Geography
Sediment Transport
Sediment transport refers to the movement of particles, such as sand, silt, and clay, by natural agents like water, wind, and ice. This process plays a crucial role in shaping the Earth's surface, as it contributes to the formation of landforms like beaches, riverbeds, and deltas. Understanding sediment transport is important for managing coastal erosion, river channel stability, and sedimentation in reservoirs.
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10 Key excerpts on "Sediment Transport"
eBook - PDFRiver Dynamics
Geomorphology to Support Management
- Bruce L. Rhoads(Author)
- 2020(Publication Date)
- Cambridge University Press(Publisher)
C H A P T E R 5 Sediment Transport Dynamics in Rivers 5.1 Why Is Sediment Transport Important in River Dynamics? The movement of sediment within rivers is the funda- mental process linking the form of river systems to the dynamics of flow. In alluvial rivers, channels are carved into material transported and deposited by the river. This accumulated sediment is referred to as the floodplain (see Chapter 14). Together, erosion and deposition, processes directly related to Sediment Transport, shape the form of alluvial river channels and floodplains. In bedrock rivers, transported sediment plays an instrumental role in abrad- ing the bed of the channel, contributing to erosion and channel change over time (Sklar and Dietrich, 2004, 2012; Lamb et al., 2008b). Given the vital link between Sediment Transport and river morphodynamics, attainment of an in-depth under- standing of the processes by which sediment moves in rivers has become a goal of paramount importance in fluvial geomorphology. A voluminous body of research has emerged on this topic over the past several decades. In some respects, the search for answers has led river scientists down a rabbit hole, where the complexity of the problem seems to grow under increasingly intense scrutiny. Sediment Transport in rivers is complicated, and ready solutions to this knotty problem have not been forthcoming. Nevertheless, a wide range of useful concepts and models have been developed through attempts to better understand how rivers transport sediment. These concepts and models provide a foundation for ongoing scientific inquiry. 5.2 What Types of Material Flux Occur in Rivers? The material flux of rivers consists of dissolved and solid loads. Chemical weathering of rock and soil produces solutes that are carried into rivers by surface runoff (over- land flow), by flow of water through soil (throughflow), and by groundwater flow. This dissolved load contributes substantially to the material flux of rivers (Table 3.1).
eBook - PDFHandbook of Environmental Fluid Dynamics, Volume One
Overview and Fundamentals
- Harindra Joseph Fernando(Author)
- 2012(Publication Date)
- CRC Press(Publisher)
453 34.1 Introduction Transport.of.solid.particles.by.flowing.water.comprises.a.wide. range. of. transport. phenomena. from. coal. transport. in. pipes. (slurry.flow).to.transport.of.mud,.clay,.sand,.or.big.blocks.in.the. fluvial.and.marine.environment . The.gradients.in.the.sediment.transport.govern.the.morpho-logical.changes.(erosion.and.deposition).in.rivers,.estuaries,.and. coastlines. In.the. fluvial environment ,.sediment.transport.is.important. for.the.sedimentation.in.reservoirs.behind.dams,.for.evolution. of. plan. form. movement. of. rivers. caused. by. bank. erosion,. for. changes.in.the.bed.levels.of.rivers,.for.scour.development.around. river.structures,.and.it.is.also.important.for.the.habitat.environ-ment.in.natural.rivers . In.the. estuarine and coastal environment ,.the.sediment.trans-port. pattern. becomes. more. complex. than. in. the. fluvial. envi-ronment.due.to.the.presence.of.tides.and.waves . .Determination. of.these.patterns.is.necessary.to.evaluate.coastal.behavior.like. coastal.erosion.and.the.functioning.of.coastal.structures . .Also. an.evaluation.of.the.need.for.dredging.of.trapped.sediment.in. navigation.channels.requires.a.complete.picture.of.the.sediment. transport.pattern . Sediment.can.also.be.transported.by.blowing.wind,.Aeolian. transport. . This. is. of. relevance. regarding. desertification,. but. wind-blown. transport. is. also. important. in. other. contexts. like. the.further.transport.of.sand.from.a.beach.to.the.hinterland . 34.2 Basic Principles of Sediment Transport 34.2.1 Sediment Properties Transport.of.sediment.depends.on.the.properties.of.the.sediment. as. well. as. the. property. of. the. transporting. fluid . . This. chapter. mainly.treats.the.case.where.the.transporting.medium.is.water . 34.2.1.1 Cohesive versus Noncohesive The. most. important. feature. regarding. sediment. transport. description.is.whether.the.sediment.is.cohesive.or.noncohesive . . Cohesive. sediment. is. mainly. in. the. clay-silt.
eBook - PDFCoastal Processes
Concepts in Coastal Engineering and Their Applications to Multifarious Environments
- Tomoya Shibayama(Author)
- 2008(Publication Date)
- WSPC(Publisher)
143 Chapter 10 Coastal Sediment Transport There are two major problems that originate from coastal processes. The first one is erosion and the other is deposition. Erosion occurs when high waves attack shorelines during stormy or monsoon conditions. Deposition, on the other hand, is a problem encountered when waterways or inner port areas are infilled by moving sediments. In this second case it would therefore be necessary for the waterway to be maintained after the construction of the port in order for vessels to continue to use it. Huge amount of dredging is sometimes required each year to maintain water way facilities and port capacities. An understanding of Sediment Transport mechanism is, therefore, imperative to solve these two problems. In this chapter, a discussion will be made on two different types of bed materials: sand and mud. Since the transport mechanisms of these materials are distinctly different from each other they shall hence be discussed in separate sections. 10.1 Sand Transport 10.1.1 General description In our study of Sediment Transport, it is very important to consider the variation changes of coastal lines. To calculate the beach profile change, we will employ the conservation equation for sediment mass which is: (See definition sketch of Fig. 10.1) 1 (1 ) y x q h q t x y ∂ ∂ ∂ =− + ∂ −Λ ∂ ∂ (10.1) Coastal Processes 144 where h : water depth, t : time, : Λ porosity and q x , q y : components of time-averaged Sediment Transport rate in the x -direction and y -directions, respectively. The Sediment Transport vector q arrowrightnosp can be expressed formally as 1 ( , , ) 0 ( , ) 1 ( , , , ) ( , , , ) T x y t s h x y q c x y z t u x y z t dzdt T η − = ∫ ∫ arrowrightnosp arrowrightnosp (10.2) where T : wave period, η 1 : water surface elevation, c : volumetric concentration of moving sediment, and s u arrowrightnosp : sediment velocity vector. In order to calculate the Sediment Transport rate by Eq.
- Wilbert Lick(Author)
- 2008(Publication Date)
- CRC Press(Publisher)
215 6 Modeling Sediment Transport In previous chapters, many of the basic and most significant Sediment Transport processes were discussed. In the present chapter, these ideas are applied to the modeling of Sediment Transport. In Section 6.1, a brief but general overview of Sediment Transport models is given. In Section 6.2, transport as suspended load and/or bedload is discussed with the purpose of describing a unified approach for modeling erosion. Simple applications of Sediment Transport models are then described in Section 6.3. More complex applications of Sediment Transport mod-els to rivers, lakes, and estuaries are presented in Sections 6.4 through 6.6; the purpose is to illustrate some of the significant and interesting characteristics of Sediment Transport in different types of surface water systems as well as to illus-trate the capabilities and limitations of different models. 6.1 OVERVIEW OF MODELS Numerous models of Sediment Transport exist. They differ in (1) the number of space and time dimensions used to describe the transport and (2) how they describe and quantify various processes and quantities that are thought to be sig-nificant in affecting transport. Some of the processes and quantities that may be significant include (1) erosion rates, (2) particle/floc size distributions (i.e., the number of sediment size classes), (3) settling speeds, (4) deposition rates, (5) floc-culation of particles, (6) bed consolidation, (7) erosion into suspended load and/ or bedload, and (8) bed armoring. In practice, most Sediment Transport models do not include accurate descriptions of all of these processes.
eBook - ePub- Arved J. Raudkivi(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
CHAPTER 7 Sediment Transport If the applied shear stress on the bed of an alluvial channel exceeds the threshold value of the bed material, it is set in motion. The resulting transport of sediment is for convenience of description subdivided into bed load, saltation and suspension. The mode of transport is approximately indicated by the ratio of fall to shear velocity as 6 > w/u * > 2 bed load 2 > w/u * > 0.6 saltation 0.6 > w/u * suspension Bed load occurs at relatively low shear stress excess (τ o − τ c) and refers to transport on bed in a sliding and rolling mode, it describes a movement which is generally in contact with the bed, whereby the individual particles move intermittently. As the shear stress excess increases more and more particles of the bed load are propelled downstream in a hopping or bouncing mode of movement, called saltation. Saltation is the dominant mode of aeolian transport. In air saltating grains can reach heights of about 1 m above the ground. The mean height of saltating grains in water is only of the order of one grain diameter, although individual grains in laboratory flumes can be seen to bounce higher and some will even remain in suspension for a while. By collisions with one another and the bed, the moving grains maintain a layer in which the grains are not continuously in contact with the bed, but are supported by the bed through the inter-particle stresses (Section 2.3.2). As the shear stress excess increases further, the amount of turbulence generated at the bed and its diffusion upwards reaches a stage where the grains lose contact with bed and are held in suspension. The upward diffusion of turbulence keeps the particles in suspension, against gravity. At this stage some particles are still rolling and bouncing on the bed, as bed load, i.e
eBook - PDF- Andrew J. Manning(Author)
- 2011(Publication Date)
- IntechOpen(Publisher)
The Iberian study case. Z. Geomorph , N.F suppl-Bd 102, pp. 119-134. Zazo, C., Silva, P.G., Goy, J.L., Hillaire-Marcel, C., Ghaleb, B., Lario, J., Bardají, T. & González A. (1999). Coastal uplift in continental collision plate boundaries: data from the Last Interglacial marine terraces of the Gibraltar Strait area (south Spain). Tectonophysics , 301, pp. 95-109. 3 The Significance of Suspended Sediment Transport Determination on the Amazonian Hydrological Scenario Naziano Filizola 1 , Jean-Loup Guyot 2 , Hella Wittmann 3 , Jean-Michel Martinez 2 and Eurides de Oliveira 4 1 Universidade Federal do Amazonas – Department of Geography, Manaus 2 IRD-LMTG – Univeristé de Toulouse 3 Deutsches GeoForschungs Zentrum Potsdam Telegrafenberg, Potsdam 4 Agência Nacional de Águas, Brasília 1,4 Brasil 2 France 3 Germany 1. Introduction Rivers play an important role in continental erosion as they are the primary agents of transferring erosion products to the ocean. Understanding rivers and their transport pathways will improve the perception of many processes of global significance, such as biogeochemical cycling of pollutants and nutrients, atmospheric CO 2 drawdown, soil formation and their erosion, crust evolution- in short the interaction between the atmospheric and the lithospheric compartment of the Earth´s system (Allen, 2008). This interaction is characterised by the relative proportions of mechanical degradation vs. chemical weathering, whose products are, in dissolved or solid form, transported by rivers. The sediment load of rivers is thereby controlled by catchment relief, the channel slope and its connectivity to the hill slope, but also by climatic factors such as precipitation. The latter, together with temperature, exert control over chemical weathering that is dependent on physical erosion to a degree that is yet unknown (Anderson et al., 2002; Gaillardet et al., 1999; Riebe et al., 2001).
eBook - PDFRiver, Coastal and Estuarine Morphodynamics
Proceedings of the 4th IAHR Symposium on River, Coastal and Estuarine Morphodynamics (RCEM 2005, Urbana, Illinois, USA, 4-7 October 2005)
- Gary Parker, Marcelo H. García, Gary Parker, Marcelo H. Garcia(Authors)
- 2005(Publication Date)
- CRC Press(Publisher)
Sediment Transport processes River, Coastal and Estuarine Morphodynamics: RCEM 2005 – Parker & García (eds) © 2006 Taylor & Francis Group, London, ISBN 0 415 39270 5 Saltating or rolling stones? Christophe Ancey Ecole Polytechnique Fédérale de Lausanne, Ecublens, Lausanne, Switzerland Tobias Böhm & Philippe Frey Cemagref, Dom. Univ. Saint Martin d’Hères Cedex, France Magali Jodeau Cemagref, bis quai Chauveau, Lyon, France Jean-Luc Reboud Université Joseph Fourier, LEMD, Grenoble, France ABSTRACT: A longstanding problem in the study of bed load transport in gravel-bed rivers is related to the physical mechanisms governing the bed resistance and particle motion. Although a number of experimental investigations have been conducted over the last three decades, there seems to be a substantial gap between the field measurements and the predictions of theoretical models, although these models provide a correct description of bed load transport for lab experiments. To elucidate this point, we investigated the motion of coarse spherical glass beads entrained by a shallow turbulent water flow down a steep two-dimensional channel with a mobile bed. This experimental facility is the simplest representation of bed load transport on the lab scale, with the tremendous advantages that boundary conditions are perfectly controlled and a wealth of information can be obtained using imaging techniques. Bed load equilibrium flows were achieved (i.e. neither erosion nor deposition of particles occurred on average, over sufficiently long time intervals). Flows were filmed from the side by a high-speed camera. Using an image processing software made it possible to determine the flow characteristics such as particle trajectories, their state of motion (rest, rolling or saltating motion), and flow depth.
eBook - PDF- Zekai Sen(Author)
- 2008(Publication Date)
- CRC Press(Publisher)
0 7 Sediment Transport in Arid Regions . GENERAL OVERVIEW Climate, geology, and the age of the ground surface define the features of an arid environment. In general, arid regions are characterized by two kinds of morphol-ogy, namely, shields (platforms) and shelves (basins) (see Figure 1.3). The former is located in extremely stable seismic zones of tectonic origin such as the western Ara-bian Peninsula, the Sahara in Africa and southern Africa, parts of Asia, India, and Australia. Arid region shields are often dominated by eroded surfaces on volcanic rocks, which constitute the base of stratigraphic sequences. There are also platforms developed on horizontally layered sedimentary rocks like the Nubian sandstone in North Africa. The origin of these plains is not connected to their current arid-ity. Intermountain basin deserts are dominated by a succession of mountains and troughs often characterized by closed drainage basins. Arid and semi-arid surfaces are subject to weathering and mass wasting pro-cesses. Most of the weathering processes are atmospheric, mechanical (physical), and chemical in origin. Similarity in the morphology among different regions does not mean that they are generated by the same geological mechanics. In fact, differ-ent processes can give rise to comparable forms in different places, starting from different beginnings. Sediment yield at a catchment outlet, or at any section downstream, is the inte-grated results of upland, gully, and channel erosion, transportation, and depositional processes. The external dynamic agents of sediment yield are water, wind, gravity, temperature change, ice, and biological activities. Although each may be important locally, water is the most widespread agent of erosion and accounts for the bulk of sediments transport.
eBook - PDF- Weiming Wu(Author)
- 2007(Publication Date)
- CRC Press(Publisher)
Chapter 3 Fundamentals of Sediment Transport Introduced in this chapter are basic theories and empirical formulas of Sediment Transport, which are essentially used to close the mathematical models of flow, Sediment Transport, and morphological change in alluvial rivers. Some of them can be found in Graf (1971), Vanoni (1975), Chien and Wan (1983), Chang (1988), Zhang et al. (1989), Raudkivi (1990), Simons and Senturk (1992), Julien (1995), and Yang (1995). However, many recently developed non-uniform Sediment Transport formulas are particularly included here. 3.1 SETTLING OF SEDIMENT PARTICLES 3.1.1 General considerations Settling or fall velocity is the average terminal velocity that a sediment particle attains in the settling process in quiescent, distilled water. It is related to particle size, shape, submerged specific weight, water viscosity, sediment concentration, etc. A sediment particle experiences gravity, buoyant force, and drag force during its settling. Its submerged weight, which is the difference between the gravity and buoyant force, is expressed as W s = (ρ s − ρ)ga 1 d 3 (3.1) where d is the sediment size, a 1 d 3 is the volume of the sediment particle, and a 1 has a value of π/6 for a spherical particle. Note that ρ is actually given as the pure water density ρ f because a single particle (or low concentration) is considered. The drag force is the result of the tangential shear stress exerted by the fluid (skin drag) and the pressure difference (form drag) on the particle. It is written in the general form: F d = C d ρ a 2 d 2 ω 2 s 2 (3.2) where C d is the drag coefficient, ω s is the settling velocity, a 2 d 2 is the projected area of the particle on the plane normal to the direction of settling, and a 2 has a value of π/4 for a spherical particle.
eBook - PDF- Sahnaz Tigrek, Tuce Aras(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
The bed load is jumping, rolling or sliding of the particles on or near the streambed surface creep. Saltation is jumping into the flow and then resting on the bed. Suspension is supported by the stream turbulence surrounding fluid during a significant part of its motion. If rolling, sliding and jumping characterize the motion of sediment particles it is called bed-load transport (Yang, 1996). On the other hand, suspended-load transport is the motion of sediment particles that is supported by the upward components of turbulent currents and stays in suspension for an appropriate length of time (Yang, 1996). Suspended particles have a diameter of less than 0.062 mm (mainly silt). Based on previous bed-load and suspended-load transport definition, total-load can be defined as the sum of bed-load and suspended-load. However, based on the source of material being transported, total load can also be defined as the sum of bed-material load and wash load. Wash load consists of fine materials that are finer than those found in the bed. The amount of wash-load depends mainly on the supply from the watershed; not on the hydraulics of river (Yang, 1996). In the light of the definitions, a mathematical representation including bed-load, suspended load, bed material-load and wash-load can be written as: (Total − Load) = (Bed − Load) + (Suspended − Load) = (Bed − Material − Load) + (Wash − Load) The ratio of bed-load to suspended load is approximately 5–25%, however, for course materials, a higher percentage of sediment may be transported as bed-load (Yang, 1996). Sediment Transport over movable boundaries of a channel starts if the necessary conditions exceed the critical condition of motion of the bed material (Simons and ¸ Sentürk, 1992). The incipient motion has been studied extensively over the past 60 years, following the work by Shields (1936), who presented a semi-empirical approach.
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