A Summary of Sediment Transportation Mechanics

The development of the mechanics of transportation of sediment by fluids has been carried on mainly in connection with the control and development of streams where its greatest economic importance lies. The difficulties of controlling rivers are concerned largely with such matters as the ability of the flow to erode the banks and bed or the possibility of aggradation due to insufficient transporting capacity. Thus, stream control problems are to a great extent problems in sediment transportation. Although sediment transportation is closely identified with streams, its application is by no means limited to this field. It is of importance in many industrial processes where solids are transported by liquids or gases or where solids need to be mixed and/or separated from fluids, and in the important field of transportation of soil by wind. In this paper a brief outline will be given of the mechanics underlying this subject. No attempt will be made to discuss the many important practical problems which provided the incentive for developing this special branch of fluid mechanics

Laboratory studies of the roughness and suspended load of alluvial streams

This report describes research work done under Contract No. DA-25-075-eng-3866 with the U. S. Army, Corps of Engineers, Missouri River Division, Omaha, during the period 1954-1957, on problems of suspended load transport in alluvial streams. A total of 94 experimental runs were made in two laboratory flumes charged with fine sand of several size distributions. Special attention was given to the variation of the friction factor caused by the changing bed configuration and the damping effect of suspended sediment. The relationship between the sediment transportation rate and the hydraulic variables was also investigated. Most of the runs (General Studies, Chap. V) were made with the bed of the flume completely covered with loose sand but some special runs (Special Studies, Chap. VII) were made with the sand bed chemically solidified in place to prevent sediment transport while preserving the bed configuration previously generated by a natural flow of the same velocity with loose sand. The principal laboratory results are as follows: 1. The friction factor f for a stream with a movable sand bed may vary several fold, being highest at low or medium flow velocities and lowest at high velocity. 2. The principal cause of the variation in f is the appearance of dunes at low or medium velocities and disappearance at high velocities. 3. A secondary cause for the reduction in f for high sediment transport rates is the damping effect of the suspended sediment on the turbulence, and the concomitant reduction in the turbulent diffusion coefficients. The maximum observed reduction due directly to the sediment load was only about 28 percent. 4. The discharge and sediment transportation rate are not unique functions of depth and slope because of the variable roughness. Slope (or shear) must probably be considered a dependent variable for alluvial streams because several equilibrium flows can yield the same slope and shear stress. The laboratory data are compared with similar data for natural streams, and the most promising existing analyses for roughness and sediment load are discussed in the light of the present findings. In addition, a critical review of early and recent literature on the resistance of sediment-laden streams is presented in Chapter II

Sediment studies in the Brazilian Amazon River Basin

The work was to be carried out as part of WMO's participation in the United Nations Development Project (UNDP) on Hydrology and Climatology of the Brazilian Amazon River Basin under the direction of Eduardo Basso, Project Manager. This project is carried out in cooperation with The General Directorate for Amazon Development of the Brazilian Government (SUDAM)

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

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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

Baffle Type Energy Dissipator for Pipe Outlets

The baffle type energy dissipator described in this paper was developed through laboratory experimentation for use in soil conservation work. It is designed to reduce the energy in high velocity pipe flow so that the water may be discharged safely into an erodible channel. This structure can be adapted to meet the many field conditions encountered in erosion control work in agriculture and elsewhere, such as at pipe outlets draining terraces or ditches, highway culverts, and drop inlet spillway outlets. Pipe sizes commonly used in such applications range from 10 to 48 in in diameter and have flows from 10 to 250 cfs discharging into channels of various widths

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