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. COLORADO STATEWIDE DRAINAGE AND FLOODPLAIN MANAGEMENT CRITERIA MANUAL . CHAPTER 4 FLOODPLAIN ADMINISTRATION AND .ELlNEATION SECTION 2.0 FLOODPLAIN DELINEATION 2.6.4 FLOODWAY DELINEATION The floodway is defined as the channel, plus any adjacent floodplain areas, that must be kept free of encroachment so that the 100-year discharge can be conveyed with no more than one (1) foot rise in the water surface above the base flood elevations (BFE). However, communities may choose to adopt stricter f100dway delineation criteria by allowing only 0.5 foot rise or no rise above BFE. The f100dway represents the community's regulatory limit of encroachment into the 100-year floodplain for those watercourses with the established f100dway boundaries. The project engineer should coordinate with the effected local agencies and CWCB to determine whether a f100dway should be delineated for the drainage-way being studied or not. Floodway limits should be determined based on the "equal conveyance reduction" method. This method reduces an equal amount of flow conveyance from both overbanks allowing potential development areas on both sides of the waterway. The f100dway delineation should be clearly shown on the floodplain delineation map in addition to the floodplain boundaries. 2.7 LIMITED FLOODPLAIN DELINEATION METHOD Communities may choose to adopt stricter f100dway delineation criteria by allowing only 0.5 foot rise or no rise above BFE as opposed to the one (1) foot rise. Floodway limits should be determined based on the "equal conveyance reduction" method. The limited method results in the delineation of approximate 100-year floodplain boundaries without base flood elevations (BFEs). This approach is usually used to delineate approximate 100-year floodplain boundaries for drainageways in the vicinity of future developments to inform the communities about the potential flood hazards. If new developments are proposed to encroach into or located adjacent to a previously delineated approximate 100-year floodplain, the previously delineated approximate floodplain limits should be restudied by using the detailed approach before the developments can occur. The hydrologic and hydraulic analysis should include, at a minimum, determination of 100-year event discharge and floodplain limits. 2.7.1 HYDROLOGIC ANALYSIS The hydrologic analysis should be based on the analysis methods and guidelines previously provided in Section 2.6.1, Chapter 4. 2.7.2 TOPOGRAPHIC INFORMATION The best available topographic base map shall be used, to develop approximate floodplain information. Such work map shall, at a minimum, be the most recent edition of a 7.5 minute quadrangle as published by the U.S. AUGUST 2002 FLOODPLAIN DELINEATION CH4-212