3D Model for Evaluation of Pollutant Concentration Distributions from Land-Based Sources of the Caspian Sea Region — Regional Study, Southern Part of the Caspian Sea

Abstract

An unstructured grid, finite-volume, and three-dimensional (3D) primitive equation ocean model has been developed to predict oceanic pollutant dispersions in depth and surface of the Caspian Sea for non-chemical reactions of dissolved constituents. The model consists of momentum, continuity, temperature, salinity, and density equations. Physical and mathematical closure has been achieved using Mellor and Yamada turbulent closure sub-models. Since determining a practical definition of salinity that enjoys acceptable accuracy is difficult; therefore, various definitions have been used in this work. A recent definition of salinity stated in the UNESCO Practical Salinity Scale of 1978, PSS78, defines salinity in terms of a conductivity ratio. However, this is dimensionless and is not useful for computational methods. The old definition of salinity is “Total amount of solid materials in grams dissolved in one kilogram of sea water when all the carbonate has been converted to oxide the bromine and iodine replaced by chlorine and all organic matter completely oxidizedâ€. Although used here but it is difficult to be used routinely explanatory this definition for computational method. We assume S (Salinity) = ΣSi and Ït (total density) = Ï(Θ,Si) ≡ Ï(Θ, S1, S2, S3, …) where in ΣSi, and S1 just is supposed salinity and other S2, S3, … are considered as pollutants. The irregular bottom slope is represented by a sigma coordinate transfor- mation, and the horizontal grids comprise unstructured triangular cells. The finite-volume method (FVM) used in this model combines the advantages of a finite-element method (FEM) for geometric flexibility and a finite-difference method (FDM) for simple discrete computation. The model was applied to the southern Caspian Sea region; including a semi-enclosed coastal ocean and inputs of geographical southern Caspian Sea which include, wind forcing, heat fluxes, precipitation via evaporation, river discharge with pollutant data and temperature. The outputs of these equations were pollutant, velocity and temperature distribution in southern Caspian Sea. A software was developed for this model by the name of SPAUM (Sea Pollutant Azad University Model).

Keywords: caspian sea, finite-volume, ocean, pollutant, unstructured grid