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At all sites cored, no significant difference was observed between materials at the top <br />or the bottom of the cores. Sediments collected from the mainstem of the South Platte <br />River were observed to consist generally of poorly sorted sand with traces of gravel, <br />with cobbles also being present at upstream site SC-02. Cobbles were also present at <br />all sample locations along the Cache la Poudre River (sites SC-11, SC-12, and SC-13). <br />Samples from tributaries overlying the Denver Basin were finer grained, with <br />lithologies ranging from poorly sorted sand to silty clay. <br />Based on median grain-size of all samples collected at a given field testing location, <br />there is a general trend of decreas>lzg grain-size in the downstream direction along the <br />mainstem of the South Platte (Figures 6 and 8). Exceptions to fllis general trend are <br />the mainstem samples collected at locations SC-28 through SC-30 fllat s11ow a larger <br />median grain-size. The South Platte River floodplain narrows over this reach, <br />therefore the higher median grain-size could indicate a higher deb ee of sorting and <br />generally more transport of f>11er bained streambed sediment material over this reach <br />due to the more constricted nature of the stream channel. <br />T11e results of the laboratory grain-size distribution testing and field observations <br />indicate that streambed materials cover a Bain-size range from clay to cobbles. In <br />order to summarize the large range in grain-size distribution for most samples, the <br />geometric mean values of the median Bain-size value of all samples collected at each <br />site were compared. T11e test locations along the mainstem have an average geometric <br />mean Bain-size of 1.8 nun, consistent wifll field observations that the streambed is <br />donunated by medium to coarse sands. In contrast, the samples collected from <br />tributaries have an average geometric mean grain-size of 1.2 nun, indicating the <br />presence of very f>11e sand to silty materials. This indicates that t11e median Bain-size <br />of streambed material in the tributaries generally consists of more f>11e-grained <br />material than in the mainstem of the South Platte and fl1e Cac11e la Poudre Rivers. <br />Figures 6 and 7 summarize median Bain-size data for samples collected at each site <br />along the South Platte mainstem and its tributaries, respectively. The data are <br />summarized in these figures using statistical box plots of each site with the median, <br />nun>lnum, upper and lower quartiles and maximum values shown. The geometric <br />mean values of samples collected at each site are shown spatially in Figure 8. <br />Geotechnical testing results are summarized in Appendix Table C1, and the full <br />laboratory haul-size distribution curves are presented in Appendix C. <br />Many investigators have observed a relationship between grain-size and K and have <br />developed empirical relationships between these parameters. One of the more <br />comprehensive studies of this type was presented by Shepherd (1989), who estimated <br />K of sediments based on their median grain-size (d5o). This empirical relationship uses <br />the following equation to relate mean Bain-size to K: <br />K=C~dSOI <br />Where: <br />K = Hydraulic conductivity (feet per day [ft/day]) <br />Fnlal T~zsl: 3~TM 06-28-07.doc <br />