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<br />between the cross sections to give the energy loss caused by the transition, <br />Where the change in river cross section is small, coefficients CEHV and CCHV <br />are on the order of 0,3 and 0,1, respectively, When the change in cross <br />sections .is abrupt such as at bridges, CEHV and CCHV may be as high as 1,0 <br />and 0,6. These values may be changed at any cross section by inserting a <br />new NC card, however, these new values will be used until changed again by <br />another NC card, <br /> <br />p. Bridge Losses, <br /> <br />(1) Energy losses caused by structures s~ch.-,,_s._~ridges and culverts <br />a);:e . comp_u.~~c:!. .in_two--El:~_S, .F.ir'!.~-,- the lQ.!l.ses_ dU~L t(L~..P.'!lls.!gn .and contraction <br />of the cross section on the upstream and downstream sides of the structure <br />are computed (see exhibits 3 and 4 for required cross sections), Variables <br />CEHV and CCHV discussed in the previous section are used to specify the <br />expansion and contraction coefficients. Secondlv. the 10"" thrnngh.the <br />structur\!.itselL.iL~QmPuted J).Y~.!the!:._t\1!Lllgrmal bridge .I.Qudne or the <br />S1l-~cial...QJ"_!c:!.g~ !:.outine, <br /> <br />(2) The normal routine handles the cross section at the bridge <br />just as it would any river cross section with the exception that the area <br />of the bridge below the water surface is subtracted from the total area and <br />the wetted perimeter is increased where the water surface elevation exceeds <br />the low chord. Th\! bridge deck is described by entering the elevation of <br />the toP. Qf.. roadway .and 10w:.ch()rd.<i.!l_v.a..riaHes _J>LTRD. all<L!lLLC. respectively <br />on card X2 or by specifying a table of roadway elevation and station and <br />co!:respondingl()w..c.hordeleyatiJIDa (HT ~"rd,,). \fuen only ELLC and ELTRD are <br />used, these elevations are extended horizontally until they .intersect the <br />g:round line.. Pier losses areaCCo1J!lJ~'!!'j:or.J,-y.the increased wetted perimeter <br />of the piers as described on card GR. The .!!QI!l!f!l.rQ\ltin_e is particularly <br />applicable for ]:>ri<iM!l..w:!.thQytl'ie!.s, bridges under high submergence, and for <br />low flow through circular and arch culverts, ..Whenever flol. cro.ss.es..critical <br />depth in a structure, the .special bridge-routine should be used. The normal <br />bridge is automatically used by the computer, even though data was prepared <br />for the special bridge routine, for bridges without piers and under low flow <br />control. <br /> <br />(3) The special bridge routine computes losses through the structure <br />for low flow, weir flow and pressure flow or for any combination of these. <br />The type of flow is determined by a series of comparisons as shown on exhibit 1 <br />and as described below, First, the energy grade line elevations are computed <br />assuming alternately low flow and pressure flow control. The higher energy <br />grade line elevation determines the appropriate type of flow. If pressure <br />flow appears to control and the energy grade line is above the minimum top <br />of roadway elevation, then a combination of pressure flow and weir flow exists. <br />If the energy gradient is below the minimum top of roadway then pressure flow <br />alone controls. If low flow appears to control, and the corresponding energy <br /> <br />8 <br />