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 thatU (M) is able to implicitly reflect the different hydraulic behavior which is determined in rough and submergedvegetated beds. Thus, the entropy-based Manning’s roughness formula has been validated and the sensitivity analysis of Manning’s coefficient with the values ofy 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.