Sediment Movement Research Articles

Surficial Sediment Distribution in a Complex Marine Setting—The Example of Coastal and Open Sea Areas of Evia Island, Central Aegean, Greece

This study examines sediment distribution patterns in the Aegean Sea, focusing on the western coast of Evia Island and the southern Evoikos and Petalioi Gulfs. A total of 200 granulometric data points were analyzed to evaluate textural characteristics, including mean grain size, sorting, and skewness. The findings reveal significant variation in mean grain size: finer sediments (ϕ = 5–8) dominate the northern Aegean near Skyros, while coarser sands (ϕ = 2–4) are prevalent in the South Evoikos and Petalioi gulfs. The coarsest materials (ϕ = 0–2) are found around Chalkis, with sorting generally poor except in those two areas. Negative skewness values in the northern part of the study area indicate a predominance of finer particles, while southern regions exhibit slightly positive skewness, suggesting a greater proportion of coarser grains. Complex net transport patterns between Evia and Skyros are influenced by north-northeast trending water currents from the northern Aegean, with fluvial influx observed in the southern Evia coastal area. Around Skyros, the interplay of water currents and prevailing north-northwest winds dictates the orientation of net transport vectors. In the Evoikos gulfs, sediment movement aligns with a general northward flow, featuring coarse sediments in the Petalioi Gulf and muddy deposits in the narrower northern segment, where minimal transport indicates stagnant conditions. Coarse-grained materials in North Evoikos are primarily influenced by strong tidal activity.

Coastal vulnerability to extreme weather events: An integrated analysis of erosion, sediment movement, and land subsidence based on multi-temporal optical and SAR satellite data.

Coastal areas undergo continuous transformations, altering their geometry under the influence of external forces like tides, waves, and extreme events. Thus, monitoring the impact of extreme weather events on coastal regions is crucial to prevent potential cascading hazards. Here, we utilized time-series optical and SAR satellite data and tide records, coupled with sophisticated analytical techniques, to analyze erosion processes, sediment transport, and vertical land movement (VLM) at an embayed sandy beach (i.e., Haeundae Beach, South Korea). We found a significant erosion rate of -4.12m/year during typhoon periods, compared to non-typhoon periods (-3.61m/year). Between 2017 and 2023, 5.63ha of beach area and 14,428.9m3 of sediment were lost due to typhoon-induced sand movement, leading to coastline retreat and foreshore erosion. The PS-InSAR-derived localized VLM trends of fast-subsiding areas (-3.57mm/year), combined with a current sea-level rise (2.34mm/year), underscores the heightened vulnerability to future extreme weather events. The findings of this study provide insights into the erosional processes, land subsidence, and sediment transport due to extreme weather events, which can contribute to the development of erosion control technologies and engineering applications to prevent cascading hazards. The proposed integrated framework can be implemented in similar coastal environments to mitigate climate-change-induced coastal vulnerabilities.

The Impact of River Mouth Sediment Deposition on Flood Risk: The Case Study of The Sakarya River

Flooding is a natural disaster that causes loss of life and property worldwide. Floods can be predicted and their damages can be reduced. Various natural and man-made factors can cause floods. Sediment movement can be counted as one of the causes of floods, albeit rarely. The Sakarya River bed and river mouth is one of the risky areas for flooding due to sediment deposition. Due to the activities of quarries on the Sakarya River, the amount of sediment carried by the river increases, and the damage to the river bed morphology. In rare cases, the mouth of the river is completely closed due to sedimentation, which has caused many disasters such as coastal flooding and capsizing of marine vessels, leading to loss of life and property. Therefore, the occurrence of floods due to sediment deposition at the mouth of Sakarya River was investigated. The 5, 10, 25, 50, 100, and 500-year return period flows in the downstream part of the Sakarya River and Karasu district were analyzed with the 2D flood model in case of insufficient discharge from the river mouth. Water depth, velocity, and flood hazard maps for these return periods were prepared. The impact of flooding on Karasu district was analyzed in terms of affected buildings and affected area (ha). Thus, the effects of the floods occurring in the downstream region as a result of the interventions to the river bed in the upstream region were analyzed.

Analysis of flood events and coastal sedimentation with X-band radar observation and XBeach computation at the mouth of Tenryu River

ABSTRACT We observed a week-long flood event in August 2021 at the mouth of Tenryu River with X-band radar and explained the changes in flow field and morphologies. Then, we reproduce the flow variation and morphological changes with the XBeach computational model. X-band radar is an imaging radar that can collect backscatter from river banks, sand dunes, and floating objects flowing downstream with the flood flow every 2 seconds. The observation area extends approximately 1,000 m × 1,000 m. From the interpretation of the time-averaged radar images, we describe the erosion process of the dunes by the flood. Further, we estimated the surface flow patterns with the Particle Image Velocimetry analysis of the radar images. Flow direction in the main river channel changed smoothly, while surface flow speeds ranged from 1 to 3 m/s depending on the discharge. To infer the sediment motion and resultant morphological changes, we did numerical computation with the XBeach. It reproduced well the flow velocities and sand dune erosions observed by the X-band radar. We estimated sediment discharged from the river to the coastal zone. Combining X-band radar observation and XBeach computation gives a better understanding of a flood event than individual analyses.

Continuous Near-Bed Movements of Microplastics in Open Channel Flows: Statistical Analysis.

The ubiquitous distribution of microplastics (MPs) in aquatic environments is linked to their transport in rivers and streams. However, the specific mechanism of bedload microplastic (MP) transport, notably their stochastic behaviors, remains an underexplored area. To investigate this, particle tracking velocimetry was employed to examine the continuous near-bed movements of four types of MPs under nine setups with different experimental conditions in a laboratory flume, with an emphasis on their streamwise transport. It was found that the streamwise velocity of MPs follows a normal distribution, which can be characterized using the proposed equations to estimate the ensemble mean and standard deviation of MP streamwise velocity. The proposed equations show low relative errors of ∼5% when compared to experimental data. This study also revealed similarities in the continuous movement of MPs and sediments in the streamwise diffusion process. A superdiffusive regime was observed, with particle inertia identified as the primary source of this anomalous diffusion. These results indicate that adopting a probabilistic framework may provide a promising avenue for improving numerical models and enhancing the understanding of MP transport behavior.

An analytical study for predicting incipient motion velocity of sediments under ice cover

This study investigates the critical impact of incipient sediment motion on sediment transport estimation and riverbed evolution prediction. In this research, we examine the effects of ice cover on the vertical distribution of flow velocity, establishing a mathematical relationship between the vertical average flow velocities in open channel and ice-covered flows. This leads to the derivation of a formula for incipient motion velocity under ice cover. Additionally, the study analyzes the riverbed evolution process under ice jam conditions. The proposed formula is applicable to both open channel and ice-covered flows, effectively capturing the characteristics of incipient sediment motion for non-cohesive and cohesive sediments. The calculated incipient motion velocities closely align with the empirical data from existing literature. The study reveals that the roughness of ice cover significantly influences the incipient motion velocity of sediment, with higher ratios of ice cover roughness to riverbed roughness promoting sediment initiation under more favorable hydraulic conditions. Furthermore, the riverbed beneath ice jams experiences significant scouring. Field observations indicate that when ice jams form in localized sections of the river, the displacement of the main flow can substantially increase flow velocity in areas away from the ice jam, leading to scouring in non-ice-jammed areas and sedimentation in ice-jammed areas. The uneven distribution of ice jam is likely a critical factor contributing to discrepancies between theoretical predictions and observed outcomes. The complexity and limited data associated with the initiation of cohesive sediments pose challenges in validating the proposed formula for these sediment types.

Quasi-harmonic analysis of fortnightly suspended sediment response to semi-diurnal tidal currents

IntroductionThe suspended sediment concentration (SSC) is an important consideration in marine engineering. Sediment movement characteristics can be studied by considering the fortnightly behavior of SSC. However, this consideration currently lacks accurate mathematical representation. MethodIn this study, a computationally efficient mathematical model capable of providing analytical solutions for predicting SSC based on resuspension, deposition, and advection was developed to further investigate the mathematical interpretation of fortnightly SSC behavior in coastal areas dominated by M2, S2, O1, K1, M4 and MS4 tides. The model decomposed the SSC into 35 quasi-harmonic terms as well as two terms with fortnightly period. ResultThe model was applied at five observation sites in the Bohai Sea, Yellow Sea and East China Sea, China, and validated to be able to reproduce the fortnightly variation of SSC. The results show that the primary fortnightly SSC term was generated by the combined action of M2 and S2 tidal currents and had a tidal frequency of 1.0159 °/h, which was equal to the difference between the frequencies of the two partial tides. DiscussionThe resuspension properties only affected the amplitude of the fortnightly SSC term but did not affect the phase. The deposition properties affected both amplitude and phase. The quasi-harmonic analysis indicates that in certain shallow sea areas with strong nonlinear tidal interactions, the amplitude of the M4 tidal elevation can influence the mean SSC, while the amplitude of the MS4 tidal elevation can affect the fortnightly SSC amplitude. As the simplified model is based on certain assumptions, the application conditions of the quasi-harmonic analytical solution include an approximate reciprocating flow pattern, a tidal range significantly smaller than the water depth. Our results provide a mathematical solution for the fortnightly evolution of suspended sediment.

An investigation of scouring mechanism and equilibrium state by the submerged jet using synthesized oblique velocity

This paper uses a numerical simulation method based on synthesized oblique velocity to simulate the process of submerged oblique jet scouring of the sand bed. The concept of the initial scouring equilibrium state is introduced, and curves showing the variation of scour hole depth over time at varying angles are fitted based on experimental data. This enables predicting the scour hole depth at any point during the scouring process and the time required to reach the initial scouring equilibrium state. An ultrasonic displacement sensor was used to measure the depth and width of the scour holes accurately. The evolution of the scour holes formed by the submerged oblique jet on the sand bed was systematically studied within the range of oblique angles from θ = 30°–80°. The flow structure during the scouring process and its interaction with sediment movement were further revealed through numerical simulations. The synthesized oblique velocity method effectively addresses the complexity of simulating the oblique jet. This provides a new approach to investigating the submerged oblique jet scouring of the sand bed. The findings of this study offer valuable guidance for practical applications, such as underwater equipment cleaning and deep-sea dredging.

Determining the Location of Coastal Protection Structures in Sealing with Sedimentation Problems using Hydrodynamic Modeling

Abstract Lamong Bay is a water area located between the coasts of Gresik and Surabaya. The geographical condition, which is the estuary of several rivers, makes this bay area face sedimentation problems. The process of sedimentation is caused by the movement of sediment, which is divided into 3 types: Bed Load, Suspended Load, and Wash Load. The relatively gentle slope of the topography also affects the accumulation of sediment. One very effective solution in dealing with sedimentation is the existence of coastal protection structures. The existence of coastal structures aims to resist the movement of sediments influenced by ocean currents. Thus, this study aims to determine the type and location of coastal protection structures in reducing the rate of sediment transport in the study area. The method used is numerical modeling using Delft3D software. Modeling validation is done by finding the deviation value of the modeled tides with tides from the BIG tide station. The validation calculation method uses statistical calculations with the Root Mean Square Error (RMSE) method, Mean Absolute Percentage Error (MAPE), and R correlation to find the relationship between modeling and measurement. Sediment types in the Lamong Bay area consist of silt, clay, and sand, with the largest composition in the silt type at 84%. Alternative 1, where the structure is placed in the south of the bay area, shows a cumulative sedimentation value of 0.130 m, while alternative 2 in the north shows 0.180 m. Hence, alternative 1 is more effective. This study contributes to SDG 9 by promoting resilient infrastructure to manage sedimentation issues effectively.

Three-Dimensional Hydrodynamic Modelling to Estimate Sediment Rate in Lamong Bay

Abstract Lamong Bay Terminal, part of Tanjung Perak Port in Surabaya, functions as a container terminal. The port in the Surabaya area causes high ship traffic activity in the waters of Lamong Bay and sediment may be carried away from rivers heading towards the sea. The sedimentation process in waters can cause problems because it can cause shallowing of the waters, so it is necessary to maintain and monitor the depth of shipping lanes to maintain the safety of sea traffic. Therefore, understanding the hydrodynamics of seawater and sediment movement in the water region is necessary for successful dredging operations and assessing the impact of silt on port areas. In this research, the approach used to determine current patterns and sediment distribution was through the application of a numerical model with three– dimensional baroclinic hydrodynamic equations. The numerical modeling study in this research uses tidal data, sediment samples, salinity, and temperature to determine current patterns and the rate of sediment distribution. This process is carried out periodically and continuously as part of the evaluation of Lamong Bay Terminal. The results can serve as a reference for dredging planning to maintain the depth of the waters at the Lamong Bay Terminal. In this study, the highest current velocity was obtained at the time of spring tide reaching 0.9 ms−1 and at the neap tide of 0.4 ms−1. The sediment distribution pattern in the waters of Lamong Bay affected the existence of the pier and the morphological conditions of the seabed. The largest siltation or sedimentation that has occurred at Lamong Bay Port is 0.055 m/month near the jetty, thus depth monitoring is needed in this area, regularly. This study supports SDG 9 by advancing resilient infrastructure solutions to manage the sedimentation process in waters.

Unintended consequences of modifying coastal river systems

Coastal infrastructure projects, particularly the modification of coastal river channels, are becoming increasingly significant to economic activities worldwide as a response to climate-driven changes and urbanization. The benefits of channel modification projects can be realized quickly, but the altered movement of sediments in the river channel can lead to unintended geomorphic changes years or decades later. An example of this is the closure of the San Bernard River mouth, located on the central coast of Texas, which was clogged with sediments by the 1990s as a result of two major projects in the area: the diversion of the Brazos River channel (1929) and the construction of the Gulf Intracoastal Waterway (GIWW) (1940s). The objective of this study was to a) document the delayed geomorphic response to the projects using a GIS analysis of historical maps and aerial imagery, and b) provide a snapshot of altered flow pathways in the area using measurements collected in situ. Results showed that the GIWW was the main conduit for river flow as it bisects the San Bernard River 2 km inland of its river mouth, reducing discharge in the terminal limb of the river. Due to reduced flow, the river mouth became clogged with wave-transported sediment supplied by the still-adjusting Brazos River which had been diverted to within 6 km of the San Bernard River. With a limited connection to the sea, altered sediment and flow pathways have led to numerous hazards and costly corrective dredging projects surpassing $12 million to date. Optimizing the cost-effectiveness of channel modification projects requires considering their long-term impact as managers continue to adapt to ever-changing coastal zones.

Impacts of El Niño-Southern oscillation on multi-scale morphodynamics of an embayed beach in southern China

Increased coastal erosion and extreme oceanographic forcing driven by El Niño-Southern Oscillation (ENSO) along the Pacific coast are increasingly receiving concerns. Despite considerable attention, the specific impact of these phenomena on Chinese shorelines, particularly along the South China beaches, remains inadequately understood. To address this gap, this study conducted high-frequency surveys on the Qing'an Bay beach in South China and employ a profile fitting model to refined waterline extraction from monthly satellite images. The goal was to investigate the relationship between high-frequency shoreline changes and interannual climate variability (such as ENSO). The findings indicate that the coastal evolution is intricately linked to a combination of strong wave events, summer storms, winter cold waves, and the amplifying effects of ENSO. During La Niña phase, the sea level in the western Pacific experiences a rise, with associated storms proving particularly destructive to the beach environment, leading to violent oscillations in the coastline. Specifically, in the strong La Niña phases, significant wave heights markedly surpass neutral conditions, precipitating intensified sediment movement. However, it is imperative to recognize that shoreline changes alone do not fully characterize coastal erosion. Assessment must also encompass alterations in beach volume. By calculating beach volume per unit width that accounts for the influence of ENSO variability on the beach, the seasonal characteristics of the beach showed sediment losses in summer and autumn, and gains in winter and spring, which was more obvious during strong La Niña. Additionally, conceptual model analysis reveals that during the La Niña phase, the bay is fully exposed, whereas during the El Niño phase, significant headland sheltering is observed.

Prediction of Scour Depth for Diverse Pier Shapes Utilizing Two-Dimensional Hydraulic Engineering Center’s River Analysis System Sediment Model

Examining scouring around bridge piers is crucial for ensuring water-related infrastructure’s long-term safety and stability. Accurate forecasting models are essential for addressing scour, especially in complex water systems where traditional methods fall short. This study investigates the application of the HEC-RAS 2D sedimentation model, which has recently become available for detailed sediment analysis, to evaluate its effectiveness in predicting scoring around various pier shapes and under different water conditions. This study offers a comprehensive assessment of the model’s predictive capabilities by focusing on variables such as water velocity, shear stress, and riverbed changes. Particular attention was paid to the influence of factors like floating debris and different pier geometries on scour predictions. The results demonstrate that while the HEC-RAS 2D model generally provides accurate predictions for simpler pier shapes—achieving up to 85% precision—it shows varied performance for more complex designs and debris-influenced scenarios. Specifically, the model overpredicted scouring depths by approximately 20% for diamond-shaped piers and underpredicted by 15% for square piers in debris conditions. Elliptical piers, in contrast, experienced significantly less erosion, with scour depths up to 30% shallower compared to other shapes. This study highlights the novel application of the HEC-RAS 2D model in this context and underscores its strengths and limitations. Identified issues include difficulties in modeling water flow and debris-induced bottlenecks. This research points to the improved calibration of sediment movement parameters and the development of advanced computational techniques to enhance scour prediction accuracy in complex environments. This work contributes valuable insights for future research and practical applications in civil engineering, especially where traditional scour mitigation methods, such as apron coverings, are not feasible.

Modeling sediment movement in the shallow-water framework: A morpho-hydrodynamic approach with numerical simulations and experimental validation

This work presents a morpho-hydrodynamic model and a numerical approximation designed for the fast and accurate simulation of sediment movement associated with extreme events, such as tsunamis. The model integrates the well-established hydrostatic shallow-water equations with a transport equation for the moving bathymetry that relies on a bedload transport function. Subsequently, this model is discretized using the path-conservative finite volume framework to yield a numerical scheme that is not only fast but also second-order accurate and well-balanced for the lake-at-rest solution. The numerical discretization separates the hydrodynamic and morphodynamic components of the model but leverages the eigenstructure information to evolve the morphologic part in an upwind fashion, preventing spurious oscillations. The study includes various numerical experiments, incorporating comparisons with laboratory experimental data and field surveys.

Discerning sediment provenance in the Outer Banks (USA) through detrital zircon geochronology

Detrital zircon data from modern barrier island and estuarine environments in the Outer Banks (Atlantic Coast, USA) were statistically compared to sands from nearby rivers to assist in determining source-to-sink pathways. Fluvial samples, collected from near the Fall Line contact between the Appalachian Orogen and sediments of the coastal plain, all have age unique distributions, making them ideal for tracing provenance. Three samples from the Atlantic foreshore showed high similarities to one another, as well as to three samples from the estuarine (back-barrier) Pamlico and Albemarle Sounds. Mixture modeling with multiple data reduction methods and three different statistical tests for similarity consistently indicated that the nearby Potomac River was the primary source for all Atlantic foreshore and estuarine zircons, followed by minor contributions from the James River in some models. The models indicate little or no sediment contribution from the Susquehanna, Roanoke, Tar, Neuse, Cape Fear, and Peedee Rivers. Both Atlantic foreshore and estuarine sands are therefore interpreted to have initially originated from Appalachian bedrock to the north of their present-day location, and subsequently to have been transported southward through the Chesapeake Bay watershed before deposition in Virginia and North Carolina. Prior to barrier island formation in the last several thousand years, differing geomorphology of the Chesapeake Bay facilitated southward movement of sediments from its constituent rivers via longshore drift, where they were deposited in coastal settings on the mainland. The modern barrier islands, formed during the most recent post-glacial transgression, may be reworked from these deposits, but may also include a contribution from sediments that were derived more recently from relict deposits on the shelf. Oceanographic and sedimentological evidence suggests that movement of sand-sized grains from southern rivers across the back-barrier sounds is unlikely. These findings can assist with coastal resilience planning and resource management in a region under severe threat from climate change and rising sea levels.

Bedform generation beneath shoaling nonlinear internal waves on a mild slope

Subaqueous sand waves have been observed where nonlinear internal waves (NLIWs) shoal on continental margins. To investigate their generation mechanisms, we propagated periodic NLIWs of depression to shoal upon a sloping bed in a laboratory flume. Following fission of the incident waves, ripple-type bedforms were observed between the point of incipient suspension and interaction point (where the quiescent pycnocline intersects the sediment bed). The largest ripples were centered on the bolus birth point, where the NLIWs of elevation, generated by fission, transform into boluses and maximum near-bed velocities occurred. The ripple height and wavelength were consistent with fluvial scaling. In two experiments, where bedload transport was not predicted, the observations showed resuspension to influence ripple generation. Net upslope sediment movement was observed beyond the turning point.

Morphological properties of two-dimensional and three-dimensional bedforms in open channel flow: A flume experiments study

Bedforms are formed by sediment particles under the action of flow, which in turn affect flow and sediment movement. However, the fundamental mechanisms behind the formation and development of bedforms under varying flow conditions, the interconnection between sediment particle movement and bed morphology development, as well as the influence of bedforms on flow and sediment transport, are still not well understood. In the current study, the moveable bed load transport flume experiments under different flow conditions were done, and the development processes of two-dimensional and three-dimensional dunes formed under different flow intensities were simulated. The detailed structure of the bedforms was measured by laser scanning technology, the characteristics of the bedforms were analyzed in detail, and the relations between the formation of the bedforms and the movement of sediment particles are discussed. The results found that the correlation coefficients of the longitudinal profile curve can serve as a quick reference for distinguishing two-dimensional and three-dimensional dunes. When the crestline ratio is used as the criterion for two-dimensional and three-dimensional dunes, the relative amplitude of the dune crestline and the included angle with the flow direction should also be comprehensively considered. The lee side angles of dunes calculated using the triangle generalization method and local section tangent method are compared and show that the values obtained by the former method are only about half of that of the latter. It is also found that the lee side angles of dunes are related to the dune height. The superimposed dunes generally exist in the downstream area of the stoss side of the dunes. The local bed slopes on the stoss side of the dunes show reverse slopes. The superimposed dunes improve the local bed height and further increase the reverse slope degree of the stoss side. A streamwise ridge is an important form located in the upstream area of the dunes stoss side, and they are symmetrically distributed on both sides. Multiple streamwise ridges divide the stoss side of the dunes into relatively independent movement areas, restricting the movement of sediment particles to specific regions. According to the distribution characteristics of bed morphologies, the effects of dunes on sediment particle movement and flow energy consumption are analyzed.

Impacts of grade control structures on riverbed degradation

Sediment flux of many rivers has been significantly reduced due to human activities caused by economic development, leading to increasingly severe riverbed degradation. To prevent riverbed degradation, grade control structures (GCSs) have been widely applied in degrading channels. Existing studies have not provided a good understanding of the effects of GCSs on flow characteristics and bed morphology in degrading channels, limiting the management of degrading channels. A series of flume tests with no sediment supply are conducted to investigate the effects of GCSs on upstream water levels and riverbed morphology in degrading channels. The experimental results indicate that: (1) in the initial stage of degradation, the water surface slope in the backwater reach is linearly and negatively correlated with the GCS-height Froude number, based on the average flow velocity upstream of the backwater reach due to GCS and the height of GCS; (2) the effective protection bed length upstream of GCS is approximately equal to the length of the reach where the flow velocity is less than the critical velocity for sediment motion in the backwater zone; (3) for sequential GCSs, the effective protection bed length will decrease if GCS is located in the backwater reach of the downstream GCS. A semi-analytical calculation method of the effective protection length and equilibrium bed profile upstream of GCS in degrading channels is proposed based on the critical condition of sediment motion and weir flow formulas. The computed values by the proposed calculation method agree well with the experimental data of the present study.

Three-dimensional modeling of hydro-morphodynamic characteristics of mining affected alluvial channel using TELEMAC and GAIA

In this numerical study, TELEMAC-3D and GAIA solvers were coupled to examine the three-dimensional (3D) flow and morphological changes in an alluvial channel due to sand mining. The 3D modeling approach enables a comprehensive analysis of the interactions between bed shear stress, velocity field, secondary flows, and turbulent kinetic energy that affect sediment transport processes near the mining pit. First, the numerical model was applied to two previous experimental studies on straight channels with mining and validated with their published data. Thereafter, model applications are demonstrated to a 180° curved channel with a mining pit at three different locations. The results indicate that the morphological changes in curved channels with a mining pit were relatively more asymmetrical in contrast to straight channels. The most severe bed degradation of 76.8% was observed at the outer bank downstream of the pit located at the end of 180° bend. The analysis of bed shear stress in the curved channel revealed higher values at the outer bank and lower values around the inner bank downstream of the pit location. Additionally, the presence of the mining pit had a significant impact on the structure and location of the secondary flow recirculation cell in the curved channel. The results indicate that turbulent kinetic energy increases significantly in the vicinity of the mining pit in both straight and curved channels. This increased turbulence due to bed topography may account for the enhanced secondary flow and sediment movement observed in the pit region.

Investigating supercritical flow characteristics and movement of sediment particles in a narrow channel bend using PTV and video footage

This experimental study investigates the cause of nonuniform invert abrasion observed at sediment bypass tunnel (SBT) bends by examining the variations in velocity distributions, turbulence properties, bed shear stress, and bulk sediment movements under three supercritical bend flow conditions, detailed investigation of such flow is scarce. Using a laboratory-scaled model (1:22) of the downstream bend at Solis SBT, Switzerland, the research utilized particle tracking velocimetry and high-speed cameras with spherical sandstones and glass spheres representing sediments. The results indicate that as the secondary currents develop in the flow direction, the flow properties and sediments redistribute across the channel: the high-momentum fluids are directed toward the outer wall, the bed shear stress increases toward the outer wall, and the sediments are pushed toward the inner wall, which then follow this path downstream, even in straight sections, despite lower bed shear stress. This distribution of sediments, driven by secondary currents, leads to deeper invert abrasions toward the inner wall at SBT bends and downstream sections. Thus, these abrasions are primarily influenced by sediment movement rather than the bed shear stress alone. The study's findings are also valuable for validating future numerical simulations.