Aquifer characteristics and groundwater flow system in a typical basement complex and Gundumi formation northwest, Nigeria

Abstract

Aquifer performance was tested in 280 locations of the study area to assess the hydraulic characteristics of the various aquifers, potential yield from the flowing boreholes of both hard rocks and sedimentary formation underlain Zamfara State Northwestern, Nigeria. Pumping test result were subjected to standard methods of Jacob’s and modified Theis equation for evaluation of aquifer parameters such as hydraulic conductivity (K), Transmissivity (T), Specific capacity and others. The results show that characteristic of areas underlain by crystalline rock units, especially migmatite, variably migmatized gneiss, schists and granites are characterized by thin/shallow overburden unit of usually less than 10m. In such settings the borehole depth varies from 38 to 78m while saturated thickness varies from 8 to 20m below ground level, with average yield of 44.1m3/day. Hydrogeological parameters obtained from pumping test analysis within the basement rock units revealed aquifer transmissivity (T) values which range from 0.14 to 141.23m2/day, with an average of 12.85m2/day. This implies aquifers of negligible to high potentials. The hydraulic conductivity (K) values vary from 5.0 x 10-2m/day and 8.8 x 10-1m/day with an average of 2.2 x 10-1m/day. The implication of these results is that the aquifers of the basement rock units cannot provide sufficient water for both domestic and agricultural needs of the area. However, Sixty-eight (68) analyzed borehole data set within Gundumi Formation, revealed the average discharge rate of 116.8m3/day. This formation shows the highest water discharge within the study area. The average penetration depth of 65m was achieved. The hydraulic conductivity of this aquifer revealed average value of 5.7 × 10-1m/day. This implies high permeability of aquifer system, which is typical of sedimentary formation of this nature. Transmissivity (T) revealed an average value of 38.89m2/day, which indicate high rate of water flow through the entire aquifer medium of this formation. The geospatial analysis of yield from the wells indicate excellent groundwater potential around the western part of the study area.