A typical cross section represents the geometric and roughness characteristics of the stream reach in question. Figure 6‑3 is an example of a plotted cross section.

Most of the cross sections selected for determining the water surface elevation at a highway crossing should be downstream of the highway because most Texas streams exhibit subcritical flow. Calculate the water surface profile through the cross sections from downstream to upstream. Generate enough cross sections upstream to determine properly the extent of the backwater created by the highway crossing structure. See Chapter 4 for details on cross sections.