Air-water and momentum exchanges in unsteady surging waters: An experimental study

Flood waves resulting from dam breaks and flash floods have been responsible for numerous losses. In the present study, sudden flood releases were investigated down a large flume with a succession of abrupt drops. A new experimental technique was developed to obtain instantaneous void fractions, bubble count rates and velocities using arrays of conductivity probes. The results showed the surge propagating as a succession of free-jets and horizontal runoff flow motion downstream of each abrupt drop. A strong aeration of the surge leading edge was observed for all investigated flow conditions. In the horizontal runoff region, instantaneous velocity measurements highlighted an unsteady turbulent boundary layer. Practically, the study provides new information on free-surface aeration in surging waters in channels and on beach slopes.