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HYDC05 12/5/05 5:35 PM Page 184

184 Chapter Five

Fig. 5.36 Comparison of log drawdown,
s, versus log time, t, for (a) ideal (Theis),
(b) leaky, (c) unconfined and (d) bounded
aquifer systems. After Freeze and Cherry
(1979).

boundary is an impermeable, no-flow boundary then infinite aquifer so that the solution methods described
a greater drawdown than expected is observed than in the previous sections can be applied. For a well
would be the case if the aquifer were infinite in extent close to a constant head boundary, the image well is
(Fig. 5.37b). a recharging well placed at an equal distance from
Analysis of pumping test data affected by bound- the boundary as the real well but reflected on the
aries requires application of the principle of super- opposite side of the boundary (Fig. 5.37a). For an
position of drawdown (see previous section). By impermeable boundary, the image well is a discharg-
introducing imaginary, or image wells with the same ing well, again placed at an equal distance from the
discharge or recharge rate as the real well, an aquifer boundary as the real well but on the opposite side
of finite extent can be interpreted in terms of an of the boundary (Fig. 5.37b). Further explanation of