GEOMETRY INFLUENCE AND DISCHARGE RATING CURVE CORRECTION IN MORNING GLORY SPILLWAYS

摘要

Spillways are structures that control the water level in a reservoir, ensuring the dam safety. Since the main cause of dam failures is related to poor discharge flooding design, the adequate determination of the discharge rating curve of the spillway is an essential parameter. Depending on the characteristics of the dam section, a morning glory spillway is an alternative to the conventional ones, as it is placed inside the reservoir. It consists of a conventional crest followed by a vertical shaft, then, a circular bend ending up into a tunnel. Each one of these components has its own design criterion. The use of physical modelling and the advances of computational modelling make the design of the structure accurate. This paper has the objective of analyze the discharge rating curve of the morning glory spillway, using a novel parabolic type bend and compare it with a 90° circular bend and a polycentric bend with variable radius. The authors carried out an experimental study in 1:51,02 scale, using the spillway model of Paraitinga Hydropower, Brazil, in the Laboratory of Fluid Mechanics and Hydraulics, School of Civil Engineering, Architecture and Urbanism, University of Campinas, Brazil. The new bend geometry presented an increase in the discharge rating curve, indicating that this geometry should be considered for the design of morning glory spillways.