Coherent structures in unsteady open-channel flows

Turbulence measurements of unsteady open-channel flows over a flat rough bed were conducted by making use of a laser Doppler anemometer (LDA). The contribution rates of each event to the Reynolds stress and the bursting period were investigated. The value of RS√RS 2 , which means the contribution ratio of the sweep event against the ejection event, decreases with an increase of the duration time in rising stage. The bursting phenomena increase in the rising stage of flood, while they decrease in the falling stage. This shows that the bursting phenomena occur more frequently in the rising stage. From this study, the characteristics, that the concentration of suspended sediment increases in the rising stage of natural river, are substantiated.