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. . . Community Response to the CWCB Desil!:nation and Approval Process The community was contacted initially by letter. In a follow up phone call a meeting was arranged with local officials to present the CWCB' s proposal to designate and approve approximate floodplain information for Custer County. A meeting was conducted by CWCB staff on February 28, 1996. Local officials in attendance included the planning director, building official, road and bridge director and a county commissioner. The officials were very receptive to the CWCB's designation and approval of the county's floodplain information. They also expressed interest in joining the National Flood Insurance Program. HYDROLOGIC ANALYSIS Hydrology information for the streams with approximate floodplain delineations on Custer County's FHBM panels has been estimated in accordance with the CWCB's Guidelines for Determining JOO-Year Flood Flowsfor Approximate Floodplains (Guidelines). The 100-year flow for each of the streams with approximate floodplains can be estimated by utilizing the regression equations for Arkansas River Basin subregions Ark-3 and Ark-6. The equations for the two subregions are as follows: Subregion Ark-3: Subregion Ark-6: QlOO = 1089.27 * (A)O.635 Ql00 = 45.98 * (A)O.717 For all of the equations, Ql00 is the estimated 100-year peak flow in cubic feet per second, and A is the upstream (contributing) drainage area in square miles. The regression equation for Subregion Ark-3 is valid only for tributary streams having drainage areas between I and 930 square miles. This equation is valid only for Low Back Creek and Hardscrabble creek downstream of its confluence with South Hardscrabble Creek. The regression equation for Subregion Ark-6 is valid for all other tributary streams in Custer County having a drainage area between 4 and 330 square miles. This equation is valid for all streams in Custer County within these parameters except for Grape Creek downstream of the Town of Westcliffe. A detailed study or other hydrologic analysis must be performed for projects involving Grape Creek downstream of the Town of West cliffe since it falls outside the applicable range of the regression equations. The boundaries for the various subregions along with other pertinent information is published in the CWCB's Guidelines. A copy of the Guidelines can be obtained by writing to the Colorado Water Conservation Board, Floodplain Management Section, 1313 Sherman Street, Room 721, Denver, Colorado, 80203. The use of the U.S. Geological Survey publication, Techniques For Estimating Regional Flood Characteristics of Small Rural Watersheds in the Plains Region of Eastern Colorado, can be used to supplement the Guidelines. The USGS publication can be used for stream reaches with drainage basins less than 25 square miles but greater than one-half (0.5) square mile, if applicable.