The Impact of Episodic Events on Nearshore-Offshore Transport in the Great Lakes:
Sediment Resuspension and Transport Modeling

K. Bedford

This proposal focuses on the construction and implementation of sediment transport and particle tracking models to study cross-margin transport in southern Lake Michigan. It is part of a multiproposal, multidisciplinary program to study the impact of episodic events on the coastal ecosystem in the Great Lakes. The overall study focuses on an episodic occurrence of a ~10 km wide plume of resuspended material extending over 100 km along the southern shore of the Lake Michigan.
An Eulerian sediment resuspension and transport model will be developed for Lake Michigan by integrating the hydrodynamic model of Schwab and Beletsky (see associated proposal) with a sediment transport model that includes the effects of wave current interaction, variable bed properties, and flocculation of fine-grained sediments. Concurrently, a Langrangian-based particle tracking model will be developed to provide predictions of particle trajectories and residence times. The primary objectives of this project are to 1) determine the sediment transport model structure necessary to reproduce measured cross-shore plume transport and behavior at hydrodynamic scales, 2) determine the important physical processes affecting cross-shore particle transport, 3) determine the particle residence time correlation with storm frequency, pattern, and intensity, 4) summarize the particle transport behavior from source to burial, and 5) quantify the occurrence of permanent versus transient particle sinks during cross-shore transport. The models will be tested and verified against the extensive set of field observations (both Eulerian and Langrangian) that are being carried out as part of this overall program (see Saylor et al. proposal).
Given the importance of episodic resuspension events to the functioning of the lake ecosystem, numerical models that predict three dimensional concentration fields of suspended material as well as track the path of particles in the flow can provide a very useful management and analysis tool for these lake systems. Currently, estimates of concentrations and particle residence times resulting from these episodic events are obtained primarily from limited field measurements, tracer studies, and simple mass balance models. Development of a fully three-dimensional sediment resuspension and transport model, together with the detailed field measurements of hydrodynamic variables and suspended particulate concentrations will allow us to test the ability of these models to reproduce and predict onshore-offshore exchanges of sediments in large lakes. However, since conventional Eulerian-based transport models cannot provide information about particle trajectories and residence times, concurrent development and testing of a Lagrangian-based particle tracking model is critical for predicting the path that particles take as they travel cross-shore and for identifying transient and permanent particle sinks along this path.
This collaborative Lake Michigan study provides an ideal framework for model testing and development. The objectives of our proposed work have been tailored to the goals of the overall program and its focus on the cross-margin transport of biological, chemical, and geological materials. Our models provide the basis for further studies and modeling efforts focusing on the coupling between biological, chemical, and physical processes (e.g. Chen) and, therefore, provide a critical link in the success of the overall program.