A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 1981

During flood period , the flow in the Chao Phraya River released from the Chao Phraya Dam overtops the river banks and spreads out over the rice fields and low lying areas along both sides of the river. Therefore , the volume and elevation relationship of flood plain is an important factor in the computation of flood flow along the Chao Phraya River . In previous studies , the volume and elevation relationships of flood plain so called the flood plain characteristics were determined by trial and error procedure along with the flood flow simulation. The computation assumed the water level in the flood plain is horizontal . However, the method was found to be very tedious and took a lot of time . To overcome this difficulty, an attempt has been made in the present study to develop a simple method to determine the characteristic of t he flood plain by using the topographical volume elevation relationship in the flood plain . The topographical map scale 1:20, 000 with the contour interval of 0.5 m was used in connection with the map of inundation which was used to delineate the extent of the flood plains. The topographical volume and elevation relationship determined from this simple method was verified against the flood plain characteristics determined from simulation by applying it to simulate the flood flow condition in the Chao Phraya River in 1978. The difference in the shape of the topographical relationship and the flood plain characteristics was explained as the effect of neglecting the water surface inclination in the flood plain . However , it is found that the topographical relationship behaves quite similar to the flood plain characteristics and also yields good results of flow simulation .