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) (original) (raw)
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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 1179). These include: 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 mixedsediment 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.
Computers & Geosciences, 2008
The one-dimensional (vertical) sediment-transport model SEDTRANS96 has been upgraded to predict more accurately both cohesive and non-cohesive sediment transport. Sedtrans05 computes the bed shear stress for a given set of flow and seabed conditions using combined wave-current bottom boundary layer theory. Sediment transport (bedload and total load) is evaluated using one of five methods. The main modifications to the original version of the model are: (1) a reorganization of the code so that the computation routines can be easily accessed from different user interfaces, or may be called from other programs; (2) the addition of the Van Rijn method to the options for non-cohesive sediment transport;
Modelling Cohesive Sediment Dynamics in the Marine Environment
One of the most challenging tasks in modelling marine processes is the description of fine sediment dynamics. Cohesive sediments enter the marine environment from physical or anthropogenic sources and affect physical, biochemical and biological processes. Their movement and fate is the result of various physical processes and forces that interact with one another. These processes extend from the scale of the microfloc and the effects of the small-scale forces, like cohesion, to the macroscale of the hydrodynamic field and the effects the local hydrodynamics. The present chapter aims at covering the most significant processes that control the motion and fate of cohesive sediment in microtidal areas, focusing both on the physical and mathematical description of the phenomena. More specifically, the physical processes that take place in the water column and near the seabed and the corresponding mass-exchanges between them are presented and analyzed. The motion of sediment in suspension is determined by the seawater velocities and local shear, the stratification of the water column and the characteristics of the cohesive flocs that control the processes of advection, dispersion flocculation-deflocculation and settling. Near-bed processes are highly dependant on the prevailing shear stress conditions and the characteristics of the sedimentary matter and control the mass-exchanges between the water column and the seabed; these processes include deposition, self-weight consolidation, resuspension and erosion of the bed. Modelling results from a three-dimensional sediment transport model, formulated based on the aforementioned considerations, are also presented and discussed; the applications were performed in the domain of Thermaikos, a microtidal gulf in the NW Aegean Sea (Eastern Mediterranean), for different (point or distributed) sources of fine particulate matter, including river-borne matter, physically and mechanically (trawling-induced) eroded sediments and aeolian transported dust.
Computerized Modeling of Sedimentary Systems, 1999
Computerized modeling is a powerful tool to describe the complex interrelations between measured data and the dynamics of sedimentary systems. Complex interaction of environmental factors with natural variations and increasing anthropogenic intervention is reflected in the sedimentary record at varying scales. The understanding of these processes gives way to the reconstruction of the past and is a key to the prediction of future trends. Especially in cases where observations are limited and/or expensive, computer simulations may substitute for the lack of data. State-of-the-art research work requires a thorough knowledge of processes at the interfaces between atmosphere, hydrosphere, biosphere, and lithosphere, and is therefore an interdisciplinary approach.
Mercator Ocean Quaterly Newsletter, 2014
The rising interest in environmental and ecosystem dynamics have lead coastal oceanographers to not only investigate the "traditional" physical parameters describing the ocean state and its dynamics (e.g. temperature, salinity, currents, water levels in coastal areas), but to also account for the dynamics of parameters describing its biogeochemical components. To that end, MARS3D regional and coastal modelling system has been coupled to ecosystem modules (ECO-MARS3D, ECO3M) as well as sediment dynamics modules (MARS3D-SEDIM): sediment, nutrient and primary production contents can be considered as the lower level environment and ecosystem descriptors of the "biogeochemical" ocean. Early investments into physical and biological analysis at the regional scale have led to the development of several operational configurations within PREVIMER since 2006 for physical and biological parameters, providing 3 to 5-day forecasts as well as hindcasts. The more recent introduction of sediment-related parameters into the operational chain required validating computed sediment transport at the regional scale. Such validation is mostly accessible through indirect measurements -namely turbidity measurements in the water column or derived from satellite data. This paper describes the main features of MARS3D sediment module, the sensitivity analyses and the validation procedures based on dedicated data acquisition, as well as the assessment of the operational configuration focused on the Bay of Biscay continental shelf. Comparison between in situ measurements and satellite data shows a fairly systematic overestimation of the satellite-derived SPM in Southern Brittany; this result stresses the need for further investigation regarding the correct quantitative satellite SPM determination at all times and all places. On the other hand, numerical results highlight the difficulty to simultaneously predict the correct magnitude of bottom and surface concentrations.
Large-scale modelling of fine-grained sediment transport: Can we do any better?
XIIèmes Journées, Cherbourg, 2012
Numerical models have become a major tool for the study of sediment transport problems in coastal engineering. Reviewing the evolution of model progress, it is noticed that advancement has mainly been achieved in higher computational performance, allowing more detailed and even 3D simulation of large-scale problems at a reasonable cost. However, the prediction capacity remained disappointing and has hardly improved since the models are still based on the same basic process descriptions. Over the past 20 years many processes have been studied in more detail. Nevertheless, attempts to incorporate more complicated models for processes such as flocculation and erosion have not really brought the expected improvement. This paper presents an overview of the major shortcomings in presently used sediment transport software. Proposals to incorporate more physics, without increasing the computational cost too excessively, will be presented. New process models have been developed for flocculation and for particle-turbulence interaction in high-concentrated suspensions, and a new bed model, accounting for both consolidation and wave-induced fluidization, is under development. Furthermore, it is demonstrated that estuarine and coastal applications require the distinction between (at least) two floc populations of cohesive sediment and (at least) one sand fraction. Remaining problems can be related to the difficulty to account for the spatial and temporal variability of sediment properties, especially with regard to the bed, and to the effect of bio-engineering agents in the environment. This keeps large uncertainties in the model results which can hardly be reduced.
Development of a Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) Modeling System
Ocean Modelling, 2010
Understanding the processes responsible for coastal change is important for managing our coastal resources, both natural and economic. The current scientific understanding of coastal sediment transport and geology suggests that examining coastal processes at regional scales can lead to significant insight into how the coastal zone evolves. To better identify the significant processes affecting our coastlines and how those processes create coastal change we developed a Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System, which is comprised of the Model Coupling Toolkit to exchange data fields between the ocean model ROMS, the atmosphere model WRF, the wave model SWAN, and the sediment capabilities of the Community Sediment Transport Model. This formulation builds upon previous developments by coupling the atmospheric model to the ocean and wave models, providing one-way grid refinement in the ocean model, one-way grid refinement in the wave model, and coupling on refined levels. Herein we describe the modeling components and the data fields exchanged. The modeling system is used to identify model sensitivity by exchanging prognostic variable fields between different model components during an application to simulate Hurricane Isabel during September 2003. Results identify that hurricane intensity is extremely sensitive to sea surface temperature. Intensity is reduced when coupled to the ocean model although the coupling provides a more realistic simulation of the sea surface temperature. Coupling of the ocean to the atmosphere also results in decreased boundary layer stress and coupling of the waves to the atmosphere results in increased bottom stress. Wave results are sensitive to both ocean and atmospheric coupling due to wave-current interactions with the ocean and wave growth from the atmosphere wind stress. Sediment resuspension at regional scale during the hurricane is controlled by shelf width and wave propagation during hurricane approach.
SEDTRANS96: the upgraded and better calibrated sediment-transport model for continental shelves
Computers & Geosciences, 2001
The sediment transport model SEDTRANS has been significantly upgraded based on new advances in both cohesive and non-cohesive sediment transport studies. For given input data of wave, current, and seabed conditions, the model applies the combined wave-current bottom boundary layer theories to derive the near-bed velocity profile and bed shear stresses, and then calculates sediment transport for currents only or combined waves and currents over either cohesive or non-cohesive sediments. Critical shear stresses for various sediment transport modes tested for combined waves and currents are adopted in SEDTRANS96. An explicit combined-flow ripple predictor is included in the model to provide time-dependent bed roughness prediction. SEDTRANS96 also predicts the vertical profiles of velocity and suspended sediment concentration and their product is integrated through depth to derive the suspended-load transport rate. More rigorous calibration of the model using measured sediment transport rates over fine and medium sands shows that the difference between the predicted and measured transport rates has been reduced from more than one order of magnitude to less than a factor of five. The proposed new cohesive sediment algorithm separates cohesive sediment transport into depositional, stable and erosional states. The applied shear stress, erosion/deposition time duration and the down-core profile of the critical shear stress for erosion are numerically integrated to predict the final erosion or deposition rate, suspension concentration and transport rate for cohesive sediment. #
Modeling Estuarial Cohesive Sediment Transport
Coastal Engineering Proceedings, 1984
Cohesive sediment related problems in estuaries include shoaling in navigable waterways and water pollution. A two-dimensional, depth averaged, finite element cohesive sediment transport model, CSTM-H, has been developed and may be used to assist in predicting the fate of sorbed pollutants and the frequency and quantity of dredging required to maintain navigable depths. Algorithms which describe the transport processes of redispersion, resuspenslon, dispersive transport, settling, deposition, bed formation and bed consolidation are incorporated in CSTM-H. The Galerkin weighted residual method is used to solve the advection-dispersion equation with appropriate source/sink terms at each time step for the nodal suspended sediment concentrations. The model yields stable and converging solutions. Verification was carried out against a series of erosion-deposition experiments in the laboratory using kaolinite and a natural mud as sediment. A model application under prototype conditions is...
A numerical model has recently been developed with incorporating a wetting and drying scheme into the Princeton Ocean Model (POM; Blumberg and Mellor, 1983) to simulate tidal currents in San Francisco Bay, CA, USA (WD-POM; Uchiyama, 2004). San Francisco Bay is encompassed by extensive intertidal area including mudflats and salt marshes where flooding and draining are predominant for overlaying hy- drodynamics. Intertidal sediment transport and associated topography changes are of interest for coastal engineers (e.g., Dyer, 1986) as well as marine biologists (e.g., Kuwae et al., 2003), whereas no three- dimensional numerical models have been developed thus far to calculate the intertidal sediment transport properly. In the present study, cohesive sediment transport and bed elevation changes are modeled and adapted to WD-POM to assess intertidal morphodynamics in San Francisco Bay. The cohesive sediment transport model contains settling speeds of cohesive flocs (Burban et al., 1990) a...