Radial flow in a confined aquifer occurs when the flow is symmetrical about a vertical axis. An example of radial flow is that of water pumped through a well in an open field or a well located at the center of an island as shown in Figure 9.3.3. The distance R, called the radius of influence zone, is the distance to the source of water where the piezometric head fi0 does not vary regardless of the amount of pumping. The radius R is well defined in the case of pumping in a circular island. In an open field, however, the distance R is theoretically infinite, and a steady-state solution cannot be obtained. In practice, this case does not occur, and R can be obtained by empirical formula or measurements.
The differential equation governing radial flow is obtained when the cartesian coordinates used for rectilinear flow are transformed into polar coordinates as d2 <f> d2<f> 3x2 + 3y2
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