A BASELINE STUDY OF GROUNDWATER POTENTIALS IN ANAMBRA STATE, NIGERIA

SOURCE:

Faculty: Engineering
Department: Agricultural And Bio-resources Engineering

CONTRIBUTORS:

ANIZOBA, D.C
ORAKWE, L.C
CHUKWUMA, G.O

ABSTRACT:

Vertical electrical sounding and water analysis were carried out in Anambra State, Nigeria, with the aim of having a baseline study of groundwater potentials across the State. Two hundred and seven (207) vertical electrical soundings (VES) data were acquired using Schlumberger configuration with maximum current electrode spacing of 300m across the study area. The VES data were interpreted with the aid of resistivity iteration and inversion software IX1D. Twenty-two borehole water samples were collected and analysed. The results of qualitative interpretation of the VES data revealed that the study area has eleven (11) typical curve types with the most predominant being the HK and KHK-curve types with 34.3% and 20.8% respectively, whereas the remaining 44.9% belongs to the other nine curve types. The generated resistivity curve types show typical H-curves, which are quite common in a sedimentary environment for multilayer structures. The results of the correlation between the VES interpretations and borehole logs show mainly four to six geo-electrical layers namely; top soil, shally-sand/clayey sand, sand, dry sandstone, water saturated sandstone, and shale. The results also show that the water saturated units have thickness between 18.73 – 64.75m and resistivity between 23.09 – 5014 Ωm across the area. The results showed that depth to the water saturated sandstones (aquifer) within the study area ranged from 63.17 – 258.26 m. The computed aquifer parameters for the interpreted VES data showed that the values of various parameters ranged from low to high across the areas: longitudinal conductance (3.03x10-3 to 1.04 mhom); transverse resistance (5.53 x102 to 1.40 x107 m-ohm); erodibility (4.90 x10-3 - 1.15 x102 m/day); fractured contrast (8.64 x10-4 – 1.36 x101); reflection coefficient (-0.8632 to 0.9983); and aquifer conductivity (1.22 x10-4 to 4.33 x10-2 mho). It also revealed that the hydraulic conductivity of the area ranged from 4.39 x10-2 to 15.61 m/day; while the transmissivity values ranged from 1.09 to 373.56 m2/day. A mathematical model generated revealed that the aquifer hydraulic conductivity is inversely related to aquifer resistivity in the area. The water analysis revealed that almost all the water samples from the boreholes fall within the acceptable limit for drinking water and therefore, they are satisfactory for human consumption. The juxtaposition of water table level with topography showed that the water table level follows the topography, which implies that the topography controls the configuration of the groundwater. The groundwater flow direction is northeastern to southwestern (NE-SW) path within the study area. The groundwater model across the study area showed that the eastern and western parts of the study area which include Ebenebe, Okpeze, Oroma-Etiti, Ukpor, Ihiala, Okija, Oguaniocha, Ossomala etc possess deeper depth to the aquifer, as such, the cost of siting borehole there will be high, compared with other areas. Based on the results, the aquifers in this study area are capable of yielding enough water that would be sustainable and reliable for the immediate environs.