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

Thesis (M.Eng.) - Asian Institute of Technology, 2002

Presently, there are a number of the salinity barrier utilization and this kind of structure becomes very 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. Nowadays, there are available and prevailing numerical models which have been used as a tool for dealing with this kind of problems. 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 derived by Vongvisessomjai and Rojanakamthorn is firstly used and adjusted for computing water level and discharge in the Bang Pakong River. The analytical model of tide and salinity barrier would then be developed by the cooperating of the analytical model of tide and river flow interaction and tidal flow cooscillating tide theory. The study presents that the analytical model of tide and river flow interaction provides the underestimated result when applying to the Bang Pakong River according to the low range of river flow and the dominated effect of bottom friction. The adjusted analytical model by observed data can be determined the water level and discharge in the Bang Pakong River appropriately. Thereafter, the analytical model of tide and salinity barrier is developed by consideration of steady flow from upstream flow, incident tide and reflected tide. The application of the analytical model of tide and salinity barrier in the Bang Pakong River presents quite good result in water level computation. Nevertheless the model contributes the overestimation of fluctuated water level during unsteady flow condition of the upstream flow.