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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . :. . . I. - ENGINEERING METHODS Hvdrolol!ic Analvsis The Nuda FHBM presents approximate floodplain delineations. Hydrologic information used for the FEMA approximate floodplain delineations are not available or were not documented by FEMA. The CWCB has developed acceptable hydrologic information for undeveloped basins using regional regression methodologies for computing lOO-year flood,flow values. However, due to a lack of information, these equations are not available for the Western San Juan River Subregion. Therefore, approximation methods developed by the USGS were used in this analysis. The CWCB methodology is fully described in a publication by the CWCB entitled "Guidelines for Determining lOO-year Flood Flows for Approximate Floodplains in Colorado". The Dolores River Subregion (DLR,I) is used for streams in the Dolores River basin. The CWCB equation is: Equation 1 Regional Regression Equations for Nuda QlOO = 213.8(A)G.601 (Only for drainage areas between 2 and 1080 square miles) For Equation I, the Ql00 is the lOO-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 the range of drainage areas as shown next to the equation. The lOO,year flow for Calamity Draw at the downstream Town Limits were estimated by utilizing the regional regression equations presented in Equation 1. Table 1 presents lOO'year flow estimate for this location. Table 1 Estimated Dischar es for Dove Creek F100din Source Location Calami Draw at dls Town of Nucla co orate bound Drainage Area (miz 3.23 1oo-year Discharge crs) 433 Nuda should regulate the approximate floodplains on a case-by-case basis. FEMA requires that a detailed floodplain analysis must be performed by a professional engineer and submitted by the developer or development proponent for development projects involving more 5 acres or more than 50 units (whichever is more restrictive). Hvdraulic Analvsis Hydraulic methods used for the approximate floodplain delineations shown on the Nuda FHBM panels are not available or have not been documented by FEMA' For future studies, an approximate lOO-year flood elevation at a particular location on the river may be obtained by 4