This paper investigates the design guidelines for stilling basins located within steep channels, i.e. in the presence of supercritical downstream flow conditions. A large number of experiments have been carried out varying both the terminal step height and the hydraulic characteristics of the upstream supercritical current. A regime chart in dimensionless parameters is built up, and the limiting working conditions of the basin are univocally individuated. Total head, local bottom pressures, and velocity field measurements, are employed to fully characterize the investigated flow conditions.