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Large wood (LW) and log jams have important implications for sediment dynamics within river systems. Although many case studies explore this topic, far fewer synthesize these results at the reach and basin scales. In this paper, we present a conceptual model that relates valley setting and landscape history of forested, mountain streams to spatiotemporal patterns of sediment storage and transport via the formation and decay processes of logjams. This conceptual model explores the function of logjams as sediment transport moderators, significantly influencing sediment retention, channel morphology, and lateral and longitudinal connectivity. Detailed wood inventories, channel topographic surveys, and channel morphology from four case studies are used to illustrate the range of channel responses to logjam formation, evolution, and decay in different valley contexts. Valley setting is shown to influence logjam formation and dynamics by determining the mechanisms and timing of sediment and wood recruitment. In steep and narrow (and thus coupled, confined) reaches, colluvial processes are the dominant mechanisms of wood and sediment delivery, and logjams grow vertically as sediment is stored in a wedge behind the jam (longitudinal disconnectivity). In contrast, in unconfined reaches (decoupled hillslopes), wood and sediment recruitment occurs primarily through fluvial processes, and logjams grow laterally as the channel shifts across the valley bottom. These logjams have long lifespans, often over a century, and gradually release sediment as the logjam decomposes. Sediment deposits stabilized by riparian vegetation behind these structures may persist long after logjam decay. This conceptual model is a testable framework and practical tool that offers insight into wood-sediment interaction mechanisms within steep, forested basins. [ABSTRACT FROM AUTHOR]

The Holocene sedimentary history of the Turbio River valley in semi-arid north-central Chile and its relationship to climate variability is presented in this study. Fluvial landforms and sedimentary deposits serve as essential records for studying the long-term dynamics of fluvial systems in response to external factors such as tectonic and climatic influences. The study area, located in the Andean Mountain range, is highly sensitive to hydrodynamic changes and sediment transport processes, making it suitable for studying fluvial dynamics and their relationship to climate fluctuations over millennia. In particular, the transitional semi-arid conditions of this region provide an opportunity to link Holocene fluvial sediments to climatic shifts. This study presents the analysis of well-preserved sedimentary deposits that outcrop along the valley walls, including grain-size distribution, stratigraphy, geochemical composition and radiocarbon dating to establish the chronological context. Facies association analysis, along with geochemical data, allowed the interpretation of depositional sub-environments and their evolution through time. We interpret the Holocene sedimentary evolution for the Turbio River valley as six time periods that reflect shifts in sediment source, energy regime, flow types, and sedimentary processes linked to fluctuations between wet and dry climatic conditions. The sedimentary sequence is interpreted as reflecting an initial high-energy period with continuous surface runoff followed by two periods of formation of extensive lakes, likely separated by periods of runoff intensification. The later part of the sequence reflects a more stable fluvial landscape that led to the excavation of the sedimentary fill. This sedimentary record provides valuable insights into past climate variations and their impact on the hydrodynamic conditions of the fluvial system in the region. Comparisons with other regional records support a broader understanding of climate change in the semi-arid Andes of Chile. • Rio Turbio sedimentary record is studied to reconstruct Holocene river dynamics. • Fluctuations in fluvial processes are related to alternating wet and dry periods. • A new model explains how the river evolved in response to Holocene climate variations. • Fluvial record provide valuable insights into past climates. [ABSTRACT FROM AUTHOR]

The structure and function of riparian ecosystems generally result from feedbacks between plant dynamics and fluvial processes and landforms, i.e., river morphodynamics. Taxonomic approaches do not allow direct identification and quantification of the mechanisms involved in the interaction between plant communities and the geomorphological environment. Although riparian ecosystems show enormous taxonomic variations, comparable patterns of plant response traits across different taxa may evolve in response to the exposure to similar hydrogeomorphological processes in relation to flow dynamics, sediment transport, and nutrient and water availability. Biogeomorphological functional classifications for plant responses to, and effects on, river morphodynamics at the levels of individual plants, populations, and communities have been proposed in the literature. They serve herein as a basis for identifying and quantifying, within a presented standardized functional trait framework, key plant response and effect traits that can help to explain feedbacks between plants and morphodynamics. In particular, functional guilds and functional diversity metrics can be applied at the population and community levels for exploring feedbacks between vegetation and river morphodynamics worldwide. In this framework, the variability in plant effects across different environments and spatiotemporal scales, related to the biological characteristics of the plants (i.e., morphological reconfiguration of plants into the flow, seasonal phenology, phenotypic plasticity, and vegetation succession), can be explored. New opportunities including remote sensing and numerical modelling approaches, coupled with the inclusion of plant traits through our original framework, will improve our understanding of feedbacks between vegetation and morphodynamics and contribute to an improved prediction of biogeomorphological river trajectories. • Taxonomical approaches do not permit the analysis of plant-geomorphology feedbacks. • Functional traits links hydrological, geomorphological and biological drivers and processes which shape river systems. • Riparian plant traits converge despite taxonomic variation. • The functional trait approach is an opportunity for quantifying riparian vegetation-river interactions worldwide. • The functional trait approach can be supported by remote sensing and numerical modelling of river trajectories of change. [ABSTRACT FROM AUTHOR]

The grain size of sediment delivered to a river by hillslope processes is an important factor which could impact fluvial erosion, sediment transport, and associated geomorphic changes. Grain size distribution (GSD) is increasingly recognised as an important factor for the impact of landslides on sediment pulses and long-term erosion rates. Therefore a better comprehension of grain size control on landslide-generated sediment transport and dynamics will help with understanding post-seismic fluvial processes and landscape evolution. In this study, we modelled the recovery of the Hongxi River basin affected by the Wenchuan earthquake under different landslide GSD scenarios. The CAESAR-Lisflood (CL) model was first modified to enable the spatial input of sediment GSD, which allows the model to distinguish the grain size composition of landslide sediment and the background sediment sourced from other areas. Using the modified CL model, we simulated three different landslide GSD scenarios (Original, Coarser, Finer) by altering the original landslide sediment GSD observed from a post-earthquake basin. In particular, we analysed the fate of landslide-generated sediment using a new sediment tracing function embedded in CL. This enabled us to evaluate the role of landslide GSD variation on the spatio-temporal heterogeneity of sediment transport. Our results show that the GSD of landslide material exerts a clear control on both sediment yield and channel deposition, the sediment transport of landslides disconnected to the fluvial system is more sensitive to grain size variation, while the GSD of landslides connected to the fluvial system has less impact on sediment dynamics. The duration of landslide disturbances on basin sediment dynamics can largely be dependent on the period of time (e.g., 20 years in this study basin) taken for grain coarsening (the grain size is increasing upward), which is dominated by the evacuation of fine sediments. The modelling results and findings highlight the importance of grain size distribution of landslide material and provide information to support basin sediment management and environmental risk mitigation. [ABSTRACT FROM AUTHOR]

• New geomorphological and geochemical records from the southern Mu Us Desert (MUD), northern China. • The sources of southern MUD sediments have evident temporal variation. • Early–Mid-Holocene southern MUD sediments are mainly derived from a local source. • The maximum CIA occurs at 8.4–6.4 ka BP and is related to enhanced monsoonal rainfall. • Late-Holocene mixed sources in the southern MUD are associated with an enhanced winter monsoon. • Summer and winter monsoons alternate in controlling the sediment source and geomorphic evolution in the southern MUD. Identifying the sources and weathering degree of sediments in the northern deserts of China is crucial to understand the evolution of the Asian monsoon system and corresponding induced changes in surface processes. Great progress has been made in the reconstruction of paleoclimate and paleoenvironment from the Early Holocene onwards based on chronostratigraphy and proxies of aeolian sedimentary sequences in the Mu Us Desert (MUD). However, previous studies have given rise to some controversial over the timing of the Holocene optimum period, and there is a scarcity of studies on the sediment provenance evolution of the desert during the Holocene and its internal relationship with the East Asian summer (EASM) and winter (EAWM) monsoons. Here, we provide new elemental geochemical data from a fluvial–aeolian sedimentary sequence in the southern MUD; we then combine these data with other available elemental data and hydroclimatology information to investigate the characteristics of sediment source evolution and their possible connection with the EASM and EAWM on the southern margin of the MUD-desert/loess transition zone since the latter part of the Early-Holocene. The elemental composition and geochemical characteristics of the studied sedimentary sequence differed markedly in the periods before and after 6.4 ka BP, suggesting a change in the source of the sediments across this boundary. From the late Early-Holocene (10.6 cal. ka BP), sediments were dominated by the chemical weathering products of local source material, with a gradual increase in chemical weathering over time, indicating a gradual strengthening of the EASM; the EASM reached its peak Holocene strength at 8.4–6.4 ka BP, accompanied by a moderate level of chemical weathering. After 6.4 ka BP, with the weakening of monsoon precipitation, the EAWM began to strengthen, and long-distance transport of source material from the west and northwest increased; however, chemical weathering of local source material driven by the EASM remained dominant until 4.0 ka BP. After 4.0 ka BP, the EAWM became dominant, and sediments showed strong sedimentary cycles, mainly transported from long-distance sources by aeolian activity, and the MUD became an important sedimentary sink for the northern-central deserts. After 0.7 ka BP, the sediments in the MUD became a mixture of different-age sediments due to river scouring and the transport of pre-existing sediments along the shoreline. Collectively, the elemental geochemical and other proxy data from Holocene sediments on the southern margin of the MUD record an inverse relationship between the EASM and EAWM; these two monsoonal circulations have alternated in their control of the sedimentary source characteristics and geomorphological environmental evolution processes across the southern margin of the MUD during the Holocene. [ABSTRACT FROM AUTHOR]

• A strong signal of reduced winter conditions i.e. duration, snow accumulation and frost days. • Hydroclimatic regime shift alters the sediment flux seasonality in near future. • Thaw-seasons have important role controlling the annual sediment flux. Climate change alters high latitude hydrological cycle by diminishing the snow accumulation and spring flood magnitude, and by altering temperature and rainfall finally leading to hydroclimatic regime shift from snow-dominated to rain-dominated. These changes in temperature, precipitation patterns, and discharge strongly influence geomorphological processes in fluvial environments, leading to alterations in sediment transport, erosion, accumulation, and landscape changes. We conducted comprehensive analysis of hydroclimatic trends and shifts on boreal Oulanka River system, spanning over the past five decades. A strong signal of warming temperatures (+0.61 Celsius/decade), reduced winter conditions and warmer summers (+0.41 Celsius/decade) was detected. The spring flood magnitude diminished 7 %, but high discharge peaks (Q > annual p90m3/s) during other seasons increased 22 % together with 28 % increase of annual minimum discharge. Simultaneously, precipitation intensity increased during summer. The meander migration rate (mean 0.89 or 2.55 m/year) and bank erosion volume were interconnected to ground frost, high snow sum, high discharge, and high-water level during spring flood, but no significant long-term trends were observed. Our findings underscore that climate is the first-order control on fluvial geomorphology and emphasizes the complex interplay between various hydrological and climatic factors that shape the dynamics of river systems. Based on the results, we expect to see changes in the spatial–temporal distribution of high latitude rivers sediment flux in future. In addition, more attention should be addressed to the thaw seasons controlling the sediment transport, as majority of the observed shifts took place in these months. [ABSTRACT FROM AUTHOR]

Up to several meters thick fine-grained Holocene overbank deposits are ubiquitously found in most Western and Central European lowland floodplains. However, despite their large importance for the geomorphological and geoecological floodplain properties, the interplay of different possible causes for their formation are not well understood yet. Most authors suggest human-induced deforestation as the main precondition for sediment mobilization and transport from the slopes to the floodplain, whereas others suggest a stronger influence of climatic factors. This current research gap is caused by often missing well-resolved fluvial chronostratigraphies and spatio-temporal information about former human activity within the studied catchments. To fill this gap we exemplarily studied Holocene overbank sedimentation and possible human or natural drivers in the meso-scale Weiße Elster catchment in Central Germany. To do so, we applied numerical dating as well as sedimentological and micromorphological analyses to Holocene fluvial sediments along three floodplain transects. Furthermore, we built up an unprecedented systematic spatio-temporal database of former human activity within the catchment from the Neolithic until the Early Modern Ages. Together with published paleoclimatic data, this database allowed an unprecedented, systematic comparison of Holocene overbank sedimentation phases with possible external controls. Our data show that some overbank sedimentation phases were directly linked with human activities in the affected site sub-catchments, whereas others were not. Instead, all phases seemed to be linked with natural factors. This difference with most former studies could possibly be explained by previously often limited numerical dating of the fluvial sediments and by largely missing spatio-temporally well-resolved regional settlement records, hindering a precise temporal link of fluvial sedimentation with former human settlement. Furthermore, this difference could possibly also be explained by a relatively high natural sensitivity of the landscape dynamics in the Central German lowlands, showing a subcontinental climate, towards climatic external controls. [Display omitted] [ABSTRACT FROM AUTHOR]

Sediment transport (bedload and suspension) plays a relevant role in the morphological response of river channels to large floods. Sediment load controls erosion and aggradation patterns during high flows, drives the migration of macroforms and contributes to the definition of thresholds for bank erosion and channel instability. Given this influence on channel morphology, it is clear that sediment transport influences both the channel geometry and water stage reached during floods and should therefore be considered in flood hazard analysis. So far, however, legislation on flood hazard and flood management plans still continues to typically disregard sediment transport. This is due mainly to the paucity of available data on sediment transport and the lack of standardized approaches for its integration into flood hazard analysis. The present work, which aims to provide some guidance on how to advance in this issue, has undertaken a bibliometric study and thorough review of the published scientific literature that had previously addressed the implications of sediment transport on flood hazards assessment. This review showed that: i) most studies on the influence of sediment transport on flood risk have focused on mountain streams, as they are highly sensitive systems to changes in sediment supply; ii) research has also focused on explaining historical changes in channel-conveyance capacity and flood frequency based on long-term trends in sediment supply; and iii) recent developments in hydrodynamic and morphodynamic numerical models provide opportunities to explicitly incorporate sediment transport in flood hazard analysis. However, despite the recent advances, we have identified important challenges and discussed needs to better consider sediment transport in flood hazards at different spatial and temporal scales. [ABSTRACT FROM AUTHOR]

• Overlapping crater populations constrain the total era of martian valley formation. • Martian valleys may have formed intermittently over hundreds of millions of years. • Long-term erosion rates would have been similar to the modern Atacama Desert. A number of studies have constrained the cessation of martian valley network activity to around the Noachian-Hesperian boundary, but the total time period over which these features formed remains poorly constrained. Most attempts to ascertain valley network formative timescales rely on an intermittency factor that varies widely for terrestrial rivers and is unknown for Mars. In this contribution, superposition relationships are used to identify crater populations that pre- and postdate valley network incision, resulting in maximum cumulative valley formation times of ∼108 years. These timescales correspond with long-term erosion rates of ∼0.25 m/Myr, similar to those calculated for the Middle to Late Noachian as well as the central Atacama Desert since the Late Miocene. Assuming sediment transport rates previously calculated for other martian valley networks, this implies a minimum fluvial intermittency of ∼10−5, several orders of magnitude lower than modern day Earth rivers but similar to values independently calculated for some martian fluvial deposits. This low intermittency suggests that martian valley incision may have been significantly hindered by erosion into existing bedrock or by boulder armoring of the valley floor. Alternatively, unlike river valleys on Earth, runoff events driving martian valley network activity may have been non-seasonal, Milankovitch-like cycles, with long eras of quiescence between periods of intensified fluvial activity. [ABSTRACT FROM AUTHOR]

Uranium (U) isotopes can be used to estimate the comminution age of sediments , i.e. the time elapsed from sediment production on continents, via weathering and physical erosion, to deposition in the sedimentary record. The calculation of this comminution age is based on measured (234U/238U) activity ratios in river sediments, and inferred time-dependent recoil effect, which leads to the preferential release of 234U from mineral lattices during erosion processes. In this study, we report on a large-scale (234U/238U) investigation of modern river sediments worldwide, with the aim to determine the extent to which parameters such as grain size, lithology, weathering, climate and geomorphology may influence the distribution of U isotopes in fine-grained sediments. Our extensive dataset (N = 64) includes U isotopic measurements for many of the world's largest rivers, but also rivers draining particular climatic and geological settings. Our results indicate that sediments collected from river basins draining mostly igneous, metamorphic or volcanic rocks often display (234U/238U) ratios > 1, with clay-size fractions (<4 µm) being less depleted in 234U (higher 234U/238U) than corresponding silt-size fractions (4–63 µm). In contrast, sediments derived from multi-lithological basins or draining sedimentary rocks are typically characterized by (234U/238U) ratios <1, with clays generally exhibiting more depleted 234U signatures than silts. Taken together, these observations suggest that the formation of secondary clay minerals in soils from basins draining mostly igneous, metamorphic is accompanied by partial incorporation by recoil injection of 234U initially released during weathering processes, possibly from U-rich minerals, such as sphene or apatite. Instead, in multi-lithological catchments draining sedimentary rocks, we propose that the erosion of recycled sediments having experienced several cycles of weathering, possibly over glacial-interglacial timescales, could explain the much lower (234U/238U) ratios observed in clay-size fractions. While no direct relationships can be identified between sediment (234U/238U) ratios and lithology, weathering intensity, climatic or geomorphic parameters in corresponding river basins, we show that the catchment size probably plays an important role in controlling the distribution of (234U/238U) in river sediments, through its direct influence on the sediment residence time. Finally, a multiple regression analysis of our data, combining various environmental parameters for the lithology, climate and geomorphology of studied river basins, indicates predicted (234U/238U) values that are very similar to measured values (with R2 ∼ 0.8). This finding provides further support for the usefulness of (234U/238U) ratios in the sedimentary record for reconstructing past landscape changes and their effect on sediment transport and residence time in river basins. [ABSTRACT FROM AUTHOR]

Sequence stratigraphic models emphasize changes in accommodation driven by relative sea level as a principal control on continental-margin development. Therefore, it has been hypothesized that there are differences in the volume and distribution of sand delivered to deep-water during the high-amplitude sea-level changes of icehouse settings versus the low-amplitude sea-level changes of greenhouse settings. Previous numerical modeling and field studies suggest an alternative hypothesis: that there would be minimal differences between each setting. Here, we used a three-dimensional numerical stratigraphic forward model to test the impact of greenhouse and icehouse sea-level changes on sand distribution in a passive margin setting. Model results were analyzed to evaluate the impacts of the rate and amplitude of relative sea-level changes on individual deep-water sand delivery events, total deep-water sand volumes, and sand distribution. Model results show that total deep-water sand volume is almost independent of the rate of relative sea-level change, which we attribute to the interaction of this sea-level change rate and the time required by the delta to reach a dynamic equilibrium state as a result of avulsion processes. However, there are major differences in the large-scale spatial distribution of sand between the icehouse and greenhouse conditions. The high amplitude sea-level changes in the icehouse model caused significant shelfal incision, which minimized deltaic avulsion processes and localized deep-water sedimentation. The relatively low amplitude sea-level changes in the greenhouse model allowed avulsion of the fluvial-deltaic system, thus causing more laterally extensive deep-water deposits. Our experimental results demonstrate that the rate of deep-water sand delivery is largest during periods of low sea level in both icehouse and greenhouse conditions, but show that there is a poor relationship between the rate of deep-water sediment delivery and the rate of sea-level change. We attribute both of these results to the nature of avulsion processes on the delta: more frequent avulsions of greenhouse deltas spread sediment across the shelf and limit sediment delivery to deep water until a dynamic equilibrium state is achieved, whereas the development of an icehouse incised valley locks the fluvial-deltaic system in place and localizes deep-water sedimentation. Moreover, our results indicate that the total volume of deep-water sand is controlled by the total sediment supply to the basin. These results provide a framework for the timing and quantity of continental-margin sedimentation and deep-water sediment delivery, with applications to sequence-stratigraphic interpretations. • Numerical stratigraphic forward models show icehouse and greenhouse settings deliver similar total deep-water sand volumes. • The equilibrium state of the delta influences deep-water sand delivery rates. • Model results show sea-level change can modulate fluvio-deltaic avulsion. • Icehouse setting limited fluvio-deltaic avulsion compared to the greenhouse setting. • Icehouse setting resulted in areally restricted deep-water sand deposition. [ABSTRACT FROM AUTHOR]

Hydrodynamic sorting has been shown to strongly influence the composition and age of organic carbon (OC) during sediment transport and burial in the marine environment, yet sorting effects on terrestrial OC (OC terr) in fluvial systems remain poorly understood. We conducted size fractionation of suspended particle samples from the lower Yellow River, China, and examined variations in mass distribution and carbon isotopic (δ13C and Δ14C) composition of bulk OC and specific biomarkers among grain size fractions in order to investigate the influence of hydrodynamic sorting and selective transport on organic matter export. In general, the 16–32 μm and 32–63 μm fractions contributed the most of sediment mass while the majority of the OC resided in the 16–32 μm fraction. Over 80% of OC and n -fatty acids (FAs) were concentrated in <32 μm fractions. Significant differences in OC%, surface area (SA), Δ14C OC , n -FAs contents, and compound-specific 13C and 14C compositions were found among size fractions. Of particular note was a progressive decrease of Δ14C values (i.e., increase in 14C age) of long-chain (C 26+28+30) FAs with decreasing grain size. Taken together, the bulk and molecular characteristics imply two distinct types of selective OC terr transport in the Yellow River. Coarser particles (>32 μm), characterized by relatively low SA, OC%, and Δ14C OC values, but higher Δ14C values of C 26+28+30 FAs, are inferred to reflect a combination of bedrock-derived detrital sediment and fresh vascular-plant material (e.g., plant fragments). In contrast, finer particles (<32 μm), exhibiting higher SA, OC%, and lower Δ14C 26+28+30FAs values, reflect preferential transport of pre-aged, mineral soil-derived OC that is susceptible to repeated mobilization, as well as widespread dispersal in marginal seas. The latter, once buried in marine sediments, could account for the high burial efficiency of OC terr in the adjacent Bohai Sea and Yellow Sea. Thus, hydrodynamic sorting processes induce heterogeneity of composition and selective transport of OC. Bulk and molecular 14C measurements of size-fractionated particles facilitate both elucidation of these processes and assessment of their impact on OC cycling in (and export from) rivers. [ABSTRACT FROM AUTHOR]

Fluvial sediment fingerprinting employs various methods, directly link sink and source. However, the identification and quantification of the transformation that sediments experience during fluvial transport remain unclear. The luminescence properties of quartz and K-feldspar change during the burial/exposure to sunlight cycles undergone by fluvial sediments, potentially allow scientists to trace fluvial sediment transport. Here, we report on changes in luminescence properties in active river bars from source to sink along the Yarlung Tsangpo-Brahmaputra River system. Optically stimulated luminescence (OSL) sensitivities and residual doses of quartz and K-feldspar within the fluvial sediments are used for the fingerprint method. Source rock is identified as the primary determinant of regional variations in quartz OSL sensitivities within fluvial sediments along the Yarlung Tsangpo River, while transportation distance governs local changes. Samples from narrower river channels with higher normalized channel steepnesses (Ksn) along the Yarlung Tsangpo River exhibit higher residual doses. Furthermore, the Brahmaputra River exhibits higher residual dose values compared to the Old Brahmaputra River. The sediments' residual doses are therefore employed to fingerprint fluvial erosion ability. Our luminescence fingerprint results indicate that coarse-grained fractions experience a "dilution" effect due to the input of new sediments after traveling approximately 50-200 km along the Yarlung Tsangpo River and about 50-100 km along the Brahmaputra-Old Brahmaputra River course. The comparison of luminescence (quartz and feldspar) and detrital zircon fingerprinting within the fluvial sediment holds the potential to trace weathering and erosion cycles during transportation in large river contexts. • Luminescence fingerprints fluvial sediment transport along the Yarlung Tsangpo River. • Source rock determine regional variations in quartz sensitivities. • Transportation distance governs local changes in quartz sensitivities. • The residual doses are employed to fingerprint fluvial erosion capabilities. • Coarse-grained fractions would likely be "diluted" by the input of local sediments. [ABSTRACT FROM AUTHOR]

Topographic relief and bedrock fractures caused by fault activity can accelerate surface erosion, suggesting that erosion rates increase with decreasing distance to the fault core. To test this hypothesis, we used 10Be cosmogenic nuclides to quantify catchment-wide erosion rates at various distances from a fault in the footwall of the Daqing Shan fault system, a 200-km-long active normal fault in Inner Mongolia, northern China. In addition, in order to examine the influence of topography and bedrock fractures on the surface erosion processes in the fault-weakened zone, their relationships with hillslope erosion, fluvial sediment grain size and transport efficiency, erosion rates, and erosion coefficients were studied. The resulting catchment-wide erosion rates ranged from 0.01 ± 0.00–0.13 ± 0.01 mm yr−1. These erosion rates and coefficients were unaffected by distance from the fault. The analysis of topography, bedrock fractures, and hillslope erosion yielded distinct hillslope erosion processes at different distances from the fault. Rapid mass wasting events, such as landslides, occurred at <15 km from the fault in steep, rocky hillslopes with abundant bedrock fractures. In contrast, at >15 km from the fault, hillslopes gradually become more gentle and soil-mantled. These spatial-slope configuration differences result in a decrease in sediment grain size delivered to river channels with increasing distance from the fault. Once sediments enter river channels, they impact fluvial transport capacity by influencing the initial motion threshold of sediment. Correlation analyses revealed that sediment transport efficiency in channels directly controls the catchment-averaged erosion rate and coefficient. This mechanism explains why the erosion rate remains insensitive to variations in topography and bedrock fractures in fault-weakened zones. • Study of patterns and controls on erosion rate across Daqing Shan fault zone. • Cosmogenic nuclide 10Be used to derive catchment-averaged erosion rate. • Erosion rates do not vary with distance from the fault. • Erosion rate remains insensitive to variations in topography and bedrock fractures. • Sediment transport efficiency in channels controls erosion rate. [ABSTRACT FROM AUTHOR]

The gross morphology of a free face and talus rampart occurs in a range of landscape settings. Semi-arid mesas, river gorges and coastal cliffs all share this geometry, but differ in how the components respond to their respective environments, to each other and to the capacity to export material from the talus rampart. Differences are reflected in the rates and processes of cliff retreat, and in the boundary conditions for rampart growth and removal. For mesas and buttes, export from the talus is controlled by the rate at which coarse material weathers to a size that can be readily washed away, leading to a stable proportional height for the rampart, which then consists of a boulder controlled slope at the angle of repose. For river gorges, a high incremental increase in fluvial sediment transport allows incision to accompany cliff retreat, while low rates lead to valley widening and rampart formation. Coastal cliffs may either lack ramparts, with supply limited development controlled by wave attack on cliffs; or be limited by the transport capacity of transverse offshore sediment processes, allowing development of a persistent rampart. In all contexts, the transport term should not be ignored in understanding both the rates of retreat and the morphology of cliffed landforms. [Display omitted] • Cliffs with a talus rampart occur in diverse settings. • Mesas, river gorges and steep coasts. • Boundary conditions depend on the process setting and geometry. • Evolution may be driven by supply- or transport-limited removal. • The rate of material transport from rampart base is always important. [ABSTRACT FROM AUTHOR]

[Display omitted] • The grain size and major element composition in sedimentary sequences of the Yellow River Basin are presented. • The provenance, transport dynamics and sedimentary characteristics of sediments of the Yellow River is disclosed. • The processes and geomorphological effects of aeolian-fluvial interactions in the Yellow River Basin are identified. • The intensity of aeolian-fluvial interactions is related to sediment erosion and transport. Understanding environmental changes requires the characterization of potential interactions between aeolian and fluvial systems. This study aimed to identify the sedimentary characteristics, provenance, and transport of sediments of the Yellow River Basin, as well as the processes and geomorphological effects of aeolian-fluvial interactions using end-member modelling analysis (EMMA), multidimensional scaling (MDS), and principal component analysis (PCA). Samples (n = 107) collected from sedimentary sequences in the source area, upper, middle, and lower reaches were analyzed for grain size and major element contents. The results showed that sediments in the source area of the Yellow River mainly originated from the Tibetan Plateau, whereas the input of materials from the Chinese Loess Plateau (CLP) gradually increased from the upper to lower reaches. The sediment transport was jointly controlled by simultaneous or alternating aeolian and fluvial processes. Asynchronism in aeolian activity and rainfall and the non-uniformity of runoff and sediment sources resulted in a concentration of aeolian-fluvial interactions in the river reaches traversing through the deserts and CLP. Fluvial sediments in the upper reaches consisted of wash loads deposited in slow-moving water, whereas rapid replenishment of sediment from the CLP in the middle reaches increased sediment transport capacity, thereby enhancing the uniformity of sedimentary characteristics from the upper to lower reaches. Moreover, numerous gullies in the CLP resulted in increased intensities of aeolian-fluvial interactions, thereby accelerating severe sedimentation in the lower reaches. This study can act as a reference for paleoclimatic reconstruction and for soil and water conservation in large-scale watersheds across a range of climatic zones. [ABSTRACT FROM AUTHOR]

• Improve the one-dimensional model with the river regulation works being considered. • Compare the fluvial processes with and without the effect of river regulation works. • Investigate the impacts of river regulation works on channel evolution. In an alluvial river, various kinds of river regulation engineering are usually constructed along the reach for the stability of channel regime and the safety of flood control, which greatly affects the process of channel evolution. Therefore, a one-dimensional (1D) morphodynamic model has been improved to simulate the fluvial processes influenced by large-scale river regulation works. In the refined model, each node of a cross-section was labeled using a specified point code representing the zones of floodplain and main-channel with or without regulation engineering, and sediment transport and bed deformation in different zones were treated separately. In the zones without regulation engineering, both bed deposition and bed erosion were permitted to occur; in the zones with regulation works, bed deposition was allowed, while bed erosion was not permitted to occur owing to the restriction of those engineering, unless there was a deposition layer newly formed over the previous simulation period. Then the improved model was calibrated and verified using field observations through the application to a 347-km-long alluvial channel located in the Middle Yangtze River in China. The results for the year 2016 show that the channel scour volume without the effect of river regulation works was 9% greater than the measured value (34.43 × 106 t), while the outcome considering this effect (35.81 × 106 t) was in closer agreement with the measurements. Moreover, the variation in channel geometry obtained from the improved model agreed better with the observed data. River regulation works would limit the channel incision, and it is likely to scour the other unprotected bed of a cross-section or the downstream cross-sections as the flow cannot carry enough sediment from the protected bed. Simulated results indicate that part of the main-channel zone at the Jing65 section was protected, but the riverbed continued to incise by about 0.68 m in the protected area when the effect of bed-protection works was not considered in the model, which was not in accord with the observed channel geometry. Therefore, this effect of large-scale river regulation works on channel evolution needs to be considered for a higher simulation accuracy. [ABSTRACT FROM AUTHOR]

• Vulnerability assessment for buildings resulted in a plethora of methods. • We present recent advances in quantitative vulnerability functions. • Multiple uncertainties can be detected if vulnerability functions are compared. • The transferability of functions between case studies is challenging. • More research is needed to understand the importance of building design. Irrespective of the magnitude and spatial extend, the consequences of a natural hazard are strongly connected to the vulnerability of elements at risk (e.g. people, buildings and infrastructure). It is, therefore, obvious that an analysis and quantification of vulnerability is required for successful disaster risk reduction. The need for vulnerability assessment is crucial due to the effects of climate change as well as the socio-economic dynamics that may directly impact vulnerabilities and coping capacities of affected communities. Vulnerability is multidimensional (physical, social, economic, etc.), however, the dimension which is mainly related to the direct costs and threat to human lives is the physical one. We focus here on the physical vulnerability of buildings subject to torrential hazards occurring in small and steep mountain catchments. These processes include fluvial sediment transport, debris floods, and debris flows. Furthermore, we included flash flood hazards if these are related to torrential catchments. Physical vulnerability to torrential hazards in mountain areas is a topic that has been under scientific investigation over the last 20 years. Several methods to assess physical vulnerability of buildings towards flash floods, debris flows and hyper-concentrated flows can be found in the literature. The plethora of methods and approaches may be classified under the following three categories: vulnerability matrices, vulnerability curves and vulnerability indices. We provide a short review of these methods which became available over the last decade and which dominate the scientific debate in mountain hazard risk management, giving an emphasis to vulnerability curves. The approaches presented herein are highlighted through case studies from the European Alps and beyond. Furthermore, challenges in vulnerability assessment including data requirements, need for improved event documentation, uncertainties and challenges related to future climate and socio-economic changes are outlined. Finally, a discussion on progress-driving factors such as new technologies (e.g. mobile apps, drones), citizen science and new innovative assessment methods is provided. [ABSTRACT FROM AUTHOR]

Abstract This paper reviews the impacts of permafrost change on hydrological and related hydrochemical, particulate and organic fluxes in small Arctic catchments. While the emphasis is directed at High Arctic systems, literature and recent developments from other Arctic regions are also included. Hydrological change, particularly a shift from nival (snowmelt) dominance to increasing pluvial (rainfall) runoff contributions has important consequences for the timing and magnitude of hydrological fluxes. A key distinction is made between thermal perturbation , where changing melt season thaw conditions result in deep thaw with minimal geomorphic or surface hydrological effects, in contrast to physical perturbation , where permafrost change results in some form of thermokarst or physical disturbance such as mass movement or enhanced erosion. The latter disturbances are commonly expressed as localized thermo erosional gullies, active layer detachments and retrogressive thaw slumps. Results from recent research emphasise the importance of hydrological connectivity in terms of the downstream effect of a particular permafrost perturbation. Well-connected systems, either at the surface as channelized flows, or in the subsurface, through new or altered active layer flow pathways, result in substantial changes in downstream fluvial fluxes. Surface hydrological connectivity of localized permafrost disturbances increases transport of suspended sediment and particulate organic matter, the latter of which is often old and comparatively labile. Exposed ice in retrogressive thaw slumps sustains discharge during the melt season, further increasing fluxes. Thermal perturbation holds a substantially greater potential downstream impact due to widespread mobilization of solutes and dissolved organic carbon and nitrogen, and several studies point to rapid microbial alteration of carbon and inorganic nitrogen transformation in the shallow subsurface. Collectively, these results point to altered runoff, sediment transport and hydrochemical fluxes with spatial and hydrological controls. [ABSTRACT FROM AUTHOR]

Highlights • This study analyzed the intensive fluctuations of runoff and sediment load at the upper Yellow River, which has not yet been studied clearly before. • Temporal variations in runoff and sediment load were discerned in terms of changing trend, abrupt change year, and multi-periods from the full measured datasets of all hydrological stations. • Impact of human activities on the hydrological variations was evaluated based on comparison of the measured and the reconstructed time series. Abstract Operations of amount of large and medium reservoirs have remarkably changed runoff and sediment loads, and consequently affected the fluvial processes intensively on the upper Yellow River. In this study, time series of runoff and sediment transport rates of four major hydrological stations on the upper Yellow River were used to analyze temporal and spatial variations of runoff and sediment loads. Mann-Kendall test and wavelet analysis were applied to analyze the datasets. Temporal variations in runoff and sediment loads were discerned in terms of changing trend, abrupt change year, and multi-periods from the time series. Additionally, a time series of runoffs was reconstructed based on a modeling scenario removing impact of reservoir impoundment and water diversion to indicate the status without human disturbances. Comparison of the measured and reconstructed datasets was conducted to evaluate the impact of reservoir impoundment and water diversion on hydrological variations. The measured runoff and sediment loads showed obvious decreasing trends due to impoundment and water diversion. However, the reconstructed runoffs regarded as only affected by climate change showed no significant changing trend at a 95% confidence level, confirming that, instead of climate change, human activities played the most important roles in variations. The measured datasets indicated that the reservoir construction and operation caused an abrupt change in runoff in 1986, while the reconstructed datasets indicated another abrupt change in 1995. Wavelet transform analysis distinguished the multi-periodical features of the time series. The first, second, and third dominant periodicities of the measured runoffs were 25–27, 16, and 8 years, respectively, whereas the first three dominant periodicities of the reconstructed runoffs were 26–31, 12, and 7 years, respectively. It was indicated that the high-frequency periodicities of runoffs decreased while the low-frequency periodicities increased, owing to reservoir impoundment and water diversion. [ABSTRACT FROM AUTHOR]

Abstract The Seč Dam Reservoir on the Chrudimka River (the Czech Republic) was studied as a possible barrier for the transport of solid particles related to fluvial pollution. To understand the damming-triggered changes in the sediment lithology and geochemistry and to establish the pollution chemostratigraphy of the reservoir deposits, we first characterized the grain-size control on the sediment composition, including concentrations of risk elements Cu, Ni, Pb, and Zn. To that end, we first examined the chemical composition of the sieved size fractions of sediments, and then we compared the grain-size parameters obtained by granulometry with the geochemical composition using either scatter plots or a compositional regression with functional covariates in framework of Bayes spaces. The onset of deposition in the dam reservoir outside of the inflow delta is marked by three major changes: (1) a decrease in the grain size and a corresponding increase in Al/Si and Ti and a decrease in K and Ca, (2) enhanced retention of the finest particulates, especially Fe and Mn, and (3) enhanced concentration of risk elements originating from local industry in the city of Hlinsko that started nearly coevally with the dam construction. In the inflow delta, these changes are not so straightforward: the lithology of the deltaic deposits resembles that of the pre-dam fluvial sediments, except for the fact they are polluted, although the pollution stratigraphy is poorly preserved. The peak of polycyclic aromatic hydrocarbons (PAHs) in the dam reservoir was found near the onset of the dam deposition. We found that Fe is the best-performing reference (normalizing) element for the geochemical background functions (GBFs), although Ti would provide better grain-size correction; clearly, post-depositional geochemical reactions also play a role. GBFs were used to calculate local enrichment factors (LEF) and show that the dam construction suppressed the downstream transport of Cu, Ni, and Zn pollution by more efficient retention and trapping of fine sediment components including Fe oxides, which are otherwise transported through the floodplain. Highlights • Application of geochemistry to distinguish floodplain and dam reservoir deposits. • Robust assessment of the Cu , Ni , and Zn-transfer through dam reservoirs. • Stratigraphic correlation for solving problem of uneven deposition in dam reservoirs. • Application of pollution chemostratigraphy in study of sedimentary archives. [ABSTRACT FROM AUTHOR]

Highlights • Geomorphic extent and character of alluvial systems change with climatic forcing. • Trends toward alluvial dynamic equilibrium are evaluated in a remote watershed. • Conceptual location-for-time-substitution model is presented for proglacial streams. • Observations of proglacial morphodynamics are presented. Abstract A remote proglacial stream in Chilean Patagonia was examined at two temporal scales to evaluate the downstream spatial progression of morphodynamics in response to chronic climatic forcing. Historic aerial imagery indicates alluvial channel response to a reduction in glacigenic sediment delivery that is driving reach-scale alterations to the channel planform and affecting the extent and character of geomorphic reaches at centurial timescales. At the decadal timescale, fluvial morphodynamics show a downstream spatial convergence toward dynamic equilibrium. The attainment of dynamic equilibrium is not considered herein, but the trend toward such a condition is discussed. Metrics of flood magnitude, hydraulic energy thresholds, inter-annual energy expenditure, variability of channel dimensions, and continuity of sediment transport capacity illustrate how alluvial systems respond to chronic climatic forcing and deglaciation subject to the constraints of valley conditions. A conceptual proglacial alluvial model is proposed in order to characterize expected fluvial changes and to evaluate the downstream spatial progression. This model is based on a combination of previous observations of alluvial evolution and a location-for-time-substitution approach validated by an intensive 3 year field data collection program. [ABSTRACT FROM AUTHOR]

Abstract A channel head is the upstream-most point of concentrated water flow and sediment transport between definable banks with a longitudinally continuous channel downstream. A channel head can be a relatively diffuse feature, the identification of which is subjective, or a very discrete and prominent break in the surface associated with a headcut. As the formal start of the channel network, channel heads reflect the location of process thresholds and thus differentiate geomorphic process domains for water, solute, and sediment fluxes. Stream order derives from mapped channel networks and the accuracy of stream ordering thus depends on the accuracy of identifying channel heads and associated first-order streams. In the absence of mapped channel heads, remote methods that under- or over-estimate the contributing area necessary to form a channel head can significantly over- or under-estimate, respectively, the extent of first-order streams and erroneously estimate drainage density. This paper reviews the current state of knowledge of the processes that form channel heads, the influences on channel head stability, and the methods used to identify the location of channel heads within a landscape unit. Individual channel heads can result from distinctly different processes, including surface fluvial erosion, surface colluvial erosion, subsurface erosion, or the intersection of subsurface preferential flow with the surface. The location of any channel head over a period of years to decades and longer is best understood as an average location that can and does change through time. The magnitude of change in the location of a channel head over time periods of years to decades will reflect the disturbance regime of the hillslope and the speed with which hillslope-channel processes recover following disturbance. If channel heads form where overland flow exerts a boundary shear stress that exceeds the critical value for substrate erosion, the channel initiation threshold, C , can be expressed as the product of contributing catchment area, A , and hillslope gradient, S : AS α ≥ C. An inverse relation between source area A and local slope S is present to a greater or lesser degree across diverse regions. Substantial variability in values of A and S reflects the influence of factors such as vegetation, slope aspect, surface versus subsurface flow paths, and substrate grain size. Analyses of published data suggest that channel head locations can be predicted with reasonable accuracy where surface runoff dominates channel initiation. Subsurface processes strongly influence the locations of many channel heads, however, and the area-slope relations for these channel heads are much less consistent and predictable. The challenges of channel heads are three-fold for any given drainage basin or portion of a drainage basin: to identify their geographic location, to predict their geographic location, and to determine the relative importance of potential control variables on the multiple processes that can create channel heads. In order to effectively address these challenges, additional research is needed to predict the regional characteristics likely to result in channel heads created by predominantly surface versus subsurface flow; develop envelope curves of A-S relations for different regions; compare channel head locations predicted based on hillslope curvature versus actual channel head locations; evaluate the spatial consistency of channel heads through time; and develop A-S relations for channel heads in little studied regions, including arid and hyperarid environments, karst and permafrost terrains, and grassland and savanna environments. [ABSTRACT FROM AUTHOR]

Subaqueous slopes of many actively prograding deltas are heavily modified by widespread submarine sediment failures, forming highly complex geomorphic features that undergo continuous evolution even over short time scales. However, the effects of wave-seabed interactions (especially liquefaction) on the evolution of seabed sediment failures are rarely studied. Here, we use side-scan sonar, sub-bottom profilers, multibeam bathymetry, and in situ and laboratory geotechnical tests to map the bottom morphology and sediment structure of the Yellow River subaqueous delta. Our results indicate that: 1) The morphology along the Yellow River subaqueous delta is highly complex and can be categorized as a moderately disturbed area and heavily disturbed area; 2) Heavily disturbed area shows notable lines of evidences of liquefication-related sediment failure and four separate morphological zones (Zones 1–4). Zone 1 consists of differently sized sediment highs, which considered to be scarp or monadnock features. Zone 2 undulates with widely distributed tabular sediment blocks, gullies, and small-scale seafloor irregularities. Zone 3 is characterized by irregular, elongate sediment ridges. Finally, Zone 4 is characterized by relatively flat terrain with some localized highs; 3) Sub-bottom profiles used to visualize failure features in Zone 1 show acoustically continuous high-amplitude parallel or subparallel reflection, and the geomorphic features in this area are mainly caused by erosion. In comparison, Zones 2, 3 and 4 lack internal structures and display chaotic/disturbed signatures in corresponding sub-bottom data, which might be an indication of liquefaction; and 4) A combination of preconditioning and triggering factors lead to sediment failures and the complex morphological features in this area; however, silt liquefaction under storm conditions is the most important controlling factor. Based on this evidence, we propose formation mechanism for the liquefaction-related sediment failure features in this area. Sediment liquefaction forms an initial depression and gully when fine particles are resuspended along the arc-shaped liquefaction boundary as sediment vents and re-solidification of the liquefied sediment leads to a stiffer bed. Gullies are then widened and deepened by the predominant currents, and the disturbed depressions develop into elongated highs because of the denser structure and higher strength following liquefaction. While disturbed by engineering activities, the sediment highs become fragmented due to intense localized erosion, having the potential for downslope transport and the formation of sediment ridges. The geometries and distributions of the sediment failure features on the Yellow River subaqueous delta provide insights into process mechanisms and causative factors, especially when compared with other, similar phenomena reported elsewhere. • The geomorphology of the Yellow River subaqueous delta was characterised. • Distinct morphological zones are identified and associated processes explored. • Silt liquefaction under storm conditions dominates. • An evolutionary model for liquefaction-related sediment failure is proposed. [ABSTRACT FROM AUTHOR]

Quantifying the timescale of sedimentary processes in river basins, such as erosion, transport and deposition, and their relationships with geomorphic parameters is important in the context of ongoing climate change. In this study, we combine uranium activity ratios (234U/238U) for fine-grained (<63 μm) fluvial sediments from the Var River basin (Southern French Alps) and inferred sediment residence times, to catchment-scale spatial analysis of geomorphic parameters with the aim to investigate the factors that influence the timescale of hillslope storage and alluvial transport. Our results show that the U isotope composition of sediments and inferred sediment residence time are mostly controlled by geomorphic parameters such as catchment elevation, slope and curvature, rather than catchment lithology. We show that sediment residence times are shorter in steep, high elevation terranes, but markedly increase wherever catchment-averaged slopes <30°, reflecting the transition from bedrock-dominated to soil-covered landscapes. Independent estimates of sediment residence times using spatial data for soil thickness and 10Be-derived denudation rates show good agreement with those calculated from U isotopes. This observation validates the suitability of U isotopes to quantify sediment residence times in river catchments and for investigating how geomorphic processes control the duration of hillslope storage and fluvial transport. Furthermore, these results show that the application of U isotopes to sedimentary deposits provides robust information on the relationship between climate variability and catchment erosion, allowing us to assess the role of intrinsic vs extrinsic controls on sediment routing at the millennial timescale. • Uranium isotopes were measured in sediments of the Var River basin (France). • Catchment elevation and slope are main controls on U isotopes, not lithology. • Elevation and slope also control sediment residence times derived from U isotopes. • Independent estimates of sediment residence times show agreement with U isotopes. [ABSTRACT FROM AUTHOR]

Fluvial systems are dynamic and the characteristics of every assessed reach are variable and difficult to quantify based on river type threshold values. The authors of this study considered whether taking into account detailed land cover data from the riparian zone could be of any help in more accurately defining river types and establishing hydromorphological reference conditions. Detailed land cover data from riparian zones (50 m and 200 m buffers along main rivers) were included among the hydromorphological characteristics of the main rivers on the territory of the Czech Republic, and the relationship between established river types and land cover in riparian zones was evaluated. Land cover data from main river reaches categorized by river type indicate fundamental land cover differences between types that closely correspond with the hydromorphological characteristics of channels. If we examine riparian zones with no or minimal anthropogenic impact, significant land cover classes emerge for distinct river types that at the same time facilitate more accurate descriptions of river types. For rivers in agricultural lowlands, land cover contributes to revealing modifications of the river network. This study demonstrates that detailed land cover data can be used to explain differences between river types and can be included among river characteristics for establishing hydromorphological reference conditions or for assessing the level of anthropogenic impact in the riparian zone, which generally has an effect on the channel as well. At the same time, detailed land cover data may significantly help locate new reference sites, or exclude unsuitable sites. [ABSTRACT FROM AUTHOR]

Lateral inputs from hillslopes and tributaries exert a variable impact upon the longitudinal connectivity of sediment transfer in river systems with differing drainage network configurations. Network topology influences channel slope and confinement at confluence zones, thereby affecting patterns of sediment storage and the conveyance of sediments through catchments. Rates of disturbance response, patterns of sediment propagation, and the implications for connectivity and recovery were assessed in two neighbouring catchments with differing network configurations on the East Cape of New Zealand. Both catchments were subject to forest clearing in the late 1940s and a major cyclonic storm in 1988. However, reconstruction of landslide runout pathways, and characterization of connectivity using a Tokunaga framework, demonstrates different patterns and rates of sediment transfer and storage in a dendritic network relative to a more elongate, herringbone drainage network. The dendritic network has a higher rate of sediment transfer between storage sites in successive Strahler orders, whereas longitudinal connectivity along the fourth-order mainstem is disrupted by lateral sediment inputs from multiple low-order tributaries in the more elongate, herringbone network. In both cases the most dynamic (‘hotspot’) reaches are associated with a high degree of network side-branching. [ABSTRACT FROM AUTHOR]

Hydraulic geometry (HG) has long enabled daily discharge estimates, flood risk monitoring, and water resource and habitat assessments, among other applications. At-many-stations HG (AMHG) is a newly discovered form of HG with an evolving understanding. AMHG holds that there are temporally and spatially invariant (‘congruent’) depth, width, velocity, and discharge values that are shared by all stations of a river. Furthermore, these river-wide congruent hydraulics have been shown to link at-a-station HG (AHG) in space, contrary to previous expectation of AHG as spatially unpredictable. To date, AMHG has only been thoroughly examined on six rivers, and its congruent hydraulics are not well understood. To address the limited understanding of AMHG, we calculated AMHG for 191 rivers in the United States using USGS field-measured data from over 1900 gauging stations. These rivers represent nearly all geologic and climatic settings found in the continental U.S. and allow for a robust assessment of AMHG across scales. Over 60% of rivers were found to have AMHG with strong explanatory power to predict AHG across space (defined as r 2  > 0.6, 118/191 rivers). We also found that derived congruent hydraulics bear little relation to their observed time-varying counterparts, and the strength of AMHG did not correlate with any available observed or congruent hydraulic parameters. We also found that AMHG is expressed at all fluvial scales in this study. Some statistically significant spatial clusters of rivers with strong and weak AMHG were identified, but further research is needed to identify why these clusters exist. Thus, this first widespread empirical investigation of AMHG leads us to conclude that AMHG is indeed a widely prevalent natural fluvial phenomenon, and we have identified linkages between known fluvial parameters and AMHG. Our work should give confidence to future researchers seeking to perform the necessary detailed hydraulic analysis of AMHG. [ABSTRACT FROM AUTHOR]

Aggregate breakdown influences the availability of soil particles for size-selective sediment transport with surface runoff during erosive rainfall events. Organic matter management is known to affect aggregate stability against breakdown, but little is known about how this translates into rainfall-induced aggregate fragmentation and sediment transport under field conditions. In this study, we performed field experiments in which artificial rainfall was applied after pre-wetting on three pairs of arable soil plots (1.5 × 0.75 m) six weeks after incorporating a mixture of grass and wheat straw into the topsoil of one plot in each pair (OI treatment) but not on the other plot (NI treatment). Artificial rainfall was applied for approximately 2 h on each pair at an intensity of 49.1 mm h − 1 . In both treatments, discharge and sediment concentration in the discharge were correlated and followed a similar temporal pattern after the onset of surface runoff: After a sharp increase at the beginning both approached a steady state. But the onset of runoff was more delayed on the OI plots, and the discharge and sediment concentration were in average only roughly half as high on the OI as on the NI plots. With increasing discharge the fraction of coarse sediment increased. This relationship did not differ between the two treatments. Thus, due to the lower discharge, the fraction of fine particles in the exported sediment was larger in the runoff from the OI plots than from the NI plots. The later runoff onset and lower discharge rate was related to a higher initial aggregate stability on the OI plots. Terrestrial laser scanning proved to be a very valuable method to map changes in the micro-topography of the soil surfaces. It revealed a much less profound decrease in surface roughness on the OI than on the NI plots. [ABSTRACT FROM AUTHOR]

Reservoirs behind dams act as deposition sites for much of the sediment being transported by rivers. As a result, the downstream river flow can be well below the transport capacity for bed-material. This promotes bed erosion and other geomorphic changes over some length of river located immediately downstream from a dam. These adjustments have been characterized for the Trinity River, TX, downstream of Livingston Dam. Field measurements and results from a 1D numerical model define a 50–60 river kilometer segment of river undergoing bed erosion as the transport capacity for bed material is reestablished. Consequences of this erosion include lowering of the channel bed, reduction in the sediment volume of channel bars, coarsening of sediment on bar tops, steepening of channel banks, and reduction in lateral migration rates of river bends. Repeat surveys of the river long profile reveals that 40 yr of dam closure has produced up to seven meters of channel-bottom incision downstream of the dam, transforming an initially linear profile into a convex-up long profile. The model output matches this observed change, providing confidence that calculated estimates for spatial and temporal changes in bed-material sediment flux can be used to explore the long-term signature of dam influence on the geomorphology of a sand-bed channel. Measurements of channel geometry, profile, lateral migration, and grain size of the lower Trinity River with distance downstream define both the trend and expected variability about the trend associated with the disruption to the bed-material load. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to introduce a novel coupled method for simulating the fluvial erosion, cantilever failure and bedload sediment transport to describe the overhanging properties of experimental banks and natural riverbanks. For fluvial erosion results, the previous relationships between the critical shear stress, and the erodibility coefficient indicated that they do not follow the values of the experimental works and the U-Tapao River, Thailand. Therefore, it is necessary to determine these relationships locally. The cantilever failure results revealed that the dominant failure mechanism of the experimental works is beam-type failure, while shear-type failure is the dominant failure in the U-Tapao River. Finally, a numerical model was developed based on a triple-grid approach to simulate the behaviour of a cantilever within the framework of fluvial erosion, cantilever failure, and bedload transportation. The simulated results showed good agreement with experimental results, and the U-Tapoa River in terms of the temporal variations of spatially averaged bank width, dominant failure mechanism, and overhanging block dimensions. [ABSTRACT FROM AUTHOR]

Dams are major obstructions to the flow of water and the transport of sediment in rivers. Much work has shown the construction of dams, and storage of sediment in reservoirs, can lead to significant changes in the morphodynamic behavior of alluvial rivers; however, in most cases, the effect of damming has a finite downstream limit as sediment is supplied back to the river through channel bed/bank erosion and/or tributary inputs. Here we present a study of a natural experiment that isolates one source of sediment downstream of a dam – the lower Rio Grande, which has no major tributary inputs of sediment over a ~450 km reach, from Falcon Dam to the coast. Analysis of the morphology and topography of the Rio Grande shows that prior to damming in the 1950s the coastal Rio Grande was a kinematically active channel with large, subaerial point bars. Subsequent to damming, lateral migration of the river shut down and exposed point bars shrunk in size, becoming static and vegetated. Bathymetric survey data show meter-scale incision of the channel bed for hundreds of kilometers downstream of the dam. Entrenchment of the river is also evidenced by the development of steep banks on the inner portions of channel bends. Damming also impacted the interaction between the river and the floodplain, resulting in the formation of persistent gullies incised into the channel banks, suggesting transport of water and sediment is net positive into, not out of, the channel. Based on all of these observations we conclude that the full ~450 km reach of the Rio Grande, from Falcon Dam to the coast, became net degradational following dam closure. We conclude that the presence of such a long degrading reach is caused by the exposure of bedrock in the Rio Grande channel for nearly 100 km downstream of the dam, which, combined with the lack of tributaries, limits downstream sediment supply to the river. Our results provide new insights into the response to damming for rivers with no tributary sediment input and thin alluvial cover, and more broadly to the kinematic and channel geometry responses to a major drop in water discharge and sediment supply for coastal meandering rivers. • We investigate the response of the coastal Rio Grande to 1950s dam construction. • Image, topography and bathymetric data show the river has become net degradational. • Degradation affects the river all the way to the coast, a length of ~450 km. • This reach has no tributary sediment input and the upstream channel exposes bedrock. • These attributes limit sediment supply resulting in large length of degradation. [ABSTRACT FROM AUTHOR]

A 3D sediment transport model based on the modified environmental fluid dynamics code (EFDC) and the nearshore waves simulation model (SWAN) is developed to study the change of suspended sediment concentration and bottom shear stress under the actions of pure current and wave-current. After being validated by the field measured data, the proposed sediment transport model is applied in the Oujiang River Estuary, China. The results show that the ratios of both bottom shear stress and suspended sediment concentration of pure current to those of wave-current show a gradually increase from shallow nearshore water to deep open sea. The results also show that the proportion of wave contributions on bottom shear stress and sediment concentration are above 60%, approximately 20-30% and less than 10% for the water depth of less than 5 m, 5-10 m and more than 20 m, respectively. For the waters among islands, the proportion of wave contribution to bottom shear stress and sediment concentration is reduced to 10-20% for -5 m water depth and this is more obvious for the waves of large amplitude. The bottom stress and suspended sediment concentration between islands are mainly controlled by tidal current, and the effect of wave is not significant. [ABSTRACT FROM AUTHOR]

Several works have discussed the morphological evolution in the Changjiang Estuary (CJE) in recent years. The erosion of its subaqueous delta in recent decades has been ascribed to a decline in fluvial sediment input. However, the interaction between the reduction of riverine sediment load and human activities in the estuary that could have caused morphological change has not been considered. In this work we provide evidence on the morphological evolution around the delta front zone since 1986 and use a numerical model to explore the correlation between the change in hydrodynamics and the evolution pattern. Bathymetric data analysis suggests a decrease of net accretion rate from 16.7 mm/year (1986–1997) to 9.1 mm/year (1997–2010) in the study area. Spatially, the tidal flats accreted whereas the subaqueous delta switched from deposition between 1986 and 1997 to erosion between 1997 and 2010. We used two indicators, tidal energy dissipation and erosion rate, to quantify the change in hydrodynamics and found that the erosion of the subaqueous delta in recent decades can readily be explained by the alteration of the hydrodynamics. The newly built navigation training works in the North Passage had a significant effect on the estuarine hydrodynamics, resulting in a local morphological adjustment. This erosion generated a new source of sediments to maintain the high suspended sediment concentration and tidal flat progradation. The erosion of the subaqueous delta may continue and gradually slow down until the altered hydrodynamics and morphology reach an equilibrium state in the future. [ABSTRACT FROM AUTHOR]

This study examines the fluvial readjustment of a Javanese river impacted by the major eruption of the Merapi volcano (Indonesia) in October and November 2010. The basin of the Opak River, located on the southern flank of the Merapi, was subject to substantial sediment input related to massive pyroclastic deposits that were remobilized by numerous lahars during the year after the eruption. Two study sites were equipped in order to evaluate the morphodynamic evolution of the riverbed of the Opak River. Topographic surveys, bedload particle marking, and suspended sediment sampling revealed an important sediment mobilization during efficient flash floods. Surprisingly, no bed aggradation related to the progradation of a sediment wave was observed. Two years after the eruptive event, marked bed incision was observed. The Opak River readjustment differs from that of other fluvial systems affected by massive eruptions in two ways. Firstly, local population extracted the sand and blocks injected by the eruption as they represent a valuable economic resource. Secondly, several dams trapped the major part of the sediment load remobilized by lahars. [ABSTRACT FROM AUTHOR]

Recent studies along the northwestern Gulf of Mexico document rapid, centennial-scale, landward retreat or back-stepping of estuarine environments up to 20 km ca. 8.0 ka, 4.8 ka, and 2.6 ka. If such rapid changes in coastal environments occurred today along the urbanized coast of the Gulf of Mexico major economical and ecological loss would occur. Although the 8.0 ka event occurs at a time of increased rates of sea-level rise, the latter two do not; leading to the hypothesis that they may be the result of past climate change. In this study, 121 cores, 4.3 km of high-resolution seismic profiles, and 53 radiocarbon dates are utilized to characterize the stratigraphic architecture and constrain the timing of stratigraphic flooding surfaces in the estuarine fill of upper Baffin Bay, Texas over the last 6 ky. Five flooding surfaces, which formed between 1.1–1.0 ka, 2.7–2.1 ka, 3.8–3.0 ka, 5.2–4.9 ka, and 6.5–5.7 ka, occur within error of drying in southern Texas driven by warming in the North Atlantic and recorded in independent paleoclimate archives. We suggest that these flooding surfaces, which occurred when sea-level in the Gulf of Mexico was rising < 2 mm/yr, were primarily driven by declines in fluvial sediment supply to the coast due to past climate changes. [ABSTRACT FROM AUTHOR]

This study describes channel changes following completion of the Provo River Restoration Project (PRRP), the largest stream restoration project in Utah and one of the largest projects in the United States in which a gravel-bed river was fully reconstructed. We summarize project objectives and the design process, and we analyze monitoring data collected during the first 7 years after project completion. Post-project channel adjustment during the study period included two phases: (i) an initial phase of rapid, but small-scale, adjustment during the first years after stream flow was introduced to the newly constructed channel and (ii) a subsequent period of more gradual topographic adjustment and channel migration. Analysis of aerial imagery and ground-survey data demonstrate that the channel has been more dynamic in the downstream 4 km where a local source contributes a significant annual supply of bed material. Here, the channel migrates and exhibits channel adjustments that are more consistent with project objectives. The upstream 12 km of the PRRP are sediment starved, the channel has been laterally stable, and this condition may not be consistent with large-scale project objectives. [ABSTRACT FROM AUTHOR]

In this study, we modified and applied an open source CFD software package, the TELEMAC, to simulate sediment transport and bed morphology on a meandering stretch of Nakdong River, between Gangjeong and Dalsung Weirs, whose length is about 20 km. The numerical simulations have been carried out on a High Performance Computing Cluster (HPC) with the real river bathymetry and with different operation scenarios of the weirs. The hydrodynamic parameters and bed evolutions obtained from the numerical results have been validated against field observation data. In addition, this study is to figure out a magnitude of bed evolution and the location where the erosion or deposition taking place under the weir operating conditions. [ABSTRACT FROM AUTHOR]

Megafans are ever-evolving landforms and sedimentary bodies produced by rivers that regularly change their courses through avulsions, in which the processes that cause the avulsions and their rates are tightly linked to the formation and evolution of the fans. The commonly cited condition required for the formation of megafans is a highly variable climate setting (monsoonal) which results in variable discharge and sediment transport capacity. However, some megafans occur in tropical settings in rivers with lower discharge variability but high sediment loads due to input from volcanic or tectonically active sources. We examine the Santa Clara Megafan (Costa Rica) to establish a model of explosive volcanism-driven megafan evolution, an alternative model to the climate-driven one. Studying chronological, archaeological, historical and remote sensing data we infer that major avulsions and shifts in the main rivers of this megafan are temporally and spatially correlated to strong eruptions (VEI ≥ 3). Furthermore, a period of ca. 1700 years with few changes in the fluvial system of the eastern sector of the megafan coincides with a low volcanic activity in its source area (i.e. Turrialba Volcano). The megafan avulsion rate was estimated as ∼1 major avulsion per century in the last five centuries, when four strong eruptions (∼0.8 eruptions/century) took place. These shifts in the rivers in response to the volcanic activity produced the activation or abandonment of megafan sedimentary lobes at a secular pace. The record of these changes will support future archaeological studies and lahar hazard assessments. Furthermore, the Santa Clara Megafan provides a model to explain the formation of megafans on Earth or on other planets through non-climatic processes. • A model for the evolution and development of a volcanogenic megafan is established. • Santa Clara Megafan exemplifies the formation of megafans through non-climatic processes. • Explosive eruptions can drive megafan formation instead of a highly variable climate regime. [ABSTRACT FROM AUTHOR]

• Quantitative reconstruction of soil erosion, sediment transport and delta deposition. • Soil erosion intensity was weak before the late Holocene, and increased afterwards. • The sediment deposition and soil erosion intensity were synchronous. • Soil erosion was dominated by climate as natural process before the middle Holocene. • Soil erosion was accelerated by human activities in the late Holocene. The Yellow River Basin is ideal for studying fluvial landscape evolution under climate change and human activities. Quantitative reconstruction of soil erosion, sediment transport, and delta deposition in the basin enhances understanding of the dynamic mechanisms of fluvial surface processes. This study reconstructs the spatial and temporal distribution of precipitation and vegetation cover based on geological profile records, paleoclimatic datasets, and historical documentation in the Yellow River basin during the Holocene. A landscape evolution model (Landlab) is introduced to simulate soil erosion and sediment deposition processes. Modeling results show that soil erosion intensity in the middle reaches of the Yellow River was weak during the early and middle Holocene. Since the late Holocene, soil erosion has increased due to vegetation degradation, as the climate became drier, but with more fluctuations. Since 2.0 ka (1 ka = 1,000 calibrated a B.P.), and especially since 1.0 ka, soil erosion in the middle reaches of the Yellow River increased rapidly due to strong human activity, with the intensity-six times higher than the average level before the late Holocene. Average sediment deposition thickness in the lower reach of the Yellow River (North China Plain) was about 2.4 m, and sediment volume was about 3.6 × 1011 m3. The deposition rate and soil erosion intensity showed synchronous changes during the Holocene. Since 2.0 ka, the sediment load and deposition rate have increased rapidly, to 6–10 times higher than in the early and middle Holocene. On this basis, the effects of climate change and human activities on the evolution of the fluvial landscape are discussed. [ABSTRACT FROM AUTHOR]

A 100–150 km-wide clustering of six large Late Cretaceous to Paleogene basin margin slope incisions along the northern Gulf of Mexico, up to 1000 m deep and 100 km long suggest a structural rather than eustatic control on their development. Counterintuitively to the existent models for canyon formation, the incisions align with the basinward trend of the San Marcos Uplift instead of forming in front of large adjacent sedimentary depocenters of the Rio Grande and Houston embayments where large rivers were discharging. Three plausible mechanisms are proposed for canyon formation, both triggered by tectonics. A shelf edge bulge scenario proposes, somewhat similar to previous continental flexure theory, a slow vertical rise of the sub-regional uplift onto the shelf and shelf-edge area that increased the gradient, triggered the initial incision and supported long term headward erosion. The high uplift rate scenario suggests a fast-vertical rise and extension of the uplift into the inner shelf area, whereby the high uplift rate diverted the rivers away from the area and protruded the shorelines as a headland. A third model envisions a deltaic headland caused by a tectonically locked (by uplift) river valley. The structural or deltaic headland diverted the longshore currents and sediment transport basinward, eventually causing a cascading over the shelf-edge and initiating incision and formation of the canyons. Erosion by sediment-laden flows played a critical role in initiating canyon formation, but with tectonics playing a preconditioning role. Other uplift regions around the Gulf of Mexico, Sabine, LaSalle and Tamaulipas (in Mexico) arches also align with large Wilcox Formation sedimentary incisions offshore, strongly suggesting that tectonism was a main control on canyon formation. • The arches in northern Gulf of Mexico relate to the Paleocene-Eocene canyons • The tectonic arches (uplifted areas) precondition the formation of a canyon • The recurrent large slope incisions formed by tectonics and shelf processes • Canyons are not aligned with fluvial valley axes but with tectonic arches [ABSTRACT FROM AUTHOR]

Central Chile has been affected by a sustained deficit in precipitation since 2010, the so-called mega drought, that has led to decreased water discharge in the fluvial basins of this region, affecting sediment fluxes. We investigate changes in sediment fluxes in the Itata River Basin (36-37°S, 11,326 km2) in central Chile over a period of 30 years (1986–2017) to evaluate the role of the mega drought in this region. We use a dataset of water discharge and suspended sediment concentration measured on a daily basis from a network of gauging stations that cover the basin from the mountain area to the river mouth. We estimated temporal variations in sediment fluxes within the basin. When comparing the pre-drought (1986–2009) and drought (2010–2017) periods, we found that annual sediment fluxes during the mega drought decreased between 28% and 67% from pre-drought values with variable intensity among the main tributaries. In addition, the season of maximum sediment transport in the basin has shifted from May–June to August during the mega drought along with a shift in the seasonality of maximum water discharge. We interpret that the precipitation deficit during the mega drought delays the recharge of the soil moisture and the establishment of favorable conditions to mobilize sediment in hillslopes. Because sediment transport in the basin occurs under conditions of lower water discharge compared to the pre-drought period, we also interpret the drought inhibits sediment transport in this system. Considering future climate projections for central Chile, it is likely that sedimentary dynamics in this basin, as well as similar fluvial basins in the region, will continue changing as the dry hydroclimatic conditions continue in the coming decades. • The mega drought has led to reduced sediment fluxes in the Itata River Basin. • Seasonality of peaks in sediment flux shifted from May–June to August. • Sediment is transported under conditions of relatively low water discharge. [ABSTRACT FROM AUTHOR]

Soil erosion, sediment transport, and delta deposition are of great importance to the evolution of fluvial landforms. In this study, we carry out a quantitative and comprehensive analysis to identify dynamic processes and mechanisms of soil erosion, fluvial plain deposition, and river delta formation in response to Holocene environmental changes over the past 10,000 years. In this investigation, the following results are achieved. First, spatial variations of the monsoon border (400 mm isohyet) resulted in dynamic changes in soil erosion on the Loess Plateau, sediment transportation downstream, and fluvial deposition on the plains and delta during the Holocene. Climate change and human activities played essential roles in variations of the plateau-plain-delta system during different periods. In the early Holocene, the number and scale of Neolithic cultural sites in the Yellow River basin increased. In the past 3000 years, human activities have strongly influenced and dominated environmental evolution in this region. Second, soil erosion was the critical contributor to the construction of the North China Plain. The Yellow River Delta provided the preliminary living environment where historical civilization in the Yellow River basin formed and developed, giving birth to the Yellow River civilization. Sediment discharge in the Loess Plateau was the primary source for river channel development and shaping of the river delta. • To identify processes and mechanisms of the Holocene soil erosion, fluvial plain deposition, and river delta formation in the middle and lower reaches of the Yellow River. • Spatial variations of the monsoon border resulted in dynamic changes in soil erosion on the Loess Plateau, sediment transportation downstream, and fluvial deposition on the plains and delta during the Holocene. • Climate change and human activities played essential roles in variations of the plateau-plain-delta system during different periods. [ABSTRACT FROM AUTHOR]

The dominant processes of sediment transport and morphological changes are different between rivers and coastal areas. In many situations rivers, estuaries and coasts need to be modelled together in an integrated way. This paper investigates the capability of a freely available, open source, coastal morphodynamic software (XBeach) to estimate sediment transport and morphological changes in fluvial environments. Four benchmark tests were designed to test code performance and included simple unidirectional flow cases, complex topography, fluvial flood flows (hydrographs) and dam break scenarios (fast transient, supercritical flow fields). The results were compared to laboratory experimental results or simulations results from industry standard software. Analysis suggested that the coastal morphodynamic code is able to simulate sediment transport and morphological changes in a fluvial environment, but there are limitations to what can be modelled and the accuracy to which they are modelled. General morphological trends are replicated reasonably well by the code however specific bed forms and rapid erosive responses are less well modelled. Suggestions are made for applicability of the code, code improvement and future work. [ABSTRACT FROM AUTHOR]

The Atchafalaya River in south-central Louisiana is of geomorphic interest because of the large volumes of flow and sediment transported and its role as a major floodway for the lower Mississippi River, notwithstanding its potential to become an avulsion pathway at Old River. Since its origin in the sixteenth century, it has undergone many transformations and currently receives flow from the Red River and partial flow of the Mississippi River through multiple pathways. Flow increased progressively beginning in the mid-1800s and continued until concerns of diversion spurred placement of engineering structures to regulate flows at the juncture between the Mississippi and Atchafalaya rivers in 1963. Prior studies, that looked at reaches or six to seven rangelines or cross sections on hydrographic surveys document areal, width, and depth increases in the uppermost 80 km (50 mi) of the Atchafalaya River from 1880 to 1974. This study assesses how channel geometry of the Atchafalaya River has changed with flow variations since the 1880s by evaluating instantaneous discharge measurements that document change at superior temporal resolution and differences in thalweg values from coupled modern hydrographic surveys which document change at better spatial resolution than prior works. While structures have regulated and limited flow into the Atchafalaya since 1963, the highest values of discharge, cross-sectional area, and width at Simmesport (upstream) follow river regulation. Associated geometry data at Simmesport and Morgan City (downstream) document that mean bed and thalweg elevations have risen. Comparison of thalweg elevations on hydrographic surveys from 1963 and 2006 show pronounced local variability in bed elevation change but also reaches dominated by degradation (including the Red River and uppermost section of the Atchafalaya) near the Old River diversion. Aggradation occurs in the lower Atchafalaya, a zone where along-channel lakes are filling, flow and sediment quantities are changing in part caused by the constructed Wax Lake Outlet, and deltas have been growing in Atchafalaya Bay. Findings are relevant to river engineering and flood management, especially navigation, and help in better understanding the evolution of large distributaries and the role of human impacts. [ABSTRACT FROM AUTHOR]

We document the detailed morphology and bed sediment size distribution of a stream channel upstream and downstream of a 200-year-old run-of-river dam on the Red Clay Creek, a fifth order stream in the Piedmont of northern Delaware, and combine these data with HEC-RAS modeling and bedload transport computations. We hypothesize that coarse bed material can be carried through run-of-river impoundments before they completely fill with sediment, and we explore mechanisms to facilitate this transport. Only 25% of the accommodation space in our study site is filled with sediment, and maximum water depths are approximately equal to the dam height. All grain-size fractions present upstream of the impoundment are also present throughout the impoundment. A characteristic coarse-grained sloping ramp leads from the floor of the impoundment to the crest of the dam. A 2.3-m-deep plunge pool has been excavated below the dam, followed immediately downstream by a mid-channel bar composed of coarse bed material similar in size distribution to the bed material of the impoundment. The mid-channel bar stores 1472 m 3 of sediment, exceeding the volume excavated from the plunge pool by a factor of 2.8. These field observations are typical of five other sites nearby and suggest that all bed material grain-size fractions supplied from upstream can be transported through the impoundment, up the sloping ramp, and over the top of the dam. Sediment transport computations suggest that all grain sizes are in transport upstream and within the impoundment at all discharges with return periods from 1 to 50 years. Our computations suggest that transport of coarse bed material through the impoundment is facilitated by its smooth, sandy bed. Model results suggest that the impoundment is currently aggrading at 0.26 m/year, but bed elevations may be recovering after recent scour from a series of large floods during water year 2011–2012. We propose that impoundments upstream of these run-of-river dams behave as long pools that adjust their bed elevation and texture to transport the load supplied by the watershed, rather than as impounded reservoirs with little bed material transport capacity. Scour may only occur during episodic high flows, followed by aggradation during periods of low flow. [ABSTRACT FROM AUTHOR]

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

This study examines the role of topography as a dynamic boundary condition that limits the efficiency of fluvial erosion in the post-glacial Teton Range landscape. The volume of sediment currently stored in two major catchments was estimated using high-resolution LiDAR and geometric reconstructions of depth to bedrock. Seismic reflection data in Moran Bay reveals post-glacial sediment preserved behind a submerged moraine, which isolates the bay from the larger Jackson Lake depocenter. The volume of post-glacial sediment stored in the canyons and bay totals 173.82 ± 19.5336.0 (×10−3 km3), which translates to a catchment-wide sediment production rate of 0.17 ± 0.02 mm/yr. The rock-equivalent sediment volume in Moran Bay is 4.4 ± 0.9 (×10−3 km3), only ∼2.6% of the total post-glacial volume. While the estimated sediment production rate in the canyons is similar to the uplift rate, the denudation rate derived from Moran Bay sediment is 0.004 ± 0.001 mm/yr, implying highly inefficient post-glacial sediment transport. The fluvial system has been disequilibrated by glacial erosion such that interglacial valley profiles lack the steepness needed to transport sediment, delaying sediment evacuation until the next glacial advance, or until uplift sufficiently steepens the fluvial system so that it regains efficiency. Furthermore, colluvial production rates in the deglaciated valleys are close to long-term denudation and uplift rates, suggesting that once topography has been equilibrated to glacial erosion processes, subsequent glaciers do not need to produce much bedrock erosion, but mainly sweep out accumulated sediment to maintain equilibrium. • Sediment budget quantified for two catchments in the Teton Range, Wyoming. • Flattened post-glacial topography limits efficient fluvial erosion. • Sediment transport delayed until next glacial advance or uplift steepens system. • Colluvial production rates are close to long-term denudation and uplift rates. • Subsequent glaciers may not need to produce much bedrock erosion. [ABSTRACT FROM AUTHOR]

• A coupled model is presented of flow and sediment transport in sewer flushing channels. • Modeling results agree with observed data in a combined sewer channel in Paris. • Sediment transport may deviate from capacity, necessitating non-capacity modeling. • Flushing sediment deposits may affect flow considerably, inviting coupled modeling. Flushing is cost-effective for mitigating sediments and constraining environmental problems in sewer systems. Previous mathematical models are almost exclusively built upon simplified governing equations evoking the assumptions of slow bed evolution and sediment transport capacity, of which the applicability remains open to question. Here a 1D coupled non-capacity model is presented for non-uniform sediment transport in sewer flushing channels, as adapted from recently established shallow water hydro-sediment-morphodynamic models for fluvial processes. The present model is tested for an experimental flushing case in Paris's Des Coteaux catchment system. The computational results agree with observed data more closely than those of a previous decoupled capacity model. While the differences between decoupled and capacity models and the present coupled non-capacity model are minor for flushing processes of short-durations, they are more pronounced for sustained long-duration flushing processes. Physically, the adaptation of suspended sediments to capacity regime cannot be fulfilled quickly, though bedload sediments can adapt to capacity regime instantly. Also, the bed deformation rate is comparable to its counterpart of the flow depth. Therefore, coupled non-capacity modelling is suggested for general applications to sewer flushing channels, of which the computing cost is essentially equivalent to simplified models built upon decoupling and capacity assumptions. [Display omitted] [ABSTRACT FROM AUTHOR]

River confluences are sites that operate with complex interactions between material and energy, provided by the combination of different flow patterns that present continuous changes in flow structure and sediment transport. In addition, river confluences have intrinsic ecological value, where biophysical processes and ecosystem services may be concentrated. This study aimed to analyze the morphology, flow structure, and hydrosedimentary interaction along tributary-trunk river confluences in a bedrock-alluvial plateau basin. The study included a field investigation into the mixed bedrock-alluvial basin of morphology, bed sediments, and hydrologic condition (including the flow structure) of 29 confluences to identify and analyze the similarities and differences between these confluences at the basin scale. For example, we considered the Ivaí River Basin, a medium-sized dam-free river that exhibits a mixed bedrock-alluvial bed and heterogeneity in both geology and longitudinal profile. Our findings show that the flow structure and morphology are conditioned by geological aspects, and the composition of the flow is extremely affected by the Ivaí River. In general, our results presented distinct differences from field-based data described in the literature for alluvial river confluences. • Study of flow structure, morphology, and bed sediments in river confluences based on field measurements. • Influence of physiographic properties on hydro-sedimentary aspects in river confluences. • The characteristics of river confluences in mixed bedrock-alluvial channels. [ABSTRACT FROM AUTHOR]