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<br />SECTIOl'i 1.0
<br />I[\;TRQDUCTION
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<br />Authori,ation
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<br />This study W3$ authorized by the Urban Drainage amI Flood Control District (UD&fCD) and the
<br />Colorado Water Cons.<:1"\'ation Board (C\.VCB) under UD&FCD Agreement No. 96+10.)3. ICON
<br />Engineering Inc., (ICON) was retained to complete th", scope of work ,ummari/.cd in Subsectilln 1.2.
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<br />'.2
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<br />Purpose and Scope
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<br />The objective of this report is to prepare an updated hydraulic model of the U.S. Army Corps of
<br />Engineers (COE) flood control channel project on the South Plaue River from Hampden Avenue
<br />upstream to the old Brown Ditch diversion al Coal Mine Road (extended).
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<br />The hydrologic analysis for th", South Platte River had previol.lsly been developed by the COE for
<br />Ihe flood control channe1 projecl. Therefore. it is not induded in this report.
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<br />Water surface profiles were computed for the South Platte River using th", U.S. AmlY Corps of
<br />Engin",ers' HEC-2 Water Surface profiles program (ver~i,m 4.6.2). ChiUlnel cross-section data was
<br />taken frum topographic mapping developed for th", projL'<:1. This data was providC'd in AutoCAD
<br />RI3 fonnat as digital. three-dimensional mapping at l.foot cllntours. In addition, field surwy data
<br />w~s taken at each er"ss-se<:tion to detennine the channel profile bt:neath the water surface.
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<br />The study area consistsofa 5.5 mile reach of the South Platte River, between Hampden Avenue and
<br />the old Brown Ditch diversion at Coal ;...tine Road (extended) in Ampalwe Count}..
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<br />1.3
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<br />Mapping
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<br />Mapping was provided b}' the eWCB through UD&FCD. Mapping eonsistC'd of I-inch to 50 fect, 1-
<br />foot contour interval mapping of the study limits. This mapping was prodllced by Transvisioll of
<br />Santa Clara, California, onder a separate agreement '-'ltt! the LW(;t:l. The mapping was compiied
<br />using aerial photogramdric methods from aerial photography flown by Huntley Aerial Surveys, Inc.,
<br />of Monl.lment, Colorado, in May 1'197. Control for the mapping was provided b~' Accorate
<br />Consultants, Inc.. of Broomfield, Colorado.
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<br />1.4 Background Information
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<br />Historically. major !1rX'ds have occum'd along the South Platte River in 1911,1933, 1942.1949,
<br />!957, :i.'l<J 19~5. Th.: !1'0~' ~.'nt m'jor 0"",\ in 1%5, x!'ll.lrred the creation ofChat{ic!d Dam and
<br />Re,ervoir aX a llood control facility_ Chatfield Reservoir dTedi,d)' ",,,ntrols major fllllJod flows in
<br />the dllwnstream rcaches of the SOl.lth Platte River. Th<' m~ximLIIT1 release di"charge from Chatfield
<br />Rescrvoiris 5.000efs. The channcl eapacit)' along mosl of the sllldy reach prior 10 the construction
<br />ofChattield Reservoir ranged from 2.000 to 6,000 cfs. FI<,,>ding wOLlld occur in areas having
<br />inadequate capadty for the design release rate. Therefore. an improved chanoel was proposed,
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<br />2.1
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<br />d"signcd.andhuiltbytheCOEtohdpcontrol!1oodingforlargerslOm1 events.
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<br />The channel improvements consisted of wid~niag, straightening. and low",ring some 4. -l miles of the
<br />South Platte River. The proposed channel was designed and modded as a prismatic. trapez(li<.lal
<br />channel with a d~sign capacity varying from 5.400 cfs just do",nstrcam of Coal Mine Road
<br />(Extended) 10 15,000 cfs downstream of West Oxford Avenue. TI1<: constrLlcted dHlnrlcl ha~ 2H : 1 V
<br />sidcslopes. and a bottom width of 100 feet from Coal ~1ine Road (Extended) downstream to the
<br />confluence with Dutch Creek. The bottom width widen~ to 130 feet from the confluence witb Dutch
<br />Creek downstream 10 Oxford Avenue (Reference I). Downstream of Oxford AvenLl~ to the
<br />conflLlenee with Bcar Creek only the east bank was stabilized. Thnll.lghout the channeled reach. both
<br />side slopes were protected with graded riprap which e.,tended up to the 5,000 cfs water surlilee
<br />elevation.
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<br />The channel improvements were con>truetcd over the period beginning April 11, 1984, and ending
<br />Apri125, 1988 (Reference I).
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<br />Acknowledgments
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<br />This report was prepared by ICON under contract with the UD&FCD. 1COl\ wishes to acknowledge
<br />the various individLlals who assisted in the preparation of the study. These individual~ were
<br />routinely coordinalecl with dLlring the planning process. The following people participated by
<br />providing technical guidance and information during the course of the ~tudy:
<br />
<br />Name
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<br />Represcntin,;:
<br />
<br />Bf)'anKohlenberg
<br />BcnUrbon<l>
<br />Ken MacKenzie
<br />Tom Browning
<br />
<br />UD&FCD
<br />UD&FCD
<br />liD&FCD
<br />CWCR
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<br />The following members of the project team contributed to the preparation of this report:
<br />
<br />[)nugWmiams
<br />Curtr.;eufeld
<br />Craig Jaeobson
<br />Calvin Heinly
<br />
<br />Project Manager
<br />Project Engineer
<br />Project Engineer
<br />ProjectSurvevor
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<br />SECTION 2.0
<br />HYDRAULIC ANAL YSlS
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<br />Methodology
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<br />\'\','al<:r surlace protile> were computed for the South Platte River using the U.S. Corp, of Engineers'
<br />HEC-2 Water Surface Profiles Program (version 4.6.1}. Water surface profiles were computed for
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