Thiem-Dupuit Equation Calculator

by Glenn M. Duffield, President, HydroSOLVE, Inc.

The Thiem Equation (Thiem 1906) with Dupuit assumptions may be used to compute the transmissivity of an unconfined aquifer from steady-state drawdowns measured around a pumping well discharging at a constant rate:

T = \frac{Q}{2 π (s_{1}^{'} - s_{2}^{'})} ln (\frac{r_{2}}{r_{1}}) (1)

where Q is pumping rate [L³/T], r₁ is radial distance from pumping well to first observation well [L], r₂ is radial distance from pumping well to second observation well [L], s′₁ is corrected drawdown in first observation well [L], s′₂ is corrected drawdown in second observation well [L], and T is transmissivity [L²/T].

Corrected drawdowns are computed as follows (Jacob 1944):

s^{'} = s - s^{2} / 2 b (2)

where b is aquifer thickness [L], s is drawdown measured in an unconfined aquifer [L] and s′ is drawdown in an equivalent confined aquifer [L].