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<br />. Previous Studies and Proiects <br /> <br />Several reports have been published regarding the Arkansas River and its tributaries within Chaffee <br />County. These reports can be found in the bibliography, Section 9,0, of the FIS, <br /> <br />Communitv Response to the CWCB Desil!nation and Approval Process <br /> <br />A letter from the CWCB was transmitted to Chaffee County regarding the Board's proposed action <br />for designation and approval of the Chaffee County FIS, The County was receptive to the Board's <br />proposed actions, and sent an official letter requesting that the CWCB designate and approve the <br />floodplain information currently available to the community. A copy of the request letter is included <br />in the Appendix of this report, A meeting was held between County officials and CWCB staff to <br />discuss hydrology issues, floodplain regulations, and the designation and approval of the FIS, In <br />addition, County officials expressed that it would be beneficial to have additional detailed <br />floodplain information for specific reaches on several streams within its jurisdiction, <br /> <br />ENGINEERING METHODS <br /> <br />Hvdrolol!ic Analvsis <br /> <br />. <br /> <br />Hydrology information used for streams with detailed floodplain delineations in Chaffee County's <br />FIS is discussed in Section 3.1 of the FIS, Hydrology information for the streams with approximate <br />floodplain delineations in Chaffee County's FIS has been estimated in accordance with the <br />CWCB's Guidelines for Determining IOO-Year Flood Flows for Approximate Floodplains <br />(Guidelines). The lOG-year flow for each of the streams with approximate floodplains (in all of <br />Chaffee County) can be estimated by utilizing the regression equation for Arkansas River Basin, <br />Subregion Ark-6, The equation is QIOO = 45.98(A)o.717, where QuJO is the lOG-year peak flow in <br />cubic feet per second, and A is the upstream (contributing) drainage area in square miles, Figure 1, <br />presented in the Appendix of this report, displays the Arkansas River Basin with Subregions Ark-I <br />through Ark-6, The regression curve for subregion Ark-6 is also presented in the Appendix, The <br />regression equation is only valid for tributary streams having drainage areas between 4 square miles <br />and 330 square miles, and is not valid for the Arkansas River mainstem, <br /> <br />The Guidelines methodology is not appropriate for development involving residential <br />subdivisions greater than 50 lots or occurring on sites greater than 5 acres, commercial <br />construction, indnstrial construction, construction of public facilities, or construction of flood <br />control facilities. The hydrologic methodology developed in the Guidelines is appropriate for <br />designation and approval of approximate floodplain information and for use in simple floodplain <br />analyses for development such as open space, agriculture, farm bridges, pole bams, and individual <br />residential structures. A procedure for determining hydrology information for approximate <br />floodplains of lakes, ponds, local storm drainage areas, or overflows from irrigation canals and <br />ditches has not been established, <br /> <br />. <br /> <br />3 <br />