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. River?????ration.or`. LLC, <br />Pt ) Bic.-? 008 1. GrilllCi JlE:1L.t10+?, l. C`!i.)r:4d1) 3 ? iu'. \=!-??JS' <br />February 1, 2006 <br />Greg Schroeder <br />Eagle County Floodplain Manager <br />PO Box 500 <br />500 Broadway <br />? .,?. <br />Eagle Colorado, 81631 <br />Lk,970-328-3560 ' .__., f <br />RE: Bob Bridge Proposed recreation enhancements: Floodplain Compliance <br />Crreg, <br />Proposed recreation enhancements at Bob the Bridge include in-channel modifications to <br />improve hydraulics for recreational whitewater experiences. This letter is to discuss how <br />the proposed modifications comply with Eagle County and FederaI floodplain <br />development guidelines. The proposed project will not increase Base Flood Elevations <br />on the Eagle River and will not have any impact on100-year flooding nor floodplain. <br />A Floodpla.in Information Report (FIR), prepared by Matrix Design Group for Eagls <br />County and the Colorado Water Conservation Board, is the cunent floodway information <br />used herein for the Eagle River (August 22, 2003). The FIR presems Base Flood <br />Elevations (BFE) through the project site based on use of the HEC-RA.S floodway model <br />developed by the U.S. Army Corps of Engineers. <br />As applied to the Eagle River, the HEGRAS model used in the 2003 FIR regresents six <br />channel cross-sections over the project reach to describe channel geometry. To evaluate <br />potential effects of the Avon recreation enhancemern structures on flood profiles for the _ <br />Eagle River, three additional control cross-sections were added to the existing HEC-RAS <br />model based on field surveys conducted in 2005 and the proposed design. These <br />additional cross-sections represent the physical changes to the channel geometry that will <br />result from construction of the stnxctures. The HEC-RAS model was then run with the <br />additional cross-sectioas ("Eagle_River Bob Design") and results were compared to the <br />original model results ("Eagle_Rivec"). The HEC-RAS model results (Tabte 1) indicate <br />water surface elevations (WSEL) will remain at or below established BFE following <br />construction oFthe proposed modifications.