Proposta de reabilitação hidráulica do sistema extravasor da PCH Pedra do Garrafão utilizando vertedouro em tecla de piano (PKW)

Abstract

Extreme hydrological events, such as severe droughts and floods, have been intensifying, posing significant challenges to global water security. These events directly impact water resource management, highlighting the need to adapt existing hydraulic infrastructure. In Brazil, despite the abundance of water resources and the prominent role of renewable sources in the energy matrix—particularly hydroelectric power—many projects were developed using limited historical data series. With advancements in hydrological monitoring and modeling technologies, it has become evident that several dams have undersized spillways, which increases the risk of structural failure during extreme flood events. In this context, conducting risk assessments is essential to determine whether both existing and planned dams meet established safety criteria or require interventions, such as structural reinforcement or increased discharge capacity. This monograph presents a case study of the Pedra do Garrafão Small Hydropower Plant, with the objective of analyzing changes in design flow rates and the discharge capacity of the existing spillway, based on updated hydrological studies considering a ten-thousand-year return period. The adopted methodology was divided into four stages: (i) a literature review, including technical and academic references on labyrinth and Piano Key Weir (PKW) spillways; (ii) characterization of the study area and hydrological update, including flood discharge estimation and the current spillway’s rating curve; (iii) modeling and design of a PKW spillway, based on geometric parameters and discharge coefficients proposed by Kabiri-Samani and Javaheri (2012); and (iv) a comparative analysis between the hydraulic performance of the existing labyrinth spillway and a proposed PKW, considering the latter as a potential rehabilitation solution for the structure. The results indicated an estimated 10,000-year flood discharge of 1,679 m³/s — approximately 34% higher than the value previously adopted in the original studies (1,250 m³/s). The current labyrinth spillway's verified discharge capacity of 966.73 m³/s proved insufficient for the updated design flood. The proposed PKW, occupying only about half the length of the labyrinth, showed equivalent hydraulic performance. Furthermore, the PKW maintained the upstream water level below the dam crest, while the labyrinth exhibited slight overtopping. Although neither configuration fully met the minimum freeboard criterion, the PKW presented a comparatively safer condition, with the potential for structural adequacy through a crest elevation increase of 44 cm.