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<br />! <br /> <br />(;eologica1 Survey. <br />U .IJSIJ. The o~erlJdnk <br /> <br />Typildl en,mne] t"Oughne" factor, rdnged froOl <br />roughness factors ranged from IJ.USu to 0.075. <br /> <br />1" <br />IJ,045 to <br /> <br />Ar'e,1 r".luetio"" fOf the hrioges dt cross sections 26, y" 47. dO, ~4, \U/, <br />112. lIb arid Coal Creek were used in the hydnulic dfldlysis to account for <br />proh~b 1 e d€~r; s b 1 oekag!!. ^ df'tai 1 ed c(lmput~r 1 i sti fig of the hydraul; c <br />dnalysis showing all parameters is inclulled in the TecMical Addendu,". <br /> <br />d) The ex; st i fig 1 e~ee wi 11 rl.'mai n intact 'Iuri ng the lU(J~yea r f1 ood. <br />b) The exi5ting levee will be sullstantially destrOyed during tile lOU-yedr <br />flood. <br /> <br />19 <br /> <br />The flood outlines dfld Wdt€r 5urfaceelevJtions for these two conditions are <br />shown on sheets 21 through 23 and Table 3 lpgs. 8 ana 9),respecthely. <br /> <br />S~ECIAL FLOOD HAZARDS <br />Special flood hazards exi st in the Crystal River ~all ey that merit detailed <br />explanation. <br /> <br />lf a regular program of levee inspection, maintenanc~ and construction CJn be <br />irhtituted so that the level! will not be eroded or overtopped. then R~dstone <br />wi 11 he ol,Jtside of the lUO-y~dr f1o()(lplain. ~ithol,Jt such d progr..m, the <br />levee m~y foi 1 and all or parts of Re'lstone wi II be suojl.'ct to shallow floo(]~ <br />lng (.:',:l.Sft.) <Juringthe)UU-yearflood. <br /> <br />MUd and Vl.'bris Flows <br />AltMugl1 not studied in gr'('at d€tail, mudalld debris flows nJvebeen observed <br />ufl5everal tributaries to theCrystoll River. Mud and debris f100ls are mass <br />IIlovements involving rapid flowage of debris that includeslllUd, sand, gravel <br />and angular r<.>d resulting from unusually heavy rainfall. The most <br />significant flows were observed on Coal Creek near Redstone, and Hawk aM <br />Hayes Creeks upstream from Redstone. Field observations indicate that mud <br />and debri s fl ows can occ ur on all tr i buta r i es to the Cr ys ta 1 :.l. i ver wi th i n t~le <br />study area. These flows may Cduse significant damage to bridges, culverts, <br />roads and other types of structures. <br /> <br />Themaint€nanceandconstrlJctionprogramShOuldinClude: <br />al Raising the top of the existing dike to at least 2 ft. above the lOO-yea r <br />wdtersurfaceprof1le, <br />I)) Protecti ng the face of the 1 evel' on the stream si _1e "i tM angul ~r rock <br />rlprap, <br />c I Cl eani ng out ;ed i'~ent brought Dy CO.l 1 Creek into the Crysta 1 Ri vcr <br />channel, <br />d I Peri od ica I 1 v (;1 ft.f'r ",~jnr fl ''''''5) i nsrec~1 ng the 1 C\/0C far ,.".~u i feJ "'a; n- <br />tenance ann n'pdirs. <br /> <br />tietorednybulld1ngpermltsarelssuedinthevicinityofatributarystream, <br />a thorough hyor01 og ie/geo 1 09 ic investi gati on shou I d tlc m~de of tne proposed <br />building site. <br /> <br />FlOOd lIaldrd a.J_R.edstone <br />The Town of Redstone i'; pr()t\'ct~d troln flooding by the Crystal Ri vcr and Coal <br />Creek bya levee along the west 51deof town. Field investigdtionsduring the <br />study indicated that the leV('fO is mostly built from river-run gravels and <br />would probably be eroded ~nd/or overtopped during the lOU-year flOOd. <br />Therefore, to eval uate the true ha~ard potential dt Redstone, nydraJl ic <br />calculations were nlade for the tollowing b\) conditions: <br />