The hydrogeology of the Gombe subcatchment, Benue Valley, Nigeria

Abstract

The area of study, which is about 90 km 2, is underlain by five major stratigraphic units of Paleocene to Cretaceous age except for the Precambrian Basement Complex inlier which forms about 2.7% of the rocks present. Results of our investigation show that the Kerri-Kerri Formation is of aquifer type material but dry in the surveyed area. The Gombe Formation with its high percentages of silts is slightly permeable, whilst the Pindiga and Yolde Formations are essentially aquicludes, although the latter has scattered water-bearing horizons. Chemical analyses of borehole water indicate good quality water despite the differences in depth of sampling. Two groups of water emerged—sodium bicarbonate rich and sodium bicarbonate deficient types. Results of isotope hydrology suggest that the sodium deficient type water has similar characteristics to the waters from the middle zone aquifer of the Chad basin and deep aquifer of the Sokoto basin. The highest computer transmissivity value ( T) of 432 m 2/d and storage coefficient ( S) of 2.3 × 10 −3 in the subcatchment were for the Bima Formation. The Bima Formation is thus the best aquifer in the subcatchment. Since the available data show that the aquifer of the Bima Formation is gradually being over-developed, and the observed characteristics of a few boreholes in the Pindiga and Yolde Formations are encouraging, a detailed hydrogeological assessment of the other Formations in the Gombe subcatchment is recommended.