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<br />4. Specifically, a coefficient of dis,charge, is utiilized in evaluation of the <br />bridge profile. This coefficient i:s a function of bridge ge10rnetry and <br />flow characteristics, <br /> <br />5. The model alse) estimates an erffective flow length upstream of the <br />bridge which provides better estimates of friction losses through the <br />bridge reach, <br /> <br />6. Comparison of WSPRO with other computer models, including <br />HEC-2, has fClund that overall, WSPRO appears to give better <br />results and tends to more completely define the profile through the <br />bridge. <br /> <br />C. COE HEC-2 Water SlLIrface Profile Computer Model. <br /> <br />1. HEC-2 is a generalized computer model for calculating water <br />surface profiles in natural and man made channels. The effects of <br />various obstrUl:tions, including bridges, may be considered in the <br />computations, <br /> <br />2. Energy losses caused by brid~les are calculated in two parts: the <br />contraction and expansion losses for the cross sections upstream <br />and downstream of the structure, and the loss through the structure <br />itself by either the normal or special bridgE~ methods, <br /> <br />3. The normal bridge method handles the bridge section as any other <br />river cross section, except that the area of the bridge below the <br />water surface is subtracted from the total area and the wetted <br />perimeter is increased when flow exceeds the low chord. <br /> <br />4, The special bridge method calculates the losses thrQugh the <br />structure for low flow with piers and for weir flow and pre~ssure flow, <br />based on various equations. <br /> <br />5. The bridge analysis methods in HEC-2 are! limited in that they only <br />account for piE~r configuration and not other differences in bridge <br />geometry, Additionally, the equations and coefficients utilized do <br />not reflect more recent research in bridge hydraulics, <br /> <br />6. The COE has recently released HEC River Analysis System (RAS), <br />their next generation water surface profile model. The current <br />version of HEC-RAS only supports steady 110w water surface profile <br />calculations. New features and additional capabilities will be added <br />in future releases. <br /> <br />3.29 <br />