The remainder of this appendix presents recommendations arising from the results documented in RD-42 (HEC, 1995). These recommendations are intended to provide the users of one-dimensional water surface profile programs, such as HEC-RAS, with guidance on modeling the flow transitions in bridge hydraulics problems.
In applying these recommendations, the modeler should always consider the range of hydraulic and geometric conditions included in the data. Wherever possible, the transition reach lengths used in the model should be validated by field observations of the site in question, preferably under conditions of high discharge. The evaluation of contraction and expansion coefficients should ideally be substantiated by site-specific calibration data, such as stage-discharge measurements just upstream of the bridge. The following recommendations are given in recognition of the fact that site-specific field information is often unavailable or very expensive to obtain.