Segurança de barragens no Brasil: um breve comparativo com a legislação internacional e análise da influência da cobertura do solo de APPs sobre manchas de inundação (estudo de caso da PCH Pedra Furada, Ribeirão–PE)
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Data
2019-07-30
Autores
Pereira, Ludmilla Freitas
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Universidade Estadual Paulista (Unesp)
Resumo
O Brasil, frente aos acidentes ocorridos em Mariana – MG (2015) e em Brumadinho – MG (2019), tem vivenciado inúmeras discussões no que tange à assuntos regulatórios e à confiabilidade das barragens construídas no país. Neste trabalho, inicialmente, fez-se um breve comparativo entre a legislação brasileira e alguns normativos internacionais (China, Portugal, Estados Unidos e África do Sul) sobre segurança de barragens, observando-se a existência de diferentes aspectos abordados entre eles. A Política Nacional de Segurança de Barragens se demonstrou uma das regulamentações menos rígidas entre as analisadas quanto a pré-requisitos técnicos para sua aplicação, deixando grande parte das barragens de pequeno porte dispensadas do cumprimento de algumas obrigações. Além disto, a legislação federal brasileira foi implementada há menos de uma década, o que implica, atualmente, em uma dificuldade muito grande do empreendedor, dos órgãos fiscalizadores e do governo federal a se adaptarem a possuir esta cultura de segurança de barragens. Diante da interface destas construções com o meio ambiente, faz-se necessário um monitoramento constante das estruturas por uma equipe multidisciplinar e um programa de segurança consistente que vise garantir a integridade do meio ambiente nas áreas de influência das barragens, bem como resguardar o bem-estar e a vida da população situada a jusante. O uso de funções matemáticas e softwares para o mapeamento das áreas sujeitas aos riscos impostos pelas barragens é um avanço grandioso no aspecto de segurança destas estruturas. Neste contexto, o presente estudo teve por objetivo prático principal analisar a influência da cobertura do solo das áreas de preservação permanente (APPs) a jusante da barragem da PCH Pedra Furada, localizada no município de Ribeirão no estado de Pernambuco, sobre características de manchas de inundação referentes a vazões hipotéticas para tempos de retorno de 10 e 10.000 anos, defluentes deste empreendimento. Foram utilizados dados de levantamento de campo como ortofotos e topografia (obtidas por VANT) assim como informações batimétricas cedidos pela empresa proprietária do empreendimento e, também, dados hidrológicos da Agência Nacional de Águas. Por meio da simulação do modelo hidrodinâmico bidimensional HEC-RAS 5.0.7, em regime transiente, variou-se os coeficientes de rugosidade (Manning) das faixas marginais ao rio Sirinhaém, fazendo-se análises em seções distantes 5, 15 e 25 km do barramento. Os resultados demonstraram que para um aumento de oito vezes da rugosidade da APP, reduziu-se o tempo de chegada de onda em 2h50 min para o cenário de TR=10 anos e em 2h10min para o cenário de TR=10.000 anos na seção distante 25 km da barragem. Já para a seção mais próxima ao barramento, este aumento de rugosidade levou ao acréscimo de profundidades da água de, cerca de, 2 metros dentro da calha fluvial, para ambos cenários de vazão. Assim, conclui-se que APPs vegetadas representam menor intensidade sobre planícies de inundações mais próximas do barramento, enquanto que, para as planícies mais distantes, representam uma janela de tempo maior para a implementação de ações contingenciais, caracterizando-se, assim, como uma boa contribuição para o rol de elementos de segurança de barragens.
Brazil, faced with the accidents that occurred in Mariana - MG (2015) and in Brumadinho - MG (2019), has experienced numerous discussions regarding regulatory issues and the reliability of the dams built in the country. In this work, it was made a brief comparison between Brazilian legislation and some international regulations (China, Portugal, United States and South Africa) on dam safety, observing the existence of different aspects addressed among them. The National Dams Safety Policy demonstrated one of the less rigid regulations among those analyzed regarding technical prerequisites for their application, leaving most of the small dams exempted from compliance with certain obligations. In addition, Brazilian federal legislation was implemented less than a decade ago, which currently implies a great difficulty for the entrepreneur, the inspection agencies and the federal government to adapt to having this dam safety culture. In view of the interface of these constructions with the environment, it is necessary a constant monitoring of the structures by a multidisciplinary team and a consistent safety program that aims to guarantee the integrity of the environment in the areas of influence of the dams, as well as to protect the well-being and the life of the downstream population. The use of mathematical functions and softwares for the mapping of the areas subject to the risks imposed by the dams is a great advance in the safety aspect of these structures. In this context, the main objective of the present study was to analyze the influence of the soil cover of the permanent preservation areas (PPAs) downstream of the Pedra Furada Hydroelectric Power Plant, located in the city of Ribeirão in the state of Pernambuco, hypothesis flow rates for return times of 10 and 10,000 years, defluents of this dam. Field survey data such as orthophotos and topography (obtained by drone) were used as well as bathymetric information provided by the company that owns the project and hydrological data from the National Water Agency. By means of the simulation of the two-dimensional hydrodynamic model HEC-RAS 5.0.7, in the transient regime, the roughness coefficients (Manning) of the marginal banks of the Sirinhaém river were varied, being analyzed in sections distant 5, 15 and 25 km of the dam. The results showed that for an eight-fold increase in PPA roughness the wave arrival time was reduced in 2h50 min for the 10-year scenario and at 2h10min for the 10,000- year scenario in the 25 km distant section of the dam. As for the section closest to the dam, this increase of roughness led to the addition of water depths of about 2 meters inside the rain gutter, for both flow scenarios. Thus, we conclude that vegetated PPAs represent a lower intensity on flood plains closer to the dam, whereas for the more distant plains, they represent a larger window of time for the implementation of contingency actions, is thus a good contribution to the role of dam safety elements.
Brazil, faced with the accidents that occurred in Mariana - MG (2015) and in Brumadinho - MG (2019), has experienced numerous discussions regarding regulatory issues and the reliability of the dams built in the country. In this work, it was made a brief comparison between Brazilian legislation and some international regulations (China, Portugal, United States and South Africa) on dam safety, observing the existence of different aspects addressed among them. The National Dams Safety Policy demonstrated one of the less rigid regulations among those analyzed regarding technical prerequisites for their application, leaving most of the small dams exempted from compliance with certain obligations. In addition, Brazilian federal legislation was implemented less than a decade ago, which currently implies a great difficulty for the entrepreneur, the inspection agencies and the federal government to adapt to having this dam safety culture. In view of the interface of these constructions with the environment, it is necessary a constant monitoring of the structures by a multidisciplinary team and a consistent safety program that aims to guarantee the integrity of the environment in the areas of influence of the dams, as well as to protect the well-being and the life of the downstream population. The use of mathematical functions and softwares for the mapping of the areas subject to the risks imposed by the dams is a great advance in the safety aspect of these structures. In this context, the main objective of the present study was to analyze the influence of the soil cover of the permanent preservation areas (PPAs) downstream of the Pedra Furada Hydroelectric Power Plant, located in the city of Ribeirão in the state of Pernambuco, hypothesis flow rates for return times of 10 and 10,000 years, defluents of this dam. Field survey data such as orthophotos and topography (obtained by drone) were used as well as bathymetric information provided by the company that owns the project and hydrological data from the National Water Agency. By means of the simulation of the two-dimensional hydrodynamic model HEC-RAS 5.0.7, in the transient regime, the roughness coefficients (Manning) of the marginal banks of the Sirinhaém river were varied, being analyzed in sections distant 5, 15 and 25 km of the dam. The results showed that for an eight-fold increase in PPA roughness the wave arrival time was reduced in 2h50 min for the 10-year scenario and at 2h10min for the 10,000- year scenario in the 25 km distant section of the dam. As for the section closest to the dam, this increase of roughness led to the addition of water depths of about 2 meters inside the rain gutter, for both flow scenarios. Thus, we conclude that vegetated PPAs represent a lower intensity on flood plains closer to the dam, whereas for the more distant plains, they represent a larger window of time for the implementation of contingency actions, is thus a good contribution to the role of dam safety elements.
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Palavras-chave
Segurança de barragens, Legislação, Cobertura do solo, Coeficiente de rugosidade de Manning, Áreas de preservação permanente, HEC-RAS, Inundação, Dams safety, Legislation, Soil coverage, Manning's roughness coefficients, Permanent preservation areas, Flood