Venezuela

In Nigena, groundwater S01Jrces supply water to aboul a quarter ol 1ls population Between 1979 and 1984, lhe Federal Government or Nigena embar1ted upon a national groundwater l)fogramme lo augment the actJv1beS of Slate Government who because of funds could not rnplcment lhoit pipe-borne water supply programme, (AdomoroU, 1987)

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57

The magnitude of Nigeria's groundwater reserves is not fully known. However, recent well and borehole invesUgations carried out by the U.S. Geological Survey and other interested bodies are yielding valuable data. Groundwater resources are smaller m quantity and are less evenly distributed than surface water, but, significantly, groundwater is available in

certain areas, such as the Chad basin, which are poorly endowed with surface water and where its e)(ploilation could be a crucial factor in economic growth and development (Areola,

1980).

Springs are very Important sources of water supply especially in the rural areas of Nigena Small water table springs and seeps, most of which are perennial, Issue from perched or confined aquifers particularly In the Basement Complex rock areas The seepage springs are important nol only because they form sources of local water supplies but also because they support perennial Rows In large rivers such as the Kaduna and the Gurara (Areola, 1980). Large springs are common 1n the sedimentary rock areas Including Sokoto and Kerri Kerri. The large springs are the major sources of water in the false-bedded sandstone areas of ldoma division of Benue State and of the Nsukka (UdQ plateau m Anambra State.

The country 1s divided Into different geological areas and these affect the water-beanng capacity of the rocks in such areas These rock areas lncludo the basement complex rock are ⁸³ and the sedimentary rock formations. The Nigerian Basement Complex occupying approximately 50% of the surface area of Nigeria Is part of the African crystall1ne shleld , It includes tho oldest ^k/lOW!1 rocks In Nigeria and Is composed mainly of gneisses. magm.nblos

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and granites. Groundwater occurs in the Basement Complex either in the weathered mantles, or in the joints and fracture system in the un-wealhered rock. The presence of

groundwater in any given area therefore depends on Whether a sufficient thickness and extent of decomposed lractures are present in the fresh rock (Faluyi and Azeez, 1981 ).

The Basement Complex rock areas of Nigeria are comparatively poor in groundwater reserves. The rock consists of igneous and metamorphic rocks, which are neither porous (porosity ranges from 1-3%) nor permeable except in areas where they are cleaved, shattered, jointed or fissured. These weak zones in the rock are too localized; however, to be of any great significance as reservoirs of water (Areola, 1980).

Nevertheless, there Is some groundwater In the Basement Complex rock area, which could provide for the needs of rural communmes with moderate rates of per capila water consumption. The major problem is how to locate the available bodies of water. In the pasl several wells dug in these areas failed to strike ,vater, which was allribuled lo the nature of

the weathering front or basal surface. Because of the locally high porosity and permeability of the weathered materials, some of the basin form Isolated or confined aquifers They exhibit a d1sconbnuous nature, which is emphasized by the dlrocllon of now ol lhe springs In these Basement Complex areas, which Is m different directions and at different poinls. The Sed,menlary rock formations contain large reserves of groundwater The coastal belt of Nigeria ¹⁹ parti:Utiltly well endowed and, In somo places the water lies very close to the surface lo lhcSO formatJons 11 Is only In a narrow bell near tho lagoon lhal !hero IS any nsk of

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contamination of groundwater sources by saltwater. The Chad Basin built up on thick deposits of marine and continental sediments ls also well endowed with groundwater although the regional water table is lower than in the coastal region. Wells dug into the main aquifers usually obtains adequate supplies by seepage from a few metres below the water

table. Since there are clean sand and gravel in the geological sequence especially or the

western part of the area, wells and boreholes are high yielding (Areola, 1980).

Groundwater occurrence in Oyo State is limited to the fractured zones or the crystalline Basement Complex rocks and to the alluvial sediments of the ftood plains ol the major streams. Most groundwater In the state occurs under water table cond1tloos and Is open to recharge during the rainy season. Alluvial aquifers in the state are also in direct contact with the streams. Because they are hydraulically connected to the streams, they both contnbute

to stream now as well as receive recharge from the streams under favorable conditions

(FEPA, 1998).