Measures to reduce dynamic plunge pool pressures generated by a free jet

Spillways often include a flip bucket as terminal energy dissipator, combined with a plunge pool. To prevent scour at the river bed for large jet fall heights additional measures are required, such as terminal chute widening or increase of the plunge pool depth. The effect of these measures was investigated in hydraulic modeling. The dynamic plunge pool bottom pressures in the jet footprint area were systematically recorded. Both, the time-averaged and the fluctuating dynamic pressure heads are considered as references for the jet scour poten-tial, beside the related pressure coefficients. The investigated measures were proven to be effec-tive in terms of reduced pressures, especially in combination. The relevant parameters of the herein presented measures were systematically varied. This research relates to the Kárahnjúkar spillway model investigation, in which the principal working conditions as canyon topography, jet fall head and discharge spectrum were determined.