Numerical analysis of drawdown in an unconfined aquifer due to pumping well by sigma/W and SEEP/W simulations

Abstract

In the present study a computer model of a pumping well has been developed and calibrated by using two slave programs of Geo-Slope software, i.e. (SIGMA/W and SEEP/W). The model has been used to study the behaviour of watertable and drawdown in an aquifer during pumping. SIGMA/W program was used to compute initial pore-pressure within an aquifer, while SEEP/W program was used to analyze the change in pore-pressure and drawdown during pumping respectively. From the results it is revealed that the vectors displaying the movement of the flow direction towards discharge well due to which decline in watertable occurs and a cone of depression and drawdown curve was formed. Comparison of the experimental and simulated data showed a good agreement among them. The drawdown line has been simulated for each concern depth and at each interval of time, which was further compared with the actual data for the computation of model efficiency. The performance of the model was evaluated on the basis of statistical parameters, i.e. mean error, root mean square error and model efficiency; these results are presented in Table 7. Statistical analysis of all the research data, i.e. RMSE, ME, R.E, and EF was found to be 0.134 m and 0.126 m, 3.05% and 98.86% respectively. Additionally verifiability of the model was also made by comparing observed and simulated values of observation wells (piezometeric heads); such graph is illustrated in Figure 5. The slope of the line was observed to be approximately at 45 degrees; thus the figure indicates no considerable difference between observed and simulated head values for all the observation wells. Consequently, it is concluded that simulated values of piezometeric heads are not much different than the observed ones. The results support the use of SIGMA/W and SEEP/W programs as a tool for investigating and designing pumping well practices.