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This study focuses on a holistic modeling approach, in which water, fluid mud, and immobile mud are all calculated by only one set of equations. To integrate the immobile mud into this concept, a holistic transport equation including sediment transport and consolidation is developed. In some estuaries, extensive deepening and dredging resulted in tidal deformation and sediment import to such extent, that hyper‐turbid conditions developed. Recent measurements from the Ems estuary show that the locations of interfaces between water, fluid mud, and consolidated mud vary during a tidal cycle. Conditions are varying from fully mixed to stably stratified. As a suitable case study for the holistic model, a 1D vertical numerical simulation of the Ems has been set up, which is able to qualitatively reproduce the observed vertical velocity, concentration, and velocity shear profile. The simulation shows mud‐induced periodic stratification. Plain Language Summary: This study describes a 1D hydrodynamic‐numerical model, which is called holistic as water, fluid mud, and immobile bed are solved by only one set of equations. Many estuaries are deepened and straightened to enable passage for ever‐larger ships. In some estuaries, those artificial changes heavily influence the flow behavior and caused a shift to very high sediment concentrations resulting in thick layers of fluid mud. The presence of mud alters the flow‐ and turbulence behavior compared to pure water and subsequently must be included into the modeling equations. The model includes the immobile mud, where flow velocities and turbulence are zero. This is possible with a rearranged consolidation equation and the adaption of model parameters to be valid in cases of very high sediment concentration. Recent measurements from the Ems estuary show that the vertical concentration profile in the estuary strongly varies with time during one tidal cycle: There are phases of a stable fluid mud layer and phases of fully mixed conditions where no mud layer is present. As a possible application of the holistic model, a 1D vertical numerical simulation of the Ems estuary has been set up. The simulation results are in good agreement with field observations. Key Points: A holistic sediment transport equation including sediment transport and consolidation is developedThe rheological viscosity, the settling velocity, and a k‐ω turbulence model are adapted to be valid in the region of the immobile mudA 1D vertical simulation of the holistic model is set up to simulate the flow and sediment processes in hyper‐turbid estuaries [ABSTRACT FROM AUTHOR]

Sediment transport modelling in estuarine environments, characterised by cohesive and non-cohesive sediment mixtures, has to consider a time variation of erodibility due to consolidation. Generally, validated by settling column experiments, mud consolidation is now fairly well simulated; however, numerical models still have difficulty to simulate accurately the sedimentation and consolidation of mixed sediments for a wide range of initial conditions. This is partly due to the difficulty to formulate the contribution of sand in the hindered settling regime when segregation does not clearly occur. Based on extensive settling experiments with mud-sand mixtures, the objective of this study was to improve the numerical modelling of mixed-sediment consolidation by focusing on segregation processes. We used constitutive relationships following the fractal theory associated with a new segregation formulation based on the relative mud concentration. Using specific sets of parameters calibrated for each test-with different initial sediment concentration and sand content-the model achieved excellent prediction skills for simulating sediment height evolutions and concentration vertical profiles. It highlighted the model capacity to simulate properly the segregation occurrence for mud-sand mixtures characterised by a wide range of initial conditions. Nevertheless, calibration parameters varied significantly, as the fractal number ranged from 2.64 to 2.77. This study investigated the relevance of using a common set of parameters, which is generally required for 3D sediment transport modelling. Simulations were less accurate but remained satisfactory in an operational approach. Finally, a specific formulation for natural estuarine environments was proposed, simulating correctly the sedimentation-consolidation processes of mud-sand mixtures through 3D sediment transport modelling. [ABSTRACT FROM AUTHOR]

Zhang, H.; Yang, H., and Jeng, D.-S., 2015. Contaminant transport in capped deformable partially saturated sediments. Contaminated sediment tends to consolidate in response to the loading imposed by an overlying cap layer. The form of transient solute advection through sediments and caps is consequently changed. Therefore, the contaminant discharge into the overlying water is expected to increase and the effectiveness of the in situ capping system will be strongly affected. In this study, a one-dimensional sediment-cap model coupling consolidation and advection-dispersion equation was established. A simplified model was proposed through the sensitivity analysis, and then a parametric study was conducted. Numerical examples concluded that the absorption, degree of sediment saturation, cap thickness, and sediment depth significantly affect the contaminant discharge from the top of the cap. Therefore, these parameters should be considered carefully during cap design. [ABSTRACT FROM AUTHOR]

In this short communication, the erosion process of the fine, cohesive sediment collected from the upper River Taw in South West England was studied in a rotating annular flume located in the National Water Research Institute in Burlington, Ontario, Canada. This study is part of a research project that is underway to model the transport of fine sediment and the associated nutrients in that river system. The erosion experimental data show that the critical shear stress for erosion of the upper River Taw sediment is about 0.09 Pa and it did not depend on the age of sediment deposit. The eroded sediment was transported in a flocculated form and the agent of flocculation for the upper River Taw sediment may be due to the presence of fibrils from microorganisms and organic material in the system. The experimental data were analysed using a curve fitting approach of Krone and a mathematical model of cohesive sediment transport in rotating circular flumes developed by Krishnappan. The modelled and measured data were in good agreement. An evaluation of the physical significance of Krone's fitting coefficients is presented. Variability of the fitting coefficients as a function of bed shear stress and age of sediment deposit indicate the key role these two factors play in the erosion process of fluvial cohesive sediment. [ABSTRACT FROM AUTHOR]

Changes in cohesive sediment density due to consolidation can cause significant changes in dam foundation stress and reservoir site permeability. The consolidation process in the Karkheh dam reservoir was investigated in this study using a settling column and varying the initial sediment concentration from 50 to 150 gr/lit. The initial sediment concentration, initial settlement height, and temperature are effective parameters for settling cohesive sediments. In addition, the effects of the bed elevation of the reservoir, as well as the scale effects on the settlement of cohesive sediments, were also studied. The results showed that the initial free settlement process and the hindered settlement phase take more time than self-weight consolidation settlement stages by increasing initial sediment concentration. Therefore, at an initial sediment concentration of 25 g/1 and 150 g/1, the samples began self-weight consolidation after 1.5 h and 17.5 h respectively. The results also showed that the final average concentration increased linearly with the initial concentration. The concentration of the settled sediments decreased with the initial height in a non-linear trend. In addition, under the same initial conditions, by increasing the diameter of the settlement column, the final concentration of the settled sediments first decreased and then increased. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of the effect of sediment consolidation on contaminant transport through a sediment-cap system for in situ cappings of subaqueous contaminated sediments. Numerical simulations were conducted using the model CST3 and consider coupled consolidation and contaminant transport for representative layer geometry, material properties, and applied stress conditions. Simulation results indicate that sediment consolidation can have significant effects on contaminant breakthrough time, mass flux, cumulative mass outflow, and concentration distribution within the sediment-cap system. These effects manifest not only during the consolidation process but also long after consolidation has been completed. Traditional advective-dispersive transport analyses fail to consider transient advection induced by sediment consolidation and associated contaminant migration and changes in material properties that can lead to significantly unconservative transport results and adverse environmental impact. For example, simulation results indicate that failure to account for sediment consolidation yields a cumulative contaminant mass outflow that is underestimated by a factor greater than 6,000 within the first 3 years after cap placement and by a factor of 2 at the end of a 100-year simulation period, even though consolidation essentially is completed in the first 1.5 years. [ABSTRACT FROM AUTHOR]

Mud forms the foundation of many coastal and tidal environments. Clay suspensions carried downstream from rivers encounter saline waters, which encourages aggregation and sedimentation by reducing electrostatic repulsion among particles. We perform experiments to examine the effects of surface charge on both the rate and style of sedimentation, using kaolinite particles as a model mud suspension and silica spheres with equivalent hydrodynamic radius as a control. Classic hindered settling theory reasonably describes sedimentation rate for repulsive clay particles and silica spheres, which form a highly concentrated jamming front. The hindered settling description breaks down for attractive clay particles, which aggregate to form clay gels that consolidate like a soft solid. Water flow form fracture‐like channels in the bulk of the gel, which disappear as gel enters a creep regime. Results may help toward understanding the effect of surface charge and particle shape on the sedimentation and erodibility of natural mud. Plain Language Summary: When suspended sediment is transported from land to the ocean by river, the water surrounding the sediment particles changes from fresh to salty. This change creates increased interparticle attraction, leading sediment to aggregate and deposit. In contrast to ocean salinity, artificial fertilizers may contain different salts that have the opposite effect on interparticle forces, creating repulsion that suppresses aggregation. These chemical effects, and the way particles sink, are modulated by the shape of the sediment too. Here we perform experiments to examine these effects on sedimentation, using kaolinite particles as a model mud suspension and glass beads as a control. We see that how the particles sink is sensitive to chemistry: when they are repulsive a classic "hindered settling" theory predicts their deposition well, and when attractive the particles link up in a network that behaves like a single structure that collapses under its own weight. The flow of water out of the structure—which we call a gel—as it collapses becomes localized into fracture‐like channels that disappear as the deformation slows down and the gel gets denser. Our observations improve understanding of mud sedimentation, which is essential to predict how estuaries and coastal environments change. Key Points: Aggregation of clay particles enhances sedimentation and forms mud in natureChanging surface charge results in a phase transition from hindered settling to a collapsing gel behaviorFormation and collapse of clay gels may be important for coastal erosion [ABSTRACT FROM AUTHOR]

Understanding the dynamics of settling, consolidation and remobilization of cohesive and contaminated sediment is an important requirement to assess the risk of erosion and to manage mud-dominated ecosystems. Here, we present data on the erodibility of cohesive sediments from the impounded Upper Rhine River and develop a modelling concept to understand the suspended sediment dynamics along the impounded Upper Rhine. The conceptual framework includes 10 reservoirs of the Upper Rhine between Basel and Iffezheim, which serve as long-term sinks of cohesive sediment. Each reservoir is represented by a 1D sediment budget model, which is coupled to its upstream and downstream neighbour. In this paper, we focus on the uncertainty associated with the measurement of the erodibility of cohesive sediments and on the implications to model the risk of erosion. The statistical analysis showed a large uncertainty of the estimated critical shear stresses and erosion rates. Root mean square errors are in the order of 50% and 100% of the average critical shear stresses and average erosion rates, respectively. Preliminary model results are in good agreement with bed changes of the Iffezheim reservoir, which were measured using approximately quarterly echo-soundings of the reservoir. The probabilistic approach that is based on Monte-Carlo simulations allows assessing the uncertainty related to our limited knowledge (i) of the dynamics of contaminated sediments and (ii) of the environmental conditions in the reservoir that control the risk of erosion of contaminated sediments. [ABSTRACT FROM PUBLISHER]

Sedimentation and consolidation of dredged slurry is very complex in practice. A new Multilayer Extraction Sampling (MES) method was developed in this study to better understand the underlying law of sedimentation and consolidation of soil particles in slurries. Comparing with previous methods, the advantages of this method include: (1) the equipment is easy to operate and the test procedures are simple; (2) the volume distribution and the settling velocity of soil particles can be measured and calculated by Volume Flux Function (VFF) approach at different time and heights during sedimentation and consolidation process; (3) soil formation from sedimentation of dredged slurry can be also further studied based on pore water pressure measurements in conjunction with the velocity and density distributions. The experimental results revealed that there were four different zones during sedimentation and consolidation process: water zone, hindered settling zone, consolidation zone and a new zone termed as 'transition zone' where soil particles are in contact with each other but effective stress are not fully developed. It is concluded that the sedimentation and consolidation of soil particles in dredged slurry was studied successfully in a holistic manner using this new experimental method. [ABSTRACT FROM AUTHOR]

To facilitate administrators' abilities to handle reservoir operations, factors on how muddy water was formed inside the reservoir should be identified. According to field observation data, during typhoon events, there were big uncertainties caused by only using the reservoir inflowing discharges to evaluate turbidity condition of raw water inside reservoirs. The data also showed that time intervals between typhoon events could be relevant. The state of the bottom silt inside the reservoir and the erosion capacity of the inflowing turbidity current both might play key roles. In view of these facts, a flume experiment was conducted to analyze the threshold condition of bottom-silt entrainment by turbidity currents. Then, to evaluate and validate muddy water phenomena during storm rainfall events, an empirical equation for evaluating the concentration of reservoir bottom silt after a long time was established by a 4-year experiment on flocculent settling with silt-clay consolidation. The results showed that when the ratio of bed shear stress of turbidity currents to critical shear stress was large, peak turbidity formed by the inflowing turbidity current was relatively high; however, the correlation between that ratio and peak turbidity could be further strengthened by considering silt-clay consolidation time on the bottom concentration of reservoirs. This explained the different levels in terms of turbidity for rainfall events of similar scale. [ABSTRACT FROM AUTHOR]

Ghezala Earth Dam was built in the city of Mateur in the North West area of Tunisia. The filling of the dam reservoir, with a storage capacity close to one hundred thousand cubic meters, started in 1985 and lasted for 2 years. The dam foundation is essentially composed of consistent clayey marl layer. At the lower level of the dam, reinforced concrete drainage, gallery was constructed to evacuate water, when needed, from the upstream side to downstream side. The gallery structure is composed of eleven 15 m length sections. During its service life (more than 26 years), an installed health monitoring system permitted, in particular, the measurement of consolidation settlement which has occurred in the soil foundation. This follow up system made it possible to observe the cracks which mainly developed progressively in the central portion of the drainage gallery due to differential settlements. In this context, a 2D numerical simulation of the behavior of dam foundation was performed by adopting the Mohr-Coulomb model for the dam's material and the soil foundation. Numerical predictions of the consolidation settlement development were compared to those measured in situ and a good agreement was found between the two. This finding highlights the effectiveness of the adopted model for the studied case. [ABSTRACT FROM AUTHOR]

Tailing dams are commonly used to safely store tailings without damaging the environment. Sand tailings (also called Sediment tailings) usually have a high water content and hence undergo consolidation during their placement. As the sediment tailings are usually placed above the ground water level, the degree of saturation and permeability of the sediment tailing is associated with the unsaturated condition due to the presence of negative pore-water pressure or suction. Current practices normally focus on the analyses saturated conditions. However, this consolidation process requires the flow of water between saturated and unsaturated zones to be considered. The objective of this study is to investigate the stability and consolidation of sediment tailings for the construction of road pillars considering the water flow between saturated and unsaturated zones. The scope of this study includes the unsaturated laboratory testing of sediments and numerical analyses of the road pillar. The results show that the analyses based on saturated conditions overestimate the time required to achieve a 90% degree of consolidation. The incorporation of the unsaturated soil properties is able to optimize the design of slopes for road pillars into steeper slope angles. [ABSTRACT FROM AUTHOR]