Upper Midwest Environmental Sciences Center
Particle size distribution of main-channel-bed sediments along the upper Mississippi River, USA
Remo, Jonathan W.F., Reuben A. Heine, and Brian S. Ickes. Particle size distribution of main-channel-bed sediments along the upper Mississippi River, USA. Geomorphology, 264: Pages 118-131, ISSN 0169-555X, http://dx.doi.org/10.1016/j.geomorph.2016.04.012.
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 (>90%) of bed sediment samples having a median diameter (D50) of fine to coarse sand. The fine tail (≤D10) of the sediment size distributions was very fine to medium sand, and the coarse tail (≥D90) 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 ~90 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.