A New Method For Estimating Hydraulic Conductivity In Un-Screened Concrete-Lined Large-Diameter Hand-Dug Wells

Abstract

The use of large-diameter hand-dug wells as main source of rural water supply for drinking, domestic and irrigation uses in many developing countries has offer an opportunity to developed Darcy-based methods for estimating hydraulic conductivity in screened-lined large-diameter hand-dug wells to determine the yield and discharge potential of the wells. However, in many rural areas of sub-Saharan African countries, the use of unscreened concrete lining is most common method of protecting large-diameter hand-dug wells against collapsing and pollution due to the affordability of the method. The use of un-screened concrete lining prevents horizontal water flow to the well and inflow of water in un-screened concrete well occur through well base, therefore, existing Darcy-based method not suitable to estimate hydraulic conductivity for this well design. This study proposed a new method for estimating aquifer hydraulic conductivity for un-screened concrete-lined largediameter hand-dug wells. To demonstrate the viability of the new method, field recovery tests were conducted in twelve (12) un-screened concrete lined large-diameter hand-dug wells to estimate apparent hydraulic conductivity (Ka) of aquifer formation. The twelve (12) un-screened concrete wells were screened for the second round of recovery tests to estimate horizontal hydraulic conductivity K. The results showed that the estimated apparent hydraulic conductivity Ka values were lower than the horizontal hydraulic conductivity K values and this show effect of un-screened concrete-lining. A relationship between Ka and K was established to make a correction factor for estimation of K from Ka by a regression analysis which showed a linear regression of 0.78 with a significant strong relationship of 0.00 between Ka and K using a bivariate Pearson correlation coefficient. The new method will be useful to determine well yield most especially in the rural areas of developing countries where un-screened concrete-lined large-diameter hand-dug wells are being practiced.