FLOOD02012

• County: Bent
• Title: Floodplain Information Report Bent County
• Date: 6/1/1996
• Prepared For: Bent County
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

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CWCB designate and approve the floodplain information currently available to the community, A
copy of the request letter is included in the Appendix at the end of this report,

ENGINEERING METHODS

Hvdrololrlc Analvsis

Hydrology information for the streams with approximate floodplain delineations on Bent County's
FHBM has been estimated in accordance with the CWCB's Guidelines for Determining lOO-Year
Flood Flows for Approximate Floodplains (Guidelines). The l00-year flow for each of the
streams with approximate floodplains (in all of Bent County) can be estimated by utilizing the
regression equation for Arkansas River Basin, Subregion Ark-I. The equation is QlllO =
1564.98(A)o,539 ,where QlOO is the lOO-year peak flow in cubic feet per second, and A is the
upstream (contributing) drainage area in square miles, Figure 1, presented in the Appendix of this
report, displays the Arkansas River Basin with Subregions Ark-l through Ark-6, The regression
curve for subregion Ark-l is also presented in the Appendix, The regression equation is only valid
for tributary streams having drainage areas between 25 square miles and 1125 square miles, and is
not valid for the Arkansas River mainstem, Table 1 presents drainage areas and estimated l00-year
flows, using the subregion Ark-l regression equation, for selected streams in Bent County,

Table 1

Drainage Area loo-year Peak
Stream Name Location (SQ. mi.) Flow (cfs)
Adobe Creek Confluence with Arkansas River 730 54,800
Caddoa Creek Confluence with Arkansas River 175 25,300
Horse Creek Confluence with Arkansas River 1340 D.A. too large
for regression
Mud Creek Confluence with Arkansas River 200 27,100
Rule Creek Confluence with Arkansas River 490 43,900

There are numerous other streams within the County having drainage basins of various sizes, Peak
flows may also be estimated for those streams using the subregion Ark-l regression equation,
providing that their drainage areas fall between 25 and 1125 square miles, The l00-year flow for
approximate floodplains of streams that have drainage areas between 0,5 and 25 square miles can
be estimated using the USGS publication entitled "Rainfall-Runoff Modeling and Regional Flood
Characteristics of Small Rural Watersheds in the Arkansas River Basin in Colorado," This
publication is available from the USGS publication center in Denver, Colorado,
A detailed study or other hydrologic analysis must be performed for projects involving most of the
Arkansas River mainstem or streams with drainage areas that fall outside the applicable range of the
two methodologies discussed above,

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