At least four cross sections are required to complete this procedure, but you often need many more than three cross sections. The number and frequency of cross sections required is a direct function of the irregularity of the stream reach. Generally speaking, the more irregular the reach, the more cross sections you may require. The cross sections should represent the reach between them. A system of measurement or stationing between cross sections is also required. Evaluate roughness characteristics (n-values) and associated sub-section boundaries for all of the cross sections. Unfortunately, the primary way to determine if you have sufficient cross sections is to evaluate the results of a first trial.

The selection of cross sections used in this method is critical. As the irregularities of a stream vary along a natural stream reach, accommodate the influence of the varying cross-sectional geometry. Incorporate transitional cross sections into the series of cross sections making up the stream reach. While there is considerable flexibility in the procedure concerning the computed water surface profile, you can use knowledge of any controlling water surface elevations.