Upper Mississippi River Flow and Sediment Characteristics and Their Effect on a Harbor Siltation Case

Abstract

Upper Mississippi River flow and sediment characteristics downstream of St. Louis are presented in this study. Available and measured data were used to assess a harbor siltation case and dredging needs. Such data are also useful to researchers and engineers conducting work in the Mississippi River and large rivers in general. Flows were characterized in terms of the mean annual hydrograph, flow duration curve, and mean annual, dominant, and effective discharges. Suspended and bed material sediments were characterized by grain-size distributions (GSDs). Suspended-sediment concentrations were characterized with a sediment rating curve, mean annual sediment graph, and duration curve. The results of the analyses were used to assess harbor sedimentation by comparing GSDs of harbor bed samples with those observed in the river. Bathymetric surveys were used to determine rates and occurrence of sedimentation. The analyses showed that harbor siltation correlates with river conditions and is driven by wash load in the river, which enters the harbor in suspension and deposits along the bottom due to the lack of flow-through velocities high enough to keep the fine sediments in suspension.