Numerical modelling to behaviour of large diameter dug wells in semi-infinite aquifers

Groundwater is a resource of vital importance especially in developing countries. It can be used as a source of water supply as well as a permanent alternative to surface water for irrigation purposes. Large dug wells are commonly used to exploit this resource. The behaviour of these wells significantly differs from other wells because of their noticeable storage effects. Thus, standard analytical methods e.g. Theis and its related methods, for estimating aquifer parameters, that ignore well storage are not applicable and lead to erroneous results. In this work a numerical model developed by Butler (1985), furthered by Thampson (1986) and modified by Regan (1988), was tested for running on IBM PC computers, and modified to consider fixed head boundaries within the a real extent of the aquifer. The model was calibrated using text problem data for aquifer parameter estimation. The model sensitivity to various changes in parameters estimate was checked. The effect of constant head boundary on time draw down was analyzed. This was done using the method of image wells. The model was found effective in estimating aquifer parameters. This was proved to be an efficient tool for modeling behaviour of large diameter dug wells.