SteadyState TopographyDriven FlowSkip ahead to run the modelIntroductionA topographydriven flow system is one in which ground water flows from higherelevation recharge areas, where hydraulic head is higher, to lowerelevation discharge areas, where hydraulic head is lower. This type of flow system is commonly encountered in groundwater basins. The main factors that control groundwater flow are basin geometry, shape of the water table, and the distribution of hydraulic properties. A key purpose of the TopoDrive model is to enable the user to investigate how these factors control groundwater flow. For a twodimensional vertical section, the boundaries of the flow domain (see above figure) are as follows :
The noflow boundaries might represent groundwater flow divides or lowpermeability bedrock that bounds the basin. Note that by specifying the position of the water table, it is assumed that the pattern of recharge and discharge is such that the water table is maintained at steady state. Governing EquationSteadystate flow of ground water in the vertical section is governed by the equation where h is hydraulic head, and K_{xx} and K_{zz} are the principal values of the hydraulic conductivity tensor. The principal directions are assumed to be parallel to the cartesian axes xand z. Boundary ConditionsAssuming the position of the water table is known, the boundary condition along the water table (AB) is where z is the elevation of the water table. Along the vertical boundaries BC and AD, the noflow boundary condition is Along bottom boundary CD, the noflow boundary condition is The computer model TopoDrive solves the above equations by the finite element method. The flow domain is represented by a deformed rectangular mesh, and each quadrilateral cell is divided into two triangular elements. Linear basis functions are used in the finite element formulation. After solving for hydraulic head h, the x and z components of the average interstitial velocity vector are computed by where n is porosity. The velocity vectors are used for calculating flow paths and the advective movement of fluid particles.
