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

沙丘对于了解河流沉积物的运输，沉积，流阻和河道流动过程至关重要。尽管先前的研究已经检查了美国下密西西比河下游河床的微观形态，但我们对这条和其他大型冲积河中沙丘形态的详细量化知识仍然有限。人们还不太了解直河段的沙丘和弯弯曲曲的特征如何不同，以及沙丘的形态如何受到人类活动的影响（即河流工程）。在这项研究中，我们利用密西西比河最下游（LmMR）的四个1.6-8.0 km长的多波束测深技术来分析河床的微观形态特征。四个河段中的三个位于LmMR的上部，介于474公里至474公里，483.6至485.2公里和491.7至493.3公里之间，另一个河段位于RK 120至RK 128之间。我们对这些河段的3258个沙丘进行了分析，发现大型沙丘在LmMR中占主导地位。这些沙丘的特征在于平均背风偏斜角低（10.8°），这表明由沙丘引起的流阻应该相对较小。与直线河段的沙丘相比，蜿蜒曲折的沙丘要大得多（1.06 m对0.81 m），床面粗糙度较高（0.91对0.68），这可能与流速的变化有关。沙丘的大小随着直河段河道水深的增加而增加，而随着曲折弯河道上水深的增加而减少。与下游河段的沙丘相比，上游河段的沙丘高度明显更高，波长更短，并显示出更高的床面粗糙度（1比0.68），这可能与河床高度相关。较大的河床坡度和河床沉积物的晶粒尺寸发生在上游，并且是旧河控制结构（RK 500）和回水的共同作用。这些发现表明湍流，坡度和沙源对沙丘形成和河床沉积的强烈影响。这可能与上游河床较大的河床坡度和河床沉积物的颗粒大小以及旧河控制结构（RK 500）和回水的综合影响密切相关。这些发现表明湍流，坡度和沙源对沙丘形成和河床沉积的强烈影响。这可能与上游河床较大的河床坡度和河床沉积物的颗粒大小以及旧河控制结构（RK 500）和回水的综合影响密切相关。这些发现表明湍流，坡度和沙源对沙丘形成和河床沉积的强烈影响。