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<br />Guide For Approximate Zone A Areas <br /> <br />Developing BFEs <br /> <br />2 <br /> <br />Waters Edge <br /> <br /> <br />w <br /> <br />FlOw <br /> <br />Roadway <br />Embankment <br /> <br />Ie <br /> <br />\ W~I <br /> <br />1 <br /> <br />3 <br /> <br />BrIdge <br />l <br />Flow ~ <br /> <br />W <br /> <br />Roadway <br />Embankment <br /> <br />Waters Edge <br /> <br />Figure 18 - Cross Section Locations at Structures <br /> <br />If the floodplain configurations upstream and downstream <br />of the structure are different and the structure is a <br />bridge, an additional cross section should be used <br />upstream of the structure. The cross section should be <br />located at a distance equal to the width of the structure <br />opening upstream of the structure as measured from the <br />foot of the embankment or wing walls. <br /> <br />The stations and elevations for cross section ground <br />points outside of the stream channel may be obtained from <br />a topographic map. The size of the structure opening, <br />piers, and channel geometry, however, should be obtained <br />by field survey. <br /> <br />Bvdroloav <br /> <br />There are a number of methodologies that may be used to <br />develop flood discharges for approximate Zone A areas. The <br />methods discussed below were selected because they are fairly <br />simple to use, require information that is easily obtainable, <br />and provide reasonable discharge estimates for streams where <br />more detailed hydrologic analyses have not been performed. <br />These methods, which have been ordered based on ease of use <br />and expected level of accuracy, include discharge-drainage <br />area relationships, regression equations, the NRCS TR-55 <br />graphical peak discharge and tabular hydrograph methods, and <br /> <br />V-15 <br />