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<br />Table 4 <br />SUW~ARY OF POTENTIAL FLOOD PEAK OI,CHARG[S <br /> <br />d velocity 01 3 fee~ or more per second croatcs a delini~r c~n~cr of <br />injury or orowning. <br /> <br />Location <br /> <br />[)rdlnaqe <br />AeN <br />-~ <br />(s~. "11.) <br /> <br />Intermediate <br />Il<XJioMI <br />Flood <br />Pe"k <br />[)is.<:harqe <br />(c.f.s;T--- <br /> <br />Standard <br />"ro.joct <br />FIOCX: <br />CM" <br />Discharco <br />rc:r.s:) <br /> <br />rlood~d drGJ a~d ilood Jamdges ~ The arCdS dlong Sf. Vr~in <br />----------------- <br /> <br />Cree~, OOth rurd I and In Longmont. rr\3t wQ>j ld be flooded "y the I nter- <br />rlUU idte [leg i"na I arm Sta,dard Project F lood~ 3re si\0~'~ o~ rlates I <br />through 4. '",ater 5uri<lce prof i I es for t!,ese I loodS '~ere ceter",i ree <br />usir>g baCKwater computdtio~~ eMployi"'J h" Stdooard Slep i.'dnod. The <br />profiles, On plates 5 a~d 6, s~ the deptMs of llooding i~ tho chan~ <br />nel and the elevation 01 the water surface5 over the adjacent tlood <br />plain. Head losses at bridgeswereccmputed using data In "Kydr"uljcs <br />of f3ridga '"'~rcrwa'{s" publ iShc<;: by tnl) U. S. Dan~r~menr oj Ccnvnercc. <br />Flood bounJaries>lore.jetermined I>y Drojocting "dter s.uriaceelev a- <br />tions to th" ~urv()yed fjood pia i n. Plates 7 "nd 8 portr~y cross <br />sect iOlls across the channel dnd valley and sho'~ gro\<nd el evatiofis and <br />depths of overbank floodjng. Relerence ~oints hnva bean provided to <br />locate t 1000 elevations at interva Is,} lone; St. VrJ in Creek. T~e <br />roterenC8 poinrs coincid~ wirh the I.ocatjon of the $urveyaJ crosS <br />sections Jsed In tne study. ~he location of the r~l~r~~8 points <br />Jre shown on both the "Flood!"j Ar!'a" pl;,\res and ~he "Prof I Ie" p I~tu$. <br />Table 5 sho~~ referonco noint da~a IncludinG the olev~tions 0' the <br /> <br />St. Yr;JinCruck <br />below Lyons m I (),2()O 21,800 <br />~" Vraln Cr"ok iloove <br />LeftHdnd Creek '" 11,200 34,800 <br />S>, ~ra i n Creek bel 0'" <br />left Kan<l Creek m 15,200 39,000 <br /> <br />Froq~()ncy <br /> <br />Floods larger than the Sta~dard Project Flood could occur. <br />Ho,"ever. floods 5milller th"n th<l I ~term<:!d late Roq iOM I Flood arc more <br />frequent and i~undato smaller areas thouoh they "Iso cause camaqe, <br />hards~lp. and irlConvcnlerlCCs. Ttle historic :lcilk di:;<;harqcs ir hble <br />~ whe~ ccrnpared with the potent io I flood ooak dl scharo<lS in toblQ 4 <br />i Ilustroto the ="llor magr+itude of tre ">ora frequ()~t II OOdS. <br /> <br />Kazards of Large Floods <br />The effects of the I n1"erm",diate ROlllo",,1 and StM.dard <br />Project Floods "ere ana lyIed to deter",i"" po~ent la I f iood hazards <br />in the study reuch flood plain. T~e analy~Is used field conditions <br />roprescfi1"edbybrid<)ean<lvallcycroSs5octions5urveved in 197i. <br />Factors con~idQreJ Include ux.lont of ar<ld flooded, I load depths, <br />11000 d"m"qes, ol>struct ions to llood i lows, v"locl ti 65 01 Iloed f lo~'s, <br />rateoiric,eofstr"Mm level. and duration 01 floodlng. Damanc5 <br />durinq fioodlng are cffectcd ov both depth aod velocity of flows. <br />Obstructions to 110"5 can i ncrOilSC f lood dO;l~nC,. In rcc1rd -0 hu",~n <br />h;j~,,~ds, <)e~ora Ily f I oed ""ter 2 IRet or ",ore dcep ..Jod t I owi n'l at <br /> <br />streambed and tha I ntermed iate il.eg ional ana Sta~dard Project FlOOdS. <br />^ be~rir3 is also ~rnvirtprt ~hnwi~ thr orirnt~tion of the cross <br />soctjon throuqh the reierence point. Depths of flow for the Inter- <br />med iate f,e'l ionill ~nd StandJrd Proji.!ct FloodS can bo esrl"'ated from <br />the pref i I ~s, cr055 s{'Ctions, or reference tilble. For l!ny ,>pecii ie <br />situlIt ion '~h>;re accuracy 01 f looJed ;'Jrp., d!!1 i ~elltlo, 15 needed it <br />wi II be nOC<JS'i.1ry t" takE> tMe "~propr iate f loo~ elevation Ircrn one <br />of these sourcosand loc"te by 3urvey thecorrC500Mlnq around eleva- <br />tlonontoefloodplain. <br /> <br />1J~~tr.'''''' fn~.' Longmont in the study reach tho Intor",ooiate <br />fle~ion~1 FlOOd ~OJld inundat",,~ "re~ aV8rilgir.g ~,OOr, I..,..~ ~'ld~ <br /> <br />10 <br /> <br />20 <br />