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The East Central coast

The East Central Coast extends from Mozambique in the south to Somalia in the north. It spreads over five countries and covers 3.4% of the continent (Map 21 and Table 81).

TABLE 81 East Central Coast: areas and rainfall by country

Rivers and discharges

The area of Malawi located in the East Central Coast region corresponds to the Lake Chilwa and the Lake Chiuta basins. Both lakes are on the border between Malawi and Mozambique. The average annual runoff in the Lake Chilwa basin is estimated at 1.06 km³, in the Lake Chiuta basin at 0.61 km³

In Mozambique the rivers, except for the Ruvuma, which is the border river between Mozambique and Tanzania, originate from the plateau and mountains within the country, and are usually not perennial. Some of them have important waterfalls and steep slopes. The contribution of the Lugenda River to the Ruvuma River is estimated at about 18 km³/year. Other important rivers flowing to the sea are the Messalo (3.0 km³/year at mouth), the Lurio (8.0 km³/year at mouth), the Ligonha (2.6 km³/year) and the Licungo (8.9 km³/year at mouth). This gives a total of 22.5 km³/year from these rivers alone, which means that the water resources are abundant.

In Tanzania many rivers drain to the coast, the most important being, from the south to the north: Ruvuma, Mbenkuru. Matandu, Rufiji, Ruvu, Wami, Sigi, Msangasi and Pangani. The water resources of Tanzania are quite abundant, but not many figures are available on river discharges. The most important rivers are the Ruvuma on the border between Mozambique and Tanzania with an annual flow to the sea of about 28 km³, of which the contribution of Tanzania is estimated at 10 km³, and the Rufiji with an annual runoff of nearly 26 km³ as measured between 1955 and 1978.

In Kenya two main rivers originate in the East Central Coast. The Tana River originates in the mountains in central Kenya and flows through a semi-arid plain to the sea. It has two seasons of high flooding corresponding to the two rainy seasons. The mean annual runoff is 4.95 km³, but with a high inter-annual variability The Athi River is a strongly seasonal river with high flows in April-June and November-December and very low flows in the two intervening seasons. The average annual flow is about 1.80 km³. The river is characterized by important losses; under low flow conditions. losses of 0.14 km /year have been measured over the middle and lower reaches. Ejjluent discharges from Nairobi make a large contribution to the river flow. Most of the water supply to Nairobi comes from the Tana basin and returns to the Athi basin.

The Lag Badana basin in Somalia is part of the East Central Coast. Surface water resources are rather scarce. Some localized runoff occurs during heavy rainfall, but little water reaches the coast.

Irrigation potential and water requirements

Most of the irrigation potential of Malawi is located in the Zambezi basin. Some small-scale development might be possible in the Lake Chilwa basin, for a total of about 1000 ha [*].

Most of the basin of the Lugenda River in Mozambique lies in the Niassa province, where the irrigation potential is estimated at 200000 ha. The irrigation potential in the Cabo Delgado and Nampula province is estimated at 556000 ha and in the Zambezia province at 300000 ha. This gives a total of 856000 ha [159, *].

For Tanzania, the irrigation potential has been identified on the basis of large contiguous areas of land on the major rivers and are therefore not exhaustive. Total irrigation potential in the East Central Coast in Tanzania, 959360 ha, is detailed below [199].

The Ruvuma and other southern basins:

The Ruvuma River forms the border between Tanzania and Mozambique. The irrigation potential in this zone is limited and has always received low priority at national level. The nature of the topography and drainage patterns of much of the zone render irrigation development of a formal nature difficult and expensive because of the need for flood protection works and pumped irrigation water. The total potential in the southern basins is estimated at 15240 ha.

The Rufiji basin:

This is the largest river basin in Tanzania. The irrigation potential has been classified under three categories:

• first stage development are those schemes which could be undertaken using runoff water flows and requiring minimal drainage or flood protection works;

• second stage developement includes storage/flood control dams and flood protection and drainage works which could be implemented at low cost per unit area developed;

• third stage development includes full control of river flows to allow the maximum possible extension of the irrigable area.

First stage development schemes (total: 34000 ha) and second stage development schemes (total: 89000 ha) are locate;! in the Upper Great Ruaha basin and the Kilobero basin, in the upstream part of the Rufiji basin. Of the third stage development schemes, 127000 ha are located in the upper Great Ruaha basin and 287000 ha in the Kilombero basin. The remaining 84800 ha are located in the lower Rufiji basin. In the lower part a large area is covered by the Selous Game Reserve. Water problems may occur in the upper Great Ruaha area (Usanga plains), where the total potential is 207000 ha, but where the annual flow is probably not more than 2.0 km³.

The Ruvu basin:

Irrigation development in this basin requires both flood control works and storage for dry season irrigation. The potential ranges from 69000 to 80000 ha.

The Wami basin:

The alluvial plains are subject to flooding and any extensive development would require flood control as well as storage for dry season irrigation water. Optimistic estimates of irrigation potential in the alluvial plains range from 40000 to 48000 ha, but other estimates are 14000 ha. In the coastal plains the identified irrigation potential ranges from 37000 to 44000 ha.

The Sigi and Msangasi basins:

The irrigation potential in the Sigi basin, by pumping from the river, is estimated at 400 ha. The irrigation potential the Msangasi basin is 4800 ha, if adequate storage is provided.

The Pangani basin:

About 150000 ha are estimated to be under traditional irrigation in the upper basin and water availability is a major constraint on future expansion. The remaining potential has been estimated at 21120 ha and would require storage dams.

In Kenya, in the Tana basin, based on mean monthly flow, 132700 ha could be irrigated. However, based on 80% dependable monthly flow, this area is reduced to 89200 ha. The area which could be irrigated by renewable groundwater is estimated at 250 ha. This brings the irrigation potential to 89450 ha. In the Athi basin, based on mean monthly flow, 22400 ha could be irrigated; based on 80% dependable monthly flow, 21000 ha. The area which could be irrigated by renewable groundwater is estimated at 650 ha. This brings the irrigation potential to 21650 ha. The total irrigation potential for the East Central Coast is estimated at 111100 ha [125].

In view of the scarce water resources in Somalia, the irrigation potential has been considered negligible [*].

Table 82 summarizes the figures on irrigation and water requirements for the East Central Coast.

TABLE 82 East Central Coast: irrigation potential, water requirements and areas under irrigation

In general, water resources are sufficient for the development of the irrigation potential in the East Central Coast, but problems may arise in the north of Tanzania in the Pangani basin, where water availability is less than required.

The North East coast

The North East Coast covers 2.4% of the continent and spreads over six countries (Map 22 and Table 83).

TABLE 83 North East Coast: areas and rainfall by country

River system and discharges

Five basins can be distinguished in the North East Coast in Somalia:

• In the Gulf of Aden basin the annual upstream runoff is estimated at 0.48 km³. The quantity of water that disappears by infiltration in the upstream parts is estimated at 0.35 km³/year, the infiltration at the coastal area at 0.13 km³/year.

• In the Darror basin there are no significant surface water resources.

• In the Tug Der basin the average annual runoff is estimated at 0.03 km³. Water flows only after heavy rainfall, but it disappears quickly. Little water reaches the coast.

• In the Ogaden basin surface water resources are scarce due to lack of rainfall.

• The Indian Ocean basin is only a very narrow strip of land along the ocean. The surface drainage is insignificant.

The surface water resources in the Ogaden and Gulf of Aden basins in Ethiopia are considered to be negligible. About 55% of Djibouti drains to the sea to the east. Surface water resources are directly dependent on rainfall (> 10 mm), resulting in rapid floods lasting only a few hours. The internal renewable water resources for the whole of Djibouti are estimated at 0.3 km /year.

The Baraka and Anseba rivers rise on the north-western slopes of the central highlands in Eritrea and flow northwards to a confluence near the border with Sudan. Only high rainfall results in flows reaching the Sudanese border, with an average estimated at about 0.8 km³/year, The Red Sea drainage basin in Eritrea comprises numerous small rivers originating in the eastern escarpment. A global estimate of annual runoff of 0.88 km³ has been made for the littoral as a whole. The renewable water resources in Egypt are negligible.

Irrigation potential and water requirements

Irrigation potential in Somalia can be estimated at about 10000 ha by spate water at different locations, if dams are constructed [*]. There is no irrigation potential in Ethiopia [*].

The cultivable area in Djibouti is estimated at about 6000 ha, but the area equipped for irrigation is only 674 ha, of which about 374 ha are in the North East Coast [93]. No detailed information is available on irrigation potential, but with the available water resources it has been estimated at 1000 ha, of which 550 ha have been estimated to be in the North East Coast [*].

The land suitable for irrigation in the Barka-Anseba basin in Eritrea is about 130000 ha [100]. It is estimated that, with dam construction, about 6500 ha can be developed under irrigation. The land suitable for irrigation in the Red Sea drainage basin is about 240000 ha. It is expected that about 31000 ha of land lying on the riversbanks can be irrigated.

In Sudan about 30000 ha are expected to be irrigated by spate water [193]. There is no irrigation potential using renewable water resources in Egypt [*].

Table 84 summarizes the figures on irrigation and water requirements in the North East Coast.

TABLE 84 North East Coast: irrigation potential. water requirements and areas under irrigation

The above irrigation potential depends mostly on spate water, which is rather irregular in space and time.

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