Contribution to the defining of the minimum acceptable flow Tiber River Basin authority experience

The defining of minimum acceptable flows has been the objective of several scientific studies spurred by the growing technical and regulatory interest in this topic. The current approach (Martini 1994) provided for the estimating of the minimum flow according to simple hydrological variables. Later works (Ubertini 1996) identified Q7 10 as a hydrologic index that is capable of representing the low flows which over time have ensured the protecting of aquatic life. This index could also be easily regionalized on the basis of hydro-geomorphological parameters that are easy to measure (Manciola 1997). The main limit to this approach, partially overcome by the results obtained by Leonard (1990) and Calenda (1993), is due to not knowing what the functional connection is between Q7 10 and the biological parameters of the fish community in a stream. This normally causes an overestimating of the minimum acceptable flow in the stretches of the river fed by carbonate hydrogeologic formations, and an underestimating in basins characterized by more impermeable formations. The Tiber River Basin Authority considered it necessary to overcome this limitation, and thus it has promoted a vast experimental investigation of the basin.