On the vertical variation of turbulence statistics in open channel flow

Nezu (1977) established a set of universal exponential expressions for the vertical variation of the turbulence intensities following a series of open channel flow laboratory experiments. Each of these relationships contains an empirical coefficient that differs with the component direction (D_u = 2.3, D_v = 1.27, D_w = 1.63). Recent laboratory experiments have demonstrated that for open channel flows these constants are not universal but vary with the Reynolds number and bed composition. A method for the remote prediction of D_u and hence, the vertical variation of the streamwise turbulence intensity is developed here. The method uses the free surface turbulence anisotropy as a proxy for the redistribution of vertical velocity fluctuations into surface parallel components enabling a correlation between the free surface turbulence intensity and D_u. Implications for the remote prediction of bed composition, sediment transport and bed shear stress are discussed.