Determination of Dar Zarouk Parameters for the Assessment of Groundwater Resources Potential: Case Study of Imo State, South Eastern Nigeria

Abstract

The vertical electrical soundings (VES) method of geophysical survey using the Schlumberger configuration with a maximum electrode spread of 900m were carried out in parts of Imo State of Nigeria in order to determine the aquifer Dar Zarouk parameters. Using the estimated value of hydraulic conductivity from drilled boreholes and interpreted electrical sounding data around the borehole, the transmissivity variation within the area were determined. The values obtained are moderate and fairly uniform, ranging from 551.695 m²/day to 556.607 m²/day and are consistent with the geology of the area. The transverse resistance values ranged from 4366 measured at Okohia (VES 12) to 953310 btained at Anara (VES 11). Similarly the isoresistivity map for L/2 = 150m shows that the area is generally underlain by fairly high resistivity materials with the Western half being more resistive than the eastern part. Separating these two regions is a very narrow low resistivity area in the central part around Okohia with value of 200. The variation in resistivity could be linked to differences in geology, topography, drainage system, water quality and degree of saturation. The low resistivity observed in the central part could be associated with the presence of Oramiriukwa River. On the basis of longitudinal conductance, three major zones are identified. Zone A which covers the western and North-eastern parts is underlain by relatively low resistive aquifer materials. This zone is more promising for siting productive boreholes. The central area makes up Zone B while the third zone (Zone C) is underlain by high resistivity (low longitudinal conductance) aquifer materials. This zone may not be good enough for drilling boreholes with high yield expectation.

Key Words: Dar Zarouk, Isoresistivity, transverse resistance, longitudinal