LIVE-BED SCOUR IN LONG CONTRACTIONS

1 INTRODUCTION Scour within a channel contraction occurs where the waterway is restricted by the foundations or road approach embankments of a bridge. Alternately, contraction scour takes place when a bridge is located at a natural contraction in the rive…     

VORTEX FLOW FIELD IN A SCOUR HOLE AROUND ABUTMENTS

The three-dimensional flow field in a scour hole around different abutments under a clear water regime was experimentally measured in a laboratory flume, using the Acoustic Doppler Velocimeter (ADV). Three types of abutments used in the experiments were vertical-wall (rectangular section), 45° wing-wall (45° polygonal section) and semicircular. The three-dimensional time-averaged velocity components were detected at different vertical planes for vertical-wall abutment and azimuthal planes for wing-wall and semicircular abutments. The velocity components were also measured at different horizontal planes. In the upstream, presentations of flow field through vector plots at vertical / azimuthal and horizontal planes show the existence of a primary vortex associated with the downflow inside the scour hole. On the other hand, in the downstream, the flow field shows a reversed flow near the abutments having a subsequent recovery with a passage of flow as a part of the main flow. The data presented in this p     

EXPERIMENTS ON FLOW AROUND A CYLINDER IN A SCOURED CHANNEL BED

The flow pattern around a cylinder, installed in a scoured channel bed, was experimentally investigated. Detailed measurements of the instantaneous 3D velocities were performed by using an Acoustic Doppler Velocity Profiler (ADVP), from which the profiles of the time-averaged velocities and turbulence stresses were obtained. It is shown that the influence of the cylinder and of the scour hole alters the approach flow; this is essentially confined to the vicinity of the cylinder and to the inside of the scour hole. The horseshoe vortex is measured as a flow reversal inside the scour hole, formed by the downward flow along the cylinder face and the reversed flow at the scour bed.     

IMPACT OF DEBRIS FLOW ON RIVER CHANNEL IN THE UPPER REACHES OF THE YANGTZE RIVER

IINTRODUCTIONDebrisflowisaphenomenonhappeninginextremeseveresit'Uationofsoilerosion(Guan,1996).ItoccursfrequentlyanddistributesdenselyinupperreachesoftheYangtzeRiverandtransportsahugeamountofsedimentilltotheriver.Debrisflowdepositinfluencesthecompositionofsedimentandthemorphologyoftheriverbedfromupstreamt6downstreamandthenaffectsthedynamiccharactersandsedimentbudgetoftheYangtzeRiver.Furthermore,itimpactsonthefloodandwaterconservancyengineering.2DEBRISFLOWGULLY--HIGHWAYOFSEDI…     

Suspended load in flows on erodible bed

Steady state suspended-load of sediment transported in flow over erodible beds usually is treated by the advection-diffusion approach, though in recent years, it is being treated as a two-phase flow phenomenon incorporating kinetics of sediment particles. Among the advection-diffusion approaches, Rouse＇s equation is the well-known, although a number of researchers in later periods have attempted to improve it by modifying the mixing length concept taking into account other aspects. In this paper, the advection-diffusion approach and associated logarithmic law of flow velocity are revisited. It is concluded from the logarithmic law that the Reynolds shear stress is a linear function of height above the bed, which reduces to bed shear stress in the case of a long horizontal channel. As a consequence, it is shown that the volumetric concentration of sediment is best approximated by the sum of two power laws of height above the bed. An equation is derived for the suspended-load transport rate in terms of elementary functions.     

Bedload transport from analytical and turbulence phenomenological perspectives

In this paper, we present the dynamics of bedload transport from two different perspectives. They are the analytical perspective and the turbulence phenomenological perspective. In bedload transport from the analytical perspective, we highlight the systematic advances in the analytical modelling of bedload transport over the decades. These advances are principally classified into three broad foundations, namely, the deterministic foundation, that includes the bed shear stress concept, stream power concept, force balance concept and bedform concept, and the probabilistic foundation and the turbulence phenomenological foundation of bedload transport. The bedload transport from the turbulence phenomenological perspective brings into focus the bedload-induced turbulence phenomenology, including the hydrodynamics of mobile-bed and water-worked bed flows. We also discuss the recent advances in the biofilm-coated bedload transport. Finally, conclusion is drawn, highlighting the major research challenges.     

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, …     

EVOLUTIONAL CHARACTERISTICS OF HYPER－CONCENTRATED FLOW IN BRAIDED CHANNEL OF THE YELLOW RIVER

ＥＶＯＬＵＴＩＯＮＡＬＣＨＡＲＡＣＴＥＲＩＳＴＩＣＳＯＦＨＹＰＥＲ－ＣＯＮＣＥＮＴＲＡＴＥＤＦＬＯＷＩＮＢＲＡＩＤＥＤＣＨＡＮＮＥＬＯＦＴＨＥＹＥＬＬＯＷＲＩＶＥＲ￥ＱＩＰｕ；ＬＩＷｅｎｘｕｅ（Ｓｅｎｉｏｒｅｎｇｉｎｅｅｒ，ＩｎｓｔｉｔｕｔｅｏｆＨｙ...     

EXPERIMENTS ON FLOW AROUND A CYLINDER IN A SCOURED CRANNEL BED

1 INTRODUCTION'LOcal scour around a pier is a result of the interatiOn amongst the pier, the aPproach flow and theerodible bed. The Presence of a pier results in a stagnation pressure build-up in front of the pier and athree-dimensional tUrbulent flow echaracterized by the downward flow ahead of the pier and the so-called horseshoe vortex along the base of the Pier forms itself The flow modifies the erothe bed inthe vicinity of the pier when local scour takes place (Graf and AJhnakar l…     

THE FORMING CONDITIONS OF ALLUVIAL RIVER CHANNEL PATTERNS

1 INTRODUCTION It is well known that the river channel patterns are determined by long-term water-sediment conditions. However, quantitative expressions for river channel patterns and their fluvial processes still remain not clear. Existing theories in this aspects, such as geomophological theory, theory of maximum energy consuming rate, stability theory, theory of probability, and statistic analysis, are developed based on certain simplified assumptions and can not be successfully used t…     

EXPERIMENTAL STUDY ON INCIPIENT MOTION OF SEDIMENT PARTICLES ON GENERALIZED SLOPING FLUVIAL BEDS

1 INTRODUCTIONWhen water flows over a fluvial bed, hydro-dynandc force induced by the flow is acting on thesediment particles lying on the bed. A further increase in flow velocity results in an increase in themagnitude of this fOrce; and sediment particles begin to move if a situation is eventu8lly reached whenthe hydro-dynandc force exceeds a certain critical value. This initial movement of sediment pallicles istermed inciPient motion. The erosion and sedimentation of nuvial beds can be…     

MAXIMUM INFORMATION ENTROPY THEORY OF EFFLUENT BAND IN OPEN CHANNEL UNIFORM FLOW

ＭＡＸＩＭＵＭＩＮＦＯＲＭＡＴＩＯＮＥＮＴＲＯＰＹＴＨＥＯＲＹＯＦＥＦＦＬＵＥＮＴＢＡＮＤＩＮＯＰＥＮＣＨＡＮＮＥＬＵＮＩＦＯＲＭＦＬＯＷＫｅＺｈｏｎｇＨＵＡＮＧ１ａｎｄＴａｏＪＩＡＮＧ２ＡＢＳＴＲＡＣＴＴｈｅｐｒｉｎｃｉｐｌｅｏｆｍａｘｉｍｕｍ...     

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…     

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.     

NONUNIFORMOPEN CHANNEL FLOW WITH UPWARD SEEPAGE THROUGH LOOSE BEDS

The Reynolds stress and bed shear stress are important parameters in fluvial hydraulics. Steady-nonuniform flow in open channels with streamwise sloping beds having upward seepage through loose beds is theoretically analyzed to estimate the Reynolds stress and bed shear stress. Equations of the Reynolds stress and bed shear stress are developed, assuming a modified logarithmic velocity distribution law due to upward seepage, and using the Reynolds and continuity equations of two-dimensional flow in open channels.     

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.     

THE THEORETICAL STUDY ON THE LAWS OF DRAG REDUCTION BY AERATION IN OPEN CHANNEL 1

ＴＨＥＴＨＥＯＲＥＴＩＣＡＬＳＴＵＤＹＯＮＴＨＥＬＡＷＳＯＦＤＲＡＧＲＥＤＵＣＴＩＯＮＢＹＡＥＲＡＴＩＯＮＩＮＯＰＥＮＣＨＡＮＮＥＬ１ＺＨＥＮＧＹｏｎｇｇａｎｇ２,ＦＡＮＧＤｕｏ３ａｎｄＬＩＧｕｉｆｅｎ４ＡＢＳＴＲＡＣＴＴｈｅｌａｗｓｏｆｄｒａｇｒｅ...     

VELOCITY PROFILES OF TURBULENT OPEN CHANNEL FLOWS

1 INTRODUCTIONThe vertical velocity profile of open channel flows is the most basic infOrmation for the stUdy of flowresistance, channel bed stability, river nuvial process and sediment transport. Although it has been asubject of great interest for many years, there does not exist a consensus on some perPlexing questions,such as the position of the theoretical bed level. In order to investigate the properties of velocity profile,data measured in open channel nows from eight sources were …     

LONGITUDINAL DISPERSION IN SEDIMENT-LADEN OPEN CHANNEL FLOWS

Laboratory experiments on longitudinal dispersion in clear-water and sediment-laden open channel flows are reported. Data from these experiments and those available from previous studies indicate that the suspended sediment present in the flow affects the longitudinal dispersion process. The observed velocity distributions over the depth of sediment-laden flows indicate that the velocity deviates from the mean velocity more in sediment-laden flows than in clear-water flows. The velocity distributions over the cross section and secondary flow in the channel are also expected to be altereddue to the presence of suspended sediments in the flow. For these reasons, more dispersion is found in sediment-laden flows than in corresponding clear-water flows. A predictor for the dispersion coefficient in sediment-laden flows is proposed.     

FLOW MECHANISMS AND SEDIMENT TRANSPORT IN COMPOUND CHANNELS

IINTRODUCTIONCompoundortWo-stagechannelshavereceivedconsiderableattentioninrecentyearsduetotheirrelevancetofloodstudiesinnaturalrivers,theirsignificanceinunderstandingrivermol'phology,andtheiruseinsomefloodalleviationschemeswherethefloodplainshavebeenartificiallyloweredtoproduceengineeredchannels.ThispaperreviewsworkwhichhasbeenundertakenintheUKFloodChannelFacility(FCF)overthepastdecade.TheACewasbuiltatHRWallingfordin1986,asalargescalenationalfacilityforhydraulicengineeringstUdies.T…