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A lagrangian model for the transport of sediments in coastal areas
Yannis N. Krestenitis, Katerina Kombiadou
Aristotle University
ynkrest@civil.auth.gr(Abstract received 05/17/2005 for session B)
ABSTRACT
A 3-D transport model for ‘ideal’ particles passively advected and dispersed by the currents is developed which is based on the Lagrange - Monte Carlo Method. A large number of particles, each representing a particular amount of mass are presented to the flow domain through various sources (rivers, seabed, and atmosphere). Their transport and fate is traced with time. The horizontal advection of the particle is controlled by the local fluid velocity and the vertical advection is controlled by the local fluid velocity and the particle settling velocity. The turbulent diffusion is simulated by the random Brownian motion of the particles due to the turbulence. Thus the motion of each particle is analyzed into a deterministic part, which expresses convection and a stochastic part that accounts for diffusive processes.
Once the cohesive sediment particles are introduced to the coastal environment they undergo various processes that affect their properties and their movement. More specifically, they flocculate or deflocculate and gradually change density, thus altering their representative diameter and settling velocity. Seawater stratification influences the vertical movement of the particles by either intercepting or enhancing settling rates. Near-bed processes are included in the simulation, with the possibility of the particles to settle onto the bed, consolidate or resuspend at a later time, and the introduction of eroded material from the sea bottom, according to the shear stress conditions.
The mathematical model is realized for the case of the Thermaikos Gulf. The four rivers, Axios, Loudias, Aliakmon and Pinios that discharge along the west coasts of the gulf, supply the coastal basin with a large amount of fine-grained sediments. The necessary hydrodynamic data, are obtained from the Northern Aegean shelf model, a 3-D hydrodynamic model based on the Princeton Ocean Model (POM). The shelf model obtains the boundary conditions (asynchronously nested) from the Aegean-Levantine area model.
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2005 LAPCOD Meeting, Lerici, Italy, June 13-17, 2005