Laserfiche WebLink
<br />Hydraulic Analysis <br /> <br />Hydraulic analysis in this study entails primarily the com- <br />putationof the back\>laterwithin the studyrea<:hes of the river. The <br />basic data for the study '1as obtain.,d fro", different !(overmoental al':en- <br />cie~ and field investigations. Topographic mapping "ith a scale of 1 <br />inch equal to 200 feet and 2 feet contour interv"l ~',-,re supplied by the <br />Colorado Water Conservation Board. The data ~as revie\>led in depth to <br />determine its adequacy and accuracy. Major sources of error;;hen <br />applying hydraulic theory are inadequacies in data \>lhich can result in <br />an improper modeling of flow conditions. Also, calibrating a simulation <br />flow model reql1ires adequate data of reasonable accuracy. <br /> <br />running parallel to the floodplain, etc. are needed to model the river <br />terrain as accurately as possible. The model \>las calibarted using the <br />diacharg" fating cufv"~ for Gunnison River n"ar Gunni~o" and Tomichi <br />Creek nenf Gunnison gaging st"ti~ns. The hydraulic roughness parameter <br />for the channel and overbank for different reach~s were estimated from <br />roughness dnta of other rivers with similar characteristics and ~as <br />further verified by field observations of the entire river reach. <br /> <br />Digitized cross sections were secured ;;hen the topographic <br />maps werc compiled. These cross sections were augmented by field- <br />surveyed cross sections for typical reaches of the river. Thelocation <br />of the cross scctions arc shown on the flood arcn m.,ps (Piates 23-31) <br />and the flood profiles (Plates 15-22). The cross sections, streambed <br />elevations, and \>later surface elevations for 10-, 50-, 100-, and 500- <br />year frequencies is shown in Table 6. <br /> <br />A detailed description of the hydraulic analysis is included <br />in the Technical Addendum. <br /> <br />The water surface elevations for the 10-, 50-, 100- and 500- <br />year recurrance interval floods were computed utilizing the Corps of <br />Engineers IlEC-2 step backwater computer program. The compl1tntion of <br />water surface profiles involves solving the one-dimensionnl energy <br />equation to determine the shape of the profUe between control sections <br />where the water S\lrf"ce elevation is known or can b~ assumed. The <br />genernlly npplicnble procedure for steady flo~ profile calculation is <br />called the "Standard Step Kethod". In thi~ method, the distance from a <br />dOWIl8tr~"m or upst,e_am poiflt where condition" "r~ kn",",fl, to tiw point <br />~h~rc hncr~ntcr cffc~t~ nTC to ~~ ~~~crT.inc~, is di~iccd into 7cnc~..s by <br />cross ~"aions 'It fjx~d locations along the riv"r ,md, starttflf, trOOl one <br />control, profile calculations proceed in step~ from cross s"ct10n to <br />cross section to the next control. HEC-2 program is capable of also <br />handling the effect of various structureg across the river ~uch n~ <br />bridges, culverts, weirs and embankments. <br /> <br />The basic dnta to run a b,-,ck;;atcr study arc Lhe ~eo...,trtc <br /> <br />d'ltJ, whi~h in<:l"J.. c.-~ss s.:<:U-:>ns 0f th" river ",<"-sur~<.l pd.p","Jic....ldl. <br /> <br />to the direction of flo~ at suitahle interval~ ~nd at p"tnt~ ;;here th., <br />geometry of thE' river changes, along "ith the distance bdwe.,n the cross <br />sections. Detailed topographic maps ;;howlng floodplain, ob~tructlonH in <br />th.. floodpl.~in thClt WO\lld ~on~rrict th{" flco,-' or r~8n-ict the floodplain, <br />8tn'ctUl-e~ .~cross tlt" river a"d tll"l.,. J~ta1b, <lik"'" ro"d~ <lnd rllilr"ml <br /> <br />" <br /> <br />'; <br />