Settling velocity of sediments at high concentrations

Baldock, T. E., Tomkins, M. R., Nielsen, P. and Hughes, M. G. (2004) Settling velocity of sediments at high concentrations. Coastal Engineering, 51 1: 91-100. doi:10.1016/j.coastaleng.2003.12.004


Author Baldock, T. E.
Tomkins, M. R.
Nielsen, P.
Hughes, M. G.
Title Settling velocity of sediments at high concentrations
Journal name Coastal Engineering   Check publisher's open access policy
ISSN 0378-3839
1872-7379
Publication date 2004-03
Sub-type Article (original research)
DOI 10.1016/j.coastaleng.2003.12.004
Volume 51
Issue 1
Start page 91
End page 100
Total pages 10
Place of publication Amstedam, Netherlands
Publisher Elsevier
Collection year 2004
Language eng
Subject 290802 Water and Sanitary Engineering
770400 Coastal and Estuarine Environment
0905 Civil Engineering
090509 Water Resources Engineering
090599 Civil Engineering not elsewhere classified
Abstract New data on the settling velocity of artificial sediments and natural sands at high concentrations are presented. The data are compared with a widely used semiempirical Richardson and Zaki equation (Trans. Inst. Chem. Eng. 32 (1954) 35), which gives an accurate measure of the reduction in velocity as a function of concentration and an experimentally determined empirical power n. Here, a simple method of determining n is presented using standard equations for the clear water settling velocity and the seepage flow within fixed sediment beds. The resulting values for n are compared against values derived from new and existing laboratory data for beach and filter sands. For sands, the appropriate values of n are found to differ significantly from those suggested by Richardson and Zaki for spheres, and are typically larger, corresponding to a greater reduction in settling velocity at high concentrations. For fine and medium sands at concentrations of order 0.4, the hindered settling velocity reduces to about 70% of that expected using values of n derived for spheres. At concentrations of order 0.15, the hindered settling velocity reduces to less than half of the settling velocity in clear water. These reduced settling velocities have important implications for sediment transport modelling close to, and within, sheet flow layers and in the swash zone.
Keyword Fall velocity
Hindered settling
Sediment concentration
Suspended sediment transport
Sheet flow
Swash zone sediment transport
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

 
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Created: Wed, 15 Aug 2007, 03:12:19 EST