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Soil may be a carbon source or sink under the effect of sediment and soil organic carbon (SOC) erosion, transport and deposition. Partial SOC processes to determine whether soil subjected to water erosion is a carbon sink or source have not been clarified but are essential for increasing and predicting SOC storage. In this review, the associations between SOC mineralization, stability and stock at erosion sites, in transported sediments and at deposition sites are clarified. An overview is given for possible determination standards that define soil carbon sinks and sources. Methods for enhancing SOC sequestration and suggestions for improving SOC prediction are also presented. Particle transport is an important intermediate process that determines the material base for SOC stability and sequestration in each erosion and deposition element. When subject to water erosion, a high probability of SOC physical stabilization and a thick soil layer are essential for soil to function as a SOC sink. Sediment transport weakens SOC physical protection in eroded areas but can promote aggregation factors at deposition sites in some cases while increasing the depth of SOC in the soil. In this circumstance, a good soil environment for plant growth facilitates the occurrence of carbon sinks. A concept for critical erosion intensity is proposed to understand SOC sink determination; the concept is presented as the volume of soil erosion per square kilometre (m3 km−2) for which the maximum reduction in vegetation cover or plant biomass still permits plants to provide enough organic matter to compensate for erosion‐induced SOC loss. If erosion intensity is higher than critical erosion intensity at the erosion site, soil degradation is obvious, and soil is presented as an OC source, and vice versa. Finally, the SOC burial method for increasing the soil carbon storage amounts in regions with thick soil layers is presented to explore the SOC sequestration potential in deep soil. The factors considered for SOC prediction should vary with research scale. We hope our review will have direct implications for the modelling of SOC dynamics under water erosion on both slopes and at large scales. Highlights: Changes in soil texture and soil thickness greatly affect the amount of SOC storage at erosion and deposition sites.Selective transport of soil materials or chemical elements promotes soil aggregation.Possible standards that define soil carbon sinks and sources and suggestions for improving SOC prediction are presented.SOC burial may be a good method for increasing C storage amounts in regions with thick layers of fine soil. [ABSTRACT FROM AUTHOR]

Erosion of sediment deposition in storm sewers is dominated by the bed shear stress and the deposition characteristics. A laboratory study investigated the critical shear stress and erosion processes for different types of deposition in storm sewers. The critical shear stress increased from 0.19 to 0.41 N/m2 for the 0.4-mm sand when the weight content of silt-clay changed from 0% to 20%, whereas the critical shear stress increased from 0.98 to 1.98 N/m2 for the 1.8-mm sand deposition. A prediction method for the critical shear stress was developed based on the particle size and silt-clay content. The erosion patterns can be classified as ripple surface, dune surface, flat surface, and rugged surface, mainly determined by the cohesive effect, particle size, and bed shear stress. The erosion rate is a function of the sediment transport rate per unit width and particle transport distance. A field sampling program was conducted to obtain sediment deposition characteristics in a storm trunk sewer. Based on the sediment characteristics and estimated flow rate, the predicted deposition profile using the method developed in this study compared well with the field measurements. [ABSTRACT FROM AUTHOR]

Wu, T. and Qin, J., 2020. Influence of flow and sediment transport processes on sedimentation in groyne fields. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 304-308. Coconut Creek (Florida), ISSN 0749-0208. Groynes have been widely used to prevent coastal erosion worldwide. Various depositional patterns have been found in groyne fields, which are affected by flow and sediment transport processes. For a groyne field dominated by a single large gyre and sediment being mainly transported in the form of suspended load, the sediment deposition pattern is consistent with the gyre structure. For groyne fields showing complex flow structures or bedload-dominant sediment transport processes, the relationship between the deposition patterns and flow and sediment transport processes remains unclear. In this study, the deposition patterns of groyne fields formed by different flow and sediment transport processes were analysed based on flume experiments. The sediment deposition patterns as well as the bedload transport process in groyne fields were accurately measured. The distribution of flow characteristics was simulated using the Horizontal Large Eddy Simulation (HLES) of the Delft3d model. The results confirmed that the deposition patterns were affected by flow structures and sediment transport processes. For suspended sediment-dominated situations, the deposition patterns were consistent with the gyre structures. For bedload-dominated conditions, sediment deposition occurred where the bed shear stress fell below the critical shear stress. [ABSTRACT FROM AUTHOR]

Nguyen, T.H.T.; Park, S.W., and Ahn, J., 2020. Numerical method to determine upstream scour slope in relation to turbulence and particle movement. Journal of Coastal Research, 36(1), 189–195. Coconut Creek (Florida), ISSN 0749-0208. Several studies have been conducted to investigate the behavior of scour hole, which happens naturally at the end of the bed protections in the streams and rivers, because this phenomenon can result in the instability or destruction of man-made structures in the area. Some formulas or equations were introduced to calculate the upstream scour slope, one of the most important scour properties, but the application shows some difficulty because of the lack of data. This paper presents a simple but reasonable method to find upstream scour slope with the employing of a numerical simulation, in particular by considering the relationship between turbulence and particle movement. [ABSTRACT FROM AUTHOR]

It is necessary to understand Sustainable urban Drainage Systems (SuDS) sediment retention efficiencies to fully comprehend SuDS pollution removal properties and urban sediment movement from source-to sink. This research presents the detention and transport of a single tagged sediment release through four SuDS devices over 12 months, with the aim of quasi-quantifying these selected SuDS devices sediment detention efficiencies. Field monitoring and mass balance analysis of deposited sediment shows that tagged sediment from the single sediment release moves through the monitored SuDS, with deposition declining over the 12-month monitoring period. Initial retention is high (>80% during the first week of monitoring) but falls below 80% after multiple consecutive rainfall-runoff events (events ≤50% ARI). The field monitoring illustrates retention to generally remain above 50%, suggesting that SuDS are highly efficient at retaining urban sediment pollution but that deposition of a single sediment release may resuspend due to cumulative rainfall-runoff events. [ABSTRACT FROM AUTHOR]

Variations in shoreline trend was examined for 21 stations between Manuvai (in the west) and Vijayapathi (in the east), along the southern tip of India. Multispectral satellite data of Landsat MSS (9th Feb, 1973), Landsat TM 5 (4th Sep 2001) and Landsat ETM+ (21st Jan 2006) were used to assess the temporal dynamics of shoreline trend present in the region. The images were pretreated by radiometric calibration in order to avoid the temporal deviation of spatial and spectral information. The exact shorelines were estimated by two steps of image processing techniques: Normalized Difference Water Index (NDWI) is used to classify the land and sea water by and Sobal edge detection techniques are used to extract boundary line between land and water body. The rate of changes between the period 1973 and 2006 has shown that, the average shoreline rate is accelerated in the study area at 1.78 m/year. However, unusual shoreline changes ranging from 3.60 m/year to 15.60 m/year has been observed between the period 2001 and 2006 due to the impact of Tsunami. The station-wise shoreline data endorsed that Chinna muttom to Visvanarayanapuram and Lipuram are under continuous depositional process whereas other stations are under erosional process. This result shows that littoral sediment movement, with respect to the wave climate and anthropogenic activities are the predominant factors that affect the shoreline trend and sediment drift prevailing in the coast. [ABSTRACT FROM AUTHOR]

This paper describes a dynamic morphological sediment transport model for determining the bed slope of dynamic stable irrigation canal. The model is supposed to help in designing process of irrigation canals. [ABSTRACT FROM AUTHOR]

As wastewater is commonly disposed of in the form of sediment-laden jet from a submarine outfall, the sediment movement when the jet evolves in the ambient water and its final deposition are of great importance to marine engineers. This study aims to investigate the settling mechanism of the sediment from an inclined discharge nozzle and quantify the deposition profile for various jet conditions in the hydrostatic environment through physical experiments and dimensional analysis. In the experimental tests, separate flow visualizations for the fluid and sediment phases are achieved to enable the simultaneous observation of sediment particles and jet fluid movement, through which the analysis of the relationship between the fluid and the sediment movement is carried out. The results show that at locations close to the nozzle (s / D = 5), sediment mean velocity has an inverse relationship with the turbulence intensity while positively correlated with the initial jet momentum. The discharge angle is found to have dominant effect on alternating the sediment velocity profile from symmetrical to asymmetrical. With the newly defined momentum settling length scale l mi , the non-dimensional formulations for deposition rate and accumulated deposition profile involving the nozzle inclination have been validated by the experimental data and are potential to be applied to the prediction of depositional rate and final deposition distribution near the outfall for the full-scale wastewater discharge events. • Fluid and sediment phases are simultaneously observed for the sediment-laden jet. • Increase of inclined discharge angle enhances the asymmetry of sediment velocity profile. • A new momentum settling length scales l mi is introduced. • Uniform equation is achieved to describe the 1D deposition profile at the bottom. [ABSTRACT FROM AUTHOR]

Fine particle deposition and streambed clogging affect many ecological and biogeochemical processes, but little is known about the effects of groundwater flow into and out of rivers on clogging. We evaluated the effects of losing and gaining flow on the deposition of suspended kaolinite clay particles in a sand streambed and the resulting changes in rates and patterns of hyporheic exchange flux (HEF). Observations of clay deposition from the water column, clay accumulation in the streambed sediments, and water exchange with the bed demonstrated that clay deposition in the bed substantially reduced both HEF and the size of the hyporheic zone. Clay deposition and HEF were strongly coupled, leading to rapid clogging in areas of water and clay influx into the bed. Local clogging diverted exchanged water laterally, producing clay deposit layers that reduced vertical hyporheic flow and favored horizontal flow. Under gaining conditions, HEF was spatially constrained by upwelling water, which focused clay deposition in a small region on the upstream side of each bed form. Because the area of inflow into the bed was smallest under gaining conditions, local clogging required less clay mass under gaining conditions than neutral or losing conditions. These results indicate that losing and gaining flow conditions need to be considered in assessments of hyporheic exchange, fine particle dynamics in streams, and streambed clogging and restoration. [ABSTRACT FROM AUTHOR]

Most of the models developed to simulate the cohesive sediment transport processes refer to estuary or marine environments and are generally not developed for the specific characteristics of irrigation schemes provided with the different types of hydraulic structures. The aim of this study is to simulate the cohesive sediment transport in irrigation canals. The fine sediment transport (FSEDT) model was developed using a software program to estimate the sediment transport and deposition rates of cohesive sediments in irrigation canals. The model has been applied in the Gezira Scheme in Sudan, which is threatened by high sediment supply from the Blue Nile River. The model was calibrated and validated using the field data selected during the flood seasons in 2011 and 2012. The hydrodynamic part of the model was verified by comparing the water surface profile obtained by the developed model and by using a microcomputer program for simulating one-dimensional steady/unsteady flow in open canals. The results of the two models show good agreement. The sensitivity of different parameters to the deposition was tested. The model is a useful tool that can be applied to study the mechanism of sediment transport under different operation and maintenance scenarios not only in the Gezira Scheme but also in similar cases. [ABSTRACT FROM AUTHOR]

The erosion, transport and fate of sediments and associated contaminants are known to be influenced by both particle characteristics and the flow dynamics imparted onto the sediment. The influential role of bitumen containing hydrophobic sediments and the microbial community on sediment dynamics are however less understood. This study links an experimental evaluation of sediment erosion with measured sediment-associated contaminant concentrations and microbial community analysis to provide an estimate of the potential for sediment to control the erosion, transport and fate of contaminants. Specifically the paper addresses the unique behaviour of hydrophobic sediments and the role that the microbial community associated with hydrophobic sediment may play in the transport of contaminated sediment. Results demonstrate that the hydrophobic cohesive sediment demonstrates unique transport and particle characteristics (poor settling and small floc size). Biofilms were observed to increase with consolidation/biostabilization times and generated a unique microbial consortium relative to the eroded flocs. Natural oil associated with the flocs appeared to be preferentially associated with microbial derived extracellular polymeric substances. While PAHs and naphthenic acid increased with increasing shear (indicative of increasing loads), they tended to decrease with consolidation/biostabilization (CB) time at similar shears suggesting a chemical and/or biological degradation. PAH and napthenic acid degrading microbes decreased with time as well, which may suggest that there was a reduced pool of PAHs and naphthenic acids available resulting in their die off. This study emphasizes the importance that any management strategies and operational assessments for the protection of human and aquatic health incorporate the sediment (suspended and bed sediment) and biological (biofilm) compartments and the energy dynamics within the system in order to better predict contaminant transport. [ABSTRACT FROM AUTHOR]

The new toolbox ScourApp is presented and applied for analysis of the complex interactions between local scour and sediment deposition at bridges during floods and to determine the relative importance of the controlling parameters on scour depth. ScourApp represents the time-dependent sediment transport processes through modern empirical formulations to compute the evolution of scour depth at a bridge pier. Results show that the mathematical model reproduces observed scour depths with high accuracy and confirm that ScourApp is a suitable tool for scour analysis. The model parameters controlling the time dependent scour depth were the equilibrium scour depth, and two constants representing the effects of pier geometry, flow and sediment. Sensitivity analysis showed that all three scour model parameters exhibited a nearly linear relation with the final scour depth. Moreover, results considering sediment deposition obtained for the Rapel Bridge showed that scour depths are highly sensitive to the sediment supply rate. ScourApp is recommended in scour assessment for bridge planning, design, management, and forensic analysis, as well as for engineering education. • The open-source toolbox ScourApp for scour analysis is developed. • Complex interactions of time-dependent scour and scour hole refilling are analysed for several laboratory and real-life cases. • The relative importance of controlling parameters on scour is analysed. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) are globally ubiquitous in sediments and surface waters. Interactions between biota and MPs are complex and influence their fate and effects in the environment. Once MPs enter aquatic systems, they are colonized by biofilms that may form from the excretion of extracellular polymeric substances (EPS) from microalgae. Biofilm accumulation may change the density of the MPs, contributing to their transport to the sediments. Furthermore, benthic plantivores may consume biofilm laden MPs allowing them to enter the food web. Thus, it is crucial to understand the role algae plays in the vertical transport of MPs in the aquatic environment. In this study, Chlamydomonas was cultured with MPs at different concentrations (0–0.4 mg/mL), and temperatures ranging from 2.5 to 32.5 °C to understand the deposition dynamics and impacts of MPs on EPS production and algal density. Temperatures ranging up to 25 °C increased algal density and MPs deposition. However, at 32.5 °C, algal density and MPs deposition declined. The quantity of MPs also affected algal cell density and EPS production. MPs concentration from 0 to 0.4 mg/mL increased EPS production at all temperatures. Similarly, an increase in algal cell density and MPs deposition occurred when MPs concentration was raised to 0.3 mg/mL. Algal cultures exposed to 0.3–0.4 mg/mL of MPs had a decrease in algal cell density, with no corresponding decline in EPS production. At certain conditions, MPs can facilitate biofilm formation by stimulating EPS production, which can increase cell density thereby expediting MPs transport to the sediment. • Microplastics (HDPE) stimulated extracellular polymeric substances production. • Microplastics (HDPE) exposure up to 0.3 mg/mL increased the growth of Chlamydomonas. • Microplastics (HDPE) exposure over 0.3 mg/mL decreased the growth of Chlamydomonas. • Temperatures up to 25 °C increased algal density and microplastics deposition. • Microplastics exposure over 0.3 mg/mL increased extracellular polymeric substances. [ABSTRACT FROM AUTHOR]

• An efficient 2D shallow water hydro-sediment-morphodynamic model is presented. • Morphodynamic processes under the impact of cascade movable weirs are studied. • Disparate morphological changes may result under different operation schemes. • An alternating operation scheme is proposed to constrain morphological changes. Cascade movable weirs have been increasingly widely used for river landscaping, water storage and ecological wellbeing. The weirs disturb the prior equilibrium in line with fluvial hydrology, sediment transport and geomorphology, and may lead to profound changes in the river, of which, however, the understanding has so far remained poor. Here, the first of its kind, a computational modelling study is presented on the morphodynamic processes under the impact of cascade hydraulic lifting dams, a type of movable weirs, as to the middle Fen River, China. A two-dimensional shallow water hydro-sediment-morphodynamic model is applied to resolve the fluvial processes, which is physically coupled and computationally efficient based on Finite Volume Method, unstructured mesh, local time stepping and parallel computing. Computational results show that the cascade dams alter the flow and sediment transport locally and on the reach scale in a distinct manner under different operation schemes, which in turn incur disparate morphological changes. Collapse of all the dams all year round would lead to net degradation in the study reach, with the floodplains aggrading and the main channel degrading. Operation of all the dams all year round may induce an overall aggradation both on the floodplains and in the main channel. If all the dams collapse in flood seasons and operate in dry seasons (CF), degradation occurs in the main channel whereas the floodplains experience aggradation, with a net degradation. When only the dams in the main channel operate all year round (OM), the floodplains degrade while the main channel aggrades, resulting in a net aggradation in the study reach. Either aggradation or degradation may prevail locally on floodplains, in main channel and individual subreaches. The present findings lead us to propose a complex operation scheme of annually alternating CF and OM to constrain significant morphological changes. [ABSTRACT FROM AUTHOR]

The earthen border wall (Great Wall) built by the Ming is largely made of wind-blown loess. However, does the composition of this loess change along the length of the wall in response to variations in regional sediment transport pathways and impacting on the wall's erosional durability? To date, defining these sediment transport pathways has been a challenge because of the paucity of spatially-comprehensive, compositional information. Here, we show that satellite ASTER mineral maps, combined with field sample measurements along a 1200 km section of the Ming's earthen wall, reveal both the compositional heterogeneity of loess as well as the complexity of the sediment transport pathways of individual loess components, including: (i) quartz sand from Cretaceous sandstones in the Gobi Desert; (ii) gypsum from evaporative lakes in the Tengger Desert; (iii) kaolinite from Devonian Molasse in the Qilian Shan; and (iv) chlorite and muscovite from meta-volcanic rocks exposed across the Alashan Block. Sediment transport pathways involve a combination of colluvial, aeolian and fluvial (ephemeral and permanent) processes shaped by the topography. ASTER enabled mapping of compositional gradients related to two pathways, namely: (i) quartz sand driven by aeolian saltation in concert with the Yellow River; and (ii) clay and fine silt travelling large distances (>500 km) by long-term wind suspension. The most intact section of wall is found along the Hexi Corridor, which is poor in quartz sand and rich in (kaolinitic) clay and fine-silt, driven by wind-shielding by the Alashan Block. We also found evidence that the Ming: (i) mined loess from close by the wall (<1 km); (ii) targeted loess richer in finer fractions; and (iii) routinely applied a Ca-rich additive (probably lime). [ABSTRACT FROM AUTHOR]

Surface gravity waves play an important role in sediment transport. Previous studies have focused on the role of bottom shear enhanced by the surface wave orbital velocity. In this study, we embedded the University of New South Wales Sediment model into the Princeton Ocean Model, which includes a three-dimensional wave module to study sediment dynamics near a sandy spit in Sanniang Bay in the South China Sea. The simulated results for the deposition rate show that wave-induced currents play a dominant role in the maintenance of the sandy spit. The spit tip was formed as a result of the separation of wave-induced coastal flow. The spit tip was shown to be a barrier to the dominant wave-induced current, and the spit base was simulated to form via sand accumulation in the shelter of the spit tip. The deposition is mainly in the low-energy region behind the tip of the spit, which can counter the erosion effect of dominant wave-induced currents. The dominant wave-induced current prompts the lateral infilling of the spit tip when both the spit tip and base are above the water surface. The sediment carried by the coastal current is deposited along the flow branch of separation and forms the spit tip, which indicates that the sediment is deposited where the longshore current changes into an offshore current. As the water depth increases along the separated flow spindle, the bottom shear stress decreases, contributing to the deposition of the spit tip. • The three dimensional wave-induced currents were modeled to study the sediment transport near a sandy spit. • The currents induced by dominant waves were shown to be relevant to the formation of the sandy spit. • The spit base was simulated to form via sand accumulation in the shelter of the spit tip. • The spit tip was formed due to the separation of wave-induced coastal flow. • The sediment was deposited where the longshore current changes into an offshore current. [ABSTRACT FROM AUTHOR]