire, the Central African Republic, Congo or Angola. In fact, neither water nor land is a limiting factor to agricultural development in these countries and other factors have to be taken into account in order to have some kind of realistic estimates of potential. Methods for assessing irrigation potential in these countries are described below.

For Zambia a national water master plan exists [212]. The identified irrigation potential in the Congo/Zaire basin in Zambia has been estimated at 101000 ha, of which 15000 ha by renewable groundwater and 20000 ha of wetlands (dambos).

There is no detailed information on the irrigation potential in Tanzania. The Luichi Delta near Kigoma on the shores of Lake Tanganyika contains a large area of good land which is seasonally flooded and unusable. Reclamation of 3000 ha has been proposed by means of a flood control dam and improved drainage. No irrigation has been proposed in this area [199].

For Burundi, about half of which is located in the Congo/Zaire basin, the irrigation potential has been estimated at about 105000 ha in the basin, of which 75000 ha for fully or partially controlled irrigation in the plains and the remaining area consisting of valley bottoms (bas-fonds) [78]. About 25 % of Rwanda is in the Congo/Zaire basin and the irrigation potential here is estimated at 9000 ha, mainly consisting of valley bottoms [176].

Of the total irrigation potential of the Central African Republic, evaluated at 1.9 million hectares [50], about 1.4 million hectares are estimated to be within the Congo/Zaire basin [*].

For Cameroon 50000 ha are estimated to be in the Congo/Zaire basin [*]. For Congo the potential is estimated at between 40000 and 340000 ha [60, 50]. In this study, the rather abitrary upper estimate has been retained and 255000 ha are considered to be located in the Congo/Zaire basin, which occupies 75 % of the country [*].

For Angola a figure of 6.7 million hectares exists for irrigation potential [17]. According to the Direction of the Hydraulical Service about 420000 ha could be irrigated at present, considering land and water as well as human resources [51]. The present study has evaluated the irrigation potential at 3% of the area of the country, which corresponds to 3.7 million hectares. It has been distributed over the six basins on the basis of the percentage of the country covered by each basin, except for the Okavango and the South Interior, which are less humid than the other ones [*]:

Table 36 Irrigation potential estimates in the different major basin groups in Angola [*]

Almost 99% of Zaire is located within the Congo/Zaire basin. About 75% of the country, which is over 170 million hectares, is covered by natural forest, most of it untouched. Of these 170 million hectares, about 139 million hectares are considered exploitable and capable of producing 700 million m³ of industrial wood per year (or 5 m³ per ha). At present only 0.5 million m³ per year is produced due mainly to infrastructure and transport problems. Of the remaining 63 million hectares, only 6 million ha is cultivated. Irrigation potential figures vary between 4 and 20 million hectares [32, 21a]. While it is true that the water resources of the country are abundant, it is not realistic to estimate that 20 million ha can be developed for irrigation, which is more than three times the total area cultivated at present! Land suitable for agriculture has been estimated at 80 million ha. When considering that no forest land will be converted into agricultural land, this area is reduced to 60 million ha, about half of which is used for other purposes. Like for Angola, this study estimates the irrigation potential at 3% of the total area of the country, or 7 million ha [*]. This area requires 108.50 km³/year of water for irrigation, which is about 12 % of the internal renewable water resources of Zaire, estimated at 935 km³/year. Of these 7 million ha, 10000 ha are considered to be in the Nile basin and 10000 ha in the West Central Coast region. The remaining area, 6.98 million hectares, is considered to be in the Congo/Zaire basin.

Unlike the drier basins, where the irrigation potential figures given in this study should be considered as a maximum from the point of view of water resources, the figures for humid basins where water is abundant are rather arbitrary.

Table 37: Congo/Zaire basin: irrigation potential, water requirements and areas under irrigation

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