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<br />I <br />I <br />I <br />I <br />I <br />J <br />I <br />I <br />il <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />C~1793 <br /> <br />from aerial photographs, flow data, land use, and inferred conditions of historic sediment <br />loading. Aerial photographs dated 1939, 1956, and 1997, were used to measure <br />progressive changes in channel width, pattern, and sinuosity. Flow conditions were <br />assessed in terms of effective discharge occurrence frequencies and associated channel <br />response. <br /> <br />2.3.4. Channel Stability <br /> <br />Channel stability was evaluated on a subreach basis with respect to historic lateral <br />channel behavior, as well as existing sediment transport conditions. The lateral stability <br />was estimated by historic trends in lateral channel migration, and current channel position <br />with respect to floodplain topography, Vertical stability and sediment transport <br />conditions were determined through a hydraulic evaluation and incipient motion <br />(sediment mobility) analysis. <br /> <br />2.3.5. Tailings Entrainment Potential <br /> <br />Subreach stability was evaluated with respect to identified tailing deposits to assess the <br />site-specific potential for short- and long-term tailings entrainment. Individual deposits <br />most prone to short-term entrainment were identified. The tailings were identified <br />generically based on mapped and geochemically analyzed distributions; the specific <br />metals concentrations and consequent level of concern was not identified as part of the <br />entrainment potential assessment. <br /> <br />2.3.6. Conceptual Rehabilitation Alternatives <br /> <br />Identified geomorphic conditions within the project reach formed the basis for <br />development of conceptual treatments that address geomorphic processes and associated <br />tailings entrainment potential. These alternatives are intended to assist in the ultimate <br />development of a restoration plan that acknowledges the geomorphology of the river <br />system. Such an integration of will optimize river function and stability, but will require <br />alterations and adaptations to address a multitude of project constraints such as cost, <br />operations and maintenance requirements, tailings treatment plans, property ownership, <br />and water rights. <br /> <br />May 7, 1999 <br /> <br />Fluvial Geomorphological Assessment <br />Upper Arkansas River <br /> <br />Page 7 <br />