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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />3.2 Diversion Structure and Intake: Assessment of Feasibility <br /> <br />Description of the Proiect and Statement of Need <br /> <br />The diversion of raw water is done about one-half mile upstream of the WTP on North St. <br />Vrain Creek, Diversion, regulation of inflow to the water treatment plant, presedimentation and <br />sediment sluicing all take place at this site, Refer to Figure 1 for the diversion location, <br />Inspection of the site and the facilities in March of 1995 determined that a major rehabilitation <br />or replacement of these facilities is required, Through time, the channel flow regime has <br />established a pool upstream of the diversion dam. The diversion structure is a rockfill dam with <br />a deteriorating concrete cap, Over time most of the concrete cap has deteriorated and eroded, <br />Water is lost through cracks, During periods of extreme low flow, sheet plastic of other material <br />must be spread to capture water for the intake gate, Additionally, sediment appears to build up <br />adjacent to and down-ditch from the intake gate, requiring periodic maintenance, Large sediments <br />are dropped just after entering this gate, The inlet slide gate is bent, making the diversion flow <br />rate difficult to set. A concrete, rectangular presedimentation channel separates smaller fines from <br />the flow, A side gate is available to sluice this channel and purge accwnulated fines, Raw water <br />next passes through a debris screen to enter the raw water pipeline, This intake system appeared <br />to operate at the time of the field visit, but will operate poorly during adverse conditions, It <br />requires significant improvement to assure reliable operations, The entire facility is subject to <br />periodic flooding, sediment intake and winter icing conditions, <br /> <br />Discussions with the former Public Works Director, Mr. Herb McConnell, have fixed the scope <br />of the rehabilitation of this site, The existing diversion dam is to be demolished and rebuilt as a <br />new structure, The existing presedimentation basin will be cleaned and substantially modified for <br />more efficient operations, All new structures must be designed to maintain sufficiently high <br />velocities to transport stream sediments downstream through the diversion dam, The head works <br />will require a trash rack and the design must exclude bedload sediments from entering the <br />presedimentation basin and grit channel. Another feature of the diversion dam is that it will <br />include a flow measuring device in the stream channel. This device is included at the suggestion <br />of the CWCB, due to discussion at the CWCB meeting of November 8, 1995, The diversion dam <br />is considered non-jurisdictional under the regulations of the Colorado Division of Water <br />Resources, <br /> <br />RED, Inc. conducted a hydrologic analysis of this portion of North St. Vrain Creek in 1991 for <br />the Apple Valley Road Bridge Project. It has been determined that much of the data generated <br />in that project may be of use in flood analysis of the site, Allowances must also be made for: <br /> <br />9 <br />