Surface Water Interaction Modelling Using Visual MODFLOW and GIS

PHYLARESApproach and methodology / ch.2__________________________________________________________________________________________5broadly divided into two classes, analytical and numerical, even though the hybrid of these twoclasses is not uncommon. Analytical methods yield exact solutions to the governing differentialequations. Darcy’s law is an example of an analytical model. To solve an analytical model, onemust know the initial and boundary conditions of the flow problem. These conditions must besimple enough that the flow equation can be solved directly by using calculus.Numerical methods approximate the differential equations with a set of algebraic equations.These recast equations are numerical approximations and the answers obtained are alsoapproximations. The equations are most commonly in matrix form and they are solved on adigital computer, unlike analytical models which can be solved rapidly, accurately andinexpensively with a programmable calculator or a spread sheet on a personal computer.Generally, analytical solutions can be obtained under many simplifying assumptions, such as aunidirectional velocity field, a set of uniform transport properties, a simple flow domaingeometry, and a simple pattern of sink and source distribution. For this reasons, numericalsolutions which are capable of approximating more general conditions, are more widely used infield applications (Zheng & Bennett, 2002). This thesis is a numerical model to approximatesteady state water balance and interaction of surface and groundwater.2.2 Groundwater modelsGroundwater models are computer programs of groundwater flow systems for the calculation ofgroundwater flux and head. Because of the simplifying assumptions embedded in themathematical equations and the many uncertainties in the values of data required by the model, amodel must be viewed as an approximation and not an exact duplication of field conditions.Groundwater models, however, even as approximations are a useful investigation tool.For the calculations one needs (hydrological) inputs, (hydraulic) parameters, initial and boundaryconditions.The input is usually the inflow into the aquifer or the recharge, which variestemporally and spatially.Important parameters are the topography, thicknesses of soil and aquifer layers and theirhorizontal and vertical hydraulic condustivity, porosity and storage coefficient, capillarity of the______________________________________________________________________________________Groundwater – Surface water interaction modeling using visual MODFLOW and GIS