Identifying Effective Distance to a Recharge Boundary

The solution to the problem of induced recharge where pumping is planned near a stream, requires determining effective distance to the line of recharge. This is generally accomplished by analyzing the drawdowns observed during the pumping test conducted near a recharge boundary. Traditional methods of estimating the distance between observation well and image well either use the concept of fully developed straight lines or make use of the type curves for matching. Hantush's method requires the locating of the inflection point on the drawdown curve. The curve matching or the Hantush method is subjective and hence involves errors due to personal judgment. A long-duration pumping test is required to be conducted in order to obtain a fully developed second straight line. In many situations, such a long-duration pumping test is not feasible. In this paper, a robust optimization method is presented that allows the use of shorter-duration pumping test data, for estimating aquifer parameters, and distance to the effective line of recharge. Thus, it saves time and costs involved in conducting a long-duration pumping test. Application of the method on published data sets shows that the new method yields reliably accurate estimates of the parameters.