Contents preface (VII) introduction 1—37

4.5.4. Wells Near Aquifer Boundaries
The equations for radial flow towards well assume infinite extent of aquifer. However, in practice, there would be situations when a well may be located near hydrogeologic boundaries and the derived equations would not be applicable as such. The influence of such boundaries on ground water movement can be determined by the image well method.
The image well method assumes straight line boundaries and replaces the real bounded field of flow with a fictitious field of flow with simple boundary conditions such that the flow patterns in the two cases are the same. Consider a pumping well located in the vicinity of a stream (i.e., recharge or permeable boundary). Obviously, the drawdown at the stream on account of pumping well would be zero. This real flow system is now assumed to be replaced with a fictitious flow system, Fig. 4.5. In addition to the real pumping well, the fictitious flow system has, in place of the boundary, an image well (which is a recharging one i.e., the one which pumps water into the aquifer) with the same capacity as that of the real well but located across the real boundary on a perpendicular thereto and at the same distance as the real well from the boundary. Obviously, this fictitious system would result in zero drawdown at the location of the boundary. This means that the flow condition of the real flow system is satisfied by the flow condition of the fictitious flow system. If the boundary is a barrier (i.e., impermeable) boundary, the method remains the same but the image well is also a pumping well. It should be noted that in the fictitious system the real and image wells operate simultaneously and the drawdowns can be obtained by considering the fictitious system as a multiple well system. When an aquifer is delimited by two or more boundaries, the effect of the other boundaries on each of the image wells is also to be considered. As a result, there would be several images, Fig. 4.6. When the image wells are too far from the region of interest, their influence on the flow system in the region of interest is negligible and are, therefore, not included in the computations.

	Pumping well			Perennial
G.S.			stream
H	Aquifer
	Impermeable		Image plane