As previously mentioned, constructing a good flow net is more art than science. Because different people would undoubtedly draw different flow nets, we may wonder about the accuracy of us ing it for seepage calculations. If carefully drawn, there is surprising consistency in seepage predictions from engineer to engineer. To lend greater credibility to this premise, perform the following exercise:
(a) With a pencil, sketch five more streamlines in Figure 7.28 (a) by bisecting the existing flow channels. Why is the result not a proper flow net? What additional step must be taken? After performing this additional step, recompute the seepage rate of Example 7.18. How do the answers compare?
(b) Trace the outline of the dam and boundaries in Figure 7.28 (a). Draw your own flow net using two streamlines instead of four. Estimate the seepage of Example 7.18 using your new flow net. How do the answers compare?