GEOLOGY AND HYDROGEOLOGY OF GROUNDWATER SYSTEMS OF YOLA AREA, NORTHEAST, NIGERIA
Gabriel .I. Obiefuna1 and Donatus M. Orazulike2
1Department of Geology;Federal University of Technology, Yola, Nigeria.
2Geology Programme, Abubakar Tafawa Balewa University, Bauchi, Nigeria.
Email: gobiefuna2000@yahoo.com
ABSTRACT
The study Area which is underlain by the Bima Sandstone Formation occupies an area of about 431Km2 in northeastern Nigeria. Groundwater in the area occurs in two aquifer systems namely the upper alluvial aquifer and the lower-semi-confined to confined aquifer systems. The upper alluvial aquifer system occur at a depth range of 20m to 80m with an average thickness of about 39m and have undergone lower diagenetic alteration, and thus behave like recent or quaternary sands. The mean hydraulic conductivity is 2.54m/d with a corresponding mean transmissivity value of 237m2/d determined from both the pumping test method and the Statistical Grain-size method with an average yield of about 9.63m3/hr which indicate poor to moderate aquifer. The lower semi-confined to confined aquifer system occur at a depth range 80m to 250m with an average thickness of about 14.52m and have undergone inherent compaction/cementation(diagenetic effect), probably arising from the longer burial history. These gave a mean hydraulic conductivity value of 3.81m/d and a mean transmissivity value of 103.51m2/d with an average yield of about 47.25m3/hr and thus a moderate to good aquifer. The average linear groundwater velocity estimated from Darcy’s Law range from 27.48m/yr to 79.33/yr for the upper unconfined aquifer system and from 48m/yr to 149m/yr for the lower semi-confined aquifer system respectively. Linear-regression analysis of the transmissivity and specific capacity indicate a good correlation between log transmissivity and log specific capacity for the underlying aquifers. Finally with a total groundwater reserve of about 5,826,904,500m3 estimated for the study area as well as the relatively high recovery rate of the boreholes indicates very high groundwater potentials of the underlying aquifers.
The above information will also give insight into the hydrogeology and assist in the overall groundwater resources management of the area.
Keywords: Groundwater, aquifer systems, transmissivity, Yola, Nigeria