Ruben A. Heine Brian Ickes Jonathan Remo 2016 <p><span>In this study, we compared pre-lock-and-dam (ca. 1925) with a modern longitudinal survey of main-channel-bed sediments along a 740-km segment of the upper Mississippi River (UMR) between Davenport, IA, and Cairo, IL. This comparison was undertaken to gain a better understanding of how bed sediments are distributed longitudinally and to assess change since the completion of the UMR lock and dam navigation system and Missouri River dams (i.e., mid-twentieth century). The comparison of the historic and modern longitudinal bed sediment surveys showed similar bed sediment sizes and distributions along the study segment with the majority (&gt;&nbsp;90%) of bed sediment samples having a median diameter (</span><i>D</i>₅₀<span>) of fine to coarse sand. The fine tail (&le;</span><i>&nbsp;D</i>₁₀<span>) of the sediment size distributions was very fine to medium sand, and the coarse tail (&ge;</span><i>&nbsp;D</i>₉₀<span>) of sediment-size distribution was coarse sand to gravel. Coarsest sediments in both surveys were found within or immediately downstream of bedrock-floored reaches. Statistical analysis revealed that the particle-size distributions between the survey samples were statistically identical, suggesting no overall difference in main-channel-bed sediment-size distribution between 1925 and present. This was a surprising result given the magnitude of river engineering undertaken along the study segment over the past ~&nbsp;90&nbsp;years. The absence of substantial differences in main-channel-bed-sediment size suggests that flow competencies within the highly engineered navigation channel today are similar to conditions within the less-engineered historic channel.</span></p> application/pdf 10.1016/j.geomorph.2016.04.012 en Elsevier Particle size distribution of main-channel-bed sediments along the upper Mississippi River, USA article