Entropic approach to estimate the mean flow velocity:experimental investigation in laboratory flumes

The paper deals with the linear entropic relationship between the maximum velocity, u max , and the mean flow velocity, u m, through a dimensionless parameter U (M), in open-channel flow. The analysis is conducted with the aid of experimental data collected in straight laboratory flumes under different bed and side-walls roughness conditions. In particular, rough/vegetated beds and smooth/rough side-walls conditions have been investigated. The results show that, in the investigated conditions (with exception of low- submergence vegetated bed— h/k v \2), U (M) can be assumed equal to a value that is very close to that found in natural channels. This demonstrates that U (M) is able to implicitly reflect the different hydraulic behavior which is determined in rough and submerged vegetated beds. Thus, the entropy-based Manning’s roughness formula has been validated and the sensitivity analysis of Manning’s coefficient with the values of y o (location of the zero-velocity plane) has been also performed. It is found that this formula is quite robust to represent the observed flow resistance also in the presence of vegetation.