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The Indian Ocean coast

The southern and south-western part of the Indian Ocean Coast is wholly situated in South Africa. The eastern part is shared between Swaziland, South Africa and Mozambique. The north-eastern part is shared between Zimbabwe and Mozambique (Map 20 and Table 77). Its total area represents 2.2% of the area of the continent.

TABLE 77 Indian Ocean Coast: Areas and rainfall by country

Country

Total area of the country (km≤)

Area of the country within the basin (km≤)

As % of total area of basin (%)

As % of total area of country (%)

Average annual rainfall in the basin area (mm)






min.

max.

mean

Swaziland

17364

17364

2.6

100.0

600

1020

780

South Africa

1221040

358648

54.0

29.4

125

1270

585

Zimbabwe

390760

102047

15.4

26.1

375

1685

650

Mozambique

801590

185726

28.0

23.2

470

1770

885

Total Ind. Oc. Coast


663785

100.0


125

1770

680

Rivers and discharges

Of the four major rivers in Swaziland, two originate inside the country, the Mbuluzi and Ngwavuma rivers, and two in South Africa, the Komati and Usutu rivers. Total inflow from South Africa to Swaziland is 1.8 km≥/year. Total outflow from Swaziland is 3.5 km≥/year, of which 2.3 km≥ flow directly into Mozambique to the Umbulezi and the Maputo rivers. The remaining 1.2 km≥ first enter South Africa before flowing into Mozambique, in the south towards the Maputo River and in the north towards the Incomati River. The Sabie River is another tributary of the Incomati River originating in South Africa.

Within South Africa, perennial rivers occur over only one quarter of the area and mainly in the southern and south-western Cape province and on the eastern plateau slopes. However, even the perennial rivers are very irregular and have important seasonal variations. The surface water resources in the Indian Ocean part are estimated at 31 km≥/year, of which about 21 km≥/year are exploitable. Less than 10 km≥/year are available for agricultural purposes.

The Save, Buzi and Pungoť rivers originate in Zimbabwe and all flow to Mozambique. Although the catchment area of the Pungoť River in Zimbabwe is only 5 % of the total catchment area, about 26% of the annual runoff originates from this area [155].

Irrigation potential and water requirements

For Swaziland the following irrigation potential figures are given for the country, based on land and water availability [197]:

TABLE 78 Water resources, irrigation potential and water requirements by sub-basin in Swaziland

Basin

Inflow from RSA (km≥/yr)

Produced in country (km≥/yr)

Outflow (km≥/yr) (ha)

Irrigation potential (km≥/yr)

Water demand

Lomati-Komati

0.738

0.415

1.153

17 925

0.161

Mbuluzi

0

0.352

0.352

24 280

0.219

Usutu

1.032

0.904

1.936

45 875

0.413

Ngwavuma

0

0.106

0.106

5 140

0.046

Total

1.770

1.777

3.547

93 220

0.839

In South Africa, about 9 km≥/year of water are estimated to be available for agricultural purposes in the Indian Ocean Coast in 2010 [190]. Table 79 summarizes the water resources, irrigation potential and water requirements for the different basins (see also Map 20).

TABLE 79 Irrigated areas, water availability, water requirements and irrigation potential in the Indian Ocean Coast in South Africa

Sub-basin

Actual irrigated (ha)

Actual water use (km≥/yr)

Water available (km≥/yr)

Irr. wat. requirem. (m≥/ha.yr)

Irrigation potential (ha)

H - S

200000

2.041

1.906

10000

190 600

T-W

158 000

1.547

5.898

10000

589 800

X

68 000

0.681

0.974

10000

97 400

Total IOC

426 000

4.269

8.778


877 800

For the whole of the Indian Ocean Coast in South Africa the irrigation potential is 877800 ha, which is more than twice the area irrigated at present, estimated at 426000 ha [*].

The surface water resources produced in the upper Save basin in Zimbabwe are estimated at 4.052 km≥/year, which corresponds to the potential yield [216]. After deducting the amount of water already committed, the quantity of water still available is 2.542 km≥/year. Of this quantity, about one-third, or 0.847 km≥, can be considered as potentially available for the development of irrigation. The surface water resources produced in the upper Buzi and Pungoť basins in Zimbabwe are estimated at 1.024 km /year, of which 0.922 km /year is still available and one - third of this, or 0.307 km≥/year, for the development of irrigation.

At present 124804 ha have been developed or planned for irrigation in the upper Save basin [216]. Based on land and water and considering an irrigation water requirement of 11000 m≥/ha per year according to the present study, it would be possible to irrigate another 77000 ha [*], which would bring the total to about 201800 ha. In the upper Buzi and Pungoť basins 7449 ha have already been developed or planned for irrigation [216] and another 1750 ha could be developed [*], bringing the total to 9200 ha. For the whole area in the Indian Ocean Coast this leads to an irrigation potential of 211000 ha. In the upper Save basin, water is the limiting factor, while in the upper Buzi and Pungoť basins the limiting factor is land.

In Mozambique the irrigation potential has been estimated at 128000 ha in the part situated to the north of the Limpopo basin and at 240000 ha in the part situated to the south of the Limpopo basin, giving a total of 368000 ha [159].

TABLE 80 Indian Ocean Coast: irrigation potential water requirements and areas under irrigation

Country

Irrigation potential (ha)

Gross potential irrigation water requirement

Area under irrigation (ha)



per ha (m3/ha per year)

total (km3/year)


Swaziland

93220

9000

0.839

67.400

South Africa

877800

10000

8.778

688000

Zimbabwe

211000

11000

2.321

65000

Mozambique

368000

11000

4.048

41710

Sum of countries

1550020


15.986

862110

Total for Ind. Oc. Coast

1500000


15.986


Problems may arise in the area where the rivers are shared by Swaziland, South Africa and Mozambique. The irrigation potential in that area has been estimated at 93220 ha for Swaziland, 100000 ha for South Africa and 240000 ha for Mozambique. The total of 433220 ha would require 4.479 km≥/year of irrigation water. The total amount of water flowing to the sea has been estimated at about 6.600 km /year.


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