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<br />C1~ <br />C- <br />"'- <br /> <br />18 I FIGU~E 9 <br /> <br />171 <br />16 f <br />, <br />1- I <br />''[ <br />14 i. <br />13 t <br /> <br />~~ l. . , ,.. . . . <br /> <br />10 ... <br />9 .... <br />\ <br /> <br />r--- , <br /> <br />fJt <br /> <br />: I <br />:1 <br />, , .. .. : I <br />" <br />.........f.... .... <br />:, <br />.. ..1 <br />, <br /> <br />FLOW VELOCITY..' <br /> <br />F"LO.. 2D <br /> <br />vs <br /> <br />H E C-:~ <br />-,----------.-- <br /> <br /> <br />---,-.--,--- <br /> <br />5000 HEC..2 :- -.-- <br /> <br />.:..... ............. <br /> <br />5000 FLO,-'2D-- <br /> <br />>., <br />-- <br />,- <br />u <br />o <br />GJ <br />> <br /> <br /> <br /> <br />.. <br />~ <br />o <br /> <br /> <br />"'- <br /> <br />.,"..\... <br />.......~. <br /> <br />. C-:-:'~ :-: f:--""~':'" -/, . <br />'_,_-1 . <br /> <br />I <br />4 I .. <br /> <br />3 ....... ,.. <br /> <br />2 <br />11 <br />o <br /> <br />, <br />25 <br /> <br />, <br />50 <br /> <br />, <br />75 <br /> <br />--'-____..L.....--..-.. <br />125 150 <br /> <br />, <br />175 <br /> <br />-'--.-.-.- <br />200 225 <br /> <br />100 <br /> <br />Channel Distance in Feet. X 100 <br /> <br />6.2 River Overbank Flows, Floodplain Simulation .- Poudre <br />River, Fort Collins, Colorado <br /> <br />A FLO-2D simulation of overbank river flows was compared with <br />a HEC-2 analysis of the Poudre River near Fort Collins, Colorado. <br />The HEC-2 results were based on the linear interpolation of water <br />surface elevations for the peak discharge between the cross <br />sections and an interpretation of .the water surface elevation on <br />the floodplain. Using the same cross section and topographic data, <br />FLO-2D routed the lOO-year flood hydrograph through a two-mile <br />reach of the Poudre Ri.ver represent<~d by seventeen cross sections. <br />The maximum water surface elevations ,.ere determined at discrete <br />points on the floodplain. <br /> <br />The results shown in Fig. 10 indicate good agreement between <br />the area of inundaticm for the two methods. The areas of zero <br />inundation in the center of the floodplain for very shallow flow do <br />not match exactly because of the flood wave attenuation predicted <br />by the FLO-2D model and because theF'LO'-2D water surface elevations <br />were not plotted inside each grid element. The inundation boundary <br />was not traced along contours within '~ach grid element, but instead <br />was drawn around the entire element. Matching the floodplain water <br />surface elevations to contours in eiich element would have improved <br />the comparison, but like the HEC-2 analysis, would have required <br />subjective interpreta1:ion. The results from the FLO-2D simulation <br /> <br />27 <br />