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

Thesis (M.Eng.) - Asian Institute of Technology, 1982

Frequent floodings occur in the Lower Mun river due to heavy rainfall over the Mun-Chi basin. A mathematical model consisting of the unsteady free surface flow equations is therefore developed to compute the flood flow conditions along the river. Both storage and dynamic effects of flow in berms or overbank portions are considered in the model. The equations in the model which also take into account the effects of lateral inflow are solved numerically using the finite difference approximation of the implicit scheme. The model is calibrated using the flood flow data in October 1975 and 1980 and then verified against the flood flow data in 1978. Good agreement between the computed and observed water levels and discharges is obtained. It is found that the main channel Manning roughness coefficients are more effective on the computed water levels, the main channel and total discharges than the berm Manning roughness coefficients. The computations of discharges and water levels carried out for the case when both dynamic and storage effects are considered in the berms and the results are compared with t he case when only storage effect is taken into consideration. It is found that the water levels when only storage effects are considered in the berms are higher than those when both storage and dynamic effects are considered. The model is then applied to compute backwater curves due to a dam located at Pak Mun near the downstream end of the model.