Velocity Measurements from a 5-Beam ADCP Reveals Varying Benthic Turbulence in Hamilton Harbour

Session: 47. - Physical Processes in Lakes

Bernard Yang, University of Toronto, [email protected]
Mathew Wells, University of Toronto Scarborough, [email protected]

Abstract

A new high resolution, 5-beam ADCP was deployed in Hamilton Harbour during the summer of 2017. During summer, the stratified waters of Hamilton Harbour have vigorous internal seiches driven by diurnal winds. These seiches have period of 24 hours, amplitude of 2-5 m, and result in sustained near-bed velocities of up to 25 cm/s. Due to the process of shear-induced convection, there is an asymmetry in turbulence between high turbulence during upwelling flows, and lower turbulence during downwelling flows. The dissipation was estimated using the structure function method. The inferred vertical eddy diffusivity suggests an increase in turbulence intensity as the thermocline moves upwards and a decrease as the thermocline moves downwards, consistent with previous estimations using the Thorpe scale method. The movements of the thermocline in Hamilton Harbour result in a dynamic wash-zone that influences a large region of the shallower waters. The increased turbulence activity during upwelling is the main physical process transporting phosphorus from the sediments to the surface layer, and we will discuss the implications upon internal nutrient loading on the Harbour. 

1. Keyword
Hamilton Harbour

2. Keyword
hydrodynamics

3. Keyword
water currents