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The University of Southampton
Ocean and Earth Science, National Oceanography Centre Southampton

Research project: Vertical turbulence structures in the benthic boundary layer as related to suspended sediment

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The Rouse profile is used to model the vertical distribution of suspended sediments. It considers that settling of individual grains towards the bed would be balanced by upward diffusion induced by vertical turbulent motions in the boundary layer. However, the underlying assumptions of this model, particularly in terms of vertical turbulence structure, are disputed in the literature (e.g. Grant and Madsen, 1986), and its validity has been contested by field results (e.g. Amos et al, 2010).

Source: H Kassem
Source: H Kassem

The Problem

The Rouse model considers that settling velocity of a sediment grain is balanced by upward turbulence (velocity fluctuations in the vertical). Devised for unidirectional flows, it also assumes eddy viscosity varies parabolically in the vertical, and the existence of a constant stress layer, and employs a reference concentration at a reference height above bed. There is no consensus on any of these assumptions, nor a definition for the reference concentration. A plethora of realisations has been suggested for eddy viscosity, and the model ignores its temporal variability. The model also ignores the feedback mechanism though drag reduction, other types of flows, and the configuration and properties of the bed.

Source: BARDEXII
Source: BARDEXII

Objectives

The primary objective of this research is to derive a new turbulence-based model describing the vertical profile of suspended sediments. This model should account for the feedback imparted by sediments, once suspended, on turbulence through the process of drag reduction. The model will then be validated through a series of lab-based experiments, in straight and annular flumes (e.g. lab carousel) and field data (e.g. BARDEX II) for cohesive/non-cohesive sediments.

Source: H Kassem, BARDEXII
Source: H Kassem, BARDEXII

Key Contacts

Dr Charlie Thompson

Prof Carl Amos

Prof Ian Townend

Prof Robert Nicholls

Dr Justin Dix

PhDs and Other Opportunities

Visit GSNOCS

Related research groups

Geology and Geophysics
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