## Q

^>0 for an unconfined aquifer 9.6(6)

Figure 9.6.2 shows the flow net for a two-well sink-and-source system. Equation 9.6(4) shows that along the y axis where r1 = r2 = ro, $ = constant. This statement means that the y axis is an equipotential line along which no flow occurs, and the drawdown is zero (^ = ^o). This result occurs because the system is in symmetry about the y axis and the problem is linear. Note that the distance R does not appear in Equation 9.6(4). This omission is because the discharge from the sink is equal to the recharge into the source, indicating that the system is in hydraulic equilibrium requiring no external supply of water.

Another example of using the principle of superposition is the case of two sinks of equal discharge Q. Equation 9.6(3) now reads

2k or

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