The Kunene River Basin

Introduction

The Kunene River rises in the central highlands of Angola at elevations between 1 700 and 2 000 meters above sea level (masl), 32 km east of the town of Huambo. This plateau is known as the “planalto” and consists of a rolling eroded surface underlain mostly by basement complex. The area is well-watered and fertile and has become a densely populated agricultural area. This area also hosts the headwaters of other important rivers such as the Kuanza, Queve and Kubango.

Geographically, the basin can be divided into three main sections: the Upper, the Middle and the Lower Kunene. The Upper Kunene is characterised by highlands with gentle rolling hills separated by broad shallow valleys in the central Angolan highlands between an altitude of 1 800 and 1 200 meters up to Huambo and Matala towns. The Middle Kunene consists of rolling hills in the northern areas with the terrain becoming flatter towards Ruacana and the Namibian border in the south, whilst the Lower Kunene exhibits mountainous topography and semi-arid to arid conditions. Near the river mouth, the river crosses the Namib desert.

The relatively small catchment and the steep river bed slope in the upper and lower sections also mean that flows run relatively quickly to the coast, leaving the river almost dry at the end of the dry season. Tributaries of the Kunene in the northern highlands are typically perennial while the middle reaches are fed by largely perennial rivers draining wide floodplains. Tributaries in the lower reaches are ephemeral, characterized by short flash floods, and contribute negligible flow to the Kunene due to the arid conditions encountered here.

The total catchment area is 106 500 km², of which 14 100 km² (13%) lies within Namibian territory.

The map below shows the relief and the drainage pattern of the basin derived from a 90 m resolution digital elevation model (CGIAR 2008). The geomorphologic variation in the three sub-basins is clearly visible from this elevation model

Longitudinal Profile

The longitudinal profile of the Kunene River system illustrates the variation of the topography in the basin. In the steeply sloping Upper Kunene , the main channel is well defined with a number of rapids and steep sections. South of Matala, in the Middle Kunene, the profile of the river changes as it flows over Kalahari sands with low gradient. The eastern bank is well defined here, while the western bank has wide flood plains (DRWS 2001). These two upper sections belong to an ancient drainage system, developed prior to the formation of the African continent, whilst the lower section has been formed by backward erosion, from the coast. Prior to this, the Middle Kunene was an inland delta area, joining with the Cuvelai channels into a lake which is now the Etosha Pan, similar to the present day Okavango delta. The old deposits are still annually flooded and act as a sediment trap for sediments produced further upstream. In the Lower Kunene, west of the Calueque dam along the whole international reach - over a distance of just under 385 km - the river drops nearly 1200 meters and includes several spectacular falls, the most important being Ruacana Falls, Epupa Falls and Kivale Falls (PJTC 1998).

Ecoregions

The geomorphical development and the climatological variation in the Kunene River basin have created an environment that is particular in terms of ecological regions. From the north to south-west, the main eco-geographical regions in the basin are:

• Angolan Afromontane Forest (with tropical and subtropical moist broadleaf forests);
• Angolan Miombo Woodland (Tropical and subtropical grasslands, savannas, and shrublands);
• Kalahari Acacia-Baikiaea Woodland (Tropical and subtropical grasslands, savannas, and shrublands);
• Angolan Mopane Woodland (Tropical and subtropical grasslands, savannas, and shrublands);
• Nama Karoo (Deserts and xeric shrublands); and
• Kaokoveld Desert (Deserts and xeric shrublands).