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<br />. <br /> <br /> <br />. <br /> <br />CHAPTER 4 <br />FLOODPLAIN <br />ADMINISTRATION <br />AND <br />DELINEATION <br /> <br />.ECTION 1.0 <br />LOODPLAIN <br />MANAGEMENT <br /> <br />COLORADO STATEWIDE <br />DRAINAGE AND FLOODPLAIN MANAGEMENT CRITERIA MANUAL <br /> <br />discussions on the hydrologic analysis procedures and <br />methods. <br /> <br />2. <br /> <br />Hydraulic analyses should be performed to determine the <br />100-year floodplain information for both the existing and <br />proposed project drainageway conditions. Detailed <br />discussions on the floodplain delineation procedures are <br />provided in Chapter 4, Section 2.0. <br /> <br />3. <br /> <br />The study must demonstrate that no new structures are <br />added to the floodplain within and adjacent to the project as a <br />result of the proposed floodplain modification. <br /> <br />The study must demonstrate how other properties that share <br />frontage along the floodplain will not be adversely impacted. <br />If other properties are impacted, the submittal must include <br />proof that the impact can be mitigated or appropriate <br />floodplain agreements can be obtained in the form of a letter <br />from the impacted property owners. At the discretion of the <br />Floodplain Administrator, a floodway delineation may be <br />required. <br /> <br />4. <br /> <br />5. <br /> <br />The analysis must demonstrate that the existing and/or <br />proposed channel alignment (horizontal and vertical) will be <br />stable and will not be subject to erosion, which may threaten <br />property or public improvements. <br /> <br />6. The analysis must show that sufficient flow conveyance <br />capacity will be maintained in the drainageway. <br /> <br />7. For subdivisions, the modified floodplain should not encroach <br />onto the residential lots. <br /> <br />1.14.2 FLOODPLAIN MODIFICATION STUDY OUTLINE <br /> <br />A floodplain Modification Study must address the following points <br />through actual analyses or through reference to adopted drainage <br />master plans: <br /> <br />1. A description of the project site. <br /> <br />2. A description of the drainage basins and waterways impacting <br />the site <br /> <br />3. <br /> <br />Identification of existing drainage master plans and/or Flood <br />Insurance Studies (FIS) with the analysis of the applicability <br />of the existing data to the proposed project site. <br /> <br />4. <br /> <br />Hydrologic analysis. This section should include a narrative <br />of the analysis methods, the source of flow rates used for the <br />existing and. proposed project conditions floodplain <br />delineations, and the proposed flow conveyance system. <br />Watershed maps should be provided for both conditions. <br /> <br />FLOODPLAIN CH4-112 <br />MANAGEMENT <br /> <br />AUGUST 2002 <br />