Motion of single particles in sand channels
Date
1969-06
Authors
Grigg, Neil S., author
U.S. Geological Survey, Water Resources Division, publisher
Journal Title
Journal ISSN
Volume Title
Abstract
The motion of single particles over ripple and dune beds was investigated in a laboratory flume. Statistical properties of the step lengths, rest periods and bed profiles were calculated and analyzed. Seven different runs were made to detect the variation of particle motion with hydraulic conditions. Two bed material sizes were used. The investigation was made possible through the use or single high-activity radioactive particles. Medical tracer particles with specific gravity of approximately 2.65 were used. Median diameters were approximately 0.33 and 0.45 mm. In general, the tracers proved quite satisfactory for studies of this type. The measurement of the statistical properties of particle motion made possible the evaluation of a general two-dimensional stochastic dispersion model developed by Sayre and Conover (1967). It was found that the model predicted well the mean velocity of the centroid of a group of particles but under predicted the rate of spreading of their concentration distribution. Other observations suggested that the assumptions made in the development of the model are too restrictive. The particle step lengths followed the gamma distribution and the rest periods followed the exponential distribution. Parameters of the distributions related to flow conditions in a predictable manner. The distribution of bed form lengths followed a gamma distribution indicati.ng a relation between step length and bed form length. The relation is most evident in the dune range. Good correlations between particle motion, hydraulic conditions and bed properties give promise that bed-load movement can be predicted either from a knowledge of hydraulic conditions or the statistical properties of the sand waves. The probability distribution for elevations of deposition is investigated through an equation relating conditional and unconditional rest periods. These investigations, along with other observations made during the tests, suggest that most deposition and erosion occurs below the mean bed elevation. Some inferences are made from this deduction about the detailed processes of sediment transport and bed form migration. The results of the study show that previously developed simple models may, not be adequate to fully describe particle motion. The experimental techniques developed can be used to study further the mechanism .of particle motion to define in a more general fashion the relations between sediment motion, sediment properties and hydraulic conditions.
Description
CER68-69NSG-42.
Open-file report.
Includes bibliographical references (pages 127-130).
June 1969.
Open-file report.
Includes bibliographical references (pages 127-130).
June 1969.
Rights Access
Subject
Particles
Sand waves