SEDIMENT TRANSPORT IN THE LOWER SAGINAW RIVER

A study of the resuspension, deposition and transport of sediments and the resulting changes in bathymetry in the lower part of the Saginaw River in Michigan has been made. The numerical model used in this study consists of a two-dimensional, vertically integrated, time-dependent hydrodynamic and transport model coupled with a three-dimensional, time-dependent model of the dynamics of the sediment bed and its properties. Transport of sediment as suspended load and bed load was included in the analysis. In the numerical calculations, curvilinear coordinates were used. For verification of the model, results of numerical calculations of changes in the thickness of the sediment bed due to time-varying flow events were compared with bathymetric measurements taken at nine transects on the river on 28 August 1991 and 13 May 1992. From the transect measurements, from measurements of flaw rates and sediment concentrations, and from the numerical modelling, a reasonably accurate description of the sediment transport and the resulting bathymetric changes has been made. The calculations and observations show that resuspension/deposition, bed load, and slumping are significant factors in changing the bathymetry. It is also shown that the largest flows are responsible for most of the sediment erosion and deposition and must therefore be understood and considered in detail. An approximate procedure for making long-term (1 to 25 year) calculations is presented and discussed. This procedure greatly reduces the required computer time but still maintains the required accuracy for the prediction of sediment and contaminant transport and fate.