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<br />19 <br /> <br />. <br /> <br />variation of roughness. The channel cross-section may be divided into <br /> <br />as many as six sub-sections, and each of the sub-sections can have a <br /> <br />linear variation of Manning's n between specified upper and lower <br /> <br />limits of elevation within each sub-section. Whether or not the rough- <br /> <br />ness factor can be estimated to this degree of accuracy is a point <br /> <br /> <br />which bears consideration prior to full utilization of this capacity <br /> <br /> <br />for roughness expression. The potential use of eighteen different <br /> <br /> <br />combinations of roughness in a single section seems to tax the powers <br /> <br />of estimation. In addition to calculating water surface profiles in <br /> <br />mild channels, the program is also able to calculate through bridge <br /> <br />sections and converging channels with incremented discharge, which is <br /> <br />accomplished by re-starting the computation scheme. Computations are <br /> <br />carried out in two phases. The first phase calculates hydraulic prop- <br />erties of depth, area, conveyance and top width of all sections at <br /> <br />specified flow elevations in each section. The second phase calculates <br /> <br />an initial energy level, from data which is read into the program, then <br /> <br />carries out solution of the energy equation for succeeding sections, <br /> <br />based on the hydrauliC properties computed in the first phase. Changing <br />of input data must retain the same number of cross-sectional stations <br /> <br />so as not to change card sequence numbering. This requirement also ap- <br /> <br />plies to the addition of intermediate stations. The card sequencing <br />requirement is the single feature which makes the program unsuitable for <br />modeling. Flows at bridges or tributaries can be included by specifying <br />new conditions for the energy level at those sections. <br /> <br /> <br />The USCE Water Surface Profiles program (HEC-2) uses a computa- <br /> <br /> <br />tional procedure similar to the USCE Method 11. In addition to <br /> <br /> <br />friction losses, it also takes account of eddy losses. If the <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br />