A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1989

Tidal barrier is a structure in estuarine areas. It serves as a barrier against the salinity intrusion or against the high tide to avoid flooding. When the barrier is constructed, it will surely affect the flow conditions of the estuary. The effects may be good or bad. Therefore, to establish a detailed model for the prediction of the backwater effects and the circulation conditions due to the structure will be important. In this study, an existing 1-D model for the Chao Phraya estuary (from river mouth to the upstream boundary in Bangsai) is applied to check the possible backwater effect due to a barrier located at 34 km from the river mouth, and a 2-D model is applied to determine the resulting circulation in the region near the barrier. Different schemes are applied to run the 1-D model for Chao Phraya river and the results obtained for the period considered (1st. 7. 5 days in Oct. 1983) show an insignificant water level increase (and always happens in the low tides) in the upstream of the barrier. The resulting circulations caused by high tide and low tide for this considered period are also found by a 2-D model. A maximum circulation range of 1 km downstream of the barrier is obtained in the low tide, and a maximum of 500 m circulation range upstream of the barrier is obtained in the high tide. In order to check the possible backwater effect during the flood period, a longer period of 7 weeks (beginning Oct. 1st., 1983 including the flood period) is simulated (by 1-D model). The results show that during the flood period the tidal effect. on water level becomes small and the discharge of fresh water would create only small water level increase in the upstream boundary at Bangsai.