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<br />a. Approximate floodplain information shall be based on detailed hydrology computed for <br />the I OO-year flood. Hydraulic information shall be produced using approximate, field, <br />or limited techniques and best available topographic/survey data. <br />b. Detailed floodplain information shall be based on detailed hydrologic and hydraulic <br />determinations for the I OO-year flood. Flood profiles and floodplain delineations for <br />the 100-year flood and other frequencies, if any, shall be plotted, preferably using a <br />digital technique. Flood profiles and floodplain delineations for the 500-year flood are <br />encouraged, but not required, by the CWCB. The CWCB shall only designate and <br />approve the 100-year floodplain. <br /> <br />C. Base Mapping. Base mapping for floodplain studies shall meet the minimurn standards as set <br />forth in Appendix A and any other method approved by the Board. <br /> <br />D. Topography and Surveys. Topographic and field survey information for floodplain studies <br />shall meet the minimum standards as set forth in Appendix A. <br /> <br />E. Vertical Datum and Horizontal Control. <br />a. New topographic information generated for floodplain studies in Colorado shall be <br />produced using the standard NA VD 1988 vertical datum. Existing flood profiles and <br />Base Flood Elevations referencing NGVD 1929 vertical daturn shall be converted to <br />NA VD 1988 vertical datum when used in the preparation of new and revised floodplain <br />mapping studies. The topographic information to be used for new and revised <br />floodplain studies, that was originally developed using NGVD 1929 vertical datum, <br />shall be converted to NA VD 1988 vertical datum. <br />b. The accepted Horizontal Projection standards are UTM (Zone 12 or 13 depending on <br />Geographic location within the state) and State Plane coordinates. <br />c. Additional requirements are set forth in Appendix A. <br /> <br />F. Geographic Information Systems (GIS). GIS information for floodplain studies in Colorado <br />shall meet the minimum standards as set forth in Appendix A. New floodplain studies <br />submitted for CWCB designation and approval shall be in conformance with CWCB approved <br />GIS standards for digital floodplain information. <br /> <br />G. Hydrology. Hydrologic analyses for floodplain studies in Colorado shall be completed in <br />conformance with the minimum standards as set forth in Appendix B or other methods <br />approved by the CWCB. In addition, the following rules apply to hydrology studies: <br />a. All floodplain studies, regardless ofthe level of detail (e.g., approximate or detailed) <br />shall utilize detailed hydrologic information. The CWCB recognizes existing and future <br />watershed conditions for the purposes of computing flood hydrology. Future watershed <br />conditions shall be evaluated when Foreseeable Development is expected. <br />b. Any new study performed by a sponsor to evaluate precipitation information or design <br />storm criteria shall be completed in such a way that it is scientifically defensible and <br />technically reproducible. <br />c. All jurisdictions and communities affected by revised precipitation data, due to their <br />geographic proximity or location within a particular watershed, shall be invited to <br />participate in the update process, and shall be given the opportunity to review, analyze, <br />and comment on the revised information. Objections to the revised information shall be <br /> <br />11 <br />