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Riparian buffers are commonly used to mitigate the negative effects of forestry operations near water, particularly sediment transport to streams. In Sweden, current practices typically involve 5-7 m wide riparian buffers along small streams. Historical forest management, which favored conifers up to the channel edge, has resulted in these narrow buffers having a simplified tree species composition and structure, making them prone to windthrow. While windthrow can contribute large wood (LW) to streams, windthrow also risks increasing sediment inputs if rootwads are exposed near stream edges. This disturbance affects sediment connectivity, or the movement of particles through the fluvial system, but the interaction between LW dynamics and sediment connectivity in small boreal streams is not well understood. We investigated sediment connectivity at the Trollberget Experimental Area in northern Sweden, where six 100 m stream reaches had either 5 m or 15 m wide riparian buffers. Pre-harvest and one-year post-harvest data on windthrow, hydrology, and sediment yields were collected. Forest harvesting increased sediment connectivity in the streams regardless of buffer width, indicating that buffers wider than 15 m are necessary to reduce sediment input impacts in small headwater streams. Windthrow affecting stream channels was more common in the 5 m buffers, leading to significantly higher deposition of very fine sediments (<250 μm) compared to the 15 m buffers. Coarse (>1 mm) and fine sediments (250 μm – 1 mm) were also higher in the 5 m buffers. We found that sediment connectivity in streams was closely linked to LW dynamics, negatively before harvest but positively after harvest. Before harvest, LW trapped sediment and prevented downstream transport, but after harvest, the increased sediment input overwhelmed this function. Our results highlight a trade-off between the recruitment of LW and minimizing sediment connectivity, two key objectives in riparian buffer management. • Riparian buffers are important to protect stream ecosystems when the adjacent forest is cut. • We applied 5 m and 15 m wide buffers and followed the impact on sediment connectivity. • Instream wood trapped sediments until harvest; windthrow disrupted this function. • All size fractions of sediment increased after harvest, regardless of buffer width. • Current buffer practices prevent providing both instream wood and sediment trapping. [ABSTRACT FROM AUTHOR]

Research into sediment provenance identification in Antarctica is emerging as a relevant field of study, providing a unique insight into understanding geomorphological processes in extreme climatic environments. This study focusses on the mechanisms of sediment redistribution in the catchment of the Korabelny Stream, located at the western end of the Bellingshausen Ice Dome on King George Island (Shetland Islands). The catchment area of the stream covers 2.83 km2, with 1.17 km2 under the glacier. Two main sediment sources have been identified: a) the glacierized part, extending along the glacier edge and represented by a complex of moraine deposits lacking protective vegetation cover, along with part of the catchment under the glacier; b) the periglacial part, occupying territory with permafrost and a thin loose cover unevenly protected by early successional vegetation. We combine a tracer-based fingerprinting technique, sediment delivery estimates based on sediment flow connectivity index and geomorphological mapping to quantify the sources contribution to sediment yield. The proportional contribution of the glacierized part was 60–66 % of the total sediment yield based on two independent methods, suggesting the reliability of the results. It is noteworthy that sediment transport from the glacierized part exceeds that from the periglacial part. However, a significant portion of the sediment is redeposited in temporary reservoirs formed along the glacier edge and Lake Mesyats, located in the central part of the Korabelny Stream catchment. The main factor determining sediment yield in the catchment is the water reserves in snow at the beginning of the ablation season. In years when water reserves in snow significantly exceed long-term average values, such as observed in the austral summer of 2014–2015 when study was conducted, sediment yield was low. This is attributed to the faster melting of ice on the glacier compared to snow, due to differences in albedo. • First time, assessed sediment sources in small Maritime Antarctica catchment. • Two independent methods used to determine proglacial and periglacial contributions. • Proglacial part contributes significantly more to sediment runoff. • The higher snow water reserves at ablation start the lower proglacial sediment runoff. [ABSTRACT FROM AUTHOR]

Soil erosion rates after wildfire are strongly controlled by intrinsic properties such as topography, weather, climate, soil, and vegetation. These landscape and hydroclimatic properties are important in determining post-fire erosion rates; however, their influence on post-fire erosion and their interaction with the intensity of a wildfire remains uncertain. A key limitation in resolving this uncertainty is the lack of conceptual models and frameworks for organising data related to the geomorphic sensitivity of landscapes to wildfire. Our aim is to develop a framework for consolidating understanding of post-fire erosion in the context of hydroclimatic conditions which contribute to system states, for example soil and vegetation properties, and wildfire regime. The framework is developed around a simple conceptual model where the change in erosion due to wildfire is a product of change in runoff generation and sediment supply, which is strongly related to landscape net primary productivity (NPP). We hypothesised that geomorphic sensitivity to wildfire should vary as a unimodal humped relationship across a gradient of NPP, peaking at an intermediate level. To develop this framework and to test the hypothesis, we first review intrinsic soil and vegetation properties related to the supply and transport of sediment from burned and unburned hillslopes. Net primary productivity is systematically related to these intrinsic properties because it integrates many processes involved in soil and vegetation development. Empirical data indicate a trend in the change in surface runoff generation with NPP after wildfire, peaking at an NPP of approximately 15 Mg C ha−1 y−1. A simple model of fuel availability and soil heating are correlated with a similar "humped" trend in sediment supply. These results are consistent with our conceptual model, which indicates that sediment supply and runoff contribute towards a distinct peak in wildfire effects on erosion at an intermediate level of NPP. We propose that landscapes of intermediate NPP typically have the highest quantity of fuel available to burn, which cause large changes to the soil surface properties. Landscapes at intermediate NPP also tend to produce intrinsic soil and vegetation properties that promote erosion after wildfire. The interplay between these short and long-term landscape characteristics is strongest at intermediate levels of NPP. Our proposed biogeographic model of geomorphic sensitivity to wildfire was supported by erosion data from burned hillslope and zero-order catchments studies from a range fire-prone landscapes in Australia and North America. Our proposed conceptual model will help identify areas most vulnerable to post-fire erosion changes. [ABSTRACT FROM AUTHOR]

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]

This study reveals the morphological transformations of a deep-water channel system within the Rakhine Basin in the northeastern Bay of Bengal through a comprehensive analysis of high-resolution 3D seismic data integrated with drilling logs. Employing the "source-channel-sink" paradigm, this investigation examined the impact of various factors, including tectonic transformations, sediment influx, slope dynamics, climatic changes, and relative sea-level fluctuations, on the evolutionary trajectory of these channel systems. Applying precise time-slicing techniques integrating root-mean-square amplitude attributes, coherent amplitude attributes, and horizontal amplitudes on seismic profiles, this investigation recognized three distinct stages in the evolution of channel-levee complexes (CLCs): the Middle Miocene erosional deep-water channel-levee complex (CLC-1), the Pliocene erosional-depositional deep-water channel-levee complex (CLC-2), and the Pleistocene depositional deep-water channel-levee complex (CLC-3). Comparative analysis revealed that the CLC-3 exhibits unique characteristics, including shallower channel depth (D), wider channel width (W C), extensive U-shaped cross-sectional area (S), broader natural levee width (W L) and height (H), and the highest tortuosity coefficient (L C /L S) when contrasted with the other two CLCs. Furthermore, this study substantiated how tectonic processes, primarily the collision between the Indo-Eurasian plates, resulting in the Himalayan and Indo-Burma Range orogenies, have shaped the region's geological and climatic framework, thereby influencing monsoon circulation and precipitation patterns, which in turn augmented detrital material influx into the basin. Moreover, this tectonic collision has led to gradual changes in the slope gradient of the Rakhine Basin and its deep-water areas, impacting internal flow velocities and channel curvature, thus governing deep-water channel systems' development and spatial distribution. Also, episodic sea level fluctuations were identified as significant contributors to sediment transport from shelves to deep-water regions and sediment deposit reworking. Overall, this study underscores the role of tectonic changes after the Eocene in driving the evolutionary dynamics of the deep-water channel system within the Rakhine Basin, Myanmar. [Display omitted] • Indo-Eurasian plate collision shaped the deep-water channel systems in the Rakhine Basin. • 3D seismic data reveals three evolutionary stages in these deep-water channel systems. • Pleistocene depositional channel-levee complex exhibits unique physical characteristics. • Tectonically affected slope dynamics have directed the channels' evolutionary dynamics. • Episodic sea level fluctuations have also supported these morphological transformations. [ABSTRACT FROM AUTHOR]

We synthesize evidence suggesting a chain of global cause-effect relationships, linking population and economic development with cumulative effects on changes in landscape dynamics, including denudation and sediment transport/deposition. Temporal trends in global patterns of geomorphic processes or process combinations such as denudation, sedimentation, or frequency of geomorphic disasters, appear to reflect growing human pressure. Erosion rates, intensified by anthropogenic factors, are currently one to two orders of magnitude greater than prior to the 20th century, and are growing further. Per capita human transfer of Earth materials has increased tenfold. A considerable increase in the frequency of disasters related to geomorphic processes has also taken place in just over half a century, outpacing changes in other natural disasters. It is especially significant that the ratio between the frequency of geomorphic (implying water/land interaction, obviously influenced by climate change) disasters and frequency of purely climate-related disasters has increased more than ten-fold since the early 20th century. The changes described in geomorphic processes (global geomorphic change) appear to respond mainly to land surface modification, which reflects a "Great Geomorphic Acceleration" after the mid-twentieth century. However, these stressors, characteristic of the "Anthropocene", likely interact with climate change, increasing concerns about future implications for Earth surface dynamics and underscoring the need to not only reduce GHG emissions, but also improve land use practices, which modify the conditions of the terrain. [ABSTRACT FROM AUTHOR]

The Bohai Sea is the receiving basin of the Yellow River (Huanghe), one of the largest contributors of global terrestrial materials to the sea. An area of fine-grained sediment deposition extends northeast of the Yellow River and its formation mechanism is still unclear. A calibrated, high-resolution coupled model of the Bohai and Yellow Seas was used to investigate sediment transport pathways in the region under the influence of strong and varying winds in winter. Numerical results highlight the importance of storm events in modifying the regional sediment resuspension and transport. During winter, the prevailing winds are typically from the northeast and northwest, interspersed by relaxation periods with weak winds. Winds influenced the currents and sediment movement in the Bohai Sea through several processes: local wind waves and resuspension, coastal-trapped waves in the Bohai Sea, and remotely forced coastal-trapped waves in the Yellow Sea. During northwesterly winds, sediment off the Yellow River Delta was mainly transported eastward along the south coast of Bohai Sea and escaped the Bohai Sea through the southern Bohai Strait. When northeasterly winds prevailed, sediment transport split into three branches: westward into the Bohai Bay, northeastward to the central Bohai Sea, and eastward along the south coast of Bohai Sea. Modeling results driven by synoptic winds indicate a more complex sediment transport pattern than previously understood with monthly average wind forcing. These findings challenge the traditional view of predominantly eastward sediment transport during winter and help to explain the observed grain size distribution in the Bohai Sea, in particular the accumulation of fine-grained sediments northeast of the Yellow River. • Storms are important in modifying the regional sediment resuspension and transport. • Sediment movement in BS depends on local winds, its related CTWs and CTWs in YS. • The formation of muddy areas northeast of the YRD is related to the varied winds. [ABSTRACT FROM AUTHOR]

Chirp profiles collected on the southern Brazilian shelf were combined with sedimentological and hydrodynamic data to characterize shelf geomorphology, focusing on the development of outer shelf bedforms and their genetic links with major oceanic currents. Outer shelf sediment accumulations are interpreted as two scales of bedforms, such as dunes and sand ridges. In the São Paulo Bight, cuspate bedforms are bounded landward by a geomorphological scarp. The sector between Florianopolis and Mostardas also exhibits frequent asymmetric bedforms, whereas the inner- middle shelf is covered by semitransparent sheets. The southern Rio Grande Cone is characterized by stratified deposits covering vast outer shelf areas. Surficial sediment samples reveal a dominantly muddy composition and relatively high carbonate contents. Hydrodynamic data indicate a major influence of the Brazil Current over the São Paulo Bight. The prolific bedform outer-shelf environment is assumed to be mostly relict formed in a transgressive shallow-water setting. The sand ridges are believed to have evolved from a moribund stage characterized by morphological degradation to a relict stage, with preservation enhanced by fine-grained winnowing, coarse sediment armoring, and early cementation. Bedform migration seems to be occurring on the São Paulo Bight due to the presence of a nearly permanent meander of the Brazil Current. Over most of the inner shelf, the northward advection of sediments mainly led by the Brazilian Coastal Current has formed extensive fine-grained deposits. The occurrence of a relict shelf scarp may have conditioned the formation of the outer-shelf bedform environment. The vast spatial distribution of bedforms over most of the outer shelf seems comparable with other shelf areas, such as the south African shelf, dominated by the influence of unidirectional oceanic currents. Dune dimensions are lower on the Brazilian shelf, due to their relict character, the geomorphological configuration of the margin, and the scarcity of sand sources. • Outer shelf along the southern Brazilian margin covered by bedforms • Inner-to-middle shelf advection of fine sediments driven by Brazilian Coastal Current • Two scales bedforms (sand ridges and very large dunes) in a relict to moribund stage • Bedform preservation aided by fine-grained winnowing by the Brazil Current, armouring and cementation • Prolific bedform environment comparable with the south African shelf [ABSTRACT FROM AUTHOR]

Marsh creeks are perceived as important conduits for transporting water and sediment between mudflats and marshes. In order to advance the understanding of the transport mechanisms in creeks, the source and ultimate sink of sediment which moves between mudflats and marshes through creek channels need further investigation. Therefore, two field campaigns were conducted in two intertidal systems with varying sediment availability. The water depth, flow velocity, suspended sediment concentration, and bed level change were measured simultaneously in a marsh creek and on the adjacent mudflat in Chongming Island (China) and in Paulina Saltmarsh (the Netherlands). Paulina Saltmarsh is much smaller, more frequently flooded, and has lower sediment concentration than Chongming. These contrasting conditions allow for a comparison of transport mechanisms and functioning of the creek. Both systems first show that the high suspended sediment concentration (SSC) measured in marsh creeks is mainly the consequence of sediment advection rather than local erosion. In addition, erosion in marsh creeks is usually limited during ebb tides, reducing the export of sediment through these creeks. However, differences have been observed between two systems. The measured SSC was highly asymmetric between flood and ebb tides in Chongming. Large peaks in SSC during the flood period can be observed for most tidal cycles. The marsh creeks in Chongming therefore function as conduits for sediment import. Additionally, there are distinct overbank and underbank tides in Chongming. Sediment was trapped and retained in creeks during underbank tides, which can then be eroded and transported to the marsh during subsequent overbank tides. We also observed that mudflats in Chongming quickly recovered after erosion. These mechanisms have not been observed in Paulina Saltmarsh, where net sediment export via the marsh creek was observed due to a lack of abundant sediment in suspension during flood tides. Furthermore, the remaining bed surface of mudflats after an erosion event was stronger than before, limiting further erosion in Paulina Saltmarsh. These findings from the two systems indicate that the role of creeks in sediment import/export depends on the availability of sediment from mudflats, shedding light on nourishment strategies for salt marshes. • High SSC during flood tides in the studied marsh creeks is attributed to advection of sediment rather than local erosion. • Ebb tides were limited in suspended sediment by various mechanisms, reducing the export of sediment via marsh creeks. • Roles of marsh creeks in sediment delivery depend on the sediment supply from mudflats and hydrodynamic forcing in creeks. [ABSTRACT FROM AUTHOR]

Sediment budgeting within a landscape is useful in understanding landscape evolution, and hazard prediction and assessment. It has been observed that only a fraction of the total volume of sediment produced within the system gets exported, implying that a part of the total volume of sediment is stored within the system. This sediment mass gets arrested and stored in compartments within the system and is mobilised during extreme stochastic events. These sediment storage compartments are poorly connected with the channel network and hence, do not supply sediment at steady rates. We have evaluated sediment connectivity and conducted field validation within a 93 km2 mountainous river basin (Pranmati catchment) in the NW Himalayas. This assessment relies on the Index of Connectivity (IC), computed through two methods: one employing the original framework and the C-factor from RUSLE, and the other utilizing a multiple flowpath model that incorporates Manning's roughness coefficient. We developed a storage potential index (SPI) by modifying the basic framework of index of connectivity; SPI indicates the potential of a point on the hillslope to arrest sediment flux and store it. Based on the difference of normalised IC and SPI, we have developed a sediment evacuation susceptibility index (ESI S) that indicates the susceptibility of various parts of the hillslope to get evacuated. Using ESI S , a sediment evacuation susceptibility zonation map was prepared that delineates areas on the basis of their stability. Our study indicates that sediment flux gets arrested at the (1) junction of land use and land cover units that have contrasting sediment transporting capacity, (2) grassland/barren land pockets surrounded by forests, (3) croplands, and (4) landslide debris deposits. The parts of the hillslope in the vicinity of the channel network and areas around steep surfaces are highly susceptible to sediment evacuation. Gentle sloped surfaces away from the channel network are relatively stable. Landslide debris are highly stable units of sediment storage. • Sediment connectivity of a catchment was assessed using index of connectivity (IC). • The IC model was modified to identify potential sediment storage zones (SPI). • Sediment evacuation susceptibility index (ESI S) was formulated using IC and SPI. • Sediment evacuation hazard zonation map was prepared using ESI S. [ABSTRACT FROM AUTHOR]

Beaches are important coastal features that provide vital ecosystem services; however, these systems are threatened by coastal erosion, sea-level rise, and coastal squeeze. Beach nourishments are a commonly applied coastal protection measure to mitigate erosion and flood risks while maintaining or enhancing recreational values. Nourishments vary in scale from mega-nourishments to small-scale nourishments, where the latter has typically been less studied due to the limited resources for monitoring. Meanwhile, with rising sea levels, the implementation of small-scale nourishments is expected to increase, and there is a need for more knowledge about the morphological evolution and technical lifetime of these interventions. In this study, the morphological responses of small-scale beach nourishment (total volume 20,000 m3 which amounts to 30 m3 added per m alongshore) are observed and quantified over various timescales, considering the initial adjustment, long-term development, and event-driven response. The investigated nourishment is implemented in a partly sheltered coastal embayment in the semi-enclosed Baltic Sea, which has a complex interaction between waves and water levels. Furthermore, the beach is surrounded by hard structures, a rock revetment at the back, and a harbor mole and a groin, influencing the longshore and cross-shore sediment transport. The results show that substantial reduction in subaerial volume can be attributed to specific events. In addition, we observed considerable spatial variation in the sediment re-distribution induced by hard structures and variability in the nearshore bathymetry. The lifetime of the beach nourishment is just over two years. The nourished material remains in the system at the end of the lifetime but is not available for beach recovery. Still, the added subaerial volume has eroded at the midsection, and the protective beach width has been reduced, leaving the rock revetment exposed with reduced protection for the hinterland. The energy conditions at the site are highly episodic, which impacts morphological evolution, and observations indicate that the development is event-driven. • Beach morphodynamics in a low-energy coastal embayment • Episodic wave activity and water level variations are influenced by basin effects. • Morphological response of a small-scale beach nourishment at different timescales • Beach nourishment performance during an extreme storm surge [ABSTRACT FROM AUTHOR]

Proglacial areas in the European Alps and other high-elevation mountains are currently undergoing rapid change due to global warming. Because of rising temperatures, glaciers and glacier forefields are subjected to increased melting and associated sediment export. This observation is increasingly important with respect to high-elevation geomorphological and ecological dynamics, emerging natural hazards and mitigation efforts, and hydropower plant management. It is therefore crucial to analyze the factors and feedback mechanisms governing sediment production, transport, and deposition in these rapidly changing areas. In this study, we investigated the sediment dynamics of a proglacial area located in the Eastern Italian Alps over the period 1969–2021 with the aims of: i) identifying the areas of sediment production; ii) quantifying volumes and rates of bedload sediment transport; and iii) determining the relative contribution of glacial export and fluvial erosion to the total sediment budget. We found that i) apart from glaciers, moraines and fluvial channels have been the most important sediment sources, albeit with substantial differences in terms of connectivity and thus supply rates; ii) the volumes and rates of sediment erosion varied by one order of magnitude (between tens and hundreds of mm per year), and were generally higher along the channel network; and iii) for a relatively shorter time interval between 2005 and 2021, the relative contribution of glacial bedload input with respect to the total sediment budget ranged between 34 % and 37 %, whereas 45 % to 59 % was derived from lateral fluvial erosion. Only a relatively small sediment volume was generated by net channel bed incision. These results imply that most of the sediment released from the proglacial area of the Sulden glacier is progressively transferred to the downstream sector of the channel network, with volumes that range between 931 and 1017 tons yr−1 km−2. These values are in the typical range of sediment export volumes from glaciated basins and highlight the high dynamicity of this region of the Alps. In general, our results confirm the complexity – in terms of spatial and temporal variability – of Alpine proglacial systems and highlight the need to systematically study these areas on a wide spatial and temporal scale, since the information provided by single locations or individual sectors of the sediment cascade, may not be adequate for understanding the dynamics acting in the entire proglacial regions. [Display omitted] • Proglacial areas change rapidly and supply sediment to the downstream valleys. • Moraines and channels are the most important sediment sources. • Glacial and fluvial erosion contribute between 35 % and 50 % to the sediment budget. • The proglacial area of the Sulden glacier is dominated by sediment transport. • In the Sulden region, sediment export may increase in the near future. [ABSTRACT FROM AUTHOR]

Concentrated Solar Power (CSP) plants are typically located in gravelly desert (Gobi) regions because of their level, steady land, and abundant sunlight. The Gobi region has many sand sources, and strong winds accelerate aeolian processes, leading to windblown sand and dust at CSP sites. Large-scale CSP plant heliostats and central building clusters affect Gobi surface aerodynamic roughness and flow field characteristics, leading to a distinct aeolian transportation mechanism compared with that of a natural Gobi surface. Field observations from the 100 MW large-scale Gobi central-tower CSP facility in Dunhuang, China, were used to study a typical aeolian transportation event to gain insight into windblown sand and dust movement in CSP plants. The plant experienced a 36 % reduction in wind friction velocity owing to the increased aerodynamic roughness compared to that in the external environment. The facility reduces the minimum wind friction velocity for sand particle initiation to 0.37 m s−1, which is 30 % lower than that over the typical Gobi surfaces, however, sand accumulation between the heliostats resulted in a 1.8 times higher sediment transport quantity than that transported externally. The blown sand mean saltation layer height in the plant was 0.09 m, similar to that of a sandy desert. The plant surface emits dust, causing PM10 levels to increase to 20,000 μg m−3. Large-scale CSP facilities should remove sand build-up and use windblown sand management methods, such as checkerboard sand barriers and sand-blocking fences, to minimize aeolian transport and dust concerns. • The friction wind velocity inside the Gobi CSP plant experiences a 36 % reduction. • The average saltation layer height inside the plant is 0.09 m, like that of a sandy desert. • Sediment transport quantity inside the plant is 1.8 times higher than that outside the plant. • The plant's surface emits dust, causing PM10 levels to rise to 20,000 μg m−3. • Windblown sand management methods are recommended to minimize aeolian transport. [ABSTRACT FROM AUTHOR]

The occurrence of extreme rainfall events over mountain catchments is likely to trigger mass failure processes on hillslopes and sediment transport within the channel network. Understanding the degree of linkage between the sediment sources and transfer pathways downstream is essential in those catchments where settlements are affected by hydro-geomorphic processes, in order to plan suitable interventions for risk mitigation. A recent storm (October 2020) named "Alex", estimated to be an extratropical cyclone with a more than 100-year return period, hit the Mediterranean Alps at the border between Italy and France, triggering deadly landslides and flooding processes. This work focuses on two adjacent mountain catchments located in the Liguria region (Italy) which share the same outlet, where a small village was damaged by high-magnitude sediment transport and deposition processes during the storm. In order to analyze sediment dynamics at the catchment scale leading to severe damage to the urban settlements at the outlet, an integrated approach was used. Very high resolution (0.5 m) satellite imagery was employed to map the mass failure processes on the hillslopes with a visual interpretation. This dataset was then compared with a map of the Index of Connectivity created using the SedInConnect 2.3 software to characterize the pre-event structural connectivity in both catchments. The integration of these two datasets permitted understanding that debris slides evolving into debris flows downstream supplied most of the sediments to the channel network. These processes concentrated mainly in a specific catchment where hillslopes have the highest connectivity with the valley bottom. This outcome provided a clear evidence that inventory maps developed soon after an extreme event, coupled with sediment connectivity datasets, can provide relevant information for future land management and risk mitigation strategies. These can be exploited to prioritize structural interventions in specific areas, to reduce the connectivity or disconnect inhabited areas from the hydro-geomorphic systems and avoid future damage. • We analyzed the geomorphic impact of a storm on two adjacent mountain catchments. • Debris slides turned into debris flows represented the principal sediment sources. • The Index of Connectivity allowed knowing the degree of linkage with valley bottoms. • Part of the mobilized sediments travelled up to the outlet damaging an urban center. • Inventory maps coupled with sediment connectivity represent relevant potentialities. [ABSTRACT FROM AUTHOR]

The morphodynamics of inlets and ebb-tidal deltas often exhibit cyclic behaviour, controlled by wave-tide interactions and the influence of these on sediment-bypassing processes. Variation in the form and timing of inlet dynamics can occur in response to changes in the key sediment transport processes and sediment supply, and particularly the relative dominance of differential wave direction driving alongshore sediment transport. This paper investigates the morphodynamics of the Deben ebb-tidal delta through multivariate analysis of multi-annual bathymetry and metocean parameters covering the period 1991 to 2023. Results show that sediment bypassing and associated morphological change in this ebb-tidal delta follows variable behaviour mid-cycle, leading to change in the morphology and configuration of the ebb-delta from cycle to cycle. In the most recent cycle (since 2003), delta volume followed a stepwise growth driven by sediment influx periods, evident primarily in the updrift shoal, followed by cross-shore redistribution. Interannual variability in wave climate was clustered into four groups that capture the relative balance between the dominant NE and SW forcing. Sediment influx periods are mostly associated with subdued SW and increased NE forcing, but the summer and winter NE wave climate play different roles on the up- and downdrift, and upper and lower components of the ebb-delta system. Tide level has increased in the last 33 years, which is strongly correlated with ebb-delta volume increase. Wave and tide conditions have discrete and independent effects on the ebb-tidal delta, whereas wave-tide interactions do not significantly change these underlying influences. • Differential within-cycle behaviour was found in multidecadal bypassing cycles. • Ebb-tidal delta volume has increased via a stepwise growth. • Sediment influx is related to reduced SW and increased NE wave forcing. • Wave and tide conditions have independent effects on the ebb-tidal delta. [ABSTRACT FROM AUTHOR]

Submarine canyons are primary conduits for turbidity currents transporting terrestrial sediments, nutrients, pollutants and organic carbon to the deep sea. The concavity in the longitudinal profile of these canyons (i.e. the downstream flattening rate along the profiles) influences the transport processes and results in variations in turbidite thickness, impacting the transfer and burial of particles. To better understand the controlling mechanisms of canyon concavity on the distribution of turbidite deposits, here we investigate the variation in sediment accumulation as a function of canyon concavity of 20 different modern submarine canyons, distributed on global continental margins. In order to effectively assess the isolated impact of the concavity of 20 different canyons, a series of two-dimensional, depth-resolved numerical simulations are conducted. Simulation results show that the highly concave profile (e.g. Surveyor and Horizon) tends to concentrate the turbidite deposits mainly at the slope break, while nearly straight profiles (e.g. Amazon and Congo) result in deposition focused at the canyon head. Moderately concave profiles with a smoother canyon floor (e.g. Norfolk-Washington and Mukluk) effectively facilitate the downstream transport of suspended sediments in turbidity currents. Furthermore, smooth and steep upper reaches of canyons commonly contribute to sediment bypass (i.e. Mukluk and Chirikof), while low slope angles lead to deposition at upper reaches (i.e. Bounty and Valencia). At lower reaches, the distribution of turbidite deposits is consistent with the occurrence of hydraulic jumps. Under the influence of different canyon concavities, three types of deposition patterns are inferred in this study, and verified by comparison with observed turbidite deposits on the modern or paleo-canyon floor. This study demonstrates a potential difference in sediment transport efficiency of submarine canyons with different concavities, which has potential consequences for sediment and organic carbon transport through submarine canyons. • The impact of submarine canyon concavity on turbidite deposition was assessed. • Distribution of turbidite deposits varies with changes in canyon concavity. • Three distinct deposition patterns were identified. • The recognized deposition patterns align well with the observed turbidite deposits. [ABSTRACT FROM AUTHOR]

While the impact of the spatio/temporal variability of grain size on morphological beach state is reasonably well understood, relatively little is known on its impact at a scale of days/months on aeolian sediment transport. This study focuses on five short intensive wind events during which aeolian sediment transport measurements, beach surface sampling and elevation change surveys were carried out for 1 to 3 days, over a 16-month period on a microtidal beach dominated by offshore winds. Monthly observations show a high temporal variability in beach grain size in relation to the decoupling between hydrodynamic and aeolian processes, from medium sand after a marine storm and inundation of the beach, to very coarse sand after several weeks of storm-force winds. During each wind event, topographic change on the beach ranged from zero, to 0.55 m. The time scale of coarsening depended on the initial beach grain size and could be very fast when the beach was composed of medium sand (e.g. 388 μm sand changed to coarse sand of 547 μm in 40 h). In contrast, it took one month to transition from a coarse median beach grain size of 883 μm to a very coarse one of 1323 μm. This variability in grain size results in dramatically different rates of sediment flux. For example, during average wind speeds of 10 to 14 m/s the sediment flux when the beach was composed of medium sized sand ranged between 21 and 154 kg/m/h compared to 0.4 to 50 kg/m/h when the beach was composed of coarse and very coarse sized grains. Overall, this study highlights the importance of beach grain size variability on aeolian sediment transport and shows that for similar incident wind and climatic conditions aeolian sediment transport rates vary dramatically. The study demonstrates the importance of taking care when using a constant median grain size in the calculation of long-term aeolian sand transport on beaches with heterogeneous spatial and temporal beach grain size variability. • Transport rates can be ten times greater on medium-sized beach than coarse one. • Offshore wind generate a grain size sorting, the finest sands are exported seaward. • Topographic variations of the beach depends on its grain size and sand supply. • The return of fine sediments depends on marine storms occurrence and intensities. [ABSTRACT FROM AUTHOR]

This research aims to distinguish genetic sedimentary processes building canyon geomorphological patterns and the factors driving different sedimentary activities in two nearby Mediterranean shelf-incised submarine canyons (Carchuna and Motril) that exhibit different degrees of incision on the narrow margin of the northern Alboran Sea. The straight Carchuna Canyon incises the shelf up to 200 m off the coastline and exhibit steep canyon walls featuring narrow terraces, muddy sands with high contents of organic matter along the thalweg, and transported shelf benthic foraminifera in distal settings. The Motril Canyon head is wider and incises the shelf edge, ca. 2 km off the coastline. It exhibits a sinuous morphology and less steep walls, wider terraces, and higher sedimentation rates with muddy sediments along the thalweg. In both canyons, cross-section relief, width, incision, and area decrease downslope, although these parameters increase locally. The downslope variations of geomorphological parameters are attributed to enhanced erosional/depositional processes promoted by tectonically controlled abrupt changes of the axial channel orientation. The degree of shelf incision, the location of the canyon heads in relation with the local sediment sources, and the seasonally variable hydrodynamic regimes determine the different degrees of recent canyon activity. The Motril Canyon is interpreted as a mature system that reflects episodic activity, collecting fine-grained sediments from the nearby Guadalfeo River. The Carchuna Canyon exhibits a youthful developmental stage whose activity is more continuous and involves sediment trapping of littoral cells and continuous downslope sand transport. • Sedimentary processes in canyons are imprinted in their submarine morphology. • The degree of canyon shelf incision determines the amount of sediment capture. • The passive Motril Canyon accumulates sediments supplied by the Guadalfeo River. • Carchuna Canyon is an active system whose canyon head traps littoral cell sediments. • Oceanographic conditions influence the canyon heads as sediment traps or conduits. [ABSTRACT FROM AUTHOR]

Arid ecohydrology relies on sporadic rainfall and flooding to sustain linear river oases, crucial for supporting flora and fauna during the long dry season and drought years. Growing water demands have led to large reservoir constructions, severely impacting the fragile arid ecosystems. We analyse the hydro-geomorphological impacts of the large Neckartal Dam (completed in 2019) on the Fish River oasis based on existing dams, regional studies, field surveys, hydrological data, and modelling. The Neckartal Dam, along with three smaller dams, impounds 80 % of the desert oasis basin (1235 Mm3, 55,870 km2), exceeding the average annual runoff threefold. A gradient of dam-induced changes was identified, varying with distance from the dam wall. Immediate downstream, hydromorphological impacts include channel narrowing (⁓15 %) and reduce mean annual sediment yield (⁓20 %). Also, water distribution losses create chronic low flows, favour for invasive flora and fauna to spread, significantly disrupting the pristine nature of the desert ecosystem. This phenomenon has been observed over a 70 km stretch below the Hardap Dam. This situation is irreversible, as the invasive flora can withstand even large floods. As the distance increases, the dam suppresses low to moderate annual floods and prolongs droughts from months to years or even decades. Based on our flood routing model, only the largest floods (recurrence interval, RI >25 years) can exceed the dam storage, continue downstream, transport sediment and maintain the pool-bar morphology along 245 km of the oasis. The lack of significant flows between major floods means that sediment from smaller, lower arid basins accumulates in the Fish River valley, filling pools and further reducing water availability during dry periods. The Neckartal Dam's impact assessment demonstrates potential changes in arid river systems globally. [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]

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]

A mega-earthquake in a mountainous region can trigger thousands of landslides. Subsequently, these loose co-seismic materials will experience the erosion-transport-sediment process. This process is closely associated with a series of cascading hazards, such as landslides, debris flows and floods. The disturbance and legacy effects of earthquakes have become the focus of attention for post-earthquake reconstruction and disaster mitigation. By combining the modeling of seismic-induced landslide magnitude with an analysis of the coseismic material sediment connectivity and transfer processes, we assessed the impacts of the 2008 Wenchuan earthquake on the mass balance and subsequent geohazard activities. The 2008 Wenchuan earthquake produced 22,785 Mt of deposit storage, 37.9 % of which (∼8636 Mt) is connected to the channels and prone to erosion and transfer by hydrodynamic forces, and the remaining 62.1 % (∼14,149 Mt) was deposited on hillslopes far from the channel network and contributed little to the sediment dynamics. Long-term field observations found a causal relationship between decreasing surface erosion rate and gradual healing of co-seismic deposits due to coarsening by progressive removal of fine grains. We evaluated the residence time of fine-grained (<0.25 mm) landslide materials using the post-earthquake sediment evacuation rate and identified three stages regarding the enhanced erosion and surface mass wasting after the 2008 Wenchuan earthquake, namely, the high activity period (within 40.6 ± 5.4 years), the low activity period (40.6 ± 5.4–107.1 ± 14.2 years), and the steady period (after 107.1 ± 14.2 years). This has important implications for the hazard assessment of landslides and debris flows in understanding and modeling the post-seismic geohazard evolution over multiple timescales. • We explored the control of geological and environmental factors on the magnitude of co-seismic landslides. • A modelling of capturing seismic-shaking patterns derived from earthquake-induced landslides was developed. • We explained how the landslide-channel connectivity regulates post-seismic sediment transport. • we quantified the timescale of the enhanced surface mass wasting related to the 2008 Wenchuan earthquake. [ABSTRACT FROM AUTHOR]

Secondary airflow occurs when the primary flow interacts with obstacles and other roughness elements such as dense vegetation. It is characterised by the deviation of the wind velocity and direction from the primary flow. Secondary airflow is often manifested as a reversing, separation, horseshoe, or deflection vortex flow, which is fully developed where the curvature of the topography changes abruptly, such as near the crest region of an aeolian dune, the edge of an escarpment, or around buildings. Secondary airflow has been proven to be one of the main driving forces for the formation of obstacle-related bedforms, such as echo dunes, climbing dunes, cliff-top dunes, falling dunes, shadow dunes, foredunes, blowouts, and parabolic dunes. Morphologies of these obstacle-related dunes have been extensively investigated, whereas the factors controlling secondary airflow and their effects on sediment erosion, transport, and deposition have been less mentioned. Here, we review the types and characteristics of secondary airflow and the controlling factors of their patterns, such as the shape and spatial alignment of obstacles and the incident flow angle. We also investigate the effects of these controlling factors on the morphodynamics of obstacle-related bedforms. As confirmed by field observations, the wind-blown sand hazards controlled by the secondary airflow are discussed. Finally, we summarize the scales of the secondary airflow, and highlight the possible focus for future investigation. • Secondary airflow has been proven to be one of the main driving forces for the formation of obstacle-related bedforms. • Secondary airflow patterns and occurrence of the associated landforms are scale-dependent. • Secondary airflow is the main driving force for wind-blown sand hazards for desert infrastructures. [ABSTRACT FROM AUTHOR]

The structural controls of sediment connectivity are poorly understood in low-gradient watersheds and stream networks. We developed a field- and modeling-based framework to understand the timescales and thresholds associated with the structural controls of sediment connectivity and continuity in the Inner Bluegrass region of Kentucky, USA. Field reconnaissance was carried out to assess stream morphology and sediment connectivity, which was leveraged to derive instream sediment connectivity indices for 181 pool-riffle sequences in the low-gradient bedrock stream network. Our model framework coupled a probability-based connectivity formulation with the sediment continuity formula to assess sediment transport and connectivity in the stream network. Results indicated that the bedrock system reflects an end-member in which lithology controls longitudinal stream morphology. Specifically, we found that regional morphology controls pool-riffle length scales via bedrock outcrops, which therein controls the timescales of sediment connectivity over multiple hydrologic regimes. The pool to riffle length ratio was found to be 4.6, an order of magnitude greater than the ratio for alluvial systems. The new formulation of the sediment continuity formula coupled with the probability of connectivity framework adequately captured both short-term and long-term continuous dynamics of sediment transport, as indicated by evaluation metrics with measured sediment flux and field reconnaissance. Based on the analysis of 362 riffles and pools, we found that sediment in pools upstream of bedrock outcrop barriers are disconnected 93 % of the time whereas riffles are connected and allow full continuity 99 % of the time. Longitudinal sediment connectivity within the stream network was found to be controlled by both functional connectivity and structural connectivity, which contrasts recent findings describing the controls of sediment connectivity over lateral pathways on hillslopes. • We investigate sediment connectivity with modeling- and field-based frameworks. • Probability of connectivity and sediment continuity equations form our approach. • Field reconnaissance assisted with soft validation of the model. • Pools are primarily disconnected whereas riffles demonstrate frequent connectivity. • Structural watershed properties control pool morphology and connectivity regimes. [ABSTRACT FROM AUTHOR]

Vegetation and biological soil crust (biocrust) cover can have a stabilizing effect on dunes by fixing sediment in-place and increasing surface roughness, thus limiting dune mobility, sediment transport, and erosion. These biological effects influence rates of aeolian activity and thus surficial changes, though variability in wind and sediment supply may obscure these topographic effects. In this study, we compare monthly measures of sediment transport and decadal estimates of dune mobility to repeat topographic changes measured as a net volume change in sediment storage (difference in volume between all positive and negative topographic changes) and total volume change (absolute summed volume of all positive and negative changes) for areas of bare, vegetated, and biocrusted sand within a dunefield with limited sediment supply and unimodal winds. We found that monthly net volume changes normalized by area were similar between bare sand and sand with at least 20 % vegetation cover. However, total volume change was significantly greater for bare sand and correlated with monthly sediment flux estimates (R2 = 0.46), though the relationship was significantly improved by including monthly changes in surface roughness (R2 = 0.8). Longer-term decadal trends in topographic change showed larger total volume changes with the greatest decreases in vegetation canopy cover. Additionally, decadal total volume changes strongly correlated with estimates of dune mobility (R2 = 0.99). We also found that increased total volume changes did not necessarily signal increased net volume changes for all land cover types. Specifically, increases in total volume change for bare sand resulted in near equal or lower net volume changes, as both positive (deposition) and negative (erosion) change increased with sediment transport. Conversely, less mobile land covers, such as biocrust covered sand, increased in erosion without significant increases in total volume change, demonstrating that more stable surfaces might exhibit a larger topographic change imbalance than mobile sediment surfaces under the same conditions. This study highlights the importance of considering multiple measures of topographic change for interpreting sediment mobility, transport, and availability. Additionally, we hypothesize a novel framework for remote sensing-based empirical studies aimed at interpreting aeolian landscape evolution resulting from climate change effects on weather as well as biological controls such as vegetation and biocrusts. • Total and net volume changes demonstrate complexity of partially stable dunefields. • Total volume changes were highest for bare sand, correlating with sand transport. • Biological cover reduced correlations between surface changes and transport. • Net volume changes related to sediment availability but not transport or mobility. [ABSTRACT FROM AUTHOR]

Since the 1950s, Moenkopi Wash, in Arizona, United States, has been transformed from a relatively wide river with little riparian vegetation, to a narrow, heavily vegetated river that is less than half of its former width. We analyzed a ∼95-years-long instantaneous-discharge record, an extensive sediment-transport record, oblique and aerial photographs, historical channel surveys, and historical stage-discharge rating relations to determine the primary mechanisms responsible for this transformation. Frequent, large floods dominated the early part of the discharge record between 1926 and 1940. A dramatic ∼30 % decrease in annual mean discharge, and ∼27 % decrease in the mean of the partial-duration flood series occurred in 1941. This decline did not result in widespread channel change but provided an opportunity for vegetation to establish along the channel margins. Widespread channel narrowing began after a second decline in mean and peak discharge in 1956 at which time the channel banks became heavily vegetated. Between 1952 and 2019, the river channel narrowed by 57–59 %. Approximately 2–4 m of bed aggradation occurred at most study sites. As the channel narrowed and became more vegetated, large floods maintained the narrower channel width but did not cause rewidening. Suspended-sediment transport data illustrate the sediment trapping effects of vegetation that lead to channel narrowing; suspended-sand concentrations decline, thereby indicating sediment deposition, as vegetation becomes progressively inundated during floods. Furthermore, dense channel-margin and floodplain vegetation provide increased roughness, resulting in flood-peak attenuation and alteration of hydrograph shape. Vegetation expansion causes positive feedbacks whereby sediment deposition during floods is exacerbated by the roughness and sediment-trapping effects of vegetation leading to further narrowing. These positive feedbacks have reduced sediment delivery to the Little Colorado River downstream. Channel widening is not likely to occur unless there are very large floods that exceed the erosional threshold of the channel-margin vegetation, or unless large-scale vegetation removal efforts are undertaken. • Vegetation plays a stronger role than hydrology alone in causing channel change. • Channel change was caused by biogeomorphic feedbacks associated with vegetation. • Channel narrowing began as vegetation trapped sediment during a low flow period. • Biogeomorphic feedbacks caused flood attenuation and reduced flood-peak discharge. • Biogeomorphic feedbacks reduced sediment delivery to downstream rivers. [ABSTRACT FROM AUTHOR]

In small headwater channels coupled to hillslopes, episodic supplies of sediment from events like landslides can dominate local channel morphodynamics and impact ecosystem health. In this study we investigate the response of a small mountain stream in British Columbia to a sediment input event that was up to 150 times the volume of sediment transported in an average flood year caused by the upstream installation of a road bridge. Using four years of repeated UAV surveys, bedload tracers, and other field monitoring techniques, we examined the spatial and temporal changes in sediment storage along the reach, identified changes to channel morphology, and characterized the interaction between the channel bed and the supplied sediment. Historical monitoring of the reach allowed for a comparison of the response to nearly 20 years of information about bedload transport and morphologic change. We observed that most of the change within the reach occurred during the first flood after bridge installation. The supplied sediment mostly moved across the bed surface with little interaction, as tracers installed in the bed had lower than expected rates of mobility. A narrow, steep segment of the channel proximal to the bridge installation stored little sediment, whereas a wider, less steep segment further downstream absorbed much of the change. This effect was exacerbated by a logjam that formed during the first flood after bridge installation. Despite the relative magnitude of the sediment transport event, there was little change to the channel pattern, with the added sediment increasing the relief of the already existing morphologic units. This suggests river managers should focus their restoration attention on segments likely to respond to a disturbance and that the pool-riffle channel morphology can persist across a wide range of sediment-supply conditions. [ABSTRACT FROM AUTHOR]

Valley bottom process reset, or the excavation of high surfaces and fill of incised channels combined with large wood addition, is a new method for creating multi-channel river-wetland corridors (also referred to as Stage 0 valley bottoms). Valley bottom process reset seeks to increase lateral flow and sediment connectivity, retain water and sediment, and kickstart geomorphic processes that may sustain aquatic and riparian habitat. This study uses this anthropogenic intervention to examine relationships among wood-induced hydraulic roughness, valley bottom topography, and geomorphic processes such as overbank flow and sediment transport, avulsion, sediment retention, and pool scour. Here, I present a 6-year case study of a two-phase valley bottom process reset along Deer Creek, Oregon. Kickstarting the floodplain reshaping processes required a substantial increase in roughness and hydrologic connectivity. The first phase of construction enhanced hydrologic but not sediment connectivity, failing to kickstart avulsion and floodplain reworking even during a likely 2- to 5-year recurrence interval flood. A second, more intensive phase of construction substantially reduced the threshold discharge necessary for overbank flow and floodplain reworking, as evidenced by the occurrence of these processes after only a <2-year recurrence interval flood. During this flood, a spatially distributed wood lattice rearranged into discrete jams that scoured pools, retained sediment, and drove geomorphically effective overbank flows. While valley bottom regrading likely contributed to these geomorphic effects, the spatial correlation between newly incised floodplain channels and areas of wood aggregation indicates wood's important role in driving floodplain reworking. I derive from these findings a conceptual model that details how wood drove floodplain reworking via two mechanisms: In-channel wood jams backwatered and constricted flow into the floodplain, and small wood jams formed in the floodplain forest further constricted flow through nascent channels to facilitate channel incision. • Valley bottom reset increased lateral hydrologic and sediment connectivity. • Lateral connectivity required substantial roughness and regrading. • Wood drove floodplain reworking by altering in-channel and overbank hydraulics. [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]

Predicting the future behavior of beach and nearshore systems requires an accurate delineation and understanding of coastal cell boundaries, sediment transport pathways, and sediment sources and sinks. Unfortunately, there is a paucity of field datasets on beach and nearshore morphological change that extend fully from the top of the dunes to beyond the depth of closure to enable quantification of the sediment budget. Here, for the first time, we employ a total sediment budget approach, examining a sandy and embayed beach located in the north coast of SW England, to investigate inter- and multi-annual embayment scale sediment dynamics over a 10-year period that includes extreme storm erosion and post-storm recovery. We demonstrate that, despite the deeply embayed nature of the beach, the shoreline orientation roughly parallel to the dominant wave direction and the overwhelmingly cross-shore forcing of the inter-tidal beach volume, the system is neither closed, nor balanced. The very significant net changes in the recorded sediment volume from dune top to depth of closure (−14.5 m ODN), representing a loss of c. 100 m3 m−1 during the extreme storm period and a gain of c. 200 m3 m−1 during the recovery period, indicate that significant sediment transport occurs seaward of the base of the terminating headlands and beyond the morphological depth of closure. The results further indicate that the inter-tidal region is partly uncoupled from the sub-tidal region, with the former region dominated by cross-shore sediment fluxes, whereas the subtidal region is also significantly affected by longshore sediment fluxes. A conceptual model is presented that balances the observed volume changes with inferred fluxes, forced by variations in total and alongshore wave power. This study contradicts the general assumption that when sediment exits the inter-tidal, it rests undisturbed in the sub-tidal, waiting for a period of low-moderate energy to bring it onshore. The large sediment volumetric variations across the lower shoreface (depth of 5–20 m), which are of the same order of magnitude as, but uncorrelated with, those occurring in the inter-tidal region, are suggestive of an energetic longshore transport system across this deeper region. It is possible that this transport system extends along the whole north coast of SW England and this finding may lead to a shift in understanding of sediment budgets along exposed and macrotidal embayments globally. Unlabelled Image • Full sediment budget was produced along an exposed macrotidal embayment and linked to wave forcing. • Inter- and sub-tidal volumes are not inversely correlated, indicating decoupling. • Sediment budget suggests significant exchange around headlands and/or across depth of closure. • Beaches on this coast type can be considered part of an extended coastal cell. [ABSTRACT FROM AUTHOR]

Water erosion on agricultural land and sediment delivery to streams are a major threat to soil productivity and surface water quality. Climate change and different national and international societal drivers now require Denmark to take action to protect soil and water resources. In this study, we adapted the spatially distributed sediment transport model WaTEM using the best data available at national scale. To calibrate and validate the model, sediment yield data from 31 catchments and 189 slope units in Denmark were compared with the model output, which was produced at a fine spatial resolution of 10 × 10 m. Residual analysis and cross-validation were used to identify potential catchment outliers and assess model robustness. We obtained a median Nash & Sutcliffe model efficiency range of 0.06–0.6 for the Danish environment. Based on the equifinality concept, an ensemble of 100, NSE-weighted model realisations for acceptable transport capacity coefficients was used to assess model uncertainty. The comparison between rill survey data and predicted values indicates that although the model captures well the spatial variability in erosion, it may underestimate the long-term average of soil erosion. Based on the modelling, 71% of the agricultural land in Denmark is mapped as stable in terms of the amount of erosion and deposited material. Overall, 6.1% of the farmland is estimated to have unsustainable erosion and 0.9% of the farmland exceeds erosion rates of 7.5 t ha−1 a−1. Sediment export into surface water in Denmark equals 92,000 t a−1, corresponding to an average sediment yield of 2.7 t km−2. The performance of WaTEM is considered satisfactory in this study. Importantly, modelled water erosion exceeds the perceived erosion risk in Denmark. Strengthened by distributed uncertainty assessment at national scale, our study provides an important national knowledge base for engaging land users and regulators in the process of targeted erosion mitigation planning that is required to comply with national and EU regulation. Future investigations concerning the deviation between predicted and observed data and specific catchment parameters for the non-behavioural catchments are required as well as studies that include the establishment of catchment sediment budgets. • High resolution national water erosion modelling for future mitigation planning • Model calibration and validation with 31 nationwide catchments and field surveys • Explicit consideration of model uncertainty [ABSTRACT FROM AUTHOR]

Sediment exchange between the shoreface and the foreshore is investigated through the analysis of sandbar and berm migration cycles at La Misión beach in Baja California, Mexico. In general, nearshore sandbars migrate onshore during low-energy wave conditions merging with the shoreline to become intertidal sandbars that later contribute to berm rebuilding. However, significant alongshore differences were observed in the sandbar welding and berm rebuilding process, which can be attributed to alongshore wave skewness and near-surfzone flow variations. The analysis of topographic and bathymetric surveys collected monthly over a 5-year period revealed larger shoreline retreat and longer recovery times in the southern beach compared to the north. This was related to the inability of sandbars to weld to the intertidal beach during spring and summer, occurring only during extended periods of low-energy waves. In the southern beach, the berm formation process exhibited less dependence on incoming wave energy, persisting during mild-energy winters, and reforming in the presence of sandbars. Hydrodynamic measurements indicated that the southern part of the beach experienced relatively more intense net offshore flows (up to −0.2 ms−1) due to undertow, and possibly related to the presence of persistent rip currents. In contrast, the berm in the northern beach followed a seasonal erosion and rebuilding process associated with sandbar migrations driven by variations in incoming wave energy and cross-shore sediment transport. This was characterized by larger near-bed wave velocity skewness compared to the south. Net flows in the north were predominantly onshore, reaching up to 0.1 ms−1 during lower-energy periods with oblique wave incidence. This study reveals the presence of considerably distinct sandbar and berm migration cycles along a relatively short beach of 2.2 km long. It also highlights how such variability can be related to the morphodynamic feedback with sandbars affecting hydrodynamics, particularly near-bed wave skewness and near-surfzone flow variations, which in turn influence sediment transport and morphological evolution. • Bar merging affects berm rebuilding, influenced by wave skewness and flow variations. • Net onshore flows and higher skewness allow seasonal berm rebuilding. • Net offshore flows and lower skewness kept the bar offshore but the berm recovered. [ABSTRACT FROM AUTHOR]

Shore platforms are generally supply-limited environments and few studies have attempted to measure sediment transport within this rock coast setting. This paper summarises a field-based pilot study that successfully collected fine-grain sediment moving across a sub-horizontal platform at Mudstone Bay, Kaikōura, New Zealand. Two large-aperture and two small-aperture Time-Integrated Mass-sediment Samplers (TIMS) were deployed for 9-days, encompassing 2 days of storm conditions (offshore significant wave heights between 2.0 and 3.6 m, with sediment trapped in both landward and seaward facing directions. The net flux of sediment captured in large aperture samplers was greatest in a seaward-direction (15.2 g), whereas the narrow-mouth samplers, that principally collected suspended sediment had a net onshore flux (5.4 g). The sediment traps yielded sufficient sample to undertake geochemical and textural analysis. Interpretation of these data suggests that the origin of transported material was autochthonous to the platform, being >80 % silt-sized and compositionally consistent with material derived from the shore platform and/or cliff colluvium. This pilot experiment demonstrates that mass-sediment samplers can be used in supply-limited intertidal shore platform settings. Further research involving greater sampling frequency and duration and concomitant detailed hydrodynamic measurements are likely to reveal important insights into the erosion environment. • TIMS can be used on an intertidal shore platform to collect saltating and suspended sediment in bi-directional flow. • Sediment caught in sufficient amounts to conduct provenance and geochemical analysis • Storm conditions were most favourable to collect both saltating and suspended sediment at Kaikōura. [ABSTRACT FROM AUTHOR]

Aeolian sediment transport is an important morphodynamic process that drives geomorphological evolution, affects the climate system, and induces various natural disasters. The creep load involves both particles of a sufficiently large size that cannot be easily lifted to the upper air, as well as smaller particles that can transition between different modes of motion, although the contribution of the latter has rarely been investigated. In this study, we investigate the features of the saltation cycle, namely the time period from the moment a particle is entrained into the air to when the particle is again trapped in the bed, and the transformation mechanism between creep, reptation, and saltation by directly simulating the steady-state sand transport of particles within the saltation regime. The results indicate that a saltation cycle generally contains one to tens of individual hop processes, with the mean and standard deviation of the hop times decreasing with the increasing friction velocity, owing to the presence of more energetic particles at the bed surface. Over half of the transported particles move in creep or reptation model because a moving particle generally experiences frequent transition between creep, reptation, and saltation. Furthermore, the fundamental reason for the change in the mode of motion is the strong impact velocity dependence of the total coefficient of restitution during the rebound process. Current rebound models predict a reasonable coefficient of restitution only if the particle impacts the bed at a moderate velocity; however, their predictions deviate from the actual situation at relatively low or high impact velocities. These findings enhance our understanding of the motion dynamics of particles within wind-blown sand movements, and further reduce the uncertainty in predicting their mass flux in different modes of motion. The rheological bed surface during steady-state sand transport resulted in the coefficient of restitution e t exhibiting three different states under different impact velocity v in regimes: the increment regime (v in < 0.25 ms−1), constant regime (0.25 < v in < 1.0 ms−1), and decrement regime (v in > 1.0 ms−1). Existing models can predict a reasonable e t value only if v in is in the constant regime. [Display omitted] • One saltation cycle contained one to tens of individual hop processes. • The mean coefficient of restitution varies with the impact velocity. • Dramatic changes in e t resulted in the mode of motion of particles to change. [ABSTRACT FROM AUTHOR]

This paper presents geomorphic evidence for the significant role of surface-subsurface connectivity in the geomorphological evolution of tabular hills (mesas) capped by moderately thick sandstone beds. The study area is located in Central Europe, in the Sudetes mountain range (Poland, Czechia), in an area built of a clastic succession of Late Cretaceous age. Research involved analysis of high-resolution LiDAR DTM and its various derivatives, providing insights into characteristics of drainage routes and patterns of ruiniform relief, as well as fieldwork. The latter included landform recognition and mapping, surveying representative cleft and cave systems. Specific surface landforms indicative of drainage diversion underground and subterranean pathways of sand removal include boulder-filled troughs and hollows, open clefts and plazas, pseudo-sinkholes and tilted blocks. Further evidence is provided by abundant, joint-aligned roofed slots and boulder caves, whose origin is attributed to selective sandstone weathering, sand evacuation by groundwater, and gradual subsidence. Sandy cones and sheets below exits of slots and fractures are the complementary sedimentary evidence. The percentage of caprock area drained via subterranean outflow varies from 16 % to 89 %. Reasons for the high efficacy of subterranean water and sediment transport include both structural factors (regular jointing pattern, high porosity) and, very likely, pre-conditioning role of dissolution of cement in the quartz arenites (arenization), which facilitates detachment of individual grains even by low flows under low hydraulic gradient. Thus, the sandstone-capped mesas show numerous analogies to the karst proper, especially silicate karst. They are manifested in both similar landform inventories, main preparatory processes, and considerable surface-subsurface connectivity. • Strong surface-subsurface connectivity in ruiniform relief of sandstone-capped mesas • Inventory of landforms indicative of subterranean erosion in rock cities presented • High-resolution DTMs help to identify closed basins, sinks and concave landforms • Analogies to karst are both morphological and morphogenetic. [ABSTRACT FROM AUTHOR]

Dune dynamics and associated sedimentary fluxes have been estimated over a period of a week in the river Seine characterised by limited sediment supply. Distributed into two corridors, typical medium and small dunes associated with fluvial environments have been characterised from multibeam data acquired on four dates, 23-29 March 2021, after a limited peak flood. Dune morphometric parameters have been quantified on cross-dune 1 m spacing of bed elevation profiles and dune migration rates have been calculated by analysing successive multibeam acquisitions. Evidence of limited sediment supply conditions have been recognised from areas uncovered by mobile sediment in the troughs between medium dunes. Under such conditions, bedload transport associated with dune migration has been estimated using three methods: differential bathymetry, dune tracking and the Van Rijn empirical formula using a correction factor accounting for limited sediment supply conditions. The three methods provide similar bedload fluxes (less than an order of magnitude difference), and the small differences are related to input data uncertainties and the capability of these methods to capture sediment transport processes, such as sediment bypassing dunes. Based on field observations, this paper brings new constrains to the relationships between dune morphological parameters, migration rates and sedimentary fluxes and environmental parameters (sediment grain size, flow velocity and water depth) under limited supply conditions in a real river. • Dune morphologies and shapes are constrained by sediment availability • Limited supply of sediment restricts bedload transport associated with dune migration • Differential bathymetry captures a portion of suspended bedload bypassing dunes [ABSTRACT FROM AUTHOR]

The twin ambits of climate change and coastal development have raised public awareness of shoreline management. Simultaneously, they have highlighted a gap in our understanding of sediment transport and morphodynamic processes at time and space scales appropriate for shoreline management purposes. Here, we analyse an exceptional set of beach surveys gathered over a period of twenty-two years along the Suffolk coast, eastern UK, that extends over approximately 80 km to investigate the meso-scale shoreline variations. The surveys have been made biannually along fixed transects spaced at approximately 1 km intervals as part of a strategic monitoring exercise undertaken by the coastal authorities to assist in shoreline management planning. Changes in beach volume, foreshore slope and shoreline position have been computed to investigate both spatial and temporal changes. The analysis reveals some distinct responses to the physical processes of tides and waves, anthropogenic interventions and geological controls. Neither a clear relationship between the presence of sea defences and beach response nor an ordered regional-scale shoreline movement are evident. Temporal variations in beach volumes and position provide a similarly complex picture with recessionary, accretionary and stable behaviour all apparent within the study site. There is evidence of quasi-cyclic behaviour at some locations as well as a reduction in variability over time-scales beyond approximately five years. • Historic beach surveys over a period of 22 years along a frontage of 80km have been analysed for their meso-scale dynamics. • Meso-scale morphological changes of protected and unprotected beaches have been classified. • The majority of beaches fronting hard defences don't exhibit erosive trends; the majority of those without hard defences do. • Beach morphodynamics are constrained to the synoptic scale, with little coherent variation at the meso-scale. [ABSTRACT FROM AUTHOR]

Sediment transport pathways and resulting erosion-deposition patterns across beach-foredune systems can be complex. Although a great deal is known about the effects of wind fetch, surface moisture, topographic forcing, and vegetation cover, the role of large woody debris (LWD) as a control on sediment redistribution across beaches is relatively understudied. Pieces of LWD act as non-porous roughness elements that induce secondary flow circulation, thereby creating unique sedimentation patterns that differ markedly from those over a flat beach. Large accumulations of LWD collectively have a bulk porosity that provides substantial sand trapping volume, yet, no studies to date have quantified the effect of LWD on aeolian sand transport. Results from a field study on a macrotidal beach on Calvert Island, British Columbia, Canada, show that the LWD matrix alters the character of the turbulent boundary layer in a way that reduces sediment flux by 99%. Sand is trapped within the LWD matrix, thereby interrupting sediment delivery from the nearshore to the foredune. As such, LWD has the potential to modulate rates of foredune recovery, growth, and evolution. The relative importance of this effect depends on the density and arrangement of LWD as a fundamental control on aeolian sediment transport, as well as on the magnitude and frequency of events that erode the beach periodically and re-organize the LWD matrix. • Large woody debris can modulate sand transport and deposition on a beach-dune system. • A large woody debris matrix stopped 99% of sand from reaching the foredune. • Large woody debris matrix density affects how far sand can travel into the matrix. • The large woody debris traps sand in the backshore to be eroded before the foredune. [ABSTRACT FROM AUTHOR]

This study investigates the impact of beach sediment supply on dune volume evolution through data analysis and model simulations of the Kennemer dunes in the Netherlands. A cross-shore sediment transport model (the CS-model) is applied with local time-averaged longshore sediment transport gradients derived from bathymetric and topographic observations. The model is used to study the relative importance of different transport processes on dune volume evolution, assuming that aeolian transport from the beach to the dune is supply-limited. The wave-driven longshore transport gradients are found to explain a large part of the observed variation in the dune evolution within the study area. In accreting parts of the coast, dunes are growing due to sediment supply from longshore transport, whereas in eroding parts, dune growth depends on supply from artificial nourishments. Seasonal constructions on the beach and vegetation removal from the dunes partly impede dune growth along the considered stretch of coast. The model performance is satisfactory, being able to reproduce a considerable part of the large variation in the alongshore dune response observed in the study area. Overall, the results are a promising contribution to the capability of simulating decadal-scale dune evolution, which is important for long-term flood risk assessments and safe designs of nature-based solutions. • Decadal-scale dune volume evolution was successfully simulated with the CS-model. • Long-shore transport gradients and nourishments control dune evolution at this site. • Seasonal beach houses are found to partly impede dune growth. [ABSTRACT FROM AUTHOR]

Patterns of sediment yield have been widely investigated across a variety of scales, but few of these studies have been carried out in urban watersheds. The design of this study represented a unique opportunity to use high-frequency sensor data to compare sediment yields across spatial and temporal scales in an urbanized watershed. Near real-time turbidity and discharge data were collected continuously for four years at five stream gages over three nested spatial scales in the highly impervious 14.2-km2 Dead Run watershed, located in Baltimore County, Maryland, USA. Monthly suspended sediment yields varied by over two orders of magnitude across all stations. Two mid-watershed stations on tributaries to the mainstem of Dead Run are located only about 500 m apart and about 500 m upstream of their confluence, yet displayed observable differences in the timing of their highest sediment yields. Average annual suspended sediment yield was higher at the headwater station with older development (78.2 t/km2/yr) than at the headwater station with more recent development (47.0 t/km2/yr). Average annual yields increased with watershed size from the headwater stations to the mid-watershed stations (87.0 t/km2/yr and 60.4 t/km2/yr). Additionally, yields at the station farthest downstream (81.7 t/km2/yr) were slightly larger than the yield calculated from the sum of both mid-watershed stations (74.6 t/km2/yr), which together represented about 80% of the upstream drainage area. Several additional patterns highlighting spatial heterogeneity of the system were observed. The ratio of sediment yields between the headwater stations increased steadily over time while the runoff ratio remained almost constant. Yields at one mid-watershed station were consistently higher than yields at the other mid-watershed station, despite similarity in runoff totals. Upstream watersheds show year-to-year variation in sediment yield. In contrast, yields at the farthest downstream station show minimal variation. This observation is consistent with the possibility that internal storage and remobilization tend to modulate downstream yields even with spatial and temporal variation in upstream sources. Observable inconsistencies in sediment yields between subwatersheds at monthly time scales suggest that there is a substantial degree of heterogeneity in terms of sediment response to large storm events. Despite significant internal variability, the overall range of sediment yield values at each site was consistent with values reported for multiple urban mid-Atlantic Piedmont watersheds. Comparison with global values indicates that sediment yields from Dead Run are in the same general range as the 25% quartile of urban sediment yields. • Urban sediment data collected from 5 gages at 3 nested scales for 4 years • Temporal patterns of sediment yield differ from temporal patterns of runoff. • Dominant sources of sediment vary spatially in a 14 km2 highly impervious catchment. • Downstream site exhibits lower variation in annual sediment yield than tributaries. • Storage has a substantial role in the sediment dynamics of a small, urban watershed. [ABSTRACT FROM AUTHOR]

Storm surge is a critical component in the evolution of barrier island systems, eroding the shoreface and depositing sediment landward as overwash deposits; this "rollover" process enables barrier islands to migrate landward during periods of rising sea level. However, cyclonic storms may also generate seaward-directed flow and sediment transport, which is not typically accounted for in barrier island modeling. A strong outflow occurred at Port Aransas, Texas during Hurricane Harvey in 2017, as evidenced from field observations, satellite photos, and tide data; modeling indicates that outflow was forced by offshore winds to the left of landfall. To investigate the impact of this event on the barrier system, we collected post-storm multibeam bathymetry data and sediment samples within Aransas Pass and Lydia Ann Channel, important conduits linking the bays to the Gulf of Mexico, and where such data were previously collected in 2009 and 2012. The 2009–2012 comparison provides a baseline against which to ascertain the storm impact contained in the 2012–2017 comparison. Both land- and marine-based evidence indicate that significant erosion accompanied the outflow event, focused at the edges of the Corpus Christi ship channel and Lydia Ann Channel. Large quantities of sand, up to 6.5 m thick, also accumulate in deeps of Aransas Pass and Lydia Ann Channel, presumably as the outflow event waned in strength. We infer that the outflow event transported a large amount of barrier system sands offshore, but do not have sufficient constraints at this time to quantify it. • Hurricane Harvey induced a seaward-directed surge on its left side. • We document loss of inshore sediment, and no overwash deposits in the study region. • Bathymetric data document a major sediment transport event. • Combined evidence suggests net loss of barrier sand to offshore around Port Aransas. [ABSTRACT FROM AUTHOR]

Mangrove forest responses to sea-level rise (SLR) are likely misestimated in many studies because current assessment methods often assume a constant rate of surface elevation change along the intertidal profile. Most studies also neglect the ecogeomorphic feedback process known to accelerate soil building with SLR. Here, an empirical, dynamic model that accounts for the above processes is constructed for the intertidal zone of a mangrove bay in Hainan, China. The model allows us to explore the response of a tide-dominated mangrove forest to different rates of SLR. Rod surface elevation table-marker horizon (RSET-MH) data (2015–2018) indicate rather high rates of surface accretion (13.3–57.9 mm yr−1) and surface elevation changes (7.9–35.5 mm yr−1). Surface accretion and surface elevation change decreased exponentially with increasing ground elevation. Our model showed that SLR (at rates of 4 and 16 mm yr−1) would not lead to the loss of mangrove cover but that it could alter mangrove species zonation along the intertidal profile by 2100 due to a rich sediment supply and ecogeomorphic feedback. Importantly, rapid SLR and landward barriers can pose a considerable threat to the high-intertidal community by causing increased inundation of the high-intertidal zone, subsequent shifts in species zones, and the loss of mangrove biological and structural diversity along the intertidal profile. Overall, this study predicts probabilities of habitat suitability for mangrove species under SLR and expands our current understanding of the impacts of SLR on tide-dominated mangrove forests in sediment-rich systems. Incorporation of extensive, long-term RSET data into this kind of dynamic model could contribute to the better prediction of mangrove responses to SLR at large scales in the future. Unlabelled Image • There is an ecogeomorphic feedback between inundation and sediment accretion. • A dynamic model was established to predict mangrove responses to sea-level rise. • Sediment-rich mangrove forests have a strong resistance to sea-level rise. • Rapid sea-level rise and seawalls would decrease mangrove structural diversity. [ABSTRACT FROM AUTHOR]

Observations of rythmic features along the inner side of the Trabucador barrier beach are coupled to two numerical models to unravel the mechanisms of its formation. The Trabucador is a long (6 Km) narrow (125 m) barrier and microtidal beach at the SW side of the Ebro delta (Catalonia). Its inner side is a low energy beach with a sandy shallow terrace featuring an intricate alongshore rhythmic morphology. Sixteen aerial orthophotos from 1946 to 2014 have been analyzed and complemented with field observations from 1986 to present. This morphology is dynamic but it is usually characterized by: a) long finger transverse bars (LFTB) and b) large scale shoreline undulations (LSSU). The LFTB are thin and elongated with a length of the order of their spacing. They are intertidal and typically attach to the shoreline by a megacusp, commonly opening an anti-clockwise angle of 10°–40° with the shore normal. There can be many, up to 90, with both the mean and the most frequent alongshore spacing in the range 15–25 m. Spectral analysis always shows peaks in this range and sometimes additional peaks in the range 30–65 m that correspond to the spacing between the largest bars with smaller bars in between. The LSSU typically have wavelengths in the range 150–250 m. Their apexes sometimes coincide with the shore attachment of the largest bars but not always. Numerical modelling shows that both features could emerge out of feedbacks between hydrodynamics and morphology during the SW wind events involving a) deflection of the longshore current by the bars combined with the refractive wave focusing and b) gradients in total alongshore sediment transport rate triggering the high-angle wave instability. • A uniqueness system of rhythmic morphology in a low energy beach is observed. • Aerial photos spanning 70 yr are analyzed and complemented with field observations. • The morphology changes over time but the essential characteristics remain. • Transverse sand bars and megacusps with a typical spacing of about 20 m are observed. • Large-scale shoreline undulations of 150–700 m wavelength are also observed. • The system interacts with waves and currents and positive feedbacks probably occur. [ABSTRACT FROM AUTHOR]

Abstract As rivers approach base level, their water and sediment dynamics are affected by a transitional reach known as the backwater zone. At low flows, backwater zones cause flow deceleration and in-channel sedimentation, but at high flows, they cause flow acceleration and erosion. Over many floods, the dynamics of deposition and erosion in the backwater zone are thought to control the locations of avulsions on some large deltaic channels. However, in various studies, the role of the backwater is often inferred or modeled, and directly observed evidence of how backwater affects channel dynamics at avulsion sites remains scarce. In this study, we show how the backwater zone impacts the evolution and avulsion of the Qingshuigou channel, a recent lobe on the Yellow River Delta, using four decades (1976–2015) of data from systematic surveys of water discharge, sediment load, cross-sectional profiles and water surface elevation. The results show that the channel was commonly eroded during flood seasons and aggraded during nonflood seasons. Erosion rates generally decreased in the downstream direction along the lower channel reach during flood seasons, primarily due to downstream channel widening and the subsequent decrease in sediment transport capacity. The erosion rate reached zero at the cross-sections farthest downstream, which is contrary to expectations under hydrodynamic backwater effects, where drawdown causes erosion to increase downstream during high flows. During nonflood seasons, maximum sedimentation occurred upstream of the backwater zone, possibly due to impacts of local topography of meandering bends or constriction from dikes. Morphodynamic backwater accompanied by the deposition and gradual progradation of a mouth bar resulted in downstream increasing sedimentation, superelevation, and lateral migration rates along the lower channel reach from 1985 to 1996. The predicted avulsion location was near cross-sections Q6 or Q7 with an avulsion length of ~20–30 km upstream of the shoreline, which was consistent with those for historical avulsions. We emphasize the close interplay between backwater effects and channel geometry and argue that morphodynamic backwater may play a more important role than hydrodynamic backwater in setting up and triggering avulsions on the Yellow River Delta. Highlights • Backwater effects are strongly influenced by the downstream changes in channel geometry. • Erosion rate decreased downstream along the widening lower reach during high flows. • Sedimentation under morphodynamic backwater effects rendered the channel unstable. • The channel may be more impacted by morphodynamic than hydrodynamic backwater. [ABSTRACT FROM AUTHOR]

Abstract Understanding the morphodynamics of surfzone sandbars is very relevant from a sediment transport perspective. Three complete annual sandbar migration cycles were studied on a single-barred beach. The study period included the 2015–2016 El Niño anomaly and the incidence of a highly energetic swell-storm. The sandbar responded directly to the seasonal wave forcing, thus, it migrated offshore during the energetic winter and onshore during the milder summer conditions. Its seasonal migration cycle comprised four stages: (1) generation in autumn (November) at lower than 1 m depth; (2) offshore migration over the winter (until January/February) while H ¯ s > 1.3 m; (3) onshore migration over the early spring (March and April) while H ¯ s < 1.0 m; and during May–June: (4a) subaerial beach welding (unbarred beach) when a dynamic equilibrium reached; or (4b) terrace-bar formation (sandbar flattening) as a consequence of a lack of a dynamic equilibrium. The energetic El Niño winter conditions induced the same amount of offshore sandbar displacement as the individual extreme swell-storm, placing the sandbar at a maximum cross-shore distance of ~190 m, beyond the dynamic equilibrium. Contrary to the expected, a period of mild wave conditions during the 2017 winter favored the landward migration of the sandbar, locating it near its generation point. The duration of mild wave energy conditions and the offshore sandbar location and volume are considered relevant factors that limit the capabilities of the sandbar to reach shallow waters and weld to the subaerial beach before the summer. Highlights • Sandbar formation, offshore and onshore migration and welding or terrace-bar creation occurs over a year. • Similar offshore sandbar displacement was measured after an individual extreme storm than by the end of El Niño winter. • A period of mild wave conditions in winter favoured onshore sandbar migration up to its generation point. [ABSTRACT FROM AUTHOR]

Abstract The fluvial science community lacks predictive equations for macroturbulence energy and timescales, which may serve useful for predicting sediment transport in rivers. Therefore, we investigated the systematic variation of macroturbulence scales by varying hydraulic parameters in an experimental facility, collecting velocimetry data and measuring macroturbulence scales with spectral analyses, and testing scaling laws for macroturbulence prediction that consider inner variables, outer variables, and turbulence kinetic energy. Experiments spanned across 11 energy gradients and aspect ratio combinations including 116 testing conditions each with 30 minute instantaneous turbulence time-series collected. Results showed velocimetry data and time-average turbulence parameters supported the presence of an equilibrium outer region and coherent double-layer assumed in the experimental design. Macroturbulence and bursting wavenumbers were constant in the outer region when scaled with the flow depth, and were independent of distance above the boundary, aspect ratio, energy gradient, Froude number, or Shields parameter. Data results agreed with the derivation herein and showed macroturbulence energy scales with the streamwise turbulence kinetic energy. Semi-theoretical equations for turbulence kinetic energy scaled macroturbulence energy reasonably well. A novel equation is presented for the macroturbulence period, and the equation's transferability is supported by consistency with past macroturbulence studies, bursting formula, and flow visualization studies. Novel equations are presented for macroturbulence energy, and transferability is supported on theoretical and empirical grounds; however open questions remain regarding a universal function for streamwise turbulence kinetic energy and the net contribution of macroturbulence to total turbulence energy. Results showed the macroturbulence wavenumber required a relatively long duration of data (i.e., 17 min) to stabilize. Results were used to formulate a time scale for minimum measurement length of turbulence data when information about macroturbulence is sought after. We discuss macroturbulence linkages with sediment transport, including, prediction of the sediment carrying capacity via macroturbulence formula as one application to help close the gap between turbulence and fluvial sediment transport. Highlights • The macroturbulence wavenumber is constant when scaled with the flow depth. • Macroturbulence energy scales with the streamwise turbulence kinetic energy • Predictive equations are presented for the macroturbulence period and energy. • Macroturbulence length scales required 17 min of velocimetry data to stabilize. [ABSTRACT FROM AUTHOR]

Abstract 18 months of at least bi-weekly topographic surveys have been conducted on a 700 m stretch of the meso- to macro-tidal Biscarrosse beach, France. Here we focus on the impact of the short-term dynamics of the beach (a few days) on the seasonal winter response of the beach. The beach was surveyed intensively during two winter seasons and the results indicate that despite similar pre-winter morphology but very contrasting energy levels (the first winter season being 1.7 times more energetic than the second winter season), the sediment budgets over the two winter periods were very similar as well as the cross-shore dynamics of the extracted proxies associated with the dune foot and the berm. The data collected suggest that this may be explained by the sequence of erosion/recovery events driven by hydrodynamic conditions (as the water level and energetic conditions), and sediment transport. Thus, during the first winter, post-storm recovery was effectively driven by energetic conditions while during the second winter, inter-storm conditions did not allow the initiation of recovery in between the storms. Apart from the control from wave conditions, the seasonal beach response is also discussed within the framework of storm chronology and tidal range. Highlights • Similar seasonal sediment budget observed under very contrasting seasonal cumulative wave energy • Post-storm initiated beach recovery not automatically interrupted by the following high energetic conditions due to a storm • Inter-storm wave conditions play a crucial role in the winter seasonal response of the beach [ABSTRACT FROM AUTHOR]

Abstract The adjustment of a gravel bed during cycles of sediment storage was analyzed for a flume experiment, designed to study the effects of episodic sediment supply regimes. As the bed aggraded and degraded due to changes in sediment feed, it developed a complex topography with bedforms at different scales (e.g., pebble-clusters, bars). Sediment inputs increased bedload rates and promoted large changes in bed morphology. Without an external supply, the bed armored, which increased bed stability, counteracted bed degradation, and decreased bedload rates. Fully-mobile gravel (2–8 mm) was the only fraction that exhibited a deficit over the experiment. Preferential storage of coarse grains caused the development of a sediment wedge upstream and downstream fining on the bed surface. The storage of sand was also significant (60 % of feed) probably because of infiltration (e.g., in the upstream wedge) and hiding effects promoted by bed armor and structures. Size-selective transport caused a cumulative increase in bed slope, which was likely to affect sediment transport capacity. The large variability in bedload rates for same levels of bed storage indicated that sediment availability and bed state were the main controls on sediment transport regime. We provide empirical evidence that cycles of aggradation and degradation, caused by changes in sediment feed upstream, condition bed composition and topography, and the rate and texture of sediment output. Highlights • Aggradation-degradation cycles condition sediment transport rates. • Partial mobility promotes coarse sediment storage upstream and downstream fining. • Sand storage is significant within lag coarse deposits. • Differences in sediment availability cause hysteresis in bedload rates. [ABSTRACT FROM AUTHOR]

Abstract Megaclast-dominated fluvial systems have been largely ignored by researchers. Yet megaclasts exert an important control on channel geomorphology, flow behaviour and sediment transport, and such systems are probably far more common than this neglect would suggest. Despite the explicit identification of megaclasts as the products of cataclysmic flow, observation of modern fluvial systems confirms that megaclasts can be entrained by flows that lie within the normal flow regime. The pattern of fining along the megaclast-dominated Sabeto River of western Viti Levu, Fiji reveals a strong negative exponential relationship between particle size and distance downstream, and a rate of downstream fining comparable with that of other gravel-bed rivers. The downstream fining pattern is straightforward and step-like discontinuities in the fining gradient are absent. This is suggestive of a sedimentary system only minimally disrupted by the supply of sediment from tributaries or the reworking of material from sources such as hillslopes and alluvial terraces. There is evidence, however, of anomalously coarse sub-populations at two sites. These coarser components must pre-date the other deposits at the sites. We speculate that they represent the products of earlier and higher-magnitude events. The bed sediments may thus be composite features, made up of individual components each transported by a specific event of particular magnitude. Our work confirms the relationship between the rate of downstream fining and particle size. This may arise because the distance over which individual particles are transported is likely to be size dependent. It is also possible that abrasion may be more effective in the case of larger particles than smaller ones, with the result that the coarser fraction of the river's bed sediment fines downstream more rapidly than the finer fraction. There is a long-standing debate about the relative roles of abrasion and sorting in downstream fining. Our data reveal little evidence for a downstream increase in the roundness of the river's gravels, implying that abrasion is likely to play a minor role in the fining process in this system. Highlights • Megaclast-dominated rivers occur widely, but have been largely ignored by researchers. • Megaclasts may be entrained by normal flows and not solely by catastrophic events. • Megaclast downstream-fining rates are comparable with those of other gravel-bed rivers. • There is a close relationship between bed-sediment size and rate of downstream fining. • Bed-sediment assemblages consist of discrete components, each transported by individual events. [ABSTRACT FROM AUTHOR]