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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Hvdraulic Analysis <br /> <br />The 100-year floodplain delineation in the City of Orchard City for Surface Creek and <br />portions of Cedar Run presented in the FIS and on the FBFM and FIRM uses the HEC-2 <br />(US ACE, 1976) hydraulic model. Updated flood peak estimates for Surface Creek are <br />similar to those in the FIS and will not significantly change the delineation of 100-year <br />floodplains shown on the regulatory floodplain maps. The approximate floodplain <br />delineated on the 1981 FIRM is also used to estimate the 100-year floodplain along <br />portions of Cedar Run and along Tongue Creek. <br /> <br />Floodplain Mapping <br /> <br />Updated 100-year floodplains and floodways shown on Figures 4A through 4D. <br />Floodplains and floodways within the City of Orchard City for Surface Creek and <br />portions of Cedar Run are based on detailed technical methods. Approximate floodplains <br />are shown for portions of Cedar Run and for Tongue Creek. Approximate floodplains for <br />Alfalfa Run near Fruit Growers Reservoir and near the southern City boundary, and for a <br />very small portion of Currant Creek were obtained from the FBFM and FIRM are also <br />shown on the Maps. As noted in the FIS, Alfalfa Run has low flooding potential and the <br />significant flooding is not expected unless upstream reservoirs fail. There is no <br />hydrologic or hydraulic data supporting the delineation for Alfalfa Run or for Currant <br />Creek, and the floodplain information from the FBFM and FIRM on these streams has <br />been copied onto Figures 4A through 4D without additional analysis. <br /> <br />Approximate floodplains for the portions of Cedar Run and for Tongue Creek are shown <br />because these reaches have not been studied with sufficient technical detail to be used for <br />floodplain delineation with any certainty. FEMA requires a detailed floodplain analysis <br />for development projects greater than 5 acres in area or more than 50 units in size in <br />approximate floodplains be performed by a professional engineer. <br /> <br />Vertical datum for the FIRM, FBFM, and FIS is NGVD 1929. To convert to the most <br />recent standard, NA VD 1988, add 3.82 feet to all elevations near the southern City <br />boundary, 3.91 feet near the center of the City, and 4.04 feet near the northern City <br />boundary (an average addition of about 3.9 feet) (USCOE, 2000). <br /> <br />17 <br />