Chow Method

Chow's procedure (1952) combines the approach of Theis and Cooper-Jacob and introduces the function

where s is the drawdown at a point. The relation between F(u), W(u), and u is shown in Figure 9.8.6. For one log cycle on a time scale log(t2/ti) = 1 9.8(24)

FIG. 9.8.6 Relations between F(u), W(u), and u. (Reprinted from V.T. Chow, 1952, On the determination of transmissivity and storage coefficients from pumping test data, Trans. Am. Geoph. Union 33:397-404.)

FIG. 9.8.6 Relations between F(u), W(u), and u. (Reprinted from V.T. Chow, 1952, On the determination of transmissivity and storage coefficients from pumping test data, Trans. Am. Geoph. Union 33:397-404.)

From the drawdown-time curve, obtain s at an arbitrary point and As over one log cycle. The ratio s/As is equal to F(u) in the Equation 9.8(25). F(u), W(u), and u can be obtained from Figure 9.8.6. With W(u), u, s, and t known, T and S can be calculated with Equations 9.7(20) and 9.7(14).

Example: Point A in Figure 9.8.3 gives s = 0.2m and As = 0.18m at r = 200m and F(u) = 0.2/0.18 = 1.11. From Figure 9.8.6, W(u) = 2.2 and u = 0.065. Substituting into Equations 9.7(20) and 9.7(14) yields T = 875 m2/d and S = 0.00011, which reasonably agree with the values obtained by the two methods just described.

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