If an aquifer is bound by one or two aquitards which allow water to be transmitted vertically from or to the confined aquifer as shown in Figure 9.3.2, then a semiconfined or leaky aquifer exists, and the flow through this aquifer is called semiconfined flow. Small amounts of water can enter (or leave) the aquifer through the aquitards of low permeability, which cannot be ignored. Yet in the aquifer proper, the horizontal flow dominates (qz = o is assumed).
The fundamental equation of semiconfined flow is derived from the principle of continuity and Darcy's law as follows:
Consider an element of the aquifer shown in Figure 9.3.2. The net outward flux due to the flow in x and y directions is
The amount of water percolating through the layers per unit time is
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