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Bed roughness induced entrainment in a high Richardson number underflow

Author(s): Rocío Luz Fernandez; Jörg Imberger

Linked Author(s): Rocío Luz Fernandez, Jörg Imberger

Keywords: Entrainment; underflow; drag coefficient; Richardson number; buoyancy; relative roughness; normal flow

Abstract: Field data, collected in a shallow underflow into a medium-sized reservoir, show that the dimensionless entrainment, E, is non-negligible at high Richardson numbers. For such underflow, the field data demonstrate that E is mainly dependent on the stress generated at the bottom, directly determined by the relative bed roughness and the properties of the current. The flow is shown to quickly reach a condition of normal flow where Ri is constant; the value of Ri being a strong function of the bottom slope. An entrainment law is presented, in terms of both Richardson number and bottom drag coefficient, written as E = E(Ri,CD), that shows good agreement with the values of E measured in the field.

DOI: https://doi.org/10.1080/00221686.2006.9521724

Year: 2006

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