NUMERICAL SIMULATION OF SEDIMENT TRANSPORT IN DYNAMIC FLOW CONDITIONS

1 INTRODUCTION Rivers as a source of life can at the same time impose devastating conditions on the environment. It is , therefore, imperative to analyse and predict river behaviour for different given conditions and engineering activities. Therefore, the use of simulation tools in this field has become a necessity. Many computational tools for simulation of sediment transport in rivers are now available that can be used for prediction and design under different flow conditions. However, …     

TRANSPORT OF THE SUSPENDED SEDIMENT IN THE CHANGJIANG ESTUARY

The Changjiang River is characterized by the enormous volume of runoff and the great amount of sediment load with remarkable seasonal variation. The annual runoff sometimes is respondent to the amount of sediment load, and sometimes not. The amount of monthly sediment load after the month of the maximum runoff is larger than those before the month. The sediment concentration and net quantity of sediment transport in the vicinity of the river mouth varies greatly in time between the ebb and flood, spring and neap, and dry seasons and flood seasons. The three bifurcations also have differences in concentration and net quantity in space. Even in the same bifurcation they have differences in and out of the sand bar. At present, the North Channel is the main passage for water and sediment load emptying into the sea from the Changjiang River. More than 50 percent of the sediments from the river basin are deposited nearby the South Branch entrance and the main depositional area is situated in subaqueous delta off the South Channel. Between 122°30'E and 123°E is an important boundary for eastward sediment dispersion from which the suspended sediment are dispersed towards the east by south.     

THREE DIMENSIONAL NUMERICAL MODELLING OF FLOW AND SEDIMENT TRANSPORT IN RIVERS

The 3D numerical model, ECOMSED (open source code), was used to simulate flow and sediment transport in rivers. The model has a long history of successful applications to oceanic, coastal and estuarine waters. Improvements in the advection scheme, treatment of river roughness parameterization and shear stress partitioning were necessary to reproduce realistic and comparable results in a river application. To account for the dynamics of the mobile bed boundary, a model for the bed load transport was included in the code. The model reproduced observed secondary currents, bed shear stress distribution and erosion-deposition patterns on a curved channel. The model also successfully predicted the general flow patterns and sediment transport characteristics of a 1-km long reach of the River Klar?lven, located in the north of the county of V?rmland, Sweden.     

A NUMERICAL MODEL OF SEDIMENT TRANSPORT IN HANDUN IRRIGATION DISTRICT

LABRIEFINTRODUCTIONOFRANDUNIRRIGATIONDISTRICTYellowRiverisoneofthemainWaterresourcesinNOrthChina.SincethefiftiesirrigationbydivertingwaterfromtheYellowforerdevelOPssteadily.AstheYdlowforerisaheavilysacmentsladenone,sedimentisdiVertedsimultaneouslywhenwaterisdiverted.HOwtoproperlytreatthedivertedsedimentboomesoneOfthekeyproblemsrestrichngthesustainingdevelOPmentofthCwaterresourcesinthatarea.LongchStanceconvopngsedimentisoneofthemainmeasuresfordealingwiththediVertedsedim…     

DEPTH-AVERAGED 2-D CALCULATION OF FLOW AND SEDIMENT TRANSPORT IN CURVED CHANNELS

The helical flow significantly affects the flow, sediment transport and morphological evolution in curved channels. A semi-empirical formula is proposed to determine the cross-stream distribution of the helical flow intensity in the developed regions of a channel bend. It is then used to evaluate the dispersion terms in the depth-averaged 2-D momentum equations and suspended-load transport equation as well as the bed-load transport angle, thus enhancing the depth-averaged 2-D model to account for the effect of helical flow. The tests in several experimental and field cases show that the enhanced depth-averaged 2-D model can much more reasonably predict the shifting of main flow from inner bank to outer bank, the erosion along outer bank and deposition along inner bank than the depth-averaged 2-D model without considering this effect.     

NUMERICAL SIMULATION OF SEDIMENT TRANSPORT IN ALLUVIAL RIVER WITH FLOODPLAINS

1 INTRODUCTION The transport of sediment in rivers with active floodplains is a two-dimensional process because the main channel and the floodplain can have very different transport capacities. Therefore, two-dimensional (2D) models are often used to simulate the streamwise and transverse variations of sediment erosion and deposition. Many 2D numerical models have been presented to simulate sediment transport in floodplains (James, 1985; Pizzuto, 1987; Howard, 1992; Nicholas and Walli…     

MATHEMATICAL MODEL FOR SEDIMENT TRANSPORT CAPACITY OF HYPERCONCENTRATED FLOW

ＭＡＴＨＥＭＡＴＩＣＡＬＭＯＤＥＬＦＯＲＳＥＤＩＭＥＮＴＴＲＡＮＳＰＯＲＴＣＡＰＡＣＩＴＹＯＦＨＹＰＥＲＣＯＮＣＥＮＴＲＡＴＥＤＦＬＯＷＩＮＤＩＶＥＲＳＩＯＮＣＡＮＡＬＳ￥ＣＡＯＲｕｘｕａｎ；ＷＵＰｅｉａｎ；ＲＥＮＸｉａｏｆｅｎｇａｎｄＬＩＵＭｉｎｇ...     

THREE-DIMENSIONAL NUMERICAL MODELING OF COHESIVE SEDIMENT TRANSPORT BY TIDAL CURRENT IN PEARL RIVER ESTUARV

IINTRODUCTIONEstUariesareprominentcoastalfeatUres.Estuariesareofgreateconomicssignificancetomankind.Attheseareas,manyharborsandwaterchannelshavetobebuiltforeconomicpurposes.ThedesignandconstrUctionofcoastalstrUctUresinestUariesrequireknowledgeofhydrodynamicsaswellassedimenttransportinsuchregions.ThenatUreofestuariesiscontrolledbyvariouscoastalhydrodynamicprocesses.Undertheactionofhydrodynamics,sedimentdepositionsorerosionswilloccurinestuariesornearcoastalstrUCtures.Tomaintainnavigati…     

ON THE VERTICAL DISTRIBUTION OF SUSPENDED SEDIMENT CONCENTRATION

The problem of sediment concentration distribution in a vertical for channel and pipe flows is studied in this paper. Considering the variation of the vertical component of the fluctuation velocity v as an independent variable, two types of sediment concentration distribution can be derived. However, only one type of distribution is commonly quoted while the other one rarely reported. In this paper explanation for such phenomena is given and conditions for the occurrence of both types are also discussed.     

OPTIMAL MODE OF SEDIMENT TRANSPORT BY SHALLOW FLOWS IN UPLAND AREAS

lNTR0DUCTI0NThemechanismofsedimenttransp0rtinshall0wchanneIfiowscanbequitec0mplicateddependingupona)themechanismofsoildetachment,b)thesizeandshaperanges0ftheavailablesediment,c)thesedimentc0ncentrati0n,d)theenergeticc0nditi0n0ftheflow,e)thechannelsurfacec0nditi0n,Dtherateofwaterinfiltrati0nandg)thechemicalc0nstituentspresentinthes0ilandthesurfacewater.Th0ughthedetachment0fs0ilparticlesbyrainfallistheprimarys0urce0favailablesediment,theeffect0fdynarnicwaterwavesandwind-gustsals0playasignifi…     

DEFORMATION OF RIVER BED AND THE CHARACTERISTICS OF SEDIMENT TRANSPORT DURING HYPER-CONCENTRATED FLOOD IN THE YELLOW RIVER

LINTRODUCTIONTheYellowforeriswellknownasaheavilysilt-caacingriverintheworld.Haaer-concentratedfloodsoftenoccurinitsmasterstemandaswellasthetriblltaries.ThecharacteristicsofdeformationandsedimellttranSportdifferfromreachtOreach.Duetohighsedimelltconcelltration,StrongfluvialactionandthenatUreofunSteadysedimenttranSPOrt,problemsandabnormalphenomenonareoflencreated.ThelaterbringinimpacttOnoodcontrolOfthelowerreach.Thus,itishelpfultoenhancetheunderstandingofthemotionlawsOfhaer-concentrat…     

DESIGN OF SEDIMENT FLUSHING OUTLETS

1 INTRODUCTION Considerable amount of sediment discharge enters in a canal at the head works. This sediment discharge is carried safely as the slopes of the canal in the head reaches are large. Subsequently, for economy, the slopes of canal are reduced in the downstream reaches. This makes the sediment concentration far excess of its carrying capacity. This excess sediment has to be removed by suitable design of a sedimentation basin. Also, one of the requirements for successful function…     

DEPTH-AVERAGE ANALYSIS OF HYSTERESIS BETWEEN FLOW AND SEDIMENT TRANSPORT UNDER UNSTEADY CONDITIONS

1 INTRODUCTION Flow and sediment transport in natural rivers are generally unsteady, and exhibit temporal and spatial lags. Traditionally, in most hydraulic engineering problems the unsteady flow and sediment transport are approximately treated as steady …     

EFFECT OF COARSENING OF SURFACE BED MATERIAL ON NON-EQUILIBRIUM SEDIMENT TRANSPORT PROCESS DURING RIVER DEGRADATION

1INTRODUCTIONNon-equilibriumsedimenttransportina"at'Uralstreamwithnon-uniformbedmaterialisasubjectofilltensiveresearch.ThesedimentconcentrationmaybenotequaltothetransportcapacityofflowinanalluvialrivedItgraduallyapproachesequilibriumbydegradationoraggradationinalongdistance.usuallyover100kilometers.Thisproblemisofgreatimportancetothepredictionofthedistributionoferosionordepositionalongachannel,especiallyforlargeriversinChina.Scientistsstudiednonequilibriumsedimenttransportandthemainresul…     

EXPERIMENTAL STUDY OF BEDLOAD TRANSPORT IN UNSTEADY OPEN-CHANNEL FLOW

I.INTRODUCTIONBedloadtransportinsteadyuniformopenchannelflowhasbeenextensiVelystudied.Manyoftheformulasdevelopedforthepredictionofbedloadtransportinuniformopen-channelflowcanbebroughtinthefollowingform(ChienandWan,1983);ac=f(O)(l)xvhereacisthedimensionlessparameterofbedloadtranSPortandOisthedimensionlessparameterofflowintensity.TheseparametersaredefinedasfwheregsisthebedloadtranspoftratePerunitwidthindryweight;disthesedimentdiameter,Sisthebedslopeofthechannel;Rbisthehydraulicradiusdue…     

DEVELOPMENT OF A SURFACE PLUME MODEL AND ITS APPLICATION TO SEDIMENT TRANSPORT MODELLING OF DREDGING IN COASTAL WATERS

I INTRODUCTIONSediment dredging operations are effective means of maintaining the natural navigation channel ofshipping for transportation of passengers and cargoes (Goldbeck 1998, Wakeman 1998). Expansions ofexisting ports to facilitate the groWth in marine traffic often necessitate navigation channel dredgingactivities (Foxworthy et. al. 1995, Luger et. al. 1998). Dredging is also heavily used for marine mining ofthe scabed deposits for gold or minerals (Anon 1996, Gamett 1996), and …     

THE SOURCE OF COHESIVE SEDIMENT AND ITS TRANSPORT IN THE YANGTZE ESTUARY AND NEAR SEA

In the light of the regional physiography and its effect on clay mineral composition of cohesive sediment (d < 0.005 mm) the source area of cohesive sediment in the Yangtze Estuary can be identified as three supplying regions: the main stem of the Yangtze River, the deltaic region of the abandoned Yellow River including the northwest Huanghai Sea and the Hangzhou Bay. Based on the evaluation of clay mineral composition in the supplying regions and the converging region, a computational model is established. More than 89.6% of cohesive sediment comes from the Yangtze River, a considerable amount is replenished from the deltaic region of the abandoned Yellow River while some part of the cohesive sediment load is transported from the Yangtze Estuary to the Hangzhou Bay. Computation results reveal that the annual deposit of cohesive sediment in the Yangtze Estuary amounts to 45.54 x 106 t. The annual cohesive sediment load replenished from the deltaic region of the abandoned Yellow River is 27.30 x 106t, while the annual cohesive sediment load transported to the Hangzhou Bay is 22.47 x 106 t. The amount of deposit in the Yangtze Estuary has been checked against the value obtained by comparing bathemetry of the Yangtze Estuary in 1915 and 1963.     

INITIATION OF SEDIMENT MOTION IN LAMINAR OVERLAND FLOW

IINTRODUCTIONWhileriverflowsareusuallydeepandturbulent,overlandflowisextremelyshallowandcanbelaminar,transitionalandturbulent.Becauseoftheshallownessoftheflolw,overlandflowhydraulicsisgreatlyaffectedbysurfaceroughness,raindropimpact,andinthecaseoflaminarflow,flui(Iviscosity.Theinitiationofsedimentmovementinoverlandflowisthereforeexpectedtodifferfromthatinriverflows.InriverstUdies,bedshearStressgbhastraditionallybeenusedtocharacterizethecriticalflowconditionatwhichsedimentbeginstomove.At…