The Lower Kunene River

Geography

The relatively flat and slower flowing character of the Middle Kunene upstream of Calueque rapids changes to a steeper river profile in the Lower Kunene. The river here has steep gradients (averaging 1:400), rapids and a channel controlled by the bed-rock structure. After the Calueque rapids, the floodplain track ends and the river narrows considerably with its character changing abruptly with a series of five rapids over the next 37 km to the Ruacana Falls.

At the Ruacana falls, the river turns sharply west forming the border between Angola and Namibia. From this point onwards, the course consists of a steep descent to the coast. Downstream of the Epupa Falls, the river morphology changes its character, cutting a deep gorge with several cataracts. From there on, short seasonal streams, including the Otjindjangi (Marienfluss), occasionally enter the river on either side of the bank. The Kunene then flows from the Baynes Gorge into the 70 km wide coastal Namib Desert, before emptying into the Atlantic Ocean.

The contrasting geomorphology of the river and its catchment area upstream and downstream of the Calueque dam can be explained by the geomorphological development of the drainage system. The upstream catchment had, like the Cubango/Okavango today, an internal drainage into the Etosha Pan in the recent geological past through a series of river channels, which today act as ephemeral rivers.

Climate and Weather

The Lower Kunene varies from ‘tropical steppe’ to ‘arid /desert’ at the coast, receiving rainfall of less than 50 mm/year at the river mouth, and 350 mm/year inland. The average temperature at the coast is 19 °C, increasing up to 22 °C near Ruacana Falls. Very high temperatures (up to 40 °C) are common in the summer months. Fog is a major source of moisture for the ecosystems living within the desert/semi-desert. The approximate number of fog days per year in the lower reaches of the Kunene River ranges from 1 to 5 days inland to 50 to 75 days at the coast.

Hydrology

Rainfall in the Lower Kunene is very low (0 to 350 mm) and extremely variable from year to year with a variability of over 40 %. As such, the river is a linear oasis passing through an otherwise arid region, and very little water in the river is contributed from the lower tributaries. Heavy storms can result in flooding in the ephemeral rivers, and small flood plains can be formed for a short period of time (DRWS 2001).

Water Quality

In contrast to the upper and middle reaches, the Lower Kunene is a young river characterised by steep gradients, rapids and a channel controlled by bed-rock structure. These differences have created two distinct sediment delivery systems, and in the lower reaches, the river beds indicate a higher amount of sediment load.

Although population densities are low in the lower reaches of the Kunene, the riparian strip still sees pressure as a result of pastoralism, agriculture and harvesting of forest products. This leads to degradation of the local ecosystems and also impacts on water quality by contributing sediment and nutrients to runoff.

Habitats and Biodiversity

Habitats in the Lower Kunene evolve from dry steppe/savannah, with stands of larger trees in the riparian zone, to specialist desert communities. Savannah is dominated by grasses including Aristida spp and Eragrostis spp; shrubs and small trees include Acacia, Commiphora, Combretum, Boscia, Terminalia, Balanites, Maerua, Maprounea and Croton. The Baobab, Adansonia digitata, is more commonly seen in these reaches.

Toward the coastal area, more ephemeral and specialist species dominate, including succulents, shrubs and grasses. Amongst the species associated with these habitats are cacti Cissus uter, Sarcocaulon mossamedensis and Hoodia currori. A more famous resident is the long-living Welwitschia - Welwitschia mirabilis, which exists along the coastal strip of northern Namibia / southern Angola and relies heavily on dew and fog for moisture. 

The isolation of important wetlands like the Etosha pan (see the Wetlands section for more information) and the Kunene River mouth, which is about 700 km away from the nearest permanent wetland, makes them important staging areas for birds and mammals.