Geography
The Middle Kunene, from Matala to Calueque, consists of rolling hills in the north and flat terrain towards the south. The river runs less steeply than in the upper reaches, dropping from 1 300 m to 1 000 m over its 430 km length. Due to the flat terrain, a broad floodplain up to 15 km wide exists, containing numerous lakes and lagoons. Within the Middle Kunene, the river is fed by largely perennial rivers draining wide floodplains.
Middle Kunene sub-basin.
Source: AHT GROUP AG 2010
( click to enlarge )
The river leaves the granite uplands at Matala where the gradient flattens markedly into a floodplain dominated by calcium rich sediments which have developed into clayey vertisols. The east side bank has a continuous scarp of soft sandstone averaging 21 m above the bed of the river, which is broken in three places in the vicinity of Calueque. Towards the southern end of the sub-basin the geography changes rapidly while entering the Lower Kunene.
The Upper and Middle Kunene belong to an ancient drainage system that developed prior to the formation of the African continent. Prior to the formation of the Lower Kunene, the Middle Kunene formed an inland delta area, similar to the present day Okavango Delta in Botswana.
Climate and Weather
The Köppen Climate Classification for this river section is ‘dry with steppes’. Towards the lower end of the Middle Kunene the climate is described as ‘semi-arid tropical’. Average temperature is higher than in the upper reaches at 24 °C (LNEC 1996). The rainy season is shorter than in the Upper Kunene and precipitation lower, decreasing from more than 1 000 mm/year near Matala to 350 mm/year at the southern end of the section.
Hydrology
The Middle Kunene experiences hot summers and warm dry winters, with a mean annual precipitation of 950 mm falling over a period of about 100 days. Precipitation is, however, very variable from year to year, and floods occur following heavy rains in the catchment. Large floods only occur when rains on the plateau are coincidently heavy. In a wet year the plains receive more than 1 000 mm, but in dry years the sub-catchment may receive less than 200 mm and the plains around 650 mm. Very little flooding occurs in dry years (Hughes and Hughes 1992).
Water Quality
Water quality in the Middle Kunene is virtually the same as that in the upper reaches, as both belong to the same well-developed ancient drainage system. In the middle reaches this is characterised by low gradients, annually flooded plains and natural deposition environments, with calcium rich sediments. Water quality impacts of human settlements are fewer in the Middle than in the Upper Kunene as population density is lower.
Marula tree (Sclerocarya birrea).
Source: Mengel 2008
( click to enlarge )
Habitats and Biodiversity
Habitats in the middle reaches of the Kunene change from open savannah with shrubs, alternating with stands of dense closed forest, to savannah associated with more arid areas and poorer soils. ‘Balcedo’ savanna includes trees/shrubs such as Acacia, Croton, Grewia, Combretum (bushwillow), Baphia, Ziziphus (buckthorn family), Peltophorum, Ximenia and Maytenus. Denser forest (‘bosque’) includes Acacia, Combretum imberbe, Capassa violacea, Dialium engleranum, Burkea Africana and Erythrophleurum africanum. In the lower reaches, as the climate becomes more arid and soils poorer, the savanna continues but with species more adapted to the harsher conditions; species such as Colophospermum mopane (Mopane), Acacia, Combretum and Commiphora can be found here. This section continues to see stands of larger trees in the immediate riparian strip, species including Jackalberry (Diospiros mespiliformis), Acacia albida, Marula (Sclerocarya birrea), and Aluka (Pterocarpus tinctorius). Rare shrubs and herbs are found in the shallow, dry soils amongst stands of Mopane.
