Multi-size, multi-source formulation for determining impacts of sediments on near-shore sensitive sites

The unconfined placement of dredged material raises the issue of potential adverse impacts on sensitive near-shore areas (e.g. water intakes) located some distance away from the placement site. Two management questions arise: first, whether the material from the placement site is actually transported to the sensitive area; and second what is the relative intensity of this load compared to other sites. In an effort to evaluate the relative impact of different sediment sources on sensitive near-shore areas we considered a multi-grain size, multi-source sediment transport model formulation. Calculations were performed using the CH3D circulation model coupled with a sediment model known as the CH3D-SED, which includes a suspended sediment and a mobile-bed sediment module. The location of interest has been the Toledo, Ohio, water intake area in the western basin of Lake Erie. The sediment disposal site is located a few miles northeast of the sensitive site. The four sediment sources selected are: the Maumee River, the Detroit River, the entrained bottom sediments and the sediments originating from the disposal site. Three representative grain sizes, one from each sediment size class (sand, silt, clay), were assigned for each source. The model was run on a 2 km spatial grid for the test period from April 1, 1997 to December 31, 1997. Model outputs include: 3-D velocity, temperature and concentration (all grain sizes) fields, vertically integrated velocities and grain size distributions at the lake bottom, from which hourly trajectory maps and time traces are generated.