Modeling of hydrodynamic and water quality processes in the Gulf of Thailand | |
| Author | Chanon Thaicharoen |
| Call Number | AIT Diss. no.WM-06-01 |
| Subject(s) | Hydrodynamics Water quality--Thailand, Gulf of |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Integrated Water Resources Management, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. WM-06-01 |
| Abstract | The Gulf of Thailand (GoT) is considered as one large single marine ecosystem owing to its unique topography, oceanography, and climate characteristics. In terms of biological resource, it is one of the richest areas in the world because of the high levels of nutrients and fish stocks in the coastal waters. Thailand was ranked the 81 h in term of fish catch export in the world. Recently, awareness in water quality problem is increasing due to the results of the country development. A combination of land-based and marine-based sources accounts for pollution problem in the GoT. More than 200,000 tons of waste is discharged into the GoT every year both from domestic and industrial sectors. Wastes from marine-based sources, for example petroleum and gas exploration, vessels and oil spills also contribute to extensive pollution in the GoT. There is also evidence of the degradation of water quality by low dissolved oxygen and high enrichment of nutrients in some coastal areas close especially nearby the river mouths and the key cities. The GoT is an enclosed embayment located in the South China Sea having an area of 300,858 sq km. The gulf is relatively shallow which its average depth and maximum depth are 45 and 83 m MSL, respectively. The northernmost of the gulf is, named as Upper Gulf of Thailand (UGoT), at the mouth of the Chao Phraya River. The boundary of the gulf is defined by a straight line, 381 km length, from tip of Cape Camau in southern Vietnam to Kota Baru city on the Malaysian coast. The topography of the boundary indicates the possibility of restriction in exchanging the1mocline water at the deeper layer from South China Sea and the GoT. In the central part of the gulf where the bottom depth exceeds 40 m, the water column is slightly stratified. The density of water changes 1-2 kg/m3 within 2-3 m depth range at the interface layer of surface and bottom waters. This zone of sharp density change, known as pycnocline, is located at depth of 35-60 m depending on location and season, reflecting the local oceanographic processes at that location. Existence of pycnocline indicates a strong vertical stability with very little exchange between the surface and bottom water masses. Besides, the water at deeper than 60 m inside the gulf may performs like a stagnant pool if less vertical exchange in water column exists. Therefore, this bottom layer, deep zone, may play a role on a pollution trap in the GoT. There are very limited researches on dynamic processes and water quality processes due to lack of available data both in spatial and temporal scales. Most of the studies were focused on the particular location where the problem has been found. The study intends to study the whole dynamic system of the GoT including the water quality transport and fate of pollutants with different characteristics of shallow and deep zone of the GoT. In the present study, two-dimensional and three-dimensional model, developed by DHI, were applied to study the dynamic processes of the GoT coupling with water quality processes. Due to the available water quality data, the two dimensional hydrodynamic and water quality model was firstly employed for the upper part of the GoT, named as the Upper Gulf of Thailand (UGoT). The benefit of this modeling work is to determine the interactions of water quality processes and use as a typical set of model parameter for the whole gulf basin in the latter state of work. The modeling the hydrodynamic of the UGoT is successfully defined by comparing the model results with the observed data in 1993 and 1996 for calibration and verification processes, respectively. The hydrodynamic process in the UGoT is principally dominated by tidal-driven force rather than wind and river freshwater inflow. However, the wind-driven force becomes more evidentially influence to shallow area where the depth is less than 10 m. Although river freshwater inflow becomes less importance than the previous two driven forces, it could not be neglected in order to study the physical and chemical processes. Most of pollutant is carried by these rivers for example the Chao Phraya River. The water quality model of the UGoT is substantially validated with limited observed data. During the falling tide, the pollutant is transported and dispersed into the coastal waters and move back and forth in limited extent due to the almost zero net tidal current. Since the tidal characteristic was rather constant over the year period, the seasonal wind becomes relatively important in pollutant plume development according to the prevailing directions. The evaluation of the constructing wastewater treatment plant (WTP) in terms of water quality is then applied using this model as a tool for justifying the operation plan of WTP. The recommendations are put forward to improve the management plan of the WTP. The hydrodynamic processes of the whole gulf basin were successfully achieved by enhancing two- and three-dimensional numerical model. By two-dimensional model results, the interaction of tidal and seasonal wind effect was analyzed. The tidal-driven force plays likely the role for the whole basin of the GoT. The diurnal tide was dominated cover the area from Mattaphon and Ko Lak at the west coast to off coast of Vietnam and Phu Quoc Island. With the amphidomic nodes of diurnal tides off Songkhla coast, the semidiurnal tides became predominant with small tidal range. The tidal current became very strong at the UGoT where the mixed tide with semidiurnal is predominant. The average seasonal wind effect contributed the wind set-up and set-down at different sides of the gulf with maximum variation of 0.25 m around Songkhla area. Seasonal wind had a greatest effect in the southern part of Thailand where the highest ratio of wind variation over the tidal range is found. For the other parts, wind effect had relatively low compared to tidal effect particularly in the UGoT region. The three-dimensional model was conducted using the open boundary condition from the two-dimensional model and the oceanographic survey data, provided by SEAFDEC, in 1995 as the initial condition. The analysis period was only covered the NE monsoon event due to data available. The vertical profile of salinity and temperature was satisfactorily calibrated. The average seasonal wind, NE monsoon, had a potential increasing the vertical mixing in the water column. Therefore, the stratification in the central of the gulf has no longer existed during NE monsoon period. After the NE monsoon, the summer time begins. The wind in the summer time is relatively low. Surface heat radiation played a role introducing the thermocline layer at 20 m depth in which well correspond to the observed data. As the numerical point of views, the two dimensional model was adequate to study the circulation in general due to an almost well mixed condition in the water column. However, the two dimensional model has limitations to complete the vertical hydrodynamic processes in the GoT. A three-dimensional model could be very useful to overcome such problems in the central of the gulf. An application of land based pollution due to rivers was conducted to determine the possibility of plume distribution in the GoT which can be used for pollution management and control in the Gulf of Thailand. This study could be useful for government agencies that have responsibility in the marine and coastal resources in the Gulf of Thailand. Last but not the least, recommendations for further study and application were put forward to improve the capability of the model analysis. |
| Year | 2006 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. WM-06-01 |
| Type | Dissertation |
| School | School of Engineering and Technology |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Water Engineering and Management (WM) |
| Chairperson(s) | Babel, Mukand Singh;Gupta, Ashim Das; |
| Examination Committee(s) | Sutat Weesakul ;Nguyen Thi Kim Oanh ;Suphat Vongvisessomjai;Isobe, Masahiko; |
| Scholarship Donor(s) | The Government of Japan; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2006 |