Storm Impacts on Sediment Deposition at a River-Coastal Confluence

To remain a viable harbor the Maumee River/Lake Erie confluence requires continuous dredging of two permanent bed mounds; the goal of this paper is to research the sediment transport, characteristics under storms in the confluence region, with the objective of seeking the origin and physics of the two mobile sediment mounds in the navigation channel of the river. An integrated three dimensional, hydrodynamic, sediment transport, wave current bottom boundary layer, and wave model is applied to simulate the hydrodynamics and sediment transport. A curvilinear grid system with 208 by 79 cells in the horizontal direction and 12 sigma layers in the vertical direction is used to cover the whole lake and the 12 km long dredged channel of the Maumee River. Four sediment transport application cases are constructed under strong and weak storms in spring and fall. The numerical simulation results reveal the sediment transport and formation mechanisms of the two mobile sediments mounds in the Maumee River/Lake Erie confluence under storms. Under strong storms/seiches, Mound 1, the upstream one, is mainly formed by riverine sediment inflow and settlement while Mound 2, the downstream one, is mainly formed by sediment resuspension in the river bottom upstream of Mound 2. During weak storms both Mounds 1 and 2 are maintained by riverine sediment settlement with bottom sediment upstream of Mound 1 being the second largest contributor to the formation and maintenance of Mound 2. Strong vertical thermal stratification exists in spring, but not in fall. This stratification influences the sediment transport in the river/coastal confluence. Under both strong and weak storms/seiches, the riverine sediment deposition at Mound 1 is more in spring than in fall, but more in fall than in spring at Mound 2; the total sediment transport into the Maumee Bay is more in fall than in spring.