survey of the irrigation potential of the lower tana river basin kenya

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inches of reliable rainfall, and the under 20-inch.rainfall zone is managed
largely as rangeland. As Plate 3 shows, most of the Tana basin receives less
than 30 inches of reliable rain annually and more than half the basin would be
classified as semi-arid, with average annual precipitation' varying from 10 to
20 inches (2)*
Vegetation
The vegetation across the basin ranges from lush tropical growth along the
narrow ooastal strip, to afro-alpine heat and moorland, high mountain forest and
grassland, on the upper slopes of Mount Kenya and the Aberdares. Between these
extremities are the vast areas of savannah and acacia forests of the upland
plateau, and the open" woodlands of low thorny species - dormant for most of the
year - which cover the lowland plains.
Population and Peoples
Population density in the basin varies widely. Some areas in the upper and
middle catohment plateau and foothills, occupied by a group of Bantu peoples
comprising the Kikuyu, Qnbu, Meru and Mkamba tribes, have more than 600 persons
per square mile. The desert lowlands in the lower basin, inhabited by several
tribes of Hamitic origin (the Orma, Galla, Boran and Somali peoples) which are
nomadio by tradition, have average densities of less than two persons per square
mile. In the narrow riverine plains of the Tana, between the Eameye swamp and
the Indian Ocean, live the Pokomo, another Bantu tribe. In the coastal strip
are found the Giriama, Swahili and Arabic peoples (2).
Communications
Road systems are well developed throughout most of the populated areas of
the upper basin, but, with the exception of the Nairobi-Thika-Nanyuki road,
surfaces are unpaved. Many of these roads are impassable from time to time
during the rainy season. The middle and lower parts of the basin are served by
only a few earthen roads, impassable during the wet seasons. The chief of these
are the Nairobi-Garissa road and the Garissa-Mombasa road, which passes through
the proposed irrigation area, Galole, Garsen and Malindi. There are only two
permanent bridges across the middle and lower Tana5 the first, at Kamburu, links
the Kitui and Qnbu areas, and the second, at Garissa, gives access to the
sparsely populated northeast desert region. The hand-operated car ferry at
Garsen is used during low and medium river stages and links the north coastal
area with the south coast of Kenya.
The main rail line between Mombasa and Nairobi passes to the southwest of
the basin and serves the lower area only from these principal termini.