The Significance of Aggregate Properties to Transport Processes
Aggregates of cohesive suspended particles in estuarial waters are formed by Brownian motion, differential settling, and velocity gradients. Aggregates formed by Brownian motion and differential settling are weak and have low densities, compared to those formed in moderate velocity gradients. The densities and shear strengths of aggregates formed in a range of velocity gradients were measured using a capillary viscometer and a concentric cylinder viscometer. It was found that different aggregate structures could exist over short ranges of velocity gradients, and that the structures stable at lower ranges of velocity gradients had lower shear strengths and lower densities. The structures can be described as aggregates of aggregates, with successively higher orders at successively lower ranges of velocity gradients.
Sediment beds formed from such aggregates have a structure that is one order higher than that of the depositing aggregates. The rate of deposition of suspended aggregates under a given bed shear stress depends on the strength of the bond between the depositing aggregate and the bed. Further, as material accumulates on the bed, the mounting overburden crushes the lower aggregates, depending on their strength, causing increasing bed density and shear strength below its surface. The properties of the depositing aggregates determine the rate of sediment deposition and the rate of increase of resistance to erosion for a short distance below the bed surface.
KeywordsClay Porosity Torque Sludge Sedimentation
Unable to display preview. Download preview PDF.
- 1.Alishahi, M. R., and Krone, R. B., “Suspension of Cohesive Sediment by Wind-Generated Waves,” Hydr. Engr. Lab., U. of Calif., Berkeley, 1964, pp 24.Google Scholar
- 2.Bradley, R. A., and Krone, R. B., “Shearing Effects on the Settling of Activated Sludge,” J. Sanitary Engr. Div., ASCE, 1971, pp 59–79.Google Scholar
- 3.Edzwald, J. K., Upchurch, J. B., and O’Melia, C. R., “Coagulation in Estuaries,” Env. Sci. and Techn. 8 1974, pp 58–63.Google Scholar
- 4.Einstein, A., “A New Determination of Molecular Dimensions,” Annals of Physics 191911, pp 289-306, 34, 1911, pp 591-592.Google Scholar
- 5.Gust, G., “Observation of Turbulent Drag-Reduction in a Diluted Suspension of Clay in Sea Water,” J. Fluid Mech., 75, 1976, pp 29–47.Google Scholar
- 8.Kandiah, A., “Fundamental Aspects of Surface Erosion of Cohesive Soils,” Ph.D. Thesis, U. of California, Davis, 1974, pp 236.Google Scholar
- 10.Kranck, K., “Dynamics and Distribution of Suspended Particulate Matter in the St. Lawrence Estuary,” Naturaliste can 106, 1979, pp 163–173.Google Scholar
- 11.Krone, R. B., “Flume Studies of the Transport of Sediment in Estuarial Shoaling Processes,” Hydr. Engr. Lab. and Sanitary Engr. Lab., U. of Calif., Berkeley, 1962, pp 110.Google Scholar
- 12.Krone, R. B., “A Study of Rheologic Properties of Estuarial Sediments,” Hydr. Engr. Lab. and Sanitary Engr. Res. Lab., U. of Calif., Berkeley, 1963, pp 91.Google Scholar
- 13.Krone, R. B., “A Field Study of Flocculation as a Factor in Estuarial Shoaling Processes,” Tech. Bull 19, Committee on Tidal Hydraulics, Corps of Engineers, U. S. Army, 1972, pp 62 plus App.Google Scholar
- 14.Krone, R. B., “Aggregation of Suspended Particles in Estuaries,” Estuarine Transport Processes, The Belle Baruch Library in Marine Science No. 7, U. South Carolina Press, 1978, pp 177–190.Google Scholar
- 15.McCave, I. N., “Size Spectra and Aggregation of Suspended Particles in the Deep Ocean,” Deep Sea Res. 1984, pp 329–352.Google Scholar
- 16.Mehta, A. J., Parchure, T. M., Dixit, J. G., and Ariathurai, R., “Resuspension Potential of Deposited Cohesive Sediment Beds,” in Estuaring Comparisons, V. S. Kennedy, Ed., Academic Press, New York, NY, 1982, pp 591–609.Google Scholar
- 17.Owen, M. W., “The Effect of Turbulence on the Settling Velocity of Silt Floes,” Proceedings of the Fourteenth Congress of the Int. Ass, for Hydr. Res., Sept., 1971, D4-1 to D4-6.Google Scholar
- 18.Parchure, T. M., “Erosional Behavior of Deposited Cohesive Sediments,” Ph.D. Dissertation, Coastal and Oceanographic Engr. Dept., U. of Florida, 1984.Google Scholar