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Kombiadou Katerina (a) , Yannis Krestenitis (a) , Margarita Tzali (b) , Sarantis Sofianos (b)

Sediment transport modelling in Thermaikos Gulf and 1-way coupling with a high resolution circulation model. Kombiadou Katerina (a) , Yannis Krestenitis (a) , Margarita Tzali (b) , Sarantis Sofianos (b). (a) Aristotle University of Thessaloniki, Laboratory of Maritime Engineering

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Kombiadou Katerina (a) , Yannis Krestenitis (a) , Margarita Tzali (b) , Sarantis Sofianos (b)

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  1. Sediment transport modelling in Thermaikos Gulf and 1-way coupling with a high resolution circulation model Kombiadou Katerina(a), Yannis Krestenitis(a), Margarita Tzali(b), Sarantis Sofianos(b) (a) Aristotle University of Thessaloniki, Laboratory of Maritime Engineering (b) University of Athens, Division of Environmental Physics

  2. Aim High Resolution Circulation ModelNASMO Atmospheric ModelSKIRON/Eta Hydrodynamic - physical parameters data Dust loads 3-D Sediment Transport Model

  3. Sediment Transport Modelling Platform • Input data: • Particle inflow (rivers, atmosphere etc) • Hydrodynamic data (U,V) • Physical properties (S,T) Simulated processes: • Transport-dispersion (random walk method) • Flocculation-deflocculation • Flock density evolution • Effects of stratification to vertical propagation • Settling • Near-bed processes: • Deposition • Consolidation • Resuspension • Erosion Model output (potential): • Particle location (x,y,z) • Alterations in characteristics (mass, diameter, state) • SPM concentrations • Sedimentation rates • Traces of specific particles • Transport patterns investigation

  4. Application in the Thermaikos Gulf

  5. Typical one-year simulation Simulation data Simulation period: one year Source-rivers: Axios – Loudias - Aliakmonas - Pinios Daily-averaged hydrodynamic-physical parameters input data 6-hour hydrological data Particle mass: 4320kg

  6. Application for aeolian-transported matter • Input data from the UOA atmospheric dust cycle model, based on the SKIRON/Eta modeling system and the Eta/NCEP regional atmospheric model* • Available time-series of matter introduced to Thermaikos from the atmosphere from 13/04/05 to 13/06/05 were employed in the simulation Time-series of aeolian inflow * Nickovic, S., Kallos, G., Papadopoulos, A. and Kakaliagou, O., 2001. A model for the prediction of desert dust cycle in the atmosphere. Journal of Geophysical Research, 106: 18113-18129

  7. Simulation of aeolian-transported matter

  8. High resolution circulation model The North Aegean Sea MOdel (NASMO) Princeton Ocean Model Area: 38.7 – 41.1°Ν 22.5 –27.1°E Resolution: 1/60° 1/60° (277x145) 25 vertical sigma-levels Bathymetry: U.S. Navy Digital Bathymetric Data Base I (1/60°  1/60°) Atmospheric Forcing: LAM (SKIRON/Eta): (0.1° , 1 hour) Initial & Boundary Conditions : ALERMO Forecast System

  9. http://www.bo.ingv.it/mfs Daily 7-day forecast http://www.oc.phys.uoa.gr/oceanf.html Daily 5-day forecast MED-OGCM ALERMO NASMO http://www.oc.phys.uoa.gr/mfstep/bulnaeg/ Daily 4-day forecast

  10. http://www.oc.phys.uoa.gr/mfstep/bulnaeg/ Daily 4-day forecast

  11. http://www.oc.phys.uoa.gr/mfstep/bulnaeg/ Daily 4-day forecast

  12. SKIRON/Eta atmospheric modeldust masses

  13. 1-way coupling with circulation model NASMOHydrodynamic (U,V) and physical parameters (S,T) data • Thermaikos Sediment Transport Model • Area: 39.5-40.8°N & 22.5-23.8°E • Horizontal discretizationfrom NASMO [dx=dy=1/60°] • Fixed vertical step dz=2m

  14. Preliminary results from a 2day simulation Simulation data Simulation period:22/11/07 13:00 – 24/11/07 12:00 Source-rivers:Axios – Aliakmonas - Pinios Hourly hydrodynamic-physical-hydrological input data Particle mass: 300kg

  15. Future planning for ECOOP • Development of an operational system able to provide short-term forecasts of sediment loads in the Thermaikos Gulf from atmospheric and/or riverine origin • Utilization of any available data for the validation of the system • Application in the North Aegean?

  16. Sediment Transport Model equations(1) 3dimensional displacements Stochastic displacements Horizontal diffusion coefficient Vertical diffusion coefficient Particle characteristic diameter(coagulation-flock break-up) Particle density Settling velocity

  17. Sediment Transport Model equations(2) where Deterministic and stochastic displacement damping functions for the parameterization of the stability of the stratification of the water column Shear stress velocity Critical shear velocity for particle deposition Erosion rate Critical shear stress for particle resuspension (shelf-weight consolidation)

  18. Effect of the stratification of the water column • The density ratio Rp, expresses the influence of temperature and salinity to the stability of the water column, and is defined as the ratio of the contribution to the ambient density of the stabilizing parameters to the contribution of the destabilizing parameters. • Rp is defined as: • where: αis the thermal expansion rate β the haline contraction rate • Double diffusive processes occur for 1  Rp  10 • Thus athreshold value of the density ratio, above which the stratification can be considered as stable is Rp10 • Density ratios that have been defined from the physical parameters one-year input data present largest values of the ratio in the surface waters in the vicinity of the river estuaries Deterministic vertical velocity damping function Stochastic vertical velocity damping function

  19. The proposed damping functions (1) Deterministic and settling velocity damping function: the experiments of Green (1987) and Parsons and Garcia (2000) were put to use. Figure presents the dimensionless finger settling velocity with relation to the value of the density ratio, whereas the fitted curve represents the damping function of the non-fluctuating components of the vertical velocity Fw.

  20. The proposed damping functions (2) Stochastic vertical velocity: the simplified parameterization of Zhurbas et al. (1987) for the vertical diffusivity of salt and temperature following exponential decrease of the density ratio has been applied. Figure presents values of the corresponding stochastic velocity damping function FKv along with experimental data by Hoyal et al. (1999) for the double diffusive flux coefficient, manipulated to express the ratio of the flux to the diffusion coefficient of the fastest diffusing substance.

  21. Stability ratios defined by hydrodynamic input data • The animation presents the regions in which the density ratio takes values of Rp>10 • Thus it depicts the areas the stratification is strong enough to trap sediments

  22. Consolidation Accepting: • full consolidation in 38 days • critical shear stress for deposition 0.1Pa • critical shear stress for erosion 0.2Pa Porosity and critical shear stress threshold for resuspension evolution with consolidation time (for n=1,5·10-5s-1)

  23. Application for aeolian-transported matter Powerful winds pulled a thick band of desert dust from Egypt and Libya over the Mediterranean Sea on April 17, 2005. The dust is so thick that Crete is completely obscured from view, and the ground of Greece is barely visible. African dust frequently blows over the Mediterranean in the spring, carrying tons of dust into Greece. The winds that produced this dust storm blew at an average of 75-89 kilometers per hour (47-55 mph) near the sea’s surface, and stronger winds prevailed higher in the atmosphere. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this photo-like image of the storm.* The image is a property of NASA *http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16887

  24. References • Burd, A., Jackson, G. A.: Prediction particle coagulation and sedimentation rates for a pulsed input, Journal of Geophysical Research, 102 C5, 10545-10610, 1997 • Green, Th.: The importance of double diffusion to the settling of suspended material, Sedimentology, 34, 319-331, 1987 • Hoyal, D.C.J.D., Bursik, M.I. and Atkinson, J.F.: Settling driven convection, a mechanism of sedimentation from stratified fluids, Journal of Geophysical Research, 104 (C4), 7953-7966, in press, 1999 • Huthnance, J. M. et al.: PROFILE – Processes in Regions of freshwater Influence, Final Report, POL Internal Document No 102 – Thermaikos Bay, 1997 • Mellor, G. L.: Introduction to Physical Oceanography, Princeton University, New Jersey, 1996 • Metha, A.J.: Hydraulic Behaviour of fine sediment, Coastal, Estuarial and harbour engineer's reference book, Abott & Price, Chapman & Hall (Pubs.), London, 577-585, 1993 • O’ Brien, J.J. (ed.): Advanced Physical Oceanographic Numerical Modelling, NATO ASI Series, 1985-86 • Parsons, J.D. and Garcia, M.H.: Enhanced sediment scavenging due to double-diffusive convection, Journal of Sedimentary Research, 70(1), 47-52, 2000 • Toorman, E.A., Bruens, A.W., Kranenburg, C. and Winterwerp, J.C.: Interaction of Suspended Cohesive Sediment and Turbulence, Proc. INTERCOH, 2000 • Winterwerp, J. C.: On the dynamics of high-concentrated mud suspensions, Judels Brinkman & Ammerlaan, Delft, 1999 • Zhurbas, V. M., Kuzmina, N. P., and Kulsha, Y.: Step-like stratification of the ocean thermocline from transformations associated with thermohaline salt finger intrusions (numerical experiment), Oceanology, 27, 277–281 English translation, 1987

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