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<br />Table 2.--Particle size statistics for sediment in the <br />Deerlodge Park studg reach <br /> <br />Median grain size <br />(dso in millimeters) <br /> <br />Silt- and clay- size content <br />(percent, by weight, finer <br />than 0.062 millimeter) <br /> <br />Type of Sample Standard Standard <br />sediment size Mean deviation Mean deviation <br />Bed material---- 34 0.61 0.17 0.1 0.1 <br />Bedload--------- 32 .57 .12 .1 .1 <br />Suspended <br />sediment------ 34 60.0 23.7 <br /> <br />in the sand-size range. Virtually all silt- and clay-size material in the <br />Yampa River at Deerlodge Park was transported in suspension. Silt- and clay- <br />size material in bed-material samples averaged less than 1 percent by weight <br />(table 2). <br /> <br />The Yampa River at Deerlodge Park had a mobile bed for the duration of <br />this study; movement of bed material was observed over the entire range of <br />discharges measured in 1982 and 1983. Material comprising the channel bed at <br />Deerlodge Park was in the sand-size range and relatively uniform in size. <br />Bedforms coul d not be observed due to turbi di ty and the depth of water. No <br />coarse-grain lag deposits were detected at the section where discharge. and <br />sediment measurements were made, and it appeared that all sizes of bed- <br />material particles in the channel could be transported by the prevailing flow <br />regime. The Shield's dimensionless shear stress relation (Shields, 1936) may <br />be used to estimate the particle size of bed material at the threshold of <br />movement for a given shear stress; therefore, the competence (maximum particle <br />size transportable) of the Yampa River at Deerlodge Park may be estimated for <br />various discharges. By definition: <br /> <br />d = 5 S (304.8 mm/ft) <br />c (Ys/y - 1) '*c <br /> <br />where: <br /> <br />d = particle size of bed material in mm at threshold <br />.c of movement, <br />o = mean channel depth in ft, <br />S = channel slope, <br /> <br />Ys/ = ratio of specific weights of sediment and water = 2.65, and <br />'i <br /> <br />t* = dimensionless critical shear stress. <br />c <br /> <br /> <br />14 <br /> <br />