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<br />Interpolated cross sections are determined by ralslnq or lowering <br />and expanding or contracting the current cross section's shape. They <br />are inserted uniformly between the two input cross sections. A proportion <br />of the elevation difference determined from the minimum elevations of the <br />two input cross sections is added (or subtracted) to the elevation coordi- <br />nates (on GR cards) of the current cross section. <br /> <br />The modification of the horizontal coordinates is a function of the <br />ratio of the channel areas of the two input cross sections. The channel <br />area (between bank stations) of the current cross section is determined <br />with the depth of flow from the previous cross section. <br /> <br />Interpolated cross sections will be identified in the output by <br />section numbers of 1.01, 1.02, and 1.03. The option will not add inter- <br />polated cross sections in the following cases: 1) if reach lengths between <br />input cross sections are less than fifty feet, 2) if encroachments have <br />been encountered in the run, or 3) if the previous cross section is a <br />special bridge cross section. <br /> <br />When there is a substantial difference in shape between the previous <br />and current cross sections, interpolated cross sections generated auto- <br />matically by the program may not be representative of the actual stream <br />geometry. The user should always check the resonab1eness of interpolated <br />cross sections. <br /> <br />The number of interpolated cross sections added to each profile may <br />vary with discharge; therfore, it is advisable not to request them for <br />multiple prOfile runs because analysis should be made using exactly the <br />same cross section data. <br /> <br />10. TRIBUTARY STREAM PROFILES <br /> <br />Water surface profiles may be computed for tributary stream systems <br />for single or multiple profiles in a single execution of the program. In <br />general data sets are arranged to compute profiles for the main stream <br />(reach 1) from the most downstream point to the study limit on the main <br />stream. Data for a tributary stream (reach 2), whose starting water surface <br />elevation was determined when reach 1 was calculated, follows the data for <br />reach 1. The first section number for reach 2 is negative and refers <br />to the section number in reach 1 where the startinq water surface eleva- <br />tion for reach 2 was determined. When a negative section number (on the <br />Xl card) is encountered the program will search its memory for the computed <br />water surface elevation that corresponds to the negative section number. <br />The program will then start computing the profile for reach 2 with the <br />previously determined water surface elevation. <br /> <br />Occasionally it may be desireab1e to calculate, in a single run, a <br />profile for a stream system with a second order tributary (a tributary to <br />a tributary). This may be accomplished if data for the tributary with the <br />tributary is treated as a portion of the main stream and the main stream <br />beyond the junction of the two streams is treated as a tributary. This <br />is illustrated in the following figure on the next page; numbers one through <br />eight locate cross sections on the main stream, numbers eleven through six- <br />teen are cross sections on the first order tributary and numbers twenty-one <br />through twenty-two are cross sections on the second order tributary. <br /> <br />22 <br />