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<br />WHEREAS, a number of U.S. Geological Survey publications, containing regional <br />regression equations for estimating I DO-year peak flows for streams in the area of interest, may <br />be utilized for streams in Cortez and Montezuma County; and <br /> <br />WHEREAS, the CWCB staff has defined terminology pertinent to the preparation of <br />approximate and detailed floodplain information and to proposed development. activity' within <br />delineated floodplains as described in Table 2 below: <br /> <br />Table 2 <br />Definitions for preparing floodplain information <br /> <br />Approximate hydrology: I aD-year peak flow values estimated for the hydrologic point of interest using <br />regional regression equations or other acceptable hydrologic methods approved by the CWCB. <br />Detailed hydrology: lOa-year (and 19-, 50-, and 500-year when applicable) peak flow values computed <br />for the hydrologic point of interest using an acceptable detailed methodology, other than the <br />"Guidelines", such as an at-site stream gage analysis, a regional stream gage analysis, or a rainfall-runoff <br />model. <br />Approximate hydraulics: Water surface elevations or flow depths computed for the location or reach of <br />interest using nonnal depth flow calculations (Le. Manning's equation/slope-area method). Computer <br />programs such as QUICK-2 and FlowMaster are excellent tools for this purpose. <br />Detailed hydraulics: Water surface elevations (base flood elevations) computed for the stream reach of <br />interest using a step-backwater computer model, or otller acceptable one-dimensional or two dimensional <br />computer model, such as HEC-2 or HEC-RAS. <br />Limited Development: Development involving parks, open space, golf courses, agriculture, bridges and <br />culverts that serve a single fann/home/cabin, pole bams, and individual single family structures. <br />Significant Development: All development that does not fall under one of the categories listed under the <br />Limited Development definition, A special case of significant development is a development that <br />involves more than 5 acres or more than 50 units (whichever is more restrictive). This special case is <br />important because federal regulations require that a detailed study be submitted to the communitY by the <br />developer. Failure of the community to require a detailed study will result in a violation of the National <br />Flood Insurance Program, which can have negative impacts on floodplain property owners within the <br />community. <br /> <br />;and <br /> <br />WHEREAS, the regulation by the City of Cortez of the approximate floodplains for <br />development proposals within the city should take place on a case-by-case basis following the <br />procedures developed by Colorado Water Conservation Board staff as outlined in Table 3 below: <br /> <br /> , ~ <br /> Are regional regression equations Hydro\ogic ',' Hydraulic <br />Type of developinent applicable to the stream of requirements requirements <br />proposal in community interest? for developer for developer <br />Limited development Yes Approximate Approximate <br />Limited development No Detailed Approximate <br />Significant development Yes Detailed Detailed <br />Significant development No Detailed Detailed <br /> <br />Table 3 - CWCB procedure for regulating approximate floodplains <br /> <br />;and <br /> <br />3 <br />