The Theis (1935) equation for transient drawdown s in a confined aquifer at distance r from a pumping well of rate Q at time t after pumping begins is:
Choose the correct answer
s = Q x T (constant)
s = (Q / 4pi T) x W(u), where u = r^2 S / (4Tt), W(u) = well function = -0.5772 - ln(u) + u - ... (exponential integral)
s = Q / (pi k b)
s = Q x r / T
Correct Answer
B. s = (Q / 4pi T) x W(u), where u = r^2 S / (4Tt), W(u) = well function = -0.5772 - ln(u) + u - ... (exponential integral)
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Theis: s = (Q/4piT) x W(u); u = r^2 S/(4Tt). W(u) = well function (tabulated). For u < 0.05 (long time or small r): Jacob approximation: s = (Q/4piT) x [ln(2.25 Tt/(r^2 S))]. Pumping test: plot s vs log(t), slope = 2.303Q/(4piT) gives T; S from Cooper-Jacob method.
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