Hello Rupak Loodh,
It looks like you have all you need to do the kind of modelling you mention. Both MIKE 21 and MIKE 3 have fields where you can define the salinity of the water and of any inflows (like outlets at the coast). ABMLab_Ecolab allows you to define the equations that define virtually any physical fenomenon you can think of, so it is appropriate to model an oil spill and it actually includes some templates to model oil spills. That being said you might have to make a few tweaks to the equations and parameters of the oil spill templates in order to assure it is adequate for the type of oil you plan on modelling. I invite you to start by doing the Ecolab tutorials, which I believe to include an oil spill example. You can then couple Ecolab with MIKE to model the oil spill in the coastal area. There are also a bunch of MIKE 3 and MIKE 21 tutorials which you might want to go through before starting your project.
Best regards,
Ricardo Machado
