Bedload Sediment Research Articles

Contrasting modes of sediment infilling and geomorphic change within a sand dominated dredge pit on the inner Louisiana shelf

While many sediment transport studies have been performed on mud capped dredge pits (MCDP), there is a paucity of sediment infilling data for sand dominated dredge pits (SDDP) in the Northern Gulf of Mexico (NGoM). In this study, bathymetry, sidescan, and subbottom data were collected in 2018, 2019, and 2020 and sediment cores were collected between the 2019 and 2020 surveys at Block 88: a dredge pit sitting on the sand-dominated Ship Shoal of Louisiana's inner shelf. The crest of Ship Shoal was 5 m below mean sea level before dredging and was excavated to a depth of 10 m below mean sea level after the dredging of 8.4 million m3 of sediment. Two years after dredging, the northern end of the eastern pit wall accumulated ∼0.09 million tons (approximately 500 m long × 50 m wide × 2.5 m deep) of sediment, driven by westward longshore sediment transport and the deposition of bed load on the shoal crest. Sediment accumulation on the pit bottom was mainly driven by suspended load at a rate of ∼0.1 m yr−1 from 2018 to 2019 and ∼0.2 m yr−1 from 2019 to 2020. Thus, the sediment infilling in Block 88 was from both bed- and suspended-loads from contrasting sources. These pit-bottom sediment accumulation rates are approximately one order of magnitude lower than the predicted rate from a previous empirical modeling study conducted on Ship Shoal and lower than the rates (0.5–2 m yr−1) of three other MCDPs on the inner Louisiana shelf. The infilling sediment was patchy and predominantly silt and clay, with lower sidescan reflectivity. The slopes of Block 88's pit walls decreased from ∼20° in 2018 to ∼8° in 2020. These values were smaller than the values of pit wall slopes in MCDPs at a similar stage (i.e., 2–3 years after dredging). Our results indicate that the highest sediment accumulation rates occur immediately adjacent to the eastern pit wall of Block 88, which is down-current of the longshore transport direction. This study helps sand resource managers and policymakers to better plan and design future sediment dredging projects on sandy shoals. This study concludes that the longest axis of a dredge pit should be aligned perpendicular to the longshore transport direction to trap the most sediments for possible reuse. Additionally, both bed load and suspended load should be considered in future modeling to better predict sediment infilling.

Analysis of the mechanics of breaker bar generation in cross-shore beach profiles based on numerical modelling

In this work, a recently developed numerical model, capable of solving the hydro- and morphodynamics of the cross-shore beach profile, is used to gain insight into the relevant processes driving the generation of a breaker bar. The bedload and suspended sediment transport contributions are analysed separately. It has been shown that the bedload transport tends to accumulate sediment on the onshore side of the undertow detachment point, at a distance that depends on the skewness of the waves and the magnitude of the friction velocity, shaping the onshore face of the breaker bar. In contrast, the suspended transport contributes to the growth of the offshore side of the breaker bar. Besides, a comparison between the sediment transport rates produced by different types of breakers shows a faster bathymetric evolution and an offshore displacement of the position of the breaker bar for high Iribarren numbers. Differences are consistent with the proposed mechanisms driving the evolution of the beach profile. The findings of this work provide a better understanding of the processes driving the formation of breaker bars, how they interact with each other and the relative importance of bedload and suspended sediment transport at each location of the cross-shore profile.

Historical development of the Regime Geometry Equations, Part-I

The present study intended to review the historical development of the regime geometry equations proposed by many researchers since 1895. Kennedy started the search for the attributes of stable channels on the Upper Bari Doab Canal of Punjab in 1980-1984. The regime concept was presented by Lindley (1919) that later on Lacey (1930) modified to a set of most widely used regime relations. Later on, Blench (1941-1957), and Simons and Albertson (1960) presented their equations. This period is called ‘canal regime period’ because most of the research focused on canal design. The concept of regime was extended to river systems by Leopold and Maddock in 1953. In 1963, Henderson proposed some regime equations that can be applied for predicting canal and river geometry. This period was the transition from canal regime period to river regime period and from an empirical approach to analytical approach and is called as ‘Transitional Period’. Many other researchers written the information based on analytical approach, or a combination between analytical and empirical approaches, and more focused to river regime especially gravel bed river regime. This period is, called ‘River regime period’. Flow discharge, sediment size, and bed-load sediment are the three main factors that influence the geometry of alluvial channels. The hydraulic geometry relationships indicate that sediment size and bed-load sediment strongly influence the channel slope, moderately influence the flow velocity, and slightly influence the channel depth and the channel width. This study also shows that in terms of Shields parameter, the exponents of discharge, sediment size, and sediment transport are dependent on the relative submergence (D/d50).

Prediction of Bed-Load Sediment Using Newly Developed Support-Vector Machine Techniques

Prediction of Bed-Load Sediment Using Newly Developed Support-Vector Machine Techniques

Modeling of 1D sediment transport in the langat river using quasi-unsteady HEC-RAS

The primary goal of this research was to investigate the sediment transport characteristics of the Langat River. The Langat River is situated in the state of Selangor, Malaysia, and is prone to flooding on a regular basis. The River Analysis System tool from the Hydraulic Engineering Center (HEC-RAS) was used to determine the sediment transport capacity of the river. The sediment transport and hydraulic models were created using elevation and cross-sectional data in HEC-RAS. The sediment transport model employed several approaches to calculate sediment transport capacity. HEC-RAS contains some useful built-in functions which were used in this study to visualize the sediment transport, calibration and calculation of Manning’s roughness coefficients, and forecast changes in bed elevation. The investigation reveals that urban development has resulted in a large rise in riverbed depth, implying that is no difference in flooding pattern in the short period of time. This paper focuses only on bed load sediment. The results of three years of stream flow show that some areas have experienced silt transport and river deposition. The river had changed slightly after utilizing the Laursen-Copeland method in HEC-RAS. The simulation outcome shows the segment that experienced sediment transport at River Stations RS 12926 from Lui, RS 9362 from Langat upper reach, and RS 3730 from Langat Lower Reach are experiencing sediment deposition activities.

Estimation of bedload sedimentation rate in a paleo-drowned river-valley

Extensive, high-resolution seismic data were correlated with borehole, land use, and geological data to calculate the mass of genetically different sediment deposits in the Middle Harbour estuary in Sydney, Australia. Middle Harbour is a drowned-river valley located adjacent to the larger Sydney estuary. The estuary follows a well-defined sedimentation model featuring small fluvial bedload delta deposits in the upper reaches of the embayments, a deep, central extensive mud basin overlying transgressive basal accumulations and a large flood-tide delta at the entrance. Deposits of an estimated 5094 t of bedload, 21,143 t of suspended sediment and 5947 t of transgressive basal material located in the estuary provided average sediment accumulation rates of 0.68 t year−1, 1.29 t year−1, and 2.86 t year−1, respectively. These rates, determined from measured accumulations, were surprisingly low and substantially smaller than modelled rates. However, low sediment accumulation rates for suspended material may be due to fine sediment escaping over the top of the marine tidal delta, which effectively traps all bedload material from exiting the Harbour. Results of this study indicate that Holocene bedload sedimentation in Middle Harbour was slow and regular until a rapid increase after urbanisation commenced in the catchment. Most pre-Holocene material was eroded from Middle Harbour during the Last Glacial period with sediment currently present in the estuary having been deposited since sea-level recovery.

Latest Pleistocene and Holocene Floodplain Evolution in Central Europe—Insights from the Upper Unstrut Catchment (NW-Thuringia/Germany)

The upper Unstrut River is located in Germany at the modern Central European climate boundary of Cfb and Dfb climate. The river drains a loess landscape, which has experienced important environmental changes throughout the last 12,000 years. To evaluate the impacts of these changes on floodplain evolution, a multi-proxy research program, consisting of 2D electrical resistivity tomography profiling (ERT), vibracoring, and sedimentological investigations, 14C and OSL dating were applied. From base to top the investigations the following fluvial deposits were revealed: (1) gravels embedded in a fine-grained sediment matrix (interpreted as fluvial bedload deposits); (2) silty sediment with pedogenic features (interpreted as overbank floodplain deposits); (3) peat and tufa deposits (interpreted as wetland deposits) intercalated by pedogenetically influenced silty sediments (interpreted as overbank deposits); (4) humic silty sediment with some pedogenic features (interpreted as overbank floodplain deposits); and (5) silty sediments (interpreted as overbank deposits). Radiocarbon and luminescence dates yielded the following periods for sediment formation: (1) Younger Dryas to Preboreal period (around 11.6 cal ka BP); (2) Preboreal to early Atlantic period (approx. 11.6 to 7.0 cal ka BP); (3) early Atlantic to late Subboreal period (approx. 7.3 to 3.4 cal ka BP); (4) late Subboreal to early Subatlantic period (2.9 to 2.3 cal ka BP); and (5) late Subatlantic period (approx. 1.0 to 0.6 cal ka BP). The results suggest that floodplain development during the latest Pleistocene and early Holocene (approx. 11.6 to 7.0 cal ka BP) was considerably controlled by climatic conditions and short-term climate variabilities, which caused gravel deposition and overbank sedimentation. Afterwards floodplain conditions varied between rather stable (peat and tufa development, initial soil formation) and active periods (deposition of overbank fines). In this context, active periods with increased sediment input prevailed from approx. 5.1 to 3.4 cal ka BP, 2.9 to 2.3 cal ka, and 1.0 to 0.6 cal ka BP, temporally corresponding well with increased land-use phases of the past. In conclusion this study demonstrates that the investigated Unstrut catchment has reacted very sensitively to natural and human-induced changes during the latest Pleistocene and Holocene. Consequently, this high vulnerability to external changes should be considered in future river predictions or river management.

A bedload transport in shallow water model applied for sediment transport in open channel flows

This paper presents the numerical approximation of bedload sediment transport due to shallow layer flows. The hydrodynamical component is modelled by a 2D shallow water system and the morphodynamical component by a solid transport discharge formula that depends on the hydrodynamical variables. The coupled system can be written as a non-conservative hyperbolic system. To discretize it, first we consider a Non-Homogeneous Riemann Solver scheme as well as a variant based on the use of flux limiters. In order to develop second-order scheme, we use a MUSCL method incorporating slope limiters in the spatial approximation and a two-step Runge-Kutta method for time integration. The comparison between results based on the proposed scheme and analytical results shows good agreement..

Stabilization of fluvial bed sediments by invasive quagga mussels (Dreissena bugensis)

AbstractRiver gravel mobility is an important control on river behaviour, morphology, and ecosystem processes. Gravel stability is dependent on abiotic flow and sediment properties, alongside less widely acknowledged biotic processes. The quagga mussel (Dreissena bugensis), a highly invasive bivalve, frequently occurs at high population densities in rivers and lakes. Quagga mussels attach to benthic sediments using byssal threads, which might affect sediment stability and thereby broader river geomorphology. We aimed to (1) characterize controls of quagga mussel sediment attachment by conducting a field survey in an invaded river, (2) investigate resultant changes in the critical shear stress needed to entrain fluvial bed materials via an ex situ flume experiment, for measured average (135 m−2) and potential future (270 m−2) mussel densities, and (3) model how this may affect sediment transport rates. From field surveys, mean quagga mussel density was 122 m−2, attaching to an average of 591 g m−2 of mineral bed sediments. Across the survey reach, mussels attached to all grain sizes available, with attachment driven by grain availability, rather than active selection of particular grain sizes. In the ex situ flume experiment, densities of 135 mussels m−2 did not significantly increase the critical shear stress of fluvial bed materials, but a density of 270 mussels m−2 significantly increased critical shear stress by 40%. Estimates of the proportion of time these critical stresses are exceeded at the field site indicated high densities of quagga mussels may reduce the occurrence of a geomorphically active flood event from Q30 to Q2. These results present feasible invasion scenarios, as quagga mussels frequently reach benthic densities orders of magnitude greater than observed here. This study indicates that substantial alterations to bedload sediment transport may occur following quagga mussel invasion. Future geomorphic modelling should include biology to better understand rates and processes of landscape development.

Probabilistic description of bedload fluxes from the aggregate dynamics of individual grains

Abstract. We formulate the bedload sediment flux probability distribution from the Lagrangian dynamics of individual grains. Individual particles obey Langevin equations wherein the stochastic forces driving particle motions are switched on and off by particle entrainment and deposition. The flux is calculated as the rate of many such particles crossing a control surface within a specified observation time. Flux distributions inherit observation time dependence from the on–off motions of particles. At the longest observation times, distributions converge to sharp peaks around classically expected values, but at short times, fluctuations are erratic. We relate this scale dependence of bedload transport rates to the movement characteristics of individual sediment grains. This work provides a statistical mechanics description for the fluctuations and observation-scale dependence of sediment transport rates.

Numerical investigation of sheet flow driven by a near-breaking transient wave using SedFoam

Sheet flow driven by a near-breaking transient wave is numerically investigated using SedFoam, a two-phase Eulerian sediment transport model in the OpenFOAM framework. SedFoam resolves the full profile of sediment transport processes within the bottom boundary layer based on closures for intergranular stresses and fluid–particle interactions. Compared with large-scale wave flume data, good agreements are obtained for streamwise flow velocity profiles, sediment concentration profiles, and the sheet flow layer thickness. Model results show near-bed velocity and sediment profile evolution within the sheet flow layer. Intense sediment suspension trailing the wave crest generates stable density stratification that dampens near-bed turbulent kinetic energy and contributes to decreasing bed shear stress. Results suggest that the buoyant flux dominates turbulent kinetic energy dissipation after the passing of the wave crest, coinciding with the reduction of bed shear stress. The instantaneous upper bound of the sheet flow layer exists in different log-law regimes under the transient wave, giving rise to a near-bed velocity profile that is highly dependent on the variable sheet flow layer wall unit. The effect of the profile shape parameter on bedload sediment transport is studied where the bedload predicted using the time-varying optimal profile shape parameter yields good agreement compared to the directly modeled bedload. Modeled sediment transport rates demonstrate that reduced bed shear stress caused by density stratification limits bedload and results in a suspended load-dominant mode.

A Predictor–corrector scheme for simulation of two-phase granular flows over a moved bed with a variable topography

In this paper, we propose a numerical simulation of two-phase shallow granular flows through a moved bed with a variable irregular topography via a predictor corrector scheme. This method consists of predictor and corrector stages. The predictor stage contains a parameter to control the numerical diffusion that is performed by utilizing limiters and Riemann invariant theory. The corrector stage recovers the balance conservation equation. In the first part, we solve numerically the one-dimensional equation for two-phase shallow granular flows over a fixed bed with irregular topography. In the second part, we consider the model equations for the bed-load sediment transport, the governing model equations consist of two components, specifically, a geophysical flows part and interstitial fluid. The sediment part is described by the Exner equation when the velocity can be considered to be the solid velocity, fluid velocity or a mean value of both of them.

Controls on riverine calcium isotope ratios during basalt weathering in the Skagafjörður watershed, Iceland

This study examines the Ca isotope (δ44/40Ca) geochemistry of Icelandic rivers with the overall aims of improving the δ44/40Ca tracer, constraining solute sources, and addressing the hypothesis that basalt weathering disproportionately regulates Earth’s long-term climate. We report Ca isotope and elemental data for mainstem rivers, tributary streams, thermal and non-thermal springs, basalt, calcite, soil, vegetation, and sediment collected from the Skagafjörður region in North Iceland. Waters and calcite were further analyzed for their carbon isotope (δ13C) composition, and we conducted experiments to characterize δ44/40Ca values of riverine colloids, the clay-size fraction (<2 µm) of soil, and exchangeable leachates obtained from soil and bedload sediment. The dataset includes analyses of travertine and coexisting water samples collected from a CO2-rich spring (Hvanná river) in South Iceland.Samples show a ∼2‰ range, with groundwater, the ultrafiltered fraction of river water, and hydrothermal calcite producing among the highest δ44/40Ca values and travertine, soil exchangeable Ca, and vegetation the lowest. Riverine δ44/40Ca values are on average ∼0.20‰ higher than those for basalt, which shows minimal isotopic variability. Mainstem glacial-fed rivers entering the Skagafjörður valley from the soil- and vegetation-free highlands have higher δ44/40Ca values than direct-runoff tributaries draining catchments to the north where pedogenesis is more pervasive. Riverine δ44/40Ca values correlate with Sr/Ca and Na/Ca ratios, as well as the saturation index of calcite (SIcal). Riverine δ13C values increase from ∼−8‰ (atmospheric) to ∼−3‰ (calcite) as SIcal values increase from highly-undersaturated to near-equilibrium. One watershed (Svartá river) shows unique trends, where riverine δ44/40Ca values and Sr/Ca ratios do not correlate, and soil exchangeable leachates produced anomalously high amounts of Ca. Clay-size fractions isolated from three horizons composing a brown andosol show slightly lower δ44/40Ca values than bulk basalt, but the values overlap with those for primary minerals. Colloids appear to have lower δ44/40Ca values than truly dissolved Ca. The proxy could be developed as a tracer for colloidal contributions to riverine dissolved loads, especially in soil-mantled catchments where the inputs appear most pronounced. Groundwater δ44/40Ca values correlate with pH, temperature, distance from the coast, and Sr/Ca ratios, all consistent with fractionation control yielding varying degrees of geochemical evolution. The combined riverine patterns largely reflect three-component mixing between basalt weathering, calcite weathering, and hydrothermal water inputs. Subsurface Ca isotope fractionation indirectly impacts riverine δ44/40Ca values by elevating the δ44/40Ca values of groundwater and hydrothermal calcite. This study highlights the significance of hydrothermal water inputs of Ca and HCO3 to Icelandic rivers, which have been previously underappreciated. Mixing calculations suggest that a maximum of ∼20% of the Ca in mainstem rivers derives from surficial basalt weathering. Small tributaries draining the flanks of the valley show the clearest signals of basalt weathering by atmospheric CO2, but these waters have much lower solute concentrations than those employed in previous attempts to estimate basalt weathering rates and parameterize the climate sensitivity of the basalt weathering feedback.

Effect of timber removal on the total nutrient fluxes from a freshwater-supplying forested watershed.

Effects of 18% thinning on nutrient fluxes were investigated in a broadleaf forest. Streamflow and suspended sediment were sampled during the calibration and treatment periods for the treatment and control watersheds to determine total nutrient fluxes through bedload sediment and runoff. Streamflow was measured, and water samples were collected from the streams of the watersheds. The volume of the bedload deposited in both weirs' pools was measured, and sediment deposits were sampled at the ends of the calibration and treatment periods. Water and sediment samples were analyzed for calcium (Ca2+ ), magnesium (Mg2+ ), Kjeldahl nitrogen (KN), sodium (Na+ ), potassium (K+ ), iron (Fe3+ ), and sulfur (S2- ). Results showed that there was only a significant increase in KN loss from 0.01 kg/ha to 0.10kg/ha and from 0.04 kg/ha to 2.41 kg/ha in the second and the third post-treatment years, respectively (P < 0.05). Thinning was not intensive to change nutrient outflow in the study site. PRACTITIONER POINTS: The 18% thinning was not intensive enough to increase the total nutrient flux, deteriorate water chemical quality, and hence threaten aquatic life in the stream water. Significant increases were found only in KN outflow after timber removal. If there is no information about the effect of timber harvest on nutrient loss in a specific watershed, the application of evenly distributed low-intensity timber harvest may be a good option to protect stream water quality in forested watersheds. Further investigations are needed about the effects of various timber harvest intensities on physical water quality (odor, color, turbidity, taste, temperature, etc.) and biological characteristics (population and biodiversity of aquatic organisms) of the stream water for making better water management plans.

Flow Strength and Bedload Sediment Travel Distance in Gravel Bed Rivers

AbstractThe quantification of bedload sediment transport in rivers is possible from statistics of individual particle displacements. However, there is a lack of empirical basis for a universal relation between particle displacement distance and hydraulic drivers. Previous work suggests that a simple linear relation exists between the energy of a flood and the mean travel distance of bedload particles. Such a relation would be advantageous, but a consistent model able to collapse the data from different rivers has not been developed. Here, we develop a predictive relation from a unique data set collected in three watersheds from a single region but contrasting hydrologic regimes due to urbanization and storm water management. Additional data from two rivers from outside the region are used to validate the model. We show that the mean of an exponential distribution of surface particle travel displacements can be reliably predicted from either the cumulative discharge or stream power exceeding the mobilization threshold, which is calibrated using field data. The strength of the relation decreases after large flood events that appear to cause tracer burial due to vertical mixing. This result indicates that the relation is most applicable for the entrainment phase of transport in which tracers are dispersing over the bed surface. Tracer movements become more challenging to predict over a long series of events due to burial and eventual tracer slowdown, but the relation remains valid for the particles located on the bed surface, making it suitable for analyzing the impact of climate and landscape changes over time.

Estimating the equilibrium scour depth around two side-by-side piers with different spacing ratios in live-bed conditions

The aim of this research was to numerically investigate the flow behaviour and evolution of the local scour around a group of two side-by-side piers in live-bed conditions. A coupled hydro-morphodynamic model was developed in OpenFOAM®. The hydrodynamic part of the model solved the unsteady Reynolds Averaged Navier-Stokes equations. The morphodynamic part of the model entailed solving both bedload and suspended load sediment transport. The model validation was performed for the available experimental data in the literature. The modelling for the pier groups was carried out with three different spacing ratios of G/D = 1, 2, and 3, where G represents the distance between the piers and D is the pier diameter. The results presented detailed information regarding the flow field and scour hole progression adjacent to two side-by-side piers. The dimensionless equilibrium scour hole depths of 1.74, 1.38 and 1.29 were predicted for the pier groups with G/D = 1, 2, and 3, respectively. The results showed an inverse correlation between the spacing ratio and the scour hole depth adjacent to the piers. The results were generalised, and an equation was obtained for the prediction of the equilibrium scour hole depth as a function of the spacing ratio.

Mineralogical Fingerprint of Iron Ore Tailings in Paraopeba River Bedload Sediments after the B1 Dam Failure in Brumadinho, MG (Brazil)

The study presents SEM-based automated mineralogy to distinguish between natural sediments and iron ore tailings deposits from the Paraopeba River, after the failure of B1 Dam in Brumadinho, Minas Gerais, Brazil. Samples were obtained from borehole cores drilled over channel bars and banks eight months after the failure. After preliminary facies description, sediments from 54 chosen intervals were subjected to density measurement, X-ray diffraction (XRD), SEM-based automated mineralogy (QEMSCAN) analysis and determination of geochemical major components. Hierarchical clustering analysis (HCA) and principal component analysis (PCA) revealed six main mineral associations governed by different contents and ratios of quartz, kaolinite and hematite. Natural sediments are predominantly composed of mineral associations containing kaolinite, quartz and quartz + hematite with density values ranging from 2.5 to 3.3 g/cm3. Tailings deposits have density values higher than 3.5 g/cm3 and are mainly composed of hematite with occasional occurrences of kaolinite + hematite. Because of geological complexity and historical terrain occupation and usage, geochemical anomalies are common in the Paraopeba River sediments. Our data suggests that mineralogical oriented studies should precede detailed geochemical investigations, to enhance the understanding of the source of such anomalies and the environmental jeopardy associated to the occurrence. In this sense, SEM-based mineralogy has an enormous potential in environment studies.

Spatial Trends and Drivers of Bedload and Suspended Sediment Fluxes in Global Rivers

AbstractBedload is notoriously challenging to measure and model; its dynamics, therefore, remains largely unknown in most fluvial systems worldwide. We present results from a global scale bedload flux model as part of the WBMsed modeling framework that well predict the distribution of water discharge, suspended sediment and bedload. The sensitivity of bedload predictions to river slope, particle size, discharge, river width, and suspended sediment were analyzed, showing the model to be most responsive to spatial dynamics in river discharge and slope. The relationship between bedload and total sediment flux is analyzed globally, and for representative longitudinal river profiles (Amazon, Mississippi, and Lena Rivers). The results show that while the proportion of bedload decreases from headwaters to the coasts, there is considerable variability between basins and along river corridors. The topographic and hydrological longitudinal profiles of rivers are shown to be the key drivers of bedload trends, with fluctuations in slope controlling its more local dynamics. Estimates of water and sediment fluxes to global oceans from 2,067 largest river outlets (draining 67% of the global continental area) are provided. Estimated water discharge at 30,579 km3/y corresponds well to past estimates; however, sediment flux is higher. Total global particulate load of 17.8 Gt/y is delivered to global oceans, 14.8 Gt/y as washload, 1.1 Gt/y as bedload, and 2.6 Gt/y as suspended bed material. The largest 25 rivers are predicted to transport more than half of the total sediment flux to global oceans.

Bulk carbon and lignin fingerprinting of catchment sediments transported by mountain rivers in Nepal Himalayas

The Himalayan rivers yield the most significant flux of continental sediments into the ocean. Organic matter (OM) transported by these rivers provides a peek at the influence of diverse geological terrains, soil types, vegetation, and climate on carbon cycling within a narrow boundary. We analyzed suspended and bedload sediments from four Himalayan rivers to trace their sources, elucidate their fate during fluvial transport, and estimate the organic carbon (OC) flux. Hence, total OC (TOC), dissolved organic carbon (DOC), C:N ratios, and lignin phenols were measured. Consistent with the erosional intensity in the rivers, suspended sediment load input followed the order: Kaligandaki > Myagdikhola > Aadhikhola > Tinahukhola. C:N values in rivers from the Lesser Himalayas and Siwalik indicate sediments from mixed biogenic sources. In contrast, high TOC and C/N values in the trans-Himalaya rivers flowing through barren landscapes reflect the erosion of catchment sediments yielding petrogenic carbon. The suspended matter in rivers from the Lesser Himalayas and Siwalik has higher lignin phenol concentrations than the trans-Himalaya and Higher Himalaya rivers. The lignin phenol ratios indicate higher degradation in rivers from the trans and Higher Himalaya sections. This implies that only a small fraction of the terrestrial OM transported by these rivers deposits in the ocean sink. In contrast, rivers from the Lesser Himalayas and Siwaliks sequester a significant amount of OM bound to their bedload. As a result, these rivers transferred lower particulate OC (POC) but higher DOC than similar rivers worldwide. Rivers from Lesser Himalayas and Siwaliks transfer > 90 % of annual POC flux during monsoons. Finally, although Himalayan rivers transport less OC than other global rivers traversing densely vegetated landscapes, the sheer number of these rivers has significant implications on the fate and transport of total OC from catchments sediments.

Phase‐resolving direct numerical simulations of particle transport in liquids—From microfluidics to sediment

AbstractThe article describes direct numerical simulations using an Euler–Lagrange approach with an immersed‐boundary method to resolve the geometry and trajectory of particles moving in a flow. The presentation focuses on own work of the authors and discusses elements of physical and numerical modeling in some detail, together with three areas of application: microfluidic transport of spherical and nonspherical particles in curved ducts, flows with bubbles at different void fraction ranging from single bubbles to dense particle clusters, some also subjected to electro‐magnetic forces, and bedload sediment transport with spherical and nonspherical particles. These applications with their specific requirements for numerical modeling illustrate the versatility of the approach and provide condensed information about main findings.