Dar Zarrouk Parameter as a Tool for Evaluation of Well Locations in Afikpo and Ohaozara, Southeastern Nigeria

Abstract

The inhabitants of this area depend solely on contact springs as supply source of potable water. However, provision of potable water to meet the needs of the people still remains an unsolved problem. Therefore, this paper attempts to solve this problem by using Dar Zarrouk (D-Z) Parameters; Total Transverse Unit Resistance, T (Ωm 2 ) and Total Longitudinal Unit Conductance, S (Ω - 1 ) to suggest optimal locations for drilling of boreholes in the study area. To attain this purpose, 50 Schlumberger Vertical Electrical Sounding (VES) curves with maximum current electrode spacing of AB /2 = 681 m were interpreted. Thus, the aquifer parameters information estimated from the (VES) curves were used to prepare contour maps of T (Ωm 2 ), S (Ω - 1 ), aquifer thickness h ( m ), aquifer resistivity ρ (Ωm), and Water Table Depth (WTD). For effective use of these parameters, iso-thickness and iso-resistivity maps were compared with contour map of transverse resistance. The good agreement between these parameters provided the basis for identification of prolific aquiferous zones. It was observed that the Southern part of the study area majorly underlain by the Afikpo Sandstone of Nkporo Formation (Campanian-Maastrichtian), relatively showed higher T (Ωm 2 ), h (m), and ρ (Ωm) values, which implies high yield aquiferous zones. The relatively loose structure of this sandstone unit, coarse grains, and sorting enables it to be porous and permeable. The Northern part of the region which shows low values for T (Ωm 2 ), h (m), and ρ (Ωm) suggests low productivity for the aquiferous zones. The paucity of water in this parts of the study area can be explained to be as a result of the dominant geology. The high S , values at the Uburu and Okposi locations in this region suggests the presence of saline aquifer. This study would be relevant to the development of effective ground water scheme and for future hydrogeological investigations in the area.