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Autogenic feedbacks can produce large‐scale, organized stratigraphic patterns in alluvial fans, but autogenic depositional signatures of specific upstream boundary conditions remain challenging to interpret. Here, a combination of theory, experiment and field application is used to explore how autogenic lithofacies changes can be interpreted as stratigraphic indicators of upstream boundary conditions. Six experiments were conducted to test the effects of sediment supply and water discharge rates on autogenic advance and retreat of the lithofacies boundary (grain‐size transition) in an alluvial fan with two dominant grain sizes. Migration of the grain‐size transition caused a short‐term zigzag pattern in the grain‐size transition position in the dip‐directional deposit section. For each experiment, time‐lapse images and laser topographic scans of the fan surface and stratigraphic cross‐sections of the final deposits were used to quantify characteristic timescales of autogenic processes. Timescales for fan‐margin migration, surface wet‐fraction change and grain‐size transition migration generally shorten as sediment supply rate increases and water discharge rate decreases. Increasing the sediment supply rate shortens the duration of the fluvial sediment storage and release cycle, producing higher frequency zigzags in the grain‐size transition trajectory. Increasing the water discharge tends to widen channels and lengthens the duration of the fluvial sediment storage and release cycle, constructing lower frequency zigzags in the grain‐size transition trajectory. Increasing the water discharge also enables more sediment to transport further downstream during release events, leading to higher magnitude zigzags in the grain‐size transition trajectory. These relationships between upstream boundary conditions and the grain‐size transition trajectory demonstrate how autogenic stratigraphic signals could be used as a tool to infer relative changes in boundary conditions. [ABSTRACT FROM AUTHOR]

Deltas are crucial for land building and ecological services due to their ability to store mineral sediment, carbon and potential pollutants. A decline in suspended sediment discharge in large rivers caused by the construction of mega‐dams might imperil deltaic flats and wetlands. However, there has not been clear evidence of a sedimentary shift in the downstream tidal flats that feed coastal wetlands and the intertidal zone with sediments. Here, integrated intertidal/subaqueous sediment samples, multi‐year bathymetries, fluvial and deltaic hydrological and sediment transport data in the Nanhui tidal flats and Nanhui Shoal in the Changjiang (Yangtze) Delta, one of the largest mega‐deltas in the world, were analysed to discern how sedimentary environments changed in response to the operations of the Three Gorges Dam. Results reveal that the coarser sediment fractions of surficial sediments in the subaqueous Nanhui Shoal increased between 2004 to 2021, and the overall grain size coarsened from 18.5 to 27.3 μm. Moreover, intertidal sediments in cores coarsened by 25% after the 1990s. During that period, the northern part of the Nanhui Shoal suffered large‐scale erosion, while the southern part accreted in recent decades. Reduced suspended sediment discharge of the Changjiang River combined with local resuspension of fine‐grained sediments are responsible for tidal flat erosion. This study found that the spatial pattern of grain‐size parameters has shifted from crossing the bathymetric isobaths to being parallel to them. Higher tide level and tidal range induced by sea‐level rise, an upstream increase in bed shear stress and larger waves likely further exacerbated erosion and sediment coarsening in deltaic flats. As a result, this sediment‐starved estuary coupled with sea‐level rise and artificial reclamations have enhanced the vulnerability of tidal flats in Changjiang Delta, this research is informative to the sedimentary shift of worldwide mega‐deltas. [ABSTRACT FROM AUTHOR]

This research is dedicated to examining downslope sediment transport on steep shorefaces. We present a model that incorporates nonlinear surface wave profiles, sediment movement thresholds, and slope effects, utilizing a set of semi-empirical formulas. The model quantitatively assesses the disparity between wave-augmented upslope transport and gravity-augmented downslope transport, and computes sediment transport rates using a single calibration coefficient. Validation of the model is carried out in the Fuji coast of Japan, where offshore wave conditions and seabed topography with a uniform grain size distribution serve as inputs. The computational outcomes reveal that sediment transport primarily occurs under high wave conditions, and downslope transport dominates on steep slopes. The calibration coefficient is determined through a comparison with observed data, demonstrating a strong agreement in the average annual sediment loss in the target area. Moreover, the model offers insights into the possible mechanism behind the existence of a transition area between the upper and lower shoreface, marked by an abrupt change in seabed slope. [ABSTRACT FROM AUTHOR]

The densely populated coast of the Gulf of Guinea (GoG) is experiencing escalating erosion from climate change (CC). To assess Longshore Sediment Transport (LST) changes in the past and future, an empirical formula was used to model the GoG's LST. Nearshore wave conditions, crucial for LST estimation, were derived by projecting significant wave height, mean wave period, and mean wave direction from deep water to the breaker zone. These wave conditions were used as input for LST computation. Analysing three time slices: Past (1979–2005), mid-century (2026–2045), and end-century (2081–2100) under RCPs 4.5 and 8.5, results indicate continuous increase in LST in most locations, with local and seasonal variations. LST magnitudes range from 104 to 105 m3y−1 in the GoG, with the Cameroonian coast having the least. This aligns with the rising wave energy from CC. LST directions are predominantly eastward, though some locations, like off Lagos and Cameroon-Gabon coasts, show westward trend, correlating with coastal orientation influenced by southward wave directions. RCP 8.5 projections suggest mid-century increase, intensifying by end of century, with yearly rates of change around 103 m3y−1 and future LST changes up to 105 m3y−1. This situation implies accelerated sediment removal, heightening erosion. [ABSTRACT FROM AUTHOR]

Erosion of banks and channel migrations are usually common phenomenon and recurring geo-hazardous problem in the Brahmaputra-Jamuna river system of Bangladesh. The present study intensively analysed multi-temporal Landsat satellite imageries (Landsat MSS, Landsat TM, Landsat ETM+, Landsat OLI TIRS), historical documents (Hunter maps), and literature information employing Remote Sensing and Geographic Information System techniques, and estimation of braiding and sinuosity indices especially emphasizing channel bar development, braiding, and bank-line migration of the river. The computed braiding indices of the river were 1.5, 10.3, 13.4, 11.0, 10.6 and 14.6 for the year of 1853–1857, 1977, 1989, 2000, 2014 and 2018, respectively (overall deciphering increasing trend). Similar to the braiding indices, the sinuosity indices (2.58, 7.02, 9.92, 8.31, 7.42 and 11.25 for the same selected years) of the river have also been changed over time. During 1853–1857 to 2018, 766.7 and 1624.2 km2 of lands extensively eroded on the east and west bank, respectively at a rate of 4.8 and 10.1 km2 yr−1. However, from 1977 to 2018, the erosion rates were 14.4 and 12.5 km2 yr−1, respectively. High discharges, sediment transport associated with random bars formation related braiding expansion, and weak bank materials are presumably the governing factors for causing such simultaneous severe bank erosion and remarkable bank-line migration phenomenon. Although, from 1853–1857 to 1977 the erosion of the river followed the river flow direction. It is expected that the outcomes of this research can contribute further research on morphodynamic characteristics of the braided river for better understanding the river characteristics, the river hydromorphology, water and sediment transport, its bank erosion, and formulating protective measurement plan for their sustainable current flow path maintenance. [ABSTRACT FROM AUTHOR]

Suspended sediment load (SSL) and discharge are closely related concepts that characterise the sediment movement and quantity within water bodies and play a crucial role in evaluating the impact of erosion, sedimentation, and land management practices on riverine ecosystems. Despite numerous studies on SSL and discharge assessments, a site-specific understanding remains essential for effective riverine ecosystem protection. This study integrates daily sediment and discharge data from the Koelwar station spanning June 2010 to May 2015, with a primary focus on analysing SSL variability relative to Sone River discharge in Bihar. SSL–discharge rating curves were computed to assess concentration shifts during low flow season (LFS), high flow season (HFS), and the annual period. Results indicate a nearly linear dependence of SSL on discharge, with r2 values of 0.72, 0.94, and 0.84 for LFS, HFS, and the annual period, respectively. The study unveils the underlying mechanics driving catchment erosion and sediment transport during lean and peak flows through hysteresis loops. Findings reveal that 50% of events are influenced by shear stress and hydraulic forces from the channel bed, 20% by sediment depletion in the channel bed due to repeated peak flows, and the remaining 30% by a combination of shear stress and sediment reduction. Additionally, MATLAB-utilized wavelet analysis explains the time-frequency variability of discharge and SSL. Cross-wavelet analysis shows the outflow of SSL closely following discharge, indicating synchronisation across all scales. The study underscores the importance of effectively managing runoff events to mitigate SSL. The proposed methodology and results offer valuable insights for water management and policymakers, aiding in the formulation of guidelines to minimise anthropogenic activities and sustain aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Quantitative investigations of ancient rivers usually provide insights into either instantaneous or mean flow conditions. There is a critical gap between these time scales of investigation, which reflects the intermittency of flow and sediment transport, and closing this gap is crucial to fully explore the dynamics and evolution of ancient fluvial landscapes. Here, we combined fluvial stratigraphic data sets, flow and sediment transport models, and paleoclimate general circulation model (GCM) results to develop new methods to estimate intermittency in the geological past, specifically flow intermittency factors (Iw) and sediment transport intermittency factors (Is), and we show how they can be used to explore past hydrograph shapes. We illustrated these methods using the Upper Cretaceous Last Chance Ferron Sandstone in Utah, western United States. For sand-transporting flow conditions in Last Chance Ferron rivers, we estimated Iw values of 0.54-0.90, which imply that channel-forming conditions were sustained for the majority of the year, consistent with perennial systems in which relatively large discharges were sustained. In contrast, for gravel-transporting flow conditions, Iw values of 0.28-0.38 suggest that the largest formative flows may have occupied Last Chance Ferron rivers for nearly a third of the year, which could be explained by a monsoonal system in which high-magnitude discharge events were sustained, or a subtropical system in which high-magnitude discharge events had short durations but high frequencies. Meanwhile, Is values of 0.075-0.15 suggest that annual sediment budgets could have been transported in as little as 10 days and up to 2 months, if channel-forming conditions were sustained, and these values highlight that small changes in the duration of channelforming conditions could significantly impact sediment budgets. Our results are consistent with independent facies- and proxy-based insights into Last Chance Ferron rivers, which point to a perennially wet system characterized by a monsoonal or subtropical discharge regime. Further, our results highlight new opportunities to use paleoclimate GCMs to constrain intermittency factors in the geological past. Going forward, paleoclimate GCMs will be particularly useful where the rock record is incomplete or inaccessible, or where stratigraphic approaches are limited, and they will enable us to tackle pertinent research questions pertaining to past surface processes on both Earth and other planets. [ABSTRACT FROM AUTHOR]

Mount Meager is a deeply eroded quaternary volcanic complex located in southwestern British Columbia (BC) and is known for its frequent large landslides. In 2010, the south face of Mount Meager collapsed, generating a long-runout debris avalanche that was one of the largest landslides (50 × 106 m3) in Canadian history. Over the past 14 years, the landslide deposit has been reworked by stream action, delivering large amounts of sediment to Lillooet River, just downstream. In this study, we investigate 10 years of geomorphic evolution of the landslide deposit using orthophotos and digital elevation models (DEMs) generated using Structure from Motion (SfM) photogrammetry on aerial photographs acquired during unmanned aerial vehicle (UAV) and Global Navigation Satellite System (GNSS) surveys. The SfM products were used to produce a series of precise maps that highlight the geomorphological changes along the lower Meager Creek within the runout area of the landslide. Comparison of DEMs produced from 2010, 2012, 2015, and 2019 imagery allowed us to calculate deposit volume changes related to erosion, transport, and redeposition of landslide material. We estimate that about 1.1 × 106 m3 of sediment was eroded from the landslide deposit over the period 2015–2019. About 5.2 × 105 m3 of that sediment was redeposited inside the study area. About 5.8 × 105 m3 of sediment, mainly sand, silt, and clay, were exported from the study area and are being carried by Lillooet River towards Pemberton, 40 km from Mount Meager, and farther downstream. These remobilized sediments likely reduce the Lillooet River channel capacity and thus increase flood hazards to the communities of Pemberton and Mount Currie. Our study indicates a landslide persistence in the landscape, with an estimated 47-year half-life decay, suggesting that higher flood hazard conditions related to increased sediment supply may last longer than previously estimated. This study shows the value of using SfM in tandem with historic aerial photographs, UAV photos, and high-resolution satellite imagery for determining sediment budgets in fluvial systems. [ABSTRACT FROM AUTHOR]

This article reviews research on sediment flux impacts on the receiving estuary, ports, and society in Cartagena, Colombia. The city hosts both the country's largest touristic and coastal industrial sectors and is home to vulnerable coastal communities whose health and livelihoods are impacted by pollution. These marginalized artisanal fishing communities lack basic water and health services but have finally been recognized in a new intersectoral committee for Cartagena Bay's environmental management. To support the governance of these complex socioenvironmental challenges, the Cartagena Bay Observatory has been developed as a scientific tool to monitor the bay's conditions and forecast the effects of future sediment remediation plans. Cartagena Bay receives large freshwater discharges from the Dique Canal, draining from the 260,000 km2 Magdalena River watershed where 80% of the national population resides. This runoff transports sediment loads of 2.3 Mt/year, dispersing large plumes that affect the marine ecosystems and tourism and make the bay one of the Caribbean's largest sediment‐receiving estuaries. Following decades of watershed deforestation and erosion, the upward trending sediment inputs and accretion of the Dique delta have resulted in deposition rates of 1.8 cm/year, and the need for frequent dredging. Mercury dumped by a chemical industry in the 1970s can be found in concentrations as high as 18.8 μg/g buried below the bay's bottom. Mercury has also been found in the bay's biota and human populations, and so the dredging needed for the port's sustainability thereby presents a health risk by allowing this trapped mercury to surface. This article is categorized under:Science of Water > Hydrological ProcessesScience of Water > Water QualityScience of Water > Water and Environmental Change [ABSTRACT FROM AUTHOR]

AlMashan, N.; Al-Attar, I., and Neelamani, S., 2024. Assessment of annual sedimentation into Failaka Marina (Kuwait) and possible solutions for reduction of siltation. Journal of Coastal Research, 40(3), 527–553. Charlotte (North Carolina), ISSN 0749-0208. Sedimentation is critical for ports, harbors, and marinas, requiring accurate assessment. Failaka Marina in Kuwait is experiencing a severe noncohesive sedimentation problem. The samples collected at the seven locations along the beach showed that the beach has a uniform grain-size diameter, meaning it is poorly graded sand. The sampling at the tip of the southern breakwater showed that the shoaling is mainly sand. The suspended-sediment concentration varies from 0.025 kg m–3 to 1.2 kg m–3, whereas the mean concentration at the marina entrance is 0.85 kg m–3. The time series of the suspended solids over a year in the seawater surrounding Failaka Island shows a range of 8 to 48,069 ppm. Such a considerable variation in suspended load is due to the massive amounts of dredging and spoil disposal at Boubyan Island and Basra Port (Iraq) when a high sediment load moves around Failaka Island with a concentration of more than 40,000 mg L–1. Annual sedimentation is about 2.35 m y–1, which is responsible for blocking the main entrance for navigation. Kuwait's Ministry of Communication allocates $4 to $6 million annually for dredging and disposal activities. This study evaluates the six marina entrance modification scenarios to determine the best scenario that achieves a measurable reduction in sedimentation rate in the Marina. Six marina breakwater modifications were studied, and annual sedimentation rates were numerically computed. The study use Coupled MIKE 21/3 to simulate hydrodynamic conditions for cohesive sediment transport in a problem area. Field data from 2015 calibrated and validated the model. The primary sediment-moving force is SE wind and sea-swell waves. Littoral drift along Failaka Island's southern coastline and high suspended-sediment concentration result in littoral drift and settling. The best scenario showed a 28% sedimentation reduction and a 26% reduction in maintenance dredging costs from the six studied scenarios. [ABSTRACT FROM AUTHOR]

Tsunamis continue to pose an existential threat to life and infrastructure in many coastal areas around the world. One of the risks associated with tsunamis is the formation of deep scour holes around critical infrastructure and other coastal buildings, compromising their structural integrity and stability. Despite its importance, tsunami-induced scour is still given limited and simplified consideration in design guidelines for coastal structures. To further improve the understanding of tsunami-induced scour processes, and thus provide the basis for safer design of coastal structures, novel large-scale laboratory experiments have been conducted. The experiments featured a unique combination of boundary conditions, including a square coastal structure on a sloping and dry sandy beach. Single broken solitary waves were used to simulate tsunami bores. The spatiotemporal scour development directly at the square column was monitored by a high-resolution camera system, allowing a detailed description of the highly dynamic flow and scour process. Differences in the scour process between the wave runup and drawdown phases are described, and maximum and final scour depths are given as a function of inundation depth, wave height, and distance of the column from the shoreline. The scour process is characterized by several distinct phases of varying intensity and scour rate, the sequence of which varies depending on the location on the sides of the column. It is shown that the drawdown phase has a large influence on the overall scour development, adding up to 58% to the scour depth obtained during the wave runup phase. As a result of significant sediment infilling during the drawdown phase, the maximum scour depths achieved during the drawdown phase are up to twice the final scour depths at the end of a test. This discrepancy between final and maximum scour depths is greater than in previous studies using a flat sediment bed. The results of this study therefore help to interpret scour depths measured during field investigations after a tsunami event and provide a basis for extending design guidelines for coastal structures. [ABSTRACT FROM AUTHOR]

Barrier islands span 10% of the world's coastlines and dominate along the Atlantic and Gulf of Mexico coasts in the USA routinely exposed to storm surge. These islands serve as buffers between the open coast and the mainland, and protect the mainland from storm damage. During storms, significant morphological change can occur, including substantial erosion of the islands' vegetated dunes. In this study, the focus is on the influence of belowground biomass – namely dune plant roots – and dune topographic characteristics on barrier-island erosion during storms. The numerical model XBeach was employed to simulate storm-induced sediment transport. A parameter study was conducted by varying distance from the shoreline to the dune, dune shape, sediment grain size, and sediment mobility as an analogue for biomass. The influence of individual parameters and the collective impact of parameters were analyzed. The results help improve our knowledge of barrier island dynamics and lay a solid groundwork for future investigations. [ABSTRACT FROM AUTHOR]

This study examines the instability of sand waves (dunes and antidunes) from both linear and weakly nonlinear perspectives. The linear and weakly nonlinear analyses use the standard linearization and the center manifold-projection technique, respectively. The mathematical framework includes the depth-averaged continuity and momentum equations, the advection–diffusion equation for suspended sediment concentration, and Exner's equation for bed evolution. The streamline curvature is treated using the Boussinesq approximation. The model considers the departure of the pressure distribution from the hydrostatic law. Both modes of sediment transport, as bedload and as suspended load, are taken into consideration. The perturbations characterize the maximum growth rate for a selected wave number, called the resonant wave number, which is the most favorable wave number for the formation of sand waves. As the flow Froude number and the relative roughness number increase, the dimensionless resonant wave number decreases. The dimensionless amplitude of sand waves increases as the flow Froude number and the relative roughness number increase to achieve a maximum, and subsequently it decreases. The predicted wave number and amplitude of sand waves satisfactorily match the available experimental data. [ABSTRACT FROM AUTHOR]

River networks are composed of a mainstem and tributaries. These tributaries dissect landscapes, regulate water and habitat availability, and transport sediment and nutrients. Despite the importance of tributaries, we currently lack theory and data describing whether and how tributary length and spacing varies within watersheds, thereby limiting our ability to accurately describe river network geometry. We address this knowledge gap by analyzing 4,696 tributaries across six landscapes with varying climate, tectonic setting, and lithology. Our results show that both tributary length and spacing systematically increase with downstream distance along the mainstem river, following a power-law scaling. This power-law scaling can be modulated by basin shape, with tributaries becoming shorter and, in some cases, more closely spaced as basin elongate. Furthermore, the power-law scaling may break down in cases where river networks have been disturbed by pervasive faulting, raising the possibility that the scaling we observe is not unique to all branching networks, and instead may be universal across undisturbed fluvial networks. These findings can be used to improve predictions of river network geometry and potentially to distinguish fluvial river networks from other branching networks. [ABSTRACT FROM AUTHOR]

Accurate modelling and prediction of sediment transport in aquatic environments is essential for sustainable coastal and riverine management. Current capabilities rely on physical process-based numerical models and fine-scale sediment flux measurements. High-resolution hydroacoustic instrumentation has emerged as a promising tool for such measurements. However, challenges arise due to the inherent complexity of ultrasound scattering processes. This study introduces a numerical modelling using a point-particle approach to simulate the echoes backscattered by such instrumentation in sediment-laden flow conditions. The model considers geometric, statistical, particle cloud, and flow-induced effects on sediment velocity, concentration, and flux estimates using an acoustic concentration and velocity profiler as a reference. The model performance is assessed here under unidirectional constant flow conditions in terms of velocity, concentration, and time-resolved sediment flux estimates for a large range of the particles' advection speed and sampled volume sizes. Application to the estimation of the measurement accuracy of sediment flux in these flows is also considered, with a final error on the flux seen to be partially controlled by the residence time of particles within the sampled volumes. The proposed model provides insights into scattering processes and offers a tool for investigating robust sediment flux estimation techniques in various flow conditions. [ABSTRACT FROM AUTHOR]

Smoothed particle hydrodynamics (SPH) is a meshless, particle-based approach that has been increasingly applied for modelling of various fluid-flow phenomena. Concerning multiphase flow computations, an advantage of the Lagrangian SPH over Eulerian approaches is that the advection step is straightforward. Consequently, the interphasial surface can be explicitly determined from the positions of particles representing different phases; therefore, there is no need for the interface reconstruction step. In this review paper, we briefly recall the basics of the SPH approach, and in particular the physical modelling and numerical implementation issues. We also mention the weaknesses of the approach and some remedies to overcome them. Then, we demonstrate the applicability of SPH to selected interfacial flow cases, including the liquid column break-up, gas–liquid flow regimes in a channel capturing the transitions between them and the wetting phenomena. Concerning the two-fluid modelling, it is illustrated with sediment transport in the presence of surface waves. Various other applications are briefly recalled from the rich and growing literature on the subject, followed by a tentative list of challenges in multiphase SPH. [ABSTRACT FROM AUTHOR]

The dating of moraine deposits can present challenges to standard geochronological methods; terrestrial cosmogenic nuclide (TCN), sediment luminescence and radiocarbon dating may suffer from problems of incomplete resetting (by inheritance, intermittent cover/exposure, transport under unfavourable conditions) and/or a lack of suitable (organic) material. Rock surface luminescence burial dating (RSLBD) offers an alternative approach with considerable potential in dating moraines. In RSLBD, large cobbles/boulders are targeted, rather than smaller grains usually used in luminescence dating. The age limit of RSLBD is much higher than that of radiocarbon dating, and rocks are much more readily available than organic material. In contrast to TCN dating, the effect of exposure prior to deposition can be measured. In this study, we sampled a broad selection of primarily granitic boulders of various sizes and shapes (e.g. different degrees of roundness and sphericity) from the Vimmerby Moraine, a prominent and accessible feature in southern Sweden dated using TCN to 14.4±0.9 ka. Our study was designed to test whether morphological characteristics can be used to discriminate in favour of the most light‐exposed boulders and minimize measurements of non‐exposed boulders. As expected, not all RSLBD ages can be attributed to the same depositional event, but the majority of the resulting ages provide a mean age of 13.0±1.5 ka, consistent with the cosmogenic nuclide dating of the Vimmerby Moraine. Despite the apparently successful TCN study, the luminescence–depth profiles measured in the buried surfaces of the sampled clasts indicate that >50% of these moraine boulders were exposed to light (and cosmic radiation) before final deposition, implying some (presumably small) TCN inheritance; seven of the 16 boulders identified as light exposed were sufficiently bleached to be useful for RSLBD. These results and their implications in regard to transport and deposition of the sampled cobbles are critically discussed and evaluated. [ABSTRACT FROM AUTHOR]

Increased wildfire activity in the western United States can lead to detrimental cascading effects to water quality. After fires, burned areas may experience significant runoff‐induced erosion and sediment transport into rivers and reservoirs, which could rapidly overwhelm existing drinking water treatment plants. This paper couples an assessment of wildfire risk with an evaluation of water utility preparedness to understand where key fire‐related drinking water vulnerabilities exist. Wildfire risk assessments were constructed and expanded from a commonly used methodology co‐developed between researchers and water managers (Edel et al., 2002), to understand drinking water impacts on water quality after wildfires. A water utility preparedness index was created for this study using publicly available information to contextualize how well utilities may be able to respond to water quality degradation after fires. Results indicate that 22% of utilities studied (10% of the population served) were underprepared for fire and 11% of watersheds used were at greater risk of wildfire (9% of the population served). However, nearly three‐quarters of utilities (76% of the population served) showed a moderate risk of fire and some need for improved fire preparedness. Information developed here could provide a useful framework from which utility managers can better assess their likely wildfire risk and preparation plans. [ABSTRACT FROM AUTHOR]

This study identifies and summarizes potential risks to operations, regulatory compliance, supply chains, and infrastructure of the electric power industry from changing surface water conditions resulting from global climate change. The results help inform companies/utilities seeking to incorporate climate change risk in their planning and decision‐making processes by ranking risk severity and likelihood of occurrence on both a regional basis and by risk receptor. The assessment includes identification of potential risks to: (1) thermal generating, (2) hydroelectric, (3) land‐based renewable generating, and (4) transmission and distribution assets. These risks may result from such projected changes as reduced water availability (e.g., for hydroelectric or once‐through cooling), increased water temperatures (e.g., decrease in cooling efficiency, inability to meet discharge permit conditions), increased flood severity (e.g., increased streambank erosion and/or damage to river‐adjacent infrastructure), and decreased water quality (e.g., from increased transport of sediment and dissolved solids). The potential risks identified from this qualitative risk‐assessment are documented in a graphical format depicting both severity and likelihood. This approach allows for comparison of risks across a portfolio and for future prioritization of adaptation strategies. A total of 32 risks were identified in the study, including nine risks to infrastructure, six risks to operations, four risks to supply chain, and 13 environmental/regulatory risks. [ABSTRACT FROM AUTHOR]

While parasitism is a common lifestyle on Earth, its importance for the functioning of marine ecosystems has been overlooked for a long time. In particular, parasites have significant potential to influence central ecological processes through their impacts on hosts that serve as ecosystem engineers. Using an ex situ experimental approach, we explored the effects of trematode parasites on the engineering bioturbation activity of a common and abundant bivalve along European Atlantic soft‐bottom coastlines, the peppery furrow shell Scrobicularia plana, as well as knock‐on effects for nutrient exchanges at the sediment–water interface (SWI). Trematodes negatively impacted the host's ability to transport sediment particles and solutes in a density‐dependent way, with parasite burden explaining 22–31% of the inter‐individual variability. This could be explained by parasitism impairing the bivalve physiological state and ability to burrow, as we observed a decrease in the condition index and the burrowing depth of the bivalves with an increase in the number of parasites they host. In contrast, the influence of S. plana on benthic biogeochemical fluxes did not vary significantly according to parasitic burden over a short time scale. Here, we focused on the effects of trematode parasites on the behaviour of S. plana alone, and thus excluded other macrofaunal organisms. We should next test whether trematodes modulate the structure and functioning of benthic communities dominated by S. plana to better understand and quantify the engineering role of parasites in soft‐bottom coastal environments. [ABSTRACT FROM AUTHOR]

The Laurentide Ice Sheet's (LIS) interior had a dynamic polythermal base, but the spatiotemporal variations of subglacial processes related to ice divide migration and other transient changes remain largely unknown, limiting our understanding of regional glacial dynamics. Previous studies focused on the regional glacial landform record, while ice sheet models lacked detailed parameterization within these regions, leading to an overestimation of cold-based subglacial conditions' extent and duration. In this study, glacial sediment dispersal patterns as identified by heavy minerals, clasts, and multivariate statistics of till matrix geochemistry were used to assess ice sheet dynamics within the Quebec–Labrador sector of the LIS. The earliest ice-flow phase produced and transported till across the study area (>175 km). However, major oxide data from till matrix geochemistry show a correlation with underlying bedrock, and this relationship is relatively common in areas of thin till cover and resistant bedrock lithologies. These results suggest a switch from an early phase of widespread erosion and long, sustained sediment transport to one of more limited erosion, perhaps abrasion dominant and shorter transport. Till compositional data and related dispersal patterns add supporting evidence to earlier ice sheet reconstructions based on ice-flow indicators and 10Be data together suggesting a transition from widespread uniform warm-based conditions during the earliest ice flow, followed by the development of an ice divide, its migration, and more sporadic warm-based conditions. Consequently, a thorough understanding of ice-flow history is essential for ice sheet modelling and future mineral exploration programs in inner ice sheet regions of the LIS. [ABSTRACT FROM AUTHOR]

Depositional processes recorded by shelf deposits may vary widely along‐strike, depending largely on the mode of delivery and deposition of sediments to the basin. In fine‐grained systems in particular, depositional processes are difficult to reconstruct with standard facies analysis of sediment cores due to the ostensibly featureless and homogenous appearance of muds. In this study, sedimentological, palaeontological, geochemical, and oceanographic data were combined in a detailed characterization of depositional conditions via sedimentary structures, type of organic matter, trace‐metal geochemistry, and benthic fauna assemblages (foraminifera and ostracods) along the 600 km long shelf delta clinothems of the West Adriatic shelf (Italy). Processes inferred from sedimentary facies and micro‐structures were then considered in the context of the modern Adriatic oceanographic regime. Specific attention was given to the Little Ice Age stratigraphic unit (1500–1850 ce), which contains a continuum of genetically related fine‐grained strata. The Little Ice Age deposit offers the opportunity to examine a source‐to‐sink system with the high resolution typical of modern analogues, at a time interval when Apennine rivers were not yet hydraulically engineered with man‐made sediment traps along their trunks. Individual beds within the Little Ice Age muddy prodelta form hectometre to kilometre‐wide bedsets that reflect the interplay between energetic meteo‐ocean conditions (storm‐dominated beds), flood supply (river‐dominated beds or hyperpycnites) and along‐shelf bottom‐current dispersion (drift‐dominated beds). The multidisciplinary approach applied at different scales of observations helped in understanding sediment provenance and the relative timing of sediment transport before final burial that strongly promoted organic matter oxygen exposure and the loss of carbon by microbial degradation. Overall, the distinctive depositional processes that acted in concert along the prodelta slope produced a subtle lateral heterogeneity of preserved sedimentary structures, faunal associations, and organic matter composition in a laterally‐continuous lithostratigraphic unit deposited at centennial scale. These findings have implications on the forcing conditions that ultimately control the location and nature of fine‐grained beds in both modern and ancient, mud‐dominated depositional systems. [ABSTRACT FROM AUTHOR]

Suspension is the key mechanism by which fine‐grained sediment (≤125 μm) is winnowed and transported across shallow‐water carbonate platforms into adjacent deep waters. Unlike sliding and saltation, which deliver sedimentary structures via bedload, the sedimentological signature of suspended sediment is more cryptic. This study focuses on suspended sediment, and its drivers – wind, waves and tides – to better constrain the processes responsible for the transport of fine‐grained sediments. By building forward from remote sensing algorithms developed for deep‐waters, sediment suspension in the shallow water column can be mapped from satellite. By applying machine learning to Moderate Resolution Imaging Spectroradiometer data for Great Bahama Bank, this study demonstrates how the drivers of sediment suspension change over 18 years across this 100 000 km2 carbonate platform. Through time, both seasonal patterns of suspension, as well as those induced by El Niño‐Southern Oscillation and, more subtly, the Atlantic Meridional Overturning Circulation were tracked. El Niño‐Southern Oscillation modulates wind‐induced currents, while Atlantic Meridional Overturning Circulation affects local sea level. Across space, this study shows how the eastern margin of Great Bahama Bank, which is traditionally considered to be wind‐dominated, primarily owes its suspended sediment to tidal currents focused between islands. Sediment suspension across the leeward margin of Great Bahama Bank, meanwhile, can be attributed to wind‐induced currents and waves. The authors consider this work a step towards delivering a quantitative, reproducible, process‐based understanding of sediment suspension atop carbonate platforms using Earth observation data. [ABSTRACT FROM AUTHOR]

The piano key weir has been successfully used to address discharge deficiencies and site limitations for run-of-river structures and new and existing spillways, serving as an economical alternative to traditional weirs. In addition to upstream sedimentation, weirs may also be exposed to floating driftwood mobilized by hydrologic events. Driftwood accumulation immediately upstream of or on a weir crest can decrease hydraulic performance, potentially increasing upstream flooding and altering hydrodynamic forces on the weir that may cause structural or foundational concerns. It is unclear if floating driftwood accumulation might also influence the sediment self-cleaning characteristics of piano key weirs. Thus, this study used physical experiments to systematically investigate the sediment self-cleaning ability of a Type A piano key weir with driftwood accumulation in a run-of-river setting. The simulated substrate was an alluvial sand bed and the driftwood was naturally shaped. Experiments included combinations of discharge and different driftwood volumes. Results indicate that driftwood accumulations can have a significant influence on the flow field upstream of a piano key weir and positively affect the self-cleaning of sediment. For the conditions considered herein, the cleaning capacity was a function of driftwood volume, accumulation surface area or its extent in the upstream reach, and discharge. Higher flow rates and increased driftwood volume increased and extended upstream scour, resulting in higher sediment transport and self-cleaning without causing a significant backwater or increase in upstream water elevation. With sufficient flow depths at the piano key weir, driftwood would also be anticipated to pass downstream. Based on the results, driftwood accumulation can positively affect the ability of a piano key weir to remove adjacent upstream noncohesive sediment deposits. [ABSTRACT FROM AUTHOR]

Recent studies show that near-bed turbulence may be better scaled using a mixed velocity scale u*U , where u* is the shear velocity and U denotes the characteristic bulk flow velocity. This implies that the classical scaling consideration for sediment transport rates could be improved by redefining the Shields number based on the mixed velocity scale. To investigate this potential improvement, a series of analyses was performed with laboratory data from 25 sources of sediment discharge studies. The data were carefully selected by minimizing effects of some factors including sidewall, particle gradation, particle density, and fluid viscosity. The findings indicate that the relationship between sediment discharges and flow conditions can be enhanced significantly when the analysis is carried out based on the redefined Shields number. The new relationship does not depend on the type of bedforms, and therefore facilitates the prediction of sediment discharge. Finally, by comparing with previous studies, it shows that the proposed formula markedly improves the prediction of bed-material sediment discharges. [ABSTRACT FROM AUTHOR]

Complex interactions between flowing water and bedforms in rivers with sand beds during changing flow rates may result in bedforms, flow resistance, and sediment transport rates that differ on the rising and falling limbs of flow hydrographs. To study this phenomenon, laboratory experiments based on six realistically shaped hydrographs with durations of 1–6 h in 1-h increments were performed in a recirculating flume at the United States Department of Agriculture-Agricultural Research Service (USDA-ARS) National Sedimentation Laboratory. Bed topography, water-surface slope, flow rate, and sediment transport rate were continuously monitored. Counterclockwise hysteresis between discharge and sediment transport rate as well as bedform dimensions were observed for all hydrograph lengths, and the magnitude of hysteresis was quantified. The amount of hysteresis in transport rate, bedform amplitude, and bedform length varied according to the length of the hydrograph, although the relationship was not monotonic. The Engelund–Hansen method was able to approximately predict sediment transport rates based on measured hydraulic parameters. Maximum bedform amplitudes increased with hydrograph length, while bedform lengths increased only minimally beyond the 4-h hydrograph period. [ABSTRACT FROM AUTHOR]

Bioroughness plays an important role in modifying the velocity and sediment flux near the riverbed. It is therefore pertinent to study the influence of benthic fauna on the bed forms. To this end, large-eddy simulations are performed to investigate the influence of the arrays of mounds and their density on the turbulence characteristics in an open-channel flow. The simulated distributions of the time-averaged streamwise velocity and the turbulence intensity are in good agreement with the experimental data. Four numerical simulations are performed with varying streamwise spacings of mounds. Details of the time-averaged and instantaneous flow velocities are analyzed by multiple visualization methods, and the effects of the bioroughness density on the equivalent roughness height and the Darcy–Weisbach friction factor are quantified. The time-averaged flow in the wake of the mounds is characterized by a symmetric pair of vortices. The mounds behave like bluff bodies, increasing the riverbed roughness and heterogeneity in the flow environment. An increase in mound density is to promote the development of secondary currents and to increase the dispersive stress near the bed. The peaks of the Reynolds shear stress distributions decrease in both the streamwise and vertical directions for the high-density case due to a blockage effect. The instantaneous flow features, in the form of various turbulence structures, are generated near the top edge and the wake zone of mounds. The spacing between low-speed streaks decreases with an increase in equivalent roughness height. Multifrequency behavior that is observed is a result of shear layer roll-up from the edges of mounds and the flapping of wake. Finally, two formulas for equivalent roughness height and Darcy–Weisbach friction factor are proposed involving the bioroughness density and height. The findings demonstrate the effects of the bioroughness on the near-bed turbulence characteristics and sediment stability. Practical Applications: Bed forms produced by aquatic benthos are usually of small scale but with a large abundance. We performed a flume experiment as well as large-eddy simulations (a high-fidelity numerical simulation approach) to answer whether these microtopographies are important when studying flow and transport processes near the riverbeds. Four numerical simulations are performed with varying mound density. It was found that the microtopographies created by benthos indeed change the near-bed turbulence characteristics and sediment stability. Specifically at high abundances, benthos-induced bed forms could raise the bed roughness and the friction factor eightfold and threefold, respectively. This suggests the necessity of a modified roughness height formula and a friction coefficient formula based on the benthos abundance, which has been carried out in this study. Thus, engineers who are concerned with the flow and sediment transport in habitats of high-abundance benthos (e.g., wetlands and estuaries) may prefer to use these modified formulas and to develop a more accurate model of sediment transport. [ABSTRACT FROM AUTHOR]

• The coupled 2D mophodynamic model considers effects of sediment concentration and bed deformation in the governing equations. • Unstructured meshes better conform with the irregular geometry of the natural rivers. • Channel adjustments play a significant role in sediment transport of alluvial rivers during a flood event. It is difficult to predict the detailed morphodynamic processes induced by heavily sediment-laden floods in alluvial rives, due to the complexity in topography and the significant channel evolution rates, especially in a braided reach of the Lower Yellow River (LYR). A two-dimensional morphodynamic model using a coupled solution approach was firstly developed, with the effects of sediment concentration and bed deformation being directly considered in the hydrodynamic governing equations. The finite volume method with the HLL-MUSCL scheme was adopted in the numerical solution, which can obtain second-order accuracy in space and time. In addition, unstructured meshes were used to accommodate the irregular boundaries. The proposed model was validated using measurements in the braided reach of the LYR during the flood events of 2020 and 2004, with general agreement obtained between the calculated and measured hydrographs of flow and sediment concentration. The highest accuracy was achieved in the simulation of discharge, with a Nash-Sutcliffe efficiency coefficient (NSE) of 0.92. The simulation accuracy in sediment concentration was improved by the coupled approach, with the relative error of the calculated peak value decreasing from 17 % to 9 %. In addition, transport characteristics of graded suspended sediments were well simulated, with the fine fraction being transported downstream and the medium fraction depositing in the study reach. Influences of channel adjustments on the sediment transport processes were investigated during a flood event. The results demonstrated that the incised channel in 2020 was characterized by a larger water depth and smaller velocity, as compared with the shallow channel in 2004. Consequently, the peak discharge decreased and the flood propagation time was extended under the 2020 topography, associated with the lower sediment discharge at the outlet due to the reduced sediment transport capacity. [ABSTRACT FROM AUTHOR]

Understanding the material properties and physical conditions of basal ice is crucial for a comprehensive understanding of Antarctic ice‐sheet dynamics. Yet, direct data are sparse and difficult to acquire. Here, we employ ultra‐wideband radar to map high‐backscatter zones near the glacier bed within East Antarctica's Jutulstraumen drainage basin. Our backscatter analysis reveals that the basal ice in an area of ∼10,000 km2 is composed of along‐flow oriented sediment‐laden basal ice units connected to the basal substrate, extending up to several hundred meters thick. Three‐dimensional thermomechanical modeling supports that these units form via basal freeze‐on of subglacial water that originated from further upstream. Our findings suggest that basal freeze‐on, and the entrainment and transport of subglacial material play a significant role in an accurate representation of material, physical, and rheological properties of the Antarctic ice sheet's basal ice, ultimately enhancing the accuracy and reliability of ice‐sheet modeling. Plain Language Summary: We investigate the lowermost portion of the ice column of the Antarctic ice sheet, known as basal ice. This part holds crucial information about how the ice sheet behaves when it flows. Using the principle of echo‐location, we use radar technology to scan the ice in East Antarctica's Jutulstraumen drainage basin. We discover that a significant portion of the basal ice in this region is filled with sediment and can be several hundred meters thick. To better understand how this distinctive type of ice forms, we used a mathematical model that suggested that these ice units likely form when water underneath the ice is transported and refreezes at particular locations. Our findings highlight the importance of these freezing and mixing of materials from beneath the ice. Understanding where these ice units are located provides important information for ice‐flow models to ultimately better understand how the Antarctic ice sheet behaves in the future. Key Points: We have identified high‐scattering basal ice in Jutulstraumen Glacier's onset region using radar, reaching several hundred meters from the bedBackscatter analysis suggests that the basal ice units contain unstratified point scatters and cause little radio‐glaciological loss3D thermo‐mechanical modeling implies that freeze‐on of basal meltwater generated upstream likely initially formed the basal ice units [ABSTRACT FROM AUTHOR]

Sediment grains are progressively rounded during their transport down a river. For more than a century, Earth scientists have used the roundness of pebbles within modern sediment, and of clasts within conglomerates, as a key metric to constrain the sediment's transport history and source area(s). However, the current practices of assessment of pebble roundness are mainly qualitative and based on time-consuming manual measurement methods. This qualitative judgement provides the transport history only in a broad sense, such as classifying distance as "near" or "far". In this study, we propose a new model that quantifies the relationship between roundness and the transport distance. We demonstrate that this model can be applied to the clasts of multiple lithologies including modern sediment, as well as conglomerates, deposited by ancient river systems. We present field data from two Himalayan catchments in Nepal. We use the normalized isoperimetric ratio (IRn), which relates a pebble's area (A) to its perimeter (P), to quantify roundness. The maximum analytical value for IRn is 1, and IRn is expected to increase with transport distance. We propose a non-linear roundness model based on our field data, whereby the difference between a grain's IRn and the maximum value of 1 decays exponentially with transport distance, mirroring Sternberg's model of mass loss or size reduction by abrasion. This roundness model predicts an asymptotic behaviour for IRn , and the distance over which IRn approaches the asymptote is controlled by a rounding coefficient. Our field data suggest that the roundness coefficient for granite pebbles is 9 times that of quartzite pebbles. Using this model, we reconstruct the transport history of a Pliocene paleo-river deposit preserved at the base of the Kathmandu intermontane basin. These results, along with other sedimentary evidence, imply that the paleo-river was much longer than the length of the Kathmandu Basin and that it must have lost its headwaters through drainage capture. We further explore the extreme rounding of clasts from Miocene conglomerate of the Siwalik zone and find evidence of sediment recycling. [ABSTRACT FROM AUTHOR]

The Levant Basin in the Eastern Mediterranean contains an ∼3-km-thick, predominantly siliciclastic section of Oligocene-Miocene age, which hosts large hydrocarbon reservoirs ("Tamar Sands Play"). Here, we present a provenance study of Oligocene-Miocene sandstones based on detrital zircon U-Pb-Hf and heavy mineral assemblages. Samples were retrieved from four boreholes across the Levant Basin: Myra-1, Dolphin-1, Leviathan-1, and Karish North-1. Our investigations revealed that the sediments are dominated by Neoproterozoic and older Precambrian zircons with variable Hf isotopic composition, indicating that they were mainly reworked from Paleozoic-Mesozoic sandstones of African-Arabian provenance, with minor derivation from the Neoproterozoic basement of the Arabian-Nubian Shield. Variations in the proportions of pre-900 Ma zircons were encountered in various levels of the siliciclastic section. These zircons were markedly enriched (44%-57%) in the Rupelian and Aquitanian-Burdigalian intervals, accompanied by abundant detrital apatite peloids in the heavy mineral fraction, and relatively sparse (21%-38%) in the Chattian-Aquitanian and Langhian-Tortonian intervals, alongside scarce Mesozoic-Cenozoic zircons. These findings allow us to associate the deep-basin detrital record with two sedimentary transport systems that reached the Levant Basin from both NE Africa and Arabia simultaneously until the late Miocene, when sediment transport from Arabia ceased. While Rupelian and Aquitanian-Burdigalian sediments, including the main section of the "Tamar Sands," were derived mainly from Arabian sources via the Levant continental margin, Chattian-Aquitanian and Langhian-Tortonian sediments were primarily sourced from NE Africa via the Nile Delta. Detrital contribution from the Eurasian side of the Eastern Mediterranean was not identified, suggesting that sand originating in the Arabia-Eurasia collision belt did not reach the Levant Basin. [ABSTRACT FROM AUTHOR]

Acoustic velocity varies in deep-water environments, and the variable-velocity seawater can affect the dispersion characteristics of Scholte wave. To improve the accuracy of inversion, a horizontal layered-seawater and layered-seabed (HLSLS) model is established with continuously varying velocities for seabed S-wave velocity inversion using Scholte wave. First, we deduced the Scholte wave dispersion equation and the amplitude-depth equation of the HLSLS model based on wave theory. Then, with the real acoustic velocity of the seawater and submarine sediments parameters of the Shenhu area in the South China Sea, we analyzed the influence of variable-velocity seawater on the dispersion characteristics of Scholte wave. Finally, we performed two-dimensional (2D) S-wave velocity inversion on the field OBS multi-component data in the South China Sea. The results showed that the variation of seawater acoustic velocity had a certain influence on the dispersion characteristics of Scholte wave in deep water. The accuracy and practicality of our method were verified through numerical and filed data experiments. [ABSTRACT FROM AUTHOR]

Feedbacks between sediment and plants in the submersed aquatic vegetation (SAV) beds of the Susquehanna Flats help modulate sediment delivery into the upper Chesapeake Bay from its major tributary (Susquehanna River). Recent modeling work has shown that SAV can steer the river plume, directly controlling sediment transport and fate. However, transport mechanisms likely differ between flood and non‐flood conditions and depend on event timing. An opportunity to evaluate these insights in the field occurred with several flood events in summer 2018. Sediment and biomass samples were collected after the flood in the large, continuous main SAV bed of the Flats and in smaller patches to the west of the main bed to evaluate the effect of SAV bed size (width). Sediment characteristics (grain size, organic content) and deposition rates were compared to previous observations during non‐flood conditions in the main bed in 2014–2015 and in the smaller patches in 2019. Overall, sediment deposition rates could be predicted by an empirical model including sediment load, vegetation biomass, and SAV bed width, reflecting the role of vegetation in steering the Susquehanna River plume and modulating sediment input to the upper Chesapeake Bay. Understanding spatiotemporal patterns of sedimentation is essential for realistic estimates of sediment and nutrient (especially nitrogen and carbon) storage in freshwater SAV systems, which have not received as much attention as their saltwater counterparts. [ABSTRACT FROM AUTHOR]

A high‐resolution wave model is crucial for accurate modeling of sediment and organic material transports, but its computational costs hinder direct coupling to an ecosystem model. We developed a machine learning model using long short‐term memory to simulate large‐scale, high‐resolution waves. Trained with numerical wave model (NWM) outputs and wind data from nine locations, our model successfully replicates NWM results for daily mean significant wave height and period in Chesapeake Bay with identical spatial resolution. Compared to the NWM, the data‐driven model has root‐mean‐square errors below 6 cm for daily mean significant wave height and 1 s for the wave period in the bay. It demonstrates excellent model skills and can accurately forecast daily mean significant wave height and period at NOAA wave stations comparable to NWMs. Using minimal wind data and having a short runtime, our data‐driven model shows promise as an alternative for wave forecasting and coupling with sediment and ecological models. Plain Language Summary: Accurately modeling sediment and organic transport necessitates the use of a high‐resolution numerical wave model (NWM). However, the computational expenses of running an NWM within an ecosystem model pose significant challenges. We conducted a study using a machine learning approach based on long short‐term memory to replicate the results of an NWM. The data‐driven wave model (DWM) was trained with the NWM outputs and wind data from nine locations. The trained DWM can replicate the NWM results of daily mean significant wave height and period in Chesapeake Bay with identical spatial resolution and the same predictive skill with a root‐mean‐square error of less than 6 cm and 1 s, respectively for the model domain. The model successfully forecasted daily mean significant wave height and period at NOAA wave stations, showing great forward prediction capability. Notably, the DWM only relied on a minimal amount of wind data from selected locations and had a short runtime. These findings indicate that machine learning is promising as an alternative approach to NWM for wave forecasting. Moreover, it can serve as an alternative wave model and be coupled to ecological models for simulating sediment transport, light attenuation, and resuspension of organic materials. Key Points: A machine learning‐based wave model reproduces the numerical wave model (NWM) results at the same spatial resolution with good accuracyThe data‐driven model, trained on daily significant wave height and period using NWM outputs, has comparable wave prediction skillThe fast‐running data wave model, driven by wind data from nine locations, can forecast waves and couple with sediment and ecological models [ABSTRACT FROM AUTHOR]

Fluvial discharge is a principal driver of suspended sediment (SS) transport in the Central Himalayan region, Nepal. The study examines the relationship between specific discharge at three hydrometric stations along the main Kali Gandaki (KG) River, four hydrometric stations on its tributaries with rainfalls across the entire basin and its sub basins, in relation to SS transport at a hydropower reservoir. Over the period of 2006–2017, the average monthly rainfall in June (388.39 ± 84.24 mm), July (674.91 ± 105.24 mm), August (571.81 ± 110.77 mm), and September (356.50 ± 104.39 mm) yielded an average of 2.469 ± 1.641, 12.952 ± 4.932, 12.629 ± 7.937, and 4.406 ± 2.363 megatons (Mt) of SS loads, respectively, flowing from the KG catchment into the hill-side dam reservoir. Results indicated that approximately 97% of SS was transported during the monsoon season (June–September). This corresponds to an estimated annual weathering rate in the basin of 4390 tons/km2/year, equivalent to 1.66 mm/year. Notably, both the specific direct runoff discharge and the monsoonal daily erosion rate during major rainfall events (> 30 mm/day) exhibited an upward linear trend with the basin's rainfall. [ABSTRACT FROM AUTHOR]

Human-induced shoreline instability is a widespread issue among the world's Mega Deltas. Out of 120 million tons/year of sediment, 30 million tons/year reached Damietta promontory before the entire operation of Aswan High Dam (AHD), which blocks most of that sediment. This study uses remote sensing techniques to investigate the Land Use Land Cover Changes (LULCC) and the shoreline dynamics around Damietta promontory. In addition, more attention was devoted to the challenges of Damietta Harbour, which regularly suffers from inlet closure using a filed validated morpho-dynamic model addressing sediment transport and erosion problem at the eastern part. The LULCC based Maximum Likelihood approach shows that the developed areas were doubled from 1984 to 2018. Besides, within the Area of Interest (AoI), 8.961 km2 were eroded during the period (1984–2000), while 2.7046 km2 were eroded during (2000–2018). Change detection technique showed that accretion area was 1.8991 and 2.4909 km2 for the periods 1984–2000 and 2000–2018, respectively. Six scenarios were tested to investigate the best combinations of interventions to mitigate the challenge of siltation inside the harbour entrance and the erosion at the eastern side. Morphodynamical results showed that scenario 4 (two groins each 1000 m length at the west side of the western jetty combined with two groins each 500 m length at the east side of the existing eastern jetty of the harbour) has considered the best scenario. [ABSTRACT FROM AUTHOR]

Atolls islands are biogenic landforms that are intrinsically capable of adjusting their size, position, and elevation to changing sea levels. The vulnerability of atoll islands to sea level rise is not intrinsically due to their low elevation but primarily due to the loss of their island building capacity. The geophysical processes that control atoll island accretion are being impacted on global and local scales. Protecting and restoring the natural geophysical processes of atoll island accretion through local conservation actions is key to unlocking nature-based opportunities for enhancing atoll resilience to global change. Atoll islands are often perceived as inevitably lost due to rising sea levels. However, unlike other islands, atoll islands are dynamic landforms that have evolved, at least historically, to vertically accrete at a pace commensurate with changing sea levels. Rather than atoll islands' low elevation per se , the impairment of natural accretion processes is jeopardising their persistence. While global marine impacts are deteriorating coral reefs, local impacts also significantly affect accretion, together potentially tipping the scales toward atoll island erosion. Maintaining atoll island accretion requires intact sediment generation on coral reefs, unobstructed sediment transport from reef to island, and available vegetated deposition sites on the island. Ensuring the persistence of atoll islands must include global greenhouse gas emission reduction and local restoration of accretion processes. [ABSTRACT FROM AUTHOR]

The study investigates textural characteristics of foreshore sediment along the central Kerala coast. The selected beaches extend from Ponnani in the north to Alleppey in the south along the west coast of India. Samples were collected from foreshore zone at 22 selected locations to assess sediment grain size distribution and its seasonality. Statistical parameters such as mean (M), standard deviation (SD), skewness (Sk), and kurtosis (K) were used to evaluate the textural characteristics. The purpose of the present study was to examine the textural behaviour of coastal sediments in different seasons from November 2014 to October 2015. Textural characteristics show that the sediment samples are unimodal and bimodal with medium and fine grain sand. The standard deviation (sorting) reveals the sediment samples are very well sorted to moderately sorted with a range of 0.24 phi to 1.03 phi, while the skewness values of the sediment samples range from −0.55 phi to 0.32 phi. The CM plot depicts that the foreshore sediments are transported by tractive currents and transporting the sediments by rolling, bottom suspension with rolling. The analysis of Linear Discriminant Function (LDF) illustrates that the sediment samples are accumulated by aeolian or coastal and shallow turbulent environments. [ABSTRACT FROM AUTHOR]

The concession of the Peruvian Amazon Waterway (PAW) project seeks to strengthen commercial transport between Brazil and Peru by using four rivers: Amazon, Ucayali, Marañón, and Huallaga, in which the Peruvian Ministry of Transportation and Communications (MTC) was in charge of developing the Terms of Reference (TOR). At the end, the TOR did not specify the methodology for the hydrogeomorphic characterization of rivers. The PAW project was designed to meet specific geometric characteristics to ensure navigable conditions: minimum water depth of 2.44 m (8 ft) and channel width ranging from 44 to 56 m, approximately. The zones where the river bottom limits the layout and dimensions of the navigation channel are called shallow zones (SZs). Based on the PAW project's TOR, the EIA-d (Detailed Environmental Impact Assessment) study was carried out using 14 SZs that required dredging 3.87 million m3 of sediments. In 2019, the EDI (Definitive Engineering Study) described 24 SZs with a total dredging volume of 4.39 million m3 of sediments. The number and locations of SZs and the volume of required dredging changed significantly, revealing a lack of understanding of meandering (i.e., Ucayali and Huallaga) and anabranching (i.e., Marañón and Amazon) river processes. This study presents an integral methodology for the hydrogeomorphic characterization of the meandering Huallaga River (the river with 56% of the total estimated volume to dredge) by using remote sensing and field measurements (hydrodynamic, sediment transport, and bathymetry). Geological confinement of river dynamics, together with the presence of anabranching structures, promote stable SZs. In regions where meandering rivers tend to develop ancient and modern geomorphic structures, SZs are temporarily and highly dependent of river dynamics. The present hydrogeomorphic characterization of the Huallaga River will support the Peruvian government to inform their technical guidelines (TOR), especially for infrastructure projects (e.g., PAW) in Amazonian rivers. Several river-related engineering projects lack a broad and comprehensive view to understand a river's spatial and temporal dynamics. One of these projects is the Amazon Waterway (Hidrovía Amazónica in Spanish) which sought to strengthen commercial transport between Brazil and Peru using four rivers: Amazon, Ucayali, Marañón, and Huallaga. The Terms of Reference (TOR) for the Environmental Impact Study (EIA) did not specify the methodology for understanding river dynamics; however, the focus was mainly concentrated on the need to develop dredging activities. During the EIA evaluation stage, more than 400 technical observations were presented, several related to fluvial geomorphology. This article presents a synthesis of how proper river studies should be carried out and how river dynamics is related to aquatic biodiversity, highlighting the importance of understanding rivers before developing infrastructure projects. [ABSTRACT FROM AUTHOR]

Shorelines face growing threats due to climate change and diminishing sand supply. Coastal headlands, common rocky features along coastlines, are crucial in shaping hydrodynamics and sediment transport. Yet, the influence of future climate conditions, including sea‐level rise (SLR) and intensified storm energy on complex shorelines with headlands has remained relatively unexplored. In this study, we model changes in hydrodynamics and headland bypassing under different SLR and higher storm wave scenarios. Our findings reveal the formation of circulation cells on both sides of a headland, where wave energy converges around the headland zone. Future climate conditions result in larger storm waves on the beach. However, SLR enhances nearshore currents through a landward shifting of the circulation cells, while higher storm waves intensify offshore flow currents due to the seaward movement of the cells. This effect, in turn, increases the potential for headland sediment bypassing. Plain Language Summary: Coastal headlands, prominent rocky features along open coastlines, play a crucial role in protecting nearby beaches from strong waves and erosion. They also affect how sand is exchanged between different beaches. We use a model to explore how future climate conditions including sea‐level rise (SLR) and larger storm waves influence coastal waves, littoral currents, and the transport of sand around headlands. Our findings reveal that headlands converge wave energy forming circulation flow cells. SLR results in stronger nearshore currents, driven by the landward movement of the rotating flow cells. In contrast, larger storm waves can move the rotating flow cells seaward, thereby increasing offshore current strength and the potential for sand transport around the headland. Understanding how coastal waves, flow and sediment transport change under future climate conditions will help determine coastal resilience. Key Points: The formation of circulation cells and wave energy convergence around headlands during storms reduce bottom shear stress at the beachSea‐level rise increases wave heights, currents, and bed shear stress in the nearshore because of landward shifting of the circulation cellsHigher storm waves expand the surf zone, shift circulation cells seaward, and enhance potential headland sediment bypassing [ABSTRACT FROM AUTHOR]

The in situ measurement of sediment transport in wave‐dominated environments presents significant challenges and currently often relies upon the use of fluorescent sediment tracers. However, this method is constrained by challenges in conducting unbiased and representative sampling, as well as facing overall logistical complexities and labour‐intensive procedures. Whilst other tracer techniques are available, such as using magnetic tracers, their performance in tracking sediment transport has not been quantified. The objective of this study is to assess the effectiveness of magnetic tracers in evaluating net transport rates and tracer dispersal patterns. Conducted in a controlled large wave flume, the experiments simultaneously employed fluorescent and magnetic tracers, allowing a comprehensive comparison of the tracers' dispersion patterns and the net transport rates. Results show that the dispersal of magnetic and fluorescent tracers displays a high degree of spatial coherence in both horizontal and vertical dimensions. Similarly, net transport rates are comparable (<16% difference), both showing net transport in the direction of the wave propagation (towards onshore) driven by non‐linear and streaming effects. Magnetic tracer recovery rate (49%) was lower than for fluorescent tracers (73%) and is attributed to the loss of magnetic ink from particles; an aspect of the magnetic technique that requires improvement. This study therefore indicates that the use of magnetic tracers to quantify sediment transport is an effective method with the advantages of being significantly less labour‐intensive than using the commonly applied fluorescent sediment tracer method. [ABSTRACT FROM AUTHOR]

Estuarine sediment transport is driven by the combined action of a multitude of influencing factors, including astronomical tides, waves dynamics, and river discharges. This study focuses on the effects of wave forces on sediment transport patterns in micro-tidal estuaries near Wanbao Beach, China. Numerical simulations are carried out using Delft3D. Modeling scenarios are configured using different wave characteristics, spanning from typical waves to those with a return period of 50 years. Results show that waves have a positive effect on landward sediment transport, resulting a larger active range of sediment. By comparing the spatial geomorphic variations under varying wave conditions, we find that modifications in significant wave height (Hs) primarily impact the position of erosion and deposition zones, whereas alterations in spectral peak period (Tp) predominantly influence the magnitude of these changes. The finding is further demonstrated by a comparison of residual currents under different wave intensities. Analysis of sediment transport rates in different transects indicates that the sediment transport rate is highest at the mouth transects and lowest at the alongshore transects. Moreover, variations in sediment transport rates exhibit distinctive patterns between the two outlet transects, even when subjected to identical wave conditions. The disparities are attributed to differences in runoff and the topographical features in proximity to the estuaries. Additionally, we find the sediment transport rate becomes insensitive to the variations in Hs when Hs is larger than a threshold value. The threshold decreases with increasing Tp. [ABSTRACT FROM AUTHOR]

The impact of raindrops on sheet flow (SF) is a common phenomenon, which plays a vital role in many important nature and engineering fields. The flow resistance of SF is critical for describing flow characteristics and calculating the sediment transport capacity. However, information regarding the theoretical resistance equations of the total resistance of SF subjected to raindrop impact (fr) and the resistance induced by raindrop impact (Δf) is limited. In this study, combination of the π-theorem of dimensional analysis and multiple experimentally simulated rainfalls and inflows was conducted to obtain and verify the deduced predictive flow resistance equations. The results indicated that using dimensionless variables deduced by the π-theorem to calculate the flow resistance equation was appropriate. The main control of fr of SF under rainfall is the ratio of surface roughness to water depth deduced by π-theorem. A newly developed equation [Eq. (24)] can be used to predict fr, with a Nash-Sutcliffe efficiency index (NSE) of 0.91 and a normalized root mean square error (NRMSE) of 0.166. Δf is a very important component to overall SF resistance, accounting for 0.34%–47.79% of fr. The deduced dimensionless variable of the ratio of rainfall intensity to flow velocity is the main controlling factor of Δf. Finally, a new equation [Eq. (26)] was developed to predict Δf, with NSE = 0.673 and NRMSE = 0.445. This study is helpful for understanding the flow resistance subjected to raindrop impact and provides new and scientific equations for flow resistance coefficient prediction. [ABSTRACT FROM AUTHOR]

The 2021 Navalacruz wildfire occurred in a mountainous area in the Sistema Central (Spain). Despite having an average low severity index (dNBR), the loss of vegetation cover associated with the fire was responsible for a high rate of sedimentation in the rivers and streams. Additionally, the burned area affected up to 60 cultural heritage sites, including archaeological and ethnological sites, and damage ranged from burnt pieces of wood to the burial of archaeological sites. In the present work, we document and analyze the post-fire evolution in several rivers and streams. This is based on a field survey of infiltration rates, hydrodynamic modeling, and the study of channel morphological changes. Our analysis revealed how the first post-fire rains caused the mobilization and transport of ashes. This created hydrophobicity in the soils, resulting in large amounts of materials being transported to rivers and streams by subsequent medium- and low-magnitude storms. A hydrological and hydraulic model of the study catchments under pre- and post-fire conditions suggests that these trends are a consequence of a post-fire increase in flow rates for similar rainfall scenarios. In this respect, our estimates point at a significant increase in sediment transport capacities associated with this post-fire increase in flow rates. The combination of locally steep slopes with high-severity fire patches, and a considerable regolith (derived from pre-fire weathering), resulted in a series of cascading responses, such as an exacerbated supply of sand to the drainage network and the triggering of debris flows, followed by erosion and entrenchment. [ABSTRACT FROM AUTHOR]

Following the eruption of the Taal Volcano in January 2020 and its continuous signs of unrest in the preceding years, this study delves into the investigation of sediment transport in the Pasig River, Philippines. The historical data of total suspended solids (TSS) and arsenic indicated a notable increase starting from the year 2020. The field measurements were conducted in February and March of 2022, two years after the eruption. Due to the observed homogeneity in the river's mixing, a refined 1D sediment transport model was developed. In this study, HEC-RAS modeling software was employed. The calibration process using the Laursen transport function yielded an impressive R2 value of 0.9989 for the post-eruption model. This predictive accuracy underscores the robustness of the developed model. The study's scope was further expanded by creating a model for February 2020, incorporating water quality data gathered by the Pasig River Coordinating and Management Office. The model simulation results showed peak TSS values of 120.63 mg/L and 225.15 mg/L in February 2022 and February 2020, respectively. The results of the study highlight the probable impact of geological events on sediment dynamics within the Pasig River, which could help manage and sustain ongoing river improvements. [ABSTRACT FROM AUTHOR]

In this study, a new remote sensing tool was used in conjunction with sampling of river bank sediments to map channel migration patterns and estimate the net contribution of bank erosion to the sediment and phosphorus (P) budget of the Nishnabotna River in southwestern Iowa. Between the years 2009 and 2018, we found that at least 1.81 ± 0.57 × 107 Mg of sediment and 8.26 ± 2.5 × 103 Mg of P entered the Nishnabotna River due to channel migration. This equates to 0.87 Mg of sediment per meter of channel per year and 0.40 kg of P per meter of channel per year. Barring additional deposition elsewhere in the river corridor, these values represent as much as 77% of annual suspended sediment and 46% of the annual P export from the watershed. Our results also indicate that the contribution of net sediment and P volume loss by stream order increases sharply from third to sixth order, even though the total channel length is much smaller in the higher orders. These results suggest that bank erosion is an important source of sediment and P within the watershed and that future attempts to decrease riparian exports of sediment and P should focus on high‐order reaches. [ABSTRACT FROM AUTHOR]

The process of removing water from sewage sludge is particularly important due to its high content in the raw sludge. This translates into problems with the transport and storage of sediments. Additionally, high water content reduces the calorific value of the sludge. The methods for selecting the appropriate parameters for sewage sludge conditioning and filtration, based on the experimental data presented in this work, may allow for the optimization of sludge dewatering lines in small and large sewage treatment plants. The optimization of the dewatering process has a significant impact on the environmental and economic benefits, which consequently results in a decrease in the power costs of the devices used, flocculants, and sludge processing, and, above all, it contributes to the reduction in the negative impact on the environment. The use of mineral substances in the preparation of sewage sludge improves the effects of its dewatering in the pressure filtration process, as expressed in the obtained values of the final hydration and process efficiency. The use of polyelectrolytes alone significantly improves the effects of sewage sludge dewatering. In this work, the polyelectrolytes were supported by the addition of cement or zeolite. The conditioning of sewage sludge in combined methods using C-494 polyelectrolyte and minerals made it possible to reduce the compressibility coefficient to the range of 0.24–0.47 and, at the same time, to achieve the best results of sludge dewatering in the filtration process. The lowest hydration of 74.9% was achieved when polyelectrolyte and cement were added to the sludge, and this hydration was 6.5 percentage points lower compared to that of the non-filtered sludge. [ABSTRACT FROM AUTHOR]