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  • A sound scientific basis for applied models of fine sediment dynamics

    Implementing mud-sand transport research
  • Implementing mud-sand transport research
  • Implementing mud-sand transport research
  • Implementing mud-sand transport research
  • Implementing mud-sand transport research

Implementing mud-sand transport research

The effective management of estuarine locations requires a sound scientific basis for applied models of fine sediment dynamics.

Work carried out during the UK Defra and Environment Agency-funded EstProc research project resulted in an empirical mud flocculation model, based purely on observational data (Manning, 2008). However, it was developed using data for predominantly muddy suspensions and therefore was only applicable to those types of situations.

To inform the extension of the applicability of the model into situations where significant amounts of suspended sand are present, a database was produced during the related Mud - Sand project to quantify the aggregational/flocculation properties of various mixtures of Tamar estuary mud and Redhill 110 sand. These measurements showed strong evidence for the flocculation of mixed sediments, while the greater understanding of the role of biology in flocculation has identified mechanisms by which this sand-mud flocculation can occur.

From the laboratory experiments, an empirical flocculation model governing the variation of settling velocity with turbulence, suspended sediment concentration and mud/sand content was developed to describe the interaction between sand and mud particles during transport. A 1DV mixed transport model was developed and used to reproduce the vertical transport of mixed sediment fractions (Spearman et al, 2011).

The 1DV model was used to reproduce the measured settling velocities in the laboratory experiments described above and also to reproduce measurements of concentration of mixed sediments in the outer Thames estuary.

In both modelling exercises the model was run using the algorithms developed in this project and repeated using an assumption of no interaction between mud and sand in the flocculation process.

The results of the modelling showed a significant improvement in the ability of the 1DV model to reproduce the observed sediment behaviour when the empirical equations including interaction were used. This represents further strong evidence of the interaction between sand and mud in the flocculation process.

The development of the algorithms and the application of the 1DV model were presented at the International Conference on Cohesive Sediments (INTERCOH) (Manning et al, 2011 and Spearman et al, 2011).

Authors

John Baugh; Andy Manning; Jez Spearman; Richard Whitehouse

Keywords

Mixed sediments Flocculation; Erosion; 1DV model

Completed

2008

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"These measurements showed strong evidence for the flocculation of mixed sediments, while the greater understanding of the role of biology in flocculation has identified mechanisms by which this sand-mud flocculation can occur."

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