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Extreme precipitation events in small alpine catchments trigger hazardous hydro‐geomorphic processes that cause considerable damage to settlements and infrastructure. In summer 2011 and 2017, two flood events mobilizing large amounts of sediments struck the town of Oberwölz (Styria, Austria) located at the outlet of the Schöttlbach catchment. We used data from local weather stations and precipitation radar to analyse the meteorological settings that caused the flooding. We compiled a consistent sediment budget for the 2017 event by combining geomorphic mapping, connectivity analysis, high‐resolution airborne LiDAR (ALS) and uncrewed aerial vehicle (UAV)‐borne LiDAR (ULS), data from other authors for the 2011 event and external information (e.g., event analysis and excavation data). The 2017 event mobilized higher sediment volumes than the 2011 event (131 000 m3 vs 90 000 m3) even though 24‐h precipitation and peak discharges were lower in 2017. First assumptions that the larger sediment output was caused by the reworking of the 2011 flood deposits proved to be incorrect. The impacts of the 2011 event affected the resilience of the geomorphic system resulting in a significantly higher hillslope sediment supply. We conclude that sediment transport in alpine catchments can increase disproportionately when recurrence intervals fall below a critical level. [ABSTRACT FROM AUTHOR]

Sediment budgets are widely used to measure reach‐scale sediment accumulation and evacuation. Such measurements, however, cannot determine when the disturbance is major and the measured sediment mass imbalance is reflective of a river adjusting to a new equilibrium state, as opposed to situations when the disturbance is minor, and the mass imbalance is reflective of a river adjusting within its existing behavioral regime. Sediment sorting among channels and floodplains can have a large effect on how a river responds to a disturbance. Fine sediment may accumulate in the floodplains while coarser sediment erodes from the channel bed. We demonstrate that if a sediment budget does not account for the different behavior and destination of grain sizes, the budget cannot reveal important channel adjustments. In this study, we evaluated how a sand bed river responded to increases in sediment supply by partitioning a sediment budget among silt/clay and five sand fractions. On average, 12 metric tons/meter (downstream)/year of sand was evacuated from the system, but sorting caused channel margins to behave differently from vegetated islands, revealing how a river can slightly narrow while in deficit. Floodplain shaving and bed coarsening evacuated sediment while channel geometry barely changed, consistent with a river adjusting to a minor disturbance within its behavioral regime. This study is an important reminder that sediment mass imbalance does not always lead to channel change. Mechanisms such as floodplain shaving and bed textural change help rivers absorb minor disturbances and resist channel change. Plain Language Summary: Rivers are experiencing increasing human interference, and global warming will significantly impact the amount of water and sediment rivers must convey, placing an even greater need to predict how rivers respond to disturbance. One important problem is predicting the susceptibility of a river to change. While measuring the amount of sediment that accumulates or evacuates from a reach provides clues to how rivers respond to disturbances, such measurements cannot determine whether reach‐average morphology, such as width, depth, slope, and planform, will significantly change or minor adjustments may occur. In this study, we evaluated how a sand bed river responded to an increase in sediment supply that occurred ∼60 years ago using continuous sediment transport measurements and aerial images to measure channel adjustment. We found that, on average, 12 metric tons/meter (downstream)/year of sand was evacuated from the system, but sediment sorting caused channel margins to behave differently from vegetated islands such that the overall channel characteristics barely changed. This study demonstrates that sediment accumulation or evacuation does not always lead to channel change because other processes related to sand sorting can accommodate disturbances, making sand bed rivers more resistant to change. Key Points: A sediment budget must be segregated by grain sizes found in the channel and floodplain to evaluate morphologic changes in sand bed riversChannel adjustment in sand bed rivers is strongly influenced by sand sorting in channel‐floodplain componentsMass imbalance doesn't necessitate channel change: floodplain shaving and bed texture absorb disturbances with minor channel adjustment [ABSTRACT FROM AUTHOR]

Elevated fine sediment accumulation in a river system's gravel bed is known to cause detrimental ecological impacts. Current sediment targets and approaches to mitigation have failed due to the oversimplification of geomorphological processes controlling fine sediment accumulation and the lack of relevant scientific knowledge underpinning them. This is particularly apparent in chalk streams (groundwater‐dominated systems) which regularly exhibit high rates of sediment accumulation despite low suspended sediment yields. A necessary first step is to better characterise their sedimentology; thus, the novelty of this study was to determine the sedimentological characteristics of chalk stream gravel beds, specifically the quantity and distribution of fine sediment with depth. We collated published and unpublished freeze‐core data, encompassing 90 sites across 11 UK chalk streams. Results showed average quantities of fine sediment (<2 mm) in chalk stream gravel beds were 25% by weight, with >75% of beds exceeding thresholds for ecological degradation. Quantities of fine sediment increased with increasing depth into the bed, with an average increase between surface and subsurface layers of 54%, and 89% of the gravel bed over‐saturated with fine sediment. Regional differences were attributed to differences in stream power and local sediment sources, including surficial geology and catchment land use. Additionally, a major contrast was identified between experimental conditions in flume studies used to establish models describing interactions/mechanisms of fine sediment infiltration into immobile gravel beds and the natural conditions observed in chalk streams. As such, the use of such models as a basis to explore sediment management scenarios is unlikely to predict the outcome of such management techniques correctly in a real‐world situation. [ABSTRACT FROM AUTHOR]

This study investigates the upper Magdalena river basin (Colombia), which is characterized by tectonic activity, tropical climate, heterogeneous lithological assemblages, and anthropic influence. It aims to comprehend factors controlling sediment generation, flux, and composition by incorporating petrographic data from 27 recent fluvial samples along with geochemistry, geomorphological parameters, historical precipitation, land cover, landsliding and suspended sediment load data. The analysis shows mismatches between sand composition and drainage lithology distribution. A new set of endmember mixing models is presented, quantifying the impacts of erodibility, sand generation potential (related to lithology), and sediment connectivity between hillslopes and river outlets (related to geomorphology). Results show enhanced sediment generation from sedimentary rocks (up to 40%) due to high erodibility, and decreased sediment flux from low‐ to medium‐grade metamorphic rocks (up to 60%) due to controlling morphometric parameters. Overrepresentation of plutonic and high‐grade metamorphic rocks and underrepresentation of volcanic rocks (up to 100%) are controlled by mineralogical and textural parameters. Enhanced landsliding activity in areas with volcanic activity occasionally overshadows basin‐wide compositional trends driven by morphological and lithological characteristics, as it controls rare overrepresentation of volcanic and low‐grade metamorphic detritus in the sand fraction. Sediment retention by hydroelectric dams significantly decreases suspended sediment flux by 30%, while deforestation plays a minor role in sediment flux. This study underscores the importance of coupling sediment generation, geomorphology and the distribution of stochastic events related to seismic activity in any sediment production‐focused study and for developing numerical models in Quantitative Provenance Analysis (QPA). Plain Language Summary: This study examines what controls the production of sand and its transport in rivers in a region with a tropical climate, earthquakes, different rock types and human interventions in nature: the upper reaches of the Magdalena River in Colombia. Compositional data of river sediment along with various spatial data sets have been used. The analysis shows that rock types do not occur in the same proportions in the sand as they do in the catchment areas. A new mathematical model is presented showing how different rock types and characteristics of the mountain slopes affect sand production and transport. Mobilization of sediment by landslides can significantly alter sand compositions, particularly in areas with active volcanism. Sediment transport in suspension decreased by 30% due to the operation of the hydroelectric Betania dam. This study underscores the importance of carefully considering rock type and geomorphology in any study on sediment production and transport as well as in creating mathematical models in this field. Key Points: Lithological characteristics and hillslope morphometry are the dominant controls on sand generation and flux in the Upper Magdalena ValleyThe distribution of landsliding events locally overshadows lithological and morphometric basin‐wide controls on sand compositionsThe construction of hydroelectric reservoirs decreased suspended sediment flux by 30% [ABSTRACT FROM AUTHOR]

The composition of 27 fluvial silt and clay sediments was used in this study to identify and quantify the processes in the upper valley of the Magdalena river in South Colombia. The combination of seismic activity, intense precipitation, and landsliding resulted in limited chemical weathering and a very efficient transfer of weathered products to the transfer zone of both tributary rivers and the main trunk. Inputs from plutonic, high‐grade metamorphic, volcanic, and low‐ to medium‐grade metamorphic lithologies vary in coarse silt‐sized versus fine silt‐ and clay‐sized sediments, reflecting inherited textural parameters and mineralogy. Plutonic and high‐grade metamorphic rocks mostly produce sand‐sized sediments, up to two times more than coase silt and up to 10 times more than fine silt to clay. The prevalence of siltstone in the area enhances the contribution of sedimentary rocks to fine silt and clay (up to 50% higher than to sand). Volcanic rocks mainly produce coarse silt (up to 2.5 times more than sand). Low‐grade metamorphic detritus is enriched in silt and clay (up to 5–7 times). These findings highlight the critical role of lithology in regulating sediment generation. The study's approach can establish or modify factors modeling lithological control on suspended sediment flux, such as in the BQART equation. Plain Language Summary: This study examines the production of sediment finer than sand (clay and silt) from different rock types in a region with enhanced sediment transfer, tropical climate and earthquakes: the upper reaches of the Magdalena river in Colombia. Compositional data of river sediments were analyzed with statistical methods and subjected to mathematical modeling. Sediment compositions demonstrate that extreme rainfall is able to move sediment produced by landslides before it is significantly modified by environmental influences. Our mathematical models show how bedrock characteristics affect the production of clay, silt and sand. This highlights the need to consider rock type as a crucial control in any sediment production‐related study. The approach presented in this study has the potential to establish or modify correction factors for local or global modeling of sediment production, transport and transfer. Key Points: Textural and compositional signatures of silt‐ and clay‐sized sediment reflect fast sediment removal from the weathering environmentTextural parameters and mineralogical assemblages of drainage lithologies determine differential contributions to sand, silt, and clayLithological characteristics have to be considered as major control in studies focusing on sediment flux and budgets [ABSTRACT FROM AUTHOR]

The geomorphological impact of base-level lowering on ephemeral alluvial streams has been extensively investigated through fieldwork, experimentation, and modeling. Yet, the understanding of hydrological parameters governing the dynamics of the stream's geometry during discrete flood events is lacking due to limited direct measurements of flood-scale erosion/deposition. The emergence of novel remote sensing methods allows for quantifying morphological modifications caused by floods in alluvial streams. This study utilizes drone surveys and hydrological data to quantitatively investigate the relation between channel evolution in alluvial tributaries draining to the receding Dead Sea and the hydrological characteristics of flash floods. Drone-based photogrammetric surveys were conducted before and after 25 floods, over a period of four years, to generate centimeter-scale Digital Elevation Models (DEM) and orthophoto maps of two major streams. The outcomes of these DEMs are maps of ground elevation changes (erosion/deposition), thalweg longitudinal profiles, and channel cross sections, revealing the incision/aggradation along and across the streams. Statistical comparison of results with flow hydrographs identified potential relations linking the hydrological characteristics of each flood and the corresponding geomorphological modifications. Peak discharge emerged as the primary factor influencing sediment removal, leading to more efficient sediment evacuation and a negative sediment budget with increased discharge. Water volumes of floods also exhibited a secondary effect on the sediment budget. The chronological order of floods, whether first or later in the season, was identified as the primary factor determining incision magnitude. Knickpoints formed at the streams' outlets during the dry period, when lake-level drops, amplifying the impact of the first flood. These findings have potential implications for infrastructure planning and environmental management in the context of climate change and altered water runoff. The research highlights the efficiency of drone-based photogrammetry for cost-effective and timely data collection, providing invaluable flexibility for field research. [ABSTRACT FROM AUTHOR]

Coral reef islands are amongst the most vulnerable environments to sea‐level rise (SLR). Recent physical and numerical modeling studies have demonstrated that overwash processes may enable reef islands to keep up with SLR through island accretion. Sediment supply to these islands from the surrounding reef system is critical in understanding their morphodynamic adjustments, but is poorly constrained due to insufficient knowledge about sediment delivery rates. This paper provides the first estimation of sediment delivery rates to coral reef islands. Analysis of topographic and geochronological data from 28 coral reef islands indicates an average rate of sediment delivery of c. 0.1 m3 m−1 yr−1, but with substantial inter‐island variability. Comparison with carbonate sediment production rates from census‐based studies suggests that this represents one quarter of the amount of sediment produced on the reef platform. Results of this study are useful in future modeling studies for predicting morphodynamic adjustments of coral reef islands to SLR. Plain Language Summary: Low‐lying coral reef islands are under threat of sea‐level rise (SLR). However, when these islands are flooded, ocean waves can bring in sediment that can increase the island elevation. This would enable coral reef islands to better withstand flooding in the future. Knowing how much sediment is brought in will help in our understanding of future changes to these islands due to SLR. In this paper, we use data from 28 Indo‐Pacific coral reef islands to compute sediment supply to the islands. We find that on average 0.1 m3 of sediment (roughly 100 kg) is delivered each year for every meter of island shoreline. We further suggest that this implies that only one quarter of the sediments produced by the coral reef system is delivered to the island shoreline. Most of the sediment produced remains on the reef flat or is exported to the ocean or the lagoon. Our results will help future studies to predict more accurately how coral reef islands will adjust to SLR. Key Points: We provide the first estimates of carbonate sediment delivery rates to 28 coral reef islands using all data available from the literatureSediment delivery to the reef islands occurs at a rate of c. 0.1 m3 m−1 yr−1, but with substantial inter‐island variabilityWhere island building has been continuous through island history, long‐term delivery rates provide valuable estimates for contemporary rates [ABSTRACT FROM AUTHOR]

Reservoirs have become an important component in the worldwide river sediment flux. Reservoirs prevent downstream sediment transport and have become a major sediment sink. In this study, sediment deposition during the last 115 years in the Urft Reservoir in western Germany is reconstructed. The Urft Reservoir is the oldest reservoir in the Eifel Mountains and was almost completely drained in 2020. This enabled a detailed mapping of the lake bottom using an unmanned aerial system and the computation of a high‐resolution digital surface model. Topographic maps with a nominal resolution of 1:1000 from the time prior to the construction of the dam (around 1900) were used to construct a pre‐reservoir elevation model. A digital elevation model of difference (DoD) was calculated from these two datasets for the reservoir floor (0.72 km2). Based on the DoD, a net sediment accumulation of 1.16 × 106 m3 was calculated alongside a propagated volume error of 6.91 × 105 m3, resulting in a mean accumulation of 1.54 m. Conservative vertical error propagation results in an average level of detection (LoD) of 1.8 m. In contrast, the comparison of the DoD with 47 cores in the upper part of the reservoir showed a mean difference of −0.11 m, indicating a high, independently assessed accuracy of the DoD. Three depositional hotspots were identified in the reservoir. One is close to the Urft dam where very fine sediments are draped across the pre‐reservoir topography. Two areas are related to reservoir management. Sediment deposition in the Urft Reservoir has been comparably low in comparison to other regions globally, resulting in a 3.25% ± 1.93% loss of reservoir volume between 1905 and 2020. To analyse the effect of strong flooding events, a subset of the reservoir was analysed after an extreme event in July 2021, but accumulation did almost entirely not exceed the LoD. [ABSTRACT FROM AUTHOR]

Introduction: The Holocene mud deposits that extend from the Yangtze River mouth to the Taiwan Strait along the Zhejiang-Fujian coast, East China Sea (ECS), have attracted considerable research attention. However, there is a lack of consensus regarding the redistribution flux of Yangtze River sediment after it enters the sea. There are many bays along the Zhejiang and Fujian coasts, but their role in the source-sink process of Yangtze River sediment is not well-documented owing to limited data. Methods: In this study, data from shallow seismic profiles, core samples, and surface sediment samples were analysed to assess the role of Sanmen Bay, the second largest bay in Zhejiang Province, in the source-sink process of Yangtze River sediments. Results: The results showed that Sanmen Bay is an important sink for Yangtze River sediments. The characteristics of the clay minerals indicate that the finegrained sediments in Sanmen Bay are mainly derived from Yangtze River sediments. The thickness of Holocene deposits in Sanmen Bay ranges from 8.2 to 32.0 m, with an average of 23.4 m and a total sediment volume of 5.06 x 10[sup 4] Mt, accounting for 1% of Yangtze River sediment in this time period. The Bayesian age-depth model based on borehole accelerator mass spectrometry (AMS) [sup 14]C dating shows that a high sedimentation rate occurred in the early and late Holocene but decreased significantly in the mid-Holocene, which is similar to that of the inner shelf of the East China Sea (ECS). Conclusion: The variation in the Holocene sedimentation rate in Sanmen Bay is related to the southward transport process and mechanism of Yangtze River sediments. The results of this study provide a basis for understanding the source-sink process of sediment in large rivers. [ABSTRACT FROM AUTHOR]

Tectonic subsidence on rifted, passive continental margins are largely controlled by patterns of extension and the nature of strain partitioning in the lithosphere. The Sunda Shelf, adjacent to the SW South China Sea, is characterized by deep basins linked to regional Cenozoic extension associated with propagating seafloor spreading caused by slab pull from the south. Analysis of seismic reflection profiles and drilled sections crossing the Nam Con Son and Cuu Long basins highlight Oligocene extension, with most of the thinning concentrated in the ductile mid-lower crust. Upper crustal extension was modest and ductile flow is inferred to be directed northwestwards, towards the oceanic crust. Basin inversion occurred in the Mid Miocene, associated with the collision of the Dangerous Grounds Block and Borneo. Subsequent accelerated tectonic subsidence exceeded predictions from uniform extension models assumed to relate to extensional collapse after inversion. We correlate this to a period of faster erosion onshore driven by strong monsoon rains in Indochina and Peninsular Thailand at that time. Erosion of the onshore basement, inducing rock uplift and coupled with loading of the basins offshore, drives ductile mid-lower crustal flow, likely to the northeast under Indochina, and/or to the west where Plio-Pleistocene subsidence of the shelf is very slow. Significant sediment delivery from the Mekong River into the Cuu Long Basin began in the Late Miocene and migrated seawards as the basin filled. Mass balancing suggests that the basins of this part of the Sunda Shelf are filled through erosion of bedrock sources around the Gulf of Thailand. There is no need for sediment delivery from a major river draining the Tibetan Plateau to account for the deposited volumes. [ABSTRACT FROM AUTHOR]

In this study, a robust non-Newtonian numerical model that can simulate coupled mudflow and sediment transport processes is used to model downstream geomorphic changes during a tailings dam failure. The catastrophic breach of the Mount Polley tailings dam is studied to assess the model performance. Spatial and temporal variation of flow properties like density, viscosity, yield stress, sediment size fractions, and friction are considered in the model. A flexible triangular mesh is adopted, and this helps reduce the computational time significantly compared with structured grid with the same average resolution. High resolution multitemporal digital elevation models (DEMs) are used for the detection of geomorphic changes and estimation of erosion and deposition volumes. The results indicate that the final distribution of tailings deposits obtained from the model results is in good agreement with that obtained from topographic analysis. The model predicted the total volume of erosion and deposition with almost 93% accuracy. The tailings characteristics followed the full Bingham model during the propagation. Different runout scenarios obtained from the mudflow-morphodynamic model and a mudflow fixed-bed model are analyzed, and it was concluded that maximum mudflow depth of the flood wave is higher when bed entrainment is considered. Sediment concentration is higher in the wavefront and middle regions and lower in the tail zone. The mudflow fixed-bed model could underestimate the downstream flood arrival time. The results also confirm that the adopted approach can efficiently model the sediment budget in the study site and the volume of tailings and bed materials released to the downstream lake. Tailings dams are used to store waste solids and water generated during mining operations. Failure of such dams can cause serious damage to human settlements and the downstream environment. For public safety, it is necessary to conduct proper risk assessment, and numerical modeling is crucial for estimating flood magnitude, flood path, and flood arrival time. Tailings water is high in sediment concentration and is viscous; thus, its flow characteristics are different from that of pure water. During the collapse of tailings dam, erosion of the downstream terrain occurs, and changes in the downstream channel morphology can be potentially significant. There can also be a change in the total sediment load when additional solids get eroded from the bed layer. The modeling approach used in this study helps to model erosion and deposition patterns and estimate the downstream flood arrival time when transport of sediment in the downstream channel is considered along with the viscous nature of tailings. When conducting risk assessment of tailings dam failures and when planning for evacuation, this mobile-bed modeling approach can be implemented by design engineers and emergency planners. [ABSTRACT FROM AUTHOR]

The Vu Gia Thu Bon (VGTB) River basin is critical for regional development and prosperity in water resources. However, human interventions (e.g., dam construction and sand mining) have significantly affected this basin's sediment budget and morphological alterations over recent decades. Such humane actions drive an imbalance in water resources in the basin from upstream to downstream. Therefore, this study investigated spatiotemporal changes in sediment budget and morphology alterations using long-term data and bathymetric surveys; from these data, dams and sand mining contributions were quantified and differentiated. Based on field survey data and interviews, we estimated the sand-mining volume by incorporating reported and a newly proposed empirical formula. The results show that the total riverbed incision volume from 2010 to 2021 was 63.30 Mm3, with an incision rate of 0.14 m/yr. The officially reported sand-mining rate was 1.12 Mm3/yr, while the newly proposed empirical formula estimated 4.4 Mm3/yr. According to the developed empirical formula, the percentage reductions in the sediment budget due to sand mining and upstream dams were 69.7 % and 30.3 %, respectively, according to reports, and 17.8 % and 82.2 %. The statistical method was thus likely too conservative compared to the developed empirical formula. We found that the natural sediment supplies sourced from upstream were insufficient to compensate for the mined bed material. Therefore, our combination of different datasets permitted the assessment of future geomorphological developments within the VGTB River basin under the ongoing sediment deficits. The results of this study provide valuable insights into the impacts of human interventions, specifically sand mining, on the sediment budget, morphological alterations, and riverbed incision. The developed assessment forms the foundation for developing and expanding the region's water/sediment resource management strategies.

There are many factors controlling the aeolian sand transport rate on the beach and thus, variation in rates can impact foredune development. This study analyses coastline orientation as one such factor. The research was conducted at two sites on the Łeba Barrier, south Baltic Sea coast, Poland, located 4.2 km apart and which differed in coastline orientation by 20°. Based on wind data the potential aeolian sand transport rate for the period 2006–2017 was calculated. It appeared that taking into account the coastline orientation, the landward sand transport strongly exceeded the seaward and alongshore transport at one site, whereas the other site was dominated by alongshore sand transport. Topographic surveys carried out every 6 months showed that net sand deposition within the foredune at the coast dominated by landward transport was two and a half times greater than at the other site and resulted in significant dune growth.

Abstract Coral reef islands are amongst the most vulnerable environments to sea‐level rise (SLR). Recent physical and numerical modeling studies have demonstrated that overwash processes may enable reef islands to keep up with SLR through island accretion. Sediment supply to these islands from the surrounding reef system is critical in understanding their morphodynamic adjustments, but is poorly constrained due to insufficient knowledge about sediment delivery rates. This paper provides the first estimation of sediment delivery rates to coral reef islands. Analysis of topographic and geochronological data from 28 coral reef islands indicates an average rate of sediment delivery of c. 0.1 m3 m−1 yr−1, but with substantial inter‐island variability. Comparison with carbonate sediment production rates from census‐based studies suggests that this represents one quarter of the amount of sediment produced on the reef platform. Results of this study are useful in future modeling studies for predicting morphodynamic adjustments of coral reef islands to SLR.

Introduction: The Holocene mud deposits that extend from the Yangtze River mouth to the Taiwan Strait along the Zhejiang–Fujian coast, East China Sea (ECS), have attracted considerable research attention. However, there is a lack of consensus regarding the redistribution flux of Yangtze River sediment after it enters the sea. There are many bays along the Zhejiang and Fujian coasts, but their role in the source–sink process of Yangtze River sediment is not well-documented owing to limited data.Methods: In this study, data from shallow seismic profiles, core samples, and surface sediment samples were analysed to assess the role of Sanmen Bay, the second largest bay in Zhejiang Province, in the source–sink process of Yangtze River sediments.Results: The results showed that Sanmen Bay is an important sink for Yangtze River sediments. The characteristics of the clay minerals indicate that the fine-grained sediments in Sanmen Bay are mainly derived from Yangtze River sediments. The thickness of Holocene deposits in Sanmen Bay ranges from 8.2 to 32.0 m, with an average of 23.4 m and a total sediment volume of 5.06 × 104 Mt, accounting for 1% of Yangtze River sediment in this time period. The Bayesian age-depth model based on borehole accelerator mass spectrometry (AMS) 14C dating shows that a high sedimentation rate occurred in the early and late Holocene but decreased significantly in the mid-Holocene, which is similar to that of the inner shelf of the East China Sea (ECS).Conclusion: The variation in the Holocene sedimentation rate in Sanmen Bay is related to the southward transport process and mechanism of Yangtze River sediments. The results of this study provide a basis for understanding the source–sink process of sediment in large rivers.

Sediment mass‐balance analysis provides key constraints on stratigraphic architecture and its controls. We use the data‐rich Middle Jurassic Brent Delta sediment routing system in the proto‐Viking Graben, Northern North Sea, to estimate sediment budgets and mass‐balance between source areas and depositional sinks. Published studies are synthesised to provide an age‐constrained sequence stratigraphic framework, consisting of four previously defined genetic sequences (J22, J24, J26, J32). Genetic sequence J32 (3.9 Myr) records transverse progradation of basin‐margin deltas, sourced from the Shetland Platform to the west and Norwegian Landmass to the east. Genetic sequences J24 (1.1 Myr) and J26 (0.9 Myr) record the rapid progradation and subsequent aggradation of the Brent Delta along the basin axis, sourced from the uplifted Mid‐North Sea High to the south, and the western and eastern source regions. Genetic sequence J32 (2.2 Myr) records the retreat of the Brent Delta. Sediment budgets for the four genetic sequences are estimated using palaeogeographical reconstructions, isopach maps, and sedimentological analysis of core and well‐log data. The estimated net‐depositional sediment budget for the mapped Brent Delta system is 2.0–2.8 Mt/year. Temporal variations in net‐depositional sediment budget were driven by changes in tectonic boundary conditions, such as the onset of uplift before the deposition of genetic sequence J24. Over the same time period, the Shetland Platform, Norwegian Landmass and Mid‐North Sea High source regions are estimated to have supplied 2.3–5.6, 5.0–14.1, and 2.8–9.4 Mt/year of sediment, respectively, using the BQART sediment load model and independent geometrical reconstruction of eroded volumes, which are constrained by isostatic uplift estimates based on the geochemistry of syn‐depositional volcanic rocks. The net‐depositional sediment budget in the sink is an order‐of‐magnitude smaller than the total sediment budget supplied by the source regions (13.9–23 Mt/year). This discrepancy suggests that along‐shore transport by wave‐generated currents into the coeval Faroe‐Shetland Basin and/or down‐dip transport by gravity flows into the coeval western Møre Basin played a key role in redistributing sediments away from the Brent Delta system. [ABSTRACT FROM AUTHOR]

This work proposes a methodological approach applied to ephemeral gravel-bed streams to verify the change in the magnitude and frequency of hydrological events affecting the morphological dynamics and sediment budget in this type of channel. For the case study, the Azohía Rambla, located in southeastern Spain, was chosen, emphasizing the research on two reference riverbed sections (RCRs): an upper one, with a predominance of erosion, and a middle one, where processes of incision, transport, and deposition were involved. First, this approach focuses on relationships between peak discharges and sediment budgets during the period 2018–2022. For this purpose, water level measurements from pressure sensors, a One-Dimensional Hydrodynamic model, and findings from comparative analyses of high-resolution differential digital elevation models (HRDEM of Difference-HRDoD) based on SfM-MVS and LiDAR datasets were used. In a second phase, the GeoWEPP model was applied to the period 1996–2022 in order to simulate runoff and sediment yield at the event scale for the watersheds draining into both RCRs. During the calibration phase, a sensitivity analysis was carried out to detect the most influential parameters in the model and confirm its capacity to simulate peak flow and sediment delivery in the area described above. Values of NS (Nash–Sutcliffe efficiency) and PBIAS (percent bias) equal to 0.86 and 7.81%, respectively, were found in the calibration period, while these indices were 0.81 and −4.1% in the validation period. Finally, different event class patterns (ECPs) were established for the monitoring period (2018–2022), according to flow stage and morphological channel adjustments (overtopping, bankfull and sub-bankfull, and half-sub-bankfull), and then retrospectively extrapolated to stages of the prior simulated period (1996–2018) from their typical sequences (PECPs). The results revealed a significant increase in the number of events and PECPs leading to lower bed incision rates and higher vertical accretion, which denotes a progressive increase in bed armoring and bank erosion processes. [ABSTRACT FROM AUTHOR]

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Deltas are densely populated industrialized regions, and home to important ports and navigation channels. Due to human interferences, the Yangtze Estuary has experienced a significant reduction in sediment load caused by the Three Gorges Dam (TGD), as well as adjustment to local morphodynamics by the Deep-water Navigation Channel (DNC). While the dramatic reduction in sediment triggers the increased channel erosion, the deposition flux of the DNC located at the estuary mouth has little change. To explore the physical mechanism of this phenomenon, a two-dimensional model is used to establish the relationship between sediment load and the sediment budget of channels based on the bathymetry in 2016. Model results show that the tidal reach and the inner estuary have a negative sediment budget. And the seasonal characteristics of water and sediment fluxes become less obvious downstream. Sensitivity analysis shows that the influence of upstream sediment load on deposition flux decreases along the channel, with a transition from deposition to erosion occurring in the tidal reach. For the last-level bifurcation, the annual siltation of sediment in the North Passage (NP) decreases by 4.5% with low sensitivity. This is attributed to the reduction of sediment load partially mitigated by riverbed erosion and cascade bifurcations. In addition, the lateral sediment supply, which accounts for 68% of the sediment input in the NP, is stable. Overall, this study strengthens the understanding of the relationship between sediment load and artificially deepened systems, thus allowing for better management of estuarine sediment and navigation channel. [ABSTRACT FROM AUTHOR]

As sediments carried by rivers enter coastal waters, fine particles can reduce the amount of light that reaches the reef through light attenuation. The Fitzroy Estuary - Keppel Bay (FE-KB), being the second-largest source of sediments to the Great Barrier Reef (GBR) poses a significant threat to the GBR ecosystem such as coral reefs and seagrass meadows, and biogeochemical cycles that influence water clarity. While monitoring and modelling capabilities for catchment and marine settings are now well-developed and operational, a remaining key gap is to better understand and model the transport, dynamics and fate of catchment derived material through tidally influenced sections of rivers that discharge into the GBR. This study aims to reveal sediment transport in the FE-KB estuary by continuously monitoring the seasonal variability over a year-long period and build a high-resolution model to predict sediment budgets under different scenarios of physical forcing and river conditions. Multiple data sources, including field surveys, historical data, and numerical modelling were used to obtain a detailed understanding of the sediment transport processes during wet (high river flow) and dry (low-to-no river flow) seasons. The use of high-resolution bathymetry and survey data for sediment model parameterization allowed for accurate mapping of the morphological changes, while numerical modeling provided insights into the hydrodynamic and sediment transport processes in the estuary. Observation and model data confirm the existence of a Turbidity Maximum Zone (TMZ) in the FE-KB (approximately 35 – 40 km from estuary head), where the topography plays a critical role in trapping sediments. By utilizing the model, a closed sediment budget was calculated under varying flow conditions and the results were used to determine the estuarine trapping coefficient that ranges from 28% (during extreme wet condition) to 100% (during dry condition) of the total catchment loads. Morphodynamic modelling demonstrated a persistent erosion pattern in the upper reach of the FE. The lower FE and southern tidal creeks serve as a large sediment storage basin during both wet and dry seasons, and sediment is exported and deposited offshore during high river flow conditions.

Chan, M.C., 2023. Sizing a small tidal inlet for restoration. Journal of Coastal Research, 39(4), 610–624. Charlotte (North Carolina), ISSN 0749-0208. Coastal inlets located on active shorelines can be vulnerable to shoaling and closure. It is not uncommon for some of these inlets to fall under the category of small tidal inlets with cross-sectional areas <100 m2 and to be transitional in stability characteristics such that neither the classic large-inlet O'Brien-Jarrett equilibrium formulas nor the small-inlet Byrne stability criteria apply fully. The Flax Pond inlet, a dual-jettied small inlet located on the south shore of Long Island Sound, New York, is an example of this class of inlets. The inlet, which connects Flax Pond, a degraded tidal marsh embayment, to Long Island Sound, was analyzed to support a proposed plan to reconstruct the twin jetties and restore the pond's tidal prism to its conditions in the early 1970s to prevent further loss of wetland and ecosystem diversity. The lack of directly suitable stability criteria presented a challenge because an extrapolative use of unsuitable criteria could entail unacceptable risks. The issue necessitated a comprehensive, process-driven analysis of the littoral and inlet conditions to frame a solution. An approach involving multiple stability criteria was followed to determine the inlet dimensions needed to achieve the restoration objectives. It was demonstrated that, with a process-based understanding and informed assumptions, a transitional small inlet can be sized with reasonable confidence. [ABSTRACT FROM AUTHOR]

Alpine mass wasting events have impacts that extend past their headwater origins, sometimes reaching populated lowlands. Understanding the processes driving these sediment pulses, and how they contribute to basin‐scale sediment fluxes, is important for hazard assessment and aquatic habitat management. The Suiattle River, which drains Glacier Peak stratovolcano in Washington State, is a dominant contributor of suspended sediment in the region. Normalized for drainage area, it supplies more suspended sediment than nearly any other river in the area and more than twice as much as the White Chuck River, which drains the opposite flank of the volcano. Despite its importance to the regional sediment budget, geomorphic processes in the basin have received relatively little attention in the literature. In this study, we build on previous work to explore the magnitude, timing and triggering mechanisms of sediment loading events in the basin. We find that outburst flood‐triggered debris flows from Chocolate Glacier are of widely varying magnitude and coincide with high temperatures in the late summer. Major debris flow activity initiated in the late 1930s, with at least eight valley‐filling debris flows since then. Smaller, more recent debris flows, likely also driven by outburst floods, occur in five of seven years of complete data. In total, the small debris flows and the subsequent autumn flushing events explain ~21% of the 'anomalous' sediment load in the basin, while reworking and abrasion of the historic events may explain another ~26%. We speculate that some of the remaining unexplained 'anomalous' load could be the result of a feedback between channel lateral instability (originally triggered by the valley‐spanning debris flows) and bluff erosion. [ABSTRACT FROM AUTHOR]

While connectivity studies are becoming common in the Earth sciences, disconnectivity has received much less attention. Sediment storage is the direct result of sediment disconnectivity and can provide concrete evidence of the spatial patterns of disconnectivity at the catchment‐scale. In this study, we explore the catchment‐scale sediment dynamics of the Tahoma Creek watershed, a high‐gradient glacio‐volcanic landscape, within a sediment budget framework and identify and map sources of disconnectivity to determine whether they explain the spatial patterns and estimated efficiencies of sediment transfers. We found that up to 80% of the total eroded sediment is sourced from the proglacial zone. The proglacial zone is characterized by high connectivity resulting from frequent debris flows and floods, and rapidly responds to changing conditions. Down valley, however, sources of disconnectivity become increasingly more prevalent, the hillslopes become decoupled from the channel, and a majority of the eroded sediment is redeposited with as little as ∼15% reaching the outlet. The spatial distribution of sources of disconnectivity and their upslope affected areas explains, to a large degree, catchment‐scale sediment dynamics and sediment transfer efficiencies and is in close agreement with quantitative connectivity estimates. We find that steep, glaciated watersheds are predominantly disconnected over human timescales and suggest that disconnectivity is the dominant state of landscapes over most timescales of interest. Mapping sources of disconnectivity provides a straightforward and concrete approach to estimating system disconnectivity and can increase confidence when paired with quantitative indices. Plain Language Summary: Mountain watersheds supply freshwater and sediment to downstream river systems affecting flooding, fish habitat, and water quality. We argue that understanding the spatial and temporal patterns of sediment movement within a landscape requires knowing where and for how long sediment is stored and the overall efficiency of sediment transfer between different parts of the landscape. We illustrate the importance and utility of mapping landforms and landscape characteristics that delay or disrupt sediment movement using the Tahoma Creek watershed as an example. This watershed drains a portion of Mount Rainier, a volcano shaped by glaciers in Washington, USA, and is incredibly dynamic. We find that landforms and landscape characteristics that limit sediment movement are common and that mapping them gives an accurate picture of sediment movement patterns. Glaciers dramatically reshape the landscape, which controls sediment supply and movement patterns, and their legacy remains for thousands of years after they retreat. We also make use of high‐resolution elevation data representing the land surface in 2002, 2008, and 2012 to quantify how much erosion, transport, and deposition occurred and how efficiently sediment was transported. We find that sediment is transported more efficiently during extreme events, such as the 2006 floods. Key Points: Disconnectivity is the dominant but inefficient state of a system in transferring matter and energy within and between system componentsSources of disconnectivity were found to accurately explain catchment‐scale sediment dynamicsDuring extreme events, the efficiency of sediment transfer increases, resulting in rapid adjustment [ABSTRACT FROM AUTHOR]

Reduction in river discharge and sediment load has left deltaic lobes in the world's many river deltas starving, but knowledge of how the subaqueous topography of these abandoned subdeltas responds to environmental changes is limited. In this study, we aimed to determine the long-term dynamics of the subaqueous seabed of abandoned delta lobes to advance current knowledge. As a case study, we selected an abandoned subdelta on the Yellow River Delta of the Bohai Sea, China, for which three-decade long (1984–2017) bathymetric data and long-term river discharge and sediment load records are available. We analyzed the seafloor surface change and quantified the void space from the sea water surface to the seafloor. In addition, we surveyed the seafloor surface with an M80 unmanned surface vehicle carrying a multibeam echo sounder system (MBES) in 2019 to obtain high-resolution microtopography information. We found that a net volume of 5.3 × 108 m3 of sediment was eroded from the study seabed within an area of 3.6 × 108 m2 during 1984–2017. This volumetric quantity is equivalent to 6.89 billion metric tons of sediment, assuming a bulk density of 1.3 t/m3 for the seabed sediment. The seabed erosion from 0 to −5 m, from −5 to −10 m, and below −10 m has showed a similar increasing trend over the past 33 years. These findings suggest that seabed erosion in this abandoned subdelta will very likely continue, and that other abandoned delta lobes in the world may have been experiencing similar seabed erosion due to the interruption of the sediment supply and sea level rise. It is not clear if the seabed erosion of abandoned delta lobes would have any effect on the stability of the coastal shoreline and continental shelf. [ABSTRACT FROM AUTHOR]

Kim, Y.-j. and Yoon, J.-s., 2023. Shoreline variation prediction of the Jeongdongjin Sea area considering effective sediment volumes. Journal of Coastal Research, 39(1), 154–166. Charlotte (North Carolina), ISSN 0749-0208. The coastal erosion in the East Sea region of Korea has been increasing because of the imbalance in the effective sediment volume and sediment transport from coasts and rivers, which causes intermittent erosion and sedimentation. The accurate prediction of the coastal sediment budget is an extremely difficult task because the sediment transport mechanism on the coast is highly complex. Studies considering the effective sediment volume supplied through rivers remain limited, although many other studies have focused on identifying the characteristics of sediment transport on the east coast. The grain-size distribution of the soil on the coast is considered the single-grain size (D50); however, the grain-size distribution of sediments flowing into and out of the coast and the topographical characteristics of the sea area need to be considered to predict shoreline variation with a high degree of accuracy. Thus, this study conducts in-depth analysis on the changing state of soil movement in wave-current co-existing fields (mountain, river, and coastal areas). The objective is to predict shoreline variation considering the environment of the Jeongdongjin Sea area by establishing a quantitative evaluation system of the effective sediment volume discharged from the area of river mouth bars. An effective sediment volume was evaluated using a sediment runoff model; the wave transformation for each survey line was calculated using SWAN to consider the wave characteristics acting on the sea area. The prediction performance was greatly improved by applying the mixed grain size to the soil in the sea area and by applying jetties to the reefs for upgrading the prediction of the shoreline variation. [ABSTRACT FROM AUTHOR]

In the Western Scheldt estuary, like in many estuaries, safe navigation, flood protection, and ecological targets require a balanced and sustainable sediment management. A thorough understanding of the morphodynamic functioning of the estuary and its response to changes in hydrodynamics (natural sediment transport) and large-scale interventions is imperative. This paper presents a detailed overview of over 65 years of morphological changes and a comprehensive sediment budget of the Western Scheldt estuary that is based on analysis of a unique series of frequent bathymetric surveys and historical data on human-sediment interactions of dredging, dredge disposal and sand mining. Solving the sediment budget reveals an annual sediment import of 2.2 million m³. The highest sediment imports occurred between 1980-1994 and 2005-2020 (2.9 and 3.7 million m³/year). A 1.3 million m³/year net export prevailed between 1994 and 2005. Natural variations in the hydrodynamics (e.g., tidal asymmetry and amplification) and sediment transports cannot explain the derived temporal variations in sediment import rates. Anthropogenic activities play a dominant role. Capital dredging of the main navigation channel has led to channel deepening and significantly increased dredge and disposal volumes. Disposal on tidal flats and in the secondary channel leads to a long-term storage of sand and, consequently, a local increase in bed level and a sand deficit in the remainder of the system that results in increased sediment imports. Large-scale disposal in the western part of the estuary can (temporarily) reverse the sediment exchange between the estuary and its mouth area, as observed between 1994 and 2005. Apparently, largescale anthropogenic reallocation of sediment by dredging and/or disposal as part of navigation channel improvement, sand mining or nourishment essentially influences the morphological development of theWestern Scheldt estuary. This reveals responsibilities as well as opportunities of sediment management for the Western Scheldt and similar estuaries worldwide. [ABSTRACT FROM AUTHOR]

In the Western Scheldt estuary, like in many estuaries, safe navigation, flood protection, and ecological targets require a balanced and sustainable sediment management. A thorough understanding of the morphodynamic functioning of the estuary and its response to changes in hydrodynamics (natural sediment transport) and large-scale interventions is imperative. This paper presents a detailed overview of over 65 years of morphological changes and a comprehensive sediment budget of the Western Scheldt estuary that is based on analysis of a unique series of frequent bathymetric surveys and historical data on human–sediment interactions of dredging, dredge disposal and sand mining. Solving the sediment budget reveals an annual sediment import of 2.2 million m3. The highest sediment imports occurred between 1980–1994 and 2005–2020 (2.9 and 3.7 million m3/year). A 1.3 million m3/year net export prevailed between 1994 and 2005. Natural variations in the hydrodynamics (e.g., tidal asymmetry and amplification) and sediment transports cannot explain the derived temporal variations in sediment import rates. Anthropogenic activities play a dominant role. Capital dredging of the main navigation channel has led to channel deepening and significantly increased dredge and disposal volumes. Disposal on tidal flats and in the secondary channel leads to a long-term storage of sand and, consequently, a local increase in bed level and a sand deficit in the remainder of the system that results in increased sediment imports. Large-scale disposal in the western part of the estuary can (temporarily) reverse the sediment exchange between the estuary and its mouth area, as observed between 1994 and 2005. Apparently, large-scale anthropogenic reallocation of sediment by dredging and/or disposal as part of navigation channel improvement, sand mining or nourishment essentially influences the morphological development of the Western Scheldt estuary. This reveals responsibilities as well as opportunities of sediment management for the Western Scheldt and similar estuaries worldwide.

Excessive sediment runoff as a result of anthropogenic activities is a major concern for watershed ecologic health. This study sought to determine the sources, storage, and delivery of sediment using a sediment budget approach for the predominantly pasture and forested Smith Creek watershed, Virginia United States, a tributary to the Chesapeake Bay. Utilizing a novel combination of the Universal Soil Loss Equation (USLE) model and an index of connectivity along with field surveys of channels, this study indicated that streambanks and pastures were major sources of sediment. Overestimation of fine‐grained sediment flux exported from the watershed according to this study's models (3811 Mg/year) compared to export measured at the outlet (2918 Mg/year) most likely indicates underestimation of storage in the watershed from unaccounted for geomorphic features (ponds, toe slopes, and colluvial slopes). Sediment budget results indicating that streambanks are a major source of sediment in the watershed support previous sediment fingerprinting results and provide a framework for managers to address the sediment problem in Smith Creek and similar tributaries to the Chesapeake Bay. [ABSTRACT FROM AUTHOR]

Lena River is one of the largest "pristine" undammed river systems in the World. In the middle and low (including delta) 1500 km course of the Lena main stem river forms complex anabranching patterns which are affected by continuous permafrost, degradation of the frozen ground and changes in vegetation (taiga and tundra). This study provides a high-resolution assessment of sediment behavior along this reach. Comprehensive hydrological field studies along the anabranching channel located in the middle, low and delta courses of the Lena River were performed from 2016 to 2022 including acoustic Doppler current profiler (ADCP) discharge measurements and sediment transport estimates by gravimetric analyses of sediment concentration data and surrogate measurements (optical by turbidity meters and acoustic by ADCP techniques). These data were used to construct regional relationships between suspended sediment concentrations (SSC, mg/L), turbidity (T, NTU) and backscatter intensity (BI, dB) values applicable for the conditions of the Lena River. Further, field data sets were used to calibrate the seasonal relationships between Landsat reflectance intensities and field surface sediment concentration data. Robust empirical models were derived between the field surface sediment concentration and surface reflectance data for various hydrological seasons. Based on the integration of in situ monitoring and remote sensing data we revealed significant discrepancies in the spatial and seasonal patterns of the suspended sediment transport between various anabranching reaches of the river system. In the middle course of the Lena River, due to inundation of vegetated banks and islands, a downward decrease in sediment concentrations is observed along the anabranching channel during peak flows. Bed and lateral scour during low water seasons effects average increase in sediment load along the anabranching channels, even though a significant (up to 30%) decline in SSC occurs within the particular reaches of the main channel. Deposition patterns are typical for the secondary channels. The anabranching channel that was influenced by the largest tributaries (Aldan and Viluy) is characterized by the sediment plumes which dominate the spatial and temporal sediment distribution. Finally, in the distributary system of the Lena delta, sediment transport is mostly increased downwards, predominantly under higher discharges and along main distributary channels due to permafrost-dominated bank degradation. [ABSTRACT FROM AUTHOR]

The study examines the shoreline (1990–2019) and nearshore morphological changes (seasonal) to understand the littoral drift and sediment budget variability. Shoreline change rate depicts erosion (− 0.06 m/year) in the northern sector and accretion (+ 0.12 m/year) in the southern sector. Seasonal nearshore morphological changes from non-monsoon to monsoon period signifies net erosion (− 1.8 × 104 m3) in northern sector and net accretion (+ 2.5 × 104 m3) in the southern sector. Although the lost sediment during monsoon is regained in non-monsoon period, the quantity of sediment gain is reduced in areas with human interventions. The results of the investigation depict the dominance of littoral drift towards north from February to October, when wave approach from east-southeast to south-southeast direction and southwards from November to January when the wave direction was from east-northeast to east-southeast. The net longshore sediment transport rate estimated during the study period was 2.6 × 105 m3/year in the northern sector and 1.5 × 105 m3/year in the southern sector with higher rate attributed to monsoon than the non-monsoon. Sediment budget results in deciphering the causes of erosion (− 1.27 × 104 m3/year) in northern sector and accretion (3.91 × 104 m3/year) in southern sector in the wave-dominated Chennai beach. [ABSTRACT FROM AUTHOR]

Historically it has been assumed that abiotic forces dominate fluvial sediment dynamics. However, a growing body of work indicates that biological energy can also exert a significant control over sediment dynamics. The role that invasive species may play in altering fine sediment dynamics is particularly pertinent given that any influence may disrupt the natural equilibrium of the ecosystem. Here we investigated the effect of invasive signal crayfish (Pacisfastcus leniusculus) on the transport and storage of fine sediment in a densely populated river compared with a nearby control river without crayfish, over an 18‐week period. We observed clear evidence of diurnal fluctuations in turbidity associated with crayfish presence including periodograms with power peaks at a period of 1 day. Fine sediment fluxes indicated that crayfish contributed on average 18.5% extra to baseflow loads than would be likely under abiotic forcing alone. Temporal variations in suspended sediment concentrations were also observed at the control site but these were different in character and exhibited no clear temporal pattern or consistency as confirmed by periodogram analysis. Crayfish did not have an effect on sediment ingress rates relative to the control site and, at the crayfish site, the reach scale sediment budget was in net equilibrium during the sampling period. Our results provide further evidence that biological energy alters riverine fine sediment dynamics and warrants consideration in sediment dynamic models. [ABSTRACT FROM AUTHOR]

• About 70% of eroded sediments remains stored within the catchment. • Initiation of soil erosion from the Neolithic and acceleration over the last 3 millennia. • A long gap is observed between the forest clearance, soil erosion and the acceleration of alluvial filling. • Alluvial sedimentation rate indicate changes in efficiency of the connectivity rather soil erosion intensity. • A sediment budget is needed to evaluate the significance of soil erosion. To contribute to the understanding of Holocene sediment dynamics in Western Europe, a Holocene sediment budget is proposed for the Thue and Mue catchments (52 and 97 km2 respectively) located in NW France. In this budget, soil erosion as well as colluvial sediment storage is estimated from soil profiles analysis for a representative catchment and extrapolated to the entire catchments. Alluvial sediment storage, including a chronology of the alluvial fills, has been quantified by augerings cores distributed on several transects located along the floodplain of the two rivers. The proposed sediment budget highlights significant sediment storage in the catchment: 12.3 Mt (32.5 %) is stored as colluvium and 15.5 Mt as alluvium (40.8 %), i.e. more than 70 % of eroded sediments on the slopes. The remaining eroded sediments (10.2 Mt) are considered to have been exported out of the catchments. The timing of slope erosion and colluvial storages indicates the initiation of soil erosion from the Neolithic period and an acceleration over the last 3 millennia. However, a long gap is observed between forest clearance, soil erosion and the acceleration of alluvial filling underlying a progressive improvement of the connectivity induced by a progressive transformation of the running water circulation within the catchment. The results thus highlight the complexity of Holocene sediment dynamics across spatial and temporal scales and emphasize the necessity to integrate the question of the efficiency of the sediment cascade particularly induced by the landscape structure and drainage density. [ABSTRACT FROM AUTHOR]

Sedimentation rates and sediment budgets are important agents to understand the source-to-sink dynamics in marginal seas. As a classical representative of mega-river dominated marginal seas globally, the South China Sea (SCS) receives huge amounts of fluvial input from mega rivers covering different climate zones. Despite its well-documented prevalence, quantifying the spatial distribution of sedimentation rate and sediment budget over the entire SCS remains a challenge due to limited data availability. In this study, we employed a comprehensive approach to quantify the modern sedimentation rates and sediment budget in the SCS. This approach combined 210Pb measurements from 409 cores, AMS14C data from 112 cores, and 33 sediment trap observations. Our results show that higher sedimentation rates >0.3 cm/a mainly occur in deltas, shelf mud areas, and upper continental slope that connects the submarine canyon. In the subaqueous Mekong Delta, for example, the sedimentation rates can exceed 10 cm/a. In contrast, there is no substantial modern sedimentation in sandy and gravelly areas of the shelf due to strong erosion by a combination of waves, tides and ocean currents. We further compare these results with the eastern China seas including the Bohai Sea, Yellow Sea and East China Sea. A similar spatial distribution of sedimentation rates can be observed in the continental shelf of the eastern China seas. The Holocene sedimentation rates in the deep-water regions of the SCS are generally <100 cm/ka. The basin floor experiences the slowest accumulation, with rates below 3 cm/ka. In contrast, sedimentation rates on the eastern island slopes range from 3 to 8 cm/ka, while the northern, western, and southern continental slopes accumulate sediment most rapidly, exceeding 25 cm/ka. Approximately 1191.1 × 106 t of fine-grained sediment is deposited annually in the continental mud areas of the SCS, with a comparable amount of 1185.4 × 106 t/a deposited on the continental shelf of the eastern China seas. The continental slope accumulates sediment at a significantly higher rate (∼161.0–239.4 × 106 t/a) compared to the deep-water basin (∼16.5–20.1 × 106 t/a) in the SCS. Most of the modern sediments (>98%) are deposited on the continental shelf and slope. In the SCS, fluvial inputs dominates modern sediment sources, contributing over 80% of the total. Coastal/seabed erosion and biogenic deposition account for approximately ∼18%, with eolian dust contributing less than <2%. The findings presented here are critical for elucidating the sources, transport pathways, and deposition patterns of modern sediments in marginal seas. • Distribution of modern sedimentation rates in the South China Sea was illustrated at the basin scale. • The sediment budget and mass balance from a source–to–sink perspective was constructed. • Comparison of sedimentation rates and sediment budgets of the South China Sea and east China seas was conducted. [ABSTRACT FROM AUTHOR]

The re-analysis of high-resolution seismic profiles collected along the narrow (2–9 km) shelf facing ∼90 km of the Calabro-Tyrrhenian coastline has enabled the reconstruction of its sequence-stratigraphic architecture, along with the quantification of sediment volumes accommodated during the last post-glacial sea level rise and highstand. The shelf volumes are compared with the gross volumes supplied by the short and steep rivers draining the uplifted hinterland area, obtained from morphometric analysis and inferred denudation rates (derived from uplift rates) of the drainage basins. The study area is divided in two main sectors based on the different morpho-stratigraphic setting and fluvial network controlling sediment distribution on the shelf. The Coastal Range sector is characterized by closely spaced mountainous rivers and narrow coastal plains; on the shelf, the post-LGM deposits show a main depocenter (up to 60 m thick) elongated ∼27 km parallel to the coastline. This shelf sector hosts up to 80% of the sediment sourced from rivers, with a small percentage of sediment loss, mainly related to off-shelf export along a network of shelf-indenting submarine canyons. Sediment deficit due to river aggradation is considered negligible based on the narrow and V-shaped thalwegs typical of the rivers in this sector. The Santa Eufemia sector is characterized by larger rivers and a wider coastal plain, with a major depocenter (up to 50 m thick) confined off the Amato River. In this sector, the entire post-LGM sequence accounts only for about 30% of the sediment supplied by rivers (60% considering only the HST), indicating that, in addition to sediment exported off-shelf, a significant part is trapped by river aggradation within the coastal plain. The volumetric comparison has also evidenced local but significant discrepancies in sedimentary budget between adjacent sub-sectors, likely related to the effect of northward-directed shelf currents on sediment distribution along the shelf. [ABSTRACT FROM AUTHOR]

Coral reefs and their associated landforms (carbonate islands and shorelines) are under increasing threat from the effects of anthropogenic climate change, including sea level rise (SLR). The ability of a reef to keep up with SLR depends on the rate of calcium carbonate accretion. Census-based carbonate budgets quantify rates of net calcium carbonate production on a reef and facilitate estimations of vertical reef accretion potential (RAP). To date, most carbonate budget studies have been undertaken in clear-water settings resulting in a limited understanding of how inshore reefs situated in more marginal environmental settings are functioning now and under future climate change. Here, we applied census-based carbonate framework across two inshore island reefs exposed to episodes of high turbidity within the Pilbara, Western Australia. Low net carbonate production (mean = 1.11 and 0.62 kg m−2 yr−1) was predominantly driven by low coral cover (<10%) and low calcification rates. Importantly, bioerosion rates were also low (<0.1 kg m−2 yr−1), maintaining positive carbonate budgetary states. Net sediment production rates were also low (mean = 0.06 kg m−2 yr−1) and were found to be mostly derived from coral, or mollusc material produced by invertivores. Calculated RAP estimates are below current and predicted rates of SLR, suggesting that these turbid reefs will soon struggle to keep up with increasing water depth and shoreline inundation. • Net carbonate production at turbid reefs within the Pilbara, Western Australia is low. • Low bioerosion rates maintain positive carbonate budgets across both reefs. • Calculated RAP estimates are below current and predicted rates of SLR. [ABSTRACT FROM AUTHOR]

This work proposes a methodological approach applied to ephemeral gravel-bed streams to verify the change in the magnitude and frequency of hydrological events affecting the morphological dynamics and sediment budget in this type of channel. For the case study, the Azohía Rambla, located in southeastern Spain, was chosen, emphasizing the research on two reference riverbed sections (RCRs): an upper one, with a predominance of erosion, and a middle one, where processes of incision, transport, and deposition were involved. First, this approach focuses on relationships between peak discharges and sediment budgets during the period 2018–2022. For this purpose, water level measurements from pressure sensors, a One-Dimensional Hydrodynamic model, and findings from comparative analyses of high-resolution differential digital elevation models (HRDEM of Difference-HRDoD) based on SfM-MVS and LiDAR datasets were used. In a second phase, the GeoWEPP model was applied to the period 1996–2022 in order to simulate runoff and sediment yield at the event scale for the watersheds draining into both RCRs. During the calibration phase, a sensitivity analysis was carried out to detect the most influential parameters in the model and confirm its capacity to simulate peak flow and sediment delivery in the area described above. Values of NS (Nash–Sutcliffe efficiency) and PBIAS (percent bias) equal to 0.86 and 7.81%, respectively, were found in the calibration period, while these indices were 0.81 and −4.1% in the validation period. Finally, different event class patterns (ECPs) were established for the monitoring period (2018–2022), according to flow stage and morphological channel adjustments (overtopping, bankfull and sub-bankfull, and half-sub-bankfull), and then retrospectively extrapolated to stages of the prior simulated period (1996–2018) from their typical sequences (PECPs). The results revealed a significant increase in the number of events and PECPs leading to lower bed incision rates and higher vertical accretion, which denotes a progressive increase in bed armoring and bank erosion processes.

Abstract Non-invasive techniques such as seismic investigations and high-resolution multibeam sonars immensely improved our understanding of the geomorphology and sediment regimes in both the lacustrine and the marine domain. However, only few studies provide quantifications of basin wide-sediment budgets in lakes. Here, we use the combination of high-resolution bathymetric mapping and seismic reflection data to quantify the sediment budget in an alpine lake. The new bathymetric data of Lake Brienz reveal three distinct geomorphological areas: slopes with intercalated terraces, a flat basin plain, and delta areas with subaquatic channel systems. Quasi-4D seismic reflection data allow sediment budgeting of the lake with a total sediment input of 5.54 × 106 t sediment over 15 years of which three-quarter were deposited in the basin plain. Lake Brienz yields extraordinarily high sedimentation rates of 3.0 cm/yr in the basin plain, much more than in other Swiss lakes. This can be explained by (i) its role as first sedimentary sink in a high-alpine catchment, and by (ii) its morphology with subaquatic channel-complexes allowing an efficient sediment transfer from proximal to distal areas of the lake.

Anthropogenic stressors on large rivers have significantly modified riverine sediment transport. However, the impacts of dredging and sand and gravel (S&G) mining are poorly monitored. We quantify these impacts on the lower Arkansas River, USA, where anthropogenic processes are well documented. The construction of dams caused a 98% reduction in suspended sediment discharge (Qss). Since dam construction, fluvially transported suspended sediment (4.4 ± 0.5 Mtyr−1) and suspended sand discharge (Qsand) (1.1 ± 0.1 Mtyr−1) are of the same order as the dredging rate (1.2 ± 0.1 Mtyr−1) and S&G mining rate (1.7 ± 0.1 Mtyr−1). While the modern sediment deficit on the Arkansas River is smaller than in rivers documented in developing countries, dredging and mining significantly alter the sediment balance in this large river, indicating that extraction management is needed worldwide, especially in developing economies, to improve ecosystem sustainability in large rivers. Plain Language Summary: Large river systems provide many services, including water resources, barge transport, and sand and gravel for construction. Dredging for navigation and sand and gravel (S&G) mining are pervasive in many rivers, but good estimates of these activities are difficult to find. Based on the long‐period records of sediment extraction in the lower Arkansas River (LAR), U.S.A, we show that the river's sediment discharge is of the same order as the sediment extraction rates by dredging and S&G mining. We show that the LAR has a sediment deficit between the cities of Van Buren and Little Rock because the amount of outgoing sediment, including dredging and S&G mining, is greater than the amount of incoming sediment. Similar situations exist and are even worse in large rivers in developing countries, indicating actions are needed to manage sediment extraction to achieve sustainable development of large rivers worldwide. Key Points: Navigation dredging and sand and gravel mining contribute significantly to the sediment discharge decline on the lower Arkansas River (LAR)Engineering sediment extraction is the same order as the magnitude of modern fluvial sediment transport on the LARSediment deficit on the LAR is smaller than in rivers documented in developing countries [ABSTRACT FROM AUTHOR]

The Burntwood River (BR) and Upper Nelson River (UNR) are regulated rivers in the subarctic region of Canada. They merge at Split Lake and then discharge into Hudson Bay via the Lower Nelson River (LNR). The BR water discharge was increased eight‐fold by a cross‐watershed diversion in 1976. The UNR drains the 11th largest lake in the world, Lake Winnipeg, which itself receives discharge from a large North American Interior Plains watershed. Sediment loads and the source fingerprinting approach in these rivers were used to: (a) identify the sediment sources; (b) examine the impact of climate change and flow regulation on the BR and UNR sediment loads; and (c) assess the influence of Split Lake on downstream delivery of sediment into the LNR. Lake Winnipeg effectively decouples the UNR from the sediment sources in its prairie watershed. Fluvial riverbank and reservoir shoreline erosion in the UNR increased in the late 1990s, in response to a multi‐decadal increase in discharge forced by climate change in the Lake Winnipeg watershed. The BR sediment load was increased seven‐fold by diversion. Since diversion, flow regulation near the licenced limit has muted the response to variability in local precipitation and runoff; however, erosion processes independent from discharge (bank failures and subaerial processes) add variability in the sediment load record. Based on sediment budgeting, Split Lake conveys almost 80% of the BR and UNR sediment load into the LNR. The greater sediment load in the UNR (~1100 Gg year−1, compared to ~530 Gg year−1 from the BR) reveals that the UNR is the primary sediment source into the LNR, so that downstream sediment transport dynamics are more sensitive to the environmental changes in the UNR than to disturbances in the BR. Whether this may change in the future depends on changes in climate and engineering responses to increasing demand for hydroelectric power. [ABSTRACT FROM AUTHOR]

Understanding trends in estuarine sediment fluxes is of great interest to sustainable estuarine management addressing anthropogenic interferences and climate change. The long‐term sediment budget of the Western Scheldt estuary, Netherlands, is investigated by a detailed analysis of a unique and long‐term bathymetric data set and data of a three‐dimensional subsurface model ('GeoTop'). Different sediment types show contrasting transport behaviour. The Western Scheldt narrowed and deepened, while the estuary exported sand (1.5 to 2.5 million m3 per year) and imported mud (0.5 to 1.5 million m3 per year) over the 1860 to 1955 period. The eroded sand originated from the channels in the seaward part of the estuary and was dispersed in all directions. A significant amount of mud permanently deposited in the side branches, which were also gradually reclaimed. These results suggest that sediment characteristics potentially play a crucial role in deriving long‐term sediment budgets and morphodynamic behaviour of estuarine environments. Future morphodynamic sand–mud model studies may reproduce and further explain the underlying transport processes of the current study. [ABSTRACT FROM AUTHOR]

This study discusses the potential impact of removing Posidonia banquette on the sediment budget of a siliciclastic-sediment-starved beach-barrier system. The morphology as well as the sediment volumes of this system were estimated. The banquette's composition and sediment content were determined with samples collected during five sampling campaigns conducted in one year. The carbonate content of the system was estimated by analyzing three 1 m long cores collected along the barrier. Five digital terrain models from DGPS surveys were used to compute the beach's average morphology to estimate the sediment volumes. The carbonate and siliciclastic sediment content from the cores were used to calculate the overall beach's sediment mass. Total sediment mass accounted for 126,000 m3, of which ca. 86% was siliciclastic quartz sand and approximately 14% was carbonate sediment. Total banquette deposition during the year accounted for 2300 m3, with a maximum and averaged sediment content of 339 kg m3 and 78 kg m−3. A permanent loss of ca. 1.31% of total mass will occur if 5000 m3 of banquette were to be removed. In such beach settings, banquette removal may limit sediment availability, reducing the overall sediment mass and decreasing beach resilience against climate change effects such as sea level rise. [ABSTRACT FROM AUTHOR]

Reduction in river discharge and sediment load has left deltaic lobes in the world’s many river deltas starving, but knowledge of how the subaqueous topography of these abandoned subdeltas responds to environmental changes is limited. In this study, we aimed to determine the long-term dynamics of the subaqueous seabed of abandoned delta lobes to advance current knowledge. As a case study, we selected an abandoned subdelta on the Yellow River Delta of the Bohai Sea, China, for which three-decade long (1984–2017) bathymetric data and long-term river discharge and sediment load records are available. We analyzed the seafloor surface change and quantified the void space from the sea water surface to the seafloor. In addition, we surveyed the seafloor surface with an M80 unmanned surface vehicle carrying a multibeam echo sounder system (MBES) in 2019 to obtain high-resolution microtopography information. We found that a net volume of 5.3 × 108 m3 of sediment was eroded from the study seabed within an area of 3.6 × 108 m2 during 1984–2017. This volumetric quantity is equivalent to 6.89 billion metric tons of sediment, assuming a bulk density of 1.3 t/m3 for the seabed sediment. The seabed erosion from 0 to −5 m, from −5 to −10 m, and below −10 m has showed a similar increasing trend over the past 33 years. These findings suggest that seabed erosion in this abandoned subdelta will very likely continue, and that other abandoned delta lobes in the world may have been experiencing similar seabed erosion due to the interruption of the sediment supply and sea level rise. It is not clear if the seabed erosion of abandoned delta lobes would have any effect on the stability of the coastal shoreline and continental shelf.

The concept of coastal sediment compartments has recently been adopted at a national scale in Australia to better understand sediment and shoreline dynamics and to underpin management of future shoreline behaviour in response to impacts of climate change. Geomorphological studies in southern NSW have provided a foundation for development of conceptual models of estuary and sandy barrier evolution. Geochronological reconstructions using radiocarbon, optically-stimulated luminescence, and other dating techniques, reviewed in this paper, demonstrate that adjacent compartments are at successive stages. Three compartments, Illawarra, Shoalhaven and Moruya, are compared, each with different catchment characteristics and different levels of human intervention. Landform change and sediment accumulation at millennial timescales enable estimates of past sediment accretion (vertical accumulation) and horizontal displacement of shorelines (particularly progradation), as a first step towards quantifying volumetric changes of morphology. Lake Illawarra is a barrier estuary at an early stage of infill, but land-use change, urbanisation, and engineering structures at the entrance have accelerated rates of sediment accumulation. The Shoalhaven River has infilled its estuary and delivers sand to the coast. It has been subject to several conspicuous anthropogenic interventions. At Moruya, ongoing supply of sand, primarily from offshore rather than from the catchment, has resulted in beach-ridge plains (strandplains) with changes in their alongshore inter-connectivity driven by differential embayment infilling. Millennial-scale geomorphology indicates landform change providing a means to determine natural trajectories of sediment transfer. However, variability is apparent at century and decadal timescales, compounded by various anthropogenic interventions. Disentangling natural and anthropogenic influences will be necessary to provide greater confidence in estimating past and present sediment budgets. Assessing sand sources and transport rates is important in relation to engineering interventions at entrances, and long-term resilience of coastal habitats. Such issues are the focus of coastal management programs, and this synthesis emphasises the relevance of a sediment budget approach to understand contemporary sediment pathways and provide an indication of future response to engineering interventions and sensitivity to climate change. [ABSTRACT FROM AUTHOR]