The Experts below are selected from a list of 5472 Experts worldwide ranked by ideXlab platform
Benedicte Ferre - One of the best experts on this subject based on the ideXlab platform.
-
Cohesive and mixed Sediment in the Regional Ocean Modeling System (ROMS v3.6) implemented in the Coupled Ocean–Atmosphere–Wave–Sediment Transport Modeling System (COAWST r1234)
Copernicus Publications, 2018Co-Authors: Christopher R Sherwood, Alfredo L Aretxabaleta, Courtney K Harris, Romaric Verney, Benedicte Ferre, J. P. RinehimerAbstract:We describe and demonstrate algorithms for treating Cohesive and mixed Sediment that have been added to the Regional Ocean Modeling System (ROMS version 3.6), as implemented in the Coupled Ocean–Atmosphere–Wave–Sediment Transport Modeling System (COAWST Subversion repository revision 1234). These include the following: floc dynamics (aggregation and disaggregation in the water column); changes in floc characteristics in the seabed; erosion and deposition of Cohesive and mixed (combination of Cohesive and non-Cohesive) Sediment; and biodiffusive mixing of bed Sediment. These routines supplement existing non-Cohesive Sediment modules, thereby increasing our ability to model fine-grained and mixed-Sediment environments. Additionally, we describe changes to the Sediment bed layering scheme that improve the fidelity of the modeled stratigraphic record. Finally, we provide examples of these modules implemented in idealized test cases and a realistic application
-
Cohesive and mixed Sediment in the regional ocean modeling system roms v3 6 implemented in the coupled ocean atmosphere wave Sediment transport modeling system coawst r1234
Geoscientific Model Development, 2017Co-Authors: Christopher R Sherwood, Alfredo L Aretxabaleta, Courtney K Harris, Paul J Rinehimer, Romaric Verney, Benedicte FerreAbstract:Abstract. We describe and demonstrate algorithms for treating Cohesive and mixed Sediment that have been added to the Regional Ocean Modeling System (ROMS version 3.6), as implemented in the Coupled Ocean–Atmosphere–Wave–Sediment Transport Modeling System (COAWST Subversion repository revision 1234). These include the following: floc dynamics (aggregation and disaggregation in the water column); changes in floc characteristics in the seabed; erosion and deposition of Cohesive and mixed (combination of Cohesive and non-Cohesive) Sediment; and biodiffusive mixing of bed Sediment. These routines supplement existing non-Cohesive Sediment modules, thereby increasing our ability to model fine-grained and mixed-Sediment environments. Additionally, we describe changes to the Sediment bed layering scheme that improve the fidelity of the modeled stratigraphic record. Finally, we provide examples of these modules implemented in idealized test cases and a realistic application.
Ulrik Lumborg - One of the best experts on this subject based on the ideXlab platform.
-
The effect of Hydrobia ulvae and microphytobenthos on Cohesive Sediment dynamics on an intertidal mudflat described by means of numerical modelling
Estuarine Coastal and Shelf Science, 2006Co-Authors: Ulrik Lumborg, Thorbjorn Joest Andersen, Morten PejrupAbstract:Previous investigations have documented spatial and temporal variations in the erosion threshold, erosion rate, and suspended Sediment settling characteristics on an intertidal mudflat in a microtidal coastal plain estuary in the Danish Wadden Sea. The differences seem to be very much controlled by the effects of benthic biology rather than by physical parameters. In order to test to what extend biology may interact with the dynamics of fine-grained Sediment in an entire estuarine system, these results have been transformed into four different sets of erodibility and settling characteristics which have been used as input to the 2D hydrodynamic numerical model MIKE 21 MT. The model was used to investigate the effect that differences in the benthic communities may have on the net deposition. The model included computation of hydrodynamics, wave fields and Cohesive Sediment dynamics. Based on the modelling results presented it is suggested that the benthic biological activity affects the net Sedimentation pattern at the investigated site. The modelling results suggest that the presence of large numbers of the destabilising mudsnail Hydrobia ulvae results in higher net accumulation on the intertidal mudflat investigated. In contrast, biofilms may change net deposition by decreasing erosion, suspended Sediment concentration and consequently the resulting settling flux of the suspended material. This study suggests that a numerical hydrodynamic model in combination with a fieldwork-based set-up of a Cohesive Sediment transport model may be used to describe and explain net Sediment dynamics in a shallow coastal plain estuary.
-
modelling of Cohesive Sediment transport in a tidal lagoon an annual budget
Marine Geology, 2005Co-Authors: Ulrik Lumborg, Morten PejrupAbstract:Abstract The annual net Sediment flux for an enclosed estuary is usually calculated as a residual value in Sediment budget studies based mainly on Sediment core dating. In this study, the numerical model MIKE 21 MT was used to directly model the annual net transport of Cohesive Sediment for the Lister Dyb tidal area in the northern part of the European Wadden Sea. The model was calibrated by use of a combination of field data and calibration parameters derived from existing literature. The model reproduced the hydrodynamics satisfactorily as well as the concentration level and variation of suspended Cohesive Sediment concentration. Net import for the year 2002 was found to be 45 000 t of Cohesive Sediment, corresponding to a mean tidal period import of 64 t which compares to an approximate deposition of 0.1 mg l −1 of the tidal prism. Gross annual transport through a control cross section of the tidal inlet was 1 million ton meaning that 4–5% of the Sediment transported in suspension was on average deposited within the tidal lagoon. This net transport was found to be rather constant from tidal period to tidal period thus supporting the theory that the processes of settling and scour lag, tidal velocity asymmetry together with Sediment floc formation are the controlling processes for import of fine-grained Sediment to shallow coastal plain estuaries. Temporary export of Sediment from the area occurred during two major wind events in January and February when the maximum loss of Sediment during one single tidal period was computed to be 40 000 t which is of the same order as the yearly net import of Sediment. This indicates that net annual import of Cohesive Sediment to shallow estuaries may be much more variable than inferred from core dating studies found in literature.
-
modelling the deposition erosion and flux of Cohesive Sediment through oresund
Journal of Marine Systems, 2005Co-Authors: Ulrik LumborgAbstract:Abstract Oresund is a narrow sound between Denmark and Sweden in Northern Europe. The sound has a complex hydrography with two- or three-layer stratifications, sometimes with opposite directed currents in the different layers. The complicated hydrography makes it difficult to investigate Sediment dynamics by use of traditional field-work based methods. In this study the three-dimensional modelling system MIKE 3 was applied in order to quantify the dynamics of the fine-grained Sediment in Oresund over a year. The model simulated the complex hydrodynamics including stratification satisfactorily. The simulated suspended Sediment concentrations were low, generally not exceeding 20 mg l−1. Over the year 2000 the model computed an annual accumulation of 136,000 tons of Sediment. Both the Sediment concentrations and the overall accumulation of fine-grained Sediment are in accordance with previously published results. This study presents some general hydrodynamic and Sedimentological characteristics from the sound. The hydrodynamic characteristics were well reproduced, making the hydrodynamic model ideal for the Sediment transport study. The description of the Sedimentology of the sound is in some aspects new and is therefore not directly verified by data. The overall result is believed to be representative for the area and the model has given information on Sedimentological transport patterns. This study demonstrated that generic numerical Cohesive Sediment transport models are capable of simulating hydrodynamics and Cohesive Sediment dynamics in complicated estuarine environments and of establishing reliable Sediment budgets.
-
hydrography and Cohesive Sediment modelling application to the romo dyb tidal area
Journal of Marine Systems, 2003Co-Authors: Ulrik Lumborg, A WindelinAbstract:Abstract Estuaries act as sinks for fine-grained Sediments and because of the Cohesive properties of these Sediments, heavy metals and nutrients tend to accumulate in estuaries. In order to quantify the erosion, transport and deposition of these pollutants, modelling of Cohesive Sediment dynamics is a very useful tool. However, the description of Cohesive Sediment dynamics through numerical analysis is a difficult task since the physical properties of Cohesive Sediments are of complex nature. In this paper, setup and calibration of a Cohesive Sediment transport model covering the period from October 20, 1999 to December 13, 1999 are described and an interpretation of the results is carried out. Further, a comparison with measured suspended Sediment concentrations and bed level measurements from the modelling period is presented. A detailed bathymetry is used. This is necessary in order to describe the water movements in a realistic way. A bottom description is created in a way so that differences in erodibility of the Sediment can be described. Further, a spatial differentiated description of critical shear stress, both for erosion and deposition of the Cohesive Sediment bottom, is made in order to describe the processes of settling and scour lag. The hydrodynamic simulation is shown to be very reliable, and therefore, it has been possible to extract key values for the area. Thus, the maximum current velocities for the Lister Dyb area are modelled to 1.2 and 0.93 m s −1 for the flood and ebb period, respectively. The tidal prism has likewise been computed to 620×10 6 m 3 . The Cohesive Sediment transport modelling has shown that the highest Sediment concentrations at a given site appear when onshore winds are prevailing. Further, it can be recognized in the results that an inward Sediment transport direction is prevailing, especially after a windy period with waves has mobilized considerable amounts of Sediment. A detailed investigation of the Cohesive Sediment's settling velocities collected in the area is used to give a site-specific description. Since the description of the settling velocity changes with temperature, several simulations using different descriptions have been carried out. These simulations have shown that this parameter is very influential for the net deposition result. Thus, an increase of the settling velocity will increase the deposition rates considerably. The modelling results and the comparisons to measured data presented in this paper show that it has been possible to calibrate the hydrodynamic model in accordance with observed values. In continuation of this, the deformation of the tidal wave has also been modelled satisfactorily. Modelling of the Cohesive Sediment dynamics has been more complicated and the modelling results show divergence from the measured results. However, the levels of the Sediment concentrations and the overall net Sedimentation pattern show accordance with observed values.
Christopher R Sherwood - One of the best experts on this subject based on the ideXlab platform.
-
Cohesive and mixed Sediment in the Regional Ocean Modeling System (ROMS v3.6) implemented in the Coupled Ocean–Atmosphere–Wave–Sediment Transport Modeling System (COAWST r1234)
Copernicus Publications, 2018Co-Authors: Christopher R Sherwood, Alfredo L Aretxabaleta, Courtney K Harris, Romaric Verney, Benedicte Ferre, J. P. RinehimerAbstract:We describe and demonstrate algorithms for treating Cohesive and mixed Sediment that have been added to the Regional Ocean Modeling System (ROMS version 3.6), as implemented in the Coupled Ocean–Atmosphere–Wave–Sediment Transport Modeling System (COAWST Subversion repository revision 1234). These include the following: floc dynamics (aggregation and disaggregation in the water column); changes in floc characteristics in the seabed; erosion and deposition of Cohesive and mixed (combination of Cohesive and non-Cohesive) Sediment; and biodiffusive mixing of bed Sediment. These routines supplement existing non-Cohesive Sediment modules, thereby increasing our ability to model fine-grained and mixed-Sediment environments. Additionally, we describe changes to the Sediment bed layering scheme that improve the fidelity of the modeled stratigraphic record. Finally, we provide examples of these modules implemented in idealized test cases and a realistic application
-
Cohesive and mixed Sediment in the regional ocean modeling system roms v3 6 implemented in the coupled ocean atmosphere wave Sediment transport modeling system coawst r1234
Geoscientific Model Development, 2017Co-Authors: Christopher R Sherwood, Alfredo L Aretxabaleta, Courtney K Harris, Paul J Rinehimer, Romaric Verney, Benedicte FerreAbstract:Abstract. We describe and demonstrate algorithms for treating Cohesive and mixed Sediment that have been added to the Regional Ocean Modeling System (ROMS version 3.6), as implemented in the Coupled Ocean–Atmosphere–Wave–Sediment Transport Modeling System (COAWST Subversion repository revision 1234). These include the following: floc dynamics (aggregation and disaggregation in the water column); changes in floc characteristics in the seabed; erosion and deposition of Cohesive and mixed (combination of Cohesive and non-Cohesive) Sediment; and biodiffusive mixing of bed Sediment. These routines supplement existing non-Cohesive Sediment modules, thereby increasing our ability to model fine-grained and mixed-Sediment environments. Additionally, we describe changes to the Sediment bed layering scheme that improve the fidelity of the modeled stratigraphic record. Finally, we provide examples of these modules implemented in idealized test cases and a realistic application.
Tianjian Hsu - One of the best experts on this subject based on the ideXlab platform.
-
the effects of flocculation and bed erodibility on modeling Cohesive Sediment resuspension
Journal of Geophysical Research, 2011Co-Authors: Minwoo Son, Tianjian HsuAbstract:[1] Flocculation and bed erodibility are two main processes causing the transport of Cohesive Sediments to be more complicated than typical nonCohesive Sediments. Earlier flocculation models assume a constant fractal dimension and/or a constant floc yield strength. However, recent studies have shown that considering both the fractal dimension and the floc yield strength to be variable is critical to the prediction of temporal evolution of floc size. Due to consolidation, it is also well established that critical bed shear stress of a mud bed cannot be parameterized as a constant. This study further investigates how flocculation models with different degrees of complexity and bed erodibility can affect the resulting Cohesive Sediment resuspension driven by tidal flows. A one-dimensional vertical numerical model for Sediment transport is revised to incorporate modules for flocculation and bed erodibility. Model results are compared with data measured in the Ems/Dollard estuary. Model study suggests that it is important to incorporate variable critical shear stress in order to properly model the supply of Sediment from the bed. When flocculation is neglected or incorporated incompletely, numerical model predicts nearly zero Sediment concentration during slack water and very steep concentration gradient, which are inconsistent with the observed data. When the fractal dimension and the floc yield strength are both considered to be variable, the numerical model predicts much smaller settling velocity and hence captures the more well-mixed condition consistent with field observations.
-
the effect of variable yield strength and variable fractal dimension on flocculation of Cohesive Sediment
Water Research, 2009Co-Authors: M Son, Tianjian HsuAbstract:Abstract A new formulation for floc yield strength of Cohesive Sediment is theoretically derived and incorporated into a flocculation model based on variable fractal dimension. The new flocculation model is validated with existing data on the temporal evolution of floc size measured in the laboratory. Comparing with existing flocculation models using a constant yield strength, it is found that new flocculation model based on variable yield strength and variable fractal dimension is superior in predicting the temporal evolution of floc size. It is also demonstrated that the present model results are very similar to that using an empirical formulation of variable yield strength suggested by Sonntag and Russel (1987. Structure and breakup of floccs subjected to fluid stressses. II. Theory. J. Colloid Interface Sci. 115(2), 378–389) when the empirical coefficient is specified according to our theoretical value. Hence, it is concluded that the new variable yield strength formulation derived in this study and the variable fractal dimension are effective in improving the prediction of flocculation process.
-
flocculation model of Cohesive Sediment using variable fractal dimension
Environmental Fluid Mechanics, 2008Co-Authors: Minwoo Son, Tianjian HsuAbstract:A new flocculation model using variable fractal dimension is proposed and validated with several experimental data and an existing model. The proposed model consists of two processes: aggregation and breakup due to flow turbulence. For aggregation process, the aggregate structure is considered to have the characteristic of self-similarity, the main concept of fractal theory. Under this assumption, a variable fractal dimension instead of a fixed one adopted by previous studies is utilized here for general Cohesive Sediment transport. For breakup, similar concept is adopted in a more empirical manner because breakup is too abrupt to entirely apply the concept of variable fractal dimension. By a linear combination of the formulations for aggregation and breakup processes, a flocculation model which can describe the temporal evolution of floc size is obtained. Flocculation model using variable fractal dimension is capable of predicting equilibrium floc size when compared with several experimental data sets using different types of mud provided that empirical coefficients are calibrated. Through model-data comparison with Manning and Dyer (Marine Geology 160:147–170, 1999), it is also clear that some of the empirical coefficients may depend on Sediment concentration. Model results for the temporal evolution of floc size are less satisfactory, despite model results shows a more smooth “S-curve” for the temporal evolution of floc size as compared with the previous model using fixed fractal dimension. The proposed model is limited to mono-size of primary particle and dilute flow condition. These other features shall be investigated as future work.
Morten Pejrup - One of the best experts on this subject based on the ideXlab platform.
-
factors controlling the field settling velocity of Cohesive Sediment in estuaries
Estuarine Coastal and Shelf Science, 2010Co-Authors: Morten Pejrup, Ole A MikkelsenAbstract:Abstract It has long been recognized that the suspended Sediment concentration (SSC) is one of the major determinants for the flocculation of Cohesive particles into Sediment flocs in estuaries. It is furthermore well known that the turbulent shear of the water significantly influences the flocculation process and the equilibrium settling velocity of flocculated Sediment in a turbulent flow. A vast number of authors have reported algorithms relating the median settling velocity ( W 50 ) to suspended Sediment concentration. However, only a few studies have dealt with the impact of the turbulent shear (in this paper expressed as the root mean square [rms] velocity gradient, [ G ]) in the water on the W 50 in situ. There is a strong need to establish algorithms based on in situ measurements describing the dual impact of both SSC and G on the flocculation process, and hence, W 50 . The present paper addresses this topic. Field settling velocities of suspended Cohesive Sediment have been measured in micro-, meso-, and macro-tidal estuaries. Regression analyses between the W 50 , SSC and G are presented. It is shown that by including both G and SSC in the regression analyses, a significant increase in the correlation of the description of W 50 and the controlling parameters from each area can be obtained. A generic algorithm describing the data from all the investigated areas is suggested. It works well within specific tidal areas but fails to give a generic description of the field settling velocity.
-
The effect of Hydrobia ulvae and microphytobenthos on Cohesive Sediment dynamics on an intertidal mudflat described by means of numerical modelling
Estuarine Coastal and Shelf Science, 2006Co-Authors: Ulrik Lumborg, Thorbjorn Joest Andersen, Morten PejrupAbstract:Previous investigations have documented spatial and temporal variations in the erosion threshold, erosion rate, and suspended Sediment settling characteristics on an intertidal mudflat in a microtidal coastal plain estuary in the Danish Wadden Sea. The differences seem to be very much controlled by the effects of benthic biology rather than by physical parameters. In order to test to what extend biology may interact with the dynamics of fine-grained Sediment in an entire estuarine system, these results have been transformed into four different sets of erodibility and settling characteristics which have been used as input to the 2D hydrodynamic numerical model MIKE 21 MT. The model was used to investigate the effect that differences in the benthic communities may have on the net deposition. The model included computation of hydrodynamics, wave fields and Cohesive Sediment dynamics. Based on the modelling results presented it is suggested that the benthic biological activity affects the net Sedimentation pattern at the investigated site. The modelling results suggest that the presence of large numbers of the destabilising mudsnail Hydrobia ulvae results in higher net accumulation on the intertidal mudflat investigated. In contrast, biofilms may change net deposition by decreasing erosion, suspended Sediment concentration and consequently the resulting settling flux of the suspended material. This study suggests that a numerical hydrodynamic model in combination with a fieldwork-based set-up of a Cohesive Sediment transport model may be used to describe and explain net Sediment dynamics in a shallow coastal plain estuary.
-
modelling of Cohesive Sediment transport in a tidal lagoon an annual budget
Marine Geology, 2005Co-Authors: Ulrik Lumborg, Morten PejrupAbstract:Abstract The annual net Sediment flux for an enclosed estuary is usually calculated as a residual value in Sediment budget studies based mainly on Sediment core dating. In this study, the numerical model MIKE 21 MT was used to directly model the annual net transport of Cohesive Sediment for the Lister Dyb tidal area in the northern part of the European Wadden Sea. The model was calibrated by use of a combination of field data and calibration parameters derived from existing literature. The model reproduced the hydrodynamics satisfactorily as well as the concentration level and variation of suspended Cohesive Sediment concentration. Net import for the year 2002 was found to be 45 000 t of Cohesive Sediment, corresponding to a mean tidal period import of 64 t which compares to an approximate deposition of 0.1 mg l −1 of the tidal prism. Gross annual transport through a control cross section of the tidal inlet was 1 million ton meaning that 4–5% of the Sediment transported in suspension was on average deposited within the tidal lagoon. This net transport was found to be rather constant from tidal period to tidal period thus supporting the theory that the processes of settling and scour lag, tidal velocity asymmetry together with Sediment floc formation are the controlling processes for import of fine-grained Sediment to shallow coastal plain estuaries. Temporary export of Sediment from the area occurred during two major wind events in January and February when the maximum loss of Sediment during one single tidal period was computed to be 40 000 t which is of the same order as the yearly net import of Sediment. This indicates that net annual import of Cohesive Sediment to shallow estuaries may be much more variable than inferred from core dating studies found in literature.