African Water Development Report 2006 - United Nations Economic ...

African Water Development Report 2006Table 6.2: Water Balance of Large Aquifer Systems in the CongoAquifer Systems P (mm) ETR (mm) P-ETR Ie (mm) Kr (%)Coastal sedimentary basinContinental lands of the CongolesedepressionOld sedimentary seriesCrystalline and schistose crystallinerocks128017641510185789511021038Depletion of Water Resources ThroughHuman ActionAvailable resources are being depleted throughhuman action which reduce their quality as wellas quantity. Water contamination is rife across thecontinent and result from industrial pollution,poor sanitation practices, discharges of untreatedsewage, throwing of solid waste into storm drainsand non-control of leachates from refuse dumps.A major problem is pollution from food processingwaste and decay from aquatic life. Theseproblems are compounded by poor land use andagricultural practices. As a consequence, concentrationsof waste frequently exceed the ability ofrivers to assimilate them, and water-borne andwater-based diseases have become widespread.The consequent deterioration of water quality isa significant form of depletion since it reducesthe availability of usable water resources, thusincreasing the cost of their development andrefinement and increasing scarcity. Figure 6.3shows the dynamics of water availability andfreshwater scarcity for the years 1990-2000.The deterioration of the quality of water, especiallysurface waters, also results from eutrophicationand the proliferation of invasive aquaticplants. Eutrophication is a factor mainly foundin lakes. Water hyacinth has already seriouslyaffected most water bodies like Lake Victoria,Lake Chivero and the Nile River. Future threatsmay include pollution from petroleum productionand refineries, pollution from agricultural956Source: AWDR National Report, 2003. Moukolo and al (1992) Note: P (mm): rainfalls in mm; ETR (mm): real evapotranspiration in mm; Ie (mm): effectiveinfiltration in mm; Kr (%): percentage of runoff coefficient.3856614729013676403396975,51,28,811,0waste, such as fertilizer and pesticides, and pollutionfrom small-scale industries dispersed inlarge urban areas. The impact of saltwater intrusionalready mentioned is felt mostly along theMediterranean coast and the oceanic islandssuch, as the Comoros, which are highly dependenton groundwater resources. It is due in partto overexploitation of groundwater resources.Water Conservation in AfricaHuman activity associated with the use ofwater bodies, through the construction of reservoirs,canals and various structures for waterintake and discharge may cause great changesin the hydrographic network and river runoffregime. Reservoirs are an important componentof the hydrographic network in Africa.There were no large reservoirs in Africa priorto the 1950s as most of Africa’s large waterprojects started during the period 1954-1977. Four out of five of the world’s largestreservoirs are in Africa. These include LakeVictoria at the Owen Falls Dam, lake Nasseron the Nile, Kariba lake on the Zambezi andAkosombo lake on the Volta (Shiklomanov,2002). At present, about twenty reservoirs areunder operation or construction, each havinga capacity of more than 5 km 3 . There are morethan one hundred reservoirs in operation orconstruction have a capacity exceeding 100mln m 3 .130