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Cutting-edge technology for fluvial monitoring has revolutionised the field, enabling more comprehensive data collection, analysis, and interpretation. Traditional monitoring methods were limited in their spatial and temporal resolutions, but advancements in remote sensing, unmanned aerial systems (UASs), and other innovative technologies have significantly enhanced the fluvial monitoring capabilities. UASs equipped with advanced sensors enable detailed and precise fluvial monitoring by capturing high-resolution topographic data, generate accurate digital elevation models, and provide imagery of river channels, banks, and riparian zones. These data enable the identification of erosion and deposition patterns, the quantification of sediment transport, the evaluation of habitat quality, and the monitoring of river flows. The latter allows us to understand the dynamics of rivers during various hydrological events, including floods, droughts, and seasonal variations. This manuscript aims to provide an update on the main research themes and topics in the literature on the use of UASs for river monitoring. The latter is achieved through a bibliometric analysis of the publication trends and identifies the field's key themes and collaborative networks. The bibliometric analysis shows trends in the number of publications, number of citations, top contributing countries, top publishing journals, top contributing institutions, and top authors. A total of 1085 publications on UAS monitoring in rivers are identified, published between 1999 and 2023, showing a steady annual growth rate of 24.44%. Bibliographic records are exported from the Web of Science (WoS) database using a comprehensive set of keywords. The bibliometric analysis of the raw data obtained from the WoS database is performed using the R software. The results highlight important trends and valuable insights related to the use of UASs in river monitoring, particularly in the last decade. The most frequently used author keywords outline the core themes of UASs monitoring research and highlight the interdisciplinary nature and collaborative efforts within the field. "River", "topography", "photogrammetry", and "Structure-from-Motion" are the core themes of UASs monitoring research. These findings can guide future research and promote new interdisciplinary collaborations. [ABSTRACT FROM AUTHOR]

The present work concerns the interaction between hydraulic processes and biological communities in rivers. In particular, the aim of this study is to investigate the interactions between flow dynamics and the freshwater mussels (FMs) to verify if the mussels' behavioural response to the hydrodynamic stress could be used to monitor natural extreme events in rivers. Although the influence of mussels on the kinematic characteristics of flow at the water–sediment interface was investigated by a certain number of studies, their behavioural response to flow, both in static and dynamic conditions, remains understudied. Laboratory experiments were performed in an artificial flume exposing Unio elongatulus to different values of flow discharge, both in steady and in unsteady conditions either with or without sediment transport. Mussels' behavioural responses were detected by using Hall sensor technology to measure gaping frequency, amplitude and duration, both in static conditions and under the effect of hydrodynamic stresses. Five categories of behavioural response were identified: Normal Activity (NA), Resting (Re), Transition (Tr), Adaptation (Ad) and Avoidance (Av). During NA (standard feeding and moving), FMs presented valve gaping, while during Re valves were kept constantly opened for water filtration. After a variation of flow discharge (ΔQ), FMs promptly reacted showing a transition from their normal behaviour, with constant gaping frequency (below 0.01 Hz), to higher valve gaping frequencies. The mean valves' gaping frequency increased as a function of ΔQ, and the highest values were reached in the presence of sediment transport. The mean valve opening amplitude was less sensitive to ΔQ. Its range of variation was very narrow with the highest values corresponding to the protrusion/retraction of the animals' foot to move or anchor to the substrate. The percentage of mussels responding to the discharge variation (Transition behaviour) increases with ΔQ confirming that mussels' behavioural response represents a promising tool for monitoring the occurrence of hydrodynamic stressors in fluvial systems. [ABSTRACT FROM AUTHOR]

This article presents a novel method to identify geometric-hydraulic relationships–in terms of mathematical formulas—in the form of segment-averaged outputs and a function of depth in rivers. There are several methods for determining geometric-hydraulic relationships in rivers, including flow area, wetted perimeter, and the flow top width. Direct field surveying and using aerial and satellite sensor instruments are the most prevalent. The model presented here, however, is based on the inverse solution of the Saint-Venant equations without costly field-surveyed river geometry data. The relationships mentioned earlier can be easily used in various hydraulic models, such as flood routing, sediment transport, pollutant transport, and so on. Moreover, this method requires the lowest number of parameters as the input of the inverse model because by minimizing the corresponding objective function, the desired parameters are estimated in the whole studied segment. The proposed inverse model is validated using hypothetical and real test cases. In one of the test cases—as the most comprehensive and practical test case—the application of the presented inverse model was validated in a river network. The Manning roughness coefficient and geometric-hydraulic relationships for different segments were simultaneously estimated at an acceptable level of accuracy and computational costs in this river network. Ultimately, the real and identified geometric-hydraulic relationships are compared for each test case, and statistical indexes are demonstrated. Overall, the results and statistical indexes indicate that the model is more successful and also cheaper than costly conventional methods. [ABSTRACT FROM AUTHOR]

This article presents a new public domain tool for generalized Lagrangian particle tracking in rivers. The approach can be applied with a variety of two‐ and three‐dimensional flow solvers. Particle advection by the flow is incorporated using flow fields from the chosen solver assuming particles follow the Reynolds‐averaged flow, although some other simple passive and active particle behaviors are also treated. Turbulence effects are treated using a random walk algorithm with spatial step lengths randomly chosen from Gaussian distributions characterized by the diffusivity from the flow solver. Our work extends this concept to a general framework that is solver and coordinate system independent to allow easy comparisons between differing flow treatments. To better treat problems where detailed information is required in specific regions, the approach includes novel cloning and colligation algorithms which enhance local resolution at modest computational expense. We also provide tools for computing local concentrations and total exposure over a user‐specified time interval. Several examples of predictions are provided to illustrate applications of the technique, including examination of the role of curvature‐driven secondary flows, storage in lateral separation eddies, treatment of larval drift, treatment of fuel spill dispersion, river‐floodplain connections, and sedimentation in floodplain ponds by tie channel connections. We also demonstrate that the model can reproduce analytically derived concentration profiles for simple diffusivities. These examples show that the Lagrangian particle tracking approach and the extensions proposed here are broadly applicable and viable for treating difficult river problems with multiple temporal and spatial scales. The examples also illustrate the utility of the cloning/colligation extensions and show how these can decrease the computational effort required on problems where high local resolution is required. Enhancement of the tools and even broader applicability can be achieved through the inclusion of multiple particle populations and particle–particle interactions. [ABSTRACT FROM AUTHOR]

This study assessed historical morphology changes of the Msimbazi River in Dar es Salaam City, Tanzania, following heavy rainfall events using historical Google earth images. The erosion and sedimentation processes that cause morphological changes of a river are also associated with flooding within the river catchments. In this study, the bank-line movement, erosion and sedimentation areas and changes in river section width were analyzed under three-time periods: 2005-2012, 2012-2018, and 2018-2020. Data shows that, the timing for floods coincides with the historical records for heavy rains. It was found that, area in the upper reaches of the river such as Kinyerezi suffer from river bank erosion most, as indicated by the large increase in river width. This has resulted into washing away of infrastructure including houses and loss of land. The river channel width at Kinyerezi has widened a lot since 2005, with some sections having widths of more than 90 m. On the lower reaches for example around Kigogo and Jangwani areas, deposition of the soil materials prevails, resulting into raised river bed and reduced river widths. As the river section an hence carrying capacity is reduced, inundation of river banks occurs. This is among the causes of river bank flooding reported at these areas whenever there is a heavy storm event. It is therefore recommended that interventions to solve the flooding events in Dar es Salaam city should also include preventing catchment and river bank erosion on the upstream areas. [ABSTRACT FROM AUTHOR]

Titan is a sedimentary world, with lakes, rivers, canyons, fans, dissected plateaux, and sand dunes. Sediments on Saturn's moon are thought to largely consist of mechanically weak organic grains, prone to rapid abrasion into dust. Yet, Titan's equatorial dunes have likely been active for 10s–100s kyr. Sustaining Titan's dunes over geologic timescales requires a mechanism that produces sand‐sized particles at equatorial latitudes. We explore the hypothesis that a combination of abrasion, when grains are transported by winds or methane rivers, and sintering, when they are at rest, could produce sand grains that maintain an equilibrium size. Our model demonstrates that seasonal sediment transport may produce sand under Titan's surface conditions and could explain the latitudinal zonation of Titan's landscapes. Our findings support the hypothesis of global, source‐to‐sink sedimentary pathways on Titan, driven by seasons, and mediated by episodic abrasion and sintering of organic sand by rivers and winds. Plain Language Summary: Like Earth, Saturn's moon Titan hosts lakes, rivers, canyons, fans, eroded plateaux, and sand dunes. On Titan, loose solid particles (or sediments) are likely made of soft hydrocarbon grains, prone to rapid breakdown into dust. Yet, Titan's equatorial dunes have been active for up to several hundreds of thousands of years, suggesting that some mechanism must produce sand‐sized particles at these latitudes. We explore the hypothesis that a combination of abrasion, when grains are transported by winds or methane rivers, and sintering, when they are at rest, could produce sand grains that maintain an equilibrium size. Our model demonstrates that seasonal sediment transport could produce sand on Titan and could explain the distribution of Titan's landscapes. Altogether, our findings support the hypothesis of global sedimentary pathways on Titan, driven by seasons, and mediated by episodic abrasion and sintering of organic sand by rivers and winds. Key Points: Long‐lived active dune fields are in apparent contradiction with the predicted rapid abrasion of windblown organic sediment on TitanEpisodic abrasion and sintering of organic sediment, driven by seasons, could generate sand with equilibrium sizes on TitanTitan's undifferentiated plains and labyrinth terrains could result from prolonged sintering and diagenesis where transport is infrequent [ABSTRACT FROM AUTHOR]

Channel processes under high magnitude flow events are of central interest to river science and management as they may produce large volumes of sediment transport and geomorphic work. However, bedload transport processes under these conditions remain poorly understood due to data collection limitations and the prevalence of physical models that restrict feedbacks surrounding morphologic adjustment. The extension of mechanistic bedload transport equations to gravel-bed rivers has emphasised the importance of variance in both entraining (shear stress) and resisting (grain size) forces, especially at low excess shear stresses. Using a fixed-bank laboratory model, we tested the hypothesis that bedload transport in gravelbed rivers collapses to a more simple 1D function (i.e., with mean shear stress and median grain size) under high excess shear stress conditions. Bedload transport was well predicted by the 1D equation based on the depth-slope product, whereas a 2D equation accounting for the variance in shear stresses did not substantially improve the correlation. Back-calculated critical dimensionless shear stress values were higher for the 2D approach, suggesting that it accounts for the relatively greater influence of high shear stresses, whereas the 1D approach assumes that the mean shear stress is sufficient to mobilise the median grain size. While the 2D approach may have a stronger conceptual basis, the 1D depth-slope product approach performs unreasonably well under high excess shear stress conditions. Further work is required to substantiate these findings in laterally adjustable channels. [ABSTRACT FROM AUTHOR]

Hydrologic connectivity controls the lateral exchange of water, solids, and solutes between rivers and floodplains, and is critical to ecosystem function, water treatment, flood attenuation, and geomorphic processes. This connectivity has been well‐studied, typically through the lens of fluvial flooding. In regions prone to heavy rainfall, the timing and magnitude of lateral exchange may be altered by pluvial flooding on the floodplain. We collected measurements of flow depth and velocity in the Trinity River floodplain in coastal Texas (USA) during Tropical Storm Imelda (2019), which produced up to 75 cm of rainfall locally. We developed a two‐dimensional hydrodynamic model at high resolution for a section of the Trinity River floodplain inspired by the compound flooding of Imelda. We then employed Lagrangian particle routing to quantify how residence times and particle velocities changed as flooding shifted from rainfall‐driven to river‐driven. Results show that heavy rainfall initiated lateral exchange before river discharge reached flood levels. The presence of rainwater also reduced floodplain storage, causing river water to be confined to a narrow corridor on the floodplain, while rainwater residence times were increased from the effect of high river flow. Finally, we analyzed the role of floodplain channels in facilitating surface‐water connectivity by varying model resolution in the floodplain. While the resolution of floodplain channels was important locally, it did not affect as much the overall floodplain behavior. This study demonstrates the complexity of floodplain hydrodynamics under conditions of heavy rainfall, with implications for sediment deposition and nutrient removal during floods. Plain Language Summary: Unaltered river floodplains can support diverse ecosystems, reduce flooding, and remove nutrients from river water. Floodplains near the coast are particularly important, as they typically experience more frequent flooding. Floodplain function relies on a high degree of connectivity with the river, where water can move easily through the floodplain during periods of high river stage. Our study explores the ways in which heavy rainfall on a floodplain impacts this connectivity. We collected flow measurements in the Trinity River floodplain (Texas, USA) during Tropical Storm Imelda in 2019 that showed distinct flooding patterns between the rainfall and river flooding. We coupled a hydrodynamic model with a particle tracking model to see how particles in the water might move through the floodplain during the transition from rainfall‐driven to river‐driven flooding. We found that the average time a particle spent in the floodplain changed significantly after the rain in the model stopped. We also noticed that rainwater generally remained in the floodplain for much longer than river water, especially after the rain stopped. This study describes the various interactions that can occur between local rainfall and river flooding and moves toward a better understanding of sediment and nutrient transport in floodplains. Key Points: Field data and modeling show distinct signals of pluvial and fluvial floodingFloodplain residence times change dramatically between pluvial and fluvial phases of the stormFlows between river and floodplain are dominated by low points in the levee and the largest floodplain channels [ABSTRACT FROM AUTHOR]

Rivers regulate the global carbon cycle by transferring particulate organic carbon (POC) from terrestrial landscapes to marine sedimentary basins, but the processes controlling the amount and composition of fluvially exported POC are poorly understood. We propose that hydrodynamic sorting processes modify POC fluxes during fluvial transit. We test this hypothesis by studying POC transported along a ∼1,200 km reach of the Rio Bermejo, Argentina. Nanoscale secondary ion mass spectrometry revealed that POC was either fine, mineral‐associated organic matter, or coarse discrete organic particles. Mineral‐associated POC is more resistant to oxidation and has a lower particle settling velocity than discrete POC. Consequently, hydraulic sorting and downstream fining amplify the proportion of fine, mineral‐associated POC from ∼55% to ∼78% over 1,220 km of downstream transit. This suggests that mineral‐associated POC has a greater probability of export and preservation in marine basins than plant detritus, which may be oxidized to CO2 during transit. Plain Language Summary: The carbon cycle regulates Earth's climate by determining the amount of carbon in our atmosphere. Rivers are important for the carbon cycle because they deliver large amounts of organic carbon from mountains to the oceans. If this carbon is quickly buried in ocean sediment, atmospheric CO2 concentrations decrease. In order to predict the fluxes of carbon to the oceans, we need to understand the processes controlling organic carbon transport from source to sink. In a 1,300‐km‐long river in Argentina, we measured the amount of sediment and carbon in river water at multiple stations along the source‐to‐sink pathway. Using geochemical methods, we identified two types of organic carbon: (a) plant fragments, which are easily oxidized to CO2, and (b) organic carbon attached to minerals, which is resistant to oxidation. We calculated the mass fluxes of these two types of organic carbon and found that export of mineral‐protected carbon is greater than the export of plant fragments. This suggests that most riverine organic carbon may be preserved upon delivery to the ocean. Our data show that we need to differentiate between plant fragments and mineral‐attached organic carbon to predict the amount of organic carbon moving between rivers, the oceans, and the atmosphere. Key Points: In lowland meandering rivers, downstream particle size fining and hydraulic sorting can modulate particulate organic carbon (POC) fluxesNano‐scale secondary ion mass spectrometry and biomarker isotope data show that mineral‐associated and discrete POC differ in composition and particle settling velocityDownstream particle size fining enhances fluvial export of recalcitrant, mineral‐associated POC that is more resistant to oxidation [ABSTRACT FROM AUTHOR]

Understanding how rivers adjust to the sediment load they carry is critical to predicting the evolution of landscapes. Presently, however, no physically based model reliably captures the dependence of basic river properties, such as its shape or slope, on the discharge of sediment, even in the simple case of laboratory rivers. Here, we show how the balance between fluid stress and gravity acting on the sediment grains, along with cross-stream diffusion of sediment, determines the shape and sediment flux profile of laminar laboratory rivers that carry sediment as bedload. Using this model, which reliably reproduces the experiments without any tuning, we confirm the hypothesis, originally proposed by Parker [G. Parker, J. Fluid Mech. 89, 127-146 (1978)], that rivers are restricted to exist close to the threshold of sediment motion (within about 20%). This limit is set by the fluid-sediment interaction and is independent of the water and sediment load carried by the river. Thus, as the total sediment discharge increases, the intensity of sediment flux (sediment discharge per unit width) in a river saturates, and the river can transport more sediment only by widening. In this large discharge regime, the cross-stream diffusion of momentum in the flow permits sediment transport. Conversely, in the weak transport regime, the transported sediment concentrates around the river center without significantly altering the river shape. If this theory holds for natural rivers, the aspect ratio of a river could become a proxy for sediment discharge--a quantity notoriously difficult to measure in the field. [ABSTRACT FROM AUTHOR]

Rivers originating in High Mountain Asia are crucial lifelines for one-third of the world’s population. These fragile headwaters are now experiencing amplified climate change, glacier melt, and permafrost thaw. Observational data from 28 headwater basins demonstrate substantial increases in both annual runoff and annual sediment fluxes across the past six decades. The increases are accelerating from the mid-1990s in response to a warmer and wetter climate. The total sediment flux from High Mountain Asia is projected to more than double by 2050 under an extreme climate change scenario. These findings have far-reaching implications for the region’s hydropower, food, and environmental security. [ABSTRACT FROM AUTHOR]

Mountain rivers often receive sediment in the form of episodic, discrete pulses from a variety of natural and anthropogenic processes. Once emplaced in the river, the movement of this sediment depends on flow, grain size distribution, and channel and network geometry. Here, we simulate downstream bed elevation changes that result from discrete inputs of sediment (∼10,000 m3), differing in volume and grain size distribution, under medium and high flow conditions. We specifically focus on comparing bed responses between mixed and uniform grain size sediment pulses. This work builds on a Lagrangian, bed‐material sediment transport model and applies it to a 27 km reach of the mainstem Nisqually River, Washington, USA. We compare observed bed elevation change and accumulation rates in a downstream lake to simulation results. Then we investigate the magnitude, timing, and persistence of downstream changes due to the introduction of synthetic sediment pulses by comparing the results against a baseline condition (without pulse). Our findings suggest that bed response is primarily influenced by the sediment‐pulse grain size and distribution. Intermediate mixed‐size pulses (∼50% of the median bed gravel size) are likely to have the largest downstream impact because finer sizes translate quickly and coarser sizes (median bed gravel size and larger) disperse slowly. Furthermore, a mixed‐size pulse, with a smaller median grain size than the bed, increases bed mobility more than a uniform‐size pulse. This work has important implications for river management, as it allows us to better understand fluvial geomorphic responses to variations in sediment supply. Plain Language Summary: Sediment often enters mountain rivers from a variety of natural and human sources. Here, we simulate how this added sediment results in downstream changes in the amount of sediment in the river channel. This work was applied to a 27 km section of the Nisqually River, Washington, USA. We compare observed changes in the level of the stream bottom and accumulation rates in a downstream lake to model results. Then we investigate the magnitude, timing, and persistence of downstream changes due to the introduction of added sediment by comparing the changes against a baseline condition (without the added sediment). We found that added sediment particles that are half as large as on the riverbed and with a range of sizes are likely to have the largest downstream impact because smaller sizes move quickly and larger sizes move slowly. Furthermore, added sediment particles that are smaller than on the riverbed and with a range of sizes help more sediment particles on the riverbed move than if that sediment addition all had the same particle size. This work has important implications for river management, as it allows us to better understand how rivers are affected by variations in added sediment. Key Points: Channel incision may occur instead of aggradation when pulse volume is relatively small and pulse grain size is finer than bedIntermediate grain size pulses have the largest downstream effects; finer sizes translate quickly and coarser sizes disperse slowlyA mixed‐distribution pulse with smaller median grain size than the bed increases bed mobility more than a uniform‐distribution pulse [ABSTRACT FROM AUTHOR]

Dunes dominate the bed of sandy rivers and they respond to flow by changing shape and size, modifying flow, and sediment transport dynamics of rivers. Our understanding of and ability to predict dune adaptation, particularly dune growth and decay, remain incomplete. Here, we investigate dune growth from an initial flatbed in a laboratory setting by continuously mapping the 3D bed topography using a line laser scanner combined with a 3D camera. High‐resolution profiles of flow velocity and sediment concentration providing both bedload and suspended sediment fluxes were obtained by deploying Acoustic Concentration and Velocity Profiler technology. Our analysis reveals that the magnitude of the dune slipface angle, which determines flow separation and controls turbulence production, adjusts to the imposed flow at time scales similar to the evolution of dune height and length. The initiation of a flow separation zone intensifies through scour, and results in acceleration of the dune growth. Gradients in sediment transport and the rate of dune growth are inherently linked to spatial variations in slipface angles. During dune growth, the slipface angle evolves differently than the ratio of dune height to length, which immediately reaches its equilibrium value after dune initiation. Key Points: Dune slipface angle adjusts to the imposed flow at time scales similar to the evolution of dune height and lengthThe initiation of a flow separation zone intensifies trough scour, and results in acceleration of dune growthSediment transport distributions reveal that bed material avalanche processes over dune lee sides depend on dune slipface angle [ABSTRACT FROM AUTHOR]

The largest deltas on Earth are tide‐dominated with multiple distributaries, which can experience different forcings. Yet, most observational studies of sediment dynamics in these systems focus on a single distributary. Comparison of the tidal‐to‐estuarine reaches of three representative distributaries of the Ayeyarwady Delta, Myanmar highlights the variability in sediment retention and export within a megadelta. The Ayeyarwady River has no mainstem dams, providing an opportunity to examine a relatively natural, monsoon‐dominated system. Observations were collected during high flow (September 2017) and low flow (March 2018 and 2019). The eastern Yangon distributary empties into the sheltered Gulf of Mottoma while the central Bogale and western Pathein distributaries are exposed to seasonal waves. During high flow, suspended‐sediment concentration (SSC) was consistent across all three distributaries (0.2–0.4 g/L). The upper delta retained 20%–60% of the mainstem sediment load, while the lower distributaries were tidal rivers exporting sediment. During low flow, the lower distributaries were partially mixed estuaries with little net discharge. However, SSC increased to >1 g/L in the Yangon distributary, remained constant in the Bogale distributary, and decreased in the Pathein distributary compared to high flow. This difference was driven by offshore sediment supply; fine sediment is retained near the mouth of the Yangon and advected away from the Pathein distributary. Consequently, nearshore sediment residence time in monsoon‐influenced megadeltas is controlled by coastal orientation, the timing of discharge with respect to ocean conditions, and tidal amplification. Changes to fluvial sediment delivery can cause non‐uniform coastal impacts due to these differing distributary processes. Key Points: Individual distributaries of tropical megadeltas can exhibit significantly different hydrodynamics and sediment transport processesIn the Ayeyarwady Delta, low‐flow estuarine processes import offshore sediment into distributaries when offshore sediment is available and resuspendedSediment residence time in the nearshore is controlled by tidal amplification and the coastal orientation with respect to monsoon winds [ABSTRACT FROM AUTHOR]

The vertical position of the streambed–water boundary fluctuates during the course of sediment transport episodes, due to particle entrainment/deposition and bedform migration, amongst other hydraulic and bedload mechanisms. These vertical oscillations define a topmost stratum of the streambed (i.e. the 'active layer or active depth'), which usually represents the main source of particles entrained during long and high‐magnitude bedload transport episodes. The vertical extent of this layer is hence a capital parameter for the quantification of bedload volumes and a major driver of stream ecology in gravel‐bed rivers. However, knowledge on how the active depth scales to flow strength and the nature of the different controls on the relation between the flow strength and the active depth is still scarce. In this paper we present a meta‐analysis over active depth data coming from ~130 transport episodes extracted from a series of published field studies. We also incorporate our own field data for the rivers Ebro and Muga (unpublished), both in the Iberian Peninsula. We explore the database searching for the influence of flow strength, grain size, streambed mobility and channel morphology on the vertical extent of the active layer. A multivariate statistical analysis (stepwise multiple regression) confirms that the set of selected variables explains a significant amount of variance in the compiled variables. The analysis shows a positive scaling between active depth and flow strength. We have also identified some links between the active depth and particle travel distances. However, these relations are also largely modulated by other fluvial drivers, such as the grain size of the bed surface and the dominant channel macro‐bedforms, with remarkable differences between plane‐bed, step‐pool and riffle‐pool channels. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We discuss the prioritization of river reaches to be selected for restoration measures under the constraints of financial resource limitation. We propose and apply a simple approach based on the quantification of major hydro‐morphological alterations and the critical comparison with locally proposed restoration actions. The available hydro‐morphological and ecological data for the approach do not go beyond the requirements posed by the implementation of the EU Water Framework and Floods Directives. We describe an example that refers to a heavily regulated Alpine river (Sarca River, NE Italy). The results indicate hydropower facilities as a key source of hydrological alteration, with sediment retention and grade control structures on lateral tributaries playing an additional relevant role in reducing sediment supply. The frequency and duration of sediment‐transporting floods have dramatically decreased, and the bed sediment composition has been markedly altered and become highly compacted. Habitat improvement has been achieved after the implementation of minimum environmental flows. The comparison between the results of the hydro‐morphological indicators and the locally proposed restoration actions highlights that reaches with lower degree of hydro‐morphological alterations do not coincide with the areas chosen for the locally planned actions, which often miss considerations of the relevant spatial scales. In a context of limited available financial resources and data compared to other flagship river restoration projects in the European Alps, the present work suggests viable options for the choice of target restoration reaches. [ABSTRACT FROM AUTHOR]

Multithread fluvial environments like anastomosing and braided rivers are fundamentally directed by the continuous concatenation of channel bifurcations and confluences, which distribute flow and sediment among different branches that are reconnecting further downstream. A large number of theoretical, experimental, and numerical studies conducted in the last two decades have provided a clear picture of stability conditions for river bifurcations. However, most analyses are focused on the dynamics of bifurcations alone, ignoring the possible mutual interaction with downstream confluences. In this work, we study the morphodynamic equilibrium and stability conditions of a bifurcation‐confluence loop, where flow splits in two secondary anabranches that rejoin after a prescribed distance. Through the formulation of a novel theoretical model for mobile bed confluences, we show that the dominating anabranch (i.e., that carrying most discharge) is subject to an increase of the water surface elevation that is proportional to the square of the Froude number. This effect causes a decrease of the slope of the dominating anabranch, which acts as a negative feedback that increases the stability of the bifurcation‐confluence system. A linear analysis of the coupled model reveals that the stabilizing effect exerted by the confluence depends on the ratio between the length of the anabranches and the average water depth, independently of channel slope and Froude number. Ultimately, this effect is potentially able to stabilize the loop even when the sediment is mainly transported in suspension, a condition which makes the classic stabilizing mechanism (i.e., the topographic effect at the bifurcation node) practically ineffective. Key Points: The dominating branch of a channel confluence shows a higher water level, depending on the square of the Froude numberThe confluence exerts a negative feedback on the upstream bifurcation, which promotes the stability of the systemThe bifurcation‐confluence system can be stable even when the bedload steering at the bifurcation is very weak [ABSTRACT FROM AUTHOR]

Ecosystems respond to climatic and anthropogenic forcings with regime shifts and reorganizations of their system structures. In river basins, changes in sediment transport can have cascading effects that cause ecosystem regime shifts. The Yellow River, once the world's most sediment-rich river, has experienced dramatic regime shifts. Although recent intervention has returned sediment discharge in the Yellow River to pristine levels, our understanding of previous regime shifts remains inadequate, particularly for the regime shift to a sediment rich period during early historical time. We reanalyzed previous datasets to clarify the first historical sediment transport regime shift in the Yellow River. Our results show that while historical climatic changes (e.g., the Medieval Warm Period, about 900–1100 AD) caused changes in sediment transport, a regime shift occurred only under increased forcing from anthropogenic stresses (started from about 1350 AD, reached the tipping point after 1900 AD). This unique behavior of the Yellow River under increasing anthropogenic forces may provide perspective for sustainable river basin management. [ABSTRACT FROM AUTHOR]

During summer 2017, two parallel trenches were excavated in the Sagavanirktok River (located in northern Alaska, United States) to acquire construction material for roadwork on the Dalton Highway nearby. A study to estimate the time it would take for the trenches to fill with the upstream sediment was needed. In undertaking this study, we used three bed sediment transport equations for gravel-bed rivers available in the Sedimentation and River Hydraulics—Two-Dimensional model, with three hydrograph input scenarios: (1) normal cumulative volumetric flow; (2) maximum discharge; and (3) maximum cumulative volumetric flow. These scenarios, coupled with the three sediment transport equations, produced a total of nine simulations. Scenario 1 predicted a time to refill of 1–3.75 years based on the sediment transport equations used. Scenarios 2 and 3 predicted shorter times to refill. All three sediment transport equations predicted that sustained high flows are capable of refilling the trenches in 1 year. This is the first time that calculations have been made to estimate the refilling time of an extraction site on the Sagavanirktok River. These calculations could expedite the permitting process, eliminating the need for a new extraction site by returning to a site that has refilled with sediment. An indirect benefit of these calculations is that they provide information for fisheries biologists working in northern regions. [ABSTRACT FROM AUTHOR]

Sediment material transported by the Indus River has two origins, the catchment and its wetted perimeter, whereas the amount of materials transported from the river itself depends on variables such as the flow type and the sediment load. The annual sediment load transported in the Indus River ranged from 270 to 600 million tons (MT) before the building of dams and barrages. The average sediment load is 0.715 MT/day or approximately 260 MT/ year after the construction of hydraulic structures. The average particle size, D50, of the bedload is approximately 0.125mm at the Sukkur barrage [1]. In this study, research was conducted to evaluate sediment problems in the Nara Canal, take-off from the left pocket of the Sukkur Barrage on the Indus River. The collected data from the left pocket, the bed, and suspended material in upper Nara and its off-taking canals were analyzed to assess sediment transport dynamics of upper Nara canal at various locations and its off-taking canals. The bed material at RD 553+600 shows a minimum size of 0.07 and a maximum of 0.7mm with 54% fine-sand mixed with 46% medium-sand in 2003. Fine-sand increased to an average of 75% while medium sand diminished to 25% at RD 553+600 in Nara canal and at RD 595+000 in Jamrao complex in 2013. The suspended load with low and high flows during 2012 exhibits that in all the cases the sand proportion was increasing in the Upper Nara canal system flowing to the Jamrao complex. The sediment concentration value indicates that there is the deposition of sand at the upper Nara canal and the Jamrao complex causing a discharge reduction in the Nara Canal system. [ABSTRACT FROM AUTHOR]

This study has hypothesized that for many rivers the trade‐off between flow accumulation and the decrease in slope along channel length means that stream power increases downstream and, moreover, that given the low slope angles in headwater and low‐order streams, they would have insufficient stream power to erode let alone transport sediment. The study considered the stream power profile, the particle travel distances and the application of the Hjulström curve based on the velocity profile of nine, large UK catchments. The study showed that: Some rivers never showed a maximum in their longitudinal stream power profile, implying that some rivers never develop a deposition zone before they discharge at the tidal limit.Particle travel distances during a bankfull discharge event showed that for some rivers 91% of the upper main channel would not be cleared of sediment. Furthermore, while some rivers could transport a 2 mm particle their entire length in one bankfull event, for another river it would take 89 such events.The Hjulström curve shows that for three of the study rivers the upper 20 km of the river was not capable of eroding a 2 μm particle.The study has shown that for all rivers studied, erosion is focused downstream and deposition upstream. Many UK rivers have a dead zone where, on time scales of the order of centuries, no erosion or transport occurs and erosion only occurs in the lower courses of the channel where discharge rather than slope dominates – we propose these as underpowered rivers. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd [ABSTRACT FROM AUTHOR]

Background In order to regulate water flow, hydraulic structures such as weirs or checks, frequently equipped with gates, are used. Water can flow below or over the gate or, simultaneously, over and below the gate. Both diversifications of hydraulic gradient, being an effect of damming up a river by the structure and shear stresses at the bed, which exceeds the critical shear stress value, invoke the local scouring downstream the structure. This phenomenon has been studied in laboratory and field conditions for many years, however Researchers do not agree on the parameters that affect the size of the local scour and the intensity of its formation. There are no universal methods for estimating its magnitude However, solutions are sought in the form of calculation formulas typical for the method of flow through the structure, taking into account the parameters that characterize a given structure. These formulas are based on factors that affect the size of the local scours, that is, their dimensions and location. Examples of such formulas are those contained in this article: Franke (1960), Straube (1963), Tarajmovič (1966), Rossinski & Kuzmin (1969) equations. The need to study this phenomenon results from the prevalence of hydrotechnical structures equipped with gates (from small gated checks to large weirs) and from potential damage that may be associated with excessive development of local erosion downstream, including washing of foundations and, consequently, loss of stability of the structure. Methods This study verifies empirical formulas applied to estimate the geometry parameters of a scour hole on a laboratory model of a structure where water is conducted downstream the gate with bottom reinforcements of various roughness. A specially designed remote-controlled measuring device, equipped with laser scanner, was applied to determine the shape of the sandy bottom. Then the formula optimization is conducted, using Monte Carlo sampling method, followed by verification of field conditions. Results The suitability of a specially designed device, equipped with laser scanner for measuring the bottom shape in laboratory conditions was demonstrated. Simple formula describing local scour geometry in laboratory conditions was derived basing on the Straube formula. The optimized formula was verified in field conditions giving very good comparative results. Therefore, it can be applied in engineering and designing practices.

Abstract Terrestrial organic carbon (OC) plays an important role in the carbon cycle, but questions remain regarding the controls and timescale(s) over which atmospheric CO2 remains sequestered as particulate OC (POC). Motivated by observations that terrestrial POC is physically stored within soils and other shallow sedimentary deposits, we examined the role that sediment storage plays in the terrestrial OC cycle. Specifically, we tested the hypothesis that sediment storage impacts the age of terrestrial POC. We focused on the Efri Haukadalsá River catchment in Iceland as it lacks ancient sedimentary bedrock that would otherwise bias radiocarbon‐based determinations of POC storage duration by supplying pre‐aged “petrogenic” POC. Our radiocarbon measurements of riverine suspended sediments and deposits implicated millennial‐scale storage times. Comparison between the sample types (suspended and deposits) suggested an age offset between transported (suspended sediments) and stored (deposits) POC at the time of sampling, which is predicted by theory for the sediment age distribution in floodplains. We also observed that POC in suspended sediments is younger than the predicted mean storage duration generated from independent geomorphological data, which suggested an additional role for OC cycling. Consistent with this, we observed interparticle heterogeneity in the composition of POC by imaging our samples at the microscale using X‐ray absorption spectroscopy. Specifically, we found that particles within individual samples differed in their sulfur oxidation state, which is indicative of multiple origins and/or diagenetic histories. Altogether, our results support recent coupled sediment storage and OC cycling models and indicate that the physical drivers of sediment storage are important factors controlling the cadence of carbon cycling.

For streams draining urban catchments, sediment transport capacity is the key driver of physical impacts including bed sediment removal and channel incision. The main unanswered question is the relative role of flow alteration compared to sediment supply in influencing sediment transport capacity. With this objective, we computed sand and gravel bed sediment transport capacity using the Wilcock and Kenworthy two-fraction bedload transport relation for nine streams in catchments covering a gradient of urbanisation. Computations were done for typical natural bed surface material, based on conditions in the least urban study streams. We compared transport capacity distributions and cumulative transport capacity over one-year between the streams. Transport capacity was up to three orders of magnitude higher in urban streams than in forested-catchment streams. This was driven overwhelmingly by the urbanisation-induced alterations to the flow regime, with only minor feedback from channel form changes. Transport capacity was two to three orders of magnitude greater than measured bedload transport in all but the least urban streams. This excess bedload transport capacity mobilises and removes bed sediment, produces channel incision and enlargement and reduces channel complexity. Rebalancing transport capacity with sediment supply therefore requires significant flow mitigation towards pre-urban conditions. Other responses, which may theoretically help to regain this balance – channel widening, grade control, increasing roughness, sediment augmentation – are either inappropriate or only feasible following flow mitigation measures. [ABSTRACT FROM AUTHOR]

Seasonal suspended sediment transfer in glaciated catchments is responsive to meteorological, geomorphological, and glacio‐fluvial conditions, and thus is a useful indicator of environmental system dynamics. Knowledge of multifaceted fluvial sediment‐transfer processes is limited in the Alaskan Arctic – a region sensitive to contemporary environmental change. For two glaciated sub‐catchments at Lake Peters, northeast Brooks Range, Alaska, we conducted a two‐year endeavour to monitor the hydrology and meteorology, and used the data to derive multiple‐regression models of suspended sediment load. Statistical selection of the best models shows that incorporating meteorological or temporal explanatory variables improves performances of turbidity‐ and discharge‐based sediment models. The resulting modelled specific suspended sediment yields to Lake Peters are: 33 (20–60) t km−2 yr−1 in 2015, and 79 (50–140) t km−2 yr−1 in 2016 (95% confidence band estimates). In contrast to previous studies in Arctic Alaska, fluvial suspended sediment transfer to Lake Peters was primarily influenced by rainfall, and secondarily influenced by temperature‐driven melt processes associated with clockwise diurnal hysteresis. Despite different sub‐catchment glacier coverage, specific yields were the same order of magnitude from the two primary inflows to Lake Peters, which are Carnivore Creek (128 km2; 10% glacier coverage) and Chamberlin Creek (8 km2; 23% glacier coverage). Seasonal to longer‐term sediment exhaustion and/or contrasting glacier dynamics may explain the lower than expected relative specific sediment yield from the more heavily glacierized Chamberlin Creek catchment. Absolute suspended sediment yield (t yr−1) from Carnivore Creek to Lake Peters was 27 times greater than from Chamberlin Creek, which we attribute to catchment size and sediment supply differences. Our results provide a foundational understanding of the current sediment transfer regime and are useful for predicting changes in fluvial sediment transport in glaciated Alaskan Arctic catchments. [ABSTRACT FROM AUTHOR]

The Tigris River in Baghdad is a large sand-bed river, supply-limited because of the implementation of a water flow regulation scheme comprising a series of reservoirs and barrages. The significant reduction in the water discharge has affected the hydraulic performance of the river and turned it into an under-fit river of complicated morphology where many islands and bank deposits have been showed up across an 18 km reach in addition to the essential sinuosity. Measuring sediment load at individual cross-sections in the river gives misleading estimates and the corresponding sediment rating curve has a locally limited using. A spatially sediment rating by investigating sediment loads over the complicated reach is required to overcome the local limitations. Sediment transport rates have been investigated at 16 cross-sections along the study reach by collecting suspended load, bed load and bed material samples. Velocity profiles were measured at the sampling stations using an Acoustic Doppler Current Profiler (ADCP). The measurement results indicated that the suspended load is the dominant mode of transport (93.5%). However, bedloads were considered in determining the total loads. A spatial total load rating curve in the form of a power function was established and examined against the sediment measurements. Twenty-two previously published total load formulae where applied at the same sections and of these the Colby1964 formula gave the closest fit to the measured loads. Based on the results from this study a recommended procedure is established for using a spatial total load rating curve to estimate sediment transport rates for similar morphologically complicated rivers. Average annual transport rates during the period 2009–13 was estimated at 3.21 million tons. [ABSTRACT FROM AUTHOR]

Rivers are dynamic systems, changing over time on their own or due to engineering measures and structures. At rivers which are regularly monitored, information on sediment balance can be used to evaluate the morphological development and to assess the impact of such measures. In this paper, we show that the performance of a numerical model can be improved by quantify boundary conditions, and that the simulation results of such a well-developed model will be more useful for civil engineers. As a case study, we develop a model system based on TELEMAC-SISYPHE to study the morphology of the Saalach River, where erosion and sedimentation impacts local ecology and human safety. Based on the available measurements and a sediment balance concept, we estimate the amount of sediment supplied to the river section downstream of a reservoir as well as the volume of the bed sediment transported along the river channel in different years. Using this information as boundary conditions for calibration and validation cases, the model provides a realistic and accurate representation of the river. Furthermore, our model has been successfully employed on the Saalach River to evaluate an alternative strategy for a more sustainable river management. [ABSTRACT FROM AUTHOR]

Gravel‐bed braided rivers are highly energetic fluvial systems characterized by frequent in‐channel avulsions, which govern the morphodynamics of such rivers and are essential for them to maintain a braided planform. However, the avulsion mechanisms within natural braided rivers remain unclear due to their complicated hydraulic and morphodynamic processes. Influenced by neighbouring channels, avulsions in braided rivers may differ from those of bifurcations in single‐thread rivers, suggesting that avulsions should be studied within the context of the entire braid network. In this study, braiding evolution processes in gravel‐bed rivers were simulated using a physics‐based numerical model that considers graded bed‐load transport by dividing sediment particles into multiple size fractions and vertical sediment sorting by dividing the riverbed into several vertical layers. The numerical model successfully produced braiding processes and avulsion activities similar to those observed in a laboratory river. Results show that bend evolution of the main channel was the fundamental process controlling the occurrence of avulsions in the numerical model, with a cyclic process of channel meandering by lateral migration that transitioned to a straight channel pattern by avulsion. The radius of bend curvature for triggering avulsions in the numerical model was measured and it was found that the highest probability for a channel bend to generate an avulsion occurs when its radius of curvature is approximately 2.0–3.3 times the average anabranch width. Other types of avulsion were also observed that did not occur specifically at meander bends, but upstream meander evolution indirectly influenced such avulsions by altering channel pattern and discharge to those locations. This study explored the processes and mechanisms of several types of avulsion, and proposed factors controlling their occurrence, namely increasing channel curvature, high shear stress, tributary discharge, riverbed gradient and upstream channel pattern, with high shear stress being a direct indicator. Furthermore, avulsions in a typical gravel‐bed braided river, the Waimakariri River in New Zealand, were analysed using sequential Google Earth maps, which confirmed the conclusions derived from the numerical simulation. [ABSTRACT FROM AUTHOR]

Sediment transport and channel morphology in mountainous hillslope‐coupled streams reflect a mixture of hillslope and channel processes. However, the influence of lithology on channel form and adjustment and sediment transport remains poorly understood. Patterns of channel form, grain size, and transport capacity were investigated in two gravel‐bed streams with contrasting lithology (basalt and sandstone) in the Oregon Coast Range, USA, in a region in which widespread landslides and debris flows occurred in 1996. This information was used to evaluate threshold channel conditions and channel bed adjustment since 1996. Channel geometry, slope, and valley width were measured or extracted from LiDAR and sediment textures were measured in the surface and subsurface. Similar coarsening patterns in the first few kilometres of both streams indicated strong hillslope influences, but subsequent downstream fining was lithology‐dependent. Despite these differences, surface grain size was strongly related to shear stress, such that the ratio of available to critical shear stress for motion of the median surface grain size at bankfull stage was around one over most of the surveyed lengths. This indicated hydraulic sorting of supplied sediment, independent of lithology. We infer a cycle of adjustment to sediment delivered during the 1996 flooding, from threshold conditions, to non‐alluvial characteristics, to threshold conditions in both basins. The sandstone basin can also experience complete depletion of the gravel‐size alluvium to sand size, leading to bedrock exposure because of high diminution rates. Although debris flows being more frequent in a basalt basin, this system will likely display threshold‐like characteristics over a longer period, indicating that the lithologic control on channel adjustment is driven by differences in rock competence that control grain size and available gravel for bed load transport. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Understanding the transport of suspended sediment and associated nutrients is of major relevance for sustainable sediment management aiming to achieve healthy river systems. Sediment rating curves are frequently used to analyze the suspended sediments and their potential sources and sinks. Here we use more than 750 000 measurements of suspended sediment concentrations (SSCs) and discharge (Q) collected at 62 gauging stations along 19 waterways in Germany based on the suspended sediment monitoring network of the German water and shipping authority, which started in the 1960s. Furthermore, we analyze more than 2000 measurements of the loss on ignition (LOI) of suspended matter at two stations along the rivers Moselle and Rhine to provide a proxy for the relative contributions of mineral load and organic matter. SSC and LOI are analyzed in terms of the power-law rating curve to identify discharge-dependent controls of suspended matter. Our results indicate that for most studied gauging stations, rating coefficients are not constant over the full discharge range, but there is a distinct break in the sediment rating curve, with specific SSC– Q domains above and below this break. The transition of the rating exponent likely results from increased supply of mineral suspended sediments from hillslope erosion at high flow and a shift of the organic matter sources from aquatic biomass-derived organic matter (i.e., high % LOI) at low flow, to mineral-associated organic matter with low % LOI eroded from hillslopes at higher flow. Based on these findings we developed a conceptual rating model for large (>10000 km 2) and low-turbidity (SSC < 1000 mg L -1) rivers separating the mineral and organic fraction of the suspended matter in German waterways. This model allows evaluating the sources of the mineral and organic fraction of the suspended matter and facilitates new insights into the first-order control of discharge on the quality and quantity of suspended sediments. [ABSTRACT FROM AUTHOR]

The Otofuke River is a tributary of the Tokachi River, Hokkaido Japan, consisting of a channelized reach with a steep slope and a relatively large designed width. In August 2016, the river witnessed four major flooding events with a record-breaking discharge within a time span of 15 days. The Otofuke River originally had a straight channelized reach. However, because of a series of flooding events, the river promptly followed a sinusoidal path, damaging the riverbank embankments. The straight channelized reach of Otofuke River faced active erosion of both banks, leading to the formation of a meandering channel planform. This also led to levee breaches at the seven locations. In order to understand the mechanism of such a quick shift in river channel planform, we collected various field survey data and conducted computational analysis. We investigated the underlying processes by capturing the complex interactions between the rapid channel migration, unsteady discharge, and sediment transport. Field surveys including aerial photographs and images showed rapid formation of a meandering planform in the Otofuke River as a result of the typhoon on 31 August 2016. According to the maximum water level traces, bank erosion developed after the peak discharge. Numerical investigation revealed that alternate sandbars continuously developed and propagated downstream until the moment of peak discharge, and a significant accumulation of sediment subsequently started on the bars at the mid-channel during the flood falling stage. Such morphological processes led to strong flow deflections transversely toward the embankment that resulted in lateral channel shifting and levee breaches at a location where vegetation along the embankments had already disappeared. [ABSTRACT FROM AUTHOR]

We developed a technique for reconstructing annual gravel yields and generated a 55‐year record of gravel transport for the North Fork catchment of the Caspar Creek Experimental Watersheds in Northern California. The technique relies on field data collection including annual surveys of weir pond volumes and suspended sediment measurements, as well as an accounting for settling of suspended sediment and organic matter in the pond. We compared these annual yields to gravel yields predicted by the Wilcock two‐fraction bed load transport model, which we calibrated from measured values at Caspar Creek. We considered three velocity‐discharge relationships and found that values of hydraulic variables measured during storms produced the best fit between reconstructed and predicted annual gravel yields when years with large disturbances were excluded. We also compared predicted gravel transport rates to bed load transport rates measured from 1988 to 1995 with bed load pit samplers. We found that the calibrated model predictions agreed well with the field‐measured bed load transport rates. To investigate the role of supply and storage on gravel transport, we compared the reconstructed gravel yields to predicted gravel yields and found that increased occurrence of landslides and headcut erosion in the 1990s and early 2000s did not lead to an increase in gravel yields. Instead, input of large downed wood in the 1990s created storage space and decreased bed load delivery to the weir pond. Plain Language Summary: Bed load sediment yields are important for understanding catchment responses to natural and human caused disturbances, but are difficult to measure. We demonstrate a method that uses pond sediment accumulations to quantify annual bed load yields at Caspar Creek, CA. We also use these data and data collected during more focused storm‐based sampling to show that a common bed load model provides relatively accurate estimates of gravel transport at Caspar Creek. Comparing annual gravel yields to predicted gravel yields reveals that gravel transport decreased in the 1990s and 2000s after a large number of trees blew down and increased the wood content in the channel. The approach presented here can be applied to other sites where similar data are available, such as other ponds or small reservoirs. Key Points: We reconstructed a 55‐year record of annual gravel yields from weir pond deposits at Caspar Creek, CAReconstructed gravel yields compare well to modeled gravel yields and to a continuous record of bed load transport ratesComparing reconstructed yields to predictions reveals a decrease in transport associated with increased downed wood and sediment storage [ABSTRACT FROM AUTHOR]

Soil erosion poses a significant threat to river health as well as the sustainability of soil resources. Management of this issue requires catchment‐specific data to be developed; however, many large catchments are poor in terms of hydrological and sediment transport data. Regional scale (thousands of square kilometres), computer‐based modelling methods are a way to generate such data. This study aims to apply the SedNet model to estimate a sediment budget for a 575 km2, ungauged, agricultural catchment of south‐eastern Australia. The model results are then compared with field measured erosion rates for the catchment, in order to assess the sustainability of soil loss and redistribution across the catchment. SedNet estimated average suspended sediment concentrations between 70 and 120 mg/L, under conditions deemed most representative of the river. These model estimates were comparable with monitoring data, showing suspended sediment concentrations between 30 and 350 mg/L. It was found that soil loss and redistribution across the catchment is low; however, the estimated base sediment loads indicate that river health may be negatively impacted by this. SedNet accurately represented current catchment and river conditions and provided a reliable estimation of sediment yield, demonstrating the ability to estimate sediment loss and redistribution across data‐poor catchments using a multifaceted modelling approach. Methodologies, such as the one presented here, offer the ability to better assess the impacts of erosion on sediment loads to develop strategies to effectively manage excess suspended sediment. [ABSTRACT FROM AUTHOR]

Terrestrial organic carbon (OC) plays an important role in the carbon cycle, but questions remain regarding the controls and timescale(s) over which atmospheric CO2 remains sequestered as particulate OC (POC). Motivated by observations that terrestrial POC is physically stored within soils and other shallow sedimentary deposits, we examined the role that sediment storage plays in the terrestrial OC cycle. Specifically, we tested the hypothesis that sediment storage impacts the age of terrestrial POC. We focused on the Efri Haukadalsá River catchment in Iceland as it lacks ancient sedimentary bedrock that would otherwise bias radiocarbon‐based determinations of POC storage duration by supplying pre‐aged "petrogenic" POC. Our radiocarbon measurements of riverine suspended sediments and deposits implicated millennial‐scale storage times. Comparison between the sample types (suspended and deposits) suggested an age offset between transported (suspended sediments) and stored (deposits) POC at the time of sampling, which is predicted by theory for the sediment age distribution in floodplains. We also observed that POC in suspended sediments is younger than the predicted mean storage duration generated from independent geomorphological data, which suggested an additional role for OC cycling. Consistent with this, we observed interparticle heterogeneity in the composition of POC by imaging our samples at the microscale using X‐ray absorption spectroscopy. Specifically, we found that particles within individual samples differed in their sulfur oxidation state, which is indicative of multiple origins and/or diagenetic histories. Altogether, our results support recent coupled sediment storage and OC cycling models and indicate that the physical drivers of sediment storage are important factors controlling the cadence of carbon cycling. Key Points: Bulk radiocarbon measurements of riverine organic matter revealed millennial‐scale aging during sediment storage in IcelandXANES identifies interparticle diversity in S redox states indicative of organic matter with multiple origins and/or diagenetic historiesPhysical storage dynamics in river floodplains may influence the carbon cycle [ABSTRACT FROM AUTHOR]

During high river discharge extremes, the growth of dunes can reach a maximum beyond which a transition to upper stage plane bed may occur, enhancing the river's conveyance capacity and reducing flood risk. Our predictive ability of this bedform regime shift in rivers is exclusively built upon high Froude number flows dominated by asymmetric dunes with steep downstream‐facing slipfaces that are rare in natural rivers. By using light‐weight polystyrene particles as a substrate in an experimental flume setting, we present striking dune morphodynamic similarity between shallow laboratory flow conditions and deep rivers, preconditioned that both flow and sediment transport parameters are accurately scaled. Our experimental results reveal the first observation of upper stage plane bed in a shallow laboratory flume that is reached for a Froude number well below unity. This work highlights the need to rethink widely used dune scaling relationships, bedform stability diagrams, predictions of flow resistance, and flood risk. Plain Language Summary: Dunes are rhythmic shapes at the river bed that significantly increase water levels and the associated flood risk. They can reach heights up to one third of the water depth and often dominate the flow field. Under extremely high river discharges, dunes are observed to undergo a transition phase, after which they are washed out and disappear from the river bed. This morphological transition is expected to substantially reduce water levels and thus flood risk, by enhancing the conveyance capacity of the river during a peak discharge event. Once such circumstances can be predicted with certainty, it will become possible to meet safety standards while reducing the height of the river embankment. Key Points: Our experimental analysis reveals striking dune morphodynamic similarity between shallow laboratory flow conditions and deep riversWe present the first observation of upper stage plane bed in a shallow laboratory flume that is reached for a Froude number well below unityDune slipface angles show a systematic decrease with increasing entrainment of bed sediment into suspension [ABSTRACT FROM AUTHOR]

High‐resolution topographic models have revolutionized monitoring of river changes by comparing sequential river topographic surveys (i.e. change detection). Nevertheless, much more may be obtained from this innovative quantification of changes. In this paper, we enhance the interpretation of geomorphic processes by presenting a new method for understanding of sources and sinks of sediment, river sediment transfers and functional sediment connectivity. Repeat digital elevation models (DEMs) obtained by photogrammetry were used to quantify topographic change after two floods by creating a DEM of difference (DoD) of a 6.5 km‐long reach of Rambla de la Viuda stream, an ephemeral gravel‐bed river in eastern Spain. The proposed method involved dividing the channel into 10 m‐long longitudinal strips that were used to systematically draw boundaries between the erosional and depositional areas of the DoD. The analysis objectively: (i) drew a series of erosional and depositional segments, from 120 to 1360 m in length; (ii) estimated ranges of source‐to‐storage sediment transport distances, 320–670 m in the upstream and middle reaches and up to 2030 m in the lower reach; and (iii) obtained values of functional connectivity (i.e. the ratio between the sediment exported (erosion) and retained (deposition), ranging from 103 to 10−3). The variability in these three parameters along the river was found to be related to the level of channel disturbance by in‐stream mining during the 1990s and 2000s. Additionally, this method indicates that the main process responsible for self‐adjustment of the present morphosedimentary conditions is intra‐reach erosion of banks and channel beds. Thus, this study proposes a new methodology to characterize morphological change, sediment transfer and connectivity that may serve as environmental indicators of the hydromorphological integrity of rivers with potential application to the European Water Framework Directive. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper we use multiple field surveys spanning several decades to systematically evaluate the geomorphic consequences of a change in flow hydraulics from uniform flow to backwater flow for the lower Trinity River in east Texas, USA. Spatial changes in lateral migration rate, channel geometry, and point bar size correspond to two distinct geomorphic zones. Within the upstream uniform flow reach, the river channel is defined by fully developed point bars and a high rate of lateral channel migration. This zone transitions where the median channel bottom elevation drops below sea level. At this point flow is affected by the backwater influence of the Trinity Bay water surface elevation, as opposed to being bed slope control dominated. The change in hydraulics within the backwater zone is reflected in the channel morphology, which is characterized by smaller point bars, narrower and more symmetrical cross‐sectional channel geometry, lower channel migration rates, and little to no bend deformation or cutoffs. Studying the connection between channel geometry, river bend kinematics, sediment transport, and fluid mechanics in each zone provides a deeper understanding of the relationship between channel shape and river mechanics. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Understanding coarse sediment transport is crucial for the prediction of sediment migration and the consequent development of fluvial morphologies. In this study, cobble displacements in a pre‐Alpine creek have been recorded by means of radio frequency identification (RFID). Pebble monitoring has been systematically performed after each rainfall event with moderate precipitation, in order to exclude the superimposition of sediment displacements induced by triggering factors acting at different times. The analysis of the collected data was carried out through the application of both a principal component analysis and the Buckingham Π theorem. The experimental trends were interpreted considering the ratio of mobile pebbles, the pebbles' displacement and virtual velocity as the dependent variables. These quantities mostly depend on the event peak discharge, with a nonlinear increase of the travelled distance and a growth of up to two orders of magnitude of the virtual velocity (for an approximately 10× increase in peak discharge). An inverse dependency of the virtual velocity on the event duration was also observed. A comparison of the results obtained with those from laboratory investigations of bedload transport mechanics evidenced the differences in parametric trends associated with sediment mobility in the two environments. This contrast brings forward the combination of multiple drivers of sediment mobility, such as local morphology, sediment dimensions and flow unsteadiness, warranting a further in‐depth investigation. Representation of results in a dimensionless form is suggested as a good practice to analyse data from case studies characterized by different scales. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This work deals with the impacts of dams on large gravel ‐bed rivers in terms of altering coarse transport regimes and the relationship with river morphodynamics. Using data collected by a tracer ‐based monitoring programme carried out in a 4 ‐km ‐long study sector of the Parma River (Italy), located downstream from a relatively recently established dam, we applied a virtual velocity approach to estimate the coarse bed material load at four river cross ‐sections. Monitoring and calculation results provided new insights into the impacts of the dam on streambed material mobility and the sediment regime over the 17 ‐month calculation period. A longitudinal gradient of effects was observed along the study sector. Sections located closer to the dam are characterized by more evident impacts due to deficits in coarse sediment input from upstream. Sediment mobility here is strongly altered, especially in the highly armoured main channel, and the overall bed material load is extremely low. A partial recovery of sediment dynamics was observed at the sections located further from the dam, where estimates indicate higher sediment yield. The observed longitudinal trend in the coarse sediment transport regime matches the morphology, as the river shifts downstream from a sinuous configuration with alternate bars to a wandering one. The novel insights into alteration of coarse sediment dynamics and the relationship with river morphodynamics are potentially applicable to many other fluvial contexts affected by similar impoundments. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Grottoli, E.; Cilli, S.; Ciavola, P., and Armaroli, C., 2020. Sedimentation at river mouths bounded by coastal structures: A case study along the Emilia-Romagna coastline, Italy. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 505–510. Seville (Spain), ISSN 0749-0208. Beach retreat in the Emilia-Romagna coast, facing the north Adriatic Sea, is well-known since decades and several factors are behind this phenomenon: a scarcity of natural sediment supply by rivers, natural and anthropogenic subsidence, and a strong urbanization of the coastal zone. Several bedload measurement campaigns in one representative river of the Ravenna province (Savio River) have been carried out since 2017. At the same time, seasonal surveys of bathymetry were undertaken at the river outlet to correlate changes in sedimentation with river input. The river mouth is constrained by artificial embankments that possibly funnel out sediment offshore during river floods. However, monitoring of bedload transport correlated with bathymetric changes between July 2017 and November 2018 still found a positive budget of almost 5000 cubic meters. Local authorities in Ravenna are planning to dredge 20000 cubic metres from the river mouth to supply small nourishments outside the studied coastal cell. According to the measurements of bathymetric changes, the Savio mouth will need almost six years to recover, assuming the occurrence of a particularly efficient rate of sediment transport, like the one observed in the monitored period. Notably, the analysed period included a very large river flood that could overshadow the modal sediment transport operated by the river. Furthermore, with deepening of the mouth, the two villages adjacent to the outlet are likely to become more exposed to sea flooding, due to the propagation of surges inside the river mouth. The paper concludes that dredging activities should be reconsidered in view of the precarious equilibrium of the system. [ABSTRACT FROM AUTHOR]

The Modaomen Estuary has evolved from a runoff-dominated to runoff-and-wave-dominated estuary; thus, waves have become an important dynamic force. However, the nearshore irregular waves and wave-induced currents in the Modaomen Estuary have not been well studied. For the first time, a coupled wave-current model was developed in which the wave properties were calculated by the hyperbolic mild-slope equation, and the flow motion was simulated using a depth-averaged shallow water equation that was modified by introducing wave radiation stresses. The computational capability of this model was well calibrated by laboratory data from published references. Subsequently, the validated model was employed to analyze the wave height distributions, flow field characteristics and residual current under irregular waves, as well as to determine the differences in the above results with the scenarios under pure wave or pure tide. The results showed that the irregular wave heights reach 0.75 m near the sand bar and its surrounding shoals, reach 0.7 m in the main channel, and are approximately 0.3 m in the wave shadow area behind the Sisha shoal, which is more powerful than that under regular waves. The effect of waves on the current at the maximum ebb tide is greater than that at the maximum flood tide, especially in the estuarine shoal zone. Compared with the current velocity under pure tide, the residual current velocity is larger, and the vortex scale and the sediment transport route are all prominent under the combined wave and tide. [ABSTRACT FROM AUTHOR]

Sand mining (used here as a generic term that includes mining of any riverine aggregates regardless of particle size) is a global activity that is receiving increasing media attention due to perceived negative environmental and social impacts. As calls grow for stronger regulation of mining, there is a need to understand the scientific evidence to support effective management. This paper summarizes the results of a structured literature review addressing the question, "What evidence is there of impacts of sand mining on ecosystem structure, process, and biodiversity in rivers, floodplains, and estuaries?" The review found that most investigations have focused on temperate rivers where sand mining occurred historically but has now ceased. Channel incision was the most common physical impact identified; other physical responses, including habitat disturbance, alteration of riparian zones, and changes to downstream sediment transport, were highly variable and dependant on river characteristics. Ecosystem attributes affected included macroinvertebrate drift, fish movements, species abundance and community structures, and food web dynamics. Studies often inferred impacts on populations, but supporting data were scarce. Limited evidence suggests that rivers can sustain extraction if volumes are within the natural sediment load variability. Significantly, the countries and rivers for which there is science‐based evidence related to sand mining are not those where extensive sand mining is currently reported. The lack of scientific and systematic studies of sand mining in these countries prevents accurate quantification of mined volumes or the type, extent, and magnitude of any impacts. Additional research into how sand mining is affecting ecosystem services, impacting biodiversity and particularly threatened species, and how mining impacts interact with other activities or threats is urgently required. [ABSTRACT FROM AUTHOR]

Purpose: Bedload transport discharge is important in river engineering and morphodynamics. The Meyer-Peter and Müller (MPM) equation for determining bedload transport rates that was introduced in 1948 is still widely used in basic and applied engineering practise. An employment of the MPM equation for sand bed rivers is rarely observed as it usually performs well for gravel-bed rivers. The MPM equation was improved by introducing a correction factor considering the effects of the bedform and sediment mixture. Materials and methods: Field measurements of bedload transport rates at 64 cross sections of different sites along the Nile River in Egypt were collected and employed to enhance the prediction of bedload transport rates based on the MPM formula. Furthermore, independent laboratory experiments were executed in a straight sand bed flume to verify the modified form of the MPM equation and to extend its application range. Results and discussion: The MPM equation was improved by introducing a correction factor considering the effects of the bedform and sediment mixture. The accuracy of several sediment transport formulas (Meyer-Peter and Müller 1948; Frijlink 1952; Wong and Parker J Hydraul Eng 132:1159–1168, 2006; van Rijn 1984; modified Abdel-Fattah 2004; Huang Water Resour Res 46 W09533, 2010) was also evaluated using cumulative field measurements. Results suggest that the modified MPM equation is more suitable for the Nile River conditions than are the other tested equations. Conclusions: The study results indicate that the modified MPM equation can predict the bedload transport rates under the Nile River conditions with high accuracy. [ABSTRACT FROM AUTHOR]

At a global scale, delta morphologies are subject to rapid change as a result of direct and indirect effects of human activity. This jeopardizes the ecosystem services of deltas, including protection against flood hazards, facilitation of navigation, and biodiversity. Direct manifestations of delta morphological instability include river bank failure, which may lead to avulsion, persistent channel incision or aggregation, and a change of the sedimentary regime to hyperturbid conditions. Notwithstanding the in‐depth knowledge developed over the past decades about those topics, existing understanding is fragmented, and the predictive capacity of morphodynamic models is limited. The advancement of potential resilience analysis tools may proceed from improved models, continuous observations, and the application of novel analysis techniques. Progress will benefit from synergy between approaches. Empirical and numerical models are built using field observations, and, in turn, model simulations can inform observationists about where to measure. Information theory offers a systematic approach to test the realism of alternative model concepts. Once the key mechanism responsible for a morphodynamic instability phenomenon is understood, concepts from dynamic system theory can be employed to develop early warning indicators. In the development of reliable tools to design resilient deltas, one of the first challenges is to close the sediment balance at multiple scales, such that morphodynamic model predictions match with fully independent measurements. Such a high ambition level is rarely adopted and is urgently needed to address the ongoing global changes causing sea level rise and reduced sediment input by reservoir building. Key Points: The predictive capacity of morphodynamic models needs to improve to better anticipate global change impacts on deltasInformation theory and dynamical system theory offer complementary analysis frameworks to improve understanding of delta resilienceThe sediment balance in a delta channel network needs to be closed such that predictions match with independent observations [ABSTRACT FROM AUTHOR]

While mountainous rivers in subtropical East Asia deliver a disproportionately large amount of sediments to the global ocean, the controlling mechanisms for sediment supply and transport remain understudied. Here we target a mesoscale tectonically stable mountainous river, the Minjiang River, in southeast China. We present petrography, heavy minerals, and Sr‐Nd isotopic data from suspended particulate matter (SPM) and riverbed sediments to characterize sediment‐climate feedback processes. Results show Sr‐Nd isotopic compositions of the SPM vary seasonally, corresponding well with the spatiotemporal variations of precipitation. River sands display low compositional and textural maturity and represent first cycle‐dominated and fast‐transported detritus. Provenance analysis suggests prominent contributions of upstream Proterozoic‐Paleozoic rocks to downstream SPM and riverbed sediments. We propose that climate‐induced hydrological variations exert a major control on sediment supply, transport, and compositions. Our study highlights the crucial role of climate in driving physical erosion of mountains in tectonically stable, subtropical East Asia. Plain Language Summary: The subtropical‐tropical rivers in East and South Asia, particularly those draining mountains, account for a significant proportion of global sediment and nutrient exports. Based on tectonic settings, river basin morphology, climatic conditions, and extents of anthropogenic impacts, two distinct types of sediment supply and transport regimes in the low‐middle latitudes of East Asia have been identified. Type 1 rivers are large rivers on the tectonically stable continent with slow, multicycled sediment transport, modulated by widespread flood plains, lakes, and human activities. Type 2 rivers are small mountainous rivers on tectonically active plate boundaries with rapid sediment transport, which are commonly triggered by extreme tectonic and climatic events. However, sediment transport mechanisms of the mountainous rivers in the tectonically stable, subtropical regions remain highly enigmatic. We combined petrology and geochemistry methods to track sediment sources of the Minjiang River (southeast China) and to characterize river sediment transfer processes. We find that hydroclimate changes, rather than anthropogenic forcings, exhibit the major control on discharged sediment compositions. We suggest that the mesoscale, tectonically stable, mountainous rivers have similar rapid sediment transport behavior to those small mountainous river systems, unlike other large river systems in subtropical East Asia. Key Points: Petrography, heavy mineral, and Sr‐Nd isotopic data were used to trace sediment provenance for a tectonically stable mountainous riverProvenance data indicates rapid sediment delivery in response to hydrological changes over seasonal timescalesClimate variability exerts a major control on sediment compositions, revealing a third type of sediment transport regime in East Asia [ABSTRACT FROM AUTHOR]

This paper is devoted to study on the sediment runoff of the Ile River downstream. The article analyses the Kapshagai reservoir impact on the regime and characteristics of the sediment runoff in the Ile River downstream before and after construction of the reservoir in 1970. Along with the calculation of characteristics of sediment runoff, an assessment of the amount of the suspended sediment, which is in the bowl of the reservoir, was shown. Furthermore, the impact reservoir on the granulometric composition of the suspended and bed sediment of Ile River was calculated. [ABSTRACT FROM AUTHOR]

Fine-grained sediment (grain size under 2,000 µm) builds floodplains and deltas, and shapes the coastlines where much of humanity lives. However, a universal, physically based predictor of sediment flux for fine-grained rivers remains to be developed. Herein, a comprehensive sediment load database for fine-grained channels, ranging from small experimental flumes to megarivers, is used to find a predictive algorithm. Two distinct transport regimes emerge, separated by a discontinuous transition for median bed grain size within the very fine sand range (81 to 154 µm), whereby sediment flux decreases by up to 100-fold for coarser sand-bedded rivers compared to river with silt and very fine sand beds. Evidence suggests that the discontinuous change in sediment load originates from a transition of transport mode betweenmixed suspended bed load transport and suspensiondominated transport. Events that alter bed sediment size near the transition may significantly affect fluviocoastal morphology by drastically changing sediment flux, as shown by data from the Yellow River, China, which, over time, transitioned back and forth 3 times between states of high and low transport efficiency in response to anthropic activities. [ABSTRACT FROM AUTHOR]

Understanding the sediment yield and transport is one of the major topics of hydrosedimentology today. Although there are several methods to evaluate the incipient movement, the Shields model is mostly-used. However, the model proposed by Shields assumes that the sediments are uniform in an homogeneous and non-cohesive mixture. As such conditions are not easily found in nature, Egiazaroff proposed a sheltering coefficient, which considers the sediments in a non-homogeneous mixture in a wide range of granulometry. This coefficient allows correcting the Shields critical shear stress for nonuniform mixtures and can be used in mountain rivers, where the sediment size varies in several orders of magnitude. The equation proposed by Egiazaroff has been neglected for so many years in Brazil, and it is not mentioned in hydraulics or hydrosedimentology books . Thus, the present paper aimed to introduce the model proposed by Egiazaroff. Applying this equation to one natural river in a canyon, southern Brazil, the paper shows the good performance of this equation and recommends its use in mountain rivers in Brazil. [ABSTRACT FROM AUTHOR]