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. . . ENGINEERING METHODS Hvdrololtic AnaIvsis Hydrology information for the Wild Horse Creek approximate floodplain delineation on the Kit Carson FHBM has been estimated in accordance with the CWCB's Guidelines for Determining IOO-Year Flood Flows for Approximate Floodplains (Guidelines). The 100-year flow for this stream can be estimated by utilizing the regression equation for Arkansas River Basin, subregion Ark-I. The equation is Q,oo = 1,564.98(A)o.",., where QlOO 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 25 square miles and 1,125 square miles. This equation is valid for Wild Horse Creek. Figure I, presented in the Appendix at the end of this report, displays the Arkansas River Basin with Subregions Ark-l through Ark-6. The regression curve for Subregion Ark-I is also included in the Appendix. Table I displays the estimated 100-year peak flows for Wild Horse Creek at the downstream city limits. Table I Estimated IOO-year peak flow for Wild Horse Creek Stream Location Drainage Area (sq mi) IOO-year Peak Flow (cfs) Wild Horse Creek at downstream city limit 175 25,300 A procedure for determining hydrology information for approximate floodplains of lakes, ponds, and local drainages has not been established. The hydrologic methodology developed in the Guidelines is appropriate for designation and approval of approximate floodplain information and for use in simple floodplain analyses for development such as open space, agriculture, farm bridges, pole bams, and individual single residential structures. The methodology is not appropriate for development involving residential subdivisions greater than 50 lots or occurring on sites greater than 5 acres, commercial construction, industrial construction, construction of public transportation facilities, or construction of flood control facilities. The Town of Kit Carson should regulate the approximate floodplains on a case-by-case basis subject to a detailed hydrologic and hydraulic analysis. A detailed floodplain analysis may be required in certain cases and should be performed by a professional engineer and submitted by the developer or development proponent. An approximate floodplain analysis can be submitted by a developer or development proponent, for the cases listed above, in accordance with the determinations of the Colorado Water Conservation Board regarding the applicability of the Guidelines. 3