Riverbed dune morphology of the Lowermost Mississippi River – Implications of leeside slope, flow resistance and bedload transport in a large alluvial river

Dunes are critical for understanding riverine sediment transport, deposition, flow resistance and channel processes. Although previous studies have examined the riverbed micromorphology of Lower Mississippi River in USA, our knowledge detailed quantification dune morphology this other large alluvial rivers is still limited. It also not well understood how dunes a straight reach meander bend differ their characteristics, as may been affected by human activities (i.e., river engineering). In study, we utilized multi-beam bathymetric measurements over four 1.6–8.0 km long reaches Lowermost (LmMR) to analyze micromorphologic features. Three were located upper part LmMR between kilometers (RK) 474–477, 483.6–485.2 491.7–493.3, was lower part, RK 120 128. We analyzed total 3258 these found that dominant LmMR. These characterized low mean leeside slope angle (10.8°), indicating caused should be relatively small. When compared with reaches, bends much larger (1.06 m vs. 0.81 m) had higher bed roughness (0.91 0.68), which related varied velocity. Dune size increased increasing water depth across reach, while it decreased bend. lower-river upper-river significantly height shorter wavelength, showed (1 closely greater grain occurred combined effect Old Control Structure (RK 500) backwater. findings indicate strong impact turbulent flow, sand source on formation deposition.