Flow Sediment Transport Research Articles

Overland Flow and Sediment Transport Simulation on Small Plots

ABSTRACT Amathematical model, OFESSD (Overland Flow, Erosion, Sediment Routing and Surface Degradation), was developed to simulate overland flow and sediment delivery and to predict soil surface geometry changes due to erosion on small fallow soil plots. Overland flow was simulated using a dynamic form of the Saint-Venant equations with a modified version of Holtan's infiltration equation and with flow resistance characterized by Manning's equation. Two dynamic conservation of mass equations were used to simulate sediment routing and soil surface degradation. Erosion was computed using Foster's rill and interrill erosion relationships. Yalin's equation was used to compute flow sediment transport. The model did well in simulating overland flow and sediment delivery. Soil surface geometry changes were better predicted after drainage patterns were estabHshed than during their establishment. The model showed potential for use as a prediction tool, with further development

Sediment Transport in Shallow Flows

The sediment transport problem in shallow flows, such as furrow flows, in the upper flow regime is formulated based upon continuum mechanics principles. Considering the dynamics of the water flow as well as the dynamics of sediment flow, a mathematical expression which is a modification of the classical stability criterion of flow over a fixed bed is obtained for the case when a movable sediment layer is present near the bed of the channel. Coincident with this stability criterion, the amount of sediment being moved is defined as the transport capacity of the flow. The results suggest the dependence of the capacity on the sediment properties, active layer thickness, channel gradient and the hydraulic properties of the flow. Comparison of the theoretical results with experimental data revealed a general agreement. In particular, the theory predicted satisfactorily the transport capacity in models of steep croprow furrows.

A depth-integrated model for suspended sediment transport

A model for suspended sediment transport in unsteady and non-uniform flow is derived, in which the vertical dimension is eliminated by means of an asymptotic solution. The resulting depth-integrated model is tested for unidirectional flow cases. Also, an application is given to the siltation of a dredged channel.

A NEW OSCILLATORY FLOW TUNNEL FOR USE IN SEDIMENT TRANSPORT EXPERIMENTS

The details of a new oscillatory flow tunnel at Scripps Institution of Oceanography are discussed. The flow tunnel has a large crosssection and large water excursion distance. The piston motion is programmable. The test bed can be tilted. These, and other aspects, make the facility useful to a wide variety of oscillatory flow sediment transport experiments.

Sediment Transport in Stratified Turbulent Flow

A mathematical model of sediment laden, density affected turbulent flows is presented. The finite element technique is used in conjunction with the Newton iterative method to solve the resulting partial differential equations. The model satisfactorily predicts velocity and concentration profiles for unidirectional open channel flows. It is concluded that the model can justifiably be extended to multidimensional flows.

Movable bed roughness in unsteady oscillatory flow

A model to predict the roughness in unsteady oscillatory flows over movable, noncohesive beds is presented. The roughness over movable beds is shown to be a function of the boundary shear stress, rather than a fixed geometrical scale as is the case for fully rough turbulent boundary shear flows over immobile beds. The model partitions the roughness into two distinct contributions. These two contributions are due to the form drag around individual bed forms and to the near‐bed sediment transport. The form drag over the bed forms is treated explicitly as a function of the boundary geometry and shear stress. The ripples are predicted as a function of the local skin friction, and a semiempirical expression is derived using standard law‐of‐the‐wall arguments, which gives the ripple or form roughness as a function of the boundary geometry. The ripple roughness is found to be proportional to the product of the ripple steepness and height. Favorable comparison of the form drag model with the results of Bagnold's (1946) fixed ripple study is found. The value of z0 associated with intense sediment transport in oscillatory flow over a flat bed is determined from Carstens et al.'s (1969) experiments. This value is found to be 7 or 8 grain diameters. An expression is derived for the roughness associated with the maximum thickness of a near‐bottom sediment‐transporting layer consistent with Owen's (1964) roughness hypothesis for saltation of uniform grains in air. At large values of the boundary shear stress relative to the critical value for initial sediment motion, the derived expression is similar to the results of Smith and McLean's (1977) unidirectional flow approach modified for oscillatory flow. The total roughness model is found to compare favorably with Carstens et al.'s (1969) data. In contrast to Smith and McLean's (1977) steady flow findings, the results here show that when ripples are present, they account for a significant portion of the boundary roughness.

Hydraulic Interpretation of Grain-size Distributions Using a Physical Model for Bedload Transport

ABSTRACT Grain-size distributions of bedload sediment are modelled by considering the time variation of sediment transport in a unidirectional turbulent flow. A frequency distribution of instantaneous bed shear stress is divided into a large number of shear stress ranges with mean values of oi. Each oi is capable of transporting a range of sediment sizes as bedload; the maximum size is just at its entrainment threshold, the minimum size is just too large to be suspended. Rates of bedload transport are calculated for each size range using a theoretical bedload function, and the proportion of time that these rates occur is obtained by integrating the frequency distribut on between the boundaries of each shear stress range. The relative weights of sediment transported in particular size ranges, determined for all oi values, constitutes the grain-size distribution obtained from bedload sampling at a fixed point on the bed. Cumulative grain-size curves have been simulated using the model in order to demonstrate the effects of the various model parameters (e.g., mean bed shear stress, viscosity). All curves show a distinct break in slope, which represents the maximum grain size transportable in suspension when the shear stress attains its maximum fluctuating value. Examination of many natural bedload distributions shows close qualitative and quantitative agreement with the model, and reasons for discrepancies can be fully explained. Typical grain-size distributions of deposited sediments can be obtained by mixing of different flow-related bedload distributions in various proportions. Thus although deposited sediments may primarily result from bedload transport during a steady flood flow, flow unsteadiness also plays a part. The effects of some deposition directly from suspended load can also be surmised.

Test of scale modelling of sediment transport in steady unidirectional flow

AbstractIn two steady uniform flows at different physical scales in a small open channel, with variables characterizing flow, sediment, and fluid adjusted for dynamic similitude by means of four dimensionless modelling parameters (a Reynolds number, a Froude number, a density ratio, and a length ratio), measured frequency distributions of height, spacing, and migration rate of current ripples were almost identical when scaled, thus verifying that exact Reynolds‐Froude modelling of loose‐sediment transport is valid and workable. Modelling should be valid as well for a wide range of other transport conditions in the same kind of flow, because no additional kinds of forces or effects would be present in transport of loose grains in modes other than as ripples. In scaled‐down modelling, a scale ratio of 2.5 is attainable without recourse to exotic fluids by use of water at 85°C to model natural flows at 10°C.

SEDIMENT TRANSPORT BY WAVE ACTION

This paper summarizes the results of a continuing study at the hydraulic laboratory at the University of California at Berkeley on this subject, which is supported by the Coastal Engineering Research Center (CERC) and which has resulted over the years in the Theses of Huon ti (1954), M. Manohar (1955), G. Kalkanis (1957, 1963), M. M. Abou-Seida (1965), M. M. Das (1968) and is at this time being continued by T. C. Mac Donald. All these researchers have greatly contributed to the success of this work while the author was mostly responsible for the continuity of the study. The aim of the study was to see if it is possible to establish for the description and prediction of sediment transport by waves a general system of approach similar to that which the author published in 1950 under the title '.'The Bed-Load Function for Sediment Transport in Open Channel Flows". ( It was hoped at the time that many of the basic steps of such a description may at least be similar to those used for uni-directional flow. It became apparent that such similarities of approach were quite feasible; but another difficulty became apparent from the beginning. While in the uni-directional flow many details of the flow, such as velocity distributions, boundary layers and turbulence had been, studied and described previously, such knowledge was almost entirely lacking for wave motion. The first part of the study consisted entirely of hydraulic measurements and of their analysis. In order to determine the necessary scope of such hydraulic studies, the analogy with sediment transport in uni-directional flow was used. Some of the principles governing uni-directional flow transport are: 1. Sediment motion can be divided into bed-load motion or surface creep and suspension. 2. While moving as bed load, the particle weight is to a large part transmitted directly to the nonmoving bed, not to the flow. 3. The rate of bed-load motion is defined by the equilibrium exchange of sediment between the bed-load and the nonmoving bed. 4. This equilibrium gives a direct relationship between the sediment rate and the flow conditions near the bed, including the turbulence. 5. The flow condition near the bed can be predicted for a uni-directional boundary layer as a function of the bed shear and the bed roughness, only.

Discussion of “Sediment Transport in Supercritical Flow”

Discussion of “Sediment Transport in Supercritical Flow”

Sediment Transport in Supercritical Flow

A study is made of the transition between flow of a solids-fluid mixture in the fully suspended regime and flow with a sediment bed. It is shown that the critical deposit condition is a function of solids concentration, Reynolds number, Froude number, and geometry of flow. A dimensional analysis is tested by experimental data. Sand-water mixtures were studied in supercritical flow in a small laboratory flume.