K. Kramer - Laboratory of Hydraulics, Hydrology and Glaciology (VAW), Swiss Federal Institute of Technology, Zurich, Switzerland
W.H. Hager - Laboratory of Hydraulics, Hydrology and Glaciology (VAW), Swiss Federal Institute of Technology, Zurich, Switzerland
H.-E. Minor - Laboratory of Hydraulics, Hydrology and Glaciology (VAW), Swiss Federal Institute of Technology,Zurich, Switzerland

For protection of spillway chutes and bottom outlets against cavitation damage, air is normally added by chute aerators in regions where the cavitation number falls below a critical value. Until today, the detrainment process downstream of an aerator has not been thoroughly investigated. This paper presents new model investigations of a hydraulic chute model focusing on the streamwise development of the air detrainment process. Results enable to predict the reduction of mean air concentration, depending on the air inflow, the inflow Froude number and the chute slope. It is also proven that the minimum air concentration on a chute is a function of the streamwise Froude number only