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CHAPTER 2 CWCS PRINCIPLES SECTION 2 CWCS PROPOSED OPERATING PRINCIPLES COLORADO FLOODPLAIN AND STORMWATER CRITERIA MANUAL 2.5 DESIGNATED FLOODWAYS The floodway represents the community's regulatory limit of encroachment into the 1 OO-year floodplain for those watercourses with the established floodway boundaries. The floodway is defined by Federal Emergency Management Agency (FEMA) 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 foot rise in the water surface above the base flood elevations (BFE). Encroachment into the designated floodway is prohibited unless it can be demonstrated using appropriate detailed engineering analyses that the proposed encroachment will not cause any rise in the 100-year water surface elevation. However, some local jurisdictions in Colorado have determined that the FEMA's 1- foot rise floodway criteria is inadequate to protect the existing and future developments within their communities, and have adopted a stricter floodway delineation criteria (i.e. UDFCD's 0.5-foot rise criteria) in addition to the FEMA criteria. PROPOSED OPERATING PRINCIPLE THE CWCB RECOGNIZES THAT DESIGNATED FLOODWAYS ARE ADMINISTRATIVE LIMITS AND TOOLS USED BY COMMUNITIES TO REGULATE EXISTING AND FUTURE FLOODPLAIN DEVELOPMENTS WITHIN THEIR JURISDICTIONS. THEREFORE, COMMUNITIES MAY CHOOSE TO DELINEATE FLOODWAYS BASED ON FEMA'S 1-FOOT RISE CRITERIA OR BASED ON MORE STRICT CRITERIA BY ALLOWING A LESSER AMOUNT OF RISE ABOVE THE BASE FLOOD ELEVATIONS. THE CWCB FLOODWAY PROPOSED OPERATING PRINCIPLE IS SYNONYMOUS WITH COMMUNITIES' ADOPTED FLOODWAY CRITERIA. WHERE NO LOCAL FLOODWAY CRITERIA EXIST, THE CWCB RECOMMENDS THE USE OF THE MINIMUM FEMA STANDARD. 2.6 HYDRAULIC STRUCTURES A drainage system may be comprised of natural open channel sections, man made channels, culverts and bridges, levees, dams and reservoirs, detention basins, drop structures, and other related facilities. Hydraulic structures are defined as the drainage facilities that are designed to convey storm or floodwater to a downstream receiving water body. The recommended design and technical standards for some of the most commonly encountered hydraulic structures are provided in the Statewide Manual, The information presented in the Statewide Manual should be considered to be the minimum hydraulic design standards. Additional analyses may be necessary for unique or unusual site conditions, Establishment of the minimum engineering standards will help to produce consistency in the design of the hydraulic structures and provide integrated drainage systems that act together to protect the public health, safety, comfort, convenience, welfare, property and commerce. The minimum design standards for the following hydraulic structures are presented in the Statewide Manual: . CWCB PROPOSED OPERATING PRINCIPLES MARCH 2004 - Draft CH2-204