Content analysis of dam break studies for tailings dams with high damage potential in the Quadrilátero Ferrífero,Minas Gerais: technical weaknesses and proposals for improvements     

de Paiva  Camilla Adriane  da Fonseca Santiago  Aníbal  do Prado Filho  José Francisco 《Natural Hazards》2020,104(2):1141-1156

Natural Hazards - Tailings dams are civil structures that have an intrinsic potential risk of failure that, if poorly managed or neglected, can lead to severe societal, environmental, and economic...  相似文献   

Community structure and functional traits of mollusks associated with coastal reef macroalgae in Northeastern Brazil     

Dbora Ferreira Barbosa  Thelma Lúcia Pereira Dias  Srgio de Faria Lopes  Rafaela Cristina de Souza Duarte  Fernanda Maria Duarte do Amaral 《Marine Ecology》2019,40(5)

This study investigated the community structure and functional traits of the mollusk fauna associated with macroalgae with different thallus morphologies in a reef environment in Northeastern Brazil. A total of 15 individuals of each species of macroalgae adhered to natural substrate and 15 individuals of Padina gymnospora detached from the substrate were collected. The structural complexity of algal habitats was measured and the associated malacofauna screened and identified. All three macroalgae differed significantly in the complexity of their habitat, with Sargassum polyceratium being the most complex. A total of 823 specimens of mollusks belonging to 22 species and 11 families were recorded, of which Columbellidae was the most represented with six species. The functional trait “size” revealed that micromollusks smaller than 10 millimeters were predominant in the community; however, individuals of larger sizes (up to 24.54 millimeters) belonging to young stages of other species were also present. Eight functional trophic groups were identified, of which “carnivorous” stood out with seven species. Six functional groups of microhabitats were identified, with intra‐specific variation in habitats, while habitat expansion was documented for species not yet recorded in association with macroalgae. The structure of the molluskan community differed among the three algae species with the greatest richness, abundance, and diversity of mollusks and functional traits occurring with S. polyceratium. Community structure differed between algae adhered to natural substrate and detached algae, with the latter having lower mollusk richness and diversity, but with greater abundance of some species that remained on algal fronds after release from the reef environment. This study reinforces the importance of algal habitat for marine invertebrate fauna, especially for micromollusks that spend their entire life cycle, or part of it, in association with macroalgae.  相似文献   

Decentralized water supply by reservoir network reduces power demand for water distribution in a semi-arid basin     

Antônia Tatiana Pinheiro do Nascimento  Natália Holanda Maia Cavalcanti  Bruno Parente Leitão de Castro 《水文科学杂志》2019,64(1):80-91

In the Brazilian semi-arid region, thousands of small dams have been built over time to enhance water availability, accumulating water and hydraulic energy at high altitudes. Simulations were performed in this study to assess how the arrangement of reservoirs impacts on the power demand for water distribution in the Banabuiú River Basin (19?800 km²), Brazil. The power required to pump water from 1405 reservoirs to all districts with diffuse demands is 6.5 GWh/year, whereas in the scenario with only the 12 larger strategic reservoirs, the power demand reached 45.3 GWh/year. Alone, the largest reservoir in the basin can supply water to all districts. Nonetheless, in that scenario, the power demand would reach 195 GWh/year, which is 30 times the power required in the real reservoir arrangement. Thus, decentralization by small reservoirs not only promotes more democratic access to water, but also increases energy efficiency by storing it at higher altitudes and closer to the diffuse demands.  相似文献   

Influence of connection typology on seismic response of MR‐Frames with and without ‘set‐backs’          下载免费PDF全文

Rosario Montuori  Elide Nastri  Vincenzo Piluso  Marina Troisi 《地震工程与结构动力学》2017,46(1):5-25

The work presented is aimed at the investigation of the influence of beam‐to‐column connections on the seismic response of MR‐Frames, with and without ‘set‐backs’, designed according to the Theory of Plastic Mechanism Control. The investigated connection typologies are four partial strength connections whose structural details have been designed to obtain the same flexural resistance. The first three joints are designed by means of hierarchy criteria based on the component approach and are characterized by different location of the weakest joint component, leading to different values of joint rotational stiffness and plastic rotation supply and affecting the shape of the hysteresis loops governing the dissipative capacity. The last typology is a beam‐to‐column connection equipped with friction pads devoted to the dissipation of the earthquake input energy, thus preventing the connection damage. An appropriate modelling is needed to accurately represent both strength and deformation characteristics, especially with reference to partial‐strength connections where the dissipation of the earthquake input energy occurs. To this aim, beam‐to‐column joints are modelled by means of rotational inelastic springs located at the ends of the beams whose moment‐rotation curve is characterized by a cyclic behaviour which accounts for stiffness and strength degradation and pinching phenomena. The parameters characterizing the cyclic hysteretic behaviour have been calibrated on the base of experimental results aiming to the best fitting. Successively, the prediction of the structural response of MR‐Frames, both regular frames and frames with set‐backs, equipped with such connections has been carried out by means of both push‐over and Incremental Dynamic Analyses. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Seismic characterization of hyperconcentrated flows in a volcanic environment          下载免费PDF全文

Velio Coviello  Lucia Capra  Rosario Vázquez  Victor H. Márquez-Ramírez 《地球表面变化过程与地形》2018,43(10):2219-2231

We present direct observations and monitoring data of a hyperconcentrated flow that occurred along La Lumbre ravine, one of the most active channels of Volcán de Colima in Mexico. Flow properties were inferred from video images and seismic data recorded by a geophone installed outside the channel. We collected flow samples 400 m upstream from the monitoring station and analyzed the variation of sediment concentration and grain‐size distribution over time. A joint analysis of hydrological (i.e. flow velocity, wetted perimeter) and rheological (i.e. yield stress τ_y and dynamic viscosity μ_m ) parameters was performed to characterize the flow. Different flow regimes and sediment transport processes were identified and analyzed in comparison with both the amplitude and spectral features of the seismic signal. We observed differing sediment concentrations at the same discharge, suggesting a decoupling between sediment transport processes and discharge for low‐magnitude flows. A straightforward correlation was found between the amplitude of the seismic signal and the sediment concentration, and a value of 1.8 × 10^?3 mm/s was identified that can be used as a threshold to recognize the hyperconcentrated phase of the flow. This information was tested on the complete seismic dataset gathered at La Lumbre ravine during the 2015 rainy season. We identified the transition from streamflow to hyperconcentrated flow (and/or vice versa) in 16 low‐magnitude events and we validated this result using the video recordings. The correlation between seismic amplitude and sediment concentration is valid at La Lumbre ravine but would need to be tested in other locations for the development of automatic flow classification methods. This work contributes to standardized seismic methods for characterizing flow processes in volcanic environments, also for the development of lahar early warning systems. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

Pyrite as a proxy for the identification of former coastal lagoons in semiarid NE Brazil     

Tiago O. Ferreira  Gabriel N. Nóbrega  Antonia G. B. M. Albuquerque  Lucas R. Sartor  Irlene S. Gomes  Adriana G. Artur  Xosé L. Otero 《Geo-Marine Letters》2015,35(5):355-366

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Estimating quality factor from surface seismic data: A comparison of current approaches     

Bonnie Ives de Castro Nunes  Walter Eugênio de Medeiros  Aderson Farias do Nascimento  José Antonio de Morais Moreira 《Journal of Applied Geophysics》2011,75(2):161-170

The performances of the spectral ratio (SR), frequency centroid shift (FCS), and frequency peak shift (FPS) methods to estimate the effective quality factor Q are compared. These methods do not demand true amplitude data and their implementations were done following an “as simple as possible” approach to highlight their intrinsic potentials and limitations. We use synthetic zero-offset seismic data generated with a simple layer-cake isotropic model. The methods can be ranked from simple to complex in terms of automation as: FPS, FCS and SR. This is a consequence of: (i) peak identification consists basically of a sorting procedure, (ii) centroid estimation involves basically the evaluation of two well-behaved integrals, and (iii) implementation of the SR method involves at least choosing a usable frequency bandwidth and fitting a gradient. The methods can be ranked from robust to sensitive in the presence of noise content in the sequence SR, FCS, and FPS. This is consequence of: (i) the gradient estimate associated to the SR method averages out the noise content in the entire usable frequency bandwidth, (ii) in the presence of moderate-to-high noise level, the centroid estimation is biassed towards overestimating Q due to noise contribution in the tail of the amplitude spectrum, and (iii) peak identification is unstable due to local noise fluctuation in the amplitude spectrum around the peak frequency. Regarding the stability of the estimates relative to the attenuation amount, SR and FCS methods show similar behaviours, whereas FPS method presents an inferior performance. This fact is an indirect consequence of the sensitivity of FPS method to the noise content because the higher is the attenuation the lower is the signal-to-noise ratio. Finally, regarding the robustness of the methods to the presence of dipping layers, only SR and FCS methods provide good estimates, at least to typical dips in non-faulted sedimentary layers, with the estimates obtained with SR method being more accurate that those obtained with FCS method. Except in relation to the automation complexity, which is less important than the performances of the methods, SR method was superior or showed similar performance to FCS method in all scenarios we tried.  相似文献   

The carbonate-hosted willemite prospects of the Zambezi Metamorphic Belt (Zambia)     

Maria Boni  Rosario Terracciano  Giuseppina Balassone  Sarah A. Gleeson  Alexander Matthews 《Mineralium Deposita》2011,46(7):707-729

Zambian willemite (Zn₂SiO₄) deposits occur in the metasedimentary carbonate rocks of the Proterozoic Katangan Supergroup. The most important orebodies are located around Kabwe and contain both sulphides and willemite in dolomites of low metamorphic grade. The Star Zinc and Excelsior prospects (Lusaka area), discovered in the early 1920s, occur in the metamorphic lithotypes of the late Proterozoic Zambezi Supracrustal sequence, which were deposited in a transtensional basin formed during the oblique collision of the Kalahari and Congo cratons. The deposits are hosted by the limestone and dolomitic marbles of the Cheta and Lusaka Formations. Structural analysis indicates that several fracture sets host the deposits, which may be genetically related to the Pan-African Mwembeshi dislocation zone (a major geotectonic boundary between the Lufilian Arc and the Zambezi Belt). In both prospects, willemite replaces the marbles and is found along joints and fissures with open-space filling textures and locally may develop colloform and vuggy fabrics as well. Silver as well as traces of germanium and cadmium have been detected within the willemite ore, and lead or zinc sulphides are scarce or absent. Calcite locally replaces willemite. Willemite is associated with specular hematite and franklinite and post-dates the Zn-spinel gahnite in the paragenesis. Genthelvite [Zn₄Be₃(SiO₄)₃S] occurs as a minor phase in irregular aggregates. The willemites from the Lusaka area, though Mn-poor, show green cathodoluminescence colours and bright green fluorescence in short-wave UV (as the high-temperature willemites in USA). Thermometric analyses of primary fluid inclusions in willemite yield homogenization temperatures that range from 160°C to 240°C and salinities of 8–16 wt.% equiv. NaCl. The homogenization temperatures suggest a hypogene–hydrothermal origin for the willemite concentrations. The geochemistry of fluid inclusion leachates suggests that the hydrothermal fluids were brines derived from highly evaporated seawater. Precise age constraints are currently lacking for the Lusaka area deposits, though the deposits are not deformed, indicating that they post-date the Lufilian orogeny (~520 Ma). The possibility of precursor ores exists; the gahnite–franklinite–willemite deposits could have been derived from a metamorphosed primary sulphide (or even nonsulphide) concentration that has subsequently been completely destroyed. However, there is no real evidence of such a primary source for the willemite mineral association. The Lusaka zinc ores may have been produced by an extensive hydrothermal system, with fluids discharging along basinal fracture zones controlled by the pre-Pan-African rifting stage. A paragenesis similar to that of the Lusaka prospects has been proposed to be a vector towards massive sulphide ores in several parts of the world; therefore, it is possible that these small willemite showings in Zambia may be part of a much bigger, and still unexplored, zinc province.  相似文献   

Selective chemical extraction of heavy metals in tailings and soils contaminated by mining activity: Environmental implications   总被引：1，自引：0，他引：1  

Paulo J.C. Favas  João Pratas  M. Elisa P. Gomes  V. Cala 《Journal of Geochemical Exploration》2011,111(3):160-171

Total concentrations of chemical elements in soils may not be enough to understand the mobility and bioavailability of the elements. It is important to characterise the degree of association of chemical elements in different physical and chemical phases of soil. Another geochemical characterisation methodology is to apply sequential selective chemical extraction techniques. A seven-step sequential extraction procedure was used to investigate the mobility and retention behaviour of Al, Fe, Mn, Cu, Zn, Pb, Cr, Co, Ni, Mo, Cd, Bi, Sn, W, Ag, As and U in specific physical–chemical and mineral phases in mine tailings and soils in the surroundings of the abandoned Ervedosa mine. The soil geochemical data show anomalies associated with mineralised veins or influenced by mining. Beyond the tailings, the highest recorded concentrations for most elements are in soils situated in mineralised areas or under the influence of tailings. The application of principal components analysis allowed recognition of (a) element associations according to their geochemical behaviour and (b) distinction between samples representing local geochemical background and samples representing contamination. Some metal cations (Mn, Cd, Cu, Zn, Co, Cr, Ni) showed important enrichment in the most mobilisable and bioavailable (i.e., water-soluble and exchangeable) fractions due likely to the acidic conditions in the area. In contrast, oxy-anions such as Mo and As showed lower mobility because of adsorption to Fe oxy-hydroxides. The residual fraction comprised largest proportions of Sn and Al and to a lesser extent Zn, Pb, Ni, Cr, Bi, W, and Ag, which are also present at low concentrations in the bioavailable fractions. The elements in secondary mineral phases (mainly Fe, Mn, Cu, Zn, Cd, Pb, W, Bi, Mo, Cr, Ni, Co, As and U) as well as in organic matter and sulphides are temporarily withheld, suggesting that they may be released to the environment by changes in physico-chemical conditions.  相似文献   

Lagrangian predictability assessed in the East China Sea     

Helga S. Huntley  B.L. Lipphardt  A.D. Kirwan 《Ocean Modelling》2011,36(1-2):163-178

A group of 30 surface drifters, launched over a 4 day period as part of a US Navy exercise in early October 2007, are used to assess the predictability of trajectories in a confined geographic region at the northwestern edge of the Kuroshio north of Taiwan. Model trajectories were computed from archives of hourly hindcast velocities from the US Navy East Asian Seas (EAS16) model with 1/16° horizontal resolution. Three metrics are defined for comparing observed and modeled trajectories. All three metrics indicated that model trajectories separated from observations by roughly 15 km after the first 24 h on average. Because of the unique launch strategy for these drifters, with six repetitions of launches from four locations, the dependence of predictability on both launch time and launch location could be assessed separately. Predictive skill displayed only modest dependence on launch time, likely influenced by the passage of a typhoon near the experiment area a few days prior to the first drifter launch. Launch location was a much more reliable indicator of predictive skill, with trajectories for launches closest to the edge of the Kuroshio typically hardest to predict, and those for launches on the shelf, where currents tended to be weaker, predicted more accurately. Comparisons of skill metric statistics for modeled trajectories from hindcasts with and without tides suggested that tidal currents have only a small impact on predictive skill. The influence of archive time and space resolution was also studied using sets of model trajectories computed from hindcast archives that were systematically subsampled separately in space and time. Coarsening by up to a factor of eight in either space or time had little impact on predictive skill. Further coarsening degraded trajectory predictions, particularly when coarsening in time leads to an archive time step too large to adequately resolve the tides. While accurate trajectory predictions remain challenging for ocean models, skill assessments like the one presented here are important for developing error estimates for users of trajectory forecasts and for gaining new insight into potential sources of model errors.  相似文献