ABSTRACT
A confined aquifer is a water containing and conducting formation bounded at the top and the bottom by impermeable formations. Aquifers are typically horizontal layers with large horizontal to vertical aspect ratios. Figure 3.1 gives a schematic view of a confined aquifer with a greatly exaggerated vertical scale. Due to the typical aquifer geometry, streamlines are assumed to be nearly horizontal. Since equipotential lines are perpendicular to the streamlines, they become nearly vertical. Changes of piezometric head in the vertical ( z) direction hence are negligible. Mathematically, this nearly horizontal flow assumption allows us to reduce the threedimensional spatial functional dependence of piewmetric head to just two-dimensional:
h = h(x,y,t) (3.1)
Another view of this simplification is based on the hydrostatic assumption. If streamlines are nearly horizontal, the vertical acceleration component is negligible. The pressure distribution is approximately hydrostatic in the vertical direction. Based on the definition Eq. (2.1), a gain or loss in piezometric head due to an elevation change, .6.z, is compensated by the loss or gain of pressure, .6.p = "fdZ. It is clear that h is independent of the vertical location if the pressure is hydrostatic. Equation (3.1) offers an opportunity to construct a two-dimensional theory for confined aquifer that is
FIGURE 3.1. A confined aquifer.
