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

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

Harbor Surging

[no abstract

A Study of Turbulence and Diffusion Using Tracers in a Water Tunnel

A study of turbulence in a water tunnel was made by observing the motion of small liquid droplets having the same density as water. These tracers were injected into the flow and their trajectories were photographed with a fixed camera using a stroboscopic light. From measurements of the photographic plates it was possible to calculate instantaneous velocities, turbulence intensities and Lagrangian correlation coefficients. Runs were made both with and without a turbulence-producing grid; three geometrically similar grids were used. From 11 to 35 separate trajectories were measured for each run. Each point value of the turbulence characteristics is an ensemble average. The biggest limitation on the practical application of this method is the inevitable sampling error in the calculated intensities and correlations. These errors were large, even when 35 trajectories were measured; they can be reduced only by greatly increasing the number of trajectories analyzed. A satisfactory experimental technique for photographing and measuring the trajectories of the tracers was developed, but the computations are still very laborious. The results of the study showed that a large fraction of the turbulent energy of the field may be attributed to substantial differences between the mean velocities of different tracers over the 3-ft observation reach. The decay of turbulence energy with distance showed a linear relation between the reciprocal of the energy and the distance, as has been previously found, but a strong Reynolds number effect was observed. The correlation curves indicated that the time scale was fairly large, and it appeared that practically all the energy was associated with relatively low frequencies. Unfortunately, the data were not extensive enough to permit calculation of the diffusion coefficients from the Lagrangian correlations in accordance with Taylor's theory

Lecture notes on sediment transportation and channel stability

These notes have been prepared for a series of lectures on sediment transportation and channel stability given by the authors to a group of engineers and geologists of the U. S. Department of Agriculture assembled at Caltech on September 12-16,1960. The material herein is not intended to serve as a complete textbook, because it covers only subjects of the one-week sequence of lectures Due to limitation of space and time, coverage of many subjects is brief and others are omitted altogether. At the end of each chapter the reader will find a selected list of references for more detailed study

Evaluation of the utility of sediment data in NASQAN (National Stream Quality Accounting Network)

Monthly suspended sediment discharge measurements, made by the USGS as part of the National Stream Quality Accounting Network (NASQAN), are analysed to assess the adequacy in terms of spatial coverage, temporal sampling frequency, accuracy of measurements, as well as in determining the sediment yield in the nation's rivers. It is concluded that the spatial distribution of NASQAN stations is reasonable but necessarily judgemental. The temporal variations of sediment data contain much higher frequencies than monthly. Sampling error is found to be minor when compared with other causes of data scatter which can be substantial. The usefulness of the monthly measurements of sediment transport is enhanced when combined with the daily measurements of water discharge. Increasing the sampling frequency moderately would not materially improve the accuracy of sediment yield determinations

Progress Report on Dynamics of Particulate Matter in Fluid Suspensions

This report describes work performed during the period from August 1, 1949 to November, 1950. When the project was started, it was financed for one year with the intention of continuing it for a second year, and the program was planned accordingly. However, after about three months of operation, it became necessary for reasons of economy to reconsider the original plans, with the result that the funds for the first year's operation were reduced and plans for continuing the work beyond the first year were dropped. In the early summer of 1950, the U. S. Air Force indicated its interest in sponsoring the work. In view of this prospect, the Office of Naval Research (ONR) allotted funds for an additional three-months' period to allow time for working out the necessary contractual arrangements with the Air Force for continuing the work. These arrangements were worked out and the studies were continued under contract with the Office of Air Research, starting November 1, 1950

The high speed water tunnel at the California Institute of Technology

The high speed water tunnel was established at the California Institute of Technology to study the forces acting upon moving bodies immersed in a fluid. The working section of the tunnel is 14 inches in diameter and 6 feet long and velocities up to 72 feet per second are obtained in it. The model to be tested is mounted on the spindle of a three component balance which measures the drag force, the yaw or lateral force and the moment about the spindle support. The angle of inclination of the model to the flow direction can be adjusted easily. From these measurements are determined the magnitude and location of the resultant forces acting on the model. In order to study cavitation, the pressure in the tunnel is made adjustable and a transparent working section is provided for visual and photographic observations. For qualitative assistance in interpreting the results of the tunnel studies in terms of the effects of the body shapes on the flow pattern, an auxiliary flume is available. The flow is made visible by use of a new technique employing polarized light