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<br />\..... <br />~ <br /> <br />-~ <br /> <br />" <br /> <br />iJ;CJG lo..:J <br /> <br />. <br /> <br />. <br /> <br />. <br />MEMORl\NDUM <br /> <br />COLORADO WATER CONSERVATION BOARD <br /> <br />! \\ ,1[i,I:11 '\1( [)O:ldld <br />i)'lv( 1<11 <br /> <br />TO: <br /> <br />Dave Walker, Deputy Director <br /> <br />FROM: <br /> <br />Larry F. Lang <br /> <br />DATE: <br /> <br />October 3, 1985 <br /> <br />SUBJECT: <br /> <br />Review of the Preliminary Design Report for the Mineral <br />~venue Extension Project <br /> <br />Pursuant to your request, I have reviewed the subject <br />report. Since, the flood control section has not been directly <br />involved in the downstream project, it is difficult to determine <br />if the proposed roadway right-of-way and embankment has an impact <br />on downstream e~re~~ project features. However, it appears that <br />the roadway design parameters may be compatible with the South <br />Platte Channel Project with some modifications. I provide you <br />with the following comments: <br /> <br />Hydrology <br /> <br />The consultant used a lOa-year discharge valve of 5200 cfs <br />for his analysis. We have established a 100-year discharge at <br />the Chatfield Dam Outlet of 5000 cfs and 8500 cfs upstream of the <br />confluence or Dutch Creek on the South Platte River. There are <br />six identified drainage basins which contributed to the South <br />Platte River downstream of Chatfield Dam and upstream of Dutch <br />Creek. The consultant is using a lOa-year design discharge of <br />5200 cfs for the bridge. I would predict a more reasonable value <br />of 7000-7500 cfs at the bridge because three contributing <br />drainage basins entrance the South Platte River upstream of the <br />bridge. <br /> <br />Hydraulics <br /> <br />The consultant used the HEC-2 hydraulic routing procedure <br />for his analysis. This procedure and his assumptions are <br />compatible to CWCB standards and criteria. <br /> <br />732 <br />rev/pre <br />