Sediment Transport Phenomena Research Articles

Unsteady flow sediment transport in a sewer model

To initiate a fundamental understanding of the complex nature of unsteady sediment transport phenomena, laboratory experiments for two types of non-cohesive material are presented. These experiments were performed in a test fiume with semi-circular cross-section. Friction velocity for the transient regime is obtained using the equations of de Saint-Venant, which are rearranged using the kinematic flow principle. Inertia of bed load material and material in suspension causes a time and forme discrepancy between the unsteady friction velocity and transport. Hence the friction velocity obtained with a steady state formula is chosen as basic parameter to setup an instantaneous relationsbip with transport. A correction for the time lag is clearly a fonction of the unsteady character of the flow.

In situ characteristics of suspended particles as determined by the floc camera assembly FCA

The Floc Camera Assembly, or FCA, provides for the in situ size, shape, concentration and settling velocity of marine particles. Through use of floc-attribute theory, FCA data also provide approximations of the in situ excess-density, porosity and mass of flocs, their population characteristics, and aggregation and sedimentation rate. Image analysis using photoCD transfer routines and recently developed image-analysis techniques make possible daily interpretation of hundreds of digital FCA images. FCA studies have demonstrated a wide variety of suspended sediment characteristics and transport phenomena. The character of marine snow is found to vary at a variety of time-scales: near-instantaneous, daily and seasonally. For example a floc's excess density also varies with floc size, but the relationship for flocs within a coastal water mass may change daily. In mid-latitude coastal basins, small flocs form when primary production is low and river input is high; conversely large flocs form when river input is very low. In Antarctic ice margins, flocculation fronts are identified beneath cold water tongues emanating out from glacier margins. In Greenland, an intermediate nephloid layer is identified, filled with large flocs formed from sediment released from melting icebergs. In the Gulf of St. Lawrence, boundary-layer turbulence near the seafloor is shown to break up flocs after their long descent through the water column and create a 50 m thick bottom turbid zone.

Sediment transport modelling in combined sewer

The classical solid transport theory has been used to analyse the experimental results obtained from the No. 13 combined sewer trunk of Marseille for more than two years. This study demonstrates that the sediment transport phenomena in a combined sewer trunk are nothing other than the classical ones. A numerical model has been established according to the analyses. Based on a permanent flow regime, this model considers not only the effects of the real channel geometry, non-uniform particles size, but also the coexistence of mineral and organically materials. Some particular sediment transport phenomena such as the armouring of bed have also been taken into account. It also shows that although the influence of the suspension particles is not necessarily considered, the simulation including the variations of particle density with each granular fraction may be improved.

Sediment transport modelling in combined sewer

The classical solid transport theory has been used to analyse the experimental results obtained from the No.13 combined sewer trunk of Marseille for more than two years. This study demonstrates that the sediment transport phenomena in a combined sewer trunk are nothing other than the classical ones. A numerical model has been established according to the analyses. Based on a permanent flow regime, this model considers not only the effects of the real channel geometry, non-uniform particles size, but also the coexistence of mineral and organically materials. Some particular sediment transport phenomena such as the armouring of bed have also been taken into account. It also shows that although the influence of the suspension particles is not necessarily considered, the simulation including the variations of particle density with each granular fraction may be improved.

Development of a New Simulation Method for Suspended Sediment Transport in a Tidal River

A one dimensional simulation model of suspended sediment transport in a tidal river was developed with erosion, deposition, and thickening processes of sediments, and inflow from tributaries. This model uses the explicit leapfrog method and its lower end boundary of the river is extended into the sea to close the boundary for calculation. Laboratory experiments were performed to determine erosional and depositional rates of sediments and to study the sediment thickening process in the river under various concentrations of chlorinity and suspended solids. Numerical simulation results with the parameter values obtained experimentally did not show good agreement with observed data. Modifying the parameter values according to physical phenomena was necessary to obtain good agreement in between. After the modification, computation results during a fortnightly cycle explain satisfactorily the sediment transport phenomena in this river.

Observations on fine sediment transport phenomena in turbid coastal environments : Parker, W.R., 1987. Continent. Shelf Res., 7(11–12):1285–1293

Observations on fine sediment transport phenomena in turbid coastal environments : Parker, W.R., 1987. Continent. Shelf Res., 7(11–12):1285–1293

Observations on fine sediment transport phenomena in turbid coastal environments

The fine sediment population in turbid coastal environments has been shown to exist within a dynamic framework of processes and inter-related phenomena. Measurements using new technology have brought a changing perspective, highlighting unsteady behaviour and the importance of the cohesive boundary—a time-dependent transition between moving fluid and stationary bed. Discrepancies between various techniques for describing the properties and behaviour of the cohesive boundary become clear when the purpose of the description is considered. Although transport processes are described in purely physical terms, the impact of biological processes is now widely recognized though substantially unquantified. Non-intrusive measurement techniques offer a route to more realistic quantification of the fine sediment transport phenomena in these environments.

The downstream gradation of particle sizes in the Squamish river, British Columbia

AbstractThe exponential downstream decline in particle size predicted by Sternberg (1875) is examined within a highly active alpine fluvial environment, the gravel‐bed Squamish River in southwestern British Columbia. Transect survey procedures for sampling within the coarse alluvial gravels are described in detail. Downstream trends for various particle size statistics, plotted with distance from a major sediment source, are considered according to two scenarios. Evaluation of overall trends indicates that the downstream expression derived by Sternberg (1875) is not the most appropriate; rather, curves are better described by power functions. This reflects a very rapid decline in particle size immediately downstream of the major sediment source. Secondly, evaluation of downstream trends in relation to channel planform determines that exponential functions with different coefficients describe adequately relations within individual planform reaches. There is insufficient evidence to suggest which of these two scenarios may be appropriate. Several lines of evidence suggest that the trends found are more the result of selective sediment transport phenomena than of abrasion, a condition attributed to channel competence within a system dominated by sediment‐supply conditions.

Numerical movable-bed models for practical engineering

Numerical modelling of sediment transport phenomena is an ambitious aim, which can only be attained in the long term by first formulating simplified models. On the basis of practical experience, these may be subsequently refined to give better results. This paper describes some simplifications of the full set of governing equations associated with sedimentation processes under time-dependent flow conditions, such as those in tidal rivers. A numerical movable-bed model is presented which, although economical in its computer requirements, nevertheless simulates some of the complex three-dimensional physical effects. Results from practical applications are given and compared with both laboratory experiments and field investigations.

Some observations on a two-dimensional model of bed-load transport based on the moving layer equation

As many hydraulic problems involving numerous independent physical variables the sediment transport phenomena are generally analysed by means of empirical formulas, that are based on dimensional analysis and experimental data fitting. A schematic mechanical moving-layer model is proposed in order to derive more informations about the local behaviour of the grains movement. Although the resulting mathematical problem seems arduous to integrate in a general way, its characteristics are analysed and the results are compared with its physical behaviour.

Underwater time-lapse motion picture systems

Application of underwater time-lapse motion picture cameras to the study of sediment transport phenomena provides an economical and quantitative tool for the investigation of sea floor processes. Two camera systems are described, one can be operated on the ocean bottom from a pier, boat or float and the second is completely self-contained, self-powered and divorced from surface support. Time-lapse photography was used to determine growth rates of scour pit development, migration of organisms, ripple crest advance and sediment dispersal patterns. Sea floor modification over several tidal cycles also was monitored with the self-contained unit for 47 hours of continuous activity.

Flume Experiments Of Sediment TransportIn Unsteady Flow

Adapted equipment of a test flume with semi-circular cross-section controls and measures flow and friction characteristics during the transient regime. A series of sediment transport measurements under unsteady flow conditions is performed for two types of non-cohesive material. Due to the inertia of the bed material, there's no agreement on form or time appearance between the unsteady friction velocity and the bedload transport. On the other hand an instantaneous relation between bedload transport and the friction velocity calculated with a steady state formula is revealed. The suspended material has obviously less inertia. Nevertheless suspension transport is also put proportional to the steady part of the friction velocity. A time shift, increasing with the unsteady character of the flow, appears between suspension transport and the steady part of the friction velocity. As a result, these experiments indicate the complex nature of unsteady sediment transport phenomena and initiate a fundamental understanding of these complex processes. Transactions on Engineering Sciences vol 18, © 1998 WIT Press, www.witpress.com, ISSN 1743-3533

Some Fundamental Particularities On PartlyCohesive Sediment Transport In A Circular TestFlume

The complex sediment transport phenomena in narrow sewer pipes are studied in a physical scale model. Since sewer deposits contain not only sand but also cohesive mud particles, the partly cohesive material will act differently than the traditional non-cohesive sediments. In recent literature, only a few studies on partly cohesive sediments have been presented. Therefore, a fundamental investigation on the erosional behaviour is set up. The major aim of the experiments is to point out essential similarities and differences in the particular behaviour of these sediments in a circular cross-section, in relation to the wellestablished non-cohesive sediment transport approach.

Recirculation and Sand-Feed Type Flume Experiments

Two types of open-channel laboratory flumes (recirculating and sand feed) are used to simulate the hydraulic and sediment transport phenomena which occur in natural sand-bed streams. A 20-cm wide by 10-m long flume which could be operated either as a feed system or as a recirculation system was used to compare the two systems with respect to the hydraulic and sediment transport conditions prevailing at equilibrium for bed configurations from ripples through antidunes. For equilibrium flow with an approximately uniform sand, no significant differences were found between the two systems. In addition to this quantitative study, some qualitative observations were made of the responses of both systems to induced non-equilibrium conditions. It was found that any change which produced a change in the sediment transport rate resulted in new equilibrium conditions for both systems. For the feed system, however, changes other than to the feed rate resulted in the system returning to the conditions prevailing before the change.

An Application of the Theory of Sediment Transport by Turbidity Currents to the Dredging of Navigable Channels

ABSTRACT By inducing artificial turbidity currents to transport the sediments of obstructing bars into deeper water, the natural phenomenon of sediment transport by turbidity currents may be applied to the dredging of navigable channels. The method may be used provided that sufficient slope is present to allow removal of the sediment by currents, that the sediments are of a type which can form turbidity flows, and that equipment is available for mixing the sediment and water. No accurate cost analysis is presently available.