Effects of pumping flow rates on the estimation of hydrogeological parameters

Abstract

Abstract In this paper, we examine the accuracy of estimating the hydrogeological parameters, transmissivity (T) and storativity (S), in a confined aquifer, when there are not enough available data for pumping flow rate values. While the most popular methods, used to estimate aquifer characteristics, assume that the pumping flow rate is constant during pumping, this is practically infeasible. Violation of this assumption results in errors, which are examined in this paper using field drawdown measurements. To find the aquifer characteristics, we use two methods, testing various pumping flow rates. Firstly, we employ the Cooper -Jacob equations to calculate (T) and (S) values. Afterwards, we use these values to create hypothetical drawdowns using Theis equation and finally we estimate the Root Mean Square Error (RMSE) between the actual and the hypothetical drawdowns. Then, we repeat the same process, replacing the Cooper -Jacob equations with Genetic Algorithms and Theis equation to find the aquifer characteristics by minimizing the RMSE between the actual and the hypothetical drawdowns. Although the process is applied only in three datasets, the results indicate that regardless of the method used, the obtained values of aquifer characteristics (T, S) are not considerably affected by inaccurate pumping flow rate estimations.