FLOOD05224

• County: Rio Blanco
• Community: Rio Blanco County
• Stream Name: White River
• Basin: Yampa/White
• Title: Floodplain Information Report
• Date: 4/1/1996
• Prepared For: Rio Blanco County
• Prepared By: CWCB
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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3.0 HYDROLOGIC ANALYSIS

3.1 Existing Data

For locations where existing detailed hydrologic analyses were available, those analyses were used
to obtain peak 50-year and 100-year flows. For some other locations, statistical analyses of
stream gages provided by the USGS were available.

Published floodplain studies prepared by Merrick and Company for Meeker, Colorado provided
50-year and 100-year flows above the upstream limit of this study. Floodplain studies prepared
by FEMA for Rangely and unincorporated Rio Blanco County provided 50-year and 100-year
flows near the downstream limit of this study. In addition, USGS gage analyses were available
for two tributary streams.

3.2 New Hvdrologic Infonnation

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The fonn of the equation is the same for the entire study reach, but the coefficients are different
for the two frequencies.

Hydrologic analyses of the 50-year and 100-year flood flows for the remainder of the hydrologic
points along the study reaches of the White River were accomplished by interpolation of the
known flovo.: values. The frequency analysis of the USGS gage for the White River near Rangely
was not included in the hydrologic analyses due to the limited number of years of data available
at that site and the inconsistency between flow versus drainage area values for the gage and the
published values at Meeker and Rangely. The three known values and the corresponding
drainage areas were entered into a curve fitting computer program which selects an equation that
provides a close description of the plotted curve. The curve fitting program computed the flows
at the other hydrologic points on the White River locations by using the drainage areas at each
location for which flows needed to be calculated.

The equation for the White River below Rio Blanco Reservoir is:

Q= 1 Ok+dl.ogA

where:

Q = 50-year or 100-year flow;
A = drainage area;
k = a constant; and
c = an exponent

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White River
Downstream of Rio Blanco Lake for 50-year frequency: k= 6.271, c= -7.486
for 100-year frequency: k= 7.157, c= -10.002

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