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3.1 Stream Channel Cross Section Survey Results <br />General stream cllarulel morphology at eac11 testing location is provided >11 Table 1 <br />and cross sections are provided in Appendix A. The stream channel cross sections <br />performed by CDM show locations of the tests performed. Figure 5 presents a typical <br />cross section surveyed at SC-26 near Iliff. The figure displays the locations where core <br />samples were obtained and the vertical gradient and K field tests were performed. <br />At fl1e time of measurement, the streamflow was moderate and the stream stage was <br />relatively low. The active (unvegetated and recently saturated) channel widths were <br />approx>lnately 50 to 100 ft across in the upper reach (upstream of La Salle, near <br />Greeley), and the channel widened to approximately 150 to 200 ft between La Salle <br />and Fort Morgan. Below Fort Morgan, t11e river became braided and the active <br />channel narrowed to less than 100 ft and was only about 30 ft wide at Julesburg. <br />Tributaries to the South Platte River were generally much narrower, ranging from just <br />a few feet wide at site SC-18 at the upper section of Box Elder Creek, to about 60 ft <br />wide on the Cache la Poudre River near Greeley. <br />Streamflow depths at the time of the field program were generally about 1 ft to 4 ft on <br />the South Platte River, wifll depths on the tributaries ranging from less than 1 ft at <br />locations on Plum Creek, Sand Creek, C1lerry Creek and West Bijou Creek to about 2.5 <br />ft on fl1e Cache la Poudre River. <br />Tl1e results of the stream channel cross section surveys indicate that the current active <br />channel of the South Platte River is narrower with a steeper gradient in its upper <br />reaches (between Chatfield Reservoir and Greeley) and is broader with a lower <br />gradient downstream of Greeley. The South Platte tends to be donunated by riffle <br />and pool morphology upstream of Greeley and exhibits bofll riffle and pool and <br />braided morphologies in the reaches downstream of Greeley. Tributaries of the South <br />Platte exhibited a variety of morphological types, includ>lzg a vegetated Swale at the <br />headwaters of West Bijou Creek, incised streambeds on Box Elder Creek and Cherry <br />Creek, and channelized streambeds on Beebe Draw and the lower reach of Box Elder <br />Creek. Stream channel data obtained from the UDFCD contained stream channel <br />cross sections from 1986 through 2003, which indicated that, for the purposes of fl1e <br />SPDSS, the stream channel geometry at the locations measured have not changed <br />significantly during that period. The stream charulel geometry and morphology <br />observations from this Task will be used in fl1e grotuldwater modeling (Task 48) to <br />develop input parameters for the stream package. <br />3.2 Streambed Sediment Sampling Results <br />The dominant lithologies observed at each site are summarized in Table 1, and <br />lithologic field descriptions are provided >11 Appendix B. Figures 6 and 7 present box <br />plot statistical summaries of the median grain-size (cL~o) at each testing location on the <br />South Platte mainstem and its tributaries, respectively. Figure 8 presents a map <br />showing fl1e geometric mean value for each test site, derived from the median (d5o) <br />grain sizes of the samples collected at the >IZdividual sample collection locations from <br />each test site. <br />Fnlal T~zsl: 3~TM 06-28-07.doc $ <br />