B, and add this to the true elevation of B above the chord ac. *This is the effective elevation*. This is done

using the following formula:

The effective elevation of B is *40 + 1.62 = 41.62 meters*. To perform the next step, compute the

effective elevation of the grade line from the ground at A to the ground at C where it passes through the

vertical of B. Use the principle of similar triangles as follows:

Therefore, the amount of obstruction at B is *41.62 - 24.38 = 17.24 meters*.

f. The computation of obstruction is essentially the solution of similar triangles. In a), Figure 2-8,

the elevations of the points are *A = 293 meters*, *B = 298 *meters, and obstruction *H = 294 meters*. The

distance from A to H is 8 kilometers and from B to H is 6 kilometers. Refer to Table 2-1, page 2-31,

and locate the effective elevations of points H and B. The effective elevation of H is *294.0 *- *4.3 *= *289.7*