PATOLOGIAS EM ESTRUTURAS HIDRÁULICAS DE MACRODRENAGEM REvESTIDAS EM CONCRETO

Belo Horizonte, capital do estado de Minas Gerais, é uma das maiores cidades do Brasil. Uma das suas características particulares é a presença de várias bacias e, por conseqüência, vários cursos d’água que permeiam todo o traçado urbano. Nas últimas décadas, para evitar a ocorrência de inundações durante os períodos de cheia, grande parte desses cursos d’água foi canalizada e revestida em concreto. Nessa concepção, as águas resultantes de precipitações pluviométricas devem ser rapidamente afastadas das áreas urbanas através do aumento de sua velocidade de escoamento. Apesar de ser uma solução rápida e eficaz, essas estruturas em concreto exigem manutenção constante, devido à possibilidade de surgimento de diversas patologias, comuns no concreto como material de construção. Soma-se a esta característica natural, o fato das águas de nossos rios serem misturadas indevidamente às águas servidas (esgotos), o que agrava o aparecimento dessas anomalias, normalmente decorrentes de ações climáticas e atmosféricas. Como exemplos de patologias, podem ser citadas a ocorrência de fissuras, eflorescências, corrosão de armaduras e desgastes do concreto. Dessa forma, este artigo tem como objetivo o estudo de patologias presentes em canais abertos e galerias, revestidos em concreto e dentro do ambiente urbano descrito. O levantamento das patologias foi obtido através de vistoria em diversas estruturas hidráulicas de macrodrenagem, ocasião em que foi realizada cuidadosa análise e cadastramento das anomalias observadas. Após o trabalho de campo, foram realizados estudos e análises, identificando as possíveis causas dos problemas e as soluções adequadas a serem adotadas para cada situação

Swimming performance of the migratory Neotropical fish Leporinus reinhardti (Characiformes: Anostomidae)

The fishways built in Latin America were mainly based on those used in the northern hemisphere for passing salmonids upstream. However, the swimming capacity in terms of speed and endurance is a major factor concerning the design of a fishway, and this information is not available for migratory neotropical fish species. Therefore, studies on swimming performance of neotropical species is fundamental. The aim of this study was to estimate the critical, sustained and prolonged speeds for the piau-três-pintas Leporinus reinhardti, and to evaluate the influence of water temperature on the swimming performance of the species. Variable (increasing) and fixed velocity tests were performed in a respirometer. When compared to other species whose critical speed data are available, the piau showed higher speeds, for a given total length. Fatigue times per prolonged speed class were estimated as well as prolonged speed per fatigue time class. The changing point from sustained to prolonged swimming was estimated to occur approximately at a speed of seven body-lengths per second (1.12 m/s for an individual with 16 cm total length: the first maturation length). In spite of the great swimming performance of piau, the adoption of efficient directives in fishway projects to allow the passage of neotropical ichthyofauna, will depend on a more detailed analysis of the swimming capacity of different species

Swimming performance of epigeal and hypogeal species of Characidae, with an emphasis on the troglobiotic Stygichthys typhlops Brittan & Böhlke, 1965

Swimming performance of fish constitutes a good ecophysiological tool to evaluate the ability of species to use different types of habitats. In order to understand how the swimming performance is related to the hydraulic environment, we compared the critical velocity of five fish (Characidae): Stygichthys typhlops (groundwater troglobiotic); Piabina argentea and Bryconamericus stramineus (riverine); Hemigrammus marginatus (generalist, found in rivers and floodplains) and Psellogrammus kennedyi (lacustrine). Swimming speed tests were performed in a respirometer-type apparatus. Total body length was the variable that best explained the maximum speed attained by all species under study. The critical swimming speed values (in body lengths per second) for each species were as follows: P. argentea (13.75); B. stramineus (9.32); H. marginatus (6.32); P. kennedyi (4.00); and lower in hypogean species, S. typhlops (3.31). All data of this study suggest a strong correlation between swimming performance and the hydraulic environment in which the species are found. The riverine, generalist and lacustrine species (the troglobiotic being included in the last group) showed a trend toward a decrease in speed

Physical habitat simulation for small-sized characid fish species from tropical rivers in Brazil

Physical habitat simulation (PHABSIM) is an important step of the instream flow incremental methodology (IFIM), which is applied to establish environmental flow regimes. This study applied the PHABSIM in two reaches of the Velhas river basin, whose long-term discharges are similar but are under different degrees of impact. Suitability curves were obtained for fish species using traditional methods (Astyanax sp., Piabarchus stramineus, Piabina argentea and Serrapinnus heterodon) and generalized additive models for fish density (Astyanax sp., P. argentea and S. heterodon). The results of habitat use depended on the method for curves generation. Applying the suitability curves by traditional methods, different discharge scenarios were simulated. The flow increasing from a dry scenario to a discharge of 1 year of return promotes a possible habitat increase for all species. However, the same hydrological flow percentiles produce different habitat proportions in different rivers. This work demonstrates that regardless of how suitability curves for the Neotropical species are generated, caution should be taken when applying them. However, the PHABSIM method allows more complex analyses than the traditional approaches based on minimal flow estimations, which is usually applied in South America.</jats:p

Disposal of iron tailings in reservoirs: a GPR application

A large volume of waste is generated by iron mining in Brazil, and the amount has been rapidly increasing. The waste is usually stored in large piles or in reservoirs formed by tailings dams, which occupy large areas in the mining complex. The limitation of natural resources and of new areas for waste disposal has led to change in paradigms. This study therefore aimed to apply a geophysical technique, known as Ground Penetrating Radar (GPR), in order to define sedimentation patterns in the subsurface reservoir created by Diogo's tailings dam in Rio Piracicaba in Minas Gerais, Brazil. To assist the recognition of patterns captured by the GPR, subsurface material samples were collected and analyzed for mineralogical composition, moisture content, electrical conductivity, mineralogical analysis, particle size, X-Ray Diffraction and X-Ray Fluorescence. The results indicated that areas with tailings that had high concentrations of hematite (around 60% in the mineralogical analysis) altered the reflection patterns. The presence of water generated some multiple reflections, which were less significant in shallower sites with more waste and more significant in deeper sites with less waste. In general, the application of the GPR was feasible in aquatic environments with rich subsurface hematite deposits