HYDROGEOPHYSICAL APPRAISAL OF RISHA, PART OF AKWANGA SHEET 209NE, NORTH CENTRAL NIGERIA

Ageological traverse was undertaken in Risha, part of Akwanga Sheet 209NE North-Central Nigeria to appraise the rock types and their structural patterns that might enhance prospect for water. The geological traversing revealed basically three rock types which include schistose-gneiss, granite-gneiss and pegmatite (as veins and/or dykes) with their main structural pattern trending mostly NW-SE. Twenty three (23) Vertical Electrical Resistivity Soundings (VES) were carried out in the area using the Campus 0? .vega digital resistivity meter. This is in order to study the subsurface geological layers with a view to deterrrT <o the thickness, geoelectric layers, the depth to basement, aquiferous zones and groundwater potential. Field i. a obtained were interpreted quantitatively and qualitatively. The field curves were typical of H, KH, HK, A and K ', oes. There are majorly five- Six geoelectric layers consisting of topsoil (sand/clay) with depth range of 0.3-2.- and resistivity value of 66- 2850Qm. The second layer is lateritic clay with depth range of 0.4-5.7m and The third layer has a depth range of 1.2-8.6m with resistivity of 40-4591 Qm while the fourth layer, weathered rocks or regolith, has a depth range of 3-33m and resistivity range of 49-236601 !m.Two locations gave six lithological layers/units being partially fractured/fresh basement with resistivity vaiues of 1028-4574Om and depth range of 11.4-24m. The geoelectric section was produced and correlated with the existing geology of the study area and it was found to be in conformity with the existing geology. The water potential of the area may be classify as poor, moderate, good and very good and varied from location to location. The groundwater potential areares . ity p-nge of 222-3575Qm. varies with high potential around Risha, Tidde and Ridam compared to Ade-Katako, Ngazzu, Angwan Dorowa, Ngakide and Adande. Based on the textures, structural pattern and well measurement interpretations, the granite gneiss was observed to have more water prospectivity than the schistose gneiss.