ABSTRACT
In general, groundwater flow is three-dimensional, but due to the geometry of ground layers, and differences in hydraulic conductivities, actual groundwater flows tend to be concentrated in certain directions, as illustrated in Figure 3.1. The reason for this is that ground layers usually extend horizontally over large distances, while the vertical dimensions are rather restricted. Also, due to the large variety in conductive properties, ground layers can be grouped into three classes: pervious formations or aquifers, semipervious formations or aquitards, and impervious formations (Figure 3.1a). Because water flows through a porous medium along the path of least resistance, groundwater moves predominantly longitudinally in pervious formations and transversely in semipervious layers. Hence, due to the horizontal layering, groundwater flow is essentially horizontal in aquifers and vertical in aquitards, as depicted schematically in Figure 3.1b. Therefore, instead of using the three-dimensional equations as presented in Section 3.2, a simplified mathematical description of groundwater flow is possible, when horizontal flow components are considered to be dominant in aquifers and vertical components in aquitards, as shown in Figure 3.1c.
