Finite element modeling of underground water flow with Ranney wells

The objectives of this study were to define the regional and local groundwater flow, and to give quantitative estimates of the groundwater dynamic parameters and of the available groundwater resources. To achieve these objectives, numerical tools are required to quantitatively model flow through porous saturated and unsaturated media. We have developed a general finite element (FE) model for underground water flow and specific algorithms for Ranney wells. Solutions for steady and unsteady conditions are obtained by using two basic models: global and local. The global model consists of 3D finite elements and 1D finite elements with the equivalent well permeability representing Ranney wells. The local models are generated around wells, using solutions for all quantities from 3D global model at a cylindrical surface which bounds the local model. The local model consists of a fine 3D FE mesh and 1D elements used to model each of the well screens. We developed a software for pre- and post-processing, Lizza, which can be used for easy modeling of complex engineering underground water flow problems with Ranney wells. The FE package PAK-P is used as the solver. This software can handle flow regions with general irregular boundaries. The flow region itself may be composed of layers of nonuniform soils having an arbitrary degree of local anisotropy. Flow can occur in the vertical plane, the horizontal plane, or in a three dimensional region exhibiting radial symmetry about the vertical axis. The water flow model includes constant or time-varying prescribed head and flux boundaries, as welt as boundaries controlled by atmospheric conditions. At a soil surface, boundary conditions may change during the time evolution from prescribed flux to prescribed head type conditions (and vice versa). The model also include a seepage face boundary through which water leaves the saturated part of the flow domain, and free drainage boundary conditions. The results of modeling several real engineering projects (Belgrade Water Supply Center) are presented.