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

African Water Development Report 2006Groundwater in AfricaGroundwater is extremely important in Africa.It is estimated that more than 75 per centof the African population uses groundwater asthe main source of drinking water supply. This isparticularly so in North African countries, suchas Libya, Tunisia, and parts of Algeria and Morocco,as well as in Southern African countries,including Botswana, Namibia and Zimbabwe.However, groundwater accounts for only about15 per cent of the continent’s total renewablewater resources. In South Africa, for example,groundwater accounts for only 9 per cent. As arule, groundwater tends to occur in small sedimentaryaquifers along the major rivers and inthe coastal deltas and plains. Groundwater resourcesare crucial for many countries and peoplein Africa, particularly during the dry season andin large arid zones. Groundwater is a main sourceof water in many rural areas, including for nearly80 per cent of the human and animal populationsin Botswana and at least 40 per cent in Namibia(GEO 2000, 1999). In Libya, groundwater accountsfor 95 per cent of the country’s freshwaterwithdrawals, while in areas such as the PanganiBasin of Tanzania groundwater is a significantsource for irrigated agriculture. In many parts ofthe continent, groundwater resources have notyet been fully explored and tapped.Renewable groundwater resources in North Africaare in the form of shallow alluvial aquifers,recharged from the main rivers (such as the alluvialaquifer beneath the Nile Delta in Egypt)or from precipitation (along the north AfricanMediterranean coast). In the Sahara Desert, themajor water resources are the combined NubianSandstone Aquifer (NSA) and the ContinentalIntercalaire non-renewable aquifer, which extendfrom Egypt to Mauritania. Current annual ratesof groundwater withdrawal in the subregion are407 per cent of the recharge rate in Egypt, and560 per cent in Libya. Exploitation of groundwaterresources over the past ten years has ledto a reduction in water pressure levels at the oasisof the western desert. Over extraction fromthe delta shallow aquifer has led to increasedwater salinization and a rapid inland advanceof the saltwater interface. NSA is a huge fossilwater resource located in the eastern Sahara. Itis shared among four countries (Chad, Egypt,Libya and the Sudan) and contains an estimated150 000 km 3 of groundwater. The total currentextraction from the NSA is estimated at 1 500million m 3 /yr (UNEP Africa Environment Outlook,2002). Owing to the highly variable levelsof rainfall in Africa, large numbers of peopleare dependent on groundwater as their primarysource of freshwater (UNEP, 2002). In Algeria,for example, more than 60 per cent of all withdrawalsare from groundwater and, in Libya, 95per cent of all withdrawals are from groundwater(fig. 4.7). Other countries, such as Algeria,Egypt, Libya, Mauritius, Morocco, South Africaand Tunisia, make use of desalinated water toassist in meeting their withdrawal requirements(UNEP 2002).64