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The Okavango basin

The Okavango basin covers 1% of the continent. It is an endorheic basin, shared between Angola, Namibia and Botswana (Map 9 and Table 41).

Table 41: Okavango basin: areas and rainfall by country

Rivers and discharges

The two main rivers, the Cubango and Cuito, originate in Angola and flow to the south, where they become the border between Angola and Namibia. After flowing together they become the Okavango River that enters the Caprivi Strip in Namibia about 50 km further downstream. The average annual discharge leaving Angola at Mukwe is 10 km³.

The Omatako tributary in Namibia is an ephemeral river, flowing north-east to enter the Cubango River at the border between Angola and Namibia.

After entering Botswana, the Okavango River flows into the Okavango Delta, a large swamp area. A spillway exists from this area to the Chobe River in the Zambezi basin in periods of high floods.

Irrigation potential and water requirements

The ecological value of the Okavango region is high and increasing abstractions of water for irrigation purposes may have a negative effect on the ecology of the Caprivi Strip area in Namibia and the Okavango Delta in Botswana [163]. This requires a very judicious use of the water resources by the three riparian countries.

The irrigation potential in Angola has been estimated at 200000 ha, as explained in the section The Congo/Zaire basin [*].

The irrigation potential of Namibia has been estimated at 2000 ha, of which 1000 ha for flood recession cropping [*]. The eastern national water carrier project in Namibia plans to transfer 60 million m³/year of water from the Okavango River to the central and western coastal areas of the country. However, it is planned to use this water mainly for domestic purposes and not for agriculture [162].

The maximum irrigation potential in the Okavango region in Botswana has been estimated at about 9060 ha, of which 3000 ha would need important constructions for water development and storage [64]. In this study, the figure of 6060 ha is retained for the irrigation potential [*].

Table 42: Okavango basin: irrigation potential, water requirements and areas under irrigation

The Limpopo basin

The Limpopo basin, located in South-eastern Africa, covers 1.3% of the continent and spreads over four countries (Map 10 and Table 43).

Table 43: Limpopo basin: areas and rainfall by country

Rivers and discharges

The Crocodile River, which is the upper part of the Limpopo River, originates in South Africa near Johannesburg. It flows north-westwards to the border with Botswana and then turns to flow northeastwards, first on the border between South Africa and Botswana and then on the border between South Africa and Zimbabwe. Several tributaries originate in Botswana, the most important being the Shashi, which forms the border between Botswana and Zimbabwe before flowing into the Limpopo River. Entering Mozambique, the river has an average annual discharge of 4.8 km³.

Another important tributary, the Elephants River (also called the Transvaal River), originates in South Africa not far from Johannesburg and flows in north-eastwards. It flows into the Limpopo River in Mozambique.

The Mozambican part of the basin area is estimated to contribute only 10% of the total mean annual runoff of the river [155]. The Limpopo River, which was initially a perennial river in Mozambique, can actually fall dry for up to a period of eight months per year, mainly due to abstractions in the upper catchment area [155].

Irrigation potential and water requirements

The quantity of water produced in the Limpopo basin within Botswana is estimated at about 0.6 km³/year [61]. The maximum irrigation potential is estimated at 15208 ha, of which about 10 000 ha would need important works for water development and storage [64]. Moreover, as several major towns of Botswana are located in this area, including the capital Gabarone at the Notwane tributary, water problems may arise. This study has retained an irrigation potential of 5000 ha for this region [*].

Surface water resources produced in the basin area in Zimbabwe are estimated at 0.54 km³/year, of which 0.41 km³ drains to the Limpopo River at the border between Zimbabwe and South Africa and 0.13 km³ enters Mozambique before flowing into the Limpopo River. After deducting the water already committed for domestic, industrial, mining and irrigation use and the water which can not he developed, about 0.076 km³/year of water is considered as being potentially available for irrigation development. At present 3992 ha have been developed or planned for irrigation [716]. Land still suitable for irrigation is about 70000 ha, but water constraints limit the area to 6900 ha [*] This brings the total irrigation potential to about 10900 ha.

For South Africa the water resources per sub-basin are known [190]. It is estimated that by 7010 in the whole of South Africa 15 to 16 km³/year of water will be available for agricultural purposes. Table 44 summarizes the irrigated areas, water availability, water requirements and irrigation potential for the Limpopo basin in South Africa [190, *1.

At present 198000 ha are already irrigated, using less than 10000 m³/ha per year instead of the 12000 m³/ha per year estimated in the present study.

The irrigation potential for Mozambique in the Limpopo basin has been estimated at 148000 ha [159].

Table 44: Irrigated areas, water availability, water requirements and irrigation potential in the Limpopo basin in South Africa

Table 45 summarizes the irrigation potential, water requirements and irrigated areas for the Limpopo basin.

Table 45: Limpopo basin: irrigation potential. water requirements and area under irrigation

In view of the fact that the Limpopo River in Mozambique can already fall dry during eight months of the year, the above potential has to be considered as an upper limit, requiring important storage works and good cooperation between the basin countries.

Should South Africa use 12000 m³/ha per year, it would already irrigate more than its potential. For Botswana and Zimbabwe the literature gives higher irrigation water requirements than the present study, which means that in such a case the already small-potential of these countries would also have to be reduced.

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