FLOOD00150

• Designation Number: 579
• County: Gunnison
• Community: Marble and Vicinity
• Stream Name: Crystal River
• Title: Floodplain Information Report - Crystal River Technical Appendix
• Date: 8/1/2004
• Prepared For: CWCB
• Prepared By: Icon Engineering, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

I
I
,
I
I
I
I
I
I
It
I

-..-------.....-.-""'

1!
.'l
]
I

MANUAL FOR ESTIMATING FLOOD CHARACTERISTICS

23

SITES NEAR GAGED SITES ON THE SAME STREAH

Peak discharge information for study sites near gaged sites on the same
stream can be computed using the method described on page 4. The first step
is to determine the drainage area ratio of ungaged site to gaged site. If
that ratio I ies between 0.5 and 2.0, the equation given on page 4 should be
used to compute the requ i red peak d i scha rges. I f the dra i nage area ra t 10
I ies outside the range, the method for "Un gaged Sites" should be used.

Flood depth information for study sites near gaged sites on the same
stream should be computed from the flood depth regression equations for the
region in which the study site I ies, The method is Illustrated in Example 2.

Example 2.--FZood Frequency near a Gaged Site

,
i
i
I
\,
'\
!
,

Determine the QIO-, Qso-, QIOO-, and QSoo-year recurrence-interval
floods for Cherry Creek at State Route 83, 4.5 mi south of Franktown, Colo.
(Iat 39019'41", long 104044'02", NW}, sec. 25, T. 8 S., R. 66 W.).

Map coverage:

Russellville Gulch quadrangle, scale = 1:24,000
Denver quadrangle, scale = 1:250,000.

From table 5, note that station 06712000
Colo. (AG =169 mi2), is located downstream.
age

Cherry Creek near Franktown,

'f,
"

I

II This meets the drainage-area requirement, and the following relation is used:

I

where x=0.48 for the Plains Region, and QT(G) Is the weighted discharge from
II table 5.

I
,
II

Determine the contributing drainage area at the site (AU=132 mi2).

Check that AU is either more than half AG or less than twice AG:

',j

AUtAG=132 mi2t169 mi2=0.78.

x
QT(U)=(AU,AG) QT(G)