DREDGING IN ALLUVIAL MUDS

Many rivers, especially the bigger tropical ones, carry large quantities of sediment which are deposited as bars across the outer limits of estuaries. The sediments typically vary from coarse silts to clay particles which are precipitated by flocculation in the salt water wedge, in areas of reduced velocities within the estuaries. To enable shipping to reach ports within the estuary of such a river it is often necessary to realign, deepen and stabilise the natural channel across the bar by means of dredging. However, in soft, silty muds it is difficult to meet the demand for increasing depths and widths of access channels and a correct understanding of the nature and condition of such material is necessary in order to achieve a reliable navigation channel. These problems were encountered in a study of dredging of the navigation channel across the bar at the mouth of the River Chao Phrava with the object of developing methods of improving the approaches to the Port of Bangkok. Considerable quantities of new sediments are deposited annually and existing siltation is re-distributed by storm action in the estuary. Special methods were evolved to obtain informtion on the variation of in situ soil density with depth, using gravity samplers some 2 m in length and a densimeter with a radioactive source. Variations in density depend upon the history of dredging and deposition in the area sampled. The studies showed that the most economic dredging should be considered in terms of the volume of silt removed from within the desired channel profile and not as might have been expected, by obtaining maximum hopper loading from the more consolidated muds and clays. An optimum relationship between in situ density, hopper density of spoil and length of dredging cycle time was evolved. The conclusion is drawn that, with such a major task of maintenance dredging in fresh alluvial muds, there was a need for a total system specifically designed for the particular channel. Factors to be considered in relation to the spoil to be handled are derived in the paper.

  • Supplemental Notes:
    • Paper E-1 from BHRA Fluid Engineering Symposium, University of Kent, Canterbury, England.
  • Corporate Authors:

    British Hydromechanics Research Association

    Cranfield MK43 0AJ, Bedfordshire,   England 
  • Authors:
    • SUMMERS, L
  • Publication Date: 1975-9

Subject/Index Terms

Filing Info

  • Accession Number: 00128412
  • Record Type: Publication
  • Source Agency: British Hydrodynamics Research Association
  • Files: TRIS
  • Created Date: Jan 14 1976 12:00AM