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<br />'h; <br />" <br />If <br />~; <br />~. <br /> <br />K value vas 1.05 as recommended in EH 1110-2-1601 for piers formed "lith a 90- <br />degree triangular nose and tail. An additional t,.,;ro feet ,.Jas added to the v.'idtil <br />of each pier to account for debris accuIDulc.tion. The car acity of ti1e e:;~istin::; <br />bridge for U. S. Highway 50 is adequate to pass the design flow of 140,000 <br />c.f.s. with 2.4 feet of clearance. <br /> <br />is' <br />"'. <br />f <br /> <br />7-G8. The existing AT&SF Railway bridge crossing the Arkan~as River will <br />reauire alterations to pass the design flow. The girders of the eAisting briJ~e <br />are about 9 feet deep with low chord at elevation 3,893.9 and obstruct channel <br />flm<7s for discharges of desiGn flood magnitude. A redesign of the 8irder port~l...on <br />of the bridge, to increase the length to 55U teet and to raise low chord to <br />elevation 3,900.7, as shown on plate 28, would provide about 3 feet of clearance <br />above the design water surface. The railway bridge opening vould be a hyclraulic <br />control for discharges of design flood magnitude. For this condition, critical <br />depth \-lould occur 1;vithin the bridge section and backHater computations Here. <br />used to determine the water surface elevation upstream of the brid~e, The <br />Yarnell fomula Has used to determine losses through the rail:oad bridge open- <br />ing for the 5- and 25-year design floHS of 13 ,000 and 46,500 c. f. s. T;'6 <br />selected K value ,,,as 1.05 as recommendecl in E,l 1110-2-1601 for t,dn-cylilldcr <br />piers 'ivithout a connecting diaphragm. An additional t\-JO feet tlas addeu to t~1e <br />width of each pier to account for debris accumulation. <br /> <br />7-09. TiH~ averaee slope of the Arkansas River throuS:1 Las Animas is about <br />0.0016. Average velocities in the channel section of the flood,,,,,y Houle' vc.ry <br />fror about 7 to 13 feet per second for a discharge of 13,000 c,f,s. to 200ct <br />10 to 21 feet per second for the clesign discharge of 140,000 c.f.s. AV8ra:e <br />overbank velocities for the design discharge would vary from 3 to 8 feet per <br />seconcl. A double rOCl of flexible type steel jetties '<QuId be placer; alone- the <br />toe of the river levees at critical locations to protect against high velocity <br />flous. Details of the jetties are shown on plate 26. Overbank clearins ,",ould <br />be' proviJed and maintained to provide: an "nil value of 0.035 oetl"een the rail- <br />Hay and hig:,vay bridges. T~ith this clearing, there ",ill be a cleared flm, <br />width of 830 feet at the higl,,"ay brid"e and 858 feet at .the rail",ay brit"lse. <br />Tile "vidth of clearinb Hould bE. transitioned to natural conditions upstream of <br />the hi3hVlay bridge and dmvus tream from the raihlay bridge. <br /> <br />7-10. Interior drainage. At the time the hydrology mel'lorandUcl Has sub- <br />f"itted, planning studies hacl not progressed to a point ",here a fir;: interior <br />clrainage system could be formulated. Pertinent information resultins fro~ more <br />detailed analysis conducted during pref"aration of this memorandum is discusseJ. <br />in the follmving paragraphs. A plan of the interior drainage systee[ is shoun <br />on plate 29. <br /> <br />7-11. The right and left bank levees vould intercept runoff frorc: 2,372 <br />and 375 acres, respectively. This reflects an increase of 313 acree Fr0111 that <br />presen tecl in the hyclrolo:;y memorandum, For analysis, the ri:;l1 t ane, left bank <br />interior drainage areas were divided into 9 and 4 subareas, respectively. <br /> <br />10 <br /> <br />c <br /> <br />. .", <br />