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It is important to understand the effects of ice cover on sediment transport in cold climates, where sub-freezing temperatures affect water bodies for a significant part of the year. The literature contains many studies on sediment transport in open channel flow, and several studies on sediment transport in completely ice-covered flow. There has been little or no research on sediment transport in partially ice-covered channels. In the current study, laboratory experiments were done in a rectangular flume to quantify the impact of border ice presence on the sediment transport rate. The effects of ice cover extent and changing flow strengths on sediment transport distribution also were investigated, and the results were compared to those for fully ice-covered and open channel flow. The ice coverage ratios considered were 0 (representing the open water condition), 0.25, 0.50, 0.67, and 1 (representing fully ice-covered flow). The partial ice cover was found to impact the sediment transport distribution within the channel. The effect of ice coverage extent on sediment transport distribution was more significant at lower flow strengths and became negligible at higher flow strengths. The conventional equations for sediment transport in open channel flow and fully ice-covered flow that relate the dimensionless bedload transport rate to the flow strength were found to be applicable to estimate the total cross-section-averaged bedload transport for partially ice-covered flow when modified appropriately. Empirical coefficients for these equations were determined using the experimental data. [ABSTRACT FROM AUTHOR]

• Lateral sediment flux from hillslopes is directly connected to the curve number. • The curve number summarized the resistance from the soil-group complex. • The lateral sedimentologic connectivity was well represented by the curve number. • The soil-cover complex in a watershed is closely related to watershed erodibility. The flux of suspended sediment and bedload in a watershed is closely linked to the resistance of soil, known as erodibility. However, the relation between the resistance generated by soil to sediment transport from the hillslope to the river flow is still a challenge. Typically, the bedload flux is related to the shear stress of the main channel. However, the link between lateral sediment flux from hillslopes to suspended sediment flux of the main channel and the relation between bedload and suspended sediment flux to soil erodibility need to be developed. For three Brazilian watersheds, suspended sediment and bedload transport, soils, and hydrological data were obtained to determine watershed soil erodibility. The landscape connectivity expressed by hydrological-sediment connectivity was applied to determine the lateral sediment transport to the primary watershed channel. The flow resistance and lateral suspended sediment discharge were represented by the curve number, which summarized the resistance from the soil-group complex leading to soil erodibility. The curve number addressed the lateral flow and suspended sediment transport to represent the lateral connectivity on the landscape. Sediment transport (sand and suspended sediment) from hillslopes was added to the bedload transport along the longitudinal axis of the watershed, and the watershed soil erodibility (K W) was, thus, obtained for each of the three evaluated watersheds. [ABSTRACT FROM AUTHOR]

Abstract This study was aimed at untangling the relative impacts of successive phases of human modifications on changes in bedload transport along a 430 km-long river reach: the Rhône River from Motz dam to the sea. We used a 1D hydraulic model to solve for water lines across a range of discharges and all along the reach. Next, using grain sizes measured in the channel, we estimate flow competence and mean annual bedload transport capacities using the Recking (2013) bedload transport equation. In addition, we used the Generalized Threshold Model to estimate the relative fine and coarse fractions of the load. Bedload transport estimates were carried out under present-day hydraulic conditions and compared to estimates based on model runs simulating an unimpeded flow regime and using grain sizes measured in bars as a proxy for conditions prior to armouring. Our results show that present-day bedload transport along the Rhône is significantly fragmented by multiple closely spaced dams. Mean annual bedload capacity varies between 2500 and 16,300 m3/year over all the reaches, with an average of 4700 m3/year. Results of the GTM analysis suggest that this load is composed of 89% fines. We find bed sediment mobility to be very low in most reaches, and that potentially mobile sediments are finer than the median grain size in the riverbed even at high flows. Our results suggest that bedload capacities were 25–35 times higher prior to bed armouring and flow modifications; dams had an impact 2–3 times more important on transport capacities than channel embankments, and bed armouring was foremost a response to channel embankments. Based on an analysis of the ratio of sediment yields to transport capacities, we propose a conceptual scheme illustrating how bedload supply, channel morphology, and surface texture coevolved in the Rhône over the past century and half. Graphical abstract Unlabelled Image Highlights • Mean annual bedload capacity is 4700 m3/year with strong intra-reach variability. • Bed mobility is very low and the majority of transported sediments are fines. • Bedload transport rates were up to 35 times higher prior to embankments and dams. • Dams had an impact 2–3 greater than changes in grain-size on BL transport capacities. • The effects of successive dams show strong overlap. [ABSTRACT FROM AUTHOR]

The processes of sediment entrainment, transport, and deposition over bedforms are highly dynamic and temporally and spatially variable. Obtaining measurements to understand these processes has led to ongoing developments in instrumentation for studying near-bed sediment dynamics, with the outputs applied to the development and assessment of sediment transport modelling. In the present study results are reported from three acoustic systems deployed to make observations of bedforms, bedload, suspended concentration and horizontal and vertical velocity components. To evaluate the instruments a series of near-bed boundary layer measurements were collected in a large scale flume facility over a rippled bed of medium sand under regular waves. The observations were conducted as part of Joint Research Activities within the EU funded Hydralab project. The suite of acoustic instruments consisted of a Bedform And Suspended Sediment Imager, BASSI, a three dimensional acoustic ripple profiler, 3D-ARP, and three Acoustic Concentration and Velocity Profilers, ACVP's. Here results are reported from the deployment of the instruments, to illustrate the ongoing developments in acoustics and the expanding capability of the application of acoustics to the study of near-bed flow and sediment dynamics. [ABSTRACT FROM AUTHOR]

Sediment transport and soil erosion can be determined by a variety of field and modelling approaches. Computer based soil erosion and landscape evolution models (LEMs) offer the potential to be reliable assessment and prediction tools. An advantage of such models is that they provide both erosion and deposition patterns as well as total catchment sediment output. However, before use, like all models they require calibration and validation. In recent years LEMs have been used for a variety of both natural and disturbed landscape assessment. However, these models have not been evaluated for their reliability in steep forested catchments. Here, the SIBERIA LEM is calibrated and evaluated for its reliability for two steep forested catchments in south-eastern Australia. The model is independently calibrated using two methods. Firstly, hydrology and sediment transport parameters are inferred from catchment geomorphology and soil properties and secondly from catchment sediment transport and discharge data. The results demonstrate that both calibration methods provide similar parameters and reliable modelled sediment transport output. A sensitivity study of the input parameters demonstrates the model’s sensitivity to correct parameterisation and also how the model could be used to assess potential timber harvesting as well as the removal of vegetation by fire. [ABSTRACT FROM AUTHOR]

During floods, the bedload transport of steep headwaters can exceed the hydraulic transport capacity of milder downstream reaches where settlements are often situated. Therefore, sediment retention barriers are typically installed upstream of such sensible areas. These barriers trigger bedload trapping via two control mechanisms, either hydraulic or mechanical. Both deposition controls, pertaining to instream sediment trapping structures, are analyzed experimentally in this study. Bedload trapping by hydraulically controlled barriers is prone to sediment flushing, i.e., the remobilization of formerly deposited sediment, in particular when the barrier is simultaneously under- and overflown. In this case, the remobilization rate is close to the bedload transport capacity of the nonconstricted channel. Mechanical deposition control by screens is in turn sensible to the grain size. Thus, both deposition control concepts may fail, and bedload may be transported downstream at a rate corresponding to the transport capacity of headwaters, thereby endangering urban areas. This study shows that the combination of both deposition control concepts is suitable for improving the control of bedload retention. With this combination, undesired sediment flushing of upstream deposits in the channel caused by insufficient hydraulic control is prevented. Furthermore, the uncertainty related to the estimation of the representative grain size in the design of mechanical control barriers is reduced. [ABSTRACT FROM AUTHOR]

Many rivers in the Mediterranean region are regulated for urban and agricultural purposes. Reservoir presence and operation results in flow alteration and sediment discontinuity, altering the longitudinal structure of the fluvial system. This study presents a 3-year sediment budget of a highly dammed Mediterranean river (the Muga, southern Pyrenees), which has experienced flow regulation since the 1969 owing to a 61-hm 3 reservoir. Flow discharge and suspended sediment concentration were monitored immediately upstream and downstream from the reservoir, whereas bedload transport was estimated by means of bedload formulae and estimated from regional data. Results show how the dam modifies river flow, reducing the magnitude of floods and shortening its duration. At the same time, duration of low flows increases. The downstream flow regime follows reservoir releases that are mostly driven by the irrigation needs in the lowlands. Likewise, suspended sediment and bedload transport are shown to be notably affected by the dam. Sediment transport upstream was mainly associated with floods and was therefore concentrated in short periods of time (i.e., > 90% of the sediment load occurred in < 1% of the time). Downstream from the dam, sediments were transported more constantly (i.e., 90% of the load was carried during 50% of the time). Total sediment load upstream from the dam equalled 23,074 t, while downstream it was < 1000 t. Upstream, sediment load was equally distributed between suspension and bedload (i.e., 10,278 and 12,796 t respectively), whereas suspension dominated sediment transport downstream. More than 95% of the sediments transported from the upstream basins were trapped in the reservoir, a fact that explains the sediment deficit and the river bed armouring observed downstream. Overall, the dam disrupted the natural water and sediment fluxes, generating a highly modified environment downstream. Below the dam, the whole ecosystem shifted to stable conditions owing to the reduction of water and sediment loads. [ABSTRACT FROM AUTHOR]

Over the last two centuries, rivers worldwide have been affected by human interventions, including dams, river training, and gravel mining. Such actions have often involved river fragmentation and sediment starvation. In this regard, gravel augmentation is an increasingly common restoration practice for mitigating sediment starvation in gravel-bed rivers. However, uncertainties remain on how to better implement and design such operations. This is the case for the Rhône River at Péage-de-Roussillon, France, where 6885 m3 of gravels were augmented in 2017. This work raised some concerns from river managers about the potential threat posed to a downstream reservoir from the arrival of the sediment, and explains why they were interested in the timeframe of sediment propagation, and travel distances and velocities of the augmented sediment. To answer these questions, we propose a modelling framework for simulating the long-term downstream propagation of a pulse of augmented sediment, with this framework being based on a combination of particle tracking data collected in the field and bedload transport capacity estimates. This workflow allowed us to successfully model propagation of gravels along the study reach, and provided useful information on how the sediment wave would behave over the long term. We believe that the methodology proposed in this study has much potential for exploring and investigating the kinematics of sediment wave propagation in gravel-bed rivers. [ABSTRACT FROM AUTHOR]

Stream sediment loads (both bedload and suspended sediment) are problematic to measure due to the time and equipment needed. There is a dearth of such data sets globally let alone for Australia. However, such data are needed to quantify sediment transport type and rates, landscape evolution, effect of human disturbance as well as patterns and temporal response. Here we present the findings from 8 steepslope forested catchments dominated by headwater streams (size range 15–100 ha) in south-eastern Australia where both bedload and suspended load have been measured over multiple years. The results demonstrate that suspended load is the dominant component and there is no consistent suspended to bedload ratio for the catchments. The suspended sediment to bedload ratio appears to be catchment specific. There was no relationship between total load (or bedload/suspended load) and average catchment slope, stream length, shape or any geomorphic descriptor. However catchment total load was found to be significantly related to catchment area. Of the 8 catchments examined here, 6 had been harvested for timber in previous decades (with large areas of forest removed) while 2 catchments had minimal disturbance (Control catchments). There was no difference in sediment loads from the harvested and Control catchments. The results demonstrate that although land disturbance had previously occurred the management practices employed in each catchment were effective in the long term. This provides confidence that the forest harvesting and subsequent management do not produce detrimental effects in the medium to long term. An assessment of erosion rates and likely soil production rates suggests that the catchments are eroding soil at the rate it is being produced. [ABSTRACT FROM AUTHOR]

Understanding of sediment transport comes largely from studies conducted on well-sorted sand-bed and poorly sorted gravel-bed channels. The aim of this study is to evaluate cross-channel patterns of transport rate and grain size in a poorly sorted sand-bed channel. Transport observations were collected from the San Antonio River using a Helley-Smith sampler during flows from 0.02 to 1.1 times bankfull capacity. Resulting transport rates and grain size distributions were pooled to describe eight sections across a channel transect that includes the lower bank and compared to local boundary material. Maximum transport rates are concentrated in the central zone of the streambed regardless of flow level, but gravels and coarse sands are conveyed preferentially on one side of the bed. Grain size distributions change relatively little with flow and approximate the local bed material supply. The size distributions associated with smaller transport rates near the channel margin become finer and more closely approximate the size characteristics of bank material at higher flows. Results extend patterns of differential routing of grain sizes to channel banks and establish the relative fluxes between the bed and bank environments. The small gravel content in poorly sorted sand beds requires further attention because it can contribute to cross-channel variation in sediment fluxes, limit the development of sandy bedforms, and influence the quality of streambed habitat. [ABSTRACT FROM AUTHOR]

• We examine eight steep slope forested headwater catchments (15–100 ha). • Bedload organic carbon (OC), soil carbon and dissolved OC was measured. • OC in the bedload was found to be significantly related to catchment area. • Dissolved OC export in stream water declined with catchment area. • There was no difference in OC export from the harvested and non-harvest catchments. Qualitative and quantitative understandings of the origin, transport and fate of organic carbon (OC) in forest systems is needed to advance our understanding of biogeochemical cycling as well as catchment management and forest harvesting. Here we present the findings from eight steep slope forested catchments dominated by headwater streams (size range 15–100 ha) in south eastern Australia where bedload, organic carbon in bedload, hillslope soil carbon together with dissolved organic carbon has been measured over multiple years. OC in the bedload was found to be significantly related to catchment area (p < 0.02). Dissolved organic carbon export in stream water declined with catchment area. Combined bedload organic carbon and dissolved organic carbon export was significantly related to catchment area. There was no significant difference between hillslope soil organic carbon and bedload organic carbon concentration. When corrected for area, OC export by bedload was not significantly different to that of dissolved OC export. Using the environmental tracer 137Cs it was found that there was no significant difference in tracer concentration between bedload and hillslope soil. This suggests a direct link between hillslope and channel and delivery of organic carbon to the channel. Of the eight catchments examined here, six had been harvested for timber in previous decades (with area of forest removed ranging from 25 to 60%) while two catchments had minimal disturbance (Control catchments- no harvest). There was no difference in organic carbon export from the harvested and Control catchments. The results demonstrate that although land disturbance had previously occurred the management practices employed in each catchment were effective in the long term. [ABSTRACT FROM AUTHOR]

The confluence of the regulated Toltén River and its tributary the unregulated Allipén (south of Chile) has proved dynamic in the last decade. Daily bedload measurements with a Helley–Smith sampler, bed surveys, and grain-size distributions of the two rivers are obtained from a field campaign that lasts 3 months in high-flow season. The goals are to quantify total bedload and to understand the balance between tributary and main river and the bedload distribution in space and texture. The bedload transport varies 200-fold, with a maximum of 5000 t/day. The discharge varies five-fold, with a maximum of 900 m 3 /s. Two-thirds of the total bedload volume are transported through the deeper area of the cross section and gravel is predominant (64%). Average bedload volumes in the confluence seem unbalanced in favour of the tributary. Main river bedload transport is predominantly at below-capacity conditions, while the tributary bedload transport is at-capacity conditions. This is deemed the main reason of inaccuracy of the bedload predictors. The roles of entrainment into suspension, helical flow, partial transport, and mobile armour are discussed. [ABSTRACT FROM AUTHOR]

The Elwha River restoration project, in Washington State, includes the largest dam-removal project in United States history to date. Starting September 2011, two nearly century-old dams that collectively contained 21 ± 3 million m 3 of sediment were removed over the course of three years with a top-down deconstruction strategy designed to meter the release of a portion of the dam-trapped sediment. Gauging with sediment-surrogate technologies during the first two years downstream from the project measured 8,200,000 ± 3,400,000 tonnes of transported sediment, with 1,100,000 and 7,100,000 t moving in years 1 and 2, respectively, representing 3 and 20 times the Elwha River annual sediment load of 340,000 ± 80,000 t/y. During the study period, the discharge in the Elwha River was greater than normal (107% in year 1 and 108% in year 2); however, the magnitudes of the peak-flow events during the study period were relatively benign with the largest discharge of 292 m 3 /s (73% of the 2-year annual peak-flow event) early in the project when both extant reservoirs still retained sediment. Despite the muted peak flows, sediment transport was large, with measured suspended-sediment concentrations during the study period ranging from 44 to 16,300 mg/L and gauged bedload transport as large as 24,700 t/d. Five distinct sediment-release periods were identified when sediment loads were notably increased (when lateral erosion in the former reservoirs was active) or reduced (when reservoir retention or seasonal low flows and cessation of lateral erosion reduced sediment transport). Total suspended-sediment load was 930,000 t in year 1 and 5,400,000 t in year 2. Of the total 6,300,000 ± 3,200,000 t of suspended-sediment load, 3,400,000 t consisted of silt and clay and 2,900,000 t was sand. Gauged bedload on the lower Elwha River in year 2 of the project was 450,000 ± 360,000 t. Bedload was not quantified in year 1, but qualitative observations using bedload-surrogate instruments indicated detectable bedload starting just after full removal of the downstream dam. Using comparative studies from other sediment-laden rivers, the total ungauged fraction of < 2-mm bedload was estimated to be on the order of 1.5 Mt. [ABSTRACT FROM AUTHOR]

A new numerical model for predicting the total sediment load in the river is presented. The model is comprised of two parts, namely flow and sediment transport parts. The flow analysis is carried out using the lateral distribution method, which distributes the flow and sediment load across the width, based on channel geometry and flow dynamics. To obtain the total sediment load, the bedload and suspended load are predicted separately. Conventional formulas are used for the bedload, and Rousean distribution with an entrainment function is used for the suspended load. Einstein partition is used to separate the form drag component from the total shear stress. The model is applied to the Danube River, a gravel-bed river in Slovakia and the Han River, a sand-bed river in Korea. Predicted distributions of sediment load in the lateral direction are given. The predicted results are compared with those obtained using the 1D approach as well as from measured data. Total sediment load rating curves are presented and the mixture effect of bed-materials is discussed. [ABSTRACT FROM AUTHOR]

In this paper we present a probabilistic/deterministic model for the evaluation of the sediment transport rate in a stream. Starting from Einstein’s theory, the approach was obtained by trying to overcome some of the intrinsic limitations. The approach is based on two distinct probability functions, one relevant to the detachment of grains and the second relevant to the length of particle jumps. The sediment transport rate is obtained by integrating the distribution of the ranges of the particle jumps multiplied by the average particle velocity. The relationship for the average ranges of particle jumps is an opportune combination of the Einstein and Yalin expressions. The final formulation was calibrated by means of a large number of experimental data and also by comparison with some of the most widely-used empirical formulas. The results show a better agreement between theory and experiments than do the other theories analyzed. [ABSTRACT FROM AUTHOR]

In this paper, we used a bedload transport data set collected at North Fork Caspar Creek, California, to examine temporal variation in sediment transport rate over a 7-year period. Using a hierarchical mixed-effects model, we examined across and within-event variation to determine whether the bedload-shear stress relation trends over time. The relation between bedload transport and shear stress was modeled using log(Qb)α+β*log(τ)+ε, where α and β are constants and ε is an error term. Depending on the length of observation, α and β can vary over several orders of magnitude, making modeling of transport based on flow challenging and highly inaccurate. We found a higher order yearly relation between bedload and shear stress, indicating systematic changes to the system over time. In the absence of significant additions to the system, α decreases roughly linearly over time, while β does not show any trend. From the systematic decline in α, we infer changes to sediment availability in the stream over time. Mixed-effects models have the potential to be a useful predictive tool in fluvial geomorphology, as they are more powerful at detecting trends in sediment transport rates than individual linear regressions. [ABSTRACT FROM AUTHOR]

Highlights: [•] We tested the effect of sediment transport on velocity measurement by acoustic Doppler. [•] Analysis was based on field observations and flume experiments in Spain, Israel and the UK. [•] Flow velocity was slightly underestimated with high suspended sediment concentrations. [•] Flow velocity was significantly underestimated in the presence of coarse bedload particles. [•] Starflow was found to be a valuable tool for discharge determination. [Copyright &y& Elsevier]

Abstract: Sediment transport and storage in mountain stream channels are closely dependent on hillslope activities and bank erosion. This paper analyses bedload measured in 13 mountain streams (989 values with slope higher than 5%) in an attempt to investigate how much the sediment supply condition impacts bedload transport rates. First, the sediment supply condition of each stream was evaluated qualitatively using information available in the original studies. In the second step, the data set was analysed by comparing bedload transport rates considering a Shields stress ratio and by comparing transport rate efficiency with consideration of a dimensionless stream power. The two analyses indicate higher sediment transport rates for the streams identified as “connected” to an active source. The consequences for bedload transport prediction are discussed with a nonthreshold bedload equation. Even though predicting the exact sediment supply condition and the associated transport rate is not yet possible, this study suggests that defining an envelope delimiting minimum and maximum transport for a given river reach should be possible. [Copyright &y& Elsevier]

Abstract: This paper reports about flow and sediment transport measurements undertaken during the rainy season (July-August) 2008 on Gereb Oda, a steep, sand-bed ephemeral stream, draining the western margin of the Kobo structural basin in northern Ethiopia. Gereb Oda streambed is dry for most of the year since it is subjected only to sporadic flash floods in response to individual, high intensity and spatially confined rainstorms. Information about hydraulic and sediment transport processes in steep sand-bed, ephemeral stream is very poor and, though only two flash floods occurred during the field campaign, the data gathered may contribute to improve our knowledge on these kind of rivers. Froude numbers were calculated in order to verify the occurrence of supercritical flow conditions as postulated by a few authors from the analysis of sedimentary structures characteristics. Flow data are also compared to simple models to predict flow velocity and discharge since flow recording systems are seldom installed on ephemeral streams in remote areas and developing countries. Dryland rivers are known for their very high suspended sediment transport, but very little bedload data exist for sand-bed, ephemeral streams. The variation of suspended sediment concentration with discharge is analysed and simple rating curves for both suspended and bed load transport are derived. A few equations to predict bedload are tested against Gereb Oda data and the relationship between en masse bedload transport processes as thin sand sheets and the development of horizontal lamination through the migration of leaf-shaped, sheet-like bedforms is investigated. Individual, large boulders were observed to move at flow depths of the same order of magnitude of their size. A few functions to predict the threshold conditions for large particles entrainment are used to verify if and to what extent they match Gereb Oda field conditions. The increased density of the water-sediment mixture, for the very high suspended sediment concentrations ranging from 100,000 to 200,000 ppm, is considered as well. [Copyright &y& Elsevier]

Abstract: We demonstrate that alluvial channel response to regulation depends on the characteristic mode of sediment transport in a channel and, thus, for a channel in supply-transport equilibrium, on the caliber of sediment mantling the channel bed, as well as changes in characteristic water discharge and sediment load. We find that regulated, coarse gravel- and cobble-bed alluvial rivers dominated by bedload transport are predicted and observed to preserve the value of a dimensionless ratio of characteristic water discharge, channel slope, width, and size of sedimentary particles mantling the bed associated with the critical conditions required for the onset of significant sediment transport. The covariant geomorphic adjustment of such rivers to regulation is independent of the degree of sediment impoundment, although the nature and rate of changes in any specific characteristic appear to be sensitive to changes in sediment supply. In contrast, covariant geomorphic changes in sand- and fine gravel-bed alluvial rivers dominated by weak suspension transport are predicted and observed to be dependent on the degree of sediment impoundment and commensurate with the change in the sediment concentration of characteristic, formative flows. In both cases, specific geomorphic characteristics of alluvial rivers exhibit varied responses to regulation in different rivers, but across all rivers a systematic covariation in channel slope, width, and grain size is observed that, for a given mode of sediment transport, preserves a characteristic value of the Shields number. [ABSTRACT FROM AUTHOR]

Abstract: The three-dimensional numerical model COHERENS (COupled Hydrodynamical-Ecological model for REgioNal and Shelf seas) has been adapted to compute the rates of transport as bedload and suspended load of heterogeneous bottom sediments induced by the dominant M2 tide in the English Channel. A pre-processing of an extensive surficial sediments dataset has been performed to determine the seabed composition (grain-size distribution or presence of rocks) at the computational grid nodes. Maximum bedload and suspended load transport rates over the tidal cycle as well as the contributions of the 10 different sedimentary classes to the mean transports are computed. Highest sediment transport rates occur in fine sediments areas located in the surroundings of high shear stresses areas. Medium sand is found to be predominant in bedload, while suspension load implies mainly silts in the inner shoreface and both fine and medium sands in the outer shoreface. The offshore residual bedload transport pathways are orientated westerly in the western part of the Channel and easterly in the eastern part defining a “parting” zone which runs from the Isle of Wight to the Cotentin Peninsula. An offshore “bedload convergence” occurs in the southwest of the Dover Strait; a narrow transport pathway bypassing it along the French coastline. These features reproduce those predicted by and provide higher resolution features like inshore headland-induced gyres, particularly along the English coastline. The new predicted general pattern of residual suspended load transport is very similar to the bedload pattern. Differences arise in the central “divergence” zone which exhibits a “Y” shape with two branches ending on both sides of the Isle of Wight, in the Baie de Seine characterized by a central “convergence” and along the English coastline studded with many headland-induced recirculations. [Copyright &y& Elsevier]

Abstract: This study investigates sediment mobility in a large gravel-bed river (Tagliamento River, northeastern Italy). Field data were used to identify the morphological effectiveness of a range of flows (floods with recurrence interval <1 to 3.5 year) and for a detailed analysis of the partial transport condition. The analyses were carried out on three cross sections where a number of areas representative of different morphological units (main and secondary channels, low and high bars, islands) were painted. Grain size of the painted area was measured using a photographic method. Monitoring of bed mobility during the study period supplied new photographs of the painted areas, measurements of size and travel distance of the mobilized particles, and estimate of flow depth after each flood event. Our analyses have shown that with dimensionless shear stress around 0.073 (17 N m− 2), the morphological effect over the painted areas was primarily partial transport; while with stresses >0.1 (25 N m− 2), the bed experienced full mobility, i.e., all the painted particles were transported or totally buried. Full sediment mobility was observed on lower morphological units (i.e., main and secondary channels) under floods with very high frequency (RI <1 y), whereas on the low bars full mobility occurred under floods with a recurrence interval slightly >1 year. Instead, fine deposition and partial transport conditions were observed on the higher bars even after the largest of the monitored floods (RI =3.5 y). The analysis of the partial transport condition relies on more than 3500 measurements of particle travel distance (travel distances range from a few centimetres up to 22 m). The transported particles were generally finer than the painted sediments, and the analysis of the sediment transport ratio revealed that partial transport occurred under equal-mobility conditions for particles finer than 32 mm and under size-selective mobility for coarser fractions. This appears to be corroborated (for D <32 mm) by the insensitiveness of particle transport distance to particle sizes, even if the exponent (≈1) of the relationship between the dimensionless shear stress and the maximum transported diameter would suggest that all fractions are transported under equal-mobility conditions. [Copyright &y& Elsevier]

Abstract: The grain-size fractions in the bedload transported over the five heterogeneous sediment beds of different values of bed roughness were computed from the flume experiments. The existence of an entrapment factor associated with the sorting observed from the bed to active layer was modeled based on the modified critical shear stress to estimate the grain-size fractions in the transport layer under given hydraulic conditions. The efficiency of these models was tested with the observed data. Subsequently, the patterns of observed grain-size distributions in the transport layer were tested to identify the distributions developed in the active layer due to sorting using three probability density functions (pdf), such as, log-normal, log-hyperbolic and log-skew-Laplace. Tests indicated that a log-skew-Laplace distribution fitted best for 49%, a log-hyperbolic for 31%, and a log-normal for 20% out of forty-five bedload samples collected under unidirectional flow with changes in flow discharge and bed roughness. The results of this study would be useful to specify the grain-size distributions in the bedload formed under different hydrodynamic conditions in various sedimentary environments. [Copyright &y& Elsevier]

Abstract: The upper Columbia River, British Columbia, Canada, shows typical anastomosing morphology — multiple interconnected channels that enclose floodbasins — and lateral channel stability. We analysed field data on hydraulic and sedimentary processes and show that the anastomosing morphology of the upper Columbia River is caused by sediment (bedload) transport inefficiency, in combination with very limited potential for lateral bank erosion because of very low specific stream power (≤2.3 W/m2) and cohesive silty banks. In a diagram of channel type in relation to flow energy and median grain size of the bed material, data points for the straight upper Columbia River channels cluster separately from the data points for braided and meandering channels. Measurements and calculations indicate that bedload transport in the anastomosing reach of the upper Columbia River decreases downstream. Because of lateral channel stability no lateral storage capacity for bedload is created. Therefore, the surplus of bedload leads to channel bed aggradation, which outpaces levee accretion and causes avulsions because of loss of channel flow capacity. This avulsion mechanism applies only to the main channel of the system, which transports 87% of the water and >90% of the sediment in the cross-valley transect studied. Because of very low sediment transport capacity, the morphological evolution of most secondary channels is slow. Measurements and calculations indicate that much more bedload is sequestered in the relatively steep upper anastomosing reach of the upper Columbia River than in the relatively gentle lower anastomosing reach. With anastomosing morphology and related processes (e.g., crevassing) being best developed in the upper reach, this confirms the notion of upstream rather than downstream control of upper Columbia River anastomosis. [Copyright &y& Elsevier]

Summary: Coarse sediment transport processes in steep headwater streams may vary between bedload and debris flows events, depending on basin geomorphology and sediment supply. This paper compares two small catchments (drainage area 4–5km2) located in the Eastern Italian Alps where the dominant sediment transport processes differ substantially, i.e., debris flows in the Moscardo Torrent and bedload events in the Rio Cordon. The two basins were selected because they provided the unique opportunity to analyze long-term data of debris flow and bedload volumes, respectively. The two basins are compared in terms of peak discharge, event duration, and magnitude–frequency characteristics of transported sediment volumes. Additional bedload data from two more Alpine experimental basins are also considered. The results show that, for comparable recurrence intervals, debris flow volumes are 2–3 orders of magnitude larger than bedload volumes. This contrasting sediment transfer activity can be attributed to different basin and channel morphologies, which are analyzed in terms of sediment supply conditions, longitudinal profiles and slope–area curves. [Copyright &y& Elsevier]

Abstract: The boundary layer flow and the net sediment transport beneath asymmetrical waves have been examined by a turbulence boundary layer model in conjunction with a diffusion model for suspended sediments based on the linearized boundary layer equations with horizontally uniform forcing. The turbulence closure is provided by a high Reynolds number k–ε model. The flow model and sediment transport model have been verified against existing laboratory measurements for sheet flow conditions. Overall, these comparisons show that the mean (wave-averaged) velocity profile, sediment flux and total sediment transport (including mean bedload transport) are well predicted by the present model. A further investigation of the boundary layer structure shows the mechanisms causing the near-bed backflow (opposing the drift direction of the outer wave velocity). The effect of roughness and asymmetry on the mean boundary layer flow and sediment transport beneath asymmetrical waves have been investigated. The wave friction factor, the mean bedload transport and the mean velocity profiles are given for a wide range of near-bed wave excursion to bed roughness ratios. Moreover, for asymmetrical waves with the same mean drift velocity, but with different asymmetry, the wave with strongest asymmetry induces the largest mean sediment transport. This demonstrates the importance of wave asymmetry. [Copyright &y& Elsevier]

Abstract: Formulae for bedload transport of sediments in conditions characteristic of coastal waters are developed from principles of physics. They cover driving forces of: current alone, current plus symmetrical waves, current plus asymmetrical waves, asymmetrical waves alone, and integrated longshore transport. In each case the transport is given as one or more analytical functions of the basic input variables. The formulae are tested against laboratory and field data, and give predictions that lie within a factor of 2 of the measured values for between 47% and 91% of the data, depending on the driving force. The formulae are suited to practical application in coastal waters, especially for transport of coarse materials such as shingle, and also for the bedload component of transport of sand. [Copyright &y& Elsevier]

Abstract: This review paper aims to present a practical, integrated procedure for the prediction of sediment transport rates in both the continental and marine environment, based on the settling velocity of particles. Such studies have important applications in diverse fields such as civil and coastal engineering, sedimentology and environmental geology, where they can assist in flood control and the prevention of contaminant dispersal by wind and water, as well as the siltation of dams and harbours. The formation of placer deposits including gold, diamonds and other heavy minerals is also controlled by sediment transport processes, so that these studies can form the basis for more efficient exploration programs. The first part of the paper discusses some basic principles important in sediment transport, followed by an overview of published methods to determine the settling velocity of differently shaped particles, including natural grains. The application of settling velocity to predict the entrainment threshold of sediments on plane, horizontal and inclined beds by unidirectional currents and oscillatory waves is then discussed, which finally leads to the determination of sediment transport rates over plane and rippled beds. The validity of this approach to natural conditions is tested against published field data where possible. Other, widely used methods are also critically discussed, pointing out severe problems in current sampling technology and the calculation of bedload transport in natural environments. [Copyright &y& Elsevier]

Abstract: Current metre deployments, suspended sediment measurements and surface sediment samples were collected from three locations within distributary channels of the tidally dominated Fly River delta in southern Papua New Guinea. Net bedload transport vectors and the occurrence of elongate tidal bars indicate that mutually evasive ebb- and flood-dominant transport zones occur in each of the distributary channels. Suspended sediment experiments at two locations show a phase relationship between tidal velocity and sediment concentration such that the net suspended sediment flux is directed seaward. Processes that control the export of fluid muds with concentrations up to 10gl−1 from the distributary channels across the delta front and onto the pro-delta are assessed in relation to the available data. Peak spring tidal current speeds (measured at 100cm above the bed) drop off from around 100cms−1 within the distributary channels to &#60;50cms−1 on the delta front. Gravity-driven, 2-m thick, fluid mud layers generated in the distributary channels are estimated to require at least 35h to traverse the 20-km-wide, low-gradient (2×10−3 degrees) delta front. The velocities of such currents are well below those required for autosuspension. A 1-month time series of suspended sediment concentration and current velocity from the delta front indicates that tidal currents alone are unable to cause significant cross-delta mud transport. Wave-induced resuspension together with tides, storm surge and barotropic return-flow may play a role in maintaining the transport of fine sediment across the delta front, but insufficient data are available at present to make any reliable estimates. [Copyright &y& Elsevier]

VPA is an Excel spreadsheet to facilitate the analysis of current velocity profiles and its application to sediment transport studies in steady, uniform, open-channel flows. The program requires input values such as the water temperature (from which the density and dynamic viscosity are calculated), the channel depth and slope, current velocities as measured at different heights above the bed, bedform length and height, as well as the sediment density and median size. The latter can be provided as sieve diameters, fall diameters or as phi values. The velocity profiles are plotted on two graphs, one being a traditional plot of velocity versus height or distance from the bed and the other comparing the observed profile with theoretical profiles for smooth, transitional and rough boundary conditions. VBA macros are provided to clear the spreadsheet before new profiles are analysed, update the formulas, straighten out the velocity profiles, calculate the shear velocity, and save the data on a separate sheet for further analysis. The programme is applied to a new and more accurate method to determine the shear velocity, which can be used to predict the bedload discharge over plane beds and is also incorporated into a dimensionally correct suspended load transport equation combining the parameters most important in sediment transport. A dimensionally correct bedload discharge equation based upon the mean excess flow velocity is also proposed for plane beds, ripples and dunes. [Copyright &y& Elsevier]

Bedload transport generally depends on the bed shear stress and Reynolds number. Many studies conducted for the condition of turbulent flows have revealed the dependence of the transport rate on the bed shear stress, while knowledge of the Reynolds number effect on the transport rate is very limited. As an extreme case to reflect the viscous effect on sediment transport, sediment transport in laminar flows is considered in this paper. A stochastic approach is adopted to explore how the transport rate can be associated with characteristics of laminar flows. First, the probability of erosion in the absence of turbulence is assumed to depend only on the randomness of bed particles. The probability is then applied to formulate the sediment transport rate, of which the derivation is made largely based on Einstein’s bedload theory. The theoretical result indicates that the dimensionless transport rate for laminar flows is dependent on the dimensionless shear stress and dimensionless particle diameter or the shear Reynolds number. Comparisons are finally made between the derived formula and an empirical correlation available in the literature. [Copyright &y& Elsevier]

The velocity profile for unidirectional currents is usually determined by two forms of the law of the wall, which are valid for smooth and rough boundaries, respectively. The law of the wall for smooth boundaries outside the viscous sublayer and buffer layer applies where the boundary Reynolds number (Re*) is less than 5. The velocity in this case depends only on the dimensionless distance (yd) from the bottom. For rough boundaries where Re* is more than 65, the law of the wall is independent of the boundary Reynolds number, but the bottom roughness (k) has to be taken into account. The mean or median particle grain size (D) is commonly substituted for bottom roughness. At present, there is no generally accepted law of the wall for the transitional flow regime between hydrodynamically smooth and rough conditions. In this paper, an integrated law of the wall is proposed for the transitional regime, yielding velocity profiles that correspond well to observed velocity profiles under these conditions. The result is applied to a set of flume data, using an improved procedure to determine the bedload transport rate. [Copyright &y& Elsevier]

To determine the effects of grain size and density gradation in oscillatory sheet-flow, experiments are conducted in an oscillating water tunnel. A formal derivation of a schematised transport model shows that the transport rates per sediment fraction can be determined with and without the assumption of an active layer. A technique that measures sediment composition from natural occurring radionuclides is used to determine the transport rates without that assumption of an active layer. The measurements on total sediment transport rates and suspended sediment concentrations show that effects of gradation are present. The effects of size gradation are mainly in the increased transport rates of the coarse fraction with respect to the uniform coarse material and the availability at the bed under similar conditions. The experiments on density graded sediments indicate that total mass-transport rates are larger than the mass-transport rates of quartz material, whilst the transport rates of the quartz fraction show that this fraction is not hindered by the availability at the bed. [Copyright &y& Elsevier]

The 1991 eruption of Mount Pinatubo generated extreme sediment yields from watersheds heavily impacted by pyroclastic flows. Bedload sampling in the Pasig–Potrero River, one of the most heavily impacted rivers, revealed negligible critical shear stress and very high transport rates that reflected an essentially unlimited sediment supply and the enhanced mobility of particles moving over a smooth, fine-grained bed. Dimensionless bedload transport rates in the Pasig–Potrero River differed substantially from those previously reported for rivers in temperate regions for the same dimensionless shear stress, but were similar to rates identified in rivers on other volcanoes and ephemeral streams in arid environments. The similarity between volcanically disturbed and arid rivers appears to arise from the lack of an armored bed surface due to very high relative sediment supply; in arid rivers, this is attributed to a flashy hydrograph, whereas volcanically disturbed rivers lack armoring due to sustained high rates of sediment delivery. This work suggests that the increases in sediment supply accompanying massive disturbance induce morphologic and hydrologic changes that temporarily enhance transport efficiency until the watershed recovers and sediment supply is reduced. [Copyright &y& Elsevier]

The present study is focused on sand transport in combined wave–current flow (at any angle between them) in the intensive flow regime. The present model is based on the 1DV approximation. The mathematical method for the continuous description of processes from the immobile bed to the formation of sheet flow and suspended load is presented. The way of modelling of sediment–flow interaction is proposed, in which the near-bed flow is divided into three layers, as done previously by Kaczmarek and Ostrowski [Kaczmarek, L.M., Ostrowski, R., 1998. Modelling of a three-layer sediment transport system in oscillatory flow. Proc. 26th ICCE, ASCE, 2559–2572] for pure oscillatory flow. Measured by Katopodi et al. [Katopodi, I., Ribberink, J.S., Ruol, P., Lodahl, C., 1994. Sediment transport measurements in combined wave–current flows. Proc. Coastal Dynamics ''94, ASCE, 837–851] and Dohmen-Janssen [Dohmen-Janssen, M., 1999. Grain size influence on sediment transport in oscillatory flow. FEBODRUK BV, ISBN 90-9012929-4, Enschede, The Netherlands], the time-averaged velocity profiles are compared with results provided by the present model for the respective conditions. The laboratory data of combined wave–current flow were further used to compare the model results for instantaneous and time-averaged concentration in the bedload (pick-up) layer and the contact load (upper sheet flow) layer, as well as for net sediment transport rate in the case of unidirectional (γ=0) wave–current interaction. The model cases for non-zero wave–current angle were tested in the context of longshore sediment transport rate against field radio-isotopic tracer data of Lubiatowo (Poland) by Pruszak and Zeidler [Pruszak, Z., Zeidler, R.B., 1994. Sediment transport in various time scales. Proc. 24th ICCE, ASCE, 2513–2526] and field luminescent tracer data of Ancao Peninsula (Portugal), by Balouin and Howa [Balouin, Y., Howa, H., 2000. Correspondence contact with University of Bordeaux].Generally, the agreement between the model results and the experimental data was found satisfactory in the context of the apparent roughness and time-averaged velocity profiles above the bed boundary layer. Further, the anti-phase behaviour of measured bedload concentration with respect to sediment concentration in the contact load layer and the asymmetric effects resulting from wave–current interaction are well represented by the model. Consequently, the present theoretical approach provides a useful tool for predictions of sand transport under wave–current flow within an accuracy factor of 1.5 either way. [Copyright &y& Elsevier]

A portable system for bedform-mapping was evaluated in the delta of the lower Sacramento and San Joaquin Rivers, California, from 1998 to 2000. Bedform profiles were surveyed with a two-person crew using an array of four single-beam transducers on boats about 6 m in length. Methods for processing the bedform profiles into maps with geographic coordinates were developed for spreadsheet programs and surface-contouring software. Straight reaches were surveyed every few days or weeks to determine locations of sand deposition, net transport directions, flow thresholds for bedform regimes, and bedform-transport rates. In one channel of unidirectional flow, the portable system was used to record changes in bedform regime through minor fluctuations of low discharge, and through high discharges near channel capacity. In another channel with reversing flows from tides, the portable system recorded directions of net bedload-transport that would be undetectable by standard bedload sampling alone. [Copyright &y& Elsevier]

• We deduced a new model for suspended and bedload sediment transport. • The model was deduced without using the Boussinesq hypothesis. • The hyperbolic system is solved using a fast and robust PVM path conservative scheme. • An efficient way to implement the erosion-deposition source term is applied. • The global numerical scheme is positivity preserving. We propose a coupled model for suspended and bedload sediment transport in the shallow water framework. The model is deduced under hydrostatic pressure assumptions and will not assume any Boussinesq hypothesis. The numerical resolution is carried out in a segregated way. First the underlying system of conservation laws is solved by using a first order path-conservative Riemann solver. Then, the source terms corresponding with the erosion and depositions rates are approximated in a semi-implicit way. The final scheme preserves the positivity of the density. Several numerical experiments were carried out in order to validate the model and the numerical scheme. The results obtained are in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

• Segregation results in the progressive establishment of a quasi-continuous region of small particles reaching a steady-state penetration depth. • Image processed concentration-depth profiles and isolines show a logarithmic time decrease. • The segregation dynamics is demonstrated to be dependent on the particle streamwise shear rate. Sediment transport in mountain and gravel-bed-rivers is characterized by bedload transport of a wide range of grain sizes. When the bed is moving, dynamic void openings permit downward infiltration of the smaller particles. This process, termed here 'kinetic sieving', has been studied in industrial contexts, but more rarely in fluvial sediment transport. We present an experimental study of two-size mixtures of coarse spherical glass beads entrained by turbulent and supercritical steady water flows down a steep channel with a mobile bed. The particle diameters were 4 mm and 6 mm, and the channel inclination 10%. The spatial and temporal evolution of the segregating smaller 4 mm diameter particles was studied through the introduction of the smaller particles at a low constant rate into the large particle bedload flow at transport equilibrium. Particle flows were filmed from the side by a high-speed camera. Using original particle tracking algorithms, the position and velocity of both small and large particles were determined. Results include the time evolution of the layer of segregating smaller beads, assessment of segregation velocity and particle depth profiles. Segregation resulted in the progressive establishment of a quasi-continuous region of small particles reaching a steady-state penetration depth. The segregation dynamics showed a logarithmic time decreasing trend. This evolution was demonstrated to be dependent on the particle streamwise shear rate which decays downwards exponentially. This result is comparable to theories initially developed for dry granular flows. [ABSTRACT FROM AUTHOR]