FLOOD05412

• County: Statewide
• Basin: Statewide
• Title: Geomorphically Effective Floods
• Date: 1/1/1995
• Prepared By: USGS
• Floodplain - Doc Type: Educational/Technical/Reference Information

4,500

4,360 eMS

4,000

o
z
8 3,500
UJ
CI)
a::
UJ
0-
CI)
a:
UJ
I-
W
::;;
()
10
:;)
()
~

3,000

2,500

2,000

W 1,500
CJ
a:
<{
13 1,000
CI)
i5

500

o
1200 1600 2000 2400 0400 OBOO 1200

JUNE 15, 1965 I JUNE 16, 1965

TIME, IN HOURS

Fig_ 7. Hydrograph for the Plum Creek, Colo_ flood of June,
1965 (from Osterkamp and Costa, 1987)_

32

31

~ 30
UJ
tu 29
;:;
z
-.28
z
o
~ 27
iii
i:rl 26

"'V $urtace_ - - - - -
~~\e..! - ~ - - -
- -

---

25

24
o 50 100 150 200 250 300 350 400 450 500 550
DISTANCE, IN METERS

Fig. 8. Cross.section used to construct a flood rating curve for
Plum Creek. Colo, flood of June. 1965.

consequent uncertainty in the exact location of alluvial
boundaries during the flood peale Judicious selection of
cross-section locations can minimize possible errors. Stage-
discharge curves (Figure 9) can be constructed for

COSTA AND O'CONNOR 53

30
29
U>
0:
UJ
>- 28
UJ
;:;
'"
ui 27
~
>-
U>

26

25
o 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500
DISCHARGE, IN CUBIC METERS PER SECOND

Fig_ 9. Stage-discharge curve for the Plum Creek flood of
June, 1965.

200

(/) 180
~~ 160
;::UJ
z ~ 140
-:;:;
ffi w 120
0:
~ :3100
"-0
:E en 80
<0:
~q~~ 60
t;

40
20
1600

1800 2000 2200 2400 0200 0400 0600 0800 1000 1200
JUNE 15, 19651JUNE 16, 1965
TIME. IN HOURS

Fig_ 10. Stream-power graph showing the distribution of
stream power over time for the Plum Creek flood of June,
1965_

individual cross-sections by computing hydraulic convey-
ance for different elevations in the cross-section. The
primary source of error in this method as we have applied
it is the assumption that the flow resistance is constant at
all stages. This is clearly untrue, but roughness values
generally change by less than a factor of two with
increasing stage once flows are overbank [Hicks and
Mason, 1991]. Using a hydrograph, cross-sections, and a
stage-discharge relation, it is possible to construct a curve
of the distribution of stream power per unit area throughout
the flood. We refer to these plots as 'stream-power
graphs' (Figure 10). From these graphs, it is possible to
integrate the area under the curve to derive the total
amount of energy expended by a flood per unit area, as
well as an average value of stream power for the flood
(Table 2)_ These data can then be compared to observations