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<br />program. Additional computer runs may be made to improve the accepta- <br /> <br /> <br />bility of tile floodway. The computerized procedure is discussed here <br /> <br /> <br />and illustrated in the example problem. <br /> <br />The computer procedure is based on calculating a natural pro- <br /> <br /> <br />file as the first profile in a multiple profile run. Other profiles <br /> <br />in tile run can be calculated using various encroachment options as <br /> <br />desired. The five encroachment methods available are described in <br /> <br />Exhibit 9A of the Users Manual. The input requirements and associated <br />output statements are also presented. The HEC-2 Standard Test T, <br />shown in Exhibit 8 of the Users ~lanual. provides an example of ap- <br />plication of Hethods 2, 3, and 4 of the encroachment options, The <br />procedure described herein is based on the use of Method 4, which <br />provides the most direct means for delineating a floodway. <br />Method 4 establishes encroachment limits at a cross section on <br /> <br />tile basis of natural (i.e., prior to encroachment) flow conditions. <br />As part of program input, the user specifies a target incremental <br />increase in water surface elevation (normally one foot). The program <br /> <br />increases the computer "natural" water surface elevation by the incremen- <br /> <br />tal amount and computes the corresponding increase in the computer con- <br /> <br /> <br />veyancel over the natural conveyance for each cross section. The pro- <br /> <br /> <br />gram then sets encroachment limits at each cross section byeliminat- <br /> <br /> <br />ing the increased conveyance from the extremities of the overbank <br /> <br /> <br />areas. The program removes an equal percent of conveyance from each <br /> <br />lconveyance is defined as K = 1.~9 AR2/3 where: n = Manning's rough- <br />ness coefficient, A = Flow area, and R = Hydraulic radius. <br /> <br />5 <br />