Left: Person holds prism against streambank. Right: Survey rod held against streambank to point of inflection. Ruler measures distance from rod to streambank at 90 degrees.

Figure 3. Methods used to survey undercut banks, including placing the prism against the streambank with 0 feet for rod height (left) and horizontal offset measurement where the bottom of the survey rod is lowered to the point of inflection and a ruler is used to measure the distance to the bank at 90° (right).