African Unification Front
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ZAMBEZI BASIN
"Mossi Ua Tonya" on the Zambezi at its greatest width [1.3 km]
The Zambezi basin is the fourth-largest river basin of Africa, after the Nile, Congo, and Niger basins. Its total area represents about 4.5% of the area of the continent and spreads over eight constituent states of the African Union. The Zambezi River flows eastwards for about 3000 km from its sources to the Indian Ocean. The basin consists of Angola, Namibia, Botswana, Zimbabwe, Zambia Tanzania, Malawi, Mozambique.
The Zambezi River is highly polluted from the Victoria Falls sewage outfall to the 18.6 km peg downstream. Effective legislation to regulate pollution and waste management on the Zambezi is critical. Except for Angola, all the states in the Zambezi basin have some air pollution regulation, although this legislation is inadequate and not easily accessible to the public.
The Zambezi River rises in the Kalene hills in north-western Zambia and flows northwards for about 30 km. It then turns west and south to run over about 280 km through Angola and re-enters Zambia with an annual discharge of nearly 18 km3. It then flows southwards through marshy plains. In the south-west of Zambia the river becomes the border between Zambia and the Caprivi Strip of Namibia for about 130 km.
The Zambezi above the Victoria falls
The Chobe tributary originates in Angola, crosses the Caprivi Strip with an annual discharge of about 1.3 km3, then forms the border between Namibia and Botswana and enters Botswana to flow southwards for about 75 km until it meets the Selinda spillway along which spillage from the Okavango occurs in high flood years. It then turns east, again forming the border between Namibia and Botswana as it flows through a swampy area and flows into the Zambezi River at the border point between Namibia, Botswana, Zimbabwe and Zambia with an annual discharge of about 4.1 km3. The discharge of the Zambezi River at this point is 33.5 km3/year.
There are two major artificial lakes on the Zambezi River, Lake Kariba on the border between Zambia and Zimbabwe, and Lake Cabora Bassa in Mozambique. The other installations on the river are the Itezhi Itezhi Reservoir upstream of the Kafue flood plain in Zambia, the Kafue Gorge dam in Zambia, and the Limbe barrage hydroelectric plant on the Shire River in Malawi.
Downstream of Lake Kariba the Kafue River, a major tributary originating in the north of Zambia, flows into the Zambezi River with a discharge of about 10 km3/year. Still further downstream, at the border with Mozambique, the Luangwa River flows into the Zambezi River with an annual discharge of over 22 km3. This tributary originates in the north-east of Zambia. The total discharge entering Lake Cabora Bassa from Zambia is estimated at 77.5 km3 /year.
Leaving the lake the Zambezi River flows south-eastwards and receives water from its last great tributary, the Shire, with an annual discharge of nearly 16 km3. The Shire drains Lake Malawi (also called Lake Nyasa) about 450 km to the north. The northern part of Lake Malawi forms the border between Tanzania and Malawi, the southern part the border between Mozambique anti Malawi. The total flow into the lake is estimated at about 29 km3/year of which 53% from Tanzania, 43% from Malawi and 4% from Mozambique. Total outflow from the lake in the Shire River in the south is 12.5 km3/year. The level of the lake has fluctuated 6 metres since the beginning of the century, with its lowest level in 1917 and its highest level in 1980.
At its mouth, the Zambezi River splits into a wide, flat and marshy delta. The annual discharge flowing to the sea is estimated at 106 km .
Annual rainfall in the basin decreases from almost 1800 mm in the north to less than 550 mm in the south. Both Botswana and Namibia are rather dry countries and only 2% of each of these countries is situated in the basin. However, rainfall in these parts, around 600 mm/year, is higher than the countries average, which is 400 mm/year for Botswana and only 280 mm/year for Namibia.
For Angola the irrigation potential has been estimated at 700,000 ha. The irrigation potential for Namibia has been estimated at between 45,000 and 50,000 ha, of which 10,000 ha for a sugar cane project in the Caprivi Strip. Flood recession cropping is evaluated at 1000 ha in this area.
The irrigation potential for Botswana in the Zambezi Basin ranges from 80 ha, considering identified soils and without the need for major water development works, to 11080 ha, including the need for major water development works. However, of this total area, 10,000 ha are located in the Padamatenga plains outside the Zambezi Basin in the north-east, to where it is planned to transfer water from the Chobe tributary. In this study, 1080 ha have been retained for the irrigation potential.
According to the irrigation subsector review of Zimbabwe, of the total internal surface water resources 13.6 km3/year, 25% is committed for domestic, industrial, mining and irrigation use. Of the remaining 9.5 km3/year, at least 3.0 km3/year is reported to be effectively inaccessible. Of the remaining 6.5 km3/year, about half is considered as potentially available for irrigation development, of which 1.94 km3/year in the Zambezi basin. In addition, there is the flow of the Zambezi River.
The Zambezi Basin in Zimbabwe has been divided into three hydrological zones. In the western and eastern zones, suitable soil is the limiting factor, while in the middle zone water is the limiting factor. At present over 70,045 ha have been developed or planned for irrigation. Based on land and water and considering an irrigation water requirement of 10,500 m3/ha per year, it would be possible to irrigate another 95,355 ha, so bringing the total to 165,400 ha. However, taking a water requirement of 18,000 m/ha per year as proposed in the irrigation subsector review would reduce the potential to 131,000 ha.
For Zambia, of the irrigation potential of 523,000 ha for the whole country the distribution of 355,000 ha over the different sub-basins is known, but no details on location are given for the remaining 168,000 ha, consisting of 100,000 ha of dambos (wetlands), 60000 ha irrigated by renewable groundwater and 8000 ha of commercial farms [214, 215]. The irrigation potential in the Zambezi Basin is estimated at 422,000 ha. An view of the rugged, very steep terrain of the southern highlands of Tanzania draining to Lake Malawi, no real possibilities for irrigation development exist and consumptive water use would be limited to domestic and industrial water supply. These are relatively small volumes and their quantities would not change the mean annual flow into the lake from Tanzania.
Malawi has abundant land where soil and topography are suitable for irrigation but only limited areas that coincide with easily obtainable water from perennial streams. An important feature of the flat lake shore and the Shire River valley landscapes are large areas of marshy land, swamps and lagoons, which are poorly drained and flood susceptible areas. The irrigation potential for the whole of Malawi has been estimated at 100,000 ha plus 61,900 ha of dambos (wetlands). 160,900 ha of this total are located in the Zambezi Basin.
The irrigation potential figure of 2 million ha given in literature for Mozambique includes the whole Zambezia province, part of which is located outside the Zambezi basin. The area within the Zambezi basin is estimated at 1.7 million ha.
For the Zambezi basin as a whole, the water requirements are much less than the water availability. Attention has to be paid, however, to the Chobe tributary, originating in Angola and shared by Angola, Zambia, Namibia and Botswana. The Zambezi River entering Zambia from Angola in the north has an annual discharge of 18 km3, which is twice the volume needed to irrigate the 700000 ha potential of Angola. The Chobe tributary, however, has a discharge of only 1.3 km3/year when leaving Angola, so if a large part of the irrigation potential area of 700,000 ha in Angola or if part of the irrigation potential of 159,000 ha in the upper Zambezi basin in Zambia is located in this sub-basin, problems may arise for Namibia and Botswana, even though irrigation potential there is very limited compared to the other countries.
Further downstream, no particular problems are expected in terms of water resources. However, water regulation would be necessary for full development of the potential.
Pollution is the poisoning of air, land and water with detrimental substances such as pesticides, sewage and heavy metals. Most pollutants cannot be seen, smelt or tasted. However, while it is easy to believe they are not there, pollutants produce a measurable change in the environment and affect human health, plants and animals.
The increase in the amount of discharges and types of pollutants in the Zambezi Basin is due to population growth, intensive urbanisation, as well as increased industrial and agricultural activities.
Pollution may originate from definite, single sources called point sources such as industrial processes, mining activities, and sewage effluent, or from sources that are not easily located, called non-point sources such as from agricultural land and traffic.
Point source pollution
Industrial Processes
Industry is the primary source of pollution in the Zambezi Basin, producing huge amounts of liquid effluents that often find their way into water bodies; solid waste, which is often dumped illegally on the land; and emissions that pollute the air.
Sources of industrial effluent range from pulp-and-paper mills to fertiliser factories and granulation plants, abattoirs, textile manufacturing using dyes and noxious cleaning chemicals, chemical and steel industries and others. These industrial processes produce large quantities of different kinds of pollutants. In steel manufacturing, for example, raw materials used include lime, iron ore and coal. The crushing and cleaning of the limestone and ore produces sludge and its disposal can pose problems. In the processing of the ore, other chemicals such as coke, sulphuric acid and tar are produced. The effluent from these processes contributes to pollution.
Wastewater from steel plants is not suitable for drinking or irrigation. Such effluent can also affect groundwater. For example, pollution by a Kwekwe-based steel company in Zimbabwe is said to discharge high quantities of iron, sulphate, oil and tar into the Kwekwe River, making the water unsuitable for irrigation and drinking.
The effects of the pollution are felt, as far afield as Lake Kariba where it is, for example, suspected to stiffen the trunks of elephants. In coastal areas, most industries dispose of untreated wastes directly into streams or rivers running into the oceans.
Thermal power generation is the largest source of transboundary air pollution in southern Africa with some of the plants located in the Zambezi Basin. Burning coal and coal-bed methane mainly generates thermal power in the region.
Gases emitted by the thermal power plants include carbon dioxide, nitrogen dioxide and sulphur dioxide.
The main effect from mining is the contamination of water bodies by soluble substances and toxic liquid effluent that are produced during mineral processing. Mining creates serious environmental problems in localised places within the Zambezi Basin. Most of the Basin's mining-related pollution comes from Zambia's copper mines, concentrated in the Copperbelt area.
In 1996-97, the copper mining industry produced over 17 million tonnes of solid waste, comprising mainly of overburden, waste rock, tailings and slag. Effluents from the mining operations discharged into the Kafue River and its tributaries, are high in suspended solids, copper, sulphates, zinc cobalt and iron.
Waste disposal
Approximately 95 percent of all the waste in the Zambezi Basin countries are disposed on land. It is therefore, essential that effective control mechanisms and guidelines be created for safe and acceptable land disposal practices. Problems with illegal dumping and littering require immediate attention.
The level of urbanisation in the basin worsens waste disposal problems. Harare, for example, generates more than 124,000 tonnes of solid waste annually. Besides poor waste disposal methods, another problem associated with such huge amounts of waste is that some of it comprises of plastics and metal cans that cannot decay or be recycled at present.
SEWAGE EFFLUENT
Sewage treatment facilities are largely inadequate in all the urban centres and are a major source of water pollution in the Zambezi Basin. Lake Chivero, outside Zimbabwe's capital Harare, for example, is highly eutrophic because sewage effluent is discharged into it from the city.
The lake is also the principal water supplier. In Zambia, the Kafue District Council discharges sewage into the Kafue River which drains into the Zambezi. In Livingstone (Zambia) and Victoria Falls town (Zimbabwe) treated effluent is discharged into the Zambezi River.
The problems, associated with pollution of Lake Chivero, are fish deaths and water hyacinth, which has covered the lake. It has also extended to Lake Kariba, threatening the lake's fishing and recreational activities.
Non-point sources
LEACHATE FROM LANDFILLS
Landfills constitute potential sources of groundwater pollution since they may contain organic micropollutants, heavy metals and high salt levels.
Landfills can either be open dumps or sanitary trenches, which are lined and can later be capped when full. Leachate from landfills impacts on water resources mainly because all landfills in the basin are not well planned and managed to monitor leachate production.
Use of pesticides and insecticides
Agriculture relies heavily on chemicals to kill unwanted disease, insects, plants and animals. The degree of environmental concern for a particular pesticide depends on how long it lasts in the environment, and how much is used.
In general terms, wildlife near commercial farms are more exposed to pesticides than those in remote areas.
DDT (dichlorodiphenyltrichloroethane) was one of the major pesticides used to control pests such as tsetse fly in the basin. Due to many risks associated with DDT and other such compounds, use has been limited and banned for many agricultural purposes.
Gold panning
The proliferation of riverbed and alluvial gold panning has resulted in serious damage to the basin's rivers, posing serious consequences on future water supplies. During heavy rains, the riverbanks often collapse, resulting in loss of vegetation, erosion and river siltation.
Siltation of rivers from gold panning can reduce river conveyance and the storage capacity of reservoirs, as well as the operational life of water bodies. A 1992 report reveals that half of Zimbabwe's dams are 50 percent silted and that for some rivers it was no longer economically viable to construct new dams.
TRANSPORT
Road, air and water transport cause various forms of pollution, including noise, air and water pollution. Vehicles driven by fossil fuels emit, for example, nitrogen oxides (NOX), carbon monoxide (CO), carbon dioxide (CO2), volatile organic compounds (VOCs) and heavy metals. Ground level ozone (O3) that reduces agricultural productivity and the growth of trees is formed from the reaction of NOX, VOCs and sunlight.
Noise pollution from aircraft is mainly restricted to airport termini, which in most areas of the Zambezi Basin tend to be located far away from residential areas. Noise from road transport is worsening due to the growth in the number of vehicles and the absence of regulations that limit the amount of noise produced by cars.
The regulations are also silent on the permissible levels and types of fumes, which cars can emit.
STORM WATER RUNOFF
Urban runoff can easily pollute water sources if the towns are not well planned to contain drainage. Drainage water is dirtier than the partially treated sewage effluent, and is difficult to manage since it emanates from non-point sources.
Runoff from towns and cities contributes to high concentrations of lead (from vehicle exhaust fumes), phosphorous and nitrogen (from decaying matter), and spillages from sewage works due to storm water entry into sewers.
The Zambezi Basin (located between 8oS and 20oS latitude, and 16.5oE and 36oE longitude), drains an area of about 1.3 million square kilometres (sq km), and covers about 23.4 percent of the total area of its riparian countries. The Zambezi River flows over a distance of nearly 3,000 km, dropping in altitude from its source in the Kalene Hills of North Western Zambia, 1,585 metres above sea level, to its delta in the Indian Ocean, 200 km north of the Mozambican port of Beira. The river's major tributaries include the Luena and Lungue-Bungo in Angola; the Chobe in Botswana; Shire in Malawi; Luiana in Namibia; Kabompo, Kafue and Luangwa in Zambia; and Manyame, Sanyati and Gwayi in Zimbabwe.
CLIMATE & GEOLOGY
Most of the basin lies about 400 m above sea level, with subdued topography. This results in extremely hot summer and low winter temperatures. The basin mainly consists of Karoo sediments. The Karoo rocks host all known coal reserves in the basin while the thick sedimentary rocks have a potential for the production of petroleum and natural gas.
WATER RESOURCES
The basin features various surface and groundwater sources. These include wetlands such as the Kafue flats (about 7,000 sq km) and the Lukanga swamp (about 2,600 sq km) both
The Zambezi River Basin has eight riparian states; Angola, Botswana, Malawi, Mozambique, Namibia, Tanzania, Zambia and Zimbabwe. This makes it the second most shared basin within the Southern African Development Community (SADC) region after the Congo. along the Kafue River, and the Barotse floodplains in the Upper Zambezi. The floodplains regulate the Zambezi River water delivery throughout the year, absorbing water during the rains and slowly releasing it downstream over time. There are also major natural lakes including, Lake Malawi (referred to as Lake Nyasa in Tanzania and Lake Niassa in Mozambique) and Lake Bangweulu (Zambia). Two major artificial lakes: Lake Kariba (shared by Zambia and Zimbabwe) and Lake Cahora Bassa (Mozambique) were created after damming the Zambezi River.
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