Application of COHERENS in modeling pollution dispersion in a shallow tide-effected bay (Bushehr Bay)



It is well known that, contaminant transportation is a major problem in coastal zones and has to be faced when coastal structures are being planned.
Sea pollution not only causes environmental damage, but also impacts quality and population of sea resources. Oil is the most important pollutant, pollutants emanating from industries, ships, drilling and exploration in the seabed, ship sewage, toxic waste dumping, and civic sewer systems.
Being alongshore the northern coasts of the Persian Gulf, Bushehr Bay is considered important in sea pollution due to the frequent sources of industrial and oil pollutants, ship transportation, and sewage and toxic waste dumping. Therefore, it is necessary to study and find the way the pollutants are dispersed along the bay. To do so, this study concentrates on physical and atmospheric factors affecting pollution dispersion.
Bingchen Liang (2008), surveyed a hydrodynamic sediment coupled model COHERENS-SED, which has been developed by the first two authors through introducing wave-enhanced bottom stress, wave dependent surface drag coefficient, wave-induced surface mixing, SWAN and sediment model to COHERENS, and is modified through introducing a contaminant transportation model. They showed that the fields of current velocity and contaminant concentration obtained by the modeling of case with wave-induced longshore current are quite different.
Using COHERENS, Mahmudi (1386) modeled pollution dispersion in the Persian Gulf. He proved that pollution dispersion in the Gulf is a function of flushing time and current movement at water surface and sea bottom.
Since Bushehr Bay is an important area from aspects of economy, marine transportation, and environment, there is a high potentiality to disperse the pollution in different ways. Due to the prevalence of the tidal current in the bay, this study uses COHERENS to simulate the horizontal dispersion of pollution affected by tidal currents in the bay.
Therefore, COHERENS, a hydrodynamic multipurpose 3D modeling system for coastal and shelf waters, has been used to model and survey dispersion of pollution in Bushehr Bay. The recorded data of the Marine Meteorology Station for a 40-year period, besides 4 major tidal components (M2, S2, O1, and K1) of the bay were used as the inputs of the model. When the model was adjusted and the data inserted, the model was run for the bay. After the model reached a stability point, tidal currents were validated with field observation which resulted in prediction of horizontal dispersion of pollution in different layers.
The results show that dispersion is highly affected by tidal currents, and the results gained from the current field are in a good accordance with field observation of the bay. These results can be applied to predict the direction and dispersion of pollution and the ways to deal with them in the future.