Design Engineering Report: Avon Exhibit 1

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[.3esigr7 £•.nhirreerrrrg Ker?oi7, C'use No.2005-C'61'-256' Trnva qf,?norr's Recreationa/ In-f'hunne( DNer.cion ('RIC"D) ti a[er Ri,?,?6ft in the Eagle River water surface elevations (WSEL) would remain at or below established BFE following construction of the RICD. Table 2 Station Description BFE (ft) WSEL (ft) 337 220 feet upstream of project area 7424.84 7424.49 336.506 Cross-Section at Baby Bob 7423.02 7422.88 336.107 Cross-Section at Bob 7unior 7421.54 7421.49 336 Upstream of Bob Bridge 7421.14 7421.14 335.5 77 Bob Bridge N/A NIA 335.2 Downstream of Bob Bridge 7417.44 7417.44 335.117 Cross-Section at Bob Senior 7417.36 7417.10 335 17 feet downstream of Bob Senior 7417.25 7417.25 334 416 feet downstream of project area 7412.87 7412.$7 Notes: 1. Base Flood Elevation established in 2003 FIR 2. Water Surface Elevations with Avon RICD 3. Cross-section from existing HEC-RAS Model 4. Cross-section added to evaluate Avon RICD VIII. Environmental Effects The reach is managed by DOW for cold water fisheries and the predominant species, Brown Trout. The substrate is armored cobble boulder bed or exposed bedrock and there is no significant spawning habitat within the reach. Preventing tubifex worm habitat in silt deposits and maintaining overhanging cover to keep temperatures cool were the most important potential project affected habitat factors identified by the DOW managers in a site visit October 13, 2005 (Andre et al., 2005). Scour and deposition of sand may occur due to changes in secondary currents and increases in eddy sizes; however, eddy velocities are expected to be sustained greater than 1 feet per second and prevent depositions of silt materials. High velocity currents with no evident silt deposits characterize the existing reach. The project increases eddy vorticity and current concentrations, further reducing the potential for siltation and reducing the potential for creating tubifex habitat. Construction of the boat ramp would remove a large serviceberry shrub growing in the bank that provides approximately 21 bank feet of overhanging cover. No long-term impacts from the project are expected. The project may have temporary construction impacts with track equipment driving on and excavating the bed material in the wet channel. Construction activity may have isolated increases in turbidity. Best management practices (as described in Plate C-8 attached) such as turbidity curtains, silt fences, construction sequencing and care of water shall be utilized to minimize potential turbid conditions and locations. 5 of 11 ; I V E R .,Ili]f.' 2006 ,? ?... . .. ?toof,? FO Bo.: 2 L; Gicm+flod iprinr;: ( clnraclo 9 1!>p? 0"10) cia? -IibR