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<br />el <br /> <br />this Manual recommends that the minimum streamflow needed for a reasonable <br />recreation experience falls within a specific flow range as identified below. The CWCB <br />recognizes that there may be other recreational experiences where a different <br />minimum stream flow may be appropriate. <br /> <br />2, Adverse Flood Impacts and Durability <br />The CWCB will carefully consider flood safety in reviewing an RICD application.. The <br />CWCB recommends that an Applicant for an RICD demonstrate, through appropriate <br />technical analyses, that the proposed boating course is designed and will be (is) <br />constructed in such a manner as to: <br />. Adequately pass all flows up to and including the lOO-year (1% probablity) flood <br />flow without causing adverse impacts to upstream, downstream or adjacent <br />property owners. Verification of. "no adverse impact" can be demonstrated <br />through the use of a eWeB approved step-backwater hydraulics model such as <br />HEC-RAS. I <br />. Adequately withstand stream forces for all flows up to and including the lOO-year <br />flood so that damage and failure of the boating course is avoided, unless the <br />Applicant demonstrates that the boating course is designed to fail in such a way <br />that it will not present a safety issue and is preferable and beneficial for flood <br />flows.2 <br /> <br />e) <br /> <br />1 "No adverse impacts" is defined as flood-related impacts addressed in the current federal regulations <br />and state floodplain management rules. As required by current federal regulations and state floodplain <br />management rules (not new guidance developed for the purposes of this document). the Applicant is <br />advised that the proposed boating facility must be analyzed for flood impacts by modeling the "existing <br />conditions" (pre-facility) scenario and the "proposed conditions" (with-facility) scenario. The hydraulic <br />computer modeling must be performed by a registered Professional Engineer (Colorado Registration) <br />having expertise in surface water hydraulic madeling. Impacts that should be analyzed include increases in <br />water surface elevations for the range of flows experienced at the proposed recreational facility. but <br />especially the lOO-yeor flood event. According to federal regulations, water surface elevations at the <br />proposed RICD facility may not increase at all (zero rise) in the event that the proposed recreational <br />facility is within a stream reach having a designated Floodway (the most hazardous portion within the <br />lOa-year floodplain). For reaches that are not within a designated Floodway. any increases in the 100- <br />year flood profile for the proposed RICD facility (up to a maximum of one foot or a lesser amount <br />specified by local floodplain ordinances or codes, whichever is more restrictive) must be documented. <br />Proper notification of adverse impacts (increased water surface elevations) must be provided to affected <br />property owners and a Letter of Map Revision (LOMR) should be obtained as required by FEMA for <br />National Flood Insurance Program purposes. <br /> <br />2It is recommended that the boating course consist of appropriate materials and installation to endure <br />velocities, shear stresses, other erosive conditions. sedimentation. and debris that would be experienced <br />during the range of expected flows and high flow (flood) conditions. For example. a boulder drop <br />structure should be constructed with material having suitable size. hardness. shape and gradation and <br />should be installed in such a manner that it is anchored into the stream bank and streambed to survive <br />lang-term operation and flood events. Proper durability of the facility will assist the Applicant in avoiding <br />2 <br />