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83 Suspended Sediment Transport – Flocculation and Particle Characteristics

Part 7. Erosion and Sedimentation

  1. Ian G Droppo

Published Online: 15 APR 2006

DOI: 10.1002/0470848944.hsa091

Encyclopedia of Hydrological Sciences

Encyclopedia of Hydrological Sciences

How to Cite

Droppo, I. G. 2006. Suspended Sediment Transport – Flocculation and Particle Characteristics. Encyclopedia of Hydrological Sciences. 7:83.

Author Information

  1. National Water Research Institute, Environment Canada, Burlington, ON, Canada

Publication History

  1. Published Online: 15 APR 2006

Abstract

In the history of sediment transport research within hydrological sciences, there has possibly been no greater paradigm shift than that which has been provided by the identification of flocculation as a dominant mechanism operating within, and mediating, cohesive suspended sediment transport. Flocculation (the process of aggregating smaller particles together to form larger particles) significantly modifies the hydrodynamic properties of the sediment by altering their effective size, shape, density, porosity, and composition. Such changes have a dramatic impact on the downward flux of sediments and as such influence the transportation and fate of suspended sediments. The traditional assumption of suspended sediment being inorganic individual grains for the quantification and modeling of sediment transport is likely to result in erroneous results and management decisions. Flocs settle faster than their individual constituent particles (but orders of magnitude slower than that predicted by Stokes' equation for a similar size), and, for large flocs, can have porosity close to 100% and a corresponding density close to that of water. Flocs are composed of significant living organic components (primarily bacteria) which produce an extracellular polymeric substance (fibrils) which glues particles together giving them greater strength than an electrochemically bound floc, and a pseudo plastic nature. Because of this active living component, flocs should be thought of as micro ecosystems (composed of a matrix of water, inorganic, and organic particles) with autonomous and interactive physical, chemical, and biological functions or behaviors operating within the floc matrix. A better understanding of how floc structure influences floc behavior will help to refine our knowledge and management of suspended sediment transport in a variety of aquatic ecosystems.

Keywords:

  • sediment transport;
  • floc;
  • flocculation;
  • aggregation;
  • cohesive sediments;
  • settling velocity;
  • density;
  • porosity;
  • bacteria;
  • EPS