Vertedouros em degraus com pré-aeração por um defletor : características do escoamento

Stepped spillways aim to dissipate part of the upstream energy during the flow passage by the chute. However, the use of these structures is limited to a restrict range of specific discharges due to the risk of cavitation damage. As the air entrainment into the flow assists the concrete protection against the aforementioned damages, a possible solution by aerators installed along the chute, already disseminated to smooth chutes, is being studied to be used also in stepped spillways. The purpose of the present paper is to characterize a flow over a stepped chute with induced aeration by deflector and air supply by an airtight chamber trough tests conducted on a reduced scale physical model. The main regions observed during the tests are presented and were developed four equations that allow to approximately predict the location of the main regions for a given spillway.Vertedouros em degraus têm por objetivo dissipar, ao longo da calha, uma parcela da energia do escoamento. No entanto, a utilização dessas estruturas está limitada a uma restrita faixa de vazões específicas devido aos riscos de cavitação e erosão. Como a introdução de ar no escoamento permite a proteção do concreto contra os danos mencionados, uma possível solução por aeradores instalados ao longo da calha, já difundida para calhas lisas, está sendo estudada para ser utilizada também em vertedouros em degraus. A presente pesquisa tem o propósito de caracterizar um escoamento sobre vertedouros em degraus com aeração induzida por defletor e fornecimento de ar por uma câmara de ar através de ensaios realizados em um modelo físico reduzido. São apresentadas zonas e posições características do escoamento observadas durante os ensaios e também, quatro equações que permitem calcular, aproximadamente, a sua localização em um protótipo

Aeração induzida em vertedouros em degraus: pressões médias, entrada de ar e comportamento do escoamento

Stepped spillways can dissipate a great amount of energy during the flow passage over the chute, however these structures have limited operation due to the risk of cavitation damage. The induced aeration may protect the concrete chute through the air concentration near the channel bottom. Furthermore, some research studies have indicated that the presence of air in flows may reduce the mean pressures. The present research aims to analyze mean pressures, air entrainment coefficient and flow behavior over a stepped spillway with aeration induced by two different deflectors, comparing the results to natural aeration flow. Despite the jet impact influence, the induced aeration does not change significantly the mean pressures compared to natural aeration flow. The air entrainment coefficient, as well as the jet impact position, is higher for the deflector with the longer extension and, although air bubbles can be seen throughout the extension of the chute due to the air entrainment through the inferior flow surface, the induced aeration did not anticipate the boundary layer inception point position.Vertedouros em degraus dissipam uma grande quantidade de energia durante a passagem do escoamento pela calha, porém essas estruturas tem sua operação limitada devido a riscos de danos por cavitação. A aeração induzida pode agir protegendo a calha de concreto através da concentração de ar próximo ao fundo do canal. Além disso, algumas pesquisas têm indicado que a presença de ar em escoamentos pode reduzir as pressões médias. A presente pesquisa tem por objetivo analisar as pressões médias, coeficiente de entrada de ar e o comportamento do escoamento sobre uma calha em degraus com dois diferentes defletores, comparando os resultados com um escoamento com aeração natural. Além da influência no ponto de impacto do jato, a aeração induzida não alterou, significantemente, as pressões medias em relação a um escoamento com aeração natural. O coeficiente de entrada de ar, assim como a posição de impacto do jato, é maior para o defletor mais extenso e, embora bolhas de ar possam ser identificadas ao longo de toda a extensão da calha, devido à entrada de ar através da superfície inferior do escoamento, a aeração induzida não antecipou a posição de afloramento da camada limite

Direct seeding in the restoration of post-mined campo rupestre : germination and establishment of 14 native species.

Direct seeding in the restoration of degraded areas requires less financial investment and facilitates the use of greater diversity of species from different functional groups than traditional planting of seedlings. However, the application of this technique in the ecological restoration of post-mined areas in grassland environments is still poorly investigated. This study evaluated seed germination under controlled conditions, seedling establishment and associated costs of 14 species native to the Brazilian campos rupestres through direct seeding in a post-mined area. The effects of the incorporation of plant material (litter) to the degraded substrate on plant establishment were also measured. Under controlled conditions, 64% (9 out of 14) of the evaluated species showed germinability between 30 and 77%. Under field conditions, one year after, it was observed that the incorporation of plant litter to the substrate allowed the establishment of 49 individuals m? 2 of nine species, four of which with establishment percentage and cost per seedling of, respectively, 1.4?6.2% and US$ 0.006?0.09. In the other treatments, no significant plant establishment was observed. Despite the low percentage of establishment, direct seeding combined with the incorporation of plant litter to the substrate allowed the revegetation of a post-mined area with viable cost. The use of suitable species for direct seeding combined with techniques that promote improvements in substrate conditions is critical to increase establishment success using direct seeding in the ecological restoration of campos rupestres post-mined areas. Further studies on techniques to improve substrate quality and seed germination of native species of campos rupestres are require

Vertedouros em degraus com pré-aeração por um defletor : características do escoamento

Stepped spillways aim to dissipate part of the upstream energy during the flow passage by the chute. However, the use of these structures is limited to a restrict range of specific discharges due to the risk of cavitation damage. As the air entrainment into the flow assists the concrete protection against the aforementioned damages, a possible solution by aerators installed along the chute, already disseminated to smooth chutes, is being studied to be used also in stepped spillways. The purpose of the present paper is to characterize a flow over a stepped chute with induced aeration by deflector and air supply by an airtight chamber trough tests conducted on a reduced scale physical model. The main regions observed during the tests are presented and were developed four equations that allow to approximately predict the location of the main regions for a given spillway.Vertedouros em degraus têm por objetivo dissipar, ao longo da calha, uma parcela da energia do escoamento. No entanto, a utilização dessas estruturas está limitada a uma restrita faixa de vazões específicas devido aos riscos de cavitação e erosão. Como a introdução de ar no escoamento permite a proteção do concreto contra os danos mencionados, uma possível solução por aeradores instalados ao longo da calha, já difundida para calhas lisas, está sendo estudada para ser utilizada também em vertedouros em degraus. A presente pesquisa tem o propósito de caracterizar um escoamento sobre vertedouros em degraus com aeração induzida por defletor e fornecimento de ar por uma câmara de ar através de ensaios realizados em um modelo físico reduzido. São apresentadas zonas e posições características do escoamento observadas durante os ensaios e também, quatro equações que permitem calcular, aproximadamente, a sua localização em um protótipo

Life-form spectra of quartzite and itabirite rocky outcrop sites, Minas Gerais, Brazil

Vascular species and their respective life-forms and coverage were recorded in a Brazilian quartzite and itabirite rocky outcrop site at Serra de Ouro Preto, producing the floristic, frequency and vegetational spectra. Three habitats in both lithologies were defined by geomorphology as: 1) Sloped areas near the mountain summit, with grasslands; 2) Plateaus in the middle of the slope, with grasslands; and 3) Lower and/or concave parts of the slopes, with woody savannas. The life-forms followed Raunkiaer's System. We aimed to answer the following questions: Do quartzite and itabirite rocky outcrops have different biological spectra? Are the biological spectra different in the geomorphologic habitats? Do the floristic, vegetational and frequency spectra differ from one another? What spectrum stacks up to a rocky outcrop physiognomy description? The results portrayed that: a) the most represented life-forms were the phanerophytes and hemicryptophytes; b) the floristic and frequency spectra did not differ from each other, but both differed from the vegetational one; c) all the floristic spectra were similar, but there were significant differences in the frequency and vegetational spectra among the lithology and geomorphology habitats; d) higher phanerophyte and lesser hemicryptophyte coverages were found in the itabirite areas and also in the lower or concave parts of the slopes of both lithologies; and e) the vegetational spectrum was more efficient for the studied rocky outcrop comparison. Relationships between the environmental aspects and life-form spectra are discussed. This study will help advance the development of restoration projects for these areas by adding knowledge of their flora composition, structure and function

Exploring Al, Mn and Fe phytoextraction in 27 ferruginous rockyoutcrops plant species.

Worldwide, substrates naturally rich in Al, Fe and Mn are the subject of mining, generating degradation oflarge areas and producing wastes with high pollution potential for water resources, soil and atmosphere,causing harm to human health and ecosystems. The present study investigated the total and phytoavail-able concentration of these elements in soils and leaves of 27 native plant species from ferruginous rockyoutcrops, finding values above the toxic limits described in literature and environmental legislation.Foliar levels of metals varied widely among species, demonstrating different phytoextraction or exclu-sion potentials, which were not explained by the total concentration of elements or available soil fractions.Although most species are not considered hyperaccumulators, the results indicate the existence of speciesrelated to sites of greater availability of certain metals or that can modify soil quality through their dif-ferent phytoextraction skills, with potential future uses in decontamination, stabilization, phytominingand ecological restoration projects

Soil-vegetation relationship in quartzitic and ferruginous Brazilian rocky outcrops.

Campo rupestre is a kind of Brazilian rocky outcrop with high biodiversity and many endemic and threatened species. It occurs mainly in the Espinha?o Range in a contact region between Cerrado and/or Caatinga and Atlantic Forest. The Espinha?o Range is recognized as a region with the highest floristic diversity in South America and with many endemic species, most of which are associated with rocky outcrop environments. These, among other peculiarities, recently granted the Espinha?o Range the status of Biosphere Reserve. The relationship between soil and vegetation was studied in campo rupestre areas with quartzite and itabirite rocks. Three habitats in both lithologies were defined by geomorphology as: 1. Slopes with grasslands; 2. Plateaus with grasslands and 3. Valleys with woody savannas. In each lithology, 30 plots (10 ? 10 m), 10 in each habitat, were defined. The species and their respective coverage were recorded and soil was sampled to perform chemical and physical analyses. The analyzed soils were similar in being sandy, acidic and with low fertility. Nevertheless, they exhibited differences in chemical and physical properties. Altogether there were 272 species, belonging to 70 families. The canonical correspondence analysis of soil variables and species coverage showed a clear segregation of lithological sites due mainly to the exchangeable content of Ca, Cu, Mg, Mn and S; soil particle size ? central tendency and sorting; and the percentage of silt, fine soil and bare rocks. A strong correlation between plant species coverage and soil properties was also found