Non-Darcian effect on a variable-rate pumping test in a confined aquifer

Groundwater flow in an aquifer has frequently been found to be non-Darcian. In this study, a transient model of a variable-rate pumping test in a confined aquifer was established considering non-Darcian flow in the aquifer. A piecewise-linear function was adopted to reproduce the variability in pumping rate, and the classical Izbash equation was employed to describe the non-Darcian flow. The type-curve analysis suggested that a smaller quasi-conductivity will result in an earlier deviation and a smaller extent of the decreasing features in the drawdown under the condition of a linearly decreasing pumping rate compared to that under the condition of a constant pumping rate. The sensitivity analysis indicated that the variability in pumping rates under non-Darcian flow can increase the sensitivity of drawdown to the radius of the well casing at inflection times of the discrete linear stages, and drawdown closer to the pumping well is more sensitive to the change in the well casing. A type-curve method was proposed and employed to interpret the pumping test data, which were collected at a field site located in Wuxi city, Jiangsu Province, China. The parameter estimates indicate a high possibility of the occurrence of prelinear flow in the aquifer of interest.