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

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

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

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

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

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

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

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

Effects of bed material and downstream flow depth on bed evolution in a right-angled channel confluence were studied through laboratory experiments. Velocity field, water surface elevation, and bed profile were measured intermittently until the flow attained equilibrium. Sediment discharges at various locations of the confluence were estimated from bed levels. Six prominent bedforms were identified, and their characteristics were quantified. The sediment discharges from different channels were initially high but decreased to approximately zero as the flow attained equilibrium. Downstream flow depth influenced overall sediment transport in the system, including the main features of bed morphology. Overall erosion in the confluence reduced as the particle size of the bed material increased. In addition, the maximum scour depth occurred at the confluence edge, and, due to the sharp corner of the confluence, its location did not change with time. Results from the present experimental study can help validate numerical models and assist in the design of a right-angled confluence. This study is related to the hydraulics of man-made confluences with mobile beds and can be useful in the following practical applications. More accurate numerical models to predict maximum scour, bed morphodynamics, and sediment transport in man-made confluences can be developed using the detailed bed profile measurements at different time instants presented in this study. Note that available numerical models use sediment discharge formulas (e.g., Meyer-Peter-Muller, Van Rijn), which are for sediment flows in straight channels. The interplay between the three-dimensional flow field, developed bed shear stress, and sediment discharge can be explored. In addition, A man-made confluence with the mobile bed can be designed with findings from the present study. The bedforms corresponding to equilibrium flow depend on discharge ratio, confluence angle, flow conditions at the exit channel, and bed material characteristics. The major bedforms can be incorporated into the confluence geometry. [ABSTRACT FROM AUTHOR]

In this study, the large eddy simulation (LES) under the Eulerian method is used to solve the Navier-Stokes equations for turbulent flow simulation. The Lagrangian point-particle model is applied to track particle trajectories and to calculate the forces exerted by the flow on the particles, and the particle–wall and particle–particle collisions are also accounted for. Nine simulations cases were carried out along the line of previous experiments that considered different bedform regimes, namely, ripples and dunes. The resulting bedload intensity parameter and the simulated bedforms for all the cases agree with the results obtained from the existing classical formulas. The three-dimensionality of sediment transport randomly occurs due to the turbulent flow. Coherent structures are formed as the near-bed low-speed fluid streaks entrain into the mainstream over the stoss-side of the ripples, and the high-speed fluid streaks from the mainstream rush toward the bed over the leeside. As a result, kolk–boil and hairpin vortices develop nearby. Ejection and sweep prevail near the bed, where the particles transport. The phenomenon disappears as the flow intensity increases. The presence of bedload particles also modifies the propagation angle and range of velocity fluctuation, especially in the streamwise direction. To conclude, a logistic regression formula for bedload intensity parameters, accounting for the fluid rotation, deformation, and translation terms that signify the fluid vortical motions, is obtained. It reveals that as long as these three terms are accurately quantified, the bed shear stress and bedload transport rate can be effectively estimated. [ABSTRACT FROM AUTHOR]

Existing knowledge about groyne-induced effects is primarily based on riverine or coastal environments where salinity gradients are absent or limited. However, in estuaries, salinity gradients drive physical processes such as longitudinal and lateral residual flows. The effect of groynes is much more complex because they can modulate channel hydrodynamics and directly affect lateral salinity gradients. In this study, an idealized model is applied to investigate the effects of groyne layouts in estuarine environments, including effects on (1) channel hydrodynamics, (2) lateral water exchange, (3) Coriolis effects, and (4) saltwater intrusion. Model results show that the aspect ratio (the width of groyne fields to the length of groynes) of groyne fields plays an important role. Groynes also induce asymmetry of lateral flows, for example, increasing near-bottom shoal-to-channel flows during low water slack. The aspect ratio has opposite effects on horizontal and vertical components of water exchange. A large aspect ratio strengthens horizontal exchange and weakens density-driven currents. For a large-scale groyne field (several kilometers), Coriolis effects introduce a substantial difference in exchange mechanisms along the north and south banks. A medium range of aspect ratio (2.0–3.0) leads to the strongest saltwater intrusion during both neap and spring tides. Dikes and groynes are common engineering structures in waterways designed to increase along-channel flow velocities and prevent sediment deposition, thereby maintaining navigability. However, especially in estuarine environments, cross-channel flow velocities resulting from these structures may generate sediment transport toward the channel, in contrast to their original intention. Another important impact of these structures is on saltwater intrusion, which is crucial to freshwater resource management. Therefore, this research investigates the groyne-induced effects on cross-channel flows and the saltwater intrusion problem by comparing different layouts of groynes and their consequences. Two important findings may benefit practical applications. First, the interaction between saltwater and freshwater in estuaries enhances cross-channel flows during certain periods, thereby influencing sediment transport. Second, the maximal saltwater intrusion occurs for intermediate width-to-length ratios of the groynes, with lower saltwater intrusion for either very small or very wide groyne fields. [ABSTRACT FROM AUTHOR]

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

The piano key weir is a unique new geometric type that can have a linear (rectangular or trapezoidal) or arc (trapezoidal) layout. Depending on the flow hydraulics and the bed type, different shapes of scour holes can form downstream of these weirs. Two types of piano key weirs—rectangular, and trapezoidal with an arced plan—were built to investigate the sediment transport patterns. The bed material comprised sand (d50=1.25 mm) and gravel (d50=8.9 mm). The results revealed that the scour hole dimensions and bed topography patterns depend on hydraulic conditions, crest geometry, and bed material gradation. Analysis of the data suggested that local scour depths behind a piano key weir with a rectangular crest might be as much as 12% larger than those for other configurations in sand or gravel. [ABSTRACT FROM AUTHOR]

The ship-generated waves in restricted waterways can influence the behavior of sediment resuspension and bank erosion. This paper explores the case study considering the effect of ship-generated waves in restricted channels. A fully nonlinear Boussinesq model (FUNWAVE-TVD) is used to simulate the ship-generated waves. The sediment transport model adopted in FUNWAVE has been changed to incorporate the modified diffusion coefficients, deposition flux, and an explicit equation for settling velocity and critical shield parameter. The sediment transport model was validated against the experimental results of solitary waves in a wave tank, and model performance in shoreline geometry was reported. The implementation of the moving vessel in the numerical model and its impact on suspended sediment concentration were evaluated against the field measurements in the Falta stretch of the Hooghly river in Indian National Waterway 1. The error value in predicting the depth-averaged suspended sediment concentration by the FUNWAVE module was 97.6%, which has been significantly reduced to 16.3% based on the present modification. The parametric study of the ship waves in a typical restricted waterway of India revealed that the concentration of the sediments gradually decreases from the navigation channel to the river banks due to dissipation in the ship waves. The change in wave height and depth-averaged sediment concentration increases with the increasing depth Froude number. Finally, the impact on sediment transport due to different scenarios, such as the movement of two vessels in close proximity, the passage of vehicles coming from the opposite direction on the navigation channel, the influence of small draft vessels, and the bed morphology changes due to the multiple vessel movements are analyzed and reported. [ABSTRACT FROM AUTHOR]

By incorporating horizontal sediment transport and bed erosion into the two-layer depth-averaged shallow water system, one can construct a hydro-sediment-morphodynamic mathematical model in which a variable sediment concentration in a denser layer and interaction between underflows and ambient water are taken into account. Numerically solving such a promising system presents challenges due to its inherent mathematical properties of being conditionally hyperbolic and nonconservative. These properties may result in instability and incorrect results near sharp hydraulic gradients in numerical solutions. The major contribution of this paper is to develop a novel numerical scheme to overcome these issues and to allow the system to be extended to a wider range of engineering applications. To this end, for a one-dimensional two-layer hydro-sediment-morphodynamic system, (1) its mathematical model is first reformulated to a novel relaxation format, which is mathematically equivalent and unconditionally hyperbolic, by relaxing interlayer surface level, and (2) this relaxation system is then solved using a novel path-conservative numerical algorithm with new discrete formulas for the fluxes and nonconservative terms. Thus, the proposed numerical scheme ensures the well-balanced property, and has a major advantage in its ability to accurately and stably handle sharp hydraulic/density gradients with second-order accuracy. Several numerical and laboratory tests are conducted to demonstrate the performance of the proposed new scheme. [ABSTRACT FROM AUTHOR]

Local scour processes can be divided into initial, progressing, and equilibrium stages. Due to its short duration and high scour rate, the initial stage has not been well investigated to date. By applying laser-based technique and particle image velocimetry, this study conducted a series of measurements of scour hole profile and flow field at the beginning of scour hole development for the case of plane jet–induced scour. The results show that the scouring process in the initial stage is dominated by the wall shear, and thus can be classified as shear scour, whereas that in the progressing stage largely is affected by the turbulent vortex, and therefore can be referred to as vortex scour. The two modes of scour could be characterized by different mechanisms of sediment erosion. A bedload model is proposed to analyze the sediment transport for the shear scour, and the results agreed well with the experimental data. [ABSTRACT FROM AUTHOR]

The Integrated, Section Surface Difference Over Time, version 2 (ISSDOTv2) method provides a means of quantifying bedload in large sandbed rivers. Like all measurements, it is important to understand the uncertainty associated with the method before making management decisions based on its results. A methodology is presented for quantifying and combining the uncertainty for each component of the ISSDOTv2 method including particle density, bed porosity, acoustically measured bed topography, the timing of measurements, sand wave identification, and regression analysis used for geometric correction of bedload measurements. The approach provides an indication of the relative magnitude of each source of uncertainty in addition to the uncertainty in the final resultant transport rate. Laboratory flume measurements were used to evaluate the uncertainty limits and verify the approach. The greatest contributor to uncertainty was found to be the bathymetric uncertainty, and, at the highest transport rates, cumulative relative uncertainty was found to be approximately 10%. Cumulative relative uncertainties grew rapidly with decreasing flow rates, driven primarily by the higher relative contribution of the effect of bathymetric uncertainty on the smaller bedforms that are typically present at lower transport rates. The approach documented here will be transferrable to real-world systems to determine the uncertainty in measured bedload sediment transport rates using the ISSDOTv2 method. [ABSTRACT FROM AUTHOR]

The ship-generated waves in restricted waterways can influence the behavior of sediment resuspension and bank erosion. This paper explores the case study considering the effect of ship-generated waves in restricted channels. A fully nonlinear Boussinesq model (FUNWAVE-TVD) is used to simulate the ship-generated waves. The sediment transport model adopted in FUNWAVE has been changed to incorporate the modified diffusion coefficients, deposition flux, and an explicit equation for settling velocity and critical shield parameter. The sediment transport model was validated against the experimental results of solitary waves in a wave tank, and model performance in shoreline geometry was reported. The implementation of the moving vessel in the numerical model and its impact on suspended sediment concentration were evaluated against the field measurements in the Falta stretch of the Hooghly river in Indian National Waterway 1. The error value in predicting the depth-averaged suspended sediment concentration by the FUNWAVE module was 97.6%, which has been significantly reduced to 16.3% based on the present modification. The parametric study of the ship waves in a typical restricted waterway of India revealed that the concentration of the sediments gradually decreases from the navigation channel to the river banks due to dissipation in the ship waves. The change in wave height and depth-averaged sediment concentration increases with the increasing depth Froude number. Finally, the impact on sediment transport due to different scenarios, such as the movement of two vessels in close proximity, the passage of vehicles coming from the opposite direction on the navigation channel, the influence of small draft vessels, and the bed morphology changes due to the multiple vessel movements are analyzed and reported. [ABSTRACT FROM AUTHOR]

Resuspension and redistribution of sediments induced by propeller wash may significantly influence aquatic ecosystems at contaminated sediment sites. This study describes a numerical modeling method developed to predict the sediment resuspension and subsequent transport processes resulting from ship traffic, with a fully coupled simulation of hydrodynamics, sediment transport, and propeller wash. By including propeller momentum effects in the flow field computation, the advection and dispersion of resuspended sediments are better represented than in previously available methods. To achieve this improvement, a computational algorithm was first developed to calculate the propeller wash effects from one or more ships (e.g., erosion rate and momentum flux); these results were then dynamically linked to a hydrodynamic and sediment transport computation using Environmental Fluid Dynamics Code Plus (EFDC+). This modeling framework was evaluated using a field experiment conducted by the US Navy. The model was calibrated with flow velocities and sediment erosion depths, and then validated with resuspended sediment concentrations in the water column. The model results reproduced the horizontal and vertical distributions of resuspended sediments better when the propeller-induced momentum was incorporated into the flow field computation. The sensitivity test indicated that the increased flow energy from propeller momentum resulted in significant dispersion of resuspended sediments in both longitudinal and lateral directions. The maximum scour was dependent on the propeller revolution speed, the ship engine power, and the distance between the propellers and the sediment bed. [ABSTRACT FROM AUTHOR]

Our data show large scatter in the critical Shields stress values for initial sediment motion. The main sources of dispersion are related to the methodological procedures defining the inception of movement (i.e., visual observations or extrapolation of sediment transport rate) and to the estimation of the bed shear stress. The threshold for sediment motion varies with many factors related not only to grain size but also to bed composition (e.g., presence of fine sediments in a coarse matrix), arrangement (e.g., bed roughness, grain orientation, and characteristic lengths of bed structures) and slope. New models to estimate the critical Shields number are proposed using grain size or bed slope or a combination of both. Model parameters and uncertainty are estimated through Bayesian inference using prior knowledge of these parameters and measured data. Apart from the uncertainty in observations, two types of uncertainty can be evaluated: one related to the parameter estimation (i.e., parametric) and one related to the choice of the model (i.e., structural). Finally, a four-parameter model based on the grain size and bed slope yields the best results and demonstrates potential interaction between these two parameters. Model uncertainty, however, remains large, which indicates that other input parameters may be needed to improve the proposed model. [ABSTRACT FROM AUTHOR]

The −1 power region of the turbulence spectrum is a constant energy region responsible for energy production. However, its scaling and their implications are underreported. Experiment results show that the production region comprises 42% of turbulence kinetic energy for open-channel flows over fine gravel and very coarse gravel beds. Energy of the production region scales similarly for these gravel bed types, and enables its prediction using logarithmic and exponential equations. Similarity scaling is evidenced for the production region's low and high wavenumber boundaries, defined as the macroturbulence and bursting wavenumbers. The macroturbulence and bursting wavenumbers have similar functions, suggesting that the production region is controlled by the same phenomena across its extent. These results are contrary to those of previous research, in which low and high wavenumber boundaries were hypothesized to be scaled by outer and inner scales, respectively. The authors introduce the macroturbulence streampower, which is derived using the energy similarity and macroturbulence wavenumber. The macroturbulence streampower is distributed across the flow depth, is dependent on roughness element, and agrees with Bagnold's streampower near the channel half-height. [ABSTRACT FROM AUTHOR]

Suspended sediment concentration is critical for many aspects of water resources management, such as sedimentation prevention in irrigation channels. Samplers from the Federal Interagency Sedimentation Project (FISP) are widely used for suspended sediment measurement. There is a need to evaluate their accuracy. This paper reports the use of a three-dimensional (3D) computational fluid dynamics (CFD) model to make such evaluation. Two selected depth-integrating samplers, D95 and D96, were studied, with the focus on the intrusion effect of the samplers. Suspended sediment transport was simulated to capture the entrainment, transport and deposition processes. The turbulence was simulated using a Reynolds-averaged Navier-Stokes (RANS) k-ω model. The samplers were placed at three different vertical locations in an open channel. The simulation results showed that the surrounding flow was disturbed by the sediment samplers. However, regardless of the vertical location of the samplers, they had a negligible effect on the sediment concentration at the inlet nozzle. The main reason is that the inlet nozzles of both samplers had enough protrusion upstream such that the intake was not affected by the sampler bodies. The results did not show significant vorticity at the inlet nozzle either, which in the past was suspected of imparting centrifugal force on sediment particles and thus having selective sampling efficiency depending on sediment sizes. [ABSTRACT FROM AUTHOR]

The effect of the intense transport of lightweight sediment without turbulent suspension (Shields numbers of mixture flow from 0.34 to 1.80) on resistance and surface elevation of water flow in an open channel is experimentally examined. Flows over fixed and mobile plane beds, at the same water flowrate and bed slope, are compared. Detailed measurements—including distributions of solids and velocity—permit to identify flow interfaces and determine the role of sediment transport on flow resistance. Two friction factors for mobile bed flows are introduced: one for water only and another one for the mixture. The first seems to be insensitive to the water submergence, while the latter follows the classic formula for the hydraulically rough regime: both increase with respect to the equivalent clear water flow. The water surface elevation seems unaltered by the presence of sediment transport, thus reducing the need for the modelling of the evolution of an erodible bed surface in, at least, some routine applications in fluvial hydraulics. [ABSTRACT FROM AUTHOR]

This paper reports a new experimental method applying medical X-ray computed tomography (CT) to estimate the bed load in sand transport. A set of current-generated sand ripple experiments were conducted in a small hydraulic flume inserted in the CT scanner. The methodology is based on the measurements of height, velocity, and density of bed forms to estimate bed load. A temporal series of bed topography is first extracted from the CT scan images. The velocity is estimated by tracking the displacement of bed forms from two successive bed topographies. The sand bed density (ρsb) is estimated from the CT scan measurements using a calibration technique. The method measuring ρsb to calculate bed load is validated comparing measurements made with sand traps. The advantages and limitations of the CT method applied to bed-load transport are discussed. Sediment transport is a fundamental physical process in Earth Sciences. It refers to the movement of sediment grains transported by water currents and deposited where or when water flow ends. This cycle seems at first inoffensive but could impact millions of human lives all around the world. River floods, sea-level rise, and storms are likely to modify the landscape of many populated areas located nearby in the next decades. A better understanding of sediment transport processes would greatly benefit our capacity to determine the impact of those extreme events on river and coastal morphology. To achieve this, physical models are used in laboratories to simulate sediment dynamics at a smaller scale. These results help researchers developing numerical models of sediment transport to better predict river dynamics as well as the movement of coastlines. This study is an insight on the application of new laboratory techniques using advanced three-dimensional imaging technique as an effort to contribute to our knowledge of sediment dynamics. [ABSTRACT FROM AUTHOR]

Process-based models are suitable tools for reproducing storm-driven erosion. However, their performance has been mainly examined on mild-slope sandy beaches and their use on steep beaches still represents a challenge. Here, open-source process-based model XBeach experiments were combined with topographical measurements collected for two storms (16- and 5-year return period) to obtain a reliable model. The model parameters "facua" (parameterized wave asymmetry and skewness sediment transport component), "bermslope" (upslope transport term for semireflective beaches), and "wetslope" (critical avalanching submerged slope) were utilized for calibration and validation. The 16-year storm simulations on an exposed beach revealed that whether bermslope increased and "facua" must be reduced, and vice versa, to properly simulate erosion. Adding bermslope provided excellent results for these storms when using facua and wetslope values close to the recommended values. In a groin-protected site, XBeach was successfully calibrated and validated for the tested storms using these parameters, although with different values. These experiments demonstrated that the appropriate use of these parameters can satisfactorily simulate morphological changes on steep beaches for different hydrodynamic conditions and coastal settings (exposed and groin protected). [ABSTRACT FROM AUTHOR]

The bed level change in rivers and estuaries due to several dynamic parameters such as tide, waves, river discharge, and wind is a common problem. The current practice is to predict the changes through numerical modeling and compare it through field measurements. The empirical relations to be adopted for the sediment transport estimation form an integral part of morphodynamic models. In this study, five different total sediment transport formulae have been incorporated in the morphodynamic routine of a circulation model. The hydrodynamic model accounts for tide-induced flows, tide being the dominant forcing in the estuaries considered for the study. The preceding sediment transport formulae for predicting bed level changes (erosion and accretion) are subjected to an assessment, through statistical approaches, to find the most suitable formula for different hydrodynamic settings of a macrotidal estuary (Hooghly) and a microtidal estuary (Cochin). The results are validated with the field measurements and finally the appropriate empirical formula is designated based on a detailed analysis. The AW model outscores in the Brier skill score (BSS) analysis and thus qualifies to be most suited sediment transport model for the macrotidal estuarine dynamics with a score of 0.55, and the AW model is followed by the VR model with a score of 0.52. As per BSS, the EH model falls under the Good model category with a score of 0.48, for the microtidal estuary and thus qualifies to be the better suited sediment transport model among the models considered. [ABSTRACT FROM AUTHOR]

Colocated sediment pore pressures at depths of approximately 0.02 and 0.22 m below the sand surface and near-bed water velocities were measured for approximately 2 weeks in approximately 1 m mean water depth on an ocean beach near Duck, North Carolina. These measurements suggest that storm wave-driven liquefaction processes may enhance local shoreward sediment transport. During the passage of tropical storm Melissa, wave heights in 26-m water depth (NDBC 44100) were 1–4 m, and storm surge (approximately 1 m) and wave-induced setup increased the water depth on the beach. Upward vertical gradients in pressure heads between the sensors increased with the storm approach, with the largest values observed before the maxima in local wave heights, wave periods, and water depths. The large gradients in pore pressure exceeded several liquefaction criteria and usually occurred when near-bed velocities were upward- and shoreward-directed. Observations on an ocean beach show that during storms the water pressure below the sand surface can be greater than the pressure near the sand surface. When that difference in pressure (called a pressure gradient) becomes large, the sediments fluidize, that is, they act like a fluid in a process called liquefaction. Unlike dry or partially wet sediments, the fluidized sand is moved easily by currents. During tropical storm Melissa, large upward-directed pressure gradients fluidized the sediment, usually as the crest of an ocean wave passed over the surface. Therefore, the sediments possibly became free to move as a liquid when the currents from waves were directed both upward and toward the shore. The liquified sediments could be transported shoreward, leading to changes to the sand surface (accretion and erosion). This phenomenon is important to understand because it contributes to how, where, and when sediment might be transported on an ocean beach. [ABSTRACT FROM AUTHOR]

This article aims to provide a comprehensive appraisal on the current status of three-dimensional (3D) numerical modeling of local scour around instream hydraulic structures. Many computer models have been developed or are in development to simulate riverbed morphology. Local scour, however, is a special category that requires in general a 3D model based on some averaged/filtered form of the Navier-Stokes (NS) equations and a 3D sediment transport model. Only limited number of 3D scour codes are available for practical usage; there is also a lack of literature on the limitations of the models in capturing the scour-producing flow and the sediment transport solvers embedded within. For 3D local scour modeling, the main intrinsic uncertainty lies primarily in the sediment part. In this article, the basic theory and the state of the art of current 3D local scour models are reviewed, focusing primarily on the sediment solver, and future research needs are discussed. [ABSTRACT FROM AUTHOR]

Forensic engineering field surveys conducted in the aftermath of large-scale tsunamis documented the presence of deep local scour holes around structures caused by extreme inundation occurring during such events. The mechanisms leading to scour in extreme flows are still not well understood, as several physical phenomena influencing the spatiotemporal extent of scour have not been adequately investigated. The authors have conducted an experimental test program that has employed a large square column in the Large Wave Flume of the Coastal Research Center, Germany, while they also used a state-of-the-art numerical model (FLOW-3D) to numerically reproduce the experimental results. An investigation of the turbulent flow structures observed around the impacted structure showed that these flow structures are largely responsible for the sediment transport during the runup phase, but the turbulent energy was far less intense during the drawdown phase. The weakness of the turbulent structures observed during drawdown indicates that a different physical phenomenon than the one corresponding to the inflow phase is responsible for the sediment transport experienced during inundation drawdown. Due to the rapid lowering of the flow depth during the drawdown phase of tsunami inundations, a loss of excess pressure occurs because of the upward pressure gradient forming within the soil. However, the pore pressure measurements taken inside the soil in the physical experiment indicate no sign of upward pressure gradient on the inshore side of the column, which is an observation that is incongruent with previous similar studies and previous theoretical concepts. This difference was explained by a layer of soil that remained with a low water content throughout the test because the column was installed on dry sand with low permeability, a condition never tested before for pore pressure change caused by tsunami-like waves. [ABSTRACT FROM AUTHOR]

The effect of wave skewness and sediment particle size on near-bed sediment dynamics and transport owing to wave-induced streaming is examined in this study. Here, wave-dominated flow over a flat rough bed is studied, with wave propagation forming a nonzero angle with the current. It was observed that the increase in wave skewness increases the mean sediment transport, which is consistent with prior findings for the particular situation of horizontally uniform Stokes forcing. The mean sediment transport beneath combined second-order Stokes waves and current has been investigated for fine, medium, and coarse sand, respectively. Due to inertia, both the mean bed-load vector and the depth-integrated suspended flux vector are less rotated (relative to the wave propagation direction) for coarse sand than for fine sand. The mean bed-load transport is largest for coarse sand, whereas the mean suspended sediment transport is largest for fine sand. [ABSTRACT FROM AUTHOR]

The rheological behavior of soil–water mixtures can affect the flow dynamics of natural processes such as flow-type landslides and sediment transport. In this study, an experimental investigation was carried out on soil–water mixtures containing particles up to 0.425 mm with volumetric solid concentrations of 0.05≤CV≤0.35 using a wide-gap rotational viscometer, and the contributions of particle–fluid, collisional, and colloidal interactions to their rheological behavior were evaluated thoroughly. The torque-scaling method was applied to identify the flow regime and extract the effective rheological parameters from turbulent flows. A transition between dilute and concentrated mixtures can be identified based on their sediment type, CV , and the predominance of particle–fluid and interparticle interactions. For dilute mixtures (CV<0.25–0.28) the particle-fluid interaction is dominant. The colloidal interactions induce another force scale that is independent of the shear rate. Thus, the Bingham model can be applied to such mixtures (debris or mud flood). For concentrated mixtures (CV>0.25–0.28), the shear-thickening rheology can be applied for granular mixtures (debris flows), because the collisional interactions are dominant, whereas shear-thinning rheology can be applied for fine-grained mixtures (mudflows), because colloidal interactions are dominant. [ABSTRACT FROM AUTHOR]

In this paper, we present a simple theoretical method of determining the optimal groin length on a sandy multibar shore of a nontidal sea. Example computations for the seashore of the Hel Peninsula (Poland, south Baltic Sea) are provided. The proposed unsophisticated method, which consumes little time and is thus innovative, is based on calculations of the mean annual sediment transport rate and a determination of the width of the surf zone. The reliability of the theoretical modeling results was demonstrated, as well as their compatibility with the features of the groin system designed and constructed along this stretch of the shore a few decades ago. Long-term field observations in the village of Kuźnica have shown that such a system effectively supports and supplements the artificial shore nourishment in the considered region. The method can be applied to other sandy and multibar shores of nontidal seas. [ABSTRACT FROM AUTHOR]

Sedimentation in a drain system has been recognized as one of the major causes of nuisance flooding produced by localized storms in Southeast Texas. The objective of the study is to assess the sediment load from runoff under different hydrological and road conditions to implement design guidance for a proper self-cleaning drain system. A diffusion wave model is developed to simulate runoff hydrodynamics on the roadway with curb inlets. An empirical sediment load equation is developed as a function of rainfall intensities, road conditions, and field sediment characteristics. The required flow velocity to erode the cohesive deposited sediment, and transport the deposited sediment incorporating the sediment from runoff in the drainpipe has been investigated to implement design guidance for a self-cleaning drain system. Regional hydrological conditions and field sediment characteristics are critical to design an effective drainage system for improving coastal resilience under severe weather conditions. [ABSTRACT FROM AUTHOR]

The mechanisms controlling sediment transport at river mouths and estuaries nearby ports are complicated interactions among waves, tidal currents, and river flows over complex bathymetry. Episodic river discharge triggered by large rainfall may contribute to significant sediment into the ocean. Over the last decade, the exposed riverine sediment from the Zhuoshui River, north of Mailiao Port, is one of the major sources of sediment supply in this region. Previous field observations shortly after the passage of a typhoon suggested fine-grained sediments settled rapidly near the river mouth, and tidal currents and strong wind-driven waves during winter were the mechanisms that transported sediment toward the navigational channel. Numerical simulations provide insights into the patterns of residual circulations for a range of spring-neap tidal forces and wave conditions. Model results show that extending North Jetty could be one of the engineering countermeasures to modify the circulation system between the port and the river mouth to mitigate the siltation problem. [ABSTRACT FROM AUTHOR]

A comprehensive case study of the coastal processes for Fortescue Inlet (New Jersey, USA) is presented with the objective of minimizing maintenance dredging of the navigational channel. This study compares the effectiveness of both traditional sedimentation control structures and modified dredging templates, including construction of a new jetty, modification of the length and orientation of an existing jetty, and the use of upland and offshore deposition basins. The alternatives were analyzed using Deflt3D Flexible Mesh. The results indicate that sediment transport near Fortescue Inlet is dominated by wave action with pronounced seasonal variations in wave direction. The site exhibits relatively shallow depths above the depth of closure and pronounced offshore bars. Consequently, much of the sediment transport occurs well offshore (approximately 300 m offshore) and beyond the existing jetty. The results indicate that structural modifications (i.e., relocation or lengthening) of the existing jetty do not improve the sedimentation rate within the channel. Instead, use of offshore deposition basins delivers the most promising improvement, with potential cost savings over 10% over existing strategies. [ABSTRACT FROM AUTHOR]

Density currents represent a broad class of flows driven by gravity acting on a density difference with the ambient environment. The understanding of the underlying mechanisms of density currents and their implications on fluid, species, and sediment transport have been studied extensively by others. Although confluences occur naturally in terrestrial and submarine settings, little attention has been given to understanding the confluence of two density currents. Here, we systematically studied the unsteady flow in confluences and developed a methodology for describing the flows based on bulk properties in pre- and post-confluence density currents. Numerical simulations were conducted with experimental validation in which the effects of the initial density difference and channel depth were studied in a junction. In the junction, the currents accelerated and thickened. However, the postconfluence front velocity and thickness values were lower than the preconfluence values. The front velocity, front thickness, maximum near-bed horizontal velocity, and maximum bed shear stress are presented as functions of a Froude number. For the range of cases tested, the peak and postconfluence front velocities were not dependent on the initial conditions. Unlike the front characteristics, the bed shear stress continued to rise as the current's combined front continued downstream. Therefore, two reestablishment lengths are presented describing the length needed for the front and, separately, the body to return to a constant-value phase. [ABSTRACT FROM AUTHOR]

Accurate flow rate prediction is essential to analyze flood control, sediment transport, riverbank protection, and so forth. The flow rate distribution becomes even more complicated in compound channels due to the momentum transfer between different subsections across the width of the channel. Conventional channel division methods estimate flow distribution at the main channel and floodplains by assuming a division line with zero apparent shear stress. The article attempts to develop a model to calculate the percentage of discharge in the main channel (%Qmc) using techniques such as Group Method of Data Handling—Neural Network (GMDH-NN) and gene-expression programming (GEP) by incorporating the effects of various geometric and hydraulic parameters. The paper proposes a modified channel division method with a variable-inclined interface, with zero apparent shear force distribution at the channel subsections according to the statistical indices employed to assess these models' performance in predicting %Qmc. This variable-inclined interface changes its slope according to the channel parameters. The model's effectiveness is verified by validating with experimental observations by conventional analytical methods. [ABSTRACT FROM AUTHOR]

This paper studies the effect of the wave front-current angle on the scour around a circular pile. An experimental study was carried out in the Coastal, Ocean and Sediment Transport (COAST) laboratory at the University of Plymouth (UK) using a single monopile of 0.125 m in diameter and an 8 m long by 1.5 m wide by 0.2 m high sand pit. The results obtained during the test campaign show the influence of the angle between waves and currents on both the maximum scour depth and the time scale of the process. Wave fronts partially aligned with current (65°) produce deeper scour holes than perpendicular forcing conditions (90°). Wave fronts partially against the current (115°) produce less scour than any of the two previous scenarios. The addition of waves reduced the maximum scour depth, compared with the current-only case. The development of the scour hole was found to be more rapid when waves are added to the current, with 50% of the final scour achieved in half the time. The results show that wave direction relative to the current is an important component in scour prediction. [ABSTRACT FROM AUTHOR]

Along sandy coastlines, submerged, shore-parallel sandbars play an essential role in shoreline morphology by dissipating wave energy through depth-induced wave breaking. While wave breaking and sediment transport around sandbars are complex three-dimensional (3D) processes, shoreline morphology is typically simulated with depth-averaged models that feature lower computational demand than do 3D models. In this context, this study examines the implications of depth-averaging the flow field and approximating the breaking process in nonhydrostatic models (e.g., XBeach nonhydrostatic) for the hydro- and morphodynamic processes around sandbars. The implications are drawn based on reproducing large-scale experiments of a barred beach profile using the single-layer (XBNH) and the reduced two-layer (XBNH+) modes of XBeach. While hydrodynamic processes were predicted with high accuracy on the sandbar's seaward side, wave heights were overpredicted on the bar's landward side. The overestimation was due to the simplified reproduction of the complex breaking process near the sandbar's peak, particularly in terms of the generated turbulence in the water column. Moreover, the velocity profile with a strong undertow could only be represented in a simplified way even using the two-layer mode XBNH+, thus resulting in inaccurate predictions of sediment loads around the sandbar. A parametric study is performed, and it revealed which model parameters control the simulation of the wave-breaking process. Thus, wave height predictions could be improved by tuning the energy-dissipation parameters. However, flow velocities and morphodynamic predictions could not be improved accordingly. Thus, this study identifies possible hydrodynamic model improvements, such as incorporating a roller dissipation model. Moreover, it improves understanding of key drivers and processes that should be included in nonhydrostatic depth-averaged models to simulate morphological changes around sandbars more efficiently. [ABSTRACT FROM AUTHOR]

A multilayer model is proposed to calculate time-dependent sediment velocity and concentration profiles with the resulting sediment transport. The model is developed here for the wave boundary layer. Measurable quantities are considered, namely, the values of transport during the wave crest and the wave trough, as well as total and net sediment transport values (averaged over the wave period) resulting from the summation and subtraction of their absolute values, respectively. The calculated value of the maximum stress at the bed during the wave period is verified by direct stress measurements. The model is tested for mixed sediments with different grain size distributions including semiuniform and poorly sorted grains. Transport calculations are carried out for acceleration-skewed oscillatory flows and waves described by Stokes' first and second approximations. Comparison with the available small- and full-scale data from flumes and oscillating tunnels yields agreement typically within plus/minus a factor of two of the measurements. [ABSTRACT FROM AUTHOR]

Sandy beaches generally are influenced by various coastal dynamic processes and undergo constant changes. The present study is an attempt to understand the hydromorphodynamic characteristics of a sandy pocket beach situated along the central west coast of India through field observation and numerical modeling. Multiple oceanographic instruments are deployed to capture the actual nearshore hydrodynamics, and sediment transport is measured using the streamer trap method suggested earlier during the premonsoon season. The observed vertical distribution of sediment fluxes showed a typical upward decrease from the seabed to the water surface. It is also noted that nearly 75% of the trap measurements showed that near-bed transport is higher than the depth-integrated values, confirming that the maximum sand remobilization is in the vicinity of the seabed rather than in suspension. The beach profiles of selected transects were measured during the pre- and postmonsoon seasons to understand the bed evolution. A one-dimensional numerical model, developed using XBeach and validated with field-observed values, demonstratively captured the effect of monsoon hydrodynamics on the beach profiles with fair accuracy. The various significant numerical parameters that govern the morphodynamics in the sandy beach are evaluated through a comprehensive analysis. In the end, the simulated beach profile that captures the effect of monsoon and storm are in good agreement with that obtained from field observations, with Brier Skill Scores (BSSs) of 0.69, 0.76, and 0.74 for Profiles 1, 2, and 3, respectively. [ABSTRACT FROM AUTHOR]

Dredged sediment is commonly placed as a submerged nearshore berm to nourish the beach or to dissipate high-energy waves, but the lifespan of such features is not easily predicted by existing methods. This paper presents a simple technique for generating order-of-magnitude estimates of the sediment transport rate of nearshore berms using offshore hindcast wave characteristics transformed to the nearshore. Total longshore transport for the entire nearshore region is calculated using eight published longshore transport equations (e.g., CERC equation and Kamphuis equation), which were evaluated for their relative performance. Because nearshore placements occupy only a portion of the cross-shore profile, the total longshore transport rate is scaled by an empirically-based fraction between 0 and 1, which is determined by the nearshore berm's position in nondimensional space. The cross-shore transport rate is calculated independently using the near-bed orbital velocity from stream-function wave theory. The longshore and cross-shore transport rates are then superimposed to generate a total transport rate for the nearshore berm's constructed footprint. The total transport rates were calculated at 11 historical nearshore berms and evaluated based on accuracy, inclusion of relevant coastal processes, and sensitivity to input parameters. The recommended total transport rate technique resulted in an average percent error magnitude of 72% and a maximum percent error magnitude of 167% at the historical placement locations. This technique is recommended for generating rapid, order-of-magnitude estimates of nearshore berm deflation rates for project design, particularly in scenarios when application of a full numerical model is prohibitive. [ABSTRACT FROM AUTHOR]

The Sidoardjo Mud Volcano in East Java, Indonesia, started on May 29, 2006. The average daily discharge of the mud volcano is 50,000 m3/day , with a 35% average concentration of sand, silt, and clay. Since 2017, the finer fractions have been diverted to the Madura Strait through the Porong River. The Ginonjo Outlet serves as a point source with a constant discharge of 45 m3/s and an average sediment concentration of 57,000 mg/L. The settling and transport of fine sediments were studied through field measurements at 106 cross sections over 16 km of the Porong River. At low flow, maximum concentrations decreased from 4,200 to 90 mg/L in the study reach. The two-dimensional mixing and settling model with flocculation resulted in better agreement with the observed data than did models without flocculation. Flocculation tests showed an increase in settling velocity from 0.013 to 0.028 mm/s. Flocculation affected settling of approximately 38% of the total sediment load. The fractions coarser than 92 μm settled within the first 4 km from the point source. [ABSTRACT FROM AUTHOR]

An accurate prediction of scour depth around bridge piers is crucial for economical and safe design of bridge pier foundations. The main objective of the present study is to identify the influencing cohesive parameters and their effects on the local scour processes around bridge piers, depending on various proportions of clay–sand–gravel mixtures. Twenty experimental tests were performed in a channel 25 m long and 1.0 m wide for this purpose. Runs lasted from 16 to 40 h. It was noted from the experimental work that an increment of clay fraction significantly reduces the scour depth around bridge piers. It was also observed that the initiation of scour occurred at the sides of the pier where separation of flow occurred. Typically, the maximum scour depth at the equilibrium stage was still observed at the sides of the pier. A dimensional analysis was used to propose mathematical relationships assessing the temporal scour depth variation at the wake and sides of the pier. The developed relationships yielded reasonable results with maximum error of two folds for 95.22% of total data sets for scour depth at the wake and 92.57% of the total data sets for scour depth at the sides of the pier. [ABSTRACT FROM AUTHOR]

We present the results of laboratory experiments specifically designed to quantify the height and migration rate of an aggrading gravel front. The experiments were performed in sediment feed mode with constant water and sediment supply. Particular care was put into the experimental procedure and the methods to determine the quantities of interest to ensure reproducibility of the results. The celerity and height of an aggradation front were modeled as functions of the Froude number of the flow for the initial bed profile and of a load ratio defined as the ratio of the sediment feed rate to the transport capacity of the flow for the initial bed. The two control parameters (Froude number and load ratio) also determined the translational or dispersive nature of a sediment front. Two predictors were provided to estimate the dimensionless height and celerity of an aggradation front. The former was an increasing function of the load ratio and a decreasing function of the Froude number, and the latter was roughly proportional to the squared Froude number and had no evident relationship with the load ratio. The present results are of interest for scholars and practitioners needing to determine the key properties of swift gravel fronts as those developing, for example, during flash floods. [ABSTRACT FROM AUTHOR]

The aim of this technical note is to present methods that allow for direct computation of the bed roughness due to sediment transport based on a formula developed in the literature for cases involving current or waves separately. The methods result in approximate nondimensional expressions for the exact solutions in terms of polynomials determined by least-square fits, where the accuracy of the polynomials is high. Using the present methods may significantly reduce calculation times of roughness due to sediment transport in numerical models of morphological change. [ABSTRACT FROM AUTHOR]

Understanding the complex flow and sediment transport on vegetated slopes is important for ecological restoration and conservation projects. This study quantifies the erodibility of sand infill through densely vegetated engineered turf on steep slopes. Flume testing was conducted on four different sand infill materials. The initially lain bed material had artificially high mobility due to the infill application method. Grains were elevated by the vegetation and protruded into the flow. Then, the bed material gradation during subsequent flows became progressively coarser. Two regimes were identified. Poorly sorted infill soils underwent noticeable changes to gradation and had decreasing mobility with increasing shear stress. Conversely, well-sorted soils had minimal changes to gradation and resulted in the expected trend of increasing sediment flux with increasing shear stress. Existing predictive formulas performed poorly, in particular for the soils with evolving gradation. An updated formulation to predict sediment flux is proposed based on a reduction to the effective bed shear stress and dimensionless parameters relating to the flow, sediment, and vegetation characteristics. The proposed modification results in greatly improved predictions for both sediment flux magnitude and trend. [ABSTRACT FROM AUTHOR]

In-stream boulders significantly affect local flow hydrodynamics, sediment transport, and aquatic habitats. This study experimentally investigates the Reynolds shear stress (RSS) profiles and turbulent events around an intermediately submerged boulder under a wake interference flow regime. The frequency of turbulent events and their contribution to the RSS are quantified at two specific submergence ratios of 1.56 and 1.90 around the boulder in the near-bed and top-boulder regions. Ejection and sweep events were generally dominant in the near-bed and top-boulder regions. The dominance of turbulent events around the boulder varied as the submergence level changed. Relationships are proposed to predict the contribution of the near-bed turbulent events to the RSS around the boulder. [ABSTRACT FROM AUTHOR]

The current state of the art on how the circular cross-section shape of a rigid boundary channel affects the incipience of sediment entrainment is not well investigated in the literature. Moreover, the incipience of sediment entrainment studies via artificial intelligence is very limited so far. The studies for rigid boundary channels to date have yielded different incipient motion data depending on the cross-sectional shape. Also, most of the existing works were proposed for rectangular cross-sectional channels. Conversely, this study investigated the effects induced by a circular cross-sectional shape on critical dimensionless shear stress by experimental procedures under smooth flow conditions. It was found that the circular cross-sectional channel shape significantly altered the conditions in favor of reducing the critical shear stress for the incipient sediment entrainment. This implies that the circular cross-sectional channel shape exhibits the advantage of self-cleansing open channel design. For a circular cross-sectional channel and smooth flow conditions, a new critical shear stress formula is proposed based on the obtained experimental data. Ninety-seven experimental observations were performed under hydraulically transitional flow conditions with a grain shear Reynolds number (Re*) range of 5.2–41.17. Most of the experiments were performed with Re*>10. The new proposed equation is an empirical approach to express the governing equations of incipient motion in rigid boundary channels. Furthermore, a novel hybrid-geno-fuzzy inference system (GENOFIS) and the adaptive neural fuzzy inference system (ANFIS) approaches were developed using experimentally obtained data to predict the incipient motion of sediment entrainment. The performance of the quantitative results of the novel GENOFIS, ANFIS, and empirical equations were evaluated via the root mean square error (RMSE), F -test, and the coefficient of efficient (CE) model evaluation criteria. The GENOFIS is a novel attempt to revolutionize the prediction of complicated nonlinear phenomena such as incipient motion. The results show that prediction of the incipient motion of sediment via the GENOFIS approach yielded more accurate results than those of ANFIS for hydraulically transitional flow conditions. [ABSTRACT FROM AUTHOR]

Driven by waves, water surface elevation, and wind conditions, a coupled wave, hydrodynamic, and sediment transport modeling system was developed to investigate the transport of placed dredged material in the surf and nearshore zones of southern Lake Michigan. With the measured bathymetric data and the implementation of a cross-shore transport routine, the modeling study focused on nearshore sediment migration, bed volume change, and subaqueous profile change due to wave action. The field datasets validated the model's capability in properly reproducing longshore and cross-shore current and wave processes that govern nearshore sediment transport. The analysis on survey data and simulation results indicates that time-averaged longshore current dominates the redistribution of sediment. Although the cross-shore transport is an order of magnitude smaller than the longshore transport, including the surf zone cross-shore process in the model contributes to net bed and subaqueous profile changes, and greatly improves the model performance. [ABSTRACT FROM AUTHOR]