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<br />17 <br /> <br />Il.YU~OLOG)C "I,D i1YllKAJ.~~~:.AL'!:.~l~ <br /> <br />16 <br />I.ltner tributaries have flooded and caused damdge to the roads. eM flash <br />floodonHayesCreek,about twomlles above Redstone, closed thehig hwaytem- <br />porarily. In 1957 when rlighway 133 was still a gn~el road, there was one to <br />tWO feet of water over the road clbout one Ill) 1 e abo~e Reds tone but the road <br />oj d not ..ash out. The road grade was ra i sed wilen it was Pd ~eo 1n 1965 and ; t <br />nas not been inundated since. rheAvalanche briogewas destroyed by the i1ign <br />water in 19S7 and was rebuilt by the U.S. Forest Service in 1%9. <br /> <br />FLOOD ctIAK^CTER1S11C~ <br />Flood flows on the Crystal River generally result from rapid melting of the <br />mountdin snowpackduring the period ofMdy to July. The .nowmeltrunoff is <br />cl1uacterized by sustained periods of high flows and diurnal fluctuation. <br />The sunnier cloudburst~ represent the greatest flooding hanrd to the tribu- <br />taries of the Crystal River. These flashflooos impact tile mainstern of the <br />Crystal for some oistance below the tributary. and also result in substan ti<ll <br />oebrist>eingwashedintotheCrysta1 River. <br /> <br />HYDROLOG1C ~N~LYS1S <br />The hydrologic <lnalysis for this study of the Crystal River drainage basin <br />was complt'ted by the U.S. Army Corps of ~nqineers D). A region<ll analysis <br />of ,trealn flow data tAken at gaging stations in the region was performed hy <br />the Corps oftngineers and natural flow frequency curves were dl.'veloped. The <br />peak flows determined for the 10-, :;0-, 10U-, ano SUIJ-year floOdS were used <br />todeterrnine the flood profiles and the lIJO-year flOOdplain for tnis report. <br />Fora det<liled description of thehydro1ogic analysis performe<l hy the Corps <br />of Engineers, refer to the Tecllnical Addendul' Ill) ana Reference 3. <br /> <br />HYDRAULIC ANALYSIS <br />The water surface elevation, for floods of the sel ected re~urrence interval s <br />were computed throuqh use ot tlleCorps of Engineers' HEC_2back",aterC(}lTIputer <br />prograr;114). One_hundredthirty_f()urcrosssf!Ctions for the hydraulic analy- <br />,is of ttll' Crystal ~jver "n<1 Coal CrelCk "",re digiti led from the aerial photG- <br />graphs. lh" locati()ns of these cross s~ctions dre shown OJ referenc~ poi nts <br />olithe fluoded area lTIaps and the floodprof1les 1n the back of this report. <br />Iii" 10-, 50-, I;JU-, ~,,<1 SUO-year nood elevation, dnd discha~ges are Hst~<1 <br />in Tab I e 3 whiCh is founo at th~ end of the repur ~ text. Channe 1 ruughness <br />factors IManning's nl for Ulese cornputatiuns were a,signed on the basi, of <br />field inspection of the floodplain areas and recommendations of tile U.S. <br />