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

Discharges of 100, 500, 1,000, 5,000, and 10,000 cfs were
simulated. Representative results from the 500 and 5,000 cfs
simulations are shown in Figs. 6 through 9. The FLO-2D predicted
flow depth and velocity compare very well with HEC-2 predictions.

The minor differences between the results from the two models
arise from interpreting the HEC-2 results in predicted critical
flow areas. For example, the transition from cross section 1 to
cross section 2 in reach 1 (see Fig. 5) appears to have unstable
hydraulic results. The HEC-2 water surface profile in the slope
transition areas had to be interpre.tE!d from either the subcritical
or supercritical profiles. This resulted in an abrupt change in
flow depth from an upstream supercritical regime cross section to
a downstream subcritical regime cre,ss section. It should also be
noted that the cross-sectional g'eometry does not necessarily
correlate with the fictitious slope and roughness values and that
the assumed associations between slope and roughness probably would
not be found in the field. other than these few transition areas,
the FLO-2D and HEC-2 results are within a few percent difference
and indicate that the FLO-2D model can simulate channel results as
well as HEC-2. FLO-2D has the added advantage of simulating flows
which vary between subcritical and supercritical regimes.

FIGURE 6

FLOW DEPTH

4.5

~-

FLO-2D VS. HEC-2

2.0

.
.
.
.
.
. .
.............;... ...f......
.
.
.
.
: : : 500: CFS H]~C..2 ,,:un: ::
1.5 .............;...............;..............~...............:..............~........,.....:.....,........~.... ....".:.. .-!-......,

: : ::: >___.:,..._J !
.. : I

:,
f
.:
..
..............~..............":.............1~
: : ,:
. . f'
: : ,:
: : ,:
. . .
: .
: ,
. .
. ............:.. ............;.............i ......................
. . .
: ; I
.
.
r--""" f
.:" : ~ : : . . .
'r:~" ....... ...:......... ............; ;...............;..............;'. ...'.........;..............; ..............;.... 0'
f " f: :::
: ':: : :
I \:, r-\ ' :
\._~.... : \::
: . . \ I: . . . .
....................... ....... ." . "~l ................................................~..............-.
: : ",: 500 CF'S F'LO--2D : .

. ,
: I .
.:.1.............:...............:......
:/
- ,
......~-':

....
,
'\ ....:........... ...:..............
, .
. .
. .
. .
. .
. .

4.0

. . .
................................................ .
. .
. .
. .

-'
Q)
Q)
Pc.

3.5

~
~
,~

30

, . . . . , . ' I

.c
-'
c.
Q)
o

~
o
Pc.

2.5

1.0
o

25

50 75
Channel

100
Distance
25

125 150
in Feet x

175
100

200

2?~
~v