Groundwater simulation models are physically based mathematical models derived from Darcy's law and the law of conservation of mass. Various established solution techniques utilizing either the finite difference or the finite element method, or a combination of both, are available for solving the governing equation of the model, provided that model parameters and initial and boundary conditions are properly specified. With the advancement of numerical computing and various user-friendly interface software, groundwater simulation models are now commonly used by groundwater planners to assist in the decision making in a variety of water resources management problems.
In simulation,groundwater models are used to predict (1) the hydraulic or water quality response of the aquifer system to a set of pumping and recharge schedules and (2) the probable hydrologic and environmental impacts associated with groundwater development. Because it can only consider a limited number of management alternatives, the simulation approach generally does not identify the optimal pumping/recharge schedules in the context of all the objectives and constraints. A recent advancement in groundwater modeling has been the development of management models that combine optimization and simulation. In contrast to simulation, optimization models identify optimal planning, design,and operational policies for the groundwater system. And because the simulation model is incorporated in a constraint set of the management model, the optimal decisions not only define the optimal pumping/recharge schedules, but also predict the time and spatial variation in the hydraulic head.