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Report for the 2nd ECOSIM Annual Project Review

University of Athens, Department of Applied Physics,
Laboratory of Meteorology and Oceanography

Authors: A. Lascaratos, L. Perivoliotis, K. Nittis

During the second year of the ECOSIM project, the University of Athens (UA) group after the recommendations of EU during the First Annual Review, developed and applied to the Saronikos gulf, a numerical model for the study of coastal water pollution. The Saronikos gulf is a semi-enclosed coastal sea lying to the south of Athens, a city of 3.5 million population. 720,000 m3 of domestic wastes per day are released inside the Inner Gulf through the Central Metropolitan Outfall after undergoing secondary treatment. Further to that, industrial wastes are discharged in the Elefsis Bay in the northern part of the gulf.

The coastal water model is based on a well known academic community model, the Princeton Ocean Model (POM). POM is a sigma-coordinate, 3-D thermodynamically active model that has been primary designed for coastal water studies. The UA group has developed a new module of POM for the dispersion of passive tracers. The scheme can simulate several surface and subsurface sources with different pollutant load. This module has been tested in several areas and has been proved to be an effective tool for monitoring the fate of tracers in the coastal environment. The sources can be either point-sources (eg. rivers, sewage...) or linear-sources (landfills).

The model grid covers an area 100X100 Km with horizontal resolution of 2Km (50x50 points). The extension and the resolution of the horizontal grid were decided in collaboration with AUT according to the requirements of MEMO. The SST values computed by POM were used by MEMO in a number of sensitivity tests.

The model was initialized using climatological temperature and salinity data provided by MODB (Mediterranean Oceanic Data Base). The data were applied to the model grid using objective analysis techniques. The atmospheric forcing data that drives the model are calculated from climatological monthly means based on the 1980-1988 re-analysis of the NMC (national Meteorological Center-USA) weather forecast. This data base has been extensively used in modeling efforts in the Mediterranean and has been proved to be the most appropriate for climatological studies. Finally, the bathymetric data used in the model runs were provided by the Hellenic Hydrographic Services.

After a close collaboration with ESS, the model has been integrated inside the ECOSIM demonstrator and can be used either locally or through Internet. In order to build the communication interface with the model, the UA group used the input supplied by the user support partners during the Athens meeting (April 2-4, 1997). Using the ECOSIM demonstrator, the end-user can specify:

  • The number of sources that will be added to the model (maximum 100), the flow rate for each one as well as the concentration value for specific pollutants.

  • The surface or subsurface release of tracer

  • The starting month of the integration. With this option, the user automatically specifies the corresponding hydrological and meteorological conditions for the simulation.

  • The output time step

  • The total duration of run in days (maximum 360 days)

Two examples of the model dispersion results are shown in figures 1 and 2. In figure 1, the dispersion from one point source that represents the Athens Sewerage System (surface release, flow rate 720000m3/day) is shown, while in figure 2 a second point source with the same characteristics has been added. Tracer concentration values are in arbitrary scale 0-30.

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