複断面水路における洪水流

Abstract

In this paper, the characteristics of steady flow and unsteady flow in a compoundcross-sectional channel are discussed by the experiments conducted in an experimentalflume (50m in length, 3m in full width, 1. 2m in flood plain width and 60cm in channelwidth)The main characteristics of the flow in the compound cross-sectional channel is theretardation phenomena of the velocity of the main channel caused by the mixing of flowbetween the flood plain and the main channel. The hitherto calculating methods whichdivide the section into the main part and flood plain part overestimate the discharge inthe main channel because they neglect the shear stress created by the mixing at theboundary of the two parts.The authors discuss the mixing effects and also the mean velocity distribution by theassumption that the turbulent viscosity is proportional to the depth and velocity.Using the results of the experiments of steady flow, the authors discuss the character-istics of flood flows theoreticaly and experimentaly. The main results are that underthis channel condition the celerity of the flood wave is less than that in the rectangularcross-section and the lateral flow discharge is very small and so the lateral water surfaceprofile is nearly horizontal.