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Measurements of critical shear stress for entraining fine sediments in a boundary layer

Vanoni, Vito A. (1964) Measurements of critical shear stress for entraining fine sediments in a boundary layer. W. M. Keck Laboratory of Hydraulics and Water Resources Report, 7. California Institute of Technology , Pasadena, CA. (Unpublished)

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Experiments were made in a flume 15-3/8 in. wide by 12 ft long to determine the shear stress for critical motion of fine sediment in a growing boundary layer. Determinations were made for two sediments, a quartz sand with geometric mean sieve size of 0. 102 mm and glass beads with geometric mean sedimentation diameter of 0. 037 mm. The intensity of sediment motion was judged from the frequency of bursts of motion over a small area varying from 7 to 18 mm in diameter. When the burst frequency fell between 1/3 and 1 burst per second, critical conditions for inception of motion were considered to obtain. Values of shear velocity, u_*, and bed shear stress, τ_0, for turbulent flow were determined from measured velocity profile data by essentially two methods. In the first the slope, N, of a straight line fitted to a semilogarithmic graph of velocity profile data was used in Eq. (8) to obtain u_*. In the other, values of point velocity, u, at a distance of .03 ft from the bed was substituted into the logarithmic equation for velocity distribution at a smooth wall, Eq. ( 5 ) , to obtain u_*. The data obtained from Eq. (8) and plotted on Fig. 14a show wider scatter than those calculated from Eq. (5) and plotted on Fig. 14b. The data obtained by means of Eq. (5) are considered the more reliable and are presented on a complete Shields diagram in Fig. 15.

Item Type:Report or Paper (Technical Report)
Additional Information:© 1964 W. M. Keck Laboratory of Hydraulics and Water Resources. California Institute of Technology. The main experiments reported herein were made by Antonio Bacalso, Assistant Research Engineer. Some of the preliminary experiments and the development of techniques used subsequently were carried out by Robert C. Y. Koh, Graduate Research Assistant. Arthur N. Schmitt, Research Technician, was responsible for designing and developing much of the special apparatus used, and assisted in carrying out some of the experiments. The construction and maintenance of the flume and other apparatus was carried out by Elton Daly, Laboratory and Shop Supervisor, and Robert Greenway, Laboratory Mechanic. The project was supported by U. S. Public Health Service Grant RG-69 15.
Group:W. M. Keck Laboratory of Hydraulics and Water Resources
Funding AgencyGrant Number
U.S. Public Health Service (USPHS)RG-69 15
Series Name:W. M. Keck Laboratory of Hydraulics and Water Resources Report
Issue or Number:7
Record Number:CaltechKHR:KH-R-7
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Usage Policy:You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format.
ID Code:25978
Deposited By: Imported from CaltechKHR
Deposited On:04 Jun 2004
Last Modified:03 Oct 2019 03:10

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