FLOOD01621

• County: Statewide
• Community: State of Colorado
• Title: Flood Hazard Delineation on Alluvial Fans and Urban Floodplains
• Date: 1/1/2001
• Prepared For: State of Colorado
• Prepared By: J.S. O'Brien
• Floodplain - Doc Type: Educational/Technical/Reference Information

were obtained in less than a wee:k. In comparison, the HEC-2
analysis took more than a month to finish.

FIGURE 10 HEC-2 AND FLO.2D PREDICTED
FLOODPLAIN BOUNDARIES FOR THE
POUDRE RIVER NEAR
FORT COLLINS, CO, I'r~

FLO-2D Delineoted 100-Ye., F1eed Boundory J/ ,
HEC'2 D,lin,ot,d 100-Y,., F1oo<1 8u ~ ~

/-

/~
_-r-

\ ,",-... "

~_ Poudre RIver

9 HEC-2 Zero inundatIOn Area

za Fl,o-2D Zero Inundation Area

lnlerslale 25

~ 7

- Representative Grid Elemenl F-~
L -- GRAPHIC SCAlJ:
'1"7 "... ~
- /r ,~..-<._,
L ._*_...

H1~C -2 Delineated toO-Year nood Boundal'Y

FLO-2D Delineated lOO-Yeor Flood Boundary

6.3 Verification of Mudflow Hydraulics

The simulation of hyperconcen'l:ra1:ed sediment flows with the
FLO-2D model was verified using field data from the 1983 Rudd Creek
mudflows in Davis county, Utah. ThE! Rudd Creek data is the best
available field data in the literature. The flood hydrograph and
data used in the simulation were developed by the Army Corps of
Engineers (USCOE, 1988). The field data to be replicated included:

(1) The area of inundation indi.cated on aerial photography;

(2) A surveyed volume of the mudflow deposit of approximately
84,000 yd';

(3) A mudflow frontal velocity on the alluvial fan of
approximately the speed t:hat a man could walk (eyewi.tness
account) ;

(4) Observed mudflow depths that ranged from approximately 12
feet at the apex of the alluvial fan to approximately 2
or 3 feet at the debris front.

Using the COE hydrograph (Fig. 11), the area of inundation
could be reproduced almost exactly (Fig. 12). The maximum computed

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