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<br />b. The flood plain of the selected flood, under existing conditions, <br />will be divided into two zones (see Figure 1): a Designated Floodway and <br />a Floodway Fringe. <br />c. The Designated Floodway, to be reserved by zoning or encroachment <br />lines, will be designated to pass the selected flood discharge without <br />raising the water surface more than 1 foot above that of the natural <br />floodflow (unless other criteria apply). <br />d. For purposes of hydraulic computations, it will be assumed that <br />the Floodway Fringe area is filled solid and has no overbank storage nor <br />floodflow capacity. <br />e. The hydrology and hydraulics for floodways will be based on <br />existing conditions unless future flood control works are under con- <br />struction and scheduled for operation within 2 years. <br />f. Because inclusion of the Designated Floodway in land use regu- <br />lations is a non-Federal responsibility, the Corps' role is to provide <br />sufficient data and guidance to enable the local officials to select <br />the appropriate limits. <br /> <br />PROCEDURE <br />The computer procedure for delineating a floodway includes: <br />a) the development of water surface profiles under natural conditions <br />(i.e., prior to encroachment) and b) the delineation of a designated <br />floodway that meets the requirements stated above. The procedure in <br />theHEC-2 encroachment routines allows a program user to make the pre- <br />liminary estimate of a designated floodway in one operation of the <br /> <br />3 <br />