For a single opening, analyze the effect of the trial opening using the method selected from those outlined in . If the resulting backwater or through-bridge velocities are unacceptable, modify the opening until the estimated conditions are satisfactory for both the design and check flood conditions. The department recommends automated procedures for such analyses.

Where a bridge must cross a relatively wide floodplain or multiple discharge concentrations, it may be necessary to design multiple openings. A multiple opening configuration usually constitutes a main channel bridge with relief openings. This type of crossing provides openings at or near the flow concentrations. The result is a reduction in along-embankment flow and backwater effects.