Determination of Aquifer Hydraulic Parameters Using Single Well Pumping Test Borehole Data within Boki Local Government Area, Cross River State, South Eastern Nigeria

Abstract

Pumping test is done to determine the performance and efficiency of a well and also to characterize and parameterize the hydraulic properties of an aquifer. Twelve (12) drilled boreholes constructed within Boki Local Government Area were subjected to a number of pumping tests: Step drawdown, Constant discharge and Recovery tests to provide estimation of hydraulic parameters of the study area. The Cooper Jacob’s Straight-line Equation was used to analyze the pumping test results of drawdown with respect to time. This method was chosen because it is built upon the most simplified assumptions. The aquifer hydraulic properties were estimated from the pumping test by fitting mathematical models (type curves) to response data (water level changes) through computer software known as AQUIFER TEST. The result obtained shows that; Transmissivity ranges from 6.67 x 10-4m2/day to 2.50m2/day with average of 2.15 x 10-1 m2/day. The hydraulic conductivity ranges from 5.13 x 10-5m/day to 1.67 x10-1m/day with average of 1.59 x 10-2 m/day. The borehole yield ( specific recharge) ranges from 1.30 l/s to 1.97 l/s. with the average of 1.50 l/s. while the specific discharge range from 8.02 x 10-4 m2/day to 11.157 m2/day with average of 1.387m2/day. The static water level ranges from 5.1m to 14.1m. The borehole drilled depth ranges from 22m to 54m. The saturated thickness of the aquifer ranges 13.8m to 42.3m. The litho-logs of the boreholes confirms that the estimated hydraulic parameters were obtained from semi confined highly weathered to fairly weathered migmatite saturated fractured basement aquifers (Aquitard). In comparison, Five boreholes (or 41.7% wells) had yield that ranges from 1.5 to 1.97 l/s above seven boreholes (or 58.3% wells) of lower yield that range from 1.3 to 1.5 l/s. Boreholes of higher yield have shallow water level and located on highly weathered and fractured basement within the high topography region of the study area. Because of the general low transmissivity values in the study area we recommend that all the boreholes should be installed at depth of at least three meters (3m) above the drilled depth. Also the mean yield value above 1.0 l/s of the boreholes indicate that the wells can sustained motorized pump over hand-pump and can produce more than 120 m3/day of groundwater.

Keywords: Pumping-test, weathered, migmatite, hydraulic-parameters,transmissivity,boreholes/wells, Boki.