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WSP10382
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Last modified
1/26/2010 2:58:39 PM
Creation date
10/12/2006 4:17:58 AM
Metadata
Fields
Template:
Water Supply Protection
File Number
8200.760
Description
Yampa River
State
CO
Basin
Yampa/White
Water Division
1
Date
6/27/1984
Author
USGS
Title
Sediment Transport in Lower Yampa River, Northwestern Colorado
Water Supply Pro - Doc Type
Report/Study
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<br />effi ci ency, whi ch is equi va 1 ent to the ratio of mean ve loci ty of water di s- <br />charge through the sampler to the mean velocity of water discharge which would <br />have occurred through the area occupied by the sampler. <br /> <br />Emmett (1980) recommended that the Helley-Smith sampler not be used for <br />measuring bedload-transport rates for sediment of particle sizes that also are <br />transported as suspended sediment. Although a large amount of sand-size <br />material (0.062 to 2.0 mm) was transported in suspension at Deerlodge Park <br />(see table, 8 in the Supplemental Data section at the end of this report), most <br />of this sand was smaller than 0.25 mm and normally passed through the <br />Helley-Smith sample collection bag. A negligible quantity of material less <br />than 0.25 mm in diameter was collected in the Helley-Smith sampler (see table <br />10 in the Supplemental Data section). Therefore, redundant sampling of. <br />material finer than 0.25 mm moving in suspension and as bedload seems to have <br />been avoided at Deerlodge Park. <br /> <br />The Modified Einstein procedure may overestimate some sediment discharges <br />at Deerlodge Park because it is based on the condition of a mobile, continu- <br />ous, bank-to-bank sand bed. During many measurements made in 1982 and 1983, <br />the Yampa River at Deerlodge Park had a continuous, bank-to-bank sand bed. <br />However, for most measurements made at di scharges greater than about 8,000 <br />ft3/s, the river bed near the left bank was scoured to bedrock for 15 to <br />30 percent of the channel perimeter (fig. 4). Field crews observed very low <br />bedload discharges in this section of the river when the channel was scoured <br />to bedrock. The Modified Einstein procedure, which extrapolates transported <br />sediment from the zone of suspended movement to the zone of bedload movement, <br />probably overestimates the total-sediment discharge of the Yampa River at <br />Deerlodge Park for most high discharges because the condition of a mobile, <br />continuous sand bed is unfulfilled at intermediate and high water discharges. <br /> <br />Sediment transport equations derived using sediment discharges estimated <br />with the Modified Einstein procedure (table 4) may be compared with equations <br />in table 3. In general, regression equation exponents are comparable in <br />tables 3 and 4 for most sediment size categories. However, exponents of. the <br />equations for discharge of sediment in the 0.25 to 1.0 mm, and coarser than <br />1.0-mm size ranges are greater in table 4 than in table 3. This implies that <br />Modified Einstein estimates of coarse sand and gravel discharges increase more <br />with water discharge than do comparable sediment discharges based on observed <br />data. <br /> <br />ANNUAL SEDIMENT LOADS <br /> <br />The Yampa River channel is adjusted to long-term streamflow and sediment- <br />load regimes. The prevailing hydrologic and sedimentologic conditions must be <br />determined before the potential effects of water resource development in the <br />watershed can be assessed. The average frequency distribution of discharges <br />has been computed from the records of two long-term streamfl ow-gagi og sta- <br />:lon~. Annual sediment loads were computed by the streamflow-duration, <br />sediment-transport-equation method described by Miller (195l). This method is <br />appl icable \"hen the gaging-station record of streamflows is sufficient to <br /> <br />18 <br />
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