開水路流れにおける分散係数

Abstract

This paper presents a part of the results from 19 dispersion experiments made in open channelflumes of rectangular cross section. The main objectives are to report the details of the exper-iments, the data processing procedure, and the dispersion coefficients obtained. Two flumes withlarge length to width ratios are used under the condition of wide aspect ratios and various bottomroughnesses. Concentration to time curves are simultaneously measured at many points in asection. In most experiments, local time-averaged velocities at 40 or more points in a cross sectionare also measured by either propellers or a hot film velocity meter. The dispersion coefficients areobtained by the moment method, the routing procedure and/or the peak concentration to timemethod. A relationship between the dispersion coefficient and aspect ratio is obtained using the di-mensional analysis. A 2nd relationship estimating the dispersion coefficient for open channel flowof rectangular cross section is derived from the Lagrangian analysis and the calculated dispersioncoefficients of flumes and natural streams are contrasted against both experimentally obtainedcoefficient and those from Fischer's (1968) formula for natural stream. Finally, the influence ofthe velocity distribution characteristics on Lagrangian- based formula is discussed.