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Gravel‐bed rivers that incise into bedrock are common worldwide. These systems have many similarities with other alluvial channels: they transport large amounts of sediment and adjust their forms in response to discharge and sediment supply. At the same time, the occurrence of bedrock incision implies behaviour that falls on a spectrum between fully detachment‐limited 'bedrock channels' and fully transport‐limited 'alluvial channels'. Here, we present a mathematical model of river profile evolution that integrates bedrock erosion, gravel transport and the formation of channels whose hydraulic geometry is consistent with that of near‐threshold alluvial channels. We combine theory for five interrelated processes: bedload sediment transport in equilibrium gravel‐bed channels, channel width adjustment to flow and sediment characteristics, abrasion of bedrock by mobile sediment, plucking of bedrock and progressive loss of gravel‐sized sediment due to grain attrition. This model contributes to a growing class of models that seek to capture the dynamics of both bedrock incision and alluvial sediment transport. We demonstrate the model's ability to reproduce expected fluvial features such as inverse power law scaling between slope and area, and width and depth consistent with near‐threshold channel theory, and we discuss the role of sediment characteristics in influencing the mode of channel behaviour, erosional mechanism, channel steepness and profile concavity. [ABSTRACT FROM AUTHOR]

Recent theoretical models and field observations suggest that fluvial bedload flux can be estimated from seismic energy measured within appropriate frequency bands. We present an application of the Tsai et al. (2012, https://doi.org/10.1029/2011gl050255) bedload seismic model to an ephemeral channel located in the semi‐arid southwestern US and incorporate modifications to better estimate bedload flux in this environment. To test the model, we collected streambank seismic signals and directly measured bedload flux during four flash‐floods. Bedload predictions calculated by inversion from the Tsai model underestimated bedload flux observations by one‐to‐two orders of magnitude at low stages. However, model predictions were better for moderate flow depths (>50 cm), where saltation is expected to dominate bedload transport. We explored three differences between the model assumptions and our field conditions: (a) rolling and sliding particles have different impact frequencies than saltating particles; (b) the velocity and angle of impact of rolling particles onto the riverbed differ; and (c) the fine‐grained alluvial character of this and similar riverbeds leads to inelastic impacts, as opposed to the originally conceptualized elastic impacts onto rigid bedrock. We modified the original model to assume inelastic bed impacts and to incorporate rolling and sliding by adjusting the statistical distributions of bedload impact frequency, velocity, and angle. Our modified "multiple‐transport‐mode bedload seismic model" decreased error relative to observations to less than one order of magnitude across all measured flow conditions. Further investigations in other environmental settings are required to demonstrate the robustness and general applicability of the model. Plain Language Summary: The conveyance of sediments in rivers, especially of coarse‐grained sediment on the riverbed, is a basic geomorphic mechanism influencing short‐term river ecology, management, and engineering as well as long‐term landscape evolution. To better predict bedload transport rates, researchers have used seismic sensors to record ground vibration due to the impacts of bedload particles on the riverbed. We revised a physics‐based model developed by Tsai et al. (2012, https://doi.org/10.1029/2011gl050255) to estimate bedload sediment transport in an ephemeral channel in the semi‐arid southwestern US. To test the model, we collected nearby seismic signals during flash floods and simultaneously monitored water depth and bedload transport at one‐minute intervals. We modified the original model to better represent alluvial rivers by adding a representation of rolling and sliding particles to the hopping particles already considered in the physics of seismic waves generated by bedload transport. Our modified "multi‐mode bedload seismic model" yields a better result compared to the original Tsai et al. (2012, https://doi.org/10.1029/2011gl050255) model in our test river. The modified model is not only applicable for the ephemeral channels on which this study is focused but also is potentially applicable to a wide range of river conditions in different environmental settings. Key Points: The Tsai et al. (2012, https://doi.org/10.1029/2011gl050255) model underestimates bedload flux at low water depth by 1–2 orders of magnitude in an alluvial channelWe modified the original model to incorporate rolling and sliding by adjusting bedload impact frequency, velocity, and angleThe modified model decreases flux error relative to observations to less than one order of magnitude across all measured water depths [ABSTRACT FROM AUTHOR]

In order to choose the maximum discharge of artificial flood of Xiaolangdi Reservoir which have a better effect of channel erosion, minimizing secondary suspended river degree of Lower Yellow River and do not causing overbanking flood, we should precisely calculate the bankfull discharge of the lower reaches of the Yellow River. The researchers have analyzed the reasons why hydraulic calculation methods such as Manning’s formula didn’t have better effect to calculate the alluvial river bankfull discharge. Then we proposed a comprehensive approach, which based on the measured data of hydrological station, water stage gauging station, water stage on the river control works and channel cross-section, to deduce the water level in flood and rising rate of water level at each cross-sections, and to calculate the bankfull discharge at each cross-section in pre-flood season. Based on the results of the field measurements during the 2020 flood season, the error between the actual bank flow and the prediction was 1%-6%, in other words the predictions were close to reality. It is concluded that, the water level data at hydrological station and water stage gauging station should be used to extrapolate the bankfull discharge at cross-sections as far as possible, and larger discharge should be used to reduce errors and improve the accuracy of the bankfull discharge predictions as far as possible. [ABSTRACT FROM AUTHOR]

【Background】 Floodplain is the ecological cradle of alluvial rive to provide a buffer to flooding. Rivers naturally function to transport runoff and sediment, making the river have the double section characteristics of river trough and beach to meet the needs of water and sediment transportation in different periods. There are also villages in the floodplain of many rivers. There will inevitably be some contradictions between the needs of human activities (such as agricultural irrigation, transportation and social development) and river functions (ecology, flood and sediment transportation). If there is no scientific coordination between the two aspects, it will lead to mutual restriction affecting the ecological health of the river as well as the Sustainable high-quality development of the beach area society. It has become an important challenge for river managers to plan traffic routes in wide floodplain areas with less environmental impact. In order to implement the protection of river health in river project construction, the characteristics of alluvial river flood must be understood under the influence of human activity. 【Objective】 Taking advantage of the vast river floodplain to conduct the appropriate development and construction, it would be helpful to promote the high-quality development of the river basin. Learning more about the flood characteristics of alluvial rivers under the influence of human activities, and proposing a solution scheme to realize the coordination of floodplain engineering construction and river safety flood discharge, would contribute to practicing the protection of river health in constructing the river engineering. 【Method】 Taking a proposed eco-tourism greenway in the wide floodplain area of an alluvial river as an example, using the comprehensive research method involving historical evolution analysis, riverbed scouring-depositing prediction and hydrodynamic numerical simulation, the flood characteristics of the engineering reach, the law of river course evolution, the riverbed adjustment factors at the lower reaches of the reservoir were analyzed. The treatment model for predicting the riverbed boundary and the equivalent resistance of the river engineering were studied. By means of two-dimensional flood numerical simulation, the flood characteristics of the river section involved in the greenway and the influence of the route on the flow field during the flood discharge period were also analyzed. 【Result】 Firstly, the simulation shows the free swing of the mainstream is restricted by the regulation projects, and the river regime in flood period remains unchanged. Secondly, the proposed greenway is far away from the main channel and the routing is in parallel with the channel, which make the water blocking ratio of the flow area in the beach area less than 2.6%, and the local backwater caused by road construction limited to 0.058 m. 【Conclusion】 The arrangement of the proposed greenway is suggested to be routed along the river and located in high beach. Through scientific planning of routes and project layout, the impact of the project on the propagation of river floods can be minimized, and the coordinated relationship between the river flood discharge safety and the beach area development can be satisfied.

Forrest Merton Holly Jr dealt extensively with numerical modelling of unsteady flows and dispersion processes associated with the operation of hydropower and thermal power plants, and often with alluvial sediment transport by rivers. His expertise, energy, and genial personality led him to become President of the International Association of Hydraulic Engineering and Research (IAHR) during 2000–2003. Holly's last hydraulics project engaged his expertise and was done with the friendly aplomb for which he was well known. This forum paper portrays Holly engaged in his last project, which involved the practical application of numerical modelling of unsteady flow to and through a navigation dam. [ABSTRACT FROM AUTHOR]

During its 6,300-km course from the Tibetan Plateau to the ocean, the Yangtze River is joined by two large lakes: Dongting Lake and Poyang Lake. We explain why these lakes exist. Deglaciation forced the ocean adjacent to the Yangtze mouth to rise ∼120 m. This forced a wave of rising water surface elevation and concomitant bed aggradation upstream. While aggradation attenuated upstream, the low bed slope of the Middle-Lower Yangtze River (∼2 × 10-5 near Wuhan) made it susceptible to sea level rise. The main stem, sourced at 5,054 m above sea level, had a substantial sediment load to “fight” against water surface level rise by means of bed aggradation. The tributaries of the Middle-Lower Yangtze have reliefs of approximately hundreds of meters, and did not have enough sediment supply to fill the tributary accommodation space created by main-stem aggradation. We show that the resulting tributary blockage likely gave rise to the lakes. We justify this using field data and numerical modeling, and derive a dimensionless number capturing the critical rate of water surface rise for blockage versus nonblockage. [ABSTRACT FROM AUTHOR]

Alluvial river in the piedmont area deposits and incises cyclically, in response to both exogenetic and endogenetic forcing across a range of timescales. The paces of these processes unveil the mechanisms governing the evolution of alluvial fan-river system and affect the policy for river management. Numerical simulation suggests that the incision of alluvial river is much faster than the deposition process. However, the field observations are rare. Alluvial rivers entrench up to 300 m into the alluvial fans built pre-Holocene on the northern piedmont of Chinese Tianshan, which provide ideal sites to unveil the pace of alluvial fan-river evolution. Jingou River is one of these rivers, with four levels of terraces identified at the downstream area. These terrace deposits are characterized by a complex of upper very coarse gravels and cobble (VCGC) unit and lower medium and coarse gravels (MCG) unit. In this study, potassium-feldspar (K-feldspar) single grain pIR 110 IR 170 luminescence dating procedure was employed to date the samples taken from sandy lens of both upper VCGC and lower MCG units, for which the depositional ages are supposed to be associated with the fan-building and river incision processes, respectively. The luminescence ages of the lower MCG unit suggests a gradual fan building phase between 16 ± 1.9 ka and 8.1 ± 0.9 ka, while the ages of the upper VCGC unit cluster around ∼5.2 ka rather than a monotonic decrease towards low level terraces. Several scenarios are discussed with respect to the attained age sequences to unravel the pace of deposition and incision of Jingou River, of which the asymmetric aggradation and incision is more preferred and echoes to the finding of previous numerical investigation. [ABSTRACT FROM AUTHOR]

Riverbank erosion is widespread in alluvial rivers in India and elsewhere. River training works are frequently used to aid in the prevention of these losses by regulating the river and therefore protecting critical human habitats. These structures often become unstable and incapable of performing adequately during periods of heavy flooding. For the first time, the three- dimensional hydrodynamic open-source Open Field Operation and Manipulation (OpenFOAM) model is used to assess the potential of a novel hybrid river training arrangement to reduce downstream flow velocity and divert downstream flow to the opposite bank. The results indicate that for single- phase approximation, algorithms such as the Semi Implicit Method for Pressure- Linked Equations (SIMPLE) with lower computational requirements can satisfactorily reproduce flow patterns discovered in the laboratory ( R 2 > 0.74 ). The hybrid configuration outperforms the porcupine and geobag layouts. When compared to geobag, dual- screen porcupine, and single- screen porcupine, its downstream velocity decreases by 1.33%, 11.62%, and 13.34%, respectively. Similarly, flow diversion to the opposing bank increases by 0.49%, 0.65%, and 0.92%. Thus, the porcupine structure reduces the intensity of the incoming flow prior to it reaching the impermeable geobag in a hybrid layout. It dissipates the flow energy to the point where it can no longer scour the bed, thereby eliminating the disadvantage associated with the formation of scour holes. [ABSTRACT FROM AUTHOR]

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Numerical simulation of sediment transport in alluvial rivers often becomes untenable due to the absence of requisite data. Over the years, artificial neural network (ANN) models have been successfully employed for tackling such scenarios. However, the effect of input and target datasets on the simulation of sediment transport using ANN has not yet been adequately addressed in the literature so far. To study the effect of input-target dataset on the performance of ANN models, the present study employs seven input-target datasets for the development of several ANN models and assessment of their performance. The limited study carried out reveals that there are multiple ANN models – having different combinations of training algorithms, transfer functions and input/target datasets – that can reliably be employed to estimate bed elevation changes in alluvial rivers. [ABSTRACT FROM AUTHOR]

Rivers exhibit a wide variety of channel patterns, and predicting changes in channel pattern is important in order to foresee river responses to climate change and river restoration. Many discriminators have been developed to define approximate boundary conditions for different channel patterns, based on channel-pattern-controlling parameters such as discharge and valley gradient. However, presently available discriminators have two main shortcomings. First, they perform poorly for rivers with cohesive, relatively erosion-resistant banks. For this subset, discriminators tend to indicate an actively meandering channel pattern, whereas the river morphology and dynamics show that many of these rivers should be classified as laterally stable. Second, channel pattern discriminators are often used to predict channel patterns, which is only valid when parameters are used that are independent of actual channel pattern. This condition is often not met, as many discriminators use the channel slope or width–depth ratio of the channel as input. To resolve both shortcomings, we first propose an additional class of rivers with scroll bars and tortuous channel patterns, which have an inhibited mobility due to their self-formed cohesive deposits. Second, we compare frequently used empirical and mechanistic channel pattern discriminators, taking into account the success in predicting channel pattern and the independence of causal factors used. Thirdly, we present a novel channel pattern discriminator and predictor that includes the effect of a cohesive floodplain, using the average silt-plus-clay fraction of the river banks as proxy. We show that this new predictor outperforms previously used empirical and mechanistic approaches, and successfully predicts channel pattern for 87% of the rivers from a dataset of 70. This new predictor is widely applicable, as it is relatively simple and based on easily obtainable, and mostly independent, parameters. [ABSTRACT FROM AUTHOR]

The alluvial river flooding problem in Inner Mongolia is prominent along the upper reaches of the Yellow River. Studying the scour and silting evolution of the river and the response mechanism of the floods can provide technical support for flood prevention and disaster mitigation in this river section. According to data on ice flood and scour and silting evolution, this paper produces the response relationship between a scour and silting evolution characteristics indicator and an ice flood condition change representation indicator based on formulaic calculations and related analyses. The results show that bankfull discharge, a characteristic indicator of river scour and siltation evolution, is closely related to the characterization indicators for ice flood sub-ice flow capacity and trough water storage increment. The under-ice flow capacity is about 1/5 that of bankfull discharge, and it decreases as bankfull discharge decreases. In addition, the channel detention increment increases as bankfull discharge decreases. The safety flow capacity in the main channel for ice flood control should not be less than 2 000 m³/s, and the increment in water storage should be kept below 1.4 billion m³ in the reach. The preliminary results can serve as a major guide for ice flood control in Inner Mongolian reaches. [ABSTRACT FROM AUTHOR]

Past research on fluvial dynamics at the confluence of two alluvial rivers has mainly focused on downstream flow structure and bed scoring, often using laboratory experiments and numerical modeling. Little is investigated about yearly and episodic dynamics of confluence mouth bars that can affect downstream morphology using field measurements. In this study, we analyzed the migration of a confluence mouth bar of two free meandering alluvial rivers, the Amite and Comite Rivers in coastal Louisiana, USA from 2002 to 2017. Remote sensing images were utilized to investigate the decade‐long morphologic changes. To assess episodic dynamics, we employed terrestrial laser scanning measurements to acquire high‐accuracy digital elevation models at the confluence before and after three floods in 2017. Our study found that the Amite‐Comite confluence mouth bar migrated downstream 55 m in the past 15 years, and its angle reduced by 55° from 100° to 45°. The fast migration was a result of sediment deposition and channel deformation around the confluence mainly during the years when the tributary‐to‐main channel discharge was lower (<0.25). The study further reveals that a single moderate flood could strongly affect the mouth bar, as shown by an increase of the projected surface area by 114% and an increase of volume of the confluence mouth bar by 68%. Research Impact Statement: This study highlights the relationship between the rapid dynamic characteristics of a river confluence and flow variations of two free meandering rivers. [ABSTRACT FROM AUTHOR]

Physical modelling was used to assess the effects of the inlet shape, angle, diverted flow discharge and submerged vanes on the rate of sediment entry, erosion and shear stress of the intake. Experiments were conducted in a 55−degree intake channel branched from a rectangular channel. The mouth of the intake was chosen in two forms of sharp and rounded edge. Sedimentation and erosion values were measured in discharges of 11 and 16.6 l/s in the main channel with the four diversion flow ratios as 0.2, 0.4, 0.6 and 0.8. The submerged vanes were used in parallel and zigzag arrangements at angles of 10° and 30°. The results showed that making the mouth of the intake as rounded edge causes increase in the erosion and decrease in the sedimentation and hence reduction in deposited sediments. The shear stress was less in the presence of submerged vanes compared to the mode without installing the vanes. [ABSTRACT FROM AUTHOR]

Health of a river mainly depends on water demand for channel forming and sediment transport, particularly on the rational allocation of water resources in alluvial river. In this paper, energy balance equation was used to investigate the energy dissipation of sediment-carrying water flow, and distribution mode for water flow channel forming and sediment-carrying energy in the Upper Reaches of Yellow River in Inner Mongolia. Energy dissipated in alluvial river can be divided into two parts: one is to form a certain scale of river channel against boundary resistance of riverbed; another for transporting sediment. Silting or scouring of the riverbed during transportation can be an inherent indicator for the energy balance of water flow. Combined with the characteristics of flow and sediment movement in alluvial rivers, a complex relationship was proposed including the bank full discharge, the incoming sediment load, and the amount of scour and silting, in order to determine the water demand for channel forming and sediment transport. A calculation method was used to present the water demand for channel forming and sediment transport in a state of scour and silting in alluvial river. A calculation equation of water demand for channel forming and sediment transport was also established based on the measured data of the Inner Mongolia Reaches from 1960 to 2013. The calculated results showed that the incoming sediment load into the Inner Mongolia reaches was 70-110 million tons in flood season, and the water demand required for channel forming and sediment transport was 9.46-14.12 billion m³, providing that the silting ratio in these reaches was controlled below 30%, and a median water river channel in a scale of 2 000-3 000 m³/s. The water demand for channel forming and sediment transport mainly depends on incoming sediment loads, scales of river channels, and various levels of silting. In the case of the water demand higher required for channel forming and sediment transport, three trends can be obtained, including that, 1) the silting ratio can be lower control in an incoming sediment load and same scale of median water river channel; 2) the scale of median water river channel can be larger in an incoming sediment load and same silting ratio controlled, and 3) the incoming sediment load in flood season can be higher in the same silting ratio controlled and requirement on scale of median water river channel. There was agreement with the calculation results and the variation law of the water demand for channel forming and sediment transport of the Inner Mongolia reach, and the energy dissipation of alluvial rivers as well. The change law of water demand was obtained for channel forming and sediment transport under various conditions of sediment level, river channel scales and siltation levels. The findings can provide a sound technical support for the regulation of water resources in the Upper Reaches of Yellow River in Inner Mongolia. [ABSTRACT FROM AUTHOR]

Based on the Late Paleozoic geological background and the latest exploration achievements of the Ordos Basin and North China platform, it is concluded that during the sedimentary period of Permian He 8 Member, the area in concern had multiple material sources, multiple river systems, flat terrain, shallow sedimentary water, widely distributed fluvial facies sand body and no continuous lake area, so alluvial river sedimentary system developed in the whole region. Based on stratigraphic correlation and division, and a large number of drilling and outcrop data, a comprehensive analysis of lithofacies and sedimentary facies types and distribution was carried out to reconstruct the ancient geographic pattern of the He 8 Member sedimentary period. The results of paleogeography restoration show that the area of Ordos Basin was the "runoff area" in the sedimentary slope in the western part of the North China platform during the sedimentary period of He 8 Member, the whole region was mainly alluvial plain sedimentation featuring alternate fluvial facies, flood plain facies and flood-plain lake facies. According to the results of flume deposition simulation experiment, a new sedimentary model of "alluvial river & flood-plain lake" is established, which reveals the genesis of large area gravel sand body in He 8 Member of this area and provides geological basis for the exploration of tight gas in the south of the basin. [ABSTRACT FROM AUTHOR]

Introduction: Interactionbetweenwater flow characteristics andthe bed erodibilityplays an important role in sediment transport process. In order to reach stability, rivers with deposition or bottom erosion make a different bed form in the riverbed. One way to identify thebehavior of therivers is to study the structure and formation of bed forms within them. Ripples are the smallest of the bed forms. The longitudinal cross section of ripples are usually not symmetrical. The upstream face is long and has a gentle slope, and the downstream face is short and steep. The height of ripples is usually between 0.5 cm and 2 cm; the height ripple is not more than 5 cm. The wave lengths normally do not exceed 30cm, and they are usually within the range of 1 cm to 15 cm. Their occurrence is the result of the unstable viscous layer near the boundary. They can form in both shallow and deep water.With an increase of the flow velocity, the plan form of the ripples gradually develops form straight line to curves and then to a pattern like fish scales, symmetrical or unsymmetrical, as shown in Fig 1. Figure1-The patterndevelopment oftheripple Raudkivi (1966) was the first person that, the flow structure over ripples was investigated experimentally.Hethenestablishseveraldifferent conditionsonthemovingsandbedinanlaboratorychannelconsisted of a rectangular cross-section with base width of 70cm, wasable toform arow ofripples , he wassucceed toform arow ofripples.JafariMianaei and Keshavarzi(2008),studied the turbulentflow betweentwoartificialripples for investigate the change of kinetic energyandshearstress on overripples. The stage- discharge rating curve is one of the most important tools in the hydraulic studies. In alluvial rivers,bed rippled are formed and significantly affect the stage- discharge rating curve. In this research, the effects of two different type of ripples (parallel and flakeshape) onthe hydraulic characteristicsof flow were experimentally studied in a flume located at the hydraulic laboratory ofShahrekordUniversity, Iran. Bass (1993) [reported in Joep (1999)], determined an empirical relation between median grain size, D50, and equilibrium ripple length, l: L=75.4 (logD50)+197 Eq.(1) Where l and D50 are both given in millimeters. Raudkivi (1997) [reported in Joep (1999)], proposed another empirical relation to estimate the ripple length that D50 is given in millimeters: L=245(D500.35) Eq. (2) Flemming (1988) [reported in Joep (1999)], derived an empirical relation between mean ripple length and ripple height based on a large dataset: hm= 0.0677l 0.8098 Eq.(3) Where hm is the mean ripple height (m) and l is the mean ripple length (m). Ikeda S. and Asaeda (1983) investigated the characteristics of flow over ripples. They found that there are separation areas and vortices at lee of ripples and maximum turbulent diffusion occurs in these areas. Materials and Methods: In this research, the effects of two different type of ripples onthe hydraulic characteristics of flow were experimentally studied in a flume located at the hydraulic laboratory of ShahrekordUniversity, Iran. The flume has the dimensions of 0.4 m wide and depth and 12 m long. Generally 48 tests variety slopes of 0.0005 to 0.003 and discharges of 10 to 40 lit/s, were conducted. Velocity and the shear stress were measured by using an Acoustic Doppler Velocimeter (ADV). Two different types of ripples (parallel and flake ripples) were used. The stage- discharge rating curve was then estimated in different ways, such as Einstein - Barbarvsa, shen and White et al. Results and Discussion: In order to investigateresult of the tests, were usedst atistical methods.White method as amaximum valueofα, RMSE, and average absolute error than other methods. Einstein method offitting the discharge under estimated. Evaluation of stage- discharge rating curve methods based on the obtained results from this research showed that Shen method had the highest accuracy for developing the stage- discharge rating curve than other methods. It also showed that theShenmethod was much accuracy by the parallel shape of ripplebed form compared with the flake shape. Conclusion: Evaluation of stage- discharge rating curve methods based on the obtained results from this research showed that Shen method had the highest accuracy for developing the stage- discharge rating curve than other methods. It also showed that theShenmethod was much accuracy by the parallel shape of ripplebedform compared with theflakeshape. The results of the estimation of statistical parameters such as root mean square error (RMSE) and mean percent error for these cases indicated that the Shen method is associated with the lowest RMSE and error percentage. Therefore it estimates the stage- discharge rating curve more accurately than other methods. Furthermore in the case of parallel and flake ripple bed forms correlation coefficient was obtained as 0.87 and 0.43 respectively. This indicates that the Shen method is more accurate for the parallel shape of rippled bed forms than the flake shape ones.

Interaction between water flow and bed erodibility, which is associated with sediment transport and creat bed forms. Ripples are the smallest of the bed forms. Experiments were performed with variety slopes of 0.0005 to 0.003 and discharges of 10 to 40 L/S, on the artificial ripple in the hydraulic Laboratory of Shahrekord University.Velocity measurements were collected using an Acoustic Doppler Velocimeter. It was observed the peak value of bed shear stress was appear on the midpoint of upstream surface and the lowest value appear on the crest. From the crest to trough, the general bed shear stress was in a trend of increasing. It was also observed that in the case of ripples bed forms were consist of about 26% of total bed shear stress.

Braiding pattern in sixteen reaches of the Brahmaputra river in Assam, India is discussed. A new braiding index has been introduced incorporating a fraction of area covered by sandbars, number of midchannel bars and maximum width of alluvial reach. Braiding parameters calculated using different formulae showed similar trend but higher values in 2014 compared to 1973. Increase of braiding in different reaches in 2014 was due to development of more sandbars and distributaries. The new index has shown comparable result with other approaches and better correlation with sinuosity. [ABSTRACT FROM AUTHOR]

The regulation water level is closely related with the regulation width and should be treated as a whole. The two influence each other and restrict each other. Under the assumption of the same scouring amount for a given shoal, we derived a formula including both regulation water level and width by applying sediment transport theory and riverbed evolution theory, and verified it by using existing data. Furthermore, we discussed the application of formula. The results show that the combination of different regulation parameters can be selected under the premise of the same effect of shoal regulation. [ABSTRACT FROM AUTHOR]

Channel bars are a major depositional feature in alluvial rivers and their morphodynamics has been investigated intensively in the past several decades. However, relatively less is known about how channel bars in alluvial rivers respond to river engineering and regulations. In this study, we assessed 30-yr morphologic changes of 30 large emerged bars located in a 223 km reach of the highly regulated Lower Mississippi River from Vicksburg, Mississippi, to the Mississippi-Atchafalaya River diversion. Landsat imagery and river stage data between 1985 and 2015 were utilized to characterize bar morphologic features and quantify decadal changes. Based on bar surface areas estimated with the satellite images at different river stages, a rating curve was developed for each of the 30 bars to determine their volumes. Results from this study show that the highly regulated river reach favored the growth of mid-channel and attached bars, while more than half of the point bars showed degradation. Currently, the mid-channel and attached bars accounted for 38% and 34% of the total volume of the 30 bars. The average volume of a single mid-channel bar is over two times that of an attached bar and over four times that of a point bar. Overall, in the past three decades, the total volume of the studied 30 bars increased by 110,118,000 m 3 (41%). Total dike length in a dike field was found mostly contributing to the bar volume increase. Currently, the emerged volume of the 30 bars was estimated approximately 378,183,000 m 3 . The total bar volume is equivalent to ~ 530 million metric tons of coarse sand, based on an average measured bulk density of 1.4 t/m 3 for the bar sediment. The findings show that these bars are large sediment reservoirs. [ABSTRACT FROM AUTHOR]

Controls on the characteristics of floodplain wetlands in drylands are diverse and may include extrinsic factors such as tectonic activity, lithology and climate, and intrinsic thresholds of channel change. Correct analysis of the interplay between these controls is important for assessing possible channel-floodplain responses to changing environmental conditions. Using analysis of aerial imagery, geological maps and field data, this paper investigates floodplain wetland characteristics in the Tshwane and Pienaars catchments, northern South Africa, and combines the findings with previous research to develop a new conceptual model highlighting the influence of variations in aridity on flow, sediment transport, and channel-floodplain morphology. The Tshwane-Pienaars floodplain wetlands have formed in response to a complex interplay between climatic, lithological, and intrinsic controls. In this semi-arid setting, net aggradation (alluvium >7 m thick) in the wetlands is promoted by marked downstream declines in discharge and stream power that are related to transmission losses and declining downstream gradients. Consideration of the Tshwane-Pienaars wetlands in their broader catchment and regional context highlights the key influence of climate, and demonstrates how floodplain wetland characteristics vary along a subhumid to semi-arid climatic gradient. Increasing aridity tends to be associated with a reduction in the ability of rivers to maintain through-going channels and an increase in the propensity for channel breakdown and floodout formation. Understanding the interplay between climate, hydrology and geomorphology may help to anticipate and manage pathways of floodplain wetland development under future drier, more variable climates, both in South African and other drylands. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The character and behaviour of dryland rivers are driven by complex interactions between extrinsic and intrinsic controls. A long-term perspective is necessary to assess the sensitivity of dryland rivers to extrinsic forcing, such as hydroclimatic changes, and to contextualise the threshold channel responses. The semi-arid Mara River in northern Tanzania is the only perennial river in the UNESCO World Heritage Serengeti-Mara ecosystem and provides water resources for human and wildlife populations. Satellite imagery and discharge modelling were used to assess the valley-scale controls and hydrogeomorphic processes driving the morphological adjustments of the lower Mara River and its floodplain wetland. Both the modern and palaeochannels undergo downstream morphological and hydrological changes as they traverse the broad, alluvial floodplain. In response to marked downstream declines in discharge (from ~300 m3·s−1 to ~45 m3·s−1) and stream power (from ~40 W·m−2 to ~0.5 W·m−2), the modern channel exhibits a nonequilibrium river response resulting in downstream declines in channel size (from ~60 m to ~10 m wide) and eventual channel breakdown in the floodplain wetland. Palaeochannels in the unconfined reaches are typically larger with higher palaeodischarges than the modern channel. While some palaeochannels exhibit similar downstream trends to the modern channel, others may have maintained a continuous channel farther into the wetland. Comparison of the Mara River to other dryland river systems highlights the importance of valley setting and hydroclimate as long-term controls that influence geomorphic river response over time. The lower Mara River represents a nonequilibrium river response to declining discharges related to transmission losses that leads to channel bed aggradation and avulsion, constituting an inherent condition in many dryland alluvial rivers. An improved understanding of the interplay between intrinsic and extrinsic controls is important for the assessment of river character, behaviour, and floodplain wetland development, particularly under future projections of more variable or extreme climate conditions. [Display omitted] • Channel breakdown and floodplain wetland formation in a dryland fluvial system • The modern channel exhibits a nonequilibrium river response to declining discharges • Long-term controls (i.e. hydroclimate) drove the transition from larger palaeochannels to the modern channel • Catchment land-use change has increased the sediment supply to discharge ratio in the lower reaches • Intrinsic threshold responses lead to contemporary channel changes and breakdown in the floodplain wetland [ABSTRACT FROM AUTHOR]

The profile of a river that conveys sediment without net deposition and net erosion is referred to as 'graded' with respect to vertical aggradation of the river segment. Three experimental series, designed in terms of the autostratigraphic view of alluvial grade, were conducted to clarify the diagnostic spatial behaviour of graded alluvial-deltaic rivers: an 'R series', which utilized a moving boundary setting with a stationary base level; an 'F series' in a fixed boundary setting with a stationary base level to produce 'forced grade'; and an 'M series' in a moving boundary setting with constant base-level fall to produce 'autogenic grade.' The results of the three experimental series, combined with geometrical modelling of the effects of basin water depth and other experimental data, suggest the following: (i) in a graded alluvial-deltaic system, lateral shifting and avulsing of active distributary channels are suppressed regardless of whether the downstream boundary of the deltaic system is fixed; (ii) in a delta with a downstream-fixed boundary, the graded streams are stabilized within a valley that is incised in the axial part of the delta plain, whereby the alluvial plain outside the valley is abandoned and terraced; (iii) in moving boundary settings, the graded river simply extends basinward as a linearly elongated channel and lobe system without cutting a valley; and (iv) a modern forced-graded alluvial river is most likely to be found in a valley incised into a fan delta in front of very deep water, and the stratigraphic signal of fossil autogenic-graded rivers will be found in deltaic successions that accumulated in the outer to marginal areas of deltaic continental shelves during sea-level falls. This renewed autostratigraphic view of alluvial grade suggests a thorough reconsideration of the conventional understanding that an alluvial river feeding a progradational delta is graded with a stationary base level. [ABSTRACT FROM AUTHOR]

Observations from field investigations showed that flow velocity greater than 3 m/s rarely occurs in nature, and high flow velocity stresses the bio-community and causes instability to the channel. For alluvial rivers without strong human disturbance, the flow velocity varies within a limited range, generally below 3 m/s, while the discharge and wet area may vary in a range of several orders. This phenomenon was studied by analyzing hydrological data, including daily average discharge, stage, cross sections, and sediment concentration, collected from 25 stations on 20 rivers in China, including the Yangtze, Yellow, Songhua, Yalu, Daling, and Liaohe Rivers. The cross-sectional average velocity was calculated from the discharge and wet area using the continuity equation. For alluvial rivers, the wet cross section may self-adjust in accordance with the varying flow discharge so that the flow velocity does not exceed a limit value. In general, the average velocity increases with the discharge increase at low discharge. As the discharge exceeds the discharge capacity of the banks, any further increase in discharge does not result in a great increase in velocity. The average velocity approaches an upper limit as the discharge increases. This limit velocity, in most cases, is less than 3 m/s. Human activities, especially levee construction, disturb the limit velocity law for alluvial rivers. In these cases, the average velocity may be approximately equal to or higher than the limit velocity. The limit velocity law has profound morphological and ecological implications on alluvial rivers and requires further study. Rivers should be trained and managed by mimicking natural processes and meeting the limit velocity law, so as to maintain ecologically-sound and morphological stability. [ABSTRACT FROM AUTHOR]

We explore the fluvial response to faulting in three low-gradient, sand-bed rivers in south-eastern Louisiana, USA, that flow across active normal faults from footwall (upstream) to hangingwall (downstream). We calculate sinuosity, migration rate and migration direction in order to identify anomalies spatially associated with fault scarps. In two of the rivers we model one-dimensional steady water flow to identify anomalies in surface water slope, width-to-depth ratio, and shear stress. In each of these rivers there is one location where flow modeling suggests potential channel incision through the footwall, as indicated by relatively high surface water slopes and shear stress values. In one of these footwall locations, the river straightens and width-to-depth ratios decrease, likely contributing to higher surface water slopes and shear stress. This is in contrast to previous studies that have proposed increased sinuosity across fault footwalls and decreased sinuosity across hangingwalls. However, in two hangingwall locations we also observe relatively less sinuous channels. Other planform changes on the hangingwall include topographic steering of channels along and towards the fault and one example of an avulsion. The most notable anomaly in migration rate occurs on the hangingwall of a fault where a river has cut off a meander loop. Although fluvial response to faulting varies here, comparatively large and small channels exhibit similar responses. Further, Pleistocene fault slip rates are orders of magnitude lower than the channel migration rates, suggesting that faulting should not be a major influence on the fluvial evolution. Nonetheless, notable channel anomalies exist near faults, suggesting that recent fault slip rates are higher than Pleistocene rates, and/or that low-gradient alluvial channels are more sensitive to faulting than previous studies have suggested. Rivers appear to be influenced by faulting in this setting, however background rates of meander loop cutoff may be just as influential as faulting. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Using hydrological and sediment data, this study investigated decadal trends in sediment erosion/deposition in the Inner Mongolia reach of the upper Yellow River. The calculated yearly sediment erosion/deposition show that the reach was dominated by aggradation, degradation, and aggradation successively in three periods with the years around 1961 and 1987 as break-points. By constructing relations between water discharge and sediment load, the contributions of key factors to the changes in sediment erosion/deposition in the reach were quantified. Results show that the sediment retention behind the main stem dams, the increase of natural runoff, and the decrease of sediment inputs from tributaries and upstream watershed were the main factors causing the transition from aggradation during 1955-1961 to degradation during 1962-1987. The reduction of natural runoff, the decrease of sediment retention behind dams, and the rise of sediment supply from tributaries were the key causes of the reversal from degradation in 1962-1987 to aggradation in 1988-2003. Water diversion has played an important role in the long-term aggradation of the Inner Mongolia reach. The main stem dams had functioned to alleviate siltation after 1961, but their effects on siltation reduction had been gradually diminishing since the 1990s. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]