Laserfiche WebLink
<br />Figure 6. the dashed lines represent the effective flow boundary for <br />low flow and pressure flow conditions. Therefore. for cross sections <br />2 and 3. ineffective flow areas to either side of the bridge opening <br />(along distance AB and CD) should not be included for low flow or pres- <br />sure flow. The elimination of the ineffective overbank areas can be <br />accomplished by redefining the geometry at sections 2 and 3 (as shown <br />in part C of Figure 7) or by using the natural ground profile and re- <br />questing the program's effective area option to eliminate the use of <br />the overbank area. By redefining the cross section. a fixed boundary <br />is used at the sides of the cross section to contain the flow. when <br />in fact a solid boundary is not physically there. The use of the ef- <br />fective area option does not add wetted perimeter to the flow bound- <br />ary above the given ground profile. <br />The bridge example shown in Figure 7 is a typical situation where <br />the bridge spans the entire floodway and its abutments obstruct the <br />natural floodway. This is the same situation as was shown in plan view <br />in Figure 6. The section numbers and locations are the same as those <br />discussed in Cross Section Locations. The input problem is to convert <br />the natural ground profile at cross sections 2 and 3 from the section <br />shown in part "b" to that shown in part "c" of Figure 7. <br />The effective area option of the program (IEARA = 10 in field 1 <br />of the X3 card) is used to keep all the flow in the channel until the <br />elevations associated with the left and/or right bank stations are ex- <br />ceeded by the computed water surface elevation. The program will allow <br />the controlling elevations of the left and right bank stations to be <br /> <br />22 <br />