Info for the media
Read the full profile
The main river basins in Namibia are:
- The Zambezi River Basin with a basin area of 17 426 km2 in Namibia is the country’s richest water source. The Zambezi has a mean flow of 40 km3/yr and in the northeastern Caprivi strip forms the border between Zambia and Namibia for about 100 km and over a short distance between Zimbabwe and Namibia.
- The Okavango River basin is an interior basin with an area of 106 798 km2 in Namibia. The river rises in Angola, then, flowing in a narrow alluvial plain up to 6 km wide, forms the border with Namibia for some 350 km before crossing the Caprivi Strip and flowing into Botswana, where it forms the Okavango Swamps. Its mean flow is slightly above 10 km3/yr. It has two major tributaries, the Cubango and the Cuito. While the flow in the Cubango River upstream of the Cuito River confluence drops to very low levels during dry years, the flow from the Cuito River is more reliable. A Namibian tributary of the Okavango is the Omatako River, which contributes no flow at all. Originating in the dry interior of Namibia, there is no evidence that the Omatako has ever flowed further than 400 km from its source.
- The southwest coast basin including the Kunene River covering an area of 17 549 km2. Rainfall over the Kunene catchment is unreliable and variable, and the mean flow of the river is 5 km3/yr. The relatively small catchment area and steep river bed slope in the upper section also mean that flows run relatively quickly to the coast, leaving the river almost dry at the end of the dry season. With the inception of the Ruacana hydroelectric scheme and its associated storage dams, flows should have become more regulated; this did not happen because the Gove Dam in Angola has never been adequately operational. In addition to being used to generate hydropower, the Kunene also supplies a significant amount of water to the four northern regions of Namibia, where approximately 700 000 people or over one third of the total population live. The demand is at its peak in October, which corresponds with the period of minimum flow in the Kunene.
- The south Atlantic coast including the Huab, Ugab, Omaruru, Swakop and Kuiseb Rivers with a total area of 264 160 km2.
- The Orange River Basin has an area of 219 249 km2 in Namibia. The river forms the southern border of Namibia with South Africa over a distance of approximately 600 km. It has a mean flow of about 11 km3/yr. The major Namibian tributary, the Fish River, has a mean flow of 0.48 km3/yr at its confluence with the Orange River. The flow in the lower parts of the Orange has been cut by nearly two thirds, especially over the last 35 years since the start of the Orange River Project (ORP) in South Africa. This project transfers water from the Caledon and Orange Rivers to rivers outside of the basin that flow towards cities in the Eastern Cape Province in South Africa. In order to operate the ORP there are more than a dozen dams with a combined capacity of 8.5 km3. The key structure in this development is the in 1979 completed Gariep Dam, previously known as the Hendrick Verwoerd Dam, with a reservoir capacity of almost 5.7 km3.
- The interior basins, including the Cuvelai River basin and part of the Kalahari desert, cover an area of 199 718 km2; The Cuvelai River enters Namibia as a 130 km wide delta of ephemeral watercourses, known as oshanas, which then converge to terminate in the Etosha Pan. Runoff in the Cuvelai is erratic and has been observed to vary from no flow to 0.1 km3/yr, as was gauged in 1995. Due to flat topography and shallow saline groundwater, surface water storage facilities are limited to shallow earth or excavation dams, which suffer from high evaporation rates.
The percentage of mean annual precipitation that ends up as river flow in ephemeral systems in Namibia varies from as little as below 1 percent up to around 12.5 percent for parts of the Fish River basin. The remainder goes to direct evaporation and evapotranspiration, with the latter being by far the greatest component. Some of the runoff recharges alluvial aquifers on its way downstream, and in so doing the majority of ephemeral river floods ultimately disappear entirely into the sand. Namibia’s ephemeral rivers are ‘effluent’ systems. This means that the river feeds the groundwater table, rather than having its flow sustained by a high groundwater table, as is the case with ‘influent’ rivers.
Namibia’s groundwater occurs in a wide range of rock types making groundwater management a complex process. It provides a buffer against drought in many regions of the country, but it does remain inherently vulnerable to overabstraction and pollution. Aquifers occurring in Namibia are classified as alluvial, Kalahari, fracture, Karst or artesian aquifers. Parts of the Grootfontein-Otavi-Tsumeb Karstland aquifer have been subject to thorough investigations and modelling, and for the Otavi Mountain Area the following recharge conditions were identified:
- The recharge rate amounts to 2 percent of the long-term mean annual rainfall after a sequence of rainy seasons in each of which the long-term annual rainfall is exceeded;
- The recharge rate amounts to 1 percent of the long-term mean annual rainfall after a single rainy season in which the long-term mean annual rainfall is exceeded;
- The recharge rate amounts to 0 percent if the rainfall does not exceed the long-term mean annual rainfall.
Although the ephemeral rivers of Namibia have dry sandy or rocky river beds for most of the year, they are conduits for subsurface flow and contain a number of wetlands defined as ‘shallow, swampy or marshy areas with little or no water flow’ or ‘waterlogged solid dominated by emergent vegetation’. In Namibia this description applies to most sections of all westward flowing rivers north of the Kuiseb River. Wetlands are periodically used for hunting and seasonal fishing. Currently, their utilization includes communal domestic stock farming, small mining enterprises and small-scale gardening. The ecology of Namibia’s wetlands is very fragile. Over-exploitation of alluvial aquifers and the building of dams, especially on the Kunene River and the Orange River, which reduce the flow downstream are potential threats to those wetlands that depend on them. The protection and conservation of wetlands is therefore an important priority and the government of the Republic of Namibia has initiated several efforts towards ensuring this. Wetlands of international importance in Namibia, and Ramsar sites, are the Etosha Pan, the Orange River Mouth, Sandwich Harbour and Walvis Bay.
Total natural renewable water resources of Namibia are estimated at 45.46 km3/yr, of which only 6.16 km3/yr are internally produced (Table 2). Over half of the external water resources comes from the Zambezi River, while smaller amounts are contributed by the Orange, Kunene and Kwando rivers and rivers from the Okavango. From the total accounted natural flow of the border rivers Zambezi, Kunene and Orange of 28 km3/yr, only 0.255 km3/yr is under agreement (0.07 from the Orange River and 0.185 from the Kunene River) and should thus be considered as actual flow. This reduces the natural renewable water resources of 45.46 km3/yr to actual renewable water resources of 17.715 km3/yr.
A number of ephemeral rivers have been tapped by building dams. The total storage capacity of the major dams is about 0.71 km3 and their 95 percent assured combined yield is 95.83 million m3/yr. In addition to these larger reservoirs, there are thousands of small farm dams scattered around the ephemeral river basins.
The total assured safe yield of Namibia’s water resources is 660 million m3/yr, distributed as follows: groundwater 300 million m3/yr, ephemeral rivers 200 million m3/yr, perennial rivers 150 million m3/yr and unconventional sources 10 million m3/yr.
Treated wastewater is used more and more often for applications that do not require drinking water quality, such as landscape irrigation. It was found that the return flow in Windhoek and urban centers equals 40 percent of freshwater consumption and can be reused after treatment. Reuse of water is practised in Namibia in many urban areas such as Swakopmund, Walvis Bay, Tsumeb, Otjiwarongo, Okahandja, Mariental, Oranjemund and Windhoek. In Windhoek, 1.14 million m3 of treated effluent were used for irrigation in 1997 and reclamation of water for potable reuse has been practised since 1968. The plant could supply 8 000 m3/day, which was about 19 percent of the average daily water demand of the city in 1997. A new reclamation plant with an increased capacity of 21 000 m3/day was completed in 2002, and the old plant will in future be used for reclaiming irrigation water. Wastewater recycling is practised by a number of mines. It is estimated that in the future 7 million m3/yr from Windhoek and 10 million m3/yr from other centres could potentially become available.
Recently a contract for the design and construction of a coastal desalination project was tendered.