Longitudinal dispersion in sinuous channel with changes in shape

Results are presented from a series of laboratory experiments conducted on a large scale channel with sinuous planform geometry. These have been used to obtain the magnitude of the longitudinal dispersion coefficient. A constant trapezoidal cross section and a variable cross-sectional "natural" shape under different discharges have been studied. Temporal concentration distributions recorded for the trapezoidal section tend towards Gaussian form and provide values of a longitudinal dispersion coefficient comparable with previous similar studies. The more "natural" cross-sectional geometry channel exhibits strongly skewed distributions and increases the value of a longitudinal dispersion parameter by over 150%. Variation of a longitudinal dispersion coefficient with discharge has been observed and has been explained by the effects of the longitudinally varying cross-sectional shape. A comparison between observed and predicted distributions from a simple routing procedure emphasizes the need for an improved method for incorporating the effects of longitudinal variations in cross-sectional shape.