Author(s): Pedro A. Manso; Erik F. R. Bollaert; Anton J. Schleiss
Linked Author(s): Anton J. Schleiss
Keywords: High-velocity jet; Plunge pool; Dynamic pressures; Confinement
Abstract: The direct impact of falling jets on the riverbed downstream of high dams is often used for dissipation of water energy from floods. The paper presents experimental evidence of the influence of the pool geometry on plunging jet diffusion, based on direct measurements of the dynamic pressures transmitted to the pool bottom. Systematic model tests were performed with circular jets at prototype velocities impacting on flat and non-flat plunge pools. Lateral confinements with confinement diameter to jet diameter ratios of 5. 5, 11 and 16. 5 and heights of 2. 7, 5. 4 and 8. 1 times the diameter of the falling jet, were tested. Dynamic pressures were measured at the pool bottom and inside a closed-end underlying fissure at frequencies of 1 kHz. Dynamic pressure coefficients and density power spectra are presented. Preliminary results show that mean dynamic pressures transmitted to the foundation are reduced by the confinement. Jet development is enhanced, notably for shallow pools. Inside underlying fissures, resonance was observed for a dimensionless pool depth (Y/D = 4. 2), normally associated to core jet impact.