Impacts of Typhoon Vae and Linda on wind waves in the Upper Gulf of Thailand and East Coast

The Upper Gulf of Thailand and east coast are the locations of the 3 important deepsea ports of Thailand, namely Bangkok port, Laem Chabang port and Map Ta Phut port which needed wind wave data for designs of port structures and navigation of cargo vessels and container ships to and from the ports. In the past, most wave data in the Gulf of Thailand were computed from wind data using the methodproposed by Silvester and Vongvisessomjai (1970). Recently, Pornpinatepong et al. (1999) used the WAM Model to predict wind waves in the Gulf of Thailand and Andaman Sea using waves initially from satellites ERS-2 and TOPEX and later from 9 oceanographic buoys in the Gulf of Thailand and 2 buoys in the Andaman Sea for model calibration. This study presents wind waves in 6 years (1997-2002) from the WAM Model at Petchaburi and Sichang buoys in the Upper Gulf of Thailand as well as Rayong and Ko Chang buoys on the east coast. Since the big waves in the study area are generated by strong winds of cyclones, emphasis is placed to the wind waves generated during the passage of cyclones Vae in 1952 formerly provided by Vongvisessomjai (1994b) and new data of Linda in 1997. Cyclonic waves are second in size to the tsunami waves in the Andaman Sea on December 26, 2004

Tropical cyclone disasters in the Gulf of Thailand

The origin of tropical cyclones in the South China Sea is over a vast deep sea, southeast of the Philippines. The severetropical cyclones in summer with northerly tracks attack the Philippines, China, Korea and Japan, while the moderate ones inthe rainy season with northwesterly tracks pass Vietnam, Laos and northern Thailand. In October, November and December, the tropical cyclones are weakened and tracks shift to a lower latitude passing the Gulf of Thailand. Tropical cyclone disasters in the Gulf of Thailand due to strong winds causing storm surges and big waves or heavy rainfall over high mountains in causing floods and land slides result in moderate damages and casualties. Analyses are made of six decades of data of tropical cyclones from 1951-2006 having averaged numbers of 3 and 13 in Thailand and the South China Sea respectively. Detailed calculation of surges and wave heights of the 5 disastrous tropical cyclones in the Gulf of Thailand reveal that the Upper Gulf of Thailand with a limited fetch length of about 100 km in north/south direction and about 100 km width in the east/west direction, resulted in a limited maximum wave height of 2.3-2.5 m and maximum storm surge height of 1.2 m generated by Typhoon Vae (1952), while the east coast, with longer fetch lengthbut still limited by the existence of its shoreline, resulted in an increased maximum wave height of 4 m and maximum storm surge height of 0.6 m in the Upper Gulf of Thailand generated by Typhoon Linda (1997). These are the Probable Maximum Cyclones here.The southern shoreline, with unlimited fetch length on the east by tropical cyclones approaching from the South China Sea, generated maximum wave height of 6-11 m by Typhoon Gay (1989), resulting in more casualties and damages. Note that storm surges on the southern shorelines with steep slopes are small due to the short distance of shallow shorelines in receiving wind stresses for piling up sea levels. These disasters can be alleviated from known characteristics of tropical cyclones and through proper warning before coming to the Gulf of Thailand

Analytical model of interaction of tide and river flow

Hydrodynamic characteristics of a river resulting from interaction of tide and river flow are important since problems regarding flood, salinity intrusion, water quality and sedimentation are ubiquitous. The lower reach of the river strongly influenced by tides from the sea, when interacting with river flows, results in a complicated pattern which is simplified to its interaction with four main constituents of tides obtained from harmonic analysis. An analytical model is developed in this study for simulating the hydrodynamic processes in estuarine waters, with the emphasis being given to the interaction between tides and river flows. The perturbation method is used to derive the analytical solution, in which the estuarine flow is separated into steady and unsteady components. Thus the analytical solutions derived consist of two distinct parts; one represents the influence of river flows and the other represents the influence of tides. The application of the model to a case study, the Chao Phraya river, which requires a time series of discharges and loadings at the river mouth to model water quality in the Gulf of Thailand, shows that the model can beautifully and completely simulate the hydrodynamic features of tide and river flow interaction especially in the rainy season when the river discharge is high. Data of tidal discharges are scarce because of high cost of measurement especially in the lower reach of the river strongly influenced by tides from the sea. From this study of relation between tidal discharges and tides, the analytical model can compute tidal discharges from tides correctly. The results of tides and tidal flow can subsequently be used to calculate eddy viscosity and dispersion coefficient for describing salinity and water quality profiles

The interaction between tide and salinity barriers

Presently, there is a number of salinity barrier utilization and this kind of structure becomes more common in estuarine areas. However, the construction of barrier at the river mouth or inside the river results in amplification of tide due to creation of standing tide at the barrier. This standing tide creates two major problems, namely, the overspill of salinewater during high water and bank erosion during low water along the tidal reach downstream of the barrier. In this study, the analytical model is developed to determine the river hydraulic behaviors which affects by tide, river flow and barrier structure of the Bang Pakong River, Thailand. The analytical model of tide and river flow of the Chao Phraya River is adopted and adjusted to determine the tide characteristics modified by river flow. Moreover, the analytical model of tide and salinity barrier would then be developed by cooperating of the analytical model of tide and river flow interaction together with tidal flow cooscillating tide theory. It is found from this study that the analytical model of the Chao Phraya River which is suitable for high freshwater discharge underestimates damping modulus and friction slope which requires adjustment for low freshwater discharge of the Bang Pakong River. The analytical model of tide and salinity barrier can be finally used to predict the water level downstream of the barrier. The model overestimated the water level fluctuation during the unsteady flow from upstream which may be because of the assumption of steady flow condition in the model development due to limited data available after the construction

Effects on the upstream flood inundation caused from the operation of Chao Phraya Dam

During the flooding events, the operation of Chao Phraya Dam to control downstream water discharge is one of the causes of the inundation occuring over the upstream area. The purposes of this research are to study the effects of the operation of Chao Phraya Dam upon the upstream flood inundation and to find out the new measures of the flood mitigation in the upstream areas of Chao Phraya Dam by using a hydrodynamic model. The results show that Manning's n in the Chao Phraya River and its tributaries is 0.030-0.035 in the main channels and 0.050-0.070 in the flood plain areas. The backwater due to the operation of the Chao Praya dam affects as far as 110 kilometers upstream. New methods of water diversion can mitigate the flood inundation without the effect on the floating rice fields. The construction of reservoirs in the Upper Sakaekang River Basin and the Upper Yom River Basin will mitigate the flood not only in their own basins but also in the Lower Chao Phraya River Basin. The coordinated operation of the Chao Phraya Dam, the regulators and the upper basin reservoirs will efficiently mitigate the flood inundation

Interaction of river flow and tide as well as storm surges

The interaction of tide and river flow is complicated due to the fact that tide consist of many constituents which interact differently with river flow. The river flow damps the tide from the river mouth and raises the mean water level. This report show that water levels in estuaries are the superposition of periodic tidal components and mean water levels. When the tidal components are filtered out, the mean water levels can correlate well with freshwater discharges and form rating curves of the estuaries. Chapter 1 describes tide and tidal current in the sea and gulf which serve as boundary conditions at river mouths. Chapter 2 applies harmonic analysis to 5 recording water level data of the Chao Phraya river and found that each constituent of tide damps exponentially along the river and the mean water level shows a linear distribution along the river. The complicated interaction of river flow with various constitutents of tide is simplified to its interaction with individual constituents. An analytical model of tide and river flow interaction is then developed using perturbation method in decomposing the steady state component of the river flow from the unsteady component of the tide. The analytical solutions can describe the interaction of tide and river flow completely. Chapter 3 attempts to analyse interaction of tide and river flow in the estuarine network of the Mekong river delta which is further complicated by branching of flow. The branching of flow can be determined from the continuity of flow and water level at the branching. Once the flow in each branch is determined, the interaction of tide and river flow in each branch is similar to that of Chapter 2. Chapter 4 analyses the interaction of tide and river flow of the Red river delta. (orig.)Available from TIB Hannover: RO 2673(5) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman