Role of Meteorologically Induced Water Level Oscillations on Bottom Shear Stress in Freshwater Estuaries in the Great Lakes

The role of meteorologically induced water level oscillations (MIWLOs) on bottom shear stresses in a freshwater estuary in the Great Lakes is investigated. Atmospheric data including air pressure, wind speed and direction, and radar reflectivity are compiled, and comprehensive field measurements including velocity profiles, water levels, river discharges, and bottom sediment properties in the Manistique River (MR) estuary, Michigan, are conducted. Wavelet and cross-wavelet analysis reveals that large velocity events (>0.5 m/s) in the MR estuary are generated by high-frequency MIWLOs (i.e., meteotsunamis and high-frequency seiches) induced by energetic oscillations in air pressure and/or wind speed and direction with periods below 2 hr. Measured velocity profiles reveal that MIWLO-dominated conditions can increase bottom shear stress by an order of magnitude in comparison with river-dominated flow conditions. The hydrodynamic model indicates that bottom shear stresses under both the downstream and upstream flows during the MIWLO-dominated event were significantly larger than those during river-dominated conditions. The interactions of MIWLOs and flood flows can significantly alter the bottom shear stresses in the main river channel, and MIWLOs are revealed to be the principal resuspension mechanism in areas such as the upstream tributary branches where flood flows individually do not cause resuspension. Furthermore, the role of MIWLOs asymmetry in fresh water Great Lakes estuaries on velocity residuals and net sediment transport is revealed and discussed. Overall, this paper fills important knowledge gaps in the role of MIWLOs on sediment transport in enclosed basin estuaries, thus providing essential information for coastal management and estuarine remediation.