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<br />May 7, 1999 <br /> <br />Fluvial Geomorphological Assessment <br />Upper Arkansas River <br /> <br />Page 6 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />- <br />I <br />I <br />I <br />I <br />I <br />I <br />, <br />I <br /> <br />the achievement of improved fluvial function will necessarily benefit aquatic and riparian <br />ecosystems, specific objectives of biological enhancement are not directly addressed <br />herein. The conceptual strategies represent basic restoration approaches that are <br />specifically applicable to identified geomorphic processes. This approach is intended to <br />assist in the future development of a detailed restoration plan that will include treatment <br />prioritizations and modifications based on issues such as relative toxicity of individual <br />deposits, feasibility ofin-situ treatments, specific biological objectives, land use, and <br />water rights. <br /> <br />The approach adopted in this investigation focuses on the achievement of geomorphic <br />stability and reduction of tailings entrainment potential rather than the redevelopment of a <br />historic channel state; consequently, the term channel rehabilitation will be utilized to <br />describe treatment options rather than the commonly utilized term of channel restoration. <br /> <br />2.3. Procedure <br />The data presented in this report represent a compilation of original material as well as <br />information obtained from various published and unpublished documents. <br /> <br />2.3.1. Existing Data <br /> <br />Photogrammetric base maps of the project reach at a 2-ft contour interval and a <br />companion hydraulic model were utilized extensively in this study for field mapping, <br />topographic characterization of subreaches, and hydraulic and sediment transport <br />analyses. The mapped delineation of previously identified tailings deposits (URS, 1997; <br />1998) was used to identify those deposits most prone to entrainment (URS, 1998). <br />Hydrology was characterized based on USGS gage data, information provided by the <br />USBR, and existing reports (URS, 1998, O'Neill, et. ai, 1997; Studzinski, 1996). Aerial <br />photographs dated 1939, 1956, 1996, and 1997 were evaluated to determine historic <br />changes in channel pattern and migration rates. <br /> <br />2.3.2. Field Investigation <br />In spring of 1998, several suites of bedload sediment data were collected within the <br />project reach. This information was subsequently utilized to calibrate the sediment <br />transport analysis. A reconnaissance field investigation of the study area was conducted <br />in July of 1998. The 2-ft photogrammetric map supplied by URS was utilized as a base <br />map. Geomorphic, sedimentologic and man-made features of interest were mapped onto <br />the base sheets. The II-mile project reach was segmented into 6 project subreaches (a <br />seventh subreach is located upstream of the project reach). Representative channel <br />segments were identified for sediment transport evaluations. Photographic <br />documentation was extensive, In September of 1998, a total of 6 representative channel <br />segments were surveyed in detail for the hydraulic/sediment transport evaluation, and are <br />referred to herein as Incipient Motion (1M) Sites (Figure 2.2). This involved surveying <br />several cross-sections for development of local hydraulic models at each site. <br /> <br />2.3.3. Human Impacts on River Geomorphology <br />The historic impacts of mining, flow augmentations, and land use on fluvial processes <br />within the project reach were assessed based on an integration of information derived <br />