Análisis de las acciones para el diseño de cuencos de disipación de energía en el desbordamiento de presas de fábrica

Abstract

The overtopping of dams is commonly adopted in concrete dams as a method for dewatering flood flows and reincorporating water back into the channel through an energy dissipation basin. To ensure the correct functioning of the dams and to avoid erosion and scour downstream of the structure, it is necessary to characterise the hydrodynamic actions present in the plunge pool. Therefore, in this work, a characterisation of pressures, velocities, and aeration rates in the dissipation basin of an overflow weir has been carried out. This Doctoral Thesis consists of two experimental campaigns. On the one hand, the measurement of velocities and aeration rates in the interior of submerged hydraulic jumps was conducted. On the other hand, an experimental campaign of pressures in the bottom of the dissipation basin was carried out. The purpose of the aeration and velocity campaign was to analyse the characteristics of the submerged hydraulic jump, formed downstream of the incident jet. For this purpose, five different hydraulic jumps have been studied, where the void fraction, free surface undulation pattern, phase change frequency, distribution of velocities and mean bubble size inside the dissipation basin have been analysed. The pressure campaign was conducted to characterise the pressure distribution in the bottom of the plunge pool in the time and frequency domain, as well as the energy dissipation of rectangular jets, from the discharge to its restitution in the riverbed. In order to carry out the temporal study of pressures, the data from four studies of rectangular jets carried out in different laboratory facilities were taken into account in conjunction with the present experimental campaign. The comparison of these five studies made it possible to differentiate between two-dimensional and three-dimensional rectangular jets. The mean dynamic pressure, the fluctuating dynamic pressure, the extreme instantaneous pressures at the stagnation point and the pressure distribution around the stagnation point were characterised. To carry out the frequency study of pressures, data were recorded at sampling frequencies of 20, 200 and 1000 Hz, in order to characterise the energy spectra and to analyse the different behaviour of the developed and undeveloped jets under effective and ineffective cushion conditions. In addition, the spectral density function in the vicinity of the stagnation point has been analysed. The energy dissipation has been studied in two-dimensional and three-dimensional rectangular jets. With this, the losses in the air or during the fall of the jet, in the water cushion depth under nappe (produced by the recirculation of the jet) and on the deflection of the jet downstream of the impact zone have been characterised, obtaining a global energy loss law for rectangular jets. Therefore, this Doctoral Thesis contributes to improving the existing knowledge on overtopping phenomena, and with it to achieving greater safety when designing new dams, or in the case of existing dams, improve their adaptation to the presence of more intense floods, due to climate change