Flow duration curves (FDCs) express the link between a selected streamflow and the percentage in time such value is exceeded. The curves provide a graphical insight into hydrological regimes, though, the absence of time-series data is a significant shortcoming. Conversely to what happens with hygrograms, flows in FDCs are represented without regard of sequence of occurrence. This paper explores FDCs of 19 catchments for which, at least, 10 years of daily discharges are available. FDCs can be built for any temporal scale (i.e. daily, weekly, monthly). In this study daily discharges have been adopted because daily scale better represents the variation in flow. A particular focus is on low flow data which are useful to the design: fish ladders, environmental passages and low flow diversions. The work also introduces a unique hydrological area having the inner catchments similar response among themselves in terms of low flow data. For such an hydrologically homogeneous area, environmental flow, namely the amount of water released uniquely for biological requirements, is appropriately detected.