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<br />The total loss coefficient K, representing losses between the cross sections <br />immediately upstream and downstream of the bridge, is equal to the sum of <br />loss coefficients for intake, intermediate piers, friction, exit and other <br />minor losses. See exhibit 2 for values of the loss coefficients. <br /> <br />(7) Often combinations of these three basic types of flow occur. <br />In these cases a trial and error procedure is used with the equations just <br />described to determine the amount of each type of flow. The procedure consists <br />of assuming energy elevations and computing the total discharge until the <br />computed discharge equals, within one percent, the discharge desired. <br /> <br />(8) To use the special bridge routine, variable IBRID on card X2 <br />is set equal to 1. Variables on card SB (Special Bridge) specifiy bridge <br />geometry and coefficients for the weir and orifice equations. Where the length <br />of roadway for the weir equation is assumed constant for any depth of flow, <br />variable RDLEN is set equal to that length. In cases where the length varies <br />with depth it is necessary to input a table of roadway stations and elevations <br />on card BT. In this case RDLEN is left blank. For some structures the user <br />may desire to input a previously computed or estimated change in water surface <br />elevation in which case the change is entered as variable BLOSS on card X2. <br />When BLOSS is specified, no computations are performed for structure loss <br />and the value entered for BLOSS is simply added to the water surface eleva- <br />tion for the previous cross section. <br /> <br />(9) Losses through culverts are handled in the same way as bridges <br />where the culvert top (BT cards) and bottom elevation (GR cards) must be at <br />the same horizontal stations (Nornlal Bridge Routine). <br /> <br />(10) The special bridge routine can be used for any bridge but should <br />be used for trapezoidal bridges with piers where low flow occurs, for pressure <br />flow through circular or arch culverts, and whenever flow passes through <br />critical when going through a structure. The computer program will auto- <br />matically shift from the special bridge routine to the normal bridge routine <br />when there are no piers and low flow controls. <br /> <br />(11) Examples of input preparation for a bridge and a culvert are <br />shown in exhibits 5 and 6. ,Test problems F, G, K, L, M, N, 0, P, Q, R, and <br />S of exhibit 8 involve bridges. <br /> <br />q. Cross Section Plot. Plots on the printer of any or all of the river <br />cross sections to any scale may be requested by using cards J2 and Xl. If <br />all cross sections are to be plotted, set variable IPLOT on card J2 equal to <br />1 or 10. If only certain cross sections are desired, IPLOT on card J2 should <br />be left blank and variable IPLOT on card Xl set equal to 1 or 10 for each <br />individual cross section to be plotted. Vertical and horizontal scales of <br />the plot may be specified constant for all cross sections in the job by using <br />variables XSECV and XSECll on card J2. If the scale is not specified, the <br />largest scale which is a multiple of I, 2 or 5 that produces three pages of <br />output or less will be used. For some deep river cross sections, flow may occupy <br />only a small portion of the total cross section. In this case it may be <br />desirable to enlarge the scale and to print only the cross section points up <br />to the water surface elevation. This may be done by using a value of 10 for <br />IPLOT instead of 1. <br /> <br />12 <br />