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RE: J-2 Contracting Company-DPG Pit <br /> Floodplain Study <br /> Page 2 <br /> 2) A mining conditions floodplain model was developed showing the effect on the 100-year <br /> floodplain from the stockpiles within the mining area relative to the Duplicate Effective <br /> model. This model incorporated modified cross-sections from the CHAMP model that <br /> included the topography and obstructed flow areas resulting from the construction of <br /> temporary stockpiles within the mining area. The duplicate effective and mining <br /> conditions HEC-RAS cross-sections and output files are included in Appendix C. <br /> The 100-year Floodplain Elevation Summary in Appendix B shows the results of the duplicate <br /> effective and future conditions models for the study area. A maximum rise of 0.15 feet from the <br /> duplicate effective 100-year flood elevations occurs at cross-section 67+57.88 of the Cache la <br /> Poudre River model. A maximum rise of 0.17 feet from the duplicate effective 100-year flood <br /> elevations occurs at cross-section 14027+08 of the South Platte River model. <br /> Please feel free to contact us if you need any additional information or have any questions or <br /> comments. <br /> Sincerely, <br /> Mr. J.C. York, E. <br /> Attachments: <br /> Appendix A—Floodplain Maps <br /> Appendix B—100-Year Floodplain Elevation Summary <br /> Appendix C—HEC-RAS Output Files <br /> N, 305 Denver Avenue—Suite D•Fort Lupton CO 80621 •Ph:303-857-6222•Fax:303-857-6224 <br />