As previously explained, the equation of groundwater flow for unconfined aquifers reduces to the same form as that for confined aquifers except that the thickness of the aquifer is not constant but varies as the aquifer is dewa-tered. Therefore, the flow must be expressed through an average thickness of the aquifer ^av. The Thiem equation is then

where ^ = ^o - s2 and ^ = - s^ From Equation 9.8(41),

which is the same form as that for a confined aquifer. The transmissibility of the aquifer T is then

Once T has been determined, S can be obtained in the same manner as a confined aquifer. Note that when the steady-state method is applied, pumping does not have to continue until true steady-state conditions are reached since As = s1 — s2 reaches an essentially constant value after a few days of pumping.

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