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Abstract
We show that in free surface flows, a uniform, streamwise current over smallamplitude wavy bottom topography generates crossstream drift velocity. This drift mechanism, referred to as the currentbathymetry interactioninduced drift (CBIID), is specifically understood in the context of a simplified nearshore environment consisting of a uniform alongshore current, onshorepropagating surface waves and monochromatic wavy bottom making an oblique angle with the shoreline. The CBIID is found to originate from the steady, nonhomogeneous solution of the governing system of equations. Similar to Stokes drift induced by surface waves, CBIID also generates a compensating Eulerian return flow to satisfy the noflux lateral boundaries, e.g. the shoreline. The CBIID increases with an increase in particle's initial depth, bottom undulation amplitude and the strength of the alongshore current. Additionally, CBIID near the free (bottom) surface increases (decreases) with an increase in bottom undulation's wavelength. Maximum CBIID is obtained for longwavelength bottom topography that makes an angle of approximately with the shoreline. Unlike Stokes drift, particle excursions due to currentbathymetry interactions might not be small, and hence analytical expressions based on the smallexcursion approximation could be inaccurate. We provide an alternative bounded approximation, which leads to highly accurate expressions for drift velocity and time period of particles especially located near the free surface. Realistic parametric analysis reveals that in some nearshore environments, CBIID's contribution to the net Lagrangian drift can be as important as Stokes drift, implying that CBIID can have major implications in crossshelf tracer transport.
Original language  English 

Article number  A15 
Number of pages  25 
Journal  Journal of Fluid Mechanics 
Volume  952 
Early online date  24 Nov 2022 
DOIs  
Publication status  Published  10 Dec 2022 
Keywords
 hydraulics
 surface gravity waves
 topographic effects
ASJC Scopus subject areas
 Condensed Matter Physics
 Mechanics of Materials
 Mechanical Engineering
 Applied Mathematics
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Tracer transport due to wavecurrentbathymetry interactions in fluvial and coastal environments
Anirban Guha (Speaker)
11 Nov 2022Activity: Talk or presentation types › Invited talk

A new crossshelf Lagrangian drift mechanism in coastal oceans: the role of alongshore current and rippled seabed interactions
Anirban Guha (Contributor) & Akanksha Gupta (Speaker)
24 Feb 2022 → 4 Mar 2022Activity: Talk or presentation types › Oral presentation

Tracer transport due to wavecurrentbathymetry interactions in fluvial and coastal environments
Anirban Guha (Speaker)
10 May 2022Activity: Talk or presentation types › Invited talk