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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />J <br />t <br />, <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />0:,1808 <br /> <br />5. Sedimentology of Upper Arkansas River <br /> <br />Recent sediments of the Upper Arkansas River include those deposits that are part of the <br />active channel and channel margin subenvironments. Active bedload sampling was <br />conducted during spring 1998; those samples were sieved in the laboratory and those <br />results are discussed in Chapter 7: Hydraulics and Sediment Transport. Supplemental <br />sediment data collected previously during summer 1996 was obtained through D. <br />Dominick (pers. comm, 1998). These data were provided as raw pebble counts <br />(Wolman, 1954) from pool, riffle, and bar environments that was then reduced to <br />determine size gradations (Appendix A). <br /> <br />The pool, bar, and riffle sediment through the project reach consists primarily of gravel <br />and coarser sediment, although locally, thick deposits of sand and finer tailings deposits <br />Ell topographically low areas on bars. Tailings samples analyzed from floodplain and bar <br />areas (URS, 1998) consist primarily of sand and silt sized particles, which are in marked <br />contrast to the coarser grained bedload sediment. Wolman count data from riffles depict <br />a general downstream coarsening trend from upstream of the project reach to Lake Fork <br />(Figure 5.1). Downstream of Lake Fork, the sediment samples collected adjacent to Mt. <br />Massive Lakes are somewhat finer than those between California Gulch and Lake Fork. <br /> <br />Within Subreach 2, terrace deposits on the eastern channel margin contribute relatively <br />coarse material to the active channel. That coarsening trend is reflected in the riffle data <br />between Tennessee Creek and Lake Fork. The coarsening of bed sediment at the Lake <br />Fork confluence is likely in response to energy increases imposed by historic flow <br />augmentations (Dominick and O'Neill, 1998). The tining trend between Lake Fork and <br />Mt. Massive lakes suggests that the reach is less affected by coarse local input, or that the <br />reach is depositional, such that gravels derived from upstream channel erosion are <br />deposited around Mt. Massive Lakes (Subreach 5). <br /> <br />May 7, 1999 <br /> <br />Fluvial Geomorphological Assessment <br />Upper Arkansas River <br /> <br />Page 33 <br />