Ana Inés Borri Genovez

Discharge Rating Curve and Scale Effects Correction in Morning Glory Spillways

Dam spillways are the structures that lead rightly and safely the outflow downstream, so that the dam integrity can be guaranteed. Many accidents with dams have been caused by an inadequate spillway design or insufficient capacity. This situation is particularly important in embankment or rockfill dams, because the possibility of overtopping failure of the dam. The morning glory spillway may be used when there is not available space for a conventional spillway. Engineers use physical modeling to design this kind of structures, and therefore scale effects can cause a difference between model and prototype discharge rating curve. This paper has the objective of analyze the discharge flow rating curve in a vertical shaft with morning glory inlet and to correct scale effects for low heads. An experimental study has been carried out, using the spillway model of Paraitinga Dam in 1:51,02 scale. As a result equations are proposed in order to correct the discharge coefficient in the discharge rating curve for low heads.

Experimental study of transient pressures generated by the impact of a liquid-liquid system

The failure of a structure, either hydraulic or coastal, may be caused by pressure propagation and distribution generated by a fluid impact, that produces uplift pressure. The mechanics of wave impacts are still not properly understood and is a complicated problem, mainly due to the fact that the water interacts with the surrounding air and the air is more compressible than water. The objective of this work was to understand the behaviour of a pressure pulse, generated by a liquid– liquid impact, propagating by a two-phase flow. An experimental facility was constructed, consisting of an upper reservoir and a lower chamber attached to a horizontal steel pipe equipped with pressure transducers. The facility enabled the impact of two masses of water and the propagation of a pressure pulse along the horizontal pipe. The impact generated pressure transients of high intensity. The presence of air in the mixture influenced the duration of the transient and decreased peak pressures.

Analyses of Minimum Submergence and Air Discharge in Vertical Shafts with Different Inlets

Intakes and dropshafts conduct water from the inlet towards a vertical shaft connecting to a tunnel, which has the function of discharging to a hydroelectric power plant, irrigation or water supply system. A problem to the hydraulic engineer is to design an intake taking into account the prevention of vortex formation. Vortex with air entrainment can carry away less efficiency of hydraulic machines, reduction of discharge coefficients and vibration. Critical submergence is one of the factors that most influences vortex formation. This study has the objective of investigating minimum submergence conditions in vertical intakes and air entrainment. An experimental study has been conducted through different vertical intake diameters, varying the intake height, submergence and flow. Vortices were classified from low intensity ones with superficial swirl and no depression, to strong ones with air entrainment. The study also compares different inlet types and flow condition, showing that the air entrainment depends on the geometry inlet, being great for radial ones. Results showed that in order to avoid vortices with air entrainment the minimum necessary rate of submergence to intake diameter should be 0,7. It was determined the discharge coefficient for vertical intakes with and without vortex formation and also an evaluation of air entrainment was done.

Dam Safety Legislation: A Focus on the Different Approaches

Dam engineering calls for a multidisciplinary team, is dependable of local site conditions and many people live in the edges of dams, therefore, it is crucial that a well-elaborated dam safety program is done. Dam safety information is needed from governmental agencies to dam owners, in order to maintain them safe, economically viable and environmentally sustainable. It has been noticed that countries that have specific dam safety laws and regulations are able to guarantee dam, environmental and public safety better than others without them. This work is to present, discuss and compare some issues regarding dam safety laws and regulations, by pointing out their importance for the dam safety evaluation programs and highlighting the stronger points of the ones under study. It is clearly noticed that a great deal of organization and articulation is necessary to guarantee the good functioning of the dam safety program. It surely depends on enforcing specific laws and governmental organization. There are many good examples to be followed by countries that do not have their own dam safety legislation and are willing to enact theirs or to the ones that are to review their existing code.