FLOW FIELD IN SCOURED ZONE OF CHANNEL CONTRACTIONS

Experiments were conducted in a laboratory flume to measure the two-dimensional turbulent flow field in the scoured zone of channel contractions under a clear-water scour condition. The Acoustic Doppler Velocimeter (ADV) was used to detect the flow field at different vertical lines along the centerline of uncontracted (main channel) and contracted zones of the channel. The distributions of time-averaged velocity components, turbulent intensity, turbulent kinetic energy, and Reynolds stresses are presented in nondimensional graphical form. The bed shear stresses are computed from the measured Reynolds stresses being in threshold condition within the zone of contraction where bed was scoured. The data presented in this paper would be useful to the investigators for the development of kinematic flow model and morphological model of scour at a channel or river contraction.     

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…     

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.     

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, …     

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.     

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…     

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.     

FLOW MECHANISMS AND SEDIMENT TRANSPORT IN COMPOUND CHANNELS

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

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.     

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…     

Revisited Vanoni-Brooks sidewall correction

The evaluation of the sidewall friction could be inconvenient in the implement of the Vanoni-Brooks sidewall correction procedure.Using the Colebrook-White equation and Nikuradse’s pipe friction data,two explicit formulae are developed in this note for finding the sidewall friction factor.They are applicable for various sidewalls that are either hydrodynamically-smooth or rough,or in the transitional regime.     

EXPERIMENTAL INVESTIGATIONS AND NUMERICAL SIMULATIONS OF REDUCING SECONDARY FLOWS AROUND A SPUR DIKE

1 INTRODUCTION The Yangtze River at the Three Gorges Project (TGP) site meanders with a complex morphology, including ridges like Jiuling Hill that projects into the approach navigation channel (Fig. 1). The approach navigation channel consists of a 530-m…     

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.     

A MATHEMATICAL QUASI-2D OVERLAND FLOW MODEL

1 INTRODUCTIONThe prediction of future impacts on terrestrial ecosystems by atmospheric, climatic and land-usechanges is the aim of watershed management. Meeting these requirements scientists, managers and policymakers try to achieve the sustainable management of the vitally important resources of watersheds due toan integrated ecosystem approach at the catchment scale. As composite landscapes often have a highdegree of contingency between its elements, the transport over these landscape s…     

A LINEAR THEORY FOR DISTURBANCE OF COHERENT STRUCTURE AND MECHANISM OF SAND WAVES IN OPEN-CHANNEL FLOW

1 INTRODUCTIONT'he early theory for tUrbulent boundare layer assumed that the now adjacent to the wall is a lndnar innature and is named lndnar bottom layer Its thickness is about V/u*, Where V is the ldnehc viscosityand u* is the fuchon velocity. Towmsend (l956) first suggested the concePt of tUrbulent strUctUre andpointod out that there are isotroPic small scale nuctUation and quasi-periodic large scale strUcture in theshear flow Einstein and Li (l956) discovered by the flow moving…     

3D CFD MODELING OF WATER AND SEDIMENT FLOW IN A HYDROPOWER RESERVOIR

１ＩＮＴＲＯＤＵＣＴＩＯＮＲｅｓｅｒｖｏｉｒｓｅｄｉｍｅｎｔａｔｉｏｎｉｓｒｅｃｏｇｎｉｚｅｄａｓｏｎｅｏｆｔｈｅｍａｉｎｐｒｏｂｌｅｍｓａｆｅｃｔｉｎｇｔｈｅｅｃｏｎｏｍｉｃｓｏｆｍａｎｙｗａｔｅｒｒｅｓｏｕｒｃｅｓｐｒｏｊｅｃｔｓ．Ｍａｎｍａｄ...     

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

ＭＡＸＩＭＵＭＩＮＦＯＲＭＡＴＩＯＮＥＮＴＲＯＰＹＴＨＥＯＲＹＯＦＥＦＦＬＵＥＮＴＢＡＮＤＩＮＯＰＥＮＣＨＡＮＮＥＬＵＮＩＦＯＲＭＦＬＯＷＫｅＺｈｏｎｇＨＵＡＮＧ１ａｎｄＴａｏＪＩＡＮＧ２ＡＢＳＴＲＡＣＴＴｈｅｐｒｉｎｃｉｐｌｅｏｆｍａｘｉｍｕｍ...     

EXPERIMENTAL STUDY ON BED SHEAR STRESS AND SEDIMENT TRANSPORT IN A MEANDERING LABORATORY CHANNEL

1 INTRODUCTION River erosion is a complex phenomenon. The rate of bank retreat is determined by flow, bed topography, sediment transport, bank properties, and water quality. Prediction of future river planform changes and the knowledge of river erosion and river meandering are required for land use planning in alluvial river valleys and determining locations for bridges and hydraulic structures. The control of riverbank erosion requires prediction of flow and bed features in a meanderin…