1 Characterization of the flow field in a stepped spillway by PIV by A. Amador (1) , G. Van der Graaf (2) , M. Sánchez-Juny (1) , J.Dolz (1) , F. Sánchez-Tembleque (3) , J. Puertas (3) . (1) Universitat Politécnica de Catalunya. Hydraulic, Maritime and Environmental Engineering. Department. Calle Jordi Girona 1-3. Building D1, 08034 Barcelona, Spain. E-mail: antonio.amador@upc.es . (2) E-mail: gerber.van.der.graaf@aaupc.upcnet.es (3) Centro de Innovación Tecnoloxica en Edificacion e Enxeneria Civil. Universidad de A Coruña. Campus Elviña, s/n 15192, La Coruña, Spain. E-mail: citeec@udc.es ABSTRACT An experimental study was conducted on a large model of a stepped spillway. The particle image velocimetry technique is used to provide the characterization of the flow field in the non-aerated region of the skimming flow regime. The region upstream and next to the inception point of air entrainment is considered critical for evaluation of the cavitation risk in the spillway. Typical flow phenomena like turbulence intensities and shear strain rates in the cavity of the steps, in the shear layer and in the main flow are described. These experimental results give insight in the flow behaviour that cause possible cavitation inception. Fig.1. Mean velocity field in skimming flow in a stepped spillway (q=0.11 m 2 /s).