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<br />ODJ826 <br /> <br />--oi'1-ici~.;..-t-'il.E-CoPV <br />RECE;~EO OOR l'I.CAO. <br />NOP.'rH::?~ D!VY-SION <br /> <br />-n: <br /> <br />TETRA TECH, INC. <br /> <br />INFIlAST1lUCTURE SoUTHWEST GROUP <br /> <br />410 S. French Street. P.O. Box 1659, 8redenridge, CO 80424 <br />.(970)453-6394. FAX (970) 453-4579 <br /> <br />Cl'IN. <br />ru>'l <br /> <br /> <br />August 20, 2003 <br /> <br />I . . <br />::::::::::!__.L~ <br /> <br />David Fox <br />Colorado Stale Parks <br />361 32 Road; POB 700 <br />Clifton. CO 81520 <br /> <br />Re: Reply to: Comments Regarding the Floodplain Habitat Restoration <br />Project at the Ela Wildlife Sanctuary; leller from David Fox, July 7,2003 <br /> <br />Dear Mr. Fox.,. <br /> <br />This is a reply to comments made by Colorado Sbte Parks in regard to "Request for <br />Input about Floodplain Habitat Restoration at the EIa Wildlife Sanctuary - Grand <br />. Valley Audubon Society Property" and the "Flood Inundation Srody Final Repon" <br />prepared by Tetra Tech,. Inc, <br /> <br />The river chanDel adjacent to the Ela Wildlife Sanctuary has a dynamic bed and channel <br />form (Le,. not fixed), Therefore, estimates of discharges herein required for <br />connection and flow-through may vary depending on the varying dimensions of the <br />adjacent river channel, which are a function of localized scour and deposition. <br />However, this variability does not impact the accuracy of design, The design of the <br />notch is based entirely on the physical conditions of the outlet, which will not be <br />modified in the proposed design, The outlet is not proposed to be modified because it <br />is considered stable with a very dense and wide corridor of established riparian <br />vegetation. The inven of the proposed notch is set such that the outlet is submerged <br />when the inlet begins flowing based on average hydraulic gradients. The variability in <br />discharge estimates only results in a wider range of predictions for frequency of <br />connection; however, that frequency is regulated by the physical conditions of the <br />oullet, If the ouDet was proposed to be modified, additional sediment transpon analyses <br />would be required. .. . <br /> <br />The natural interaction of the river and the Ela Wildlife Sancroary (EWS) currenlly <br />starts at approximately 11 ,000 cfs when a backwater condition begins to submerge this <br />area near the boat ramp with very low velocities and probably only depositing silts. As <br />flows rise to approximately 35,000 cfs the existing degraded levee upstream of the boat <br />launch is ovenopped and essentially the main channel splits and flows through the <br /> <br />~. <br />