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1.
Bedload and river morphology interact in a strong feedback manner. Bedload conditions the development of river morphology along different space and time scales; however, by concentrating the flow in preferential paths, a given morphology controls bedload for a given discharge. As bedload is a non‐linear response of shear stress, local morphology is likely to have a strong impact on bedload prediction when the shear stress is averaged over the section, as is usually done. This was investigated by comparing bedload measured in different bed morphologies (step‐pool, plane bed, riffle‐pool, braiding, and sand beds), with bedload measured in narrow flumes in the absence of any bed form, used here as a reference. The initial methodology consisted of fitting a bedload equation to the flume data. Secondly, the morphological signature of each river was studied as the distance to this referent equation. It was concluded that each morphology affects bedload in a different way. For a given average grain shear stress, the larger the river, the larger the deviation from the flume transport. Narrow streams are those morphologies that behave more like flumes; this is particularly true with flat beds, whereas results deviate from flumes to a greater extent in step‐pools. The riffle‐pool's morphology impacts bedload at different levels depending on the degree of bar development, considered here through the ratio D84/D50 which is used as a proxy for the local bed patchiness and morphology. In braiding rivers morphological effects are important but difficult to assess because width is dependent on transport rate. Bed morphology was found to have negligible effects in sand bed rivers where the Shields stress is usually sufficiently high to minimize the non‐linearity effects when hydraulics is averaged over the section. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

2.
Evolution of bed material mobility and bedload grain size distributions under a range of discharges is rarely observed in braiding gravel-bed rivers. Yet, the changing of bedload grain size distributions with discharge is expected to be different from laterally-stable, threshold, channels on which most gravel bedload theory and observation are based. Here, simultaneous observations of flow, bedload transport rate, and morphological change were made in a physical model of a gravel-bed braided river to document the evolution of grain size distributions and bed mobility over three experimental event hydrographs. Bedload transport rate and grain size distributions were measured from bedload samples collected in sediment baskets. Morphological change was mapped with high-resolution (~1 mm precision) digital elevation models generated from close-range digital photogrammetry. Bedload transport rates were extremely low below a discharge equivalent to ~50% of the channel-forming discharge (dimensionless stream power ~70). Fractional transport rates and plots of grain size distributions indicate that the bed experienced partial mobility at low discharge when the coarsest grains on the bed were immobile, weak selective mobility at higher discharge, and occasionally near-equal mobility at peak channel-forming discharge. The transition to selective mobility and increased bedload transport rates coincided with the lower threshold for morphological change measured by the morphological active depth and active width. Below this threshold discharge, active depths were of the order of D90 and active widths were narrow (< 3% of wetted width). Above this discharge, both increased so that at channel-forming discharge, the active depth had a local maximum of 9D90 while active width was up to 20% of wetted width. The modelled rivers approached equal mobility when rates of morphological change were greatest. Therefore, changes in the morphological active layer with discharge are directly connected to the conditions of bed mobility, and strongly correlated with bedload transport rate. © 2018 John Wiley & Sons, Ltd.  相似文献   

3.
A comprehensive monitoring programme focusing on bedload transport behaviour was conducted at a large gravel‐bed river. Innovative monitoring strategies were developed during five years of preconstruction observations accompanying a restoration project. A bedload basket sampler was used to perform 55 cross‐sectional measurements, which cover the entire water discharge spectrum from a 200‐year flood event in 2013 to a rare low flow event. The monitoring activities provide essential knowledge regarding bedload transport processes in large rivers. We have identified the initiation of motion under low flow conditions and a decrease in the rate of bedload discharge with increasing water discharge around bankfull conditions. Bedload flux strongly increases again during high flood events when the entire inundation area is flooded. No bedload hysteresis was observed. The effective discharge for bedload transport was determined to be near mean flow conditions, which is therefore at a lower flow discharge than expected. A numerical sediment transport model was able to reproduce the measured sediment transport patterns. The unique dataset enables the characterisation of bedload transport patterns in a large and regulated gravel‐bed river, evaluation of modern river engineering measures on the Danube, and, as a pilot project has recently been under construction, is able to address ongoing river bed incision, unsatisfactory ecological conditions for the adjacent national park and insufficient water depths for inland navigation. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

4.
Bedload, the transport of sediment remaining in contact with the stream bed, has mainly been studied from the perspective of the correlation between fluid driving forces and the responding sediment flux. Yet grain–grain interactions are important and bedload should also be considered as a granular phenomenon. We review progress made recently in the study of granular flows, especially on segregation and rheology, that better illuminates the nature of bedload. Granular flows may exhibit gas‐like or fluid‐like flow, or quasi‐solid deformation. All three conditions might be duplicated in bedload. Understanding of intense bedload transport occurring continuously in a layer several grains deep – typical of sand beds – might greatly benefit from results in granular physics, as illustrated by grain‐inspired bedload results. However, processes restricted to the surface of the bed, when particles move intermittently and the bed becomes structured, while characteristic in gravel‐bed channels, are not well addressed in granular physics. Mutual study of these phenomena may benefit both physics and fluvial geomorphology. We intend, therefore, to contribute to an enhanced dialogue between granular physics and bedload science communities. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

5.
Unsteady bedload transport was measured in two c. 5 m wide anabranches of a gravel‐bed braided stream draining the Haut Glacier d'Arolla, Switzerland, during the 1998 and 1999 melt seasons. Bedload was directly sampled using 152 mm square Helley–Smith type samplers deployed from a portable measuring bridge, and independent transport rate estimates for the coarser size fractions were obtained from the dispersion of magnetically tagged tracer pebbles. Bedload transport time series show pulsing behaviour under both marginal (1998) and partial (1999) transport regimes. There are generally weak correlations between transport rates and shear stresses determined from velocity data recorded at the measuring bridge. Characteristic parameters of the bedload grain‐size distributions (D50, D84) are weakly correlated with transport rates. Analysis of full bedload grain‐size distributions reveals greater structure, with a tendency for transport to become less size selective at higher transport rates. The bedload time series show autoregressive behaviour but are dif?cult to distinguish by this method. State–space plots, and associated measures of time‐series separation, reveal the structure of the time series more clearly. The measured pulses have distinctly different time‐series characteristics from those modelled using a one‐dimensional sediment routing model in which bed shear stress and grain size are varied randomly. These results suggest a mechanism of pulse generation based on irregular low‐amplitude bedforms, that may be generated in‐channel or may represent the advection of material supplied by bank erosion events. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

6.
Bedload pulses in gravel-bed rivers have been widely reported in recent years and attempts have been made to relate them to channel morphology. Bedload transport and channel morphology were measured in a small-scale generic model of braided gravel-bed streams. Two experiments are described in which braided channels developed in a 14 m × 3 m sand tray. Total bedload output from the tray was weighed every 15 minutes. Stream bed geometry was surveyed every four hours. Pulses were observed in the bedload output time series, and were qualitatively related to the channel morphology immediately upstream of the measuring section. The Bagnold (1980) bedload equation generally overpredicts measured bedload transport rates when applied to channels that were in equilibrium or aggrading. Underprediction occurred when applied to degrading channels. Aggradation was associated with channel multiplication and bar deposition. Channel pattern simplification occurred when degradation took place, and bars emerged from the water flow. Development of phases of aggradation and degradation is dependent upon the three-dimensional geometry of the stream beds. Spatial and temporal feedback loops can be identified, enabling links between channel morphology and bedload transport rate to be directly identified.  相似文献   

7.
Passive acoustic monitoring of the self‐generated noise of particle impacts has been shown to be correlated to bedload flux and bedload size. However, few studies have concentrated on the role of acoustic wave propagation in a river. For the first time, the river environment is modeled as a Pekeris waveguide, where a wave number integration technique is used to predict the transformation of sounds through their propagation paths. Focusing on the distance of a hydrophone from the channel bed and cutting off the low frequencies produced by impacts between gravel particles, we demonstrate that acoustic propagation modifies the spectral content of bedload‐generated sound. Acoustic signals analyzed with the proposed model are interpreted by comparison to Helley–Smith bedload data obtained during flood conditions on the large gravel‐bedded Arc‐en‐Maurienne River, France. This study shows that careful attention to acoustic propagation effects is required when estimating bedload grain size distribution with hydrophones in rivers, especially for rivers with slopes higher than 1%. Bedload monitoring with a hydrophone is particularly appropriate for large gravel‐bed rivers – especially so during large floods, when in situ sampling is difficult or impractical and the impact of acoustic propagation is weaker relative to the self‐generated noise of bedload impacts. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

8.
Coarse bedload transport dynamics are investigated utilizing hydrodynamic and sediment transport data obtained in an extensively instrumented study reach located in Squaw Creek, Montana, USA. During 1991 and 1992, a number of discrete bedload transport events associated with the daily rise and fall in stream discharge were investigated. Data show that initiation of sediment transport was accompanied by a reduction in bed roughness and by changes in bulk hydraulic parameters. For larger discharges, coarser fractions of the bed material mobilized, and bedload transport rates and average hydraulic parameters stabilized. As discharge reduced, mobile coarse particles became less frequent and deposited fine particles were removed, resulting in an increase in bed roughness. These observations are attributed to the downstream translation of bar sediments during the passage of a hydrograph. Bedload pulses were aperiodic but spatially variable. Flow turbulence and velocity profile data obtained during low flows allowed comparison between average bed shear stress and apparent bed roughness estimates obtained using different approaches. © 1998 John Wiley & Sons, Ltd.  相似文献   

9.
It is important to evaluate bedload discharge and temporal changes of the bed surface, and bed deformation can be estimated during floods if the bedload discharge is properly evaluated in an arbitrary cross‐section. With the exception of grain size and its distribution within the bedload, bedload discharge has been measured using both direct and indirect methods. Bedload slot is a direct method but cannot be used to measure bedload during a flood because of volume limitations. Indirect methods require correlation between the signals and sediment volume measured using another method. In the present study, a small, automatically recording bedload sensor with an iron plate and a pair of load cells is developed in order to evaluate not only large particles but also sand particles as bedload. Bedload mass is calculated by integrating with respect to both the velocity of sediment particles and the averaged particle weight as measured by a pair of load cells, and, as an example, the velocity is estimated by the cross‐correlation function of weights measured by load cells. The applicability of the proposed sensor is discussed based on the results of flume tests in the laboratory (2014) and the observation flume of the Hodaka Sedimentation Observatory of Kyoto University in Japan (2015). The system was installed in the observation flume in November of 2012, and flume data were obtained using natural sediment particles. In particular, it was difficult to estimate the velocity of averaged bedload particles, and it was better to apply a cross‐correlation function in the laboratory tests. However, it appears that the previous estimation can estimate these velocities in the observation flume using a connecting tube and submerged load‐cell systems. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

10.
A laboratory study was undertaken to investigate how changes in flow regime and hydrograph shape (number of cycled hydrographs and duration of each hydrograph) together impact bedload transport and resulting bed morphology. Three hydrologic conditions (experiments) representing different levels of urbanization, or analogously different flow regimes, were derived from measured hydrometric field data. Each experiment consisted of a series of hydrographs with equal peak discharge and varying frequency, duration and flashiness. Bedload transport was measured throughout each hydrograph and measurements of bed topography and surface texture were recorded after each hydrograph. The results revealed hysteresis loops in both the total and fractional transport, with more pronounced loops for longer duration hydrographs, corresponding to lower rate of unsteadiness until reaching the peak discharge (pre-urbanization conditions). Shorter duration hydrographs (urban conditions) displayed more time above critical shear stress thresholds leading to higher bedload transport rates and ultimately to more variable hysteresis patterns. Surface textures from photographic methods revealed surface armoring in all experiments, with larger armor ratios for longer duration hydrographs, speculated to be due to vertical sorting and more time for bed rearrangements to occur. The direction of bed surface adjustment was linked to bedload hysteresis, more precisely with clockwise hysteresis (longer hydrographs) typically resulting in bed coarsening. More frequent and shorter duration hydrographs result in greater relative channel adjustments in slope, topographic variability and surface texture. © 2019 John Wiley & Sons, Ltd.  相似文献   

11.
Bedload yields were calculated by 39 methods at the East Tributary gauge, nine methods at Upper Swift Creek gauge and 11 methods at Swift Creek gauge in the Ngarradj Creek catchment in northern Australia. These methods involved combining various significant bedload rating curves determined for a measured bedload data set for a 4‐year period with either the hourly or daily hydrographs or flow duration curves for the same period, 1 September 1998 to 31 August 2002. Bedload ratings were both statistically significant (ρ ≤ 0.05) and explained at least 60% of the variance in bedload flux. Bias corrections were used with all methods based on log10‐transformed ratings. Estimated mean annual bedload yields varied by three orders of magnitude at the East Tributary gauge and by two orders of magnitude at Upper Swift Creek and Swift Creek gauges. Hourly discharges usually produced higher estimated yields than daily discharges. The bedload rating‐flow duration curve technique overestimates yields and bias correction methods always produce even higher yields. Ratings using both immersed bedload weight and adjusted immersed bedload weight always under‐predicted yields because they contain an implicit threshold of motion condition that is at least four times greater than that predicted by Bagnold's threshold equation. Such a result questions the applicability of Bagnold's threshold equation to the Ngarradj Creek catchment. The best estimates of mean annual bedload yield at East Tributary, Upper Swift Creek and Swift Creek gauges are 600 ± 170 (SE), 1065 ± 150 and 1795 ± 270 t/year, respectively. © 2015 Commonwealth of Australia. Hydrological Processes © 2015 John Wiley & Sons Ltd.  相似文献   

12.
A 1:50 scale hydraulic model was designed, based on Froude number similarity and using hydrological and sediment data from a small braided gravel-bed river (the North Branch of the Ashburton River, Canterbury, New Zealand). Eighteen experiments were conducted; seven using steady flows, and eleven using unsteady flows. The experiments were carried out in a 20 m × 3 m tilting flume equipped with a continuous sediment feed and an automated data acquisition and control system. In all experiments water at 30°C was used to reduce viscosity-related scale effects. Analyses of the experimental data revealed that bedload transport rates in braided channels are highly variable, with relative variability being inversely related to mean bedload transport rate. Variability was also found to be cyclic with short-term variations being caused by the migration of bedforms. Bedload transport was found to be more efficient under steady flow than under unsteady flow, and it was postulated that this is caused by a tendency for channel form to evolve towards a condition which maximizes bedload transport for the occurring flow. Average bedload transport rate was found to vary with channel form, although insufficient measurements were made to define a relationship.  相似文献   

13.
Maps are presented of the spatial distribution of two‐dimensional bedload transport velocity vectors. Bedload velocity data were collected using the bottom tracking feature of an acoustic Doppler current pro?ler (aDcp) in both a gravel‐bed reach and a sand‐bed reach of Fraser River, British Columbia. Block‐averaged bedload velocity vectors, and bedload velocity vectors interpolated onto a uniform grid, revealed coherent patterns in the bedload velocity distribution. Concurrent Helley‐Smith bedload sampling in the sand‐bed reach corroborated the trends observed in the bedload velocity map. Contemporaneous 2D vector maps of near‐bed water velocity (velocity in bins centered between 25 cm and 50 cm from the bottom) and depth‐averaged water velocity were also generated from the aDcp data. Using a vector correlation coef?cient, which is independent of the choice of coordinate system, the bedload velocity distribution was signi?cantly correlated to the near‐bed and depth‐averaged water velocity distributions. The bedload velocity distribution also compared favorably with variations in depth and estimates of the spatial distribution of shear stress. Published in 2004 by John Wiley & Sons, Ltd.  相似文献   

14.
We provide field evidence for the role of bedload in driving fluvial incision and knickpoint propagation. Using aerial photographs, field surveys, and hydrological data, we constrain the incision history of a bedrock gorge 1200 m long and up to 20 m deep cut by Da'an River in western Taiwan. This reach of the river experienced 10 m of uplift during the 1999 Chi‐Chi earthquake. For five years following the earthquake, bedload was prevented from entering the uplift zone, the knickpoint was static and little incision took place. Bedload transport across the uplift zone resumed in 2004, initiating extremely rapid incision, with 620 m of knickpoint propagation and up to 20 m of downcutting by 2008. This change highlights the relative inefficiency of suspended sediment and the dominant role of bedload as a tool for fluvial erosion and knickpoint propagation. Once bedload tools became available, knickpoint propagation was influenced by geological structure, lithology, and drainage organization. In particular, a change in dip of the sandstone beds at the site caused a decrease of knickpoint propagation velocity. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

15.
A continuous record reveals that the incidence of bedload in a coarse-grained river channel changes from flood to flood. Long periods of inactivity encourage the channel bed to consolidate sufficiently so that bedload is largely confined to the recession limb of the next flood-wave. But when floods follow each other closely, the bed material is comparatively loose and offers less resistance to entrainment. In this case, substantial amounts of bedload are generated on the rising limb. This is confirmed by values of bed shear stress or stream power at the threshold of initial motion which can be up to five times the overall mean in the case of isolated floods or those which are the first of the season. This produces a complicated relationship between flow parameters and bedload and explains some of the difficulties in establishing bedload rating curves for coarse-grained channels. Besides this, the threshold of initial motion is shown to occur at levels of bed shear stress three times those at the thresholds of final motion. This adds further confusion to attempts at developing predictive bedload equations and clearly indicates at least one reason why equations currently in use are unsatisfactory. Bedload is shown to be characterized by a series of pulses with a mean periodicity of 1.7 hours. In the absence of migrating bedforms, it is speculated that this well-documented pattern reflects the passage of kinematic waves of particles in a slow-moving traction carpet. The general pattern of bedload, including pulsations, is shown to occur more or less synchronously at different points across the stream channel.  相似文献   

16.
This paper investigates variability in bedload transport and channel morphology for 11 replicate experimental runs in an approximately 1:50 braided river model. The experiments, each of 90 h duration, were carried out in a 20 × 3m tilting flume. All the experiments started with the same initial conditions. Bedload transport was measured at 5 min intervals in a collection drum at the exit from the flume. The model showed reasonable hydraulic similarity when compared to prototype rivers. Results show that mean bedload transport rates for the 11 runs vary in the range 0·98 to 1·49gs?1 (mean + 1·21, coefficient of variation 11 per cent). Within-run transport rates commonly vary from close to zero, to two and occasionally three or four times the mean rate. Within the bedload series, several irregular phases of transport intensity can be observed, but time series analysis of the data show little underlying serial structure (an AR(2) autoregressive model is appropriate). Channel patterns are narrow/braided, are established quickly and remain relatively stable throughout the runs, although channel widths increase between 20 and 103 per cent over the 11 runs. Channel behaviour varies from aggradational to transitional between aggradation and degradation. Time-averaged bedload transport rate is weakly correlated with braiding intensity. In general, these results demonstrate that for a given set of controlling variables, bedload transport and channel morphology can be approximately replicated.  相似文献   

17.
Bedload transport is a complex phenomenon that is not well understood, especially for poorly sorted sediment and low transport rates, which is what is typically found in alpine gravel-bed rivers. In this paper, the interaction between bedload rate, bed stability and flow is investigated using flume experiments. Significant differences in bedload rates were observed for experiments conducted on beds formed with the same gravel material but presenting diverse arrangements and bedforms. Tests were performed under regimes of low transport rate, which are mainly controlled by gravel-bed roughness. Different scales of roughness were identified using the statistical characteristics of detailed bed elevation measurements: grain, structure and large bedform scales. The role played by these different roughness scales in bedload dynamics was examined. For quasi-flat beds, bed stability was quantified using a combination of bed surface criteria describing grain and structure scales. It was found that bed stability affects the bedload rate directly and not only through its influence on the flow or on the incipient motion. For beds with large bedforms, the analysis of bedload dynamics also showed the importance of accounting for effective bed shear stress distributions. An empirical bedload model for low transport regimes was suggested. Compared with previous formulae developed for alpine rivers, this model accounts for bed stability and distribution of effective bed shear stress. It significantly improves the understanding of gravel dynamics over complex beds such as arranged beds or those with large bedforms. However, further tests are needed to use the model outside the range of conditions of this study. © 2019 John Wiley & Sons, Ltd.  相似文献   

18.
Declining sand inputs to a channel with bimodal bed sediment can lead to degradation, armoring, and reduced bedload transport rates. Where sand loading is episodic, channels may alternate between high‐sand and low‐sand conditions, with ensuing responses in bed texture and bedload transport rates. The effects of episodic sand loading are explored through flow, grain size, and bedload transport measurements on the Pasig‐Potrero River, a sediment‐rich channel draining Mount Pinatubo, Philippines. Sand loading on the Pasig‐Potrero River is highly seasonal, and channel adjustments between seasons are dramatic. In the rainy season, inputs from sand‐rich 1991 eruption deposits lead to active, sand‐bedded, braided channels. In the dry season, many precipitation‐driven sand sources are cut off, leading to incision, armoring, and significantly lower bedload transport rates. This seasonal transition offers an excellent opportunity to examine models of degradation, incision, and armoring as well as the effectiveness of sediment transport models that explicitly encapsulate the importance of sand on transport rates. During the fall 2009 seasonal transition, 7·6 km of channel incised and armored, carving a 2–3 m deep channel on the upper alluvial fan. Bedload transport rates measured in the August 2009 rainy season were over four orders of magnitude greater than gravel‐bedded dry‐season channels surveyed in January 2010, despite having similar shear stress and unit discharge conditions. Within dry‐season incised channels, bed armoring is rapid, leading to an abrupt gravel‐sand transition. Bedload transport rates adjust more slowly, creating a lag between armoring and commensurate reductions in transport. Seasonal channel incision occurred in steps, aided by lateral migration into sand‐rich banks. These lateral sand inputs may increase armor layer mobility, renewing incision, and forming terraces within the incised seasonal channel. The seasonal incised channel is currently being reset by precipitation‐driven sand loading during the next rainy season, and the cycle begins again. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

19.
The morphological active width, defined as the lateral extent of bed material displacement over time, is a fundamental parameter in multi‐threaded gravel‐bed rivers, linking complex channel dynamics to bedload transport. Here, results are presented from five constant discharge experiments, and three event hydrographs, covering a range of flow strengths and channel configurations for which morphological change, bedload transport rates, and stream power were measured in a physical model. Changes in channel morphology were determined via differencing of photogrammetrically‐derived digital elevation models (DEMs) of the model surface generated at regular intervals over the course of ~115 h of experimental runs. Independent measures of total bedload output were made using downstream sediment baskets. Results indicate that the morphological active width increases with total and dimensionless stream power and is strongly and positively correlated with bulk change (total volume of bed material displaced over time) and active braiding intensity (ABI). Although there is considerable scatter due to the inherent variability in braided river morphodynamics, the active width is positively correlated with independent measurements of bedload transport rate. Active width, bulk change, and bedload transport rates were all negligible below a dimensionless stream power threshold value of ~ 0.09, above which all increase with flow strength. Therefore, the active width could be used as a general predictor of bulk change and bedload transport rates, which in turn could be approximated from total and dimensionless stream power or ABI in gravel‐bed braided rivers. Furthermore, results highlight the importance of the active width, rather than the morphological active depth, in predicting volumes of change and bedload transport rates. The results contribute to the larger goals of better understanding braided river morphodynamics, creating large high‐resolution datasets of channel change for model calibration and validation, and developing morphological methods for predicting bedload transport rates in braiding river systems. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

20.
It is widely recognized nowadays that there are at least two different phases of bedload sediment transport in gravel‐bed rivers. However, the transition between these phases is still poorly or subjectively defined, especially at bends in rivers, where cross‐stream sediment transport can strongly influence changes in the texture of the transported sediment. In this paper, we use piecewise models to identify objectively, at two points in the cross‐section of a river bend, the discharge at which the transition between bedload transport phases occurs. Piecewise models were applied to a new bedload data set collected during a wide range of discharges while analysing the associated changes in sediment texture. Results allowed the identification of two well‐differentiated phases of sediment transport (phase I and phase II), with a breakpoint located around bankfull discharge. Associated with each phase there was a change in bedload texture. In phase I there was non‐dominance in the transport of fine or coarse fractions at a particular sampling point; but in phase II bedload texture was strongly linked to the position of the sampling point across the channel. In this phase, fine particles tended to be transported to the inner bank, while coarse sizes were transferred throughout the middle parts of the channel. Moreover, bedload texture at the inner sampling point became bimodal while the transport of pebble‐sized particles was increasing in the central parts of the river channel. It is suggested that this general pattern may be related both to secondary currents, which transfer finer particles from the outer to the inner bank, and to the progressive dismantling of the riverbed surface layer. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

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