Skip to main content

Size and settling velocity distributions of flocs in the Tamar estuary during a tidal cycle


Data extracted from video recordings of individual estuarine flocs near the estuary bed during the advance and retreat of the salt intrusion show changes in size and settling velocity distributions. The recordings were taken using INSSEV —IN Situ SEttling Velocity instrument. Size coupled with effective density variations due to both changes in floc structure and ambient salinity result in changes in the settling velocity during the tidal cycle. In particular, just after high water slack, the appearance of high settling velocity medium size flocs and individual particles suggest that the lower density flocs have been broken up by the intense vertical shear in the currents caused by the salt wedge intrusion. Current shear is shown to have a significant influence on floc effective density.

This is a preview of subscription content, access via your institution.


  • AL ANI, S., K.R. DYER and D.A. HUNTLEY, 1991. Measurement of the influence of salinity on floc density and strength. Geo-Mar. Lett., 11: 154–158.

    Google Scholar 

  • ALLEN, T., 1975. Particle size measurement. Chapman and Hall, London.

    Google Scholar 

  • BALE, A.J. and A.W. MORRIS, 1987.In situ measurement of particle size in estuarine waters. Estuar. Coast. Shelf Sci., 24: 253–263.

    Article  CAS  Google Scholar 

  • BARTZ, R., J.R.V. ZANEFELD, I.N. McCAVE, F.R. HESS and A.R.M. NOWELL, 1985. ROST and BEAST: devices forin situ measurement of particle settling velocity. Mar. Geol., 66: 381–395.

    Article  Google Scholar 

  • DYER, K.R., 1989. Sediment processes in estuaries: future research requirements. J. Geophys. Res., 94(C10): 14327–14339.

    Google Scholar 

  • EISMA, D., T. SCHUHMACHER, H. BOEKEL, J. VAN HEERWAARDEN, H. FRANKEN, M. LANN, A. VAARS, F. EIJGENRAAM and J. KALF, 1990. A camera and image analysis system forin situ observation of flocs in natural waters. Neth. J. Sea Res., 27: 43–56.

    Google Scholar 

  • FENNESSY, M.J., K.R. DYER and D.A. HUNTLEY, 1994. INSSEV: an instrument to measure the size and settling velocity of flocsin situ. Mar. Geol., 117: 107–117.

    Article  Google Scholar 

  • GIBBS, R.J., 1983. Coagulation rates of clay minerals and natural sediments. J. Sed. Petrol., 52: 1193–1203.

    Google Scholar 

  • GRAF, W.H., 1971. Hydraulics of sediment transport. MGraw-Hill, New York.

    Google Scholar 

  • HUNTER, K.A. and P.S. LISS, 1982. Organic matter and the surface charge of suspended particles in estuarine waters. Limnol. Oceanogr., 27: 322–335.

    CAS  Google Scholar 

  • KINEKE, G.C., R.W. STERNBERG and R. JOHNSON, 1989. A new instrument for measuring settling velocitiesin situ. Mar. Geol. 90: 149–158.

    Google Scholar 

  • KRANCK, K. and T.G. MILLIGAN, 1992. Characteristics of Suspended Particles at an 11-Hour Anchor Station in San Francisco Bay, California. J. Geophys. Res., 97(C7): 11373–11382.

    Google Scholar 

  • LOVELL, C.J. and C.W. ROSE, 1991. The effects of sediment concentration and tube-diameter on particle settling velocity measured beyond Stokes' range: experiment and theory. J. Sed. Petrol., 61: 583–589.

    Google Scholar 

  • McCABE, J.C., K.R. DYER, D.A. HUNTLEY and A.J. BALE, 1992. The variation of floc sizes within a turbidity maximum at spring and neap tides. Proceedings of 23rd International Conference on Coastal Engineering, Venice, p. 3178–3188.

  • McCAVE, I.N. and T.F. GROSS, 1991.In situ measurement of particle settling velocity in the deep sea. Mar. Geol., 99: 403–411.

    Article  Google Scholar 

  • MEHTA, A.J. and J.W. LOTT, 1987. Sorting of fine sediment during deposition. In Proceedings of Specialty Conference on Advances in Understanding of Coastal Sediment Processes (New Orleans), American Society of Civil Engineers, New York, p. 348–362.

  • OWEN, M.W., 1971. The effect of turbulence on the settling velocity of silt flocs. Proceedings of 14th Congress of International Association for Hydraulics Research, Paris, D4.1–D4.6.

  • PULS, W., H. KUEHL and K. HEYMANN, 1988. Settling Velocity of Mud Flocs: Results of Field Measurements in the Elbe and the Weser Estuary. In: J. Dronkers and W. Van Leussen, Eds., Physical Processes in Estuaries, Springer Verlag, Berlin Heidelberg, p. 404–424.

    Google Scholar 

  • SPINRAD, R.W., R. BARTZ and J.C. KITCHEN, 1989.In Situ Measurements of Marine Particle Settling Velocity and Size Distributions using the Remote Optical Settling Tube. J. Geophys. Res., 94(C1): 931–938.

    Google Scholar 

  • TEN BRINKE, W.B.M., 1993. The Impact of Biological Factors on the Deposition of Fine-grained Sediment in the Oosterschelde (The Netherlands), PhD Thesis, University of Utrecht.

  • UNCLES, R.J. and J.A. STEPHENS, 1993. Nature of the turbidity maximum in the Tamar Estuary, U.K. Estuar. Coast. Shelf Sci., 36: 413–431.

    Google Scholar 

  • VAN LEUSSEN, W., 1988. Aggregation of particles, settling velocity of mud flocs: a review. In: J. Dronkers and W. Van Leussen, Eds. Physical Processes in Estuaries. Springer Verlag, Berlin Heidelberg New York, p. 347–403.

    Google Scholar 

Download references

Author information

Authors and Affiliations


Rights and permissions

Reprints and Permissions

About this article

Cite this article

Fennessy, M.J., Dyer, K.R. & Huntley, D.A. Size and settling velocity distributions of flocs in the Tamar estuary during a tidal cycle. Netherlands Journal of Aquatic Ecology 28, 275–282 (1994).

Download citation

  • Issue Date:

  • DOI:


  • Flocs
  • settling velocity
  • size distribution
  • Tamar Estuary