عملكرد مدل كوهيرنس (COHEHRENS) در مدل‌سازي پخش آلودگي در يك خليج كم‌‌عُمق تحت تاثير كِشند (خليج بوشهر)

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

خليج بوشهر، خليج كوچكي در امتداد سواحل شمالي خليج فارس است كه به‌خاطر ورود انواع آلاينده‌هاي صنعتي، آلودگي ناشي از تردد كشتي‌ها، وجود منابع آلاينده نفتي، تخليه مواد زايد و سمي و فاضلاب‌هاي خانگي واردشونده به اين خليج تاثير فراواني بر آلودگي زيست‌‌محيطي حوضه خليج فارس دارد. بنابراين نياز مبرم به شناسايي و بررسي نحوه پخش اين آلودگي‌ها، كاملاً مشهود است. به‌‌اين‌‌منظور در اين تحقيق از مدل كوهيرنس كه يك مدل هيدروديناميكي سه‌بُعدي چند ‌‌منظوره است و براي آب‌هاي كرانه‌اي درياها و فلات قاره‌ها طراحي شده؛ براي مدل‌سازي و بررسي آلودگي در خليج بوشهر استفاده شده است. براي ورودي مدل، داده‌هاي ثبت شده ايستگاه هواشناسي دريايي بوشهر در يك دوره آماري 40 ساله و چهار مولفه اصلي كِشندي (جزر و مدي) (M2 ، S2 ، O1و K1) بندر بوشهر مورد استفاده قرار گرفته است. پس از تنظيم مدل براي خليج بوشهر و وارد كردن داده‌هاي موردنياز؛ مدل براي اين خليج اجرا شد كه پس از رسيدن به حالت پايداري، جريان‌هاي كِشندي با مشاهدات ميداني مورد اعتبارسنجي قرار گرفت و پيرو آن نحوه پخش آلودگي افقي در لايه‌هاي متفاوت پيش‌بيني شد. نتايج مدل نشان مي‌‌دهد كه پخش آلودگي در خليج بوشهر، تحت تاثير جريان‌هاي اغلب كِشندي اين خليج رخ مي‌‌دهد و نتايج مربوط به ميدان جريان هم‌خواني خيلي خوبي با مشاهدات ميداني مربوط به حركت شناورهاي روي آب دارند. نتايج اين مدل را مي‌توان در نحوه پخش آلودگي و مسير حركت آلاينده در خليج بوشهر و پيشنهاد راهكار مناسب براي مقابله با پخش بيشتر آن مورد استفاده قرار داد.

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.