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Some minor problems arose while collecting bed-material-size data. Large boulders and embedded particles had to be measured in place. Only two of the three particle diameters could be measured when the particle was embedded in the stream bottom. An interesting problem existed at the Cache La Poudre River at Fort Collins. Here, large strips of fine sandy material were bordered by bedrock and large particles. The Wolman method was used as described at the beginning of this section. When the large strips of fines were observed, bulk samples were collected. These bulk samples were combined, and 8 single, composite sieve analysis was made. The sieve and Wolman pebble- count data were then combined into a single overall size-frequency distribution. This was accomplished by: (1) Computing separate frequency distributions for the sieve data and the pebble-count data; and (2) combining the two distributions into one by weighting each size class percentage by the proportion of bed surface area occupied by the large stones or the fine sand. The method is described in detail by Williams and Guy (1973, p. 44-45) and by Benson and Dalrymple (1967, p. 19-20). At the Cache La Poudre River station 11 percent of the surface area was bedrock. The vertical height of the smooth, rounded bedrock was measured, a~d the particle size-frequency distri- bution was completed using the bedrock vertical height as an intermediate diameter (Benson and Dalrymple, 1967, p. 20). If the bedrock vertical height was assumed equal to zero, very little change occurred in the high and low ends of the size-frequency distribution. Therefore, the bedrock measurements were excluded when constructing particle size-frequency distributions for the short and long diameters. This produced consistent results between frequency distributions for the short, intermediate, and long diameters as shown in tables 2, 3, and 4. The method of dealing with the bedrock measurements, therefore, is considered satisfactory. Table 2.--Summarg of short diameter (c-axis) bed material Statistical size distribution, in feet, Particles Particles Site shown for the following percentiles vertically horizontally number oriented oriented 16 25 50 75 84~ . -'1J1 q~ ..~ppr~ent ) (percent) -------- ~-- 1 0.05 0.12 0.26 0.34 0.45 0.70 93 3 2 0.04 .06 .17 .35 .47 .60 .78 93 5 3 .06 .08 .15 .26 .33 .40 .51 91 7 41 .001 .002 .12 .37 .50 .57 .62 93 2 52 1 6 .08 .10 .16 .22 .26 .32 .43 92 5 I 7 .17 .22 .38 .61 .77 .96 1.25 91 4 8 .04 .05 .10 .20 .28 .37 .52 93 2 I 9 .11 .15 .27 .43 .54 .67 .83 80 6 10 .08 .10 .16 .26 .33 .39 .49 94 0 I 11 .10 .13 .23 .35 .43 .54 .68 89 6 1Combined Wolman method and sieve analysis (Wolman, 1954) . \ 2Sieve analysis only. 11