combined visual and quantitative techniques in the study of natural turbulent flows an important difficulty in understanding turbulence in natural flows is that one does not see what is being measured by devices recording velocity fluctuations this study shows how visualization of turbulent structures can be effectively implemented in natural river flows in order to match turbulent flow structures with their velocity signatures flow visualization is combined with high frequency 20 hz velocity measurements from electromagnetic current meters two fluvial environments are examined in a river confluence where the difference in turbidity provides a natural tracer very strong negative velocity fluctuations for the streamwise component are concomitant with an upwelling motion a video recording made from a bridge of the passage of turbulent structures delineated by turbid and clear water allowed us to relate the marked fluctuations in velocity to eddies of a duration of 1 2 s in the mixing layer in a gravel bed river we have examined patterns of eddy shedding in the lee of a pebble cluster these patterns were highlighted by dye milk injected in the separation zone downstream black and white images were obtained from an underwater lens linked to a video camera recorder we observed a complex dynamic characterized by two dominant patterns of eddy shedding one with a clear motion of eddies toward the water surface and another with a downward expansion toward the bed of the structures this pattern is related to the passage of intermittent wedges of low speed fluid separated by wedges of fast moving fluid

obtuse angle vs confluent sharp meander bends insights from the paraguay cuiaba confluence in the tropical pantanal wetlands brazil abstract river confluences are notable features in the drainage system with complex hydrodynamics bed morphology sediment transport and mixing processes junction planform plays a pivotal role in the confluence hydrodynamics however most investigations have concentrated on the junction of two straight channels and few studies have focused on confluent meander bends or obtuse angle confluences here we analyze a confluence with an obtuse angle planform the tributary enters the confluence at an angle higher than 180 that abruptly curves to join the main river in the pantanal wetlands the strong flood wave is responsible for significant variations of the discharge and momentum flux ratios within the confluence consequently the paraguay cuiaba confluence is able to shift from an obtuse angle working mode to a confluent meander bend working mode according to the hydrological conditions when the momentum ratio is greater than 1 mr 1 the confluence works as an obtuse angle junction whereas when the ratio is less than 1 mr

numerical modelling of self potential signals associated with a pumping test experiment summary the study of electrical signals associated with groundwater flow is a powerful method to determine in a non invasive way the distribution of hydraulic heads in aquifers hence the distribution of the hydraulic conductivity and storativity experimental hydraulic heads and electrical self potential sp signals associated with a pumping test in an unconfined aquifer were reproduced with a numerical model based on the finite difference method for simplicity we assumed axial symmetry around the pumping well we assessed the equivalent hydraulic conductivity and specific storage of the aquifer by fitting the piezometric levels obtained in the course of the pumping against synthetic hydraulic heads produced by the model the current coupling coefficient is obtained from the best fit between the experimental and modelled sp signals at the end of the pumping phase then keeping the previously determined hydraulic parameters the relaxation of both the hydraulic heads and the sp signals were modelled and found to be consistent with the measured values the data show almost linear relationships between the hydraulic heads in the aquifer and the electrical signals recorded at the ground surface these results show that sp signals allow monitoring subsurface flow in the course of pumping experiments

the influence of tributary flow density differences on the hydrodynamic behavior of a confluent meander bend and implications for flow mixing abstract the goal of this study is to evaluate the influence of tributary flow density differences on hydrodynamics and mixing at a confluent meander bend a detailed field characterization is performed using an acoustic doppler current profiler adcp for quantification of the 3d flow field flow discharge and bathymetry as well as ctd measurements conductivity temperature depth to characterize the patterns of mixing satellite images of the confluence taken at complementary times to the field surveys were analyzed to evaluate the confluence hydrodynamics at different flow conditions the results illustrate the differences in hydrodynamics and mixing length in relation to confluences with equal density tributaries at low density differences and higher discharge ratio qr between the two rivers the flow is similar to equi density confluent meander bends in contrast at high density differences low qr the tributary flow is confined to near the confluence but the density difference causes the flow to move across channel in this case the density difference causes the lateral spread of the tributary flow to be greater than at a greater qr when the density difference is less these results illustrate the potential importance of density differences between tributaries in determining the rate and spatial extent of mixing and sediment dispersal at confluent meander bends

turbulent mixing in the amazon river the isotopic memory of confluences earth and planetary science letters 290 2010 pp 37 43

effects of bed discordance on flow dynamics at open channel confluences although a discordance in bed elevation between mainstream and tributary channels is a common feature of most river confluences this height differential is largely ignored in many models of junction flow dynamics here we present new laboratory flume data that demonstrate the significant influence of bed discordance on flow at an acute angled confluence a difference in bed height between mainstream and tributary channels is shown to obliterate flow deflection at the bed and create a distortion of the mixing layer between the flows resulting in fluid upwelling at the downstream junction corner this upwelling is responsible for the absence of a flow separation zone near the bed at the downstream junction corner and the lack of a zone of marked flow acceleration in the postconfluence channel these experiments reveal complex flow fields generated by bed discordance and suggest the need for major revisions to current models of river channel confluence flow dynamics and their application to sediment routing at these sites

a semi analytical solution for transient streaming potentials associated with confined aquifer pumping tests we consider the transient streaming potential response due to pumping from a confined aquifer through a fully penetrating line sink confined aquifer flow is assumed to occur without fluid leakage from the confining units however since confining units are typically clayey and hence more electrically conductive than the aquifer they are treated as non insulating in our three layer conceptual model we develop a semi analytical solution for the transient streaming potentials response of the aquifer and the confining units to pumping of the aquifer the solution is fitted to field measurements of streaming potentials associated with an aquifer test performed at a site located near montalto uffugo in the region of calabria in southern italy this yields an average hydraulic conductivity that compares well to the estimate obtained using only hydraulic head data specific storage is estimated with greater estimation uncertainty than hydraulic conductivity and is significantly smaller than that estimated from hydraulic head data this indicates that specific storage may be a more difficult parameter to estimate from streaming potential data the mismatch may also be due to the fact that only recovery streaming potential data were used here whereas head data for both production and recovery were used the estimate from head data may also constitute an upper bound since head data were not corrected for pumping and observation wellbore storage estimated values of the electrical conductivities of the confining units compare well to those estimated using electrical resistivity tomography our work indicates that where observation wells are unavailable to provide more direct estimates streaming potential data collected at land surface may in principle be used to provide preliminary estimates of aquifer hydraulic conductivity and specific storage where the latter is estimated with greater uncertainty than the former

bed morphology and sedimentology at the confluence of unequal depth channels abstract spatial and temporal variations in the bed geometry and bed material size of a sand bed river confluence with unequal depth channels were monitored during a sequence of floods additionally two other sand bed confluences were surveyed to test the replicability of these observations the confluences studied here have only one avalanche face which corresponds to the front of a tributary mouth bar in the shallower channel and do not exhibit a marked scour zone three distinct morpho sedimentological zones are present 1 an area around the upstream corner of the junction where the sediments are generally finer than the mean 2 a maximum depth zone with coarser than average particles and 3 a bar at the downstream junction corner where grain size is finer than the mean and decreases slightly downstream changes in relative discharge between the two channels had little effect on the grain size of the downstream junction corner bar but exerted a strong influence on the position of the maximum depth zone and the front of the tributary mouth bar the downstream junction corner bar showed little evidence of the separation zone which is commonly observed at the confluences of laboratory channels the contrasting depths of the approach channels at the sites studied here may be partly responsible for the absence of the separation zone

on the mixing of rivers with a difference in density the case of the negro solimoes confluence brazil abstract confluences are common components of all riverine systems and characterized by converging streamlines and potential mixing of separate flows the fluid dynamics of confluences possess a highly complex structure with several common types of flow features observed an investigation was carried out in both low and relatively high flow conditions at the confluence of the negro and solimoes rivers brazil which ranks among the largest river junctions on earth during this field research acoustic doppler velocity profiling adcp and water quality sampling were applied to investigate hydrodynamics sediment transport and mixing characteristics at this confluence it was found that the location and the width of the mixing interface were closely related to changes of the discharge ratio between the tributaries due to both seasonal and annual variations second a timescales analysis was applied to comparatively identify the contribution to mixing at the negro solimoes confluence of four processes difference in 1 velocity and 2 density between the rivers 3 bed friction including form drag and 4 change in channel width the analysis demonstrated that adjustments of confluence hydrodynamics and morphodynamics can modify the relative importance of each contribution immediately downstream of the junction the effects of differences in velocity and density were comparable while farther downstream the latter was predominant and the role of bed friction was significant at the end this study suggests that mixing at the negro solimoes confluence can be explained as a combination of the four hydrologic and morphologic processes

an investigation of the flow and scour mechanisms around isolated spur dikes in a shallow open channel 1 conditions corresponding to the initiation of the erosion and deposition process 1 the present study investigates the flow physics and the role played by the main coherent structures in the scouring processes around a vertical spur dike in a straight channel at conditions corresponding to the start flat bed of the scouring process large eddy simulation les is performed at a relatively low channel reynolds number re 18 000 in the range where most flume studies with clear water scour conditions are conducted similar to these studies the incoming flow is fully turbulent and contains realistic turbulence fluctuations visualization experiments are conducted to better understand the nature of the interactions between the dominant coherent structures playing a role in the erosion process it is found that the structure of the horseshoe vortex hv system at the base of the spur dike changes considerably in time and in vertical sections perpendicular to the trajectory defined by the axis of the main necklace vortex however its intensity is the largest at vertical sections situated around the tip of the spur dike it is in this region that the core of the main necklace vortex oscillates aperiodically between two preferred modes in one of them zero flow mode the necklace vortex is closer to the spur dike and more compact and the near bed jet flow beneath it is weak in the other one back flow mode a strong near bed jet flow convects the primary necklace vortex away from the spur dike and its core is more elongated and less compact this explains the large amplification by about 1 order of magnitude compared to the surrounding turbulent flow of the turbulent kinetic energy and pressure fluctuations inside the hv system in the region situated around the tip of the spur dike and the double peak distribution of the turbulent kinetic energy past the spur dike in the legs of the necklace vortex the intensity of the bimodal oscillations decreases such that they are not observed in spanwise sections situated at more than one channel depth behind the spur dike it is found that the legs of the horseshoe vortices can interact at times with the vortex tubes shed in the detached shear layer dsl and with the tip of the spur dike these events typically result in a significant change in the coherence of the hv system the largest bed shear stress values in the mean flow are present in the strong acceleration region near the tip of the spur dike but high bed shear stress values are also observed beneath the upstream part of the dsl the bed shear stress fluctuations around the local mean values can be very high especially in the region situated beneath the upstream part of the dsl at random times some of the vortices shed in the dsl merge or interact with eddies from the recirculation region this leads to an increase in their strength and to a large increase of the bed shear stress along their path

the linkage between velocity patterns and sediment entrainment in a forced pool and riffle unit a field based project was initiated in order to characterize velocities and sediment entrainment in a forced pool and riffle sequence three dimensional velocities and turbulence intensities were measured with an acoustic doppler velocimeter at 222 different points at three similar flows that averaged approximately 4 35 m 3 s 1 within a large pool riffle unit on north saint vrain creek colorado sediment sorting patterns were observed with the introduction of 500 tracer particles painted according to initial seeding location tracer particles moved sporadically during a 113 day period in response to the annual snowmelt peak flow which reached a maximum level of 14 8 m 3 s 1 velocity data indicate high instantaneous velocities and turbulence levels in the centre of pools patterns of sediment deposition support the notion that stream competence is higher in the pool than the downstream riffle flow convergence around a large channel constriction appears to play a major role in multiple processes that include helical flow development and sediment routing and backwater development with low velocities and turbulence levels above the constriction that may locally limit sediment supply jet flow flow separation vortex scour and turbulence generation enhance scour in the centre of pools ultimately multiple processes appear to play some role in maintenance of this forced pool and the associated riffle copyright 2008 john wiley and sons ltd

field measurements of three dimensional hydraulics in a step pool channel we investigated the effects of morphologic position and discharge on flow structure in a steep 0 10m m mountain channel by collecting three dimensional measurements of time averaged and turbulent velocity components with a sontek flowtracker handheld adv acoustic doppler velocimeter on a 30 m reach of a step pool channel in the colorado rockies velocity profiles were measured at morphologic positions characteristic of steep channels above steps step lips base of steps pools cascades runs and at five different discharges a marked three dimensionality of flow structure was documented in east st louis creek velocities in the streamwise component were the largest contributors to overall velocity vector magnitudes cross stream and vertical components contributed averages of 20 and 15 respectively to overall vector magnitudes turbulence intensities were especially multi dimensional however with large contributions to turbulent kinetic energy from the vertical component of velocity analysis of variance indicated that discharge and morphologic position significantly affected mean streamwise velocities with substantially higher velocities upstream from steps than in pools discharge and morphology effects on cross stream and vertical velocity components however were not significant discharge and morphologic position also significantly affected turbulence intensities for all flow components with the greatest turbulence intensities occurring in pools and at high discharges these results illustrate the strong discharge dependence of hydraulics in step pool channels where relative submergence of bedforms changes rapidly with discharge and the substantial spatial variation in hydraulics created by step pool sequences

field investigation of three dimensional flow structure at stream confluences 2 turbulence stream confluences are among the most highly turbulent locations in fluvial systems this paper examines the three dimensional structure of turbulence at three stream confluences in east central illinois the analysis focuses on the characteristics of turbulence both within the shear layer and in the ambient flow results show that at the upstream end of each confluence the shear layer occupies a limited portion of the flow cross sectional area but turbulence kinetic energy within this layer is 2 3 times greater than the turbulence kinetic energy of the ambient flow which has turbulence characteristics similar to those for flow in straight channels turbulence within the shear layer can be characterized as quasi two dimensional in the sense that large scale turbulence generated by transverse shear is predominantly two dimensional whereas small scale turbulence associated with bed friction is three dimensional spectral analysis suggests that the structure of fluid motion within the shear layer differs for confluences with symmetrical versus asymmetrical planforms the shear layer dissipates rapidly as flow enters the downstream channel even though a well defined mixing interface persists at downstream locations

causes of rapid mixing at a junction of two large rivers rio parana and rio paraguay argentina 1 airborne and satellite observations show that when large rivers join they can take hundreds of kilometers to mix completely but on occasion may mix very rapidly application of established semitheoretical analyses shows that long mixing lengths should be expected the first measurements of mixing processes at a large river junction rio parana and rio paraguay argentina combined width 2 8 km are presented at two occasions first when they mix in 400 km and second when mixing is complete in only 8 km downstream of the junction for the case of slower mixing at a point surveys showed that mixing driven by turbulent shear associated with a near vertical shear layer was restricted to close to the junction to 0 272 multiples of the postconfluence width downstream transect surveys showed penetration of more turbid water from the rio paraguay underneath the rio parana but this was insufficient to promote more rapid mixing there was no clear channel scale circulation present and slow mixing was compounded by reverse topographic forcing on the mainstream rio parana side of the river this kept more turbid water on the rio paraguay side of the river close to the bed in the case of rapid mixing we found clear channel scale circulation the momentum ratio between the combining flows reinforced the effects of the discordance in bed height between the tributaries at the confluence and allowed penetration of more turbid rio paraguay water further across the channel width deeper within the flow the importance of the interaction between momentum ratio and bed morphology at channel junctions makes mixing rates at the confluence dependent upon basin scale hydrological response which is more likely to differ between large confluent rivers than small rivers as a result of the different climatic topographic zones that they may capture

investigation of controls on secondary circulation in a simple confluence geometry using a three dimensional numerical model recent research into river channel confluences has identified confluence geometry and particularly bed discordance as a control on confluence flow structures and mixing processes and this has been illustrated using both field measurements in natural confluences and laboratory measurements of simplified confluences generalization of the results obtained from these experiments is limited by the number of confluence geometries that can be examined in a reasonable amount of time this limitation may be overcome by numerical models in which confluence geometry is more readily varied and data acquired more rapidly this paper aims to i validate the application of a three dimensional numerical model to a simple confluence geometry ii simulate the effects of different boundary condition values upon flow structures and iii interpret the implications of these simulations for river channel confluence dynamics the model used in this research solves the three dimensional form of the navier stokes equations and is used to simulate the flow in a parallel confluence of unequal depth channels and to investigate the effect of different combinations of velocity and depth ratio between the two tributaries the results generally agree with empirical evidence that secondary circulation is generated in the absence of streamline curvature but only for specific combinations of depth and velocity ratio this research shows how understanding of the interaction of these controls is enhanced if pressure gradients are considered the velocity ratio is the prime determinant of the cross stream pressure gradient that initiates cross stream velocities however for significant secondary circulation to form cross stream velocities must lead to significant transfer of fluid in the cross stream direction this depends on the vertical extent of the cross stream pressure gradient which is controlled by the depth ratio in this study strong secondary circulation occurred for a depth differential of 25 or more as long as the velocity in the shallower tributary was at least as great as that in the deeper channel this provides an important context for interpretation of previous work and for the design of new experiments in both the field and the laboratory 1998 john wiley sons ltd

electrokinetic spontaneous polarization in porous media petrophysics and numerical modelling abstract the behaviour of streaming potential is directly related to movement of groundwater the responses for typical subsurface flows are modelled to investigate possibilities of spontaneous polarization sp when performing quantitative data interpretation the physical properties of geomaterials related to streaming potential are described a magnitude range of streaming current coefficient is assessed for geomaterials and found to be from 10 10 to 10 8 a pa m depending on water salinity and rock composition the electrical sources of sp caused by groundwater flow in saturated media are theoretically described it is shown that sp is completely defined by three types of electrical sources situated 1 on boundaries where water enters or quits porous media 2 in areas with transient regime and 3 on the boundaries of rocks with different properties hydraulic conductivity streaming current coefficients and electrical conductivity a 2d computer program based on the method of finite difference was created to provide numerical successive modelling of both groundwater flow and sp using sill s geophysics 48 1983 76 approach first the water heads are calculated then electrical sources of sp are obtained on the basis of the calculated heads and coefficient of streaming current finally the sp is obtained on the basis of calculated electrical sources and subsurface electrical conductivity numerical examples illustrating sp responses of infiltration of barrage with different electrical conductivity and of well pumping are discussed field data obtained at the site containing the dam between superficial artificial reservoir and the river are interpreted on the basis of numerical modelling the discussed method can be mainly used for additional calibration of groundwater flow models

mixing layer distortion at the confluence of channels of different depth channel confluences have received considerable recent attention in the fields of geomorphology1 3 sedimentology4 9 and hydraulic engineering10 13 where channels join rapid changes in fluid velocity turbulence intensity channel hydraulic geometry and bed geometry may occur14 17 previous models of junction dynamics have tended to assume that the confluent channels are of equal depth10 18 a condition that may be found only rarely in natural junctions more often the depths of confluent channels are different19 this discordance is commonly the result of the forma tion at the mouth of each confluent channel of bars that possess steep avalanche faces which dip into a central junction scour1 2 5 20 here we suggest that when channels of different depth join the mixing layer that forms at their confluence is distorted by interacting with a separation zone which forms in the lee of the mouth of the shallower channel this mixing layer distortion imparts a complex three dimensional flow to the junction promoting vertical fluid upwelling and significantly enhancing rapid mixing within the flow of the shallow tributary while retarding the rate of mixing across the flow of the deeper channel suspended sediments or contaminants within the deeper channel may be transferred rapidly across the flow of the shallower tributary upwelling downstream of the junction

flow and sediment dynamics in channel confluences confluences with relatively low discharge and momentum flux ratios where a small steep tributary with a high supply of poorly sorted sediment joins a large low gradient main channel commonly occur in nature but they have not yet been investigated measurements of the three dimensional velocity field turbulence sediment transport bed material grain size and morphology are reported in a laboratory setting that is representative of confluences on the upper rhone river switzerland the difference between the low flow depth in the steep tributary and the higher flow depth in the main channel creates a marked bed discordance in the tributary zone due to this bed discordance the tributary flow penetrates into the main channel mainly in the upper part of the water column whereas the main channel flow is hardly hindered by the tributary in the lower part of the water column giving rise to a two layer flow structure in the confluence zone in confluences with high supply of coarse sediment from the tributary the development of a deposition bar downstream from the confluence reduces the flow area and causes flow acceleration that contributes to an increase in sediment transport capacity the sediment supplied by the tributary is mainly sorted and transported on the face of the bar by the near bed flow originating from the main channel the sediment transport capacity is further increased by the three dimensionality of the flow which is characterized by maximum velocities occurring near the bed and by a considerable increase in turbulent kinetic energy generated in the shear layer at the interface of the flows originating from the main channel and the tributary a conceptual model is proposed for the hydro morpho sedimentary processes and compared to existing conceptual models for confluences with different characteristics

numerical evaluation of the effects of planform geometry and inflow conditions on flow turbulence structure and bed shear velocity at a stream confluence with a concordant bed this study numerically investigates the effects of variations in inflow conditions and planform geometry on large scale coherent flow structures and bed friction velocities at a stream confluence with natural bathymetry and concordant bed morphology several numerical experiments are conducted in which either the kelvin helmholtz mode or the wake mode dominates within the mixing interface mi between the two confluent streams as the junction angle and alignments of the tributaries are altered in the kelvin helmholtz mode the mi contains mostly corotating vortices driven by the mean transverse shear across the mi while in the wake mode the mi contains counterrotating vortices forming by the interaction of the separated shear layers on the two sides of a zone of stagnant fluid near the junction corner a large angle between the two incoming streams is not necessary for the development of strongly coherent streamwise oriented vortical sov cells in the immediate vicinity of the mi results show that such sov cells can develop and produce high bed friction velocities even for cases with a low angle between the two tributaries and for cases where the downstream channel is approximately aligned with the axes of the two tributaries low curvature cases sov cells tend not to develop only when the incoming streams are parallel and aligned with the downstream channel junction angle of zero and the incoming flows produce a strong kelvin helmholtz mode under such conditions quasi 2 d mi vortices play the primary role in mixing and the production of high bed shear velocities simulations with and without natural bed morphology local bank line irregularities indicate that planform geometry and inflow conditions primarily govern the development of coherent flow structures but that bathymetric and bank line effects can locally modify details of these structures

dynamics of a river channel confluence with discordant beds flow turbulence bed load sediment transport and bed morphology 1 river channel confluences play a major role in the dynamics of all fluvial systems and yet our understanding of bed load routing at these sites is very sparse the dynamics of confluences are a function of the momentum ratio between the combining flows and the three dimensional geometry of the junction recent experiments have shown that discordance in bed height between the confluent rivers increases turbulence intensity and enhances upwelling of flow within the confluence however the significance of these flow characteristics on sediment transport is still unknown to examine the relations between flow and sediment transport we have measured near bed flow turbulence bed load transport rates and changes in bed morphology for eight different flow conditions at a sand bed discordant confluence detailed analysis of the near bed flow patterns reveals that within the shear layer low mean flow velocities are combined with the highest values of reynolds shear stresses and that turbulence generation is associated with intense upward movements of flow high sediment transport rates are found at the edges of the shear layer region where horizontal vertical cross stresses uw are high these patterns match changes in bed morphology where erosion occurs along the shear layer the relation between the shear layer and sediment transport confirms the role of bed discordance on the dynamics of the confluence migration of the shear layer into the confluence as a result of a change in momentum ratio modifies local near bed flow characteristics sediment transport rates and the spatial distribution of deposition and erosion zones

hydraulic conditions in experimental rill confluences and scour in erodible soils 1 few studies have examined processes active within rill networks or the effect of confluence geometry on rill sediment flux and it is not clear if observations from river confluences also apply at rill scale laboratory experiments were carried out in artificial rectangular rill channels with fixed and erodible beds to identify the effects of confluence geometry on hydraulic conditions and scour patterns symmetrical and asymmetrical confluences with angles from 19 to 90 were used hydraulic changes in the confluence zone in fixed bed experiments included decreased flow velocity increased shear velocity transition from supercritical to subcritical and from transitional to turbulent flow bed scour in the confluence zone resulted generally increasing with confluence angle but a more important influence was junction symmetry or asymmetry symmetrical confluences produced a symmetrical scour pattern mirroring the original channels but in asymmetrical confluences scour was more complex evolving to a symmetrical pattern with confluence angles higher than the original system results are consistent with channel evolution to an optimally branched system controlled by minimum power criteria but validation requires testing with more precise velocity measurement

on the evolution and form of coherent flow structures over a gravel bed insights from whole flow field visualization and measurement the microtopography of a gravel bed river has been shown to generate turbulent flow structures that originate from shear flow generated in the near bed region although field and laboratory measurements have shown that such flows contain a range of coherent flow structures cfs the origin evolution and characteristics of the turbulent structures are poorly understood here we apply a combined experimental methodology using planar laser induced fluorescence and particle imaging velocimetry lif piv to measure simultaneously the geometric kinematic and dynamic characteristics of these cfs the flow structures were analyzed by applying standard reynolds decomposition and lagrangian vortex detection methods to understand their evolution propagation and growth in the boundary layer and characterize their internal dynamical complexity the lif results identify large individual fluid packets that are initiated at the bed through shear that generate a bursting mechanism when these large individual fluid packets are analyzed through direct flow measurement they are found to contain several smaller scales of fluid motion within the one larger individual fluid parcel flow measurements demonstrate that near bed shear controls the initiation and evolution of these cfs through merging with vortex chains that originate at the bed the vortex chains show both the coalescence in the formation of the larger structures and also the shedding of vortices from the edges of these packets which may influence the life span and mixing of cfs in open channels the life span and geometric characteristics of such cfs are critical in influencing the duration and intensity of near bed stresses that are responsible for the entrainment of sediment

petroleum inclusions in sedimentary basins systematics analytical methods and applications abstract fluid dynamics in sedimentary basins is of tremendous interest both from a scientific and an economic point of view integration between fluid inclusion and present day fluid data provides the time aspect necessary for reconstruction of fluid flow paths and can be used for mapping fluid dynamics both on a regional basin scale or on the more local scale of petroleum reservoirs this paper presents a review of analytical and modelling methods for petroleum in fluid inclusions essentially four types of data for petroleum inclusions can be established through analysis and modelling 1 textures which give indirect information of the time aspect 2 fluid composition 3 fluid properties and 4 pressure temperature of trapping during the last decade development of analytical methods for determination of inclusion fluid compositions has taken place traditional correlation studies for characterisation of maturity and source facies may now therefore include fluid inclusion data the development has also been directed towards an improved understanding of the physical properties of petroleum inclusions although these methods are in their early stages concerning precision and accuracy data necessary for fluid flow modelling such as fluid densities viscosities pressure and temperature can be estimated

resolving two dimensional flow structure in rivers using large scale particle image velocimetry an example from a stream confluence large scale particle image velocimetry lspiv has emerged as a valuable tool for measuring surface velocity in a variety of fluvial systems lspiv has typically been used in the field to obtain velocity or discharge measurements in relatively simple one dimensional flow detailed two dimensional or three dimensional characterization of flow structure has been relegated to laboratory settings because of the difficulty in controlling piv limiting factors such as poor particle seeding the need for camera rectification and challenging field conditions in this study we implement a low cost lspiv setup using a high resolution action camera mounted above a stream confluence and water seeded with recycled landscape mulch time averaged 2d velocities derived from lspiv are compared with those measured with an acoustic doppler velocimeter adv in the camera s field of view we also assess the capabilities of this setup to resolve both turbulent and time averaged flow structures at a stream confluence our results reveal that even in challenging field conditions a basic lspiv setup can yield accurate data on velocity and resolve in detail the temporal evolution of flow structures on the surface of rivers the resulting dataset contains velocity information at high spatial and temporal resolution a significant advance in understanding flow processes at stream confluences our lspiv analysis provides support for previous numerical modeling studies that have distinguished between kelvin helmholtz and wake modes of turbulent behavior within the mixing interface at confluences this study shows that lspiv should be considered as both an alternative for traditional methods and a tool that can provide unprecedented levels of resolution of surface velocity patterns on rivers that can be used to evaluate numerical predictions of flow structure in complex fluvial environments this article is protected by copyright all rights reserved

structure of flow over alluvial bedforms an experiment on linking field and laboratory methods this paper presents results of a field study designed to examine the structure of flow over mobile and fixed bedforms in a natural stream and to compare the results with findings of previous laboratory studies within the framework of double time space averaging approach measurements of turbulence were obtained in a small river in illinois usa over a fine spatial grid of sampling points above a mobile sandy bedform and its artificially moulded replica flow structure over the artificial bedform is similar to that observed in laboratory studies but is markedly different from the flow structure over natural bedforms these differences are most pronounced in the roughness sublayer whereas flow in the logarithmic layer over natural and artificial sand waves is fairly similar and exhibits spatial uniformity the double time space averaged distributions of turbulence statistics conform to the multilayer model of flow structure over bedforms mean velocity distributions indicate neither classical flow recirculation nor substantial reduction of velocities in the lee of bedform crests however vertical patterns of turbulence statistics over depth suggest that stacked wakes similar to those observed in laboratory studies exist above the bedforms thus despite the absence of flow separation wake development seems to be induced by the systematic influence of upstream bedforms on the vertical structure of turbulence copyright 2006 john wiley sons ltd

estimating aquifer hydraulic properties from the inversion of surface streaming potential sp anomalies 1 electrokinetic effects of water flow during pumping tests have been shown to generate surface streaming potential sp anomalies of several tens of mv that are well correlated with the geometry of the water table it follows that sp measurements can be used to estimate aquifer hydraulic properties we have developed an inversion scheme for surface sp data generated by flow pumping and found that we are able to estimate the hydraulic conductivity and the depth and the thickness of the aquifer we applied our inversion scheme to the data from bogoslovsky and ogilvy 1973 and found a hydraulic conductivity of 10 5 m s 1 an aquifer thickness of roughly 28 m and an electrokinetic coupling coefficient of 1 mv m 1 these values are in the range of what is expected for this kind of environment

the application of computational fluid dynamics to natural river channels eddy resolving versus mean flow approaches in the last decade as computing power has increased there has been an explosion in the use of eddy resolving numerical methods in the engineering earth and environmental sciences for complex geomorphic flows where accurate field investigations are difficult to perform and where experiments may be difficult to scale these numerical approaches are beginning to give key insights into the nature of these flows eddy resolving methods such as large and detached eddy simulation les des may be contrasted with the time averaged three dimensional simulations that only really began to be applied seriously in geomorphology fifteen years ago while the potential of les for geomorphology has been examined previously des is a relatively recent method that deserves further consideration in this paper we explain the method and then utilise examples from meander and confluence flows as well as flow near the bed of a gravel bed river to highlight the improvements to both the representation of the mean flow and to the representation of time varying processes that result from the use of les des some suggestions are provided for the future use of such techniques in geomorphology

impact of confluence on hydrological and morphological characters of the trunk stream a study on the manu river of north east india tributaries play a significant role in changing flow structure of the main river through their additional discharge a study was conducted at the point of convergence of the river deo with the river manu using simple geospatial technique and field work to justify the hydrological and morphological changes in downstream of the confluence point the spatio temporal change of both the river channels for 10 km length in upstream and downstream of the confluence point was considered moreover field measurements and post field work were carried out to examine the spatial variation of hydrodynamic characteristics like flow velocity depth water discharge wetted perimeter and hydraulic radius of the selected stretches sieving method was applied for grain size analysis of river bed sediment samples the result revealed that both the aggradation and degradation processes were equally active in the upstream segment of the manu river but in downstream segment aggradation exceeded the degradation activity though all the hydrodynamic variables were boosted up in downstream except flow velocity the present research highlighted that the steeper gradient of the r deo had enhanced its competency to transport medium sized grains to the r manu where fine grains were commonly found moreover increased wetted perimeter in downstream specified more friction between channel bed and its flow consequent upon reduced flow velocity with extra sediment load accumulation

principles of electrography applied to self potential electrokinetic sources and hydrogeological applications 1 the electrical potential field passively recorded at the ground surface of the earth and termed self potential can be analyzed to determine the shape and the depth of the piezometric surface the coupling between hydraulic flow and electrical current density is electrokinetic in nature the electrokinetic coupling coefficient entering into the integral equation relating the depth of the water table to self potential signals is analyzed for various types of porous materials it is simply related to the electrical conductivity of the pore water in steady state conditions each element of the water table can be seen as an elementary dipole with an inclination locally perpendicular to the water table and strength proportional to the water table elevation then we propose three methods to obtain the shape and range of possible depths of the water table from the study of the self potential distribution recorded at the ground surface the nonuniqueness of the solution is removed if one knows either the electrokinetic coupling coefficient or the water table at one location and under the assumption of the spatial homogeneity of the electrokinetic coupling coefficient two field cases are discussed to show the success of the proposed methods for estimating the shape and depth of the water table at two different scales of investigations they concern the study of self potential signals associated with the shape of the water table in the vicinity of a pumping well and in the flank of the kilauea volcano

spatial and temporal structure of shear layer turbulence at a stream confluence 1 the shear layer that develops at the interface between converging flows is a prominent but poorly understood hydrodynamic feature at stream confluences to examine the spatial and temporal characteristics of turbulence and coherent turbulent structures within a shear layer three dimensional velocity measurements were obtained at a small stream confluence in illinois using two acoustic doppler velocimeters spaced at various separation distances results indicate that coherent structures can be readily identified through cross correlation analysis of the velocity time series for different measurement locations maximum correlations decrease relatively slowly over short separation distances but decrease rapidly for separation distances greater than about 2 times the flow depth convective velocities of coherent structures derived from the correlation analysis differ from local mean velocities and from spatially averaged mean velocities indicating that coherent structures evolve as they are transported along the shear layer a finding consistent with dye tracing experiments despite this evolution correlation and spectral analyses indicate that the frozen turbulence hypothesis holds for frequencies corresponding to length scales of at least some shear generated coherent vortices a domain of quasi two dimensional turbulence energy at low frequencies appears to be associated with large scale intrusions of fluid from one stream into the other along the mixing interface

effects of vegetation canopy density and bank angle on near bank patterns of turbulence and reynolds stresses abstractvegetation growing on the surface of a streambank has been shown to alter the shear stresses applied to the boundary but basic questions remain regarding the influence of vegetation and streambank configurations on near bank hydraulics in the present study froude scaled flume experiments were used to investigate how changes in vegetation density ratio of frontal area to channel area including both stems and leaves and bank surface angle influence near bank turbulence intensities rmsu v w and reynolds stresses uv and uw estimated using velocities obtained with an acoustic doppler velocimeter positioned beneath the canopy results illustrate how with increasing vegetation density turbulence intensities and reynolds stresses decreased along the sloped bank surface but increased at the base of the slope and within the main channel the steeper bank angle resulted in greater vertical stresses on the bank surface than the shallower angle but lateral momentum exchange was larger than verti

velocity profiles and the structure of turbulence at the outer bank of a compound meander bend abstract few studies have quantified near bank turbulence at the field scale in meander bends as a result details of the structure of turbulence at the outer bank of bends are poorly understood despite recognized linkages among turbulence bank erosion and channel migration this study uses high frequency measurements of flow velocities to analyze the characteristics of turbulence in close proximity to the outer bank of an actively migrating compound meander bend results show that the structure of turbulence in the bend is linked to curvature induced effects through the progressive advection of high momentum fluid toward the outer bank as flow moves through the bend vertical profiles of streamwise vertical reynolds stresses near the outer bank differ considerably from those in wide straight channels because of the effects both of curvature induced helical motion and of local frictional effects associated with the complex bank morphology the results of the study provide the basis for a conceptual model of the structure of outer bank turbulence in this meander bend

three dimensional structure of flow at a confluence of river channels with discordant beds this paper presents three dimensional data of the mean and turbulent structure of flow collected at a natural confluence of rivers with discordant beds to 1 describe the three dimensional flow field of a natural junction of channels 2 assess the role of changes in bed morphology occurring during transport effective events on the structure of flow at a confluence and 3 examine how the three dimensional structure of flow varies with changes in the ratio of momentum flux between the two confluent streams three dimensional measurements of velocity were reconstructed from the measurements obtained with an array of four two component electromagnetic current meters six detailed velocity profiles were taken at five cross sections in a wide range of flow conditions the mean field of flow is characterised by 1 the acceleration of flow in the downstream portion of the post confluence channel but by lower velocities upstream in the mixing layer area 2 a stagnation zone at the apex of the junction 3 a zone of flow deviation and strong fluid upwelling close to the avalanche face and at the margin of the tributary mouth bar and 4 reduced velocities over the depositional bar at the downstream junction corner the position and extent of these zones vary with changes in the ratio of momentum flux very high intensity of turbulence peaks up to 50 and turbulent kinetic energy were observed in the mixing layer region distortion of the mixing layer characteristic of flow where bed discordance is present between the two tributary channels was evident from mean and turbulent flow data this field study suggests that the effects of bed discordance on flow sediment transport and the resultant bed morphology must be incorporated into conceptual and numeric models of these sites of complex flow

response of bed morphology and bed material texture to hydrological conditions at an asymmetrical stream confluence changes in bed morphology and sedimentology at stream confluences in relation to specific hydrological events have not been documented extensively moreover few if any studies have investigated the effect of net hydrological conditions on channel change at a confluence over a period of many years repeat cross section surveys and sampling of bed material at a small asymmetrical stream confluence reveal the short term effects of hydrological variability on bed morphology and spatial patterns of bed material texture survey data over a 15 year period illustrate the long term response of channel morphology at the confluence to net hydrological conditions results confirm that this confluence is a dynamic fluvial environment involving shifts in the zone of scour and repeated deposition and erosion of a bar complex at the downstream junction corner as the discharge ratio changes in response to hydrological variability in the tributary streams persistent faster runoff response times of the lateral tributary compared to the main stem have resulted in long term net erosion of the channel bank opposite this tributary the documented morphological and sedimentological changes are consistent with and can be explained by results of experimental studies and by past investigations at this confluence that have documented changes in patterns of mean flow structure and turbulence in response to variation in the discharge ratio of contributing streams

three dimensional measurement of river channel flow processes using acoustic doppler velocimetry this paper describes and assesses i the use of a new instrument for the determination of three dimensional flow velocities in natural rivers the acoustic doppler velocimeter adv and ii a method for positioning and orienting such measurements relative to a single local coordinate system to relate flow velocity vectors with the bed and water surface the adv uses the doppler shift principle to measure the velocity of small particles assuming to be moving at velocities similar to the fluid velocity is resolved into three orthogonal components and measured in a volume 5 cm below the sensor head minimizing interference of the flow field and allowing measurements to be made close to the bed a simple method for positioning and orienting the instrument using digital tacheometry is described and is used to obtain velocity measurements concurrently with measurements of both bed and water surface topography the paper includes a preliminary field assessment of the adv by comparing velocity profiles with those generated from marsh mcbirney electromagnetic current meters and a full field assessment of the position and orientation methodology these results suggest that the recommended methods in combination with an adv are able to provide reliable mean three dimensional velocity field information and accurate bed and surface topography copyright 1998 john wiley sons ltd

an experimental study of fluvial processes at asymmetrical river confluences with hyperconcentrated tributary flows abstract this paper reports findings from experimental studies of sediment transport and bed morphology at asymmetrical confluences with hyperconcentrated tributary flows in the upper yellow river the results indicate that the hyperconcentrated flow confluence can be divided into four hydraulic regions including the backwater zone above the upstream junction corner the maximum velocity area the separation flow zone and the post confluence region downstream of the junction corner the bed morphology also consists of four basic elements including the sandbar in the backwater zone the bar in the separation flow zone the thalweg for flow conveyance and sediment transport and bars in the reach downstream of the separation zone the sediment load of the hyperconcentrated flow from the tributary was the most important control on fluvial processes at such confluences the increase in deposition in the backwater zone as the sediment load increased was almost linear and the depth of sediment deposition in the backwater zone was approximately normal in distribution the validity of a conceptual model for discriminating the status of the backwater effect developed earlier from field data using the relationship between the sediment load and water volume of hyperconcentrated flows was confirmed by the experiments deposition in the reach downstream of the junction sandbar height in the backwater zone and the width and length of the separation zone bar all tended to increase as the sediment load in the tributary increased an obvious upstream directed density current occurred in the backwater zone when the sediment concentration of the hyperconcentrated flow exceeded a critical value the travel distance of the density current increased as the sediment load in the tributary increased a formula was proposed based on sediment continuity for estimating the deposition volume in the reach downstream of the junction compared with ordinary sediment laden flow confluences hyperconcentrated flow confluences have a sandbar in the backwater zone associated with an upstream directed density current that may sometimes block the main channel hyperconcentrated flow confluences have a thalweg and so are different from debris flow confluences which have a fan shaped deposit

discussion of three dimensional numerical study of flows in open channel junctions by jianchun huang larry j weber and yong g lai

rates and patterns of thermal mixing at a small stream confluence under variable incoming flow conditions confluences are important locations for river mixing within drainage networks yet few studies have examined in detail the dynamics of mixing within confluences this study examines the influence of momentum flux ratio the scale of the flow cross sectional area and the density differences between incoming flows on thermal mixing at a small stream confluence results reveal that rates and patterns of thermal mixing depend on event specific combinations of the three factors the mixing interface at this confluence is generally distorted towards the mouth of the lateral tributary by strong helical motion associated with curvature of flow from the lateral tributary as it aligns with the downstream channel as the momentum flux from the lateral tributary increases mixing is enhanced because helical motion from the curving tributary flow expands over the width of the downstream channel the cross sectional area of the flow is negatively correlated with mixing rates suggesting that the amount of mixing over a fixed distance downstream of the confluence is inversely related to the scale of the flow density differences are not strongly related to rates of mixing results confirm that mixing rates within the region of confluent flow interaction can be highly variable among flow events with different incoming flow conditions but that in general length scales of mixing are short and rates of mixing are high at this small confluence compared with those typically documented at large river confluences copyright 2015 john wiley sons ltd

time averaged flow structure in the central region of a stream confluence previous process oriented field studies of stream confluences have focused mainly on fluvial dynamics at or immediately downstream of the location where the confluent flows enter the downstream channel this study examines in detail the spatial evolution of the time averaged downstream velocity cross stream velocity and temperature fields between the junction apex where the flows initially meet and the entrance to the downstream channel a well defined vertically oriented mixing interface exists within this portion of the confluence suggesting that lateral mixing of the incoming flows is limited the downstream velocity field near the junction apex is characterized by two high velocity cores separated by an intervening region of low velocity or recirculating fluid in the downstream direction the high velocity cores move inwards towards the mixing interface and high velocity fluid progressively extends downwards into a zone of scour resulting in an increase in flow velocity in the centre of the confluence the cross stream velocity field is dominated by flow convergence but also includes a component associated with a consistent pattern of secondary circulation this pattern is characterized by two surface convergent helical cells one on each side of the mixing interface the helical cells appear to be the mechanism by which high momentum fluid near the surface is advected downwards into the zone of scour for transport ineffective flows the dimensions and intensities of the cells are controlled by the momentum ratio of the confluent streams and by the extant bed morphology within the confluence although the flow structure of formative events was not measured directly in this study documented patterns of erosion and deposition within the central region of the confluence suggest that these events are dynamically similar to the measured flows except for the fact that formative flows are not constrained by but can reshape the bed morphology the results of this investigation are consistent with and augment previous findings on time averaged flow structure in the downstream portion of the confluence 1998 john wiley sons ltd

effect of bed morphology on flow mixing length at river confluences mixing processes at river confluences have an important bearing on problems such as pollutant dispersal and the management of river systems but remain poorly understood previous studies1 11 have indicated that flow mixing downstream of a confluence is a slow process typically completed at distances greater than 100 times the channel width bed morphology is now emerging as a critical factor flume experiments have shown that the width to depth ratios12 and height discordance13 14 between the confluent channels should influence mixing rates12 14 but the magnitude of these effects in real rivers is not known here we report measure ments from three river confluences of moderate size which show that bed discordance can markedly increase mixing rates for the rivers studied mixing is complete at distances five to ten times shorter than those reported previously

turbulence structure in a river reach with sand bed measurements and analysis of the three dimensional turbulence structure in a straight lowland river reach are presented accurate measurements of velocity profiles were taken with an acoustic doppier velocimeter adv and a multichannel micropropeller based system it is shown that analytical expressions derived from investigations of laboratory open channel flows agree well with the measured data only in the central part of the river where flow can be considered weakly three dimensional at the same time clear differences of empirical parameters between river and laboratory flows are detected it was established that river turbulence is isotropic for spatial scales smaller than the river depth the data also allowed the detection and analysis of the turbulence anisotropy impact on the formation of secondary currents special attention is paid to the investigation of coherent structures their spatial scales were evaluated applying the conditional average procedure based on uw quadrant analysis on average the scales of ejection and sweep events are as large as 1 5 times the flow depth

dynamics of shallow lateral shear layers experimental study in a river with a sandy bed shallow lateral shear layers forming between flows with different velocities though essential for mixing processes in natural streams have been examined only in laboratory settings using smooth fixed bed channels this paper reports the results of an experimental study of a shear layer in a straight reach of a natural river where the layer in contrast to the two dimensional structure observed in the laboratory is highly three dimensional the study included pronounced transverse pressure gradients which influenced shear layer structure compared to flume experiments it also introduces an analysis that complements conventional theory on mixing layers the lateral velocity gradient between the flows downstream from a splitter plate placed in the river the principal controlling factor was adjusted for three experimental runs to determine the influence of different gradients on shear layer dynamics in each run detailed three dimensional measurements of mean and turbulent characteristics were obtained at five cross sections downstream from the splitter plate although experimental results agreed with conventional mixing layer theories with respect to turbulence the dynamics of the shear layers were dominated by the mean lateral fluxes of momentum after re examining the governing equations we developed a parabolic equation describing the shear layer evolution and several scaling relations for essential terms of the energy budget mean and turbulent lateral fluxes of momentum turbulent kinetic energy and dissipation rates the study also provides insight into the spectral dynamics of turbulence in the shear layer and clarifies previous observations reported for confluences in natural streams

1 min in the life of a river selecting the optimal record length for the measurement of turbulence in fluvial boundary layers in the analysis of instantaneous velocity measurements it is important to consider carefully the properties of the instruments as well as the sampling frequency and the record length although several studies have examined the influence of instrument settings on velocity measurements in rivers little information is available on the effects of the record length on these measurements and on the turbulence parameters that can be extracted from the time series decisions on the record length are often made ad hoc here we quantify the effects of the sampling period on the precision of turbulence statistics e g mean standard deviation skewness reynolds stress quadrant analysis obtained from velocity measurements in fluvial turbulent boundary layers a bootstrapping method is used to determine the standard errors s e of turbulence statistics from 19 time series the time series were sampled in three gravel bed rivers using both electromagnetic current meters ecm and acoustic doppler velocimeters adv the record lengths ranged between 20 and 60 min the sampling frequencies were 20 and 25 hz for the ecms and advs respectively we show that for most turbulence statistics the optimal record length minimum sampling effort to achieve low standard errors ranges between 60 and 90 s we discuss the implication of these record lengths for standard errors estimates and variance losses

flow structure and channel morphodynamics of meander bend chute cutoffs a case study of the wabash river usa received 25 october 2012 revised 23 september 2013 accepted 25 september 2013 published 12 december 2013 1 this paper documents the three dimensional structure of flow and bed morphology of two developing chute cutoffs on a single meander bend on the lower wabash river usa and relates the flow structure to patterns of morphologic change in the evolving cutoff channels the upstream end of the cutoff channels is characterized by 1 a zone of flow velocity reduction stagnation and bar development in the main channel across from the cutoff entrance 2 flow separation and bar development along the inner left bank of the cutoff channel immediately downstream from the cutoff entrance and 3 helical motion and outward advection of flow momentum entering the cutoff channel leading to erosion of the outer right bank of the cutoff channel at the downstream end of the cutoff channels the majorhydrodynamic and morphologic features are 1 flow stagnation along the bank of the main channel immediately upstream of the cutoff channel mouth 2 convergence of flows from the cutoff and main channels 3 helical motion of flow from the cutoff 4 a zone of reduced velocity along the bank of the main channel immediately downstream from the cutoff channel mouth and 5 development of a prominent bar complex that penetrates into the main channel and extends from the stagnation zone upstream to downstream of the cutoff mouth these results provide the basis for a conceptual model of chute cutoff dynamics in which the upstream and downstream ends of a cutoff channel are treated as a bifurcation and confluence respectively

the planform mobility of river channel confluences insights from analysis of remotely sensed imagery river channel confluences are widely acknowledged as important geomorphological nodes that control the downstream routing of water and sediment and which are locations for the preservation of thick fluvial deposits overlying a basal scour despite their importance there has been little study of the stratigraphic characteristics of river junctions or the role of confluence morphodynamics in influencing stratigraphic character and preservation potential as a result although it is known that confluences can migrate through time models of confluence geomorphology and sedimentology are usually presented from the perspective that the confluence remains at a fixed location this is problematic for a number of reasons not least of which is the continuing debate over whether it is possible to discriminate between scour that has been generated by autocyclic processes such as confluence scour and that driven by allocyclic controls such as sea level change this paper investigates the spatial mobility of river confluences by using the 40 year record of landsat imagery to elucidate the styles rates of change and areal extent over which large river confluence scours may migrate on the basis of these observations a new classification of the types of confluence scour is proposed and applied to the amazon and ganges brahmaputra meghna gbm basins this analysis demonstrates that the drivers of confluence mobility are broadly the same as those that drive channel change more generally thus in the gbm basin a high sediment supply large variability in monsoonal driven discharge and easily erodible bank materials result in a catchment where over 80 of large confluences are mobile over this 40 year window conversely this figure is 40 for the amazon basin these results highlight that i the potential areal extent of confluence scours is much greater than previously assumed with the location of some confluences on the jamuna brahmaputra river migrating over a distance of 20 times the tributary channel width ii extensive migration in the confluence location is more common than currently assumed and iii confluence mobility is often tied to the lithological and hydrological characteristics of the drainage basins that determine sediment yield

modeling complex flow structures and drag around a submerged plant of varied posture although vegetation is present in many rivers the bulk of past work concerned with modeling the influence of vegetation on flow has considered vegetation to be morphologically simple and has generally neglected the complexity of natural plants here we report on a combined flume and numerical model experiment which incorporates time averaged plant posture collected through terrestrial laser scanning into a computational fluid dynamics model to predict flow around a submerged riparian plant for three depth limited flow conditions reynolds number 65 000 110 000 plant dynamics were recorded through high definition video imagery and the numerical model was validated against flow velocities collected with an acoustic doppler velocimeter the plant morphology shows an 18 reduction in plant height and a 14 increase in plant length compressing and reducing the volumetric canopy morphology as the reynolds number increases plant shear layer turbulence is dominated by kelvin helmholtz type vortices generated through shear instability the frequency of which is estimated to be between 0 20 and 0 30 hz increasing with reynolds number these results demonstrate the significant effect that the complex morphology of natural plants has on in stream drag and allows a physically determined species dependent drag coefficient to be calculated given the importance of vegetation in river corridor management the approach developed here demonstrates the necessity to account for plant motion when calculating vegetative resistance

hydraulic evaluation of w weir for river restoration various structural measures have been advocated for river restoration and habitat improvement schemes the w weir is one such structure that can be used in mobile bed alluvial rivers to diversify habitat and provide grade control laboratory studies have been carried out in a large scale meandering channel with a mobile bed to investigate their effects on flow and sediment transport processes a w weir placed immediately downstream of a riffle section created a strongly three dimensional flow pattern and high turbulence zones two adjacent scour holes of different depths and substrate are formed under clearwater and live bed conditions the continuity of sediment transport along the channel was not interrupted by the structure and the upstream afflux is minimal overbank flow significantly influenced the action of the weir and the scour hole was shifted closer to the structure in a relatively tight bend followed by a short crossover reach the weir may affect bed load transport pathways in the downstream bend finally the study provides insights to guide their design for restoration projects

coherent flow structures in a depth limited flow over a gravel surface the role of near bed turbulence and influence of reynolds number 1 in gravel bed rivers the microtopography of the bed exerts a significant effect on the generation of turbulent flow structures although field and laboratory measurements have indicated that flows over gravel beds contain coherent macroturbulent flow structures the origin of these phenomena and their relationship to the ensemble of individual roughness elements forming the bed is not quantitatively well understood here we report upon a flume experiment in which flow over a gravel surface is quantified through the application of digital particle imaging velocimetry which allows study of the downstream and vertical components of velocity over the entire flow field the results indicate that as the reynolds number increases 1 the visual distinctiveness of the coherent flow structures becomes more defined 2 the upstream slope of the structures increases and 3 the turbulence intensity of the structures increases analysis of the mean velocity components the turbulence intensity and the flow structure using quadrant analysis demonstrates that these large scale turbulent structures originate from flow interactions with the bed topography detection of the dominant temporal length scales through wavelet analysis enables calculation of mean separation zone lengths associated with the gravel roughness through standard scaling laws the calculated separation zone lengths demonstrate that wake flapping is a dominant mechanism in the production of large scale coherent flow structures in gravel bed rivers thus we show that coherent flow structures over gravels owe their origin to bed generated turbulence and that large scale outer layer structures are the result of flow topography interactions in the near bed region associated with wake flapping

analytic potentials for the forward and inverse modeling of sp anomalies caused by subsurface fluid flow classical interpretation techniques developed primarily for gravity and magnetic data have been adapted to electric self potential sp data from a recently developed wavelet based technique for potential field interpretation we propose a novel approach for the forward and inverse modeling of sp anomalies caused by subsurface fluid flow we use analytic signals and wavelets associated with the electric and fluid flow potentials fluid flow singularities have typical signatures in the wavelet domain sp data that can be used in the inversion scheme for cases where electrokinetics is unambiguously the origin of sp anomalies our interpretation method provides key parameters of the subsurface fluid flow e g position geometry flow rate to illustrate the theory we consider synthetic 2d flows for which analytic solutions exist and actual sp data acquired around the vulcarolo fissure on mount etna that show sources between 3 to 18 m depths