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. . . Communitv 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 Westcliffe. A meeting was conducted by CWCB staff on February 28, 1996. Local officials in attendance included the mayor. The mayor was 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. ENGINEERING METHODS Hvdrologic Analvsis Hydrology information for the streams with approximate floodplain delineations on Westcliffe's FHBM has been estimated in accordance with the CWCB's "Guidelines for Determining 100- Year Flood Flows for Approximate Floodplains" (Guidelines). The 100-year flow for the streams with approximate floodplains can be estimated by utilizing the regression equation for Arkansas River Basin, Subregion Ark-6. The equation is QIOO = 45.98(A)o.717, where QIOO is the 100-year peak flow in cubic feet per second, and A is the upstream (contributing) drainage area in square miles. The regression equation is only valid for tributary streams having drainage areas between 4 square miles and 330 square miles. This equation is valid for Grape Creek. Table 1 Estimated lOO-Year Peak Flows For Grape Creek, Mill Gulch and South Tributary to Grape Creek at Westcliffe, CO Stream Location Drainage Area (sq mi) tOO-Year Peak Flow in CFS Grape Creek at 249.3 2,404 upstream town limit Grape Creek at d/s town 254.1 2,438 limit Mill Gulch at d/s town limit 3.8 D.A. too small for regression equation s. Trib. to Grape Creek at 2.9 D.A. too small for town limit regression equation