Events

Please join us for Parsons Environmental Science Seminar Series with speaker Tong Bo, Ph.D. from MIT-WHOI, this Friday.

Abstract Title: Increased Drag in Estuaries with Meandering Channels

The drag force is a key factor affecting flow and transport in rivers, estuaries, and other coastal ocean environments, and it directly influences tidal propagation, flooding potential, and marsh inundation as well as mixing processes, stratification, and salinity intrusion. Channel curvature creates distinct flow processes that affect the drag and overall momentum balance, including secondary circulation in the cross-section and flow separation in the horizontal plane. Observations from the North River estuary, a sinuous tidal channel in Massachusetts, found much greater drag than is typical for similar estuaries with straight channels. We built a numerical model of the estuary to investigate how channel curvature increases drag through three-dimensional flow processes. In channel bends, flow separation generates recirculating eddies on the lee side that have lower pressure than the upstream flow, and this creates bend-scale form drag that accounts for much of the drag increase. Additionally, the secondary circulation due to flow curvature in bends transports high-momentum fluid from the surface toward the bed. Consequently, the near-bed shear and bottom stress are enhanced compared with a traditional logarithmic velocity profile. Both form drag due to flow separation, and the enhanced bed stress due to secondary circulation are important contributors to the high drag in sinuous channels, with potential implications for coastal flooding, sediment transport, and channel morphodynamics.

Bio:
Tong Bo is a Ph.D. candidate in the MIT-WHOI joint program in
Applied Ocean Physics and Engineering. He uses numerical and
observational methods to study estuarine dynamics and coastal
fluid dynamics. He received his B.S. (2018) at Peking University
in Theoretical and Applied Mechanics.