Boundary layer development over a bottom covered with rigid submerged vegetation

This Chapter deals with a topic which is new in international literature, that is the boundary layer behaviour flowing in a channel over a vegetated surface. For sake of brevity and clearness, only the zero pressure gradient equilibrium boundary layer on one side, and the rigid submerged vegetation on the other, have been taken into consideration. First of all, there is a long introductory paragraph, which reminds the main literature knowledge on two single topics (boundary layers and vegetated surfaces); this paragraph has been conceived also for teaching purposes. Afterwards, the results of a long-term research, carried out by the authors, are reported. The topic is tackled mainly in experimental way, using an LDA facility. Basically, local mean velocity value distributions have been measured in different flow test sections, and, consequently, they have been suitably modelled too. Eight different vegetation typologies have been experimentally considered: six of them with sparse vegetation, and two with dense vegetation. Unlike what is customary in international literature, in case of sparse vegetation, velocity distributions have been thinly measured up to the bottom of the current. Modelling has been performed always referring to suitable non dimensional quantities, and it regards the whole height of the velocity distributions, including the current layers flowing through the same vegetation. Data processing gave intriguing results on holding or not holding of boundary layers equilibrium characteristics, as a function of the different considered vegetation typologies. In the Conclusion paragraph, new hypotheses, to go further in this research type, are given too.