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<br />I <br />l <br />, <br /> <br />- 3 - <br /> <br />. <br /> <br />It is recommended that the flow rates, for the purpose of floodplain delineations, be calculated in <br />accordance with the hydrology criteria presented in the statewide manual or by using other technically <br />acceptable methods as approved by the CWCB and/or FEMA. <br /> <br />Proposed Instructions <br />The Technical Advisory Committee met on January 14,2004 to review 3 new draft Instruction <br />statements developed by the CWCB staff and the consultant. Revisions were made to the draft <br />instructions based on input from CWCB staff and the Committee, and staff is presenting the 3 new <br />Instructions at this time for Board consideration. Additional Instruction statements will be brought to <br />the Board at future meetings as they are completed and endorsed by the Committee. <br /> <br />Instruction #7: Stormwater Runoff Detention <br />The CWCB recommends that local government entities require adequate detention facilities be <br />appropriately designed and constructed by development proponents to mitigate the increase in flows <br />caused by urbanization or development activities. The flood attenuation benefits of ~blicly owned (or <br />publicly controlled), operated, and maintained detention facilities should be fully recognized foiThe <br />purpose of determining flood hazard areas downstream of the detention facilities. Detention facilities <br />that are not owned and maintained by public agencies should not be considered in floo<jplain analyses. <br />This instruction shall be in compliance with C.R.S. 30-28-133(4)(b). <br /> <br />Rationale: This Instruction is intended to reduce the impact of increased stormwater runoff from <br />urbanized areas, and will not affect the existing administration of Colorado water rights. <br /> <br />. <br /> <br />Implementation: Construction of detention facilities within or downstream of urbanized areas could <br />reduce peak flow rates within the natural receiving channels. This action would reduce the flood threat <br />to downstream properties in and along the floodplain that would otherwise result from developed <br />impervious surfaces in the watershed. <br /> <br />Instruction #8: Flood Convevance within Irrirzation Ditches/Channels <br />The CWCB recommends that irrigation facilities (i.e. ditches and canals) not be used as stormwater or <br />flood conveyance facilities, unless specifically approved and designated by local governing <br />jurisdictions and acknowledged by the irrigation facility owners. The flood conveyance capacity of <br />irrigation facilities should be acknowledged only by agreement between ditch companies and local <br />govemingjurisdictions. The CWCB may designate and approve I DO-year floodplain information for <br />irrigation facilities if the above recommendations are met. <br /> <br />Rationale: The use of irrigation facilities for conveying storm and floodwater runoff is of significant <br />concern to the CWCB, water providers, and floodplain managers. This Instruction is intended to <br />clarify the role of irrigation facilities for use in floodplain management operations. <br /> <br />Implementation: It is our understanding that existing case law has provided water resource interests <br />with definitions and guidance related to this issue. This Instruction is not intended to supersede <br />existing laws and statutes that relate to floodwaters within irrigation facilities. <br /> <br />. <br /> <br />Instruction #9: Floodolain Develooment Practices <br />Areas that are subject to flooding from a I DO-year storm event should be regulated by communities <br />through appropriate floodplain management practices. The policy ofthe CWCB is to recommend that <br />communities adopt and enforce the floodplain management criteria presented in the statewide manual. <br />Flood Protection. Water Project Planning and Finance. Stream and Lake Protection 3 <br />Water Supply Protection. Conservation Planning <br />