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on ch~nnel and flood plain conditions "5 represented by survey data gathered in I~al' 1977 and as su,plerr,(lnted by later flel d investi- gations. The detailed topographic mapping utfll<:ed to assist In dallnedtlngthooutllneoftheIOO-ye!lr!lnd500-ye!lrtloodsconsIsts Ofll'l1lpSh!lvlnga.'Jcaleot I Inchaquals200feetwltha2footcon- tour Interval. These maps were preperad under contract with the Colorado Water Conservetion Board In cooperation wIth Larimer County. These maps, now used tor admlnlstr~tlve purposes, are On tile ~nd iilV~ I labia for public InspectIon ~t tho Planning Department, L~rlmer County Courthouse, Fort Collins, Colorado. ne profiles On plates 6 through 12 5h"", thewatersurf<lce elevations and wat!lr dep~h of the 10-Yeilr, 5.:)-YAllr. I OO-year, and 500-year flood5 relatIve to the streaMbed. I n this particular cilse ~n<l throughout the study. the streambed Is actually the channel low flow water 5urface elevatIon since the surveys were conducted by aerlal photogr<lMetrlc methods. The water surf"ce elevations of th!l lOG-year a~d 500-yoar floods were used to determine flood limits on the cross secticns and topogrdphlc map5. The results are shown on the ~Iccdcd MGJ5, ~iMes 3 through~. An index!" the Fiooded Area5 pl"teslsonplate2. RepresentlltlveCr05Ssection5ara Illust,.."ted on 01 ~tas 13 and 14. The Cr055 5ections show ground elevations JCrOSS the valley on both sides of the channel andthedeptnsof cverbenk fiooding. Reference points, coinciding with the loc~tlon5 of ti,,~ cros~ sKtI(JrlS and pertinent planim~tric feature~ arc 5hown on ~~e FlOOded Are~s and profll~ far correlation beTween the drawlngs. ;ables 6, 7. 8, 9, 10, 'md II provlde dllta "t ref"rence point loc~- tlon5, Including distance along the mal~ Channel center I ine, eleva- tions of the 5Tre~mbed, and elev~tio~s and disChar90S of the 10~year. 50-Y*lr, iOG-ye"r, and 5CO-ye",r floods. Araference line Is Shown On the Fiooded Areas for theC"che I~ Poudre River. Hewlett Gulch, HIli Gulch, Fllll s Gulch, Wllth~ Gul ch, ",ndUnndmadGulch. This line is used for reference only "nd dOllS not neceSS8rlly coincide with the existing stre8m chllnnol. The flood elevations shown on the profile "nd in t"bles 6-11 apply laterally from the channel over moST of the flood plaIn wldtn.Rolldcrossln<lsandothert~rllphlcI811turescanillterthe lateral flood olev~tlons. Depending On whether these f~tures divert or block flows, the flood elevations 8t the edge ot the flood plain may be higher or lower than "t the channel. The FlOOded Areas shew the area that would be flooded by the IOO-yearand 500-ycar floods. The flood IImlt5were Icca+edat eac~ cross section a~d the i ntcrven ing 11000 ootl Ines "ere drawn based upon dehllo<1 lopo~raphlc mappIng, e~gineering judgment. and field oh~ervatlon~. It is, hCo'ever. pass. I ble t~at rore or 1<:<55 f loodi ng sho~ I d be shown On The Flooded areas. For" speci f Ie situation, where "",...e, cet", i I c:d accuracy of a f loaded "re~ is rO<;'JI ~ed, the flood li",i+scdnbecooroile;curaTolyestJbliShedbvdeterrrlnln!'lth" '",,-ce'. ~Jrt~ce cleva'" ion 'fre-re, tM" >,rofl I e or reference '"able$ and tr,en loca~,in~; th~+ "iev,,~lon by 5\,rveV on th~ f:ood plai". Flood plllin widths very trom One ~rell to another through- out the study reach. The 100-year flood plain width of the Ciilche III Poudre River varies from a minimum noar 110 feet to II mllxlmum near 650 feet with an average 01 350 feet. The IOO-yellr tloodpl"in ,,'dth 01 Hewlett Gulch, Hili Gulch, F"'lls Gulch, W;'Itha Gulch, and Unnamed Gulch generally rllnges betw6e<l a ml<limumot 20 faet and a m""lmum of 250 feet with an aV9rageot 75 teet. All road"ayslnPoudrePllrkllrO overtopped by the IOO-year tlood at some 10Clltlon In the study reach. Obstructlonstofloodflows_Sever...1 rOlld""yscros5the flood plain of the Cache Ii! Poudre RIver and tributaries ln the study 14 "