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FLOOD02750
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FLOOD02750
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Last modified
8/15/2009 11:49:02 PM
Creation date
10/4/2006 11:06:50 PM
Metadata
Fields
Template:
Watershed Protection
Document ID
125
County
Routt
Stream Name
Elk River
Basin
Yampa/White
Water Division
6
Title
Streambank Stabilization Limited Watershed
Date
11/1/1999
Prepared For
CWCB
Prepared By
ICON Engineering, Inc.
Watershed Pro - Doc Type
Educational/Technical/Reference Information
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<br /> <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 />During the field reconnaissance, several other possible breakout areas were identified <br />downstream of the diversion to the West Fork. The most pronounced was a cut in the bank that <br />appeared to have been created by a bulldozer. The remaining locations were low areas along <br />the west bank over a distance of about 2500 feet (between Sections 6 and 8), Typically these <br />breakout areas would have elevations slightly above the water surface that was observed on <br />September I, 1999. As observed from the aerial photo, flows that breakout do not return to the <br />channel below Section 7, Instead, the water continues to flow in a southwesterly direction <br />either through low areas in the adjacent meadow or along the West Fork until it collects near <br />the intersection of Highway 40 and County Road 44, <br /> <br />For this study it was necessary to develop a relationship between the amount of flow that leaves <br />the Elk River along the west bank and the flow that remains within the Elk River channel. A <br />series of rating curves were developed for flow breakout at Section 8, The first rating curve <br />was developed to represent flow at the diversion structure for the West Fork. This rating curve <br />was based on a combination of inlet control of the four 24-inch corrugated metal pipes and weir <br />flow, <br /> <br />A second rating curve was developed to represent a trapezoidal section at the bulldozed area <br />immediately downstream of the diversion structure, Since minimal survey information was <br />available in this area, a cross-section consisting of a I2-foot bottom width, 2: I sideslopes, and <br />channel slope of 0,5% was assumed, During the September I. 1999, field visit, the minimum <br />elevation of this overflow section was observed to be around 6 inches above the water surface <br />elevation in the channel. Stream flow records for September I, 1999, indicated a discharge of <br />120 cfs, The hydraulic model was run using 120 cfs to estimate the water surface elevation at <br />Section 8 the day of the field visit. The resulting water surface elevation was used to set the <br />elevation of the trapezoidal overflow area (6548.36 feet), This bulldozed section may not have <br />been as well-defined of a breakpoint in 1997 as it is currently, However, given the nature and <br />extent of the spill potential along the west bank and the minimal survey and topographic <br />information available, the assumptions described above appeared to be reasonable for the <br />estimation of overflows to the West Fork for the purposes of this study, <br /> <br />The two rating curves described above were added together to produce a composite rating <br />curve for total breakout flow near Section 8, As previously mentioned, a pool exists in order to <br />maintain flows to the West Fork during periods of low flow in the Elk River. To account for <br />this condition, it was assumed that the pipes would be submerged before water began to flow <br />through the bulldozer section and the water would be 1.6 feet higher at the head gates than at <br />the bulldozer section, Figure 3,2 displays the composite rating curve sections, This composite <br />rating curve was used to separate the Elk River flow and the flow to the West Fork, A <br />distribution of flows between the Elk River and the West Fork are given in Table 3,1. <br />Supporting calculations are provided in Appendix F, <br /> <br />15 <br />
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