A thesis submitted in partial fulfillment of the requirement for the degree of Master of Engineering, school of Engineering and Technology

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

Subsidence of flood peak discharge and flood wave celerity in channels with overbank areas considering f l ow velocity in overbank portions is investigated. Based on dimensional analysis the subsidence of peak flow along the channel and the flood wave celerity is expressed as a function of seven nondimensional parameters each raised to a certain exponent. These nondimensional parameters are related to the widths of the main channel and overbank areas, bankfull depth and conveyance, duration of flood hydrograph and its volume , peak inflow, bankfull discharge, bed slope, Manning' s n coefficients of main channel and overbank flow areas. The exponents of each nondimentional parameters in the subsidence function are evaluated based on the results of the numerical simulations using finite difference method of implicit scheme. The subsidence function developed is tested in the Chao Phraya river from the Chao Phraya dam to Singburi with two set of data of flood flow in 1978 and 1980. Good results are found in these tests. The wave speed function, developed is tested with data obtained from numerical simulations, good agreement of the results are found. However further study considering backwater effects in deriving t he subsidence function and testing these subsidence and wave speed functions in wide range of field data in other rivers are recommended.