Optimal dewatering of an excavation site

Optimal dewatering of an excavation area in an unconfined aquifer is studied using a combined optimisation-simulation approach. In combining a groundwater model with an optimisation model, a response matrix approach, generated on the basis of linear superposition, is used. ModMan, which calls Modflow repeatedly to generate a response matrix, is utilised to transform the groundwater management problem into a linear integer programming problem. A hypothetical dewatering area is considered to examine the effects of non-linearity due to pumpage. Two different iterative methods, revised unit rates and revised coefficients, are applied to account for the non-linear response of the unconfined aquifer to pumpage. The study shows that a modified linear optimisation procedure used in conjunction with Modflow provides a useful and computationally efficient tool for the analysis of groundwater dewatering problems in unconfined aquifers.