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<br />"0 <br /> <br />300 <br /> <br />200 <br /> <br />~ <br />~ <br />. <br />~ <br /> <br />.00 <br /> <br />I;; <br />~ <br />~ <br /> <br />"0 <br /> <br />. <br /> <br />! <br />. <br /> <br />'00 <br /> <br />.0 <br /> <br /> <br /> <br /> <br />~ <br /> <br />VI. <br /> <br />HYDRAULIC ANALYSIS <br /> <br />\<"ater surface pr.)files have t-een computed for the litudy r<"flcrt f.,r <br />the 10-, 50-, 100-, and SOQ-year frequency floods. The flows are <br />listed in Tables 11-13 presented on pages 29-31. <br /> <br />The hydraulic characteristics of the study reach ""ere docum.mted <br />based on a field investigation. Culvert and bridge_ geometry, <br />channel and overbank roughness coefficients, fhr..' obstructions, <br />and the overall characteristics ,)f the arca ",,,re assessed during <br />this investigation. The Manning's roughness coefficeints used in <br />the hydraulic analysis were documented in a separate report <br />prepared as part of the technical addendum. Photographs I.-ere <br />included in the report to support the reCoOmmended values. <br />ReCoOmmended roOughness coOefficients range fram 0.045 toO 0.075 f'Jr <br />the channels and froOm 0.040 toO O.lZO far the averbank areas. <br /> <br />". <br /> <br />The water surface elevations were computed using the U.S. Army <br />Corps of Engineers HEC~Z Step Backwater Computer Program <br />(Reference 13). The loOcations of the field surveyed croOSS <br />sections, digiti:>.ed crass sections fr.)m the digit1<'ed cross <br />sections from the topographic maps "f the Arkansas River, Lake <br />Creek, and Evans Gulch are $ho,,'o by stream stati"rdng oOn the <br />floOoOded area maps (Plates 3 through 14) and the flood profilea <br />(Plates 15 through 27). The stream stationing, 100~year flood <br />elevatians, as well as the 10, 50, 100, and 500~year flood <br />discharges are also listed in Tablea 11~13, Pages 29-31. <br />The water surface elevations presented in Tahle 11-13 'lre hased <br />on camputatians ,,'hich aSSUele n.;l reductian in the bridge <br />c,)nveyance capabilities due to debris. Water surface elevations <br />may incre-<Ise if significant d.,bris blockage shvuld occur. <br /> <br /> 4-~ HJIl '~" <br /> , , <br /> , <br /> .' <br />. -:~:.1---'-- +, <br /> , ,- ..--- <br />C 2 . 6 , '0 <br /> <br />o <br /> <br />STREAM DISTANCE IN FEET X 1000 <br /> <br />FIGURE iO. DISCHARGE PROFILE FOR EVANS GULCH <br /> <br />-2B- <br /> <br />-27- <br />