Diffusion Of Suspended Sediment Research Articles

Numerical simulation of turbidity currents using consistent particle method

This paper expands the Consistent Particle Method (CPM) to simulation of turbidity currents with focus on turbulent water-sediment flow. A mixture model is adopted in solving the sediment transport equation to simulate the sediment mass transfer due to settling convection and turbulent diffusion. To compute the gravity-driven convection term, the proposed CPM-upwind scheme is relatively easy to implement as it avoids the use of a kernel function which has the requirements of symmetry and unity. Two sand settling problems demonstrate the good accuracy of the CPM-upwind scheme. For suspended sediment diffusion caused by turbulence, CPM is able to model anisotropic diffusion without the averaging effect caused by the isotropy requirement if a kernel function is used. The validated CPM methodology is then applied to simulate a sudden flow of water-sediment mixture into ambient water. The results of the mixture front motion and sediment deposit density agree well with published experimental results.

Non-Fickian transport models for characterising the sediment suspension in unsteady flows

Non-Fickian transport of suspended sediment has been observed at field and laboratory scales. Such as turbulent bursting, resulting in complex dynamics for the sediment particles movement. The erosion and deposition of sediment have an impact on the hydraulic engineering and environment. This study makes an attempt to develop the variable-order fractional advection-diffusion equation (VOFADE) and variable-order Hausdorff fractal derivative advection-diffusion equation (VOHADE) models to describe the vertical distribution of suspended sediment in unsteady turbulent flows. From a classical viewpoint, the distribution of the concentration in sediment-laden flows is determined based on Fick?s first law. However, the vertical diffusion of suspended particles exhibits the non-locality/space scale dependency and history memory/time scale dependency properties due to turbulent bursting. Moreover, previous literatures have indicated that turbulence structure changes with the water depth. Hereby, we employ the space-dependent VOFADE and VOHADE models to describe the vertical diffusion of suspended sediment in unsteady flows, and further test its applicability with the experimental data. Numerical simulation results confirm that the VOFADE and VOHADE models give a better agreement with the experimental data and can well characterise the space-dependent anomalous transport. Hence, the models proposed by this study may help to provide a powerful mathematical physical model in the quantification of suspended sediment transport.

Tracking and monitoring of suspended sediment diffusion generated during the trenching of submarine pipeline in Northern Beibu Gulf

ABSTRACT To figure out the law of diffusion of suspended sediment in water, researchers have tracked and monitored the diffusion of suspended sediment during thetrenching of submarine pipeline in Beibu Gulf based on the actual analytical results on ocean currents adjacent to the project area. Research findings indicate that during the procedures of tracking and monitoring, the average velocity of ocean current amounted to 19 cm/s, 30 cm/s and 22 cm/s, respectively, whereas the average direction of ocean current amounted to 228°, 226°and 231° respectively. In addition, the average content of suspended sediment of seawater in the surface layer, middle layer and bottom layer amounted to 1.8mg/L and 3.7 mg/L, 5.9 mg/L, respectively. In the ascending order, the relationship of the content of suspended sediment was: surface layer seawater < middle layer seawater < bottom layer seawater.

The spatio-temporal distribution and transport of suspended sediment in Laizhou Bay: Insights from hydrological and sedimentological investigations

Suspended sediment transport and deposition are crucial physical processes controlling the geomorphological evolution of estuaries and bays. Specially, under the context of worldwide coastal erosion, knowledge of the spatio-temporal distribution of suspended sediment concentration (SSC) and its associated sediment load have become increasingly important for bay management. However, our understanding of the mechanisms of suspended sediment dynamics continues to be hampered by the lack of high-resolution observations. Here, we present a study of the transport mechanisms and controlling factors of suspended sediment over Laizhou Bay. For this, we conducted continuous measurements of SSC, salinity, temperature, and flow velocity at nine stations throughout Laizhou Bay for one 25-h period during each of the spring and moderate tides. Based on these data, residual current, gradient Richardson numbers, and suspended sediment flux were calculated. Our results indicate that a strong current field occurs near the Yellow River mouth, corresponding to the zone with high SSC. The overall diffusion characteristics of suspended sediment are controlled by the tidal current field. Furthermore, our findings suggest that different degrees of stratification occur in the water column, which inhibit the effective vertical diffusion of suspended sediment; Higher water temperature was the main cause of stronger water column stratification of spring tide than moderate tide. Finally, our results reveal that the type of seabed sediment is an important factor controlling SSC by influencing resuspension flux. We conclude that the primary mechanisms controlling suspended sediment transport in Laizhou Bay are advection and tidal pumping, especially advection. Our research provides both a foundational reference for the sediment source-to-sink process from the Yellow River to the sea, as well as guideline implications for coastal engineering construction and channel dredging.

Impact of Suspended Sediment Diffusion from the Implementation of Arresting Facilities on Cross-Sea Bridges

In order to ensure the safety of bridges and ships, non-navigable channel arresting facilities for ships have become an important part of cross-sea bridges, and the diffusion of suspended sediment caused by their implementation has an impact on seawater quality. Taking the Jintang bridge as an example, a two-dimensional tidal current and sediment numerical model was applied to predict the distribution of suspended sediment diffusion caused by the implementation of arresting facilities, in order to analyze seawater quality. We adopted a new formula for the equivalent roughness method, to generalize the bridge piers, and obtained good results. The results showed that the zone where the SSC (suspended sediment concentration) reached 10 mg/L was concentrated in the area from 4.5 km north to 6.5 km south of the arresting facility, when it was implemented near the western channel. The sea area by the main channel was concentrated within 500 m of the arresting facility. The impact of the implementation of the arresting facility on seawater quality was relatively limited. Only the protected marine area in the Zhenhai Section of the Hangzhou Bay Estuary Coastal Wetland was affected by the suspended sediment from the construction of the western channel.

Study of Suspended Sediment Diffusion Coefficients in Submerged Vegetation Flow

AbstractThe traditional profile model of the sediment diffusion coefficient (), which is parabolic along the water depth, cannot precisely predict the vertical distribution of in vegetated flow. Therefore, in this study, a series of flume experiments were conducted to clarify the influence of submerged vegetation on the diffusion characteristics of suspended load particles. First, the submerged canopy increases the efficiency of momentum exchange but restrains the vertical diffusion of suspended sediment, indicating that the presence of submerged plants promotes the siltation of solid particles. Second, the depth‐averaged sediment diffusion coefficient () monotonically decreases with increasing relative water depth, while the depth‐averaged momentum exchange coefficient () presents two opposite trends, likely owing to the dominant turbulence event changing from ejections to sweeps and the different variation tendencies of the velocity gradient and Reynolds shear stress with increasing vegetation density. Compared with the ratio () of to the momentum exchange coefficient in nonvegetated flow, in submerged canopy flow is significantly less than 1, which means that the solid particles diffuse less readily than liquid particles because of the stem‐scale vortices generated by the vegetation. In addition, vertical profile models of and suspended sediment concentration were proposed and validated by experimental data. The models exhibit a high accuracy, correlation and applicability and can provide critical information to promote research on riverbed deformation and nutrient dynamics in vegetated rivers, wetlands and estuaries.

Limited Installation Ranges of Silt Curtain in Ocean and River Hydrodynamic Environment

Youn, S.; Jung, B., and Lee, S., 2021. Limited installation ranges of silt curtain in ocean and river hydrodynamic environment. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 106–110. Coconut Creek (Florida), ISSN 0749-0208. A silt curtain is a flexible ocean structure and is applied to control the diffusion of suspended sediment and pollution materials in the whole world. Specially, the silt curtain is the rational method to control the diffusion of suspended sediment and pollution materials in most ocean construction fields in Republic of Korea. However, this flexible ocean structure has the limitation to install and to maintain in rough hydrodynamic condition due to wave, tidal current, and wind. In this study, the limitation of installation range of silt curtain in countries, where have the rule of installation guide of silt curtain, were reviewed to decide available installation of silt curtain. Designing methods of silt curtain were also reviewed. The applied designing methods in this study were studied in ‘Research to increase the effectiveness of silt curtain (2018)’. To check designing methods, various wave, tidal current, and wind conditions were applied based on designing methods. When tidal current and wave height are over the specific wave height and the speed of tidal current, no more installation of silt curtain was available to use from the result of this study. According to the result, the installation range of silt curtain due to hydrodynamic forces in Republic of Korea is required for safety and protection of ocean environment around maritime area.

The Impact of Waves and Tidal Currents on the Sediment Transport at the Sea Port

Dredged sediments in estuarine and coastal waters can cause sediment transport and water pollutant in marine environment since the sediments are diffused to waterbodies under the influence of wave and flow regimes. As a result, it increases turbidity and enhances sediment deposition at dump sites. In Vietnam, few authors have studied and assessed the environmental impact of dumping and dredged materials to the port areas. This paper combines a coupled spectral wind-wave, hydrodynamic, and sediment transport models in order to study the impact of tide and wave conditions to regional sediment transport patterns at Vung Ang port area in Vietnam. The results for the currents and waves were evaluated and validated using field data. Wind and wave data for the calculated domain are extracted from the WAVEWATCH-III (wave data) and NOAA global climate change models (wind data). The calibration and validation of the MIKE 21/3 showed a high conformity between the observed and simulated data based on the mean absolute error (MAE), the RMSE-observation standard deviation ratio (RSR) and the Percent bias (PBIAS). The MIKE 21/3 sediment transport simulation results showed that the highest suspended sediment concentrations were 2.5-3 g/m3 at the dredging position and the increased concentration along the transport route ranged from 1-1.5 g/m3. The simulation results showed the bed level change of the simulated domain. We found that the suspended sediment diffusion area decreased with the respective depth: Layer 1 (65.5 km2), Layer 2 (45.7 km2), and Layer 3 (37.4 km2). Therefore, the simulation results of the dredged materials activities were significantly affected by the wave and tidal regime on the sediment transport. Doi: 10.28991/cej-2021-03091749 Full Text: PDF

Numeric Simulation of Suspended Sediment Transportation during Dredging of Harbor Basin

Huang, Y.; Sheng, Y.H.; Min, X.Q.; He, Y.F., and Chen, P., 2020. Numeric simulation of suspended sediment transportation during dredging of harbor basin. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 276–280. Coconut Creek (Florida), ISSN 0749-0208.Maintaining the safe water depth of the harbor basin is important to ensure the safety of ships, while dredging is the major method to accomplish this task. However, the dispersion and transportation of suspended sediment during the degrading process, may change the seawater quality. This research utilizes the 2D tidal flow model and 2D sediment numerical model to simulate the distribution of suspended sediment during dredging, and then analyzes the influence on the nearby sea area. The major conclusions can be summarized as follows: (1) the equivalent roughness method can simulate well in the research area; (2) the dredging in Xiazhi Harbor basin has limited influence on the seawater quality. When the increased Suspended Sediment Concentration (SSC) reaches 10 mg/L, the impact distances of both flood current and ebb current are 1.66 km and 0.99 km, respectively; (3) since the tidal dynamic is stronger at the ebb current, the suspended sediment diffusion at this period is more significant, and has less impact on the water quality. Thus, it is recommended to dredge the harbor basin during ebb current.

Vertical Distribution of Sediment Concentration in Offshore Waters

Li, C.; Fu, X.; Xiao, Q.; Pan, X., and Cao, H., 2018. Vertical distribution of sediment concentration in offshore waters. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and Ocean Engineering. Journal of Coastal Research, Special Issue No. 83, pp. 167–171. Coconut Creek (Florida), ISSN 0749-0208.The existing formulae of vertical distribution of sand concentration are difficult to integrate. Based on the formula of vertical distribution of the flow velocity obtained in the previous study and the suspended sediment diffusion equation in equilibrium, a formula of the distribution of suspended sediment is deduced. It can effectively avoid the phenomena that the Rouse formula equals zero at the water surface. The field measurement data of Jiangsu Sea is used to verify and analyze the deuced formula. And results show that it has a high accuracy and it solve the difficulties caused by lack of data in engineering, such as only the sediment concentration on the surface is given.

Suspended sediment diffusion mechanisms in the Yangtze Estuary influenced by wind fields

The complexity of suspended sediment concentration (SSC) distribution and diffusion has been widely recognized because it is influenced by sediment supply and various hydrodynamic forcing conditions that vary over space and over time. Sediment suspended by waves and transported by currents are the dominant sediment transport mechanisms in estuarine and coastal areas. However, it is unclear to what extent the SSC distribution is impacted by each hydrodynamic factor. Research on the quantitative influence of wind fields on the SSC diffusion range will contribute to a better understanding of the characteristics of sediment transport change and sedimentary geomorphic evolution. This study determined SSC from three Envisat Medium-Resolution Imaging Spectrometer acquisitions, covering the Yangtze Estuary and adjacent water area under the same season and tidal conditions but with varying wind conditions. SSC was examined based on the Semi-Empirical Radiative Transfer model, which has been well validated with the observation data. Integrating the corresponding wind field information from European Centre for Medium-Range Weather Forecasts further facilitated the discussion of wind fields affecting SSC, and in turn the influence of water and suspended sediment transportation and diffusion in the Yangtze estuarine and coastal area. The results demonstrated that the SSC present much more distinctive fluvial features in the inner estuary and wind fields are one of the major factors controlling the range of turbid water diffusion.

Numerical Simulation of Suspended Sediment Transportation Based on Particle Tracking Model

Coastal engineering that carried out on the muddy seabed were always accompanied by diffusion of suspended sediment, and that would impact on the surrounding marine environment. A 2-D tidal flow mathematical model of the Yueqing Bay was established based on the Lagrange particle tracking model, the diffusion of suspended sediment in pile foundation construction process of a new wharf in the Yueqing Bay was simulated through a continuous moving points method, the calculation results were compared with the one calculated by the traditional convection diffusion method, it showed that the results calculated from the two different methods were similar, therefore it proved the suitability of the Lagrange particle tracing model in the suspended sediment diffusion problems.

Vertical Distribution of Suspended Sediment under Steady Flow: Existing Theories and Fractional Derivative Model

The fractional advection-diffusion equation (fADE) model is a new approach to describe the vertical distribution of suspended sediment concentration in steady turbulent flow. However, the advantages and parameter definition of the fADE model in describing the sediment suspension distribution are still unclear. To address this knowledge gap, this study first reviews seven models, including the fADE model, for the vertical distribution of suspended sediment concentration in steady turbulent flow. The fADE model, among others, describes both Fickian and non-Fickian diffusive characteristics of suspended sediment, while the other six models assume that the vertical diffusion of suspended sediment follows Fick’s first law. Second, this study explores the sensitivity of the fractional index of the fADE model to the variation of particle sizes and sediment settling velocities, based on experimental data collected from the literatures. Finally, empirical formulas are developed to relate the fractional derivative order to particle size and sediment settling velocity. These formulas offer river engineers a substitutive way to estimate the fractional derivative order in the fADE model.

Hydrodynamic condition and suspended sediment diffusion in the Yellow Sea and East China Sea

AbstractBased on monthly averaged current, temperature, and salinity, we analyzed the changes of suspended sediment concentration (SSC) and the relationship with the warm current, coastal current, and cold water mass (CWM) in the East China Seas (ECSs). The result shows that the coastal current and surface diluted water are the route for transporting suspended sediment. The Kuroshio and its derived warm current branches play the important role of the continental shelf circulation system and control the diffusion of suspended sediment. High SSC has been mainly concentrated in coastal current and CWM. Two sedimentary dynamic patterns have been identified. The winter‐half‐year pattern lasts almost 7 months. The coastal currents off the Shandong Peninsula, northern Jiangsu, Zhejiang‐Fujian coast are the main routes for diffusion and deposition of the suspended sediment from the Yellow River and Changjiang River. The summer‐half‐year pattern is characterized by the well‐developed CWM. All CWMs have a unique function to trap suspended sediment under the thermocline due to weakening tidal current and residual current there. These CWMs in the Yellow Sea (YS) and north ECS are connected together. The layer above the thermocline is characterized by diluted water with low salinity, high temperature. Suspended sediment can be transported into the Okinawa Trough and the South Korea coast during this period. A strong eddy always occur nearby the Kuroshio bend at northeast Taiwan, which has promoted the exchange between the ECS shelf and Okinawa Trough, and the development of the shelf edge current and Taiwan warm current (TWC).

Hydrodynamic and suspended sediment transport controls on river mouth morphology

AbstractRiver mouths building into standing bodies of water have strikingly varied growth habits. This presents a compelling pattern formation problem that is also of great practical relevance for subsurface prediction and managing coastal wetlands. Here we present a generalized 2.5‐dimensional potential vorticity (PV) theory that explains sedimentation patterns of a sediment‐laden stationary jet by coupling an understanding of vorticity with suspended sediment concentration fields. We explore the physical meaning of this new sediment‐PV definition, and its impact on outflow depositional patterns, by analyzing data from a shallow wall‐bounded plane jet experiment and by discussing new theoretical insights. A key result is that lateral advection and diffusion of suspended sediment are directly proportional to jet vorticity, a feature that reveals the mechanistic process that forms elongated channels by focused levee deposition. The new PV theory constitutes a more generalized mathematical framework that expands the Rouse theory for the equilibrium of suspended sediment.

Vertical suspended sediment diffusivity for uniform currents

Vertical diffusivity of suspended sediment with wide size distribution is concerned. The sediment size is expressed by ϕ scale, and the ϕ values are assumed to be normally distributed. The suspended sediment concentration is divided into two groups, 2% of fine side, and 98% of the rest, and single representative settling velocity for median size is used to calculate the vertical diffusion coefficient of the suspended sediment. The computed distribution of the vertical sediment diffusion coefficient is larger than the distribution of the vertical fluid eddy viscosity. A set of equations is proposed for description of the distribution of the vertical suspended sediment diffusion coefficient for engineering purposes. The new equation improves correlation with a set of measured diffusion coefficient values by Barton and Lin.

The Analysis and Discussion of Sediment Transport Capacity Formula

Combined with the equilibrium condition, the formula of vertical average sediment concentration has been derived from the vertical two-dimensional suspended sediment diffusion equation. Based on analyzing and comparing two hydrodynamic formulas, a new formula of sediment carrying capacity has been deduced. Some river and inshore sediment data has been collected to validate the formula and find that the new formula has higher accuracy and applicability comparing with the two hydrodynamic formulas, it shows that the new formula has a high application value.

Preliminary Study about the Sediment Carrying Capacity Formula

Combined with the equilibrium condition, the formula of vertical average sediment concentration has been derived from the vertical two-dimensional suspended sediment diffusion equation. Based on analyzing and comparing two hydrodynamic formulas, a new formula of sediment carrying capacity has been deduced. Some river and inshore sediment data has been collected to validate the formula and find that the new formula has higher accuracy and applicability comparing with the two hydrodynamic formulas, it shows that the new formula has a high application value.

Flow movement and sediment transport in compound channels

There are many studies on the flow movement in compound channels, yet few are concerned with sediment transport. An experimental study on the flow movement and sediment transport in compound channels is presented. The experimental results indicate that the distribution of longitudinal velocity with depth in the main channel and the floodplains has a logarithmic component. The longitudinal velocity with flow depth in the interactive region does not obey a logarithmic distribution, but involves a wake function. In the boundary region, the longitudinal velocity obeys a parabolic distribution. In addition, based on the suspended sediment diffusion equation and the flow interaction between main channel and floodplains, expressions are derived to predict the lateral eddy viscosity and the sediment diffusion coefficients. Finally, an analytical solution for the lateral distribution of the depth-averaged velocity and sediment concentration in a compound channel is obtained. The results from the analytical solution agree well with experimentation.

環境対応型密閉グラブバケットによる浚渫工事の濁りの発生量調査

When dredging in rivers, lakes and canals, control on diffusion of suspended sediment contaminated by toxic substances such as dioxin and PCB has become a matter of utmost concern in recent years. Particularly for shallow and narrow waters, development of a new grab dredging system which minimizes turbidity and affect on the ecosystem has been longed for.In this research, the degree of turbidity and characteristic of suspended sediment diffusion generated by the new Spill Controlled Bucket (SCB) Dredging System and by the conventional method using excavator had been monitored and compared in Lake Biwa. As a result, the degree of turbidity generated by the SCB had reached only 27.1% of that of the conventional method. Furthermore, numerical simulation of the turbidity showed a good match with the actual measurement and suggested that the forecast of diffusion process would be practical.