# Optimal Dewatering System of an Excavation

**By H. Önder, M. Değirmenci**

**Abstract**

A management model for the control of groundwater flow for the purpose of dewatering an excavation site is presented. It predicts the optimum number of wells, their locations, and the rates of pumping needed to maintain the groundwater levels below specified elevations at the excavation site. The management model combines a groundwater simulation model with an optimization model. In the coupling of the two models, the response matrix approach is used. For the generation of the response matrix an external simulation model, MODFLOW of USGS is used. The optimal pumping strategy is formulated by minimizing either the total discharge or the global costs, subject to a set of possible constraints. The optimization model uses either a simple linear programming (LP) or mixed integer linear programming (MILP). The objective function in the first optimization model was defined as minimizing the total withdrawal rate, and in the second one as minimizing the total cost consisting of initial and operational cost of pumping. The advantage in this management model is that it uses available software and requires only a small amount of computer coding. The proposed methodology was applied to a hypothetical excavation site. The case study demonstrated that the combined use of a numerical finite difference simulation model with an optimization linear programming procedure was a useful tool in the analysis and design of a dewatering scheme. It provides the designer with objective criteria for the implementation of an operative scheme, which best satisfy the needs for a technically sound and economically valuable solution.

**Link to material:** http://www.ifors.org/developing_countries/downloads/oct31_2011/1.doc