Non-cohesive Sediment Research Articles

Multiple linear regression and genetic algorithm approaches to predict temporal scour depth near circular pier in non-cohesive sediment

Pier scour is a major problem for the safe and economical design of bridges. Large number of field and laboratory studies have been conducted to investigative the effect of significant variables. Present study is an attempt to develop a generalized scour prediction equation to investigate temporal variation of scour around circular bridges utilizing the data generated from our experimental study as well as data collected by earlier researchers. Nearly 1100 laboratory experimental data-sets were compiled and utilized to develop the generalized scour equation using MLR and GA. The scour depth predicted using GA was found to be more accurate than MLR. Further, the equation developed in the present study was compared to the previously proposed equations. It was found that the present equation complies with observed data better than the previously proposed equations. About 20% and 35% data-sets are found to be within the ±25% error line using previously proposed equations, while GA-based relationship gave about 52% of the data points within ±25% error line.

Issues in Eulerian–Lagrangian modeling of sediment transport under saltation regime

The saltation regime is very important for understanding the sediment transport mechanism. However, there is no consensus on a model for the saltation regime. This study answers several questions raised with respect to the Eulerian–Lagrangian modeling of sediment transport. The first question is why the previous saltation models that use different combinations of hydrodynamic forces yielded acceptable results? The second question is which shear lift model (i.e. a shear lift expression and its coefficient) is more appropriate? Another important question is which hydrodynamic forces have greater contributions to the saltation characteristics of a sediment particle? The last question is what are the contributions of the turbulence fluctuations as well as effects of using two- and three-dimensional (2D and 3D) models on the simulation results? In order to fairly answer these questions, a systematic study was done by considering different scenarios. The current study is the first attempt to clearly discuss these issues. A comprehensive 3D saltation model for non-cohesive sediment was developed that includes all the hydrodynamic forces acting on the particle. The random nature of sediment transport was included using turbulent flow and bed-particle collision models. The eddy interaction model was applied to generate a 3D turbulent flow field. Bed-particle collisions were considered using the concept of a contact zone and a corresponding contact point. The validation of the model was done using the available experimental data for a wide range of sediment size (0.03 to 4.8 cm). For the first question, the results indicated that some of the hydrodynamic effects show opposing trends and some have negligible effects. With these opposing effects it is possible to adjust the coefficients of different models to achieve acceptable agreement with the same experimental data while omitting some aspects of the physics of the process. A suitable model for the shear lift force was developed by linking the lift coefficient to the drag coefficient and the contributions of the hydrodynamic forces and turbulence fluctuations as well as the consequences of using of 2D and 3D models were studied. The results indicate that the shear lift force and turbulent flow fluctuations are important factors for the saltation of both sand and gravel, and they cannot be ignored.

Prediction of bed level variations in nonuniform sediment bed channel

In the present study, a numerical model, based on one-dimensional de Saint-Venant equations along with sediment continuity equation, is developed for prediction of bed levels in non-cohesive sediments in aggrading alluvial channels. One-dimensional, unsteady flow equations and sediment continuity equations are solved using ‘shock-capturing’, second order accurate, explicit MacCormack finite difference scheme while considering upstream and downstream boundary conditions in the channel. Series of experimental investigations have been undertaken for measurements of bed and water levels in an aggrading channel due to overloading of nonuniform sediments, extracted from the bed of Tapi River at Surat City, in a flume installed in Advanced Hydraulics Laboratory of SVNIT, Surat, India. A satisfactory coupling between the water flow and sediment flow has been achieved. The sediment continuity equation is used for the each size class to compute the volume of each size class after each time step at any computational node in the computational grid. The fractional bed and suspended load transport capacities for different size fractions have been computed using fractional transport laws for nonuniform sediments. The active bed layer concept has been implemented in finite difference scheme to consider the interaction and exchange of sediment and water flow near the mixing layer. The performance of developed numerical model has been satisfactorily verified with independent experimental data of nonuniform sediment bed. Also, consideration of sediment nonuniformity in computation of bed level variation has been demonstrated by comparing the results based on sediment transport functions of uniform and nonuniform sediments.

A Direct‐Push Freezing Core Barrel for Sampling Unconsolidated Subsurface Sediments and Adjacent Pore Fluids

Core Ideas A direct‐push freezing core barrel (DPFCB) was developed and field tested. The DPFCB is suitable for sampling in coarse, unconsolidated sediments. The DPFCB freezes a 10‐ to 15‐cm plug that retains fluid and sediment in core sleeves. The DPFCB is interchangeable with unsaturated zone sampling tool strings. Contaminants passing through the unsaturated zone can undergo changes in narrow reaction zones upon reaching saturated sediments. Understanding these reactions requires sampling of sediment together with adjacent water and microbes in a manner that preserves in situ redox conditions. Use of a basket‐type core catcher for saturated, noncohesive sediments results in redistribution or loss of fluids during sample retrieval. Previously developed sample‐freezing drive shoes for hollow‐stem auger drilling rigs lessened fluid redistribution and retained all material that entered the core barrel in noncohesive sediment cores by freezing the base of the core with liquid CO2. This technology has not previously been compatible with direct‐push rigs that are commonly used for contaminated site assessments. Here, we describe a freezing core barrel designed for direct‐push rigs that is compatible with commercially available tool strings. The device can be used interchangeably with unsaturated‐zone direct‐push tool strings, enabling core collection for studies of contaminant transport and transformation spanning unsaturated to saturated profiles. In all 10 attempts during testing near Bemidji, MN, the device froze a 10‐ to 15‐cm (4–6‐in) plug that retained fluids and sediments in a 1.2‐m (4‐ft)‐long, 5.0‐cm (2.0‐in)‐diameter polyvinyl chloride (PVC) sleeve. Cores were collected from variably saturated sediments spanning the capillary fringe through the upper 2 m of the saturated zone in sandy glacial outwash sediments. The median recovery was 81% of the drive length, similar to a sample‐freezing drive shoe developed for a wire‐line piston core sampler operated with a hollow‐stem auger drill rig.

Toward an operational approach for the characterization and modelling of fine sediments dynamics in reservoirs

Achieving a sustainable management of sediment fluxes in existing or proposed reservoirs is a challenging but essential requirement for dam operators. Such objective is of utmost importance to avoid sedimentation-related consequences. Numerical modelling is of great interest to understand the flow and sediment dynamics in a reservoir, to simulate the long-term evolution of sediment deposits and to evaluate the efficiency of various management strategies. This paper presents recent case studies, which validate the feasibility and relevancy of such technical option. The progresses obtained on essential stages of the numerical modelling of sediments dynamics in reservoirs are particularly emphasized. Concerning the distribution of deposits, a promising field method based on an optimum combination of direct samplings with acoustic measurements and video auscultations is detailed. Feedbacks are then provided concerning an innovative device deployed in the field for a direct measurement of the settling velocity. Issues about the assessment of calibration parameters are also addressed in this communication. Lab experiments performed on deposits sampled in several reservoirs provide practical guidance to evaluate the erosion parameters of sediments. Finally, several examples of sediment dynamics modelling in reservoirs including both cohesive and non-cohesive sediment are presented.

Comparing the Scour Upstream of Circular and Square Orifices

Scour pattern upstream of square and circular orifices with equal opening areas of 38.45 cm2 are compared experimentally. A total of 16 tests for four constant heads, two initial conditions of fixed bed versus mobile bed and two non-cohesive sediments used as the bed layer are performed. The bed profile is surveyed by an acoustic bed profiler and the velocity distribution is measured using an ADV instrument. In the fixed-bed tests the thickness of sediment layer below the orifices’ invert is 2 mm and the observations show that the influence zone, which is the zone exposed to excess shear stress in which particles are removed, is elliptically shaped in both orifices with larger ellipse radius in transverse direction. The influence zone area upstream of square orifice is 1.46 times larger than the circular orifice. Observations of the mobile-bed tests indicate that the geometrical scour parameters, namely maximum depth of scour, length and width of the scour hole increase with the head of water upstream of both orifices. It is also found that the maximum scour depth upstream of square orifice is approximately two times deeper than that of circular orifice. Meanwhile, scour length and width, upstream of square orifice are, respectively, 10–15 and 20–33% larger than those of circular orifice. Finally, the measurements of the longitudinal velocity profiles along the centrelines of the orifices for both orifices are performed. The results indicate the existence of three separate zones of velocity distribution upstream of the orifices.

A SPH elastic-viscoplastic model for granular flows and bed-load transport

An elastic-viscoplastic model (Ulrich, 2013) is combined to a multi-phase SPH formulation (Hu and Adams, 2006; Ghaitanellis et al., 2015) to model granular flows and non-cohesive sediment transport. The soil is treated as a continuum exhibiting a viscoplastic behaviour. Thus, below a critical shear stress (i.e. the yield stress), the soil is assumed to behave as an isotropic linear-elastic solid. When the yield stress is exceeded, the soil flows and behaves as a shear-thinning fluid. A liquid-solid transition threshold based on the granular material properties is proposed, so as to make the model free of numerical parameter. The yield stress is obtained from Drucker–Prager criterion that requires an accurate computation of the effective stress in the soil. A novel method is proposed to compute the effective stress in SPH, solving a Laplace equation. The model is applied to a two-dimensional soil collapse (Bui et al., 2008) and a dam break over mobile beds (Spinewine and Zech, 2007). Results are compared with experimental data and a good agreement is obtained.

On incipient motion of silt-sand under combined action of waves and currents

Sediment incipient motion is a fundamental issue in sediment transport theory and engineering practice. Silt has transitional behavior between cohesive and non-cohesive sediment and its incipient motion is still poorly understood. This study aims to find an expression for incipient motion from silt to sand from a unified perspective and analysis. From the analysis of forces, using the derivation method for the Shields curve, an expression for sediment incipient motion is proposed for both silt and sand under conditions of combined waves and currents. The differences and similarities in the sediment motion threshold were analyzed under the effects of waves and currents, and fine and coarse sediment. The Shields number was revised by introducing the cohesive force and additional static water pressure, which indicates that this study could be seen as an extension of the Shields curve method for silt. A number of experimental datasets as well as field data were used to verify the formula. The effect of bulk density on fine sediment was discussed and tested using experimental data.

Modelling of Sediment Transport of the Mehadica River, Caras Severin County, Romania

Study case is situated in Caras-Severin County. Every sediment transport model application is different both in terms of time and space scale, study objectives, required accuracy, allocated resources, background of the study team etc. For sediment transport modelling, it is necessary to know the characteristics of the sediment in the river bed. Therefore, it is recommended to collect a number of bed sediment grap samples. These samples should be analysing in terms of grain size distribution. To solve theoretical problems of movement of water in the river Mehadica, it requires modelling of water flow in this case. Numerical modelling was performed using the program MIKE11. MIKE 11 is a user-friendly, fully dynamic, one-dimensional modelling tool for the detailed analysis, design, management and operation of both simple and complex river and channel systems. With its exceptional flexibility, speed and user friendly environment, MIKE 11 provides a complete and effective design environment for engineering, water resources, water quality management and planning applications. The Hydrodynamic (HD) module is the nucleus of the MIKE 11 modelling system and forms the basis for most modules including Flood Forecasting, Advection- Dispersion, Water Quality and Non-cohesive sediment transport modules. The MIKE 11 HD module solves the vertically integrated equations for the conservation of mass and momentum, i.e. the Saint-Venant equations. The input data are: area plan with location of cross sections; cross sections topographical data and roughness of river bed; flood discharge hydrograph. Advanced computational modules are included for description of flow over hydraulic structures, including possibilities to describe structure operation.

Application of a weakly compressible smoothed particle hydrodynamics multi-phase model to non-cohesive embankment breaching due to flow overtopping

The subject of present study is the application of mesh free Lagrangian two-dimensional non-cohesive sediment transport model applied to a two-phase flow over an initially trapezoidal-shaped sediment embankment. The governing equations of the present model are the Navier-Stocks equations solved using Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method. To simulate the movement of sediment particles, the model considers a powerful two-part technique; when the sediment phase has rigid behavior, only the force term due to shear stress in the Navier-Stokes equations is used for simulation of sediment particles’ movement. Otherwise, all the Navier-Stokes force terms are used for transport simulation of sediment particles. In the present model, the interactions between different phases are calculated automatically, even with considerable difference between the density and viscosity of phases. Validation of the model is performed using simulation of available laboratory experiments, and the comparison between computational results and experimental data shows that the model generally predicts well the flow propagation over movable beds, the induced sediment transport and bed changes, and temporal evolution of embankment breaching.

Effects of bioturbation on the erodibility of cohesive versus non-cohesive sediments along a current-velocity gradient: A case study on cockles

Soft-bottom bioturbators are ecosystem engineers in the sense that they can have considerable effects on sediment erodibility and resuspension. The common cockle Cerastoderma edule is a bioturbating filter feeder that is widespread along the European Atlantic coastline. Its presence and activity can decrease sediment erosion thresholds in cohesive sediments but little is known about its effect on non-cohesive sediments. Using controlled annular flume experiments, we investigated the relative effects of different cockle densities on sediment resuspension in cohesive vs. non-cohesive sediments by assessing the following: (i) the mud and sand burrowing behavior of cockles, (ii) critical erosion thresholds, (iii) the mass of eroded sediment and (iv) erosion rates. Our results show that cockles were more active in non-cohesive sediment compared with cohesive sediment. Despite their lower activity, the presence of cockles in cohesive sediment increased sediment erodibility by reducing the critical erosion threshold (Ucrit) and increasing both the mass of eroded sediment and erosion rate. In contrast, cockles had no effect on erodibility in non-cohesive sediment, especially on the eroded sediment mass and erosion rate. The mass eroded was not significantly different between cohesive and non-cohesive sediments when cockles were present. Our experiments show that the increased erodibility of cohesive sediment due to the bioturbation by cockles is density dependent: higher cockle density results in stronger effects on erodibility. Moreover, this increase in cohesive sediment erosion due to cockle bioturbation was positively correlated with current velocity. In contrast, the erosion of non-cohesive sediment only depended on the current stress and was unaffected by cockle density. Considering the high abundance of C. edule, its widespread distribution and its extensive activities, the results of this study could be widely applicable to intertidal mud flats around the world.

Migration of radioactivity in multi-fraction sediments

A new 3D radioactivity transport model coupled with multiscale circulation and multi-fractional sediment transport modules is presented. The sediment transport module simulates the transport of a mixture of one cohesive sediment fraction and a number of fractions of non-cohesive sediments of different sizes and densities. The model of radionuclide transport describes the key transport and exchange processes in the system of water-suspended and bottom multi-fraction sediments. Two-step kinetics with two successive reversible fast and slow reactions is used in the model. A noticeable feature of the model is approximation of the sediment and contamination profiles in the bed by multiple well-mixed layers to describe the vertical migration of radioactivity within bottom sediments due to erosion/deposition, molecular diffusion and bioturbation. The model accurately reproduced a laboratory experiment on the uptake of radiocesium by lake sediments. An analytical solution describing mutual adjustment of the concentrations of radioactivity in the pore water and in the multi-fraction sediment showed that activity was redistributed between different fractions of sediments far slower than between water and the total concentration in the sediment. The extended one-layer model of bottom contamination of multi-fraction sediments was derived from a general model and compared with a multi-layer model. It was found, however, that the one-layer approximation was not capable of correctly predicting the inventory due to the fact that one-layer averaged concentration can essentially differ from the near-surface value in the multi-layer model. Radionuclide transport in channel with bottom depression was simulated to estimate the effects of erosion/deposition and the multi-fractionality of sediments on the transport process. It was shown that these factors affect the distribution of sediments by forming local maxima and minima of activity at the beginning and end of the depression, respectively, due to the redistribution of contaminated bottom sediments by flow. The developed model can also be used to simulate the transport of a wide class of toxic substances sorbed on sediments.

Short-term CO2 exposure and temperature rise effects on metazoan meiofauna and free-living nematodes in sandy and muddy sediments: Results from a flume experiment

Global concern over increasing CO2 emissions, and the resultant CO2 driven temperature rises and changes in seawater chemistry, necessitates the advancement of understanding into how these changes will affect marine life now and in the future. Here we report on an experimental investigation into the effects of increased CO2 concentration and elevated temperature on sedimentary meiofaunal communities. Cohesive (muddy) and non-cohesive (sandy) sediments were collected from the Eden Estuary in St. Andrews, Scotland, UK, placed within a flume setup and exposed to 2 levels of CO2 concentration (380 and 750ppmv, current at the time of the experiment, and predicted CO2 concentration by 2100, respectively) and 2 temperature levels (12°C and 16°C, current in-situ and predicted temperature by 2100, respectively). We investigated the metazoan meiofauna and nematode communities before and after 28days of exposure under these experimental conditions. The most determinative factor for abundance, diversity and community structure of meiofauna and nematodes was sediment type: on all levels, communities were significantly different between sand and mud sediments which agrees with what is generally known about the influence of sediment structure on meiofaunal organisms. Few CO2 and temperature effects were observed, suggesting that meiofauna and nematodes are generally much less responsive than, for instance, microbial communities and macrofauna to these environmental changes in estuarine environments, where organisms are naturally exposed to a fluctuating environment. This was corroborated by the observed effects related to the different seasons in which the samples were taken from the field to run the experiment. After 28days, meiofauna and nematode communities in muddy sediments showed a greater response to increased CO2 concentration and temperature rise than in sandy sediments. However, further study is needed to investigate the underlying mechanisms and meiofauna species-specific resilience and responses to ocean acidification and warming, and their interactions with other biota, to understand what such changes may mean for meiofauna communities and the ecosystem processes and functions they contribute to.

Optimizing romanian maritime coastline using mathematical model Litpack

There are many methods and tools to study shoreline change in coastal engineering. LITPACK is a numerical model included in MIKE software developed by DHI (Danish Hydraulic Institute). With this matehematical model we can simulate coastline evolution and profile along beach. Research and methodology: the paper contents location of the study area, the current status of Midia-Mangalia shoreline, protection objectives, the changes of shoreline after having protected constructions. In this paper are presented numerical and graphycal results obtained with this model for studying the romanian maritime coastline in area MIDIA-MANGALIA: non-cohesive sediment transport, long-shore current and littoral drift, coastline evolution, crossshore profile evolution, the development of the coastline position in time.

Sediment properties, biota, and local habitat structure explain variation in the erodibility of coastal sediments

AbstractSediment resuspension is a frequent phenomenon in coastal areas and a key driver for many ecosystem functions. Sediment resuspension is often linked to biological and anthropogenic activities, which in combination with hydrodynamic forcing initiate sediment erosion and resuspension, if the erosion threshold (τc) is exceeded. Despite its importance to ecosystem functions very few studies have provided measurements on natural assemblages for subtidal sediments. The aim of this study was to determinate key environmental variables regulating sediment resuspension potential across a sedimentary gradient in a subtidal coastal environment. In order to explore this, we sampled 16 sites encompassing a wide variety in environmental variables (e.g., grain size distribution, macrofaunal communities, vegetation) in the Gulf of Finland, Baltic Sea. A core‐based erosion device (EROMES) was used to determine sediment resuspension potential measures of erosion threshold, erosion rate (ER), and erosion constant (me). Based on abiotic and biotic properties sampled, sediments diverged into two distinct groups; cohesive (“muddy”) and noncohesive (“sandy”) sediments. Results showed that abiotic sediment properties explained 38–53% and 15–36% of the total variation in resuspension potential measures in “muddy” and “sandy” sediments, respectively. In cumulative models, biota accounted for 12–26% and 6–24% to the total variation in “muddy” and “sandy” sediments, respectively. Sediment erodibility and resuspension potential of natural sediments is highly variable from local habitats to a larger seascape scale. Our results underline the importance of biota to resuspension potential measures in spatially variable environments.

PROPELLER JET FLOW, PILE SUPPORTED PIERS AND SEA BED INTERACTION

In maritime trade, from all over the world, transportation performed over the seas has been rapidly increasing due to high technological improvements leading the ships to have huge power and high speeds. The approach of even the big ships to the piers is now done by using the ship’s own engine power without the help of tugs because of the operation and economic reasons. However; this has been observed to cause local scour around the piers. Local scour commonly defined as the scour which is occurred in the immediate vicinity of the hydraulic structures due to the direct impact of the structure on the flow. It is very important to reduce local scour caused by ships propeller jets. A thorough understanding of the erosion of the bed due to local scour remains a challenge since it is associated with a highly turbulent flow field. The propeller jet has 3D flow area and high velocities. The erosion problem around the berthing structures due to propeller jet can occur in three ways. These are; a) On a slope, b) At the bottom of vertical wall, c) Around piles. In this study, propeller jet flow was considered to investigate scour formations around piles with non-cohesive sediment bed. The scour mechanism induced by propeller jet with and without pile conditions were investigated experimentally and their comparisons were made. Because there was not enough study for the scouring process for pile type berthing structures under propeller jet flow in the literature.

Mediation of macronutrients and carbon by post-disturbance shelf sea sediment communities

Benthic communities play a major role in organic matter remineralisation and the mediation of many aspects of shelf sea biogeochemistry. Few studies have considered how changes in community structure associated with different levels of physical disturbance affect sediment macronutrients and carbon following the cessation of disturbance. Here, we investigate how faunal activity (sediment particle reworking and bioirrigation) in communities that have survived contrasting levels of bottom fishing affect sediment organic carbon content and macronutrient concentrations ([NH4–N], [NO2–N], [NO3–N], [PO4–P], [SiO4–Si]). We find that organic carbon content and [NO3–N] decline in cohesive sediment communities that have experienced an increased frequency of fishing, whilst [NH4–N], [NO2–N], [PO4–P] and [SiO4–Si] are not affected. [NH4–N] increases in non-cohesive sediments that have experienced a higher frequency of fishing. Further analyses reveal that the way communities are restructured by physical disturbance differs between sediment type and with fishing frequency, but that changes in community structure do little to affect bioturbation and associated levels of organic carbon and nutrient concentrations. Our results suggest that in the presence of physical disturbance, irrespective of sediment type, the mediation of macronutrient and carbon cycling increasingly reflects the decoupling of organism-sediment relations. Indeed, it is the traits of the species that reside at the sediment–water interface, or that occupy deeper parts of the sediment profile, that are disproportionately expressed post-disturbance, that are most important for sustaining biogeochemical functioning.

Vulnerability of macronutrients to the concurrent effects of enhanced temperature and atmospheric pCO2 in representative shelf sea sediment habitats

Fundamental changes in seawater carbonate chemistry and sea surface temperatures associated with the ocean uptake of anthropogenic CO2 are accelerating, but investigations of the susceptibility of biogeochemical processes to the simultaneous occurrence of multiple components of climate change are uncommon. Here, we quantify how concurrent changes in enhanced temperature and atmospheric pCO2, coupled with an associated shift in macrofaunal community structure and behavior (sediment particle reworking and bioirrigation), modify net carbon and nutrient concentrations (NH4-N, NOx-N, PO4-P) in representative shelf sea sediment habitats (mud, sandy-mud, muddy-sand and sand) of the Celtic Sea. We show that net concentrations of organic carbon, nitrogen and phosphate are, irrespective of sediment type, largely unaffected by a simultaneous increase in temperature and atmospheric pCO2. However, our analyses also reveal that a reduction in macrofaunal species richness and total abundance occurs under future environmental conditions, varies across a gradient of cohesive to non-cohesive sediments, and negatively moderates biogeochemical processes, in particular nitrification. Our findings indicate that future environmental conditions are unlikely to have strong direct effects on biogeochemical processes but, particularly in muddy sands, the abundance, activity, composition and functional role of invertebrate communities are likely to be altered in ways that will be sufficient to regulate the function of the microbial community and the availability of nutrients in shelf sea waters.

Hindered erosion: The biological mediation of noncohesive sediment behavior

AbstractExtracellular polymeric substances (EPS) are ubiquitous on tidal flats but their impact on sediment erosion has not been fully understood. Laboratory‐controlled sediment beds were incubated with Bacillus subtilis for 5, 10, 16, and 22 days before the erosion experiments, to study the temporal and spatial variations in sediment stability caused by the bacterial secreted EPS. We found the biosedimentary systems showed different erosional behavior related to biofilm maturity and EPS distribution. In the first stage (5 days), the biosedimentary bed was more easily eroded than the clean sediment. With increasing growth period, bound EPS became more widely distributed over the vertical profile resulting in bed stabilization. After 22 days, the bound EPS was highly concentrated within a surface biofilm, but a relatively high content also extended to a depth of 5 mm and then decayed sharply with depth. The biofilm increased the critical shear stress of the bed and furthermore, it enabled the bed to withstand threshold conditions for an increased period of time as the biofilm degraded before eroding. After the loss of biofilm protection, the high EPS content in the sublayers continued to stabilize the sediment (hindered erosion) by binding individual grains, as visualized by electron microscopy. Consequently, the bed strength did not immediately revert to the abiotic condition but progressively adjusted, reflecting the depth profile of the EPS. Our experiments highlight the need to treat the EPS‐sediment conditioning as a bed‐age associated and depth‐dependent variable that should be included in the next generation of sediment transport models.

Development and validation of a morphological model for multiple sediment classes

The complexity of sediment dynamics in aquatic systems can be better understood by applying numerical models. The development of a comprehensive morphological model is presented in this paper. The model aims to predict the sediment transport and bed evolution in natural systems composed of different sediment types. The morphological model was implemented in MOHID, a modelling system that solves the three-dimensional hydrodynamics and advection-diffusion transport of suspended sediments. Multiple sediment classes were taken into account (non-cohesive and cohesive) considering the effects of sediment mixtures and bed consolidation on resistance to erosion. To represent bottom stratigraphy, the bottom column can be divided into several layers. The key points of the simulated processes are discussed in this paper. Model results are assessed in six test cases through comparison with analytic solutions or experimental data. The outcomes demonstrate the model׳s capacity to simulate the transport dynamics of non-cohesive and cohesive sediments. The speed up of morphological changes by an acceleration factor permitted modelling bed evolution for long time periods. Moreover, a test case for the Tagus Estuary demonstrated the model׳s capacity for generating realistic sediment distribution based on the local hydrodynamic conditions. Limitations in the availability of bed composition data can be overcome by considering a warm-up run to provide realistic initial conditions for further predictions of morphological developments.