tidally generated turbulence over the knight inlet sill very high turbulent dissipation rates above 5 1024 wk g 21 were observed in the nonlinear internal lee waves that form each tide over a sill in knight inlet british columbia this turbulence was due to both shear instabilities and the jumplike adjustment of the wave to background flow conditions away from the sill turbulent dissipation was significantly lower 5 1027 to 5 1028 wk g 21 energy removed from the barotropic tide was estimated using a pair of tide gauges a peak of 20 mw occurred during spring tide approximately twothirds of the barotropic energy loss radiated away as internal waves while the remaining one third was lost to processes near the sill observed dissipation in the water column does not account for the near sill losses but energy lost to vortex shedding and near bottom turbulence though not measured could be large enough to close the energy budget

the relationship between u s east coast sea level and the atlantic meridional overturning circulation a review scientific and societal interest in the relationship between the atlantic meridional overturning circulation amoc and u s east coast sea level has intensified over the past decade largely due to 1 projected and potentially ongoing enhancement of sea level rise associated with amoc weakening and 2 the potential for observations of u s east coast sea level to inform reconstructions of north atlantic circulation and climate these implications have inspired a wealth of model and observation based analyses here we review this research finding consistent support in numerical models for an antiphase relationship between amoc strength and dynamic sea level however simulations exhibit substantial along coast and intermodel differences in the amplitude of amoc associated dynamic sea level variability observational analyses focusing on shorter generally less than decadal timescales show robust relationships between some components of the north atlantic large scale circulation and coastal sea level variability but the causal relationships between different observational metrics amoc and sea level are often unclear we highlight the importance of existing and future research seeking to understand relationships between amoc and its component currents the role of ageostrophic processes near the coast and the interplay of local and remote forcing such research will help reconcile the results of different numerical simulations with each other and with observations inform the physical origins of covariability and reveal the sensitivity of scaling relationships to forcing timescale and model representation this information will in turn provide a more complete characterization of uncertainty in relevant relationships leading to more robust reconstructions and projections

estuary enhanced upwelling of marine nutrients fuels coastal productivity in the u s pacific northwest 2014 american geophysical union all rights reserved the pacific northwest pnw shelf is the most biologically productive region in the california current system a coupled physical biogeochemical model is used to investigate the influence of freshwater inputs on the productivity of pnw shelf waters using realistic hindcasts and model experiments that omit outflow from the columbia river and strait of juan de fuca outlet for the salish sea estuary outflow from the strait represents a critical source of nitrogen to the pnw shelf accounting for almost half of the primary productivity on the vancouver island shelf a third of productivity on the washington shelf and a fifth of productivity on the oregon shelf during the upwelling season the columbia river has regional effects on the redistribution of phytoplankton but does not affect pnw productivity as strongly as does the salish sea a regional nutrient budget shows that nitrogen exiting the strait is almost entirely 98 of ocean origin upwelled into the strait at depth mixed into surface waters by tidal mixing and returned to the coastal ocean from the standpoint of nitrogen availability in the coastal euphotic zone the estuarine circulation driven by freshwater inputs to the salish sea is more important than the supply of terrigenous nitrogen by rivers nitrogen rich surface waters exiting the strait follow two primary pathways to the northwest in the vancouver island coastal current and southward toward the washington and oregon shelves nitrogen flux from the juan de fuca strait and eddy region to these shelves is comparable to flux from local wind driven upwelling

response of the north atlantic dynamic sea level and circulation to greenland meltwater and climate change in an eddy permitting ocean model the response of the north atlantic dynamic sea surface height ssh and ocean circulation to greenland ice sheet gris meltwater fluxes is investigated using a high resolution model the model is forced with either present day like or projected warmer climate conditions in general the impact of meltwater on the north atlantic ssh and ocean circulation depends on the surface climate in the two major regions of deep water formation the labrador sea and the nordic seas the basin mean ssh increases with the increase of the gris meltwater flux this ssh increase correlates with the decline of the atlantic meridional overturning circulation amoc however while in the labrador sea the warming forcing and gris meltwater input lead to sea level rise in the nordic seas these two forcings have an opposite influence on the convective mixing and basin mean ssh relative to the global mean the warming leads to less sea ice cover in the nordic seas which favours stronger surface heat loss and deep mixing lowering the ssh and generally increasing the transport of the east greenland current in the labrador sea the increased ssh and weaker deep convection are reflected in the decreased transport of the labrador current lc which closes the subpolar gyre in the west among the two major components of the lc transport the thermohaline and bottom transports the former is less sensitive to the gris meltwater fluxes under the warmer climate the ssh difference across the lc which is a component of the bottom velocity correlates with the long term mean amoc rate

turbulence and entrainment in a buoyant surface plume in winter tidal outflow from the leschenault estuary forms a buoyant sheared stratified plume in koombana bay on each outgoing tide the turbulence in the plume and the local entrainment into the plume are examined based on measurements collected in an intensive field program coherency measurements between horizontally separated sensors are used to examine the anisotropy of the turbulence the effects of viscosity and buoyancy on the turbulence are studied using an activity diagram which is also an indicator of the mixing efficiency and total mixing the osborne cox model is tested and found to be valid in the plume

spatial variability of sea level rise in twenty first century projections abstract a set of state of the science climate models are used to investigate global sea level rise slr patterns induced by ocean dynamics in twenty first century climate projections the identified robust features include bipolar and bihemisphere seesaws in the basin wide slr dipole patterns in the north atlantic and north pacific and a beltlike pattern in the southern ocean the physical and dynamical mechanisms that cause these patterns are investigated in detail using version 2 1 of the geophysical fluid dynamics laboratory gfdl coupled model cm2 1 under the intergovernmental panel on climate change s ipcc special report on emissions scenarios sres a1b scenario the steric sea level changes relative to the global mean the local part in different ocean basins are attributed to differential heating and salinity changes of various ocean layers and associated physical processes as a result of these changes water tends to move from the ocean interior to continental shelves in the north at

the passive and active nature of ocean heat uptake in idealized climate change experiments the influence of ocean circulation changes on heat uptake is explored using a simply configured primitive equation ocean model resembling a very idealized atlantic ocean we focus on the relative importance of the redistribution of the existing heat reservoir due to changes in the circulation and the contribution from anomalous surface heat flux in experiments in which the surface boundary conditions are changed we perform and analyze numerical experiments over a wide range of parameters including experiments that simulate global warming and others that explore the robustness of our results to more general changes in surface boundary conditions we find that over a wide range of values of diapycnal diffusivity and southern ocean winds and with a variety of changes in surface boundary conditions the spatial patterns of ocean temperature anomaly are nearly always determined as much or more by the existing heat reservoir redistribution than by the nearly passive uptake of temperature due to changes in the surface boundary conditions calculating heat uptake by neglecting the existing reservoir redistribution which is similar to treating temperature as a passive tracer leads to significant quantitative errors notably at high latitudes and secondarily in parts of the main thermocline experiments with larger circulation changes tend to produce a relatively larger magnitude of existing reservoir redistribution and a faster growing effective heat capacity of the system the effective heat capacity is found to be sensitive to both vertical diffusivity and southern ocean wind

separating the influence of projected changes in air temperature and wind on patterns of sea level change and ocean heat content we present ocean model sensitivity experiments aimed at separating the influence of the projected changes in the thermal near surface air temperature and wind near surface winds forcing on the patterns of sea level and ocean heat content in the north atlantic the distribution of sea level change is more due to the thermal forcing whereas it is more due to the wind forcing in the north pacific in the southern ocean the thermal and wind forcing have a comparable influence in the ocean adjacent to antarctica the thermal forcing leads to an inflow of warmer waters on the continental shelves which is somewhat attenuated by the wind forcing the structure of the vertically integrated heat uptake is set by different processes at low and high latitudes at low latitudes it is dominated by the heat transport convergence whereas at high latitudes it represents a small residual of changes in the surface flux and advection of heat the structure of the horizontally integrated heat content tendency is set by the increase of downward heat flux by the mean circulation and comparable decrease of upward heat flux by the subgrid scale processes the upward eddy heat flux decreases and increases by almost the same magnitude in response to respectively the thermal and wind forcing regionally the surface heat loss and deep convection weaken in the labrador sea but intensify in the greenland sea in the region of sea ice retreat the enhanced heat flux anomaly in the subpolar atlantic is mainly caused by the thermal forcing

observational estimates of entrainment and vertical salt flux in the interior of a spreading river plume 1 observational estimates of entrainment and vertical salt flux into the tidally pulsed columbia river plume are presented drifting buoys deployed in ebbing plume water downstream of the lift off region are used to make measurements of velocity salinity and horizontal divergence in the surface layer drifters released near the river mouth shoreward of the propagating ocean plume front catch up to the front consistent with classical models of plume front circulation during their offshore transit drifter streamwise velocities decrease while salinities increase assuming drifter measured quantities are representative of plume averaged quantities conservation equations evaluated between adjacent spreading drifters are used to determine the plume depth and entrainment velocity throughout the experiment this approach provides knowledge of the mixing involved between the active lift off region and the offshore ocean plume front as the flow evolves because the surface drifters do not downwell at the ocean plume front we do not estimate mixing in that region we find that entrainment and vertical salt flux are largest near the river mouth as expected with typical values of o 10 3 m s 1 and o 10 2 practical salinity units psu m s 1 respectively and that these quantities steadily decrease as the drifters move offshore profiles of water properties following the drifters provide knowledge of vertical stratification 0 5 4 psu m 1 at the plume base allowing for discrete estimates of the eddy diffusivity of salt ks typical plume values of ks are o 10 3 m2 s 1 similar to estimates made in other plume systems and 2 orders of magnitude larger than open ocean eddy diffusivity estimates

temporal and spatial variability of vertical salt flux in a highly stratified estuary 1 the temporal and spatial variability of vertical salt flux in the fraser river estuary british columbia was investigated observationally using several different direct and indirect indicators of buoyancy flux data were collected from the estuary using shipboard instrumentation primarily an acoustic doppler current profiler and a towed conductivity temperature depth unit direct estimates of buoyancy flux were made from along channel control volume analyses and from measurements of overturn scales the spatial and temporal evolution of the salt wedge structure through a tidal cycle was evaluated using the results of these buoyancy flux calculations as well as gradient richardson number froude number and stratification profiles observations indicate that buoyancy flux is driven primarily by interfacial stress and not bottom stress as is common in many estuaries vertical salt flux as opposed to seaward advection of high salinity fluid was found to be the dominant mechanism responsible for removal of salt from the estuarine channel during each daily tidal cycle buoyancy flux was highly variable in time and space however with vertical salt flux during ebb tides on the order of 2 to 3 times greater than that estimated during floods this is due to an increase in the vertical shear of horizontal velocity and a sharp increase in stratification which was observed during early ebb enhanced mixing was observed spatially within a region dominated by a channel constriction in which the channel narrows by approximately 25

the rhine outflow plume studied by the analysis of synthetic aperture radar data and numerical simulations the dynamics of the rhine outflow plume in the proximity of the river mouth is investigated by using remote sensing data and numerical simulations the remote sensing data consist of 41 synthetic aperture radar sar images acquired by the first and second european remote sensing satellites ers 1 and ers 2 over the outflow region of the river rhine most of them show sea surface signatures of oceanic phenomena for example surface current and wind variations ship wakes and oil slicks in particular in 36 of these images pronounced frontal features are visible as narrow zones of mainly enhanced sometimes enhanced reduced radar backscatter that can be associated with the rhine surface front within the area enclosed by the frontal line large zones characterized by a lower radar backscatter than in the outer area are often visible the analysis of the ers sar images suggests that the form and the location of the frontal features are mainly linked to the semidiurnal tidal phase in the outflow region although their variability suggests also that they weakly depend on river discharge residual currents and neap spring tidal cycle in order to test this observational hypothesis the results obtained from the analysis of the ers sar images are compared with the results obtained from the numerical simulation of the hydrodynamics of the rhine outflow region carried out using a two layer frontal model which is based on the nonlinear hydrostatic shallow water equations on an f plane the model is forced by prescribing tidal and residual currents and river discharge at the open boundaries several simulations are performed by varying the values of these forcing parameters the numerical results corroborate the observational conjecture it is found that the form and the location of the simulated interface outcropping lines in the proximity of the river mouth are mainly determined by the semidiurnal tidal phase in the outflow region and that river discharge residual currents and neap spring tidal cycle contribute only secondarily to their determination inserting the simulated surface velocity field into a simple radar imaging model that relates the modulation of the backscattered radar power to the surface velocity convergence in radar look direction narrow elongated bands of enhanced radar backscatter emerge near the model frontal line while patches of low radar backscatter appear within the simulated rhine plume area the consistency of the model results with the results obtained from the analysis of the sar images enables one to infer a mean spatial and temporal evolution of the rhine outflow plume over a semidiurnal tidal cycle from the analysis of spaceborne sar images acquired during different tidal cycles over the rhine outflow area and suggests the possibility of using numerical modeling in conjunction with the analysis of spaceborne measurements for monitoring the oceanic variability in the rhine outflow area

understanding the spatial variation of sea level rise in the north sea using satellite altimetry this paper examines the spatial variation of sea surface height trends in the north sea basin as seen by satellite altimetry and assesses its underlying causes changes in the potential temperature and salinity of the north sea are transposed into corresponding changes in sea surface height and regional anomalies of linear sea level trend calculated the same is carried out for the meteorological processes which act on the sea surface the steric and meteorological regional sea level rise anomalies are summed with those from contributions from land ice and compared against the values seen by satellite altimetry over the period 1993 2014 results show that there is good agreement between the observations and the reconstruction the local meteorological contribution appears to be most important in describing regional variation in linear sea level rise and is reinforced with a local halosteric contribution which shows a similar spatial pattern

observations of shoaling density current regime changes in internal wave interactions abstractwe present in situ and remote observations of a mississippi plume front in the louisiana bight the plume propagated freely across the bight rather than as a coastal current the observed

convergence and downwelling at a river plume front abstract the small scale structure of the circulation and hydrography at the frontal boundary of the connecticut river plume in long island sound has been resolved using a novel combination of instruments a towed acoustic doppler current profiler adcp and a rigid array of current meters and conductivity temperature sensors observations were made during the latter half of the eastward ebb tide when the river plume was well established and the front was moving to the west at approximately 0 3 m s 1 two across front transects revealed a horizontal convergence rate in the across front velocity components at 0 6 m of 0 05 0 1 s 1 this was associated with a salt induced horizontal density gradient of 10 2 kg m4 observations obtained during a period in which the towed adcp was caught in the zone of maximum surface convergence showed significant downwelling with a near surface maximum of 0 2 m s 1 vertical velocities of this magnitude are consistent with observed magnitudes of the convergence rate at 0 6

the drivers of projected north atlantic sea level change sea level change predicted by the cmip5 atmosphere ocean general circulation models aogcms is not spatially homogeneous in particular the sea level change in the north atlantic is usually characterised by a meridional dipole pattern with higher sea level rise north of 40 n and lower to the south the spread among models is also high in that region here we evaluate the role of surface buoyancy fluxes by carrying out simulations with the famous low resolution aogcm forced by surface freshwater and heat flux changes from co2 forced climate change experiments with cmip5 aogcms and by a standard idealised surface freshwater flux applied in the north atlantic both kinds of buoyancy flux change lead to the formation of the sea level dipole pattern although the effect of the heat flux has a greater magnitude and is the main cause of the spread of results among the cmip5 models by using passive tracers in famous to distinguish between additional and redistributed buoyancy we show that the enhanced sea level rise north of 40 n is mainly due to the direct steric effect the reduction of sea water density caused by adding heat or freshwater locally the surface buoyancy forcing also causes a weakening of the atlantic meridional overturning circulation and the consequent reduction of the northward ocean heat transport imposes a negative tendency on sea level rise producing the reduced rise south of 40 n however unlike previous authors we find that this indirect effect of buoyancy forcing is generally less important than the direct one except in a narrow band along the east coast of the us where it plays a major role and leads to sea level rise as found by previous authors

nonlinear internal waves and plumes generated in response to sea loch outflow auv and time lapse photography observations the tidally modulated outflow of brackish water from a sea loch forms a thin surface layer that propagates into the coastal ocean as a buoyant gravity current transporting nutrients and sediments as well as fresh water heat and momentum the fresh intrusion both propagates into and generates a strongly stratified environment which supports trains of nonlinear internal waves nliws nliws are shown to propagate ahead of this buoyancy input in response to propagation of the outflow water into the stratified environment generated by the previous release as well as in the opposing direction after the reflection from steep bathymetry oblique aerial photographs were taken and photogrammetric rectification led to the identification of the buoyant intrusion and the subsequent generation of nliws an autonomous underwater vehicle auv was deployed on repeated reciprocal transects in order to make simultaneous ctd adcp and microstructure shear measurements of the evolution of these phenomena in conjunction with conventional mooring measurements auv based temperature and salinity signals of nliws of depression were observed together with increased turbulent kinetic energy dissipation rates of over two orders of magnitude within and in the wake of the nliws repeated measurements allow a unique opportunity to investigate the horizontal structure of these phenomena simple metric scaling demonstrates that these these processes are likely to be feature of many fjordic systems located on the west coast of scotland but may also play a key role in the assimilation of the outflow from many tidally dominated fjordic systems throughout the world

determining azimuthal variations in frontal froude number from sar imagery 1 river plume fronts are the locus of strong mixing between plume and ambient coastal waters contribute to coastal productivity and exert a major impact on coastal ecosystems the frontal froude number fr is an important parameter characterizing the frontal status with respect to both propagation and vertical mixing in this study we examine azimuthal variations in fr using a new remote sensing method we derive fr from sar image data on the basis of the sar imaging theory and the mechanism of internal wave fission at front this method is applied to a sar image showing a front off the columbia river cr mouth taken on 31 may 2003 at 14 33 19 utc under weak wind conditions fr increases from south to north along the front this variation is consistent with potential vorticity conservation and the influence of tidal currents on the plume this calculation confirms arguments based on vessel observations by jay et al 2009

correction to bistability of the atlantic overturning circulation in a global climate model and links to ocean freshwater transport 1 in the paper bistability of the atlantic overturning circulation in a global climate model and links to ocean freshwater transport by e hawkins et al geophysical research letters 38 l10605 doi 10 1029 2011gl047208 2011 an error was made in figure 3 the corrected figure 3 is shown here and the conclusions are unchanged 2 the error was in the calculation of fov for depresysff pink line the corrected estimate is now more consistent with the results for the other ocean reanalyses references

the role of turbulence stress divergence in decelerating a river plume 1 turbulence controls the composition of river plumes through mixing and alters the plume s trajectory by diffusing its momentum while believed to play a crucial role in decelerating river source waters the turbulence stress in a near field river plume has not previously been observationally quantified in this study finely resolved density velocity and turbulence observations are combined with a control volume technique to describe the momentum balance in the columbia river s near field plume during 10 tidal cycles that encompass both large and small river flow turbulence stress varies by 2 3 orders of magnitude both within a given ebb and between ebbs with different tidal or river forcing its magnitude scales with the strength of the instantaneous ebb outflow i e high stresses occur during peak flow of strong ebbs during these periods the momentum equation is represented by a balance between stress divergence and plume deceleration as the flow relaxes the stress divergence weakens and other terms pressure gradient and coriolis may become appreciable and influence plume deceleration while the momentum balance could not be closed during these weaker flow periods during strong tidal pulses the time scale for decay based on observed stress is significantly less than a tidal half period indicating that stress divergence plays a fundamental role in the initial deceleration of the plume

the influence of tide and wind on the propagation of fronts in a shallow river plume in this study we used field data and radar images to investigate the influence of winds and tides on the propagation of tidal plume fronts the measurements were collected in a shallow shelf region off the dutch coast 10 km north of the rhine river mouth and they clearly show the passage of distinct freshwater lenses and associated fronts at the surface that propagate all the way to the coastline these fronts are observed as a sudden drop in near surface salinity accompanied by high cross shore shear with onshore velocities at the surface we determined the arrival time to our measurement site frontal propagation speed and structure of the fronts by combining the in situ data and radar images frontal froude numbers show a wide range of values with an average of 0 44 our results show that fronts during spring tides are thinner more mixed and move faster relative to the ground during calm spring tides when compared to calm neap tides downwelling winds during spring tides result in thicker and faster fronts however the intrinsic frontal propagation speed indicates that the wind and tide control the frontal propagation mainly due to advection rather than by changing the frontal structure strong return currents in the near bed layer resulting from fast and thick fronts increase near bed turbulence and bed stresses these high stresses suggest that the passage of fronts in shallow coastal areas can initiate sediment resuspension and contribute to transport processes

effects of ambient velocity shear on nonlinear internal wave associated mixing at the columbia river plume front 1 large amplitude nonlinear internal waves nliws are frequently observed propagating away from columbia river tidal plume fronts they are generated because of the deceleration of the frontal bulge during the river influences on shelf ecosystems project cruises the velocity density structure and acoustic backscatter of the plume fronts and frontal nliws were observed using a towed vehicle vessel mounted instrumentation and a vessel x band radar these observations indicate that in the presence of strong ambient velocity shear the nliws with maximum amplitudes occur well below the density interface and at a depth deeper than in the absence of shear this deepening of the nliw shear is associated with intensified vertical mixing below the interface this is consistent with a dynamic analysis of nliws under the influence of sheared ambient flow obtained from a high order kdv model there are two mechanisms responsible for the vertical turbulent mixing intensification the nonlinear interaction between ambient shear and the nliws increases total velocity shear and causes the gradient richardson number rig to decrease below a critical value in certain depth ranges also because of the presence of the ambient shear the maximum nliw velocity shear occurs at a depth below the density interface where there is less stratification

a simple theory for the fate of buoyant coastal discharges abstract a simple theory that predicts the vertical structure and offshore spreading of a localized buoyant inflow onto a continental shelf is formulated the theory is based on two competing mechanisms that move the buoyant fluid offshore 1 the radial spread of the lighter water over the ambient water being deflected by the coriolis force and producing an anticyclonic cyclostrophic plume and 2 offshore transport of buoyant water in the frictional bottom boundary layer that moves the entire plume offshore while maintaining contact with the bottom the surface expression of the cyclostrophic plume moves offshore a distance ys 2 3g h0 2i 2g h0 2i 1 2f where g is reduced gravity based on the inflow density anomaly h0 is the inflow depth i is the inflow velocity and f is the coriolis parameter the plume remains attached to the bottom to a depth given by hb 2l ih0f g 1 2 where l is the inflow width both scales are based solely on parameters of the buoyant inflow at its source there

observations at the tidal plume front of a high volume river outflow 1 we present shipboard observations of very strong convergence vertical velocities and mixing and near bed impacts associated with the leading edge front of the tidally pulsed columbia river plume with upwelling favorable winds and riverflow of 4900 m3s 1 the plume propagates as a buoyant gravity current with a rotary bore like vertical frontal circulation and downwelling as strong as 0 35 m s 1 in waters as deep as 65 m near bed currents intensify to as much as 1 0 m s 1 after frontal passage and are often associated with elevated acoustic backscatter mixing is locally strong with an eddy diffusivity of o 0 2 m2s 1 50 m behind the front and t s diagrams imply plume mixing with 10 m deep ocean water these observations indicate that the leading edge front of a surface advected plume can cause exchanges of a nutrients between cold subsurface shelf waters and the river plume and b nutrients and sediments across the sediment water interface

structure and dynamics of the columbia river tidal plume front 1 time dependent buoyant plumes form at the outflow of tidally dominated estuaries when estuary discharge velocity exceeds plume internal wave speed c a sharp front forms at the plume s leading edge that expands from the time dependent source using observations of the columbia river tidal plume from multiple tidal cycles we characterize time evolving plume structure and quantify front speed uf plume internal wave speed c front curvature and ultimate extent we identify three distinct stages of propagation 1 initially the plume is strongly influenced by shallow bathymetry near the river mouth 2 as the front advances offshore the plume detaches from the bottom and expands as a freely propagating gravity current with relatively constant uf c and frontal froude number f uf c ambient currents explain intracycle variability in uf and winds alter front shape variability in ambient stratification associated with previous cycles plume remnants leads to complex fronts and internal waves 3 finally the plume decelerates adjusts toward geostrophy and may radiate additional internal waves using a simple kinematic model we suggest that constant frontal propagation speed uf 0 9 0 1 m s during stage 2 is primarily controlled by linearly increasing volume flux from the columbia river mouth as this discharge rate subsides the plume expands as a fixed volume with decreasing front speed stage 3 the plume s final extent is controlled by the rossby radius which scales with a length based on the total volume discharged this provides an integral description of plume front evolution based on the time dependent estuary discharge

capturing the spatiotemporal variability of bedload transport a time lapse imagery technique monitoring sediment transport in morphologically complex and labile channels remains a difficult task even at the laboratory scale to address this challenge a fully automated imagery technique for continuously mapping the spatial and temporal variability of bedload transport is proposed this method uses differentiated time lapse imagery taken from a fixed camera to detect bed variations induced by grain displacement the technique is not based on tracking the individual particles rather it evaluates macroscopic colour changes within a region that contains several grains which depend on the occurrence and intensity of the bedload transport image derived data were compared with the sediment flux measured during four flume experiments and produced good correspondence the method provides continuous tracking of the location of the transporting channels and enables estimation of local variations in the magnitude of the bedload flux moreover the spatial extent of the monitoring area offers an unprecedented opportunity to aggregate spatially dense and continuous data at the reach scale as needed to properly capture the full range of variability of morphologically complex and rapidly evolving gravel bed rivers despite being limited to laboratory scale physical experiments the method provides useful data to investigate fundamental morphodynamic processes such as bar migration bank erosion anabranches opening closure and the associate spatial and temporal scales further the data obtained have the potential to enhance numerical model calibration and improve our understanding of the complex dynamics of real world settings copyright 2017 john wiley sons ltd