Vortex-Induced Oscillations at Low-Head Weirs

Low-head river barrages convey flood discharge at raised weir gates. From the downstream end of the intermediate piers, eddies separate periodically. The paths of the eddy-series separating from the neighboring piers intersect about the bisector of the openings. These points of intersection are places of interference and represent increased danger from tailrace scour. The eddies separating at the end of the piers initiate a surge wave along the piers towards upstream. This wave, going round the pier, will superimpose in the case of resonance, on the wave generated by eddies at the opposite side of the pier. This effect will increase the amplitude of the wave until the dynamic condition of equilibrium is established. The wave going periodically around the piers initiates translatory waves in the headrace, which are dangerous because of the erosion of the upstream banks. A suggestion was made for the reduction or even for the elimination of such phenomena.