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rJAGGART III IIIIIIIIIIIIIIII <br /> ENIGMER,HG A33= 12.:RG <br /> RW WW;Em•venue e3wazo acS'1 •!OG]f+7a•71GG•FUt 011i:aa•iYn 999 <br /> December 18, 1986 <br /> Mr. Bill DeGroot <br /> Chief, Floodplain Management <br /> Urban Drainage and Flood Control District <br /> 2480 West 26th Avenue, Suite 156E <br /> Denver, CO 80211 <br /> RE: Evaluation of Certain Engineering Studies of Scuth Boulder Creak, From Upstream of <br /> Highway 93 to Downstream of South Boulder Road, Phase I <br /> Dear Mr. DeGroot: <br /> We have reviewed the ;:cod Hezere Delineation IF4AO) - Scut)+ 9culder Croak- Greenhorns <br /> and O'Mara (G&O), July 198E for the Urban Drainage ano Flood Control District ?UDFCO), <br /> and Boulder Counr/ !County); and the fl^odolaic Anelvsis of Scu•h RQuIdar Creek At the <br /> Fletirona P•e arty in eeulder Cnuntv, Love & Associates, Inc. (Lovel, 1995. Our evaluation <br /> was to determine which of these two studies was more appropriate to use, with or without <br /> modification, for South Boulder Creek floodplain.management efforts in the reach from <br /> upstream of State Highway 93 to just below South Boulder Road. <br /> For the purposes of cur analysis, the 100•year stern hydrology, originally prepared by the <br /> U.S. Army Corps of Engineers (Corps) and used in the G&O FHAD was assumed. We <br /> obtained a copy of the Corps' mocei and were able to determine a more derailed distribution <br /> of the flow front the tributaries, such as Viere and along the floodpiain. The hydraulic <br /> models used in our analysis were largely basso on current topographic conditions including <br /> the Fiatirons Pit area and levees. <br /> It is important to note that tf+a G&O and Love studies were done for different purposes. The <br /> G&O study was a general floodplain delineation study of South Boulder Creek from the C&S <br /> Railroad upstream into the canyon. The Love study was intended to identify conservative <br /> flood hazards associated with the Flatirons gravel mining property, as a pert of due diligence <br /> invest;gatlons initiated by the University of Colorado (CUI. Most of Love's effort focused <br /> on the shor, reach from the upstream side of the Flatiron's Levee to Highway 36. <br /> The Love study identified a spill from South Boulder Creek that could overflow U.S. 36 into <br /> existing neighborhoods on the west side of the South Boulder Valley. Previous studies <br /> (G&C, R.W. Beck, Corps of Engineers) reflected the potential for this, but did not include any <br /> details on flows, probabilities, areas of flooding, and the potential hazards. <br /> BACKGROUND <br /> Prior studies don't adequately explain the hazards of the changing alluvial floodpiain. South <br /> Boulder Creek historically created an alluvial fan .forming a wide valley bottom over a mile <br /> Mvamwpr • • fw".MeAl TV.SCtlR <br /> C.v.. RQQC :;MM.. Wma' evl Wr.w$W9y WC Pam& <br /> F.r., ,vY M4�t•e^ • 1.,1.14C SwvCN <br /> WMI <br /> EXHIBIT NO.15 <br />