The plot (Fig. 22.4) between time  and drawdown relation is a straight line when time is plotted in logarithmic scale. Projecting the line to s = 0, the time of zero drawdown t₀ can be obtained.

Now for s = 0 at t = t₀

                                                                                   (22.11)

Thus,

                                                                                                      (22.12)

                                                                                                 (22.13)

Now consider one log cycle as shown in Fig. 22.4

                                                 (22.14)

                                                                                     (22.15)

As we have considered one log cycle, t₂ / t₁ = 10

                                                                                         (22.16)

                                                                                                 (22.17)

Thus,

                                                                                                        (22.18)

 

It may be noted that this method is not applicable for early drawdown data as it will violate the basic assumption used in developing the method.