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Community Response to the CWCB Desil!llation and Approval Process A letter from the ewCB was transmitted to the City of Leadville regarding the Board's proposed action for designation and approval of this Floodplain Information Report and the Leadville FHBM, The City was very receptive to the Board's proposed actions, The City sent an official letter requesting that the ewCB designate and approve 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 Hvdrolol!ic Analvsis Hydrology information for the streams with approximate floodplain delineations on Leadville's FHBM has been estimated in accordance with the ewCB's Guidelines for Determining lOO-Year Flood Flows for Approximate Floodplains (Guidelines). The lOO-year flow for the streams with approximate floodplains can be estim2.ted by utilizing the regression equation for Arkansas River Basin, subregion Ark-6, The equation for Subregion Ark-6 is QUMl = 45.98(A)o.717 ,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 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-6 is also included in the Appendix. 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 the Arkansas River mainstem upstream of the Lake Creek confluence only. The remainder of the Arkansas River mainstem (downstream of the Lake Creek confluence) is exempt from the regression equation, 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, Table I displays the estimated lOO-year peak flows for California Gulch at the upstream and downstream city limits, Table 1 Estimated loo-year peak flows for California Gulch Stream Location California Gulch at u stream ci limit California Gulch at downstream ci limit 100- ear Peak Flow (cfs) A procedure for determining hydrology information for approximate floodplains of lakes, ponds, and local drainages has not been established, In addition, a procedure for estimating lOO-year peak flows for streams that have drainage areas that fall outside of the drainge area limits, as specified in the Guidelines, 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 barns, and individual single residential structures, The methodology is not appropriate for