A MATHEMATICAL MODEL FOR UNSTEADY SEDIMENT TRANSPORT IN THE LOWER YELLOW RIVER

1 INTRODUCTIONMany mathematical models for sediment transport have been developed for solving practical Problemsin hydraulic engineering. HoweveT, most of them are not able to simulate the hyper-concentratd flows inthe Lower Yellow Xiver because of the extremely high load concentration of the flows. This paper isdevoted tO the simulation of unsteady sediment trallsport in the Lower Yellow mveLIn this paPer, the riverbed deformation equation is modified and the new expressions for sedi…     

TWO-DIMENSIONAL SEDIMENT MATHEMATICAL MODEL FOR UNSTEADY FLOW IN THE LOWER YELLOW RIVER

IINTRODUCTIONTheYellowRiverisfamousforitsheaVysedimentloadandcompledpluvialprocessesobviousadvanceshavebeenmadeinthetwo-dimensionalsedimentmathematicalmodel.Amongtile1llodelscreatedbeforethemechanismofsedimenttransportandrelatedphysicalparametel's,suchassedimentvelocity,sedimentcan'yingcapacityandriverfi.ictionetc.arenotyetundel.stoodvery\veil.Thesynchronousobserveddataoftheflowwithsediment,especiallyathyperconcentration,arenotenougllforthemodelcalibration.Thereforethedevelopmentoftwo-di…     

SEDIMENT TRANSPORT EXPERIMENTSIN UNSTEADY FLOWS

l INTRODUCTIONThe theories and formulas of sediment dynamics were established based on steady and uniform flows.These theories and formulas often fail to aPply in engineering projects because, in nthee, sediment istransported often by unsteady and non-uniform fiows (Wang et al., l997).TWo cases ofnon-stationarity can be distinguished f long-tertn and short-term (Plate, l994). Long-termnon-stationarity tfansport can be defined as a sediment process which can be treated by sequences ofstat…     

EFFECT OF SUSPENDED SEDIMENT ON THE TRANSPORT AND TRANSFORMATION OF 4 - NITROCHLOROBENZENE IN THE YELLOW RIVER

I.INTaonUCTIOXP-NCBisatoxiccompoundwhichmaycausecarcinogenicoramutation.NowthetransPOrtandtransformationofthiskindOfsubstanceinnaturalwaterbodyisthefocusofresearchofscientistsintheworld.ThroughthestudytherelationshipbetweennonionicorganiccomPOunds,suchasP-NCB,andsuspendedsedimentisfoundtobeveryclOSe,suspendedsedimentareload-supPOrtingofmovementandmediateagentofreactionofP-NCBinwater.TheYellowRiverisheavilysediment-laidenriverintheworld.Sometimesthesuspendedsedimentcanbeupto200kgpe…     

SEDIMENT HAZARDS IN THE LOWER YELLOW RIVER

1DEFINITIONOFSEDIMENTHAZARDHazardsaredefinedasthenaturaleventsthatcauselossesofhumanlifeandproperty.Reasonably,thesedimenthazardsarethehazardsoccasionedbythenatUralphenomenonandprocessesthatarerelatedwithsedimenterosion,transport,andaccumulation.Thelandslideandsoilerosionarethedirectresultsofsedimentmovement.Theoccurrenceofsomeotherhazardsisnotthedirectresultofbutrelatedtosedimentmovement.Forexample,inadditiontometeorolog.icalconditions,somekindsoflandformsarefavorabletoformationoff…     

REGULATION OF FLOW AND SEDIMENT LOAD IN THE YELLOW RIVER

Small runoff, large sediment load, and incompatible relationship of flow and sediment load are very important characteristics of the Yellow River. They are also the crux of the most prominent problems of the Yellow River. To solve these problems, the regimes of flow and sediment load have to be improved by increasing water, reducing sediment load, and by using reservoirs to regulate flow and sediment load. The results of experiments for regulating the flow and sediment load in the last three years by the Xiaolangdi Reservoir have indicated that this measure is a realistic and effective way to mitigate the prominent problems in flood control of the Lower Yellow River at present and in the near future. However, the regulation system is still imperfect. It is advisable to speed up the pace of research and construction of the system for regulating flow and sediment load.     

MATHEMATICAL MODEL FOR SEDIMENT TRANSPORT CAPACITY OF HYPERCONCENTRATED FLOW

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RATIONAL BASIS FOR SUSPENDED SEDIMENT MODELING

This paper presents a rational basis to model the transport of suspended sediment. The loose-boundary condition for 3D models and the adjustment coefficients for both the depth-integrated 2D and laterally integrated 1D models are treated comprehensively. A combination of Dirichlet and Neumann conditions is proposed as the loose-boundary condition. The adjustment coefficient for 2D models is obtained on the basis of the proposed boundary condition and analytical solutions developed for some simple cases of non-equilibrium transport of sediment in uniform flows. The adjustment coefficient for 1D models for natural rivers is further obtained from lateral integration. Comparisons with analytical solutions and a considerable amount of laboratory and prototype data show that mathematical models developed along the proposed line of attack would well simulate the transport of suspended sediment in practical problems.     

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…     

FLUVIAL PROCESSES AND SEDIMENT SCOUR RATE OF THE YELLOW RIVER UNDER ACTION OF UNSTEADY FLOWS

1 wrsoooCTIoxThe Yeuow mver crtes a huge amoun of sedimcht and the noods often cause raPid and severeerosinn and dePOsihon. The channl bed of the YelOw mver often exPeriences degIadation in the mainchannel during fioods. In some cases vigorous erosion uP to l0 meters takes place in a shOrt Period oftiIn. Such phenomenon usually occurs in the ndddie reaChs of the Yelow mver and its tributaries suchas the Wdse mVer the Beiluohe mver etc. For examPle, th6 hyPenconcentraed nood in July l…     

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 …     

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, …     

CHARACTERISTICS OF SEDIMENT TRANSPORT AND CHANNEL FORMATION BY FLOODS AT HYPERCONCENTRATIONS OF SEDIMENT IN THE YELLOW RIVER

1. INTRODUCTIONThe Yellow River is a heavily sediment--laden river. Floods at Hyperconcentrationso f sediment (hereinafter simply referred to as hyperconcentrated flood) frequently occurring in the main river and its tributaries possess different characteristics of sedimenttransport. Sometimes they cause severe deposition whereas at other times they are capable of carrying substantial amount of sediment over long distances. The study on the lawof sediment transport is of significance to …     

NUMERICAL SIMULATION OF INUNDATION IN SHENZHEN CITY BY FINTE DIFFERENCE MODEL MIXED WITH 1D AND 2D UNSTEADY FLOW

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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.     

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.     

THE OPTIMAL GRAINSIZE COMPOSITION OF SUSPENDED SEDIMENT OF HYPERCONCENTRATED FLOW IN THE MIDDLE YELLOW RIVER

LINTRODUCTIONThetributariesofmiddleYellowRiverarefamousintheworldforthehighestsuspendedsedimentconcentrationandsedimentyield.Forexample,atWenjiachuanstationofKuyeheRiverthemeasuredhighestsuspendedconcentrationis1700kg/m',andthemeanannualsedimentyieldis25000t/(kln'.a).Theformationofhyperconcentratedflowsandtheirinfluenceonerosionprocessesareofgreatimportancenotonlyfromatheoreticalpointofviewbutalsoforpracticalpurposes.Therefore,scientistsfromChinaandallovertheworldhavedrawntheirintensio…     

A 2D MATHEMATICAL MODEL FOR THE BED DEFORMATION IN THE LOWER YELLOW RIVER

1 BANK EROSION IN THE LOWER YELLOW RIVER In alluvial rivers, riverbeds are always in a state of transition and development. Two kinds of deformations result for the fluvial process according to certain basic characteristics. One is longitudinal deformation that is characterized by the deformation of a riverbed in the direction of streamwise flow such as riverbed scour or deposition. The other is transverse or lateral deformation that is distinguished by the deformation of a riverb…     

STREAM-SUBSURFACE EXCHANGE, SUSPENDED SEDIMENT TRANSPORT, AND THE COUPLED TRANSPORT OF COLLOIDS AND CONTAMINANTS IN SEDIMENT BEDS

1 INTRODUCTION Alluvial streams generally have permeable bed sediments that can admit significant pore water flows. Steady flow of surface water over bed roughness features such as sand waves or pools and riffles can then drive water flow into and out of the shallow subsurface. This is often termed hyporheic exchange, and the subsurface region where mixing between stream and ground waters occurs is the hyporheic zone (Hynes, 1983). The hyporheic zone has been shown to be a critical com…     

SUSPENDED SEDIMENT TRANSPORT CAPACITY OF OPEN CHANNEL FLOW

I.~ODUCTIONSuspendedsedimenttransportcapacity(SSTC)ofopenchannelflowisoneofthebasicsubjectsinsedimenttransportmechanicsandsedimentationengineeringpractice.Mostexistingformulationsareempiricalandsemiempiricalorrestheavilyonassumptionswhicharenotyetjustified.Thisarisesmostlybecauseofthecomplexityoftheproblem.Forafullydeveloped,in-equilibriumflowinawiderectangularchannel,theSSTCcanbbdeterminedasfollowsor=n:,ty)cab)-dy=Ca'I(l)1I=J4(D)'exp[--V,(n)]'da(2)unwhereCTIsSSTC,uistheaveragedflo…