Hydrology and chemistry of surface and groundwater resources of the Aguata area, SE Nigeria

Abstract

The project area is underlain by two Tertiary sedimentary rock sequences, i.e. the Imo and the Ameki Formation. The Imo shales generally occupies the Eastern lowlands, with patches of relatively resistant crust of laterite and ironstone forming rounded to sub-rounded, oval-shaped hills and small ridges often standing above the general ground level. The elevations vary from 92 to 166 m. One outstanding feature of the study area is the N-S trending escarpment, underlain by the Nanka Sands of Ameki Formation. The cuesta which attains its maximum altitude of about 366 m at Igbo-Ukwu forms the Western Upland with gullies of variable magnitude deeply incised at different locations along the scarp fronts. The soil erosion is, on the whole, very active and devastating, especially along the eastern slopes.The map area is drained by the Aghomili river system. The western tributaries of this river run parallel to one another. The headwaters forming the drainage pattern emerge as numerous groundwater effluents, generally with small yields. The low discharge is thought to be due to the direction of flow being opposite in character to the dip of the sand beds—obsequent discharges.The Aguata area, on basis of lithology, is split into two hydrogeologic provinces, namely the eastern region with fairly high density of rivers, streams, springs and lakes, and the western region generally devoid of these surface water bodies. Whereas most of the eastern district appears to have adequate sources of surface water and commonly lacks good ground water potentials, the western region (Western Upland) is rich in ground water but generally is deficient in surface water. Surface water can only be found at the lower eastern slope of the cuesta and to the southwest of the town of Uga. The towns and villages located in this area (the cuesta zone) experience acute water shortage. Information of boreholes from adjacent areas show that the depth of water table of the Nanka Sands varies from 93 m at the St. Joseph's Hospital compound at Adazi to 264 m at Igbo-Ukwu. The Imo Shale environment contains several thin aquifers with water seepages issuing at different horizons.Most of the tested water samples are wholesome, springs are clear and colourless, but streams, rivers, etc. are, more often than not, turbid because of sediments and organic matters in suspension. pH range 5.2–6.8 and TDS of 24–112 ppm classifies the sampled streams, rivers, etc. as almost meteoric water. All the water samples are characteristically low in total dissolved solids (TDS) and ostensibly in specific conductance. Coliform count test suggested that coliform organisms lie between 25 and 900 per 100 ml. This range is considered too high for potable water. However, the physical and chemical test produced water with properties generally satisfactory for most domestic and industrial vantages.