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<br /> <br />CHAPTER 2 <br />C\\'CB PRINCIPLES <br /> <br />SECTION 2 <br />CWCS OPERATING <br />PRINCIPLES <br /> <br />COLORADO <br />FLOODPLAIN AND STORMWATER CRITERIA MANUAL <br /> <br />irrigation facilities are not designed and constructed to safely convey storm runoff <br />flows. they should not be used as outfall points for urbanized area storm drainage <br />systems. unless It can be proven safe through appropriate detailed engineering <br />analysis and the facility owner's consent can be secured. Since the owner's liability <br />from ditch failure increases with the acceptance of storm runoff, the responsibility <br />should be clearly defined before a combined system is approved. <br /> <br />OPERATING PRINCIPLE <br /> <br />THE CWCB RECOMMENDS THAT IRRIGATION FACILITIES (I.E DITCHES AND <br />CANALS) NOT BE USED AS STORM WATER OR FLOOD CONVEYANCE <br />FACILITIES. UNLESS SPECIFICALLY APPROVED AND DESIGNATED BY <br />LOCAL GOVERNING JURISDICTIONS AND ACKNOWLEDGED BY THE <br />IRRIGATION FACILITY OWNERS. THE FLOOD CONVEYANCE CAPACITY OF <br />IRRIGATION FACILITIES SHOULD BE ACKNOWLEDGED ONLY BY <br />AGREEMENT BETWEEN THE FACILITY OWNERS AND LOCAL GOVERNING <br />JURISDICTIONS. THE CWCB MAY DESIGNATE AND APPROVE 100-YEAR <br />FLOODPLAIN INFORMATION FOR IRRIGATION FACILITIES IF THE ABOVE <br />RECOMMENDATIONS ARE MET. <br /> <br />2.10 STORMWATER RUNOFF DETENTION <br /> <br />Detention basins have been commonly used to mitigate increase in peak flows due <br />to new developments. Detention is also considered a viable method to reduce urban <br />drainage costs. Temporarily detaining storm runoff can reduce downstream flood <br />hazards as well as reduce pipe and channel sizes in urban areas. Storage also <br />provides for sediment and debris collection, which helps to maintain water quality in <br />downstream channels and streams. However, detention may not be necessary <br />where downstream drainage <br />facilities In their original or <br />previously improved condition are <br />adequate in capacity to carry <br />flows from fully developed <br />upstream areas without negatively <br />impacting downstream properties. <br /> <br />OPERATING PRINCIPLE <br /> <br /> <br />THE CWCB RECOMMENDS <br />THAT LOCAL GOVERNMENT <br />ENTITIES REQUIRE ADEQUATE <br />DETENTION FACllITES BE <br />APPROPRIATELY DESIGNED <br />AND CONSTRUCTED BY DEVELOPMENT PROPONENTS TO MITIGATE THE <br />INCREASE IN FLOWS CAUSED BY URBANIZATION AND INCREASED <br />IMPERVIOUS SURFACES. THE FLOOD ATTENUATION BENEFITS OF <br />PUBlICALLY OWNED, OPERATED, AND MAINTAINED DETENTION FACILITIES <br />OR PUBlICALL Y CONTROLLED PRIVATELY OWNED DETENTION FACILITIES <br />SHOULD BE FULLY RECOGNIZED FOR THE PURPOSE OF DETERMINING <br />FLOOD HAZARD AREAS DOWNSTREAM OF THE DETENTION FACILITIES. <br />THE ATTENUATION BENEFITS OF PRIVATELY OWNED DETENTION <br />FACILITIES THAT ARE NOT CONTROLLED BY PUBLIC AGENCIES SHOULD <br />NOT BE CONSIDERED IN FLOODPLAIN ANALYSES. <br /> <br />CWCB OPERATING <br />PRINCIPLES <br /> <br />APRIL 2004 <br /> <br />CH2-209 <br />