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Bore-generated macrovortices on erodible beds

Published online by Cambridge University Press:  11 October 2013

M. Brocchini
M. Brocchini*
Affiliation:
Department I.C.E.A., Università Politecnica delle Marche, 60131 Ancona, Italy
*
†Email address for correspondence: [email protected]
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Abstract

The interaction of free-surface bores and an erodible porous channel bed in a shallow-water flow is analysed based on the assumption of weak coupling between free-surface discontinuities and bed discontinuities and on the simplest closure for the sediment transport rate (cubic with the mean flow velocity). It is shown that free-surface bores with finite cross-stream extent can evolve over the erodible bed by generating vertically oriented macrovortices in a manner similar to, but more complex than, that of free-surface bores of finite cross-stream extent over a rigid channel bottom. An equation for the potential vorticity is derived, which shows that on an erodible bed the vortices are generated by a combination of various mechanisms related to energy dissipation of both surface bores and bed discontinuities. The model is verified and the physics explored by comparison with a number of numerical simulations, typical of both riverine (dam-break test and pit test) and nearshore (bore on a beach test) flows, and with previously published experimental results. For all cases a fairly good agreement is found between the analytically estimated potential vorticity and that computed numerically.

JFM classification

Geophysical and Geological Flows: Sediment transport Geophysical and Geological Flows: Shallow water flows Waves/Free-surface Flows: Waves/Free-surface Flows
Type
Papers
Information
Journal of Fluid Mechanics , Volume 734 , 10 November 2013 , pp. 486 - 508
Copyright
©2013 Cambridge University Press 

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