Extent and Distribution of Groundwater Resources in Parts of Anambra State, Southeastern, Nigeria

The extent and distribution of groundwater resources in parts of Anambra State, Nigeria has been investigated. The results show that the study area is directly underlain by four different geological formations including, Alluvial Plain Sands, Ogwashi-Asaba Formation, Ameki/Nanka Sands and Imo Shale, with varying water storage and yielding capacities. Borehole depths within the Alluvial Plain Sands are shallow (5-30m) yet the sands are excellent aquifers with high yields (3-5 litres/sec) especially along the Anambra West – Onitsha - Ogbaru L.G.A. axis. Elsewhere the yield is low (about 0.5litres/sec) and may dry up at peak dry season periods. The Ogwashi-Asaba Formation occurs in a north-southerly trend and underlies Ekwusigo, Nnewi North and South and Ihiala Local Government Areas. This formation consists of multiple aquifers and a depth to water table ranging from 50 to 110m. Within it, transmissivity values of 37.54 to 95.5m2/day and a yield of up to 5litres/sec were recorded. The Ameki/Nanka Sands is a prolific water producer and underlies Aguata, Anaocha, Njikoka, Dunukofia, Oyi and Anambra East Local Government Areas. Four aquifer horizons were identified within this formation, designated; shallow, upper, middle and deep aquifers. The most exploited are the upper and middle aquifers, while the least, but most prolific is the deep aquifer with an average yield of 5litres/sec. Imo Shale, because of its sedimentological nature is a poor aquifer. The gravelly intercalations within this formation are usually too thin to sustain continuous water pumping. This study indicates that the extent and distribution of groundwater within the study area is controlled predominantly by lithology and other secondary factors including topography and nearness to source of recharge.