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VI. COMPUTATION OF BRIDGE BACKWATER A, FHWA Methodology-"Hydraulics of Bridge Waterways," Hydraul!ic Design Series No 1. 1, "Hydraulics of Bridge Waterways" was first published in 1960, and was based largely on results of hydraulic model studies wiith limited field verification. A revised publication issued in 1978 updated the methodology based on more extensive field data (HDS No, 1 is currently being revised), 2, The method is based largely on a backwater coefficient applied to the velocity head to evaluate loss, The backwater coefficient takes into account the degree of constriction, the number, size, shape and orientation of piers, the asymmetric position of the bridge, and bridge skew. 3, The method may be applied manually using nomographs provided in the document. Portions of this methodology were incorporated in FHWA HY-4 computer program, 4, The method is limited to Type I flow only, and provid,es better results when applied to relatively straight reaches of relatively uniform shape. 5, The results are generally adequate in the absence of complexities in physical setting and/or flow condition. Major problems arise in the solutions for more complex conditions. B. FHWA WSPRO Computer Model. 1, WSPRO is a generalized computer model for calculating water surface profiles in natural and manmade channels. The program was specifically developed to simplify bridge design. 2. The program also analyzes combined road overflow and bridge flow and utilizes a state-of-the-art procedure for multiplei-opening analysis. 3, Water surface profiles calculations for free surface flow through bridge openings are based on relatively recent developments in bridge backwater analysis and recognize the influence of bridge geometry variations, 3.28