Damaging flood severity assessment in Northern Portugal over more than 150 years (1865–2016)     

Mónica Santos  Marcelo Fragoso  João A. Santos 《Natural Hazards》2018,91(3):983-1002

Floods are a major natural hazard, with vast implications over a wide range of socio-economic activities. A harmonized post-flood classification is critical for a better understanding of this hazard, by providing homogeneous flood catalogues for future research on triggering mechanisms. We apply a flood severity index (FSI) to damaging floods in Northern Portugal over a 152-year period (1865–2016) and identify the most critical areas to flood occurrences. The index is a damage-based post-event assessment tool, which includes five categories ranging from minor flooding (1) to catastrophic flooding (5). FSI is applied to a historical damaging flood database with 2318 occurrences. In Northern Portugal, serious floods (3) are the most frequent typology, while catastrophic floods are typically river floods occurring in the Douro basin. Overall, damaging flood occurrences are favoured by the positive phase of the East Atlantic pattern and by the negative phase of the North Atlantic Oscillation. Furthermore, the north-western areas reveal higher concentrations of damaging flood occurrences, mainly due to higher population density, higher precipitation values and more flood plain areas. In particular, 48% of all occurrences are concentrated in the Porto Metropolitan Area, mainly the Porto city centre and nearby riverside areas of the Douro River. High-population density and heavily urbanized areas lead to greater exposure to flood risk, whereas the most peripheral municipalities, with large agricultural/forested areas, show much lower numbers of damaging floods. FSI is tool to communicate the magnitude of the flood risk and is, therefore, of foremost relevance to civil protection and risk management.  相似文献   

The bubble bursts for cavitation in natural rivers: laboratory experiments reveal minor role in bedrock erosion          下载免费PDF全文

Paul A. Carling  Mauricio Perillo  Jim Best  Marcelo H. Garcia 《地球表面变化过程与地形》2017,42(9):1308-1316

The erosion of rock‐bedded channels generally is considered a slow process caused mainly by abrasion due to bedload or suspended sediments, but the mechanisms of rapid erosion remain unclear. Cavitation is a clear‐fluid erosive process, well known for its effect on engineering structures, when water vapour bubbles collapse and the resultant pressure shocks erode the boundary. However, although the occurrence of cavitation erosion in natural watercourses has long been a matter of debate, as yet there are no incontrovertible examples of cavitation damage to natural river beds. Using flume experiments, we show for the first time that only weakly‐cavitating clear‐water flows can occur for the range of flow velocities observed in rivers, and these do not erode medium‐hardness rocks after 68 hours. During this time period, only a very soft rock featured erosional marks due to dissolution. Thus, our results cast significant doubt on the likelihood of identifying cavitation damage in most rivers, and provide pointers to those river systems that might be investigated further to identify cavitation erosion. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Spatial distribution of morphometric parameters of glacial cirques in the Central Pyrenees(Aran and Boí valleys)     

Luis LOPES  Marc OLIVA  Marcelo FERNANDES  Paulo PEREIRA  Pedro PALMA  Jesús RUIZ-FERNáNDEZ 《山地科学学报》2018,15(10):2103-2119

Glacial cirques are typical landscape features of mid-latitude mountain environments like the Central Pyrenees. Their morphology as well as their spatial distribution provides insights about past glaciers and climates. In this study, we examine the distribution, morphometrical and topographical characteristics of glacial cirques in two U-shaped glacial valleys located in the Central Pyrenees – the Aran and the Boí valleys. They are located in different aspects of this mountain range(north vs south) under different climatic influences that promoted distinct glaciation patterns during the late Pleistocene. The spatial mapping of these landforms was carried out using high-resolution imagery and field observations. We analysed the data of the morphometrical and topographical variables of the glacial cirques by using different statistical and geospatial methods in order tounveil the factors controlling their formation and development. A total of 186 glacial cirques were mapped in the study area, including 119 in the Aran and 67 in the Boí valleys. The local topography and microclimate conditions lead to substantial differences in both areas in terms of the morphology and dimensions of the cirques. Glacial cirques in Boí are distributed at slightly higher elevations than in Aran and they are also larger, though their dimensions decrease with elevation in both valleys. Aran cirques are mostly oriented NE, while Boí landforms do not show any prevailing aspect. Even though lithology does not control the distribution of the glacial cirques, some specific lithological settings may favour the development of larger cirques. In general, glacial cirques in the Aran and the Boí valleys show morphometrical properties similar to those reported in other mid-latitude mountain ranges.  相似文献   

Comparative reproductive biology of two southwestern Atlantic populations of the hermit crab Pagurus exilis (Crustacea: Anomura: Paguridae)     

Mariana Terossi  Lucas S. Torati  Ivana Miranda  Marcelo A. Scelzo  Fernando L. Mantelatto 《Marine Ecology》2010,31(4):584-591

Pagurus exilis (Benedict, 1892) is an endemic South Atlantic hermit crab with a distribution ranging from Rio de Janeiro State, Brazil, to Buenos Aires Province, Argentina. The present study analyzed the reproduction of two populations at the extremes of this geographical distribution, and compared their reproductive period, fecundity, and changes in egg size and egg volume during the incubation period in order to assess the variability over this latitudinal range. Hermit crabs were collected monthly over a 2‐year period. In total, 108 females were analyzed for Brazil (44 non‐ovigerous and 64 ovigerous), and 141 for Argentina (87 non‐ovigerous and 54 ovigerous). Reproduction in Brazil occurs year‐round, with peaks in the fall and winter seasons; in Argentina reproduction occurs only in spring and summer. The Brazilian ovigerous females were significantly larger than the Argentina ones (Brazil: SL = 5.33 ± 1.45 mm; Argentina: SL = 4.15 ± 0.52 mm; P < 0.001). The fecundity was 1447 ± 831 eggs (317 to 2885) in Brazil and 987 ± 711 eggs (114 to 2665) in Argentina, with a trend towards higher fecundity in Brazil. Eggs in the Argentina population were larger than those in Brazil for all the three stages investigated, and no changes in egg volume were found during egg development for both populations. The reproductive traits of the two populations showed some important differences, which may reflect adaptations to local environmental conditions, demonstrating a high plasticity of reproductive features of the species in Brazilian and Argentine waters. The strategy adopted by the Argentina population involves a lower production of larger eggs compared to the population in Brazil; this lower production is associated with reproduction in cold‐water regions.  相似文献   

Understanding how environmental heterogeneity and elevation drives the distribution of woody communities across vegetation types within the campo rupestre in South America     

Marcelo Leandro BUENO  Vanessa Leite REZENDE  Luiza Fonseca A.DE PAULA  Joo Augusto Alves MEIRA-NETO  José Roberto Rodrigues PINTO  Andreza Viana NERI  Vanessa PONTARA 《山地科学学报》2021,(5):1192-1207

The campo rupestre sensu lato is a vegetation type that occurs in South American mountains, supports a distinctive flora characterized by high rates of endemism, high herbaceous species richness and often-neglected but also species-rich of the arboreal stratum. We aimed to investigate how environmental factors and elevation are associated with the distribution and diversity of woody species in different rupestrian vegetation types across South America. Using a database of 2,049 woody species from 185 sites across four vegetation types within the campo rupestre, we assessed how the vegetation types were grouped according to their floristic composition and number of shared indicator species, as well as by using different beta diversity indices. The most important variables from a set of 27 variables(e.g. altitude, geo-edaphic and climatic) explaining species distribution were identified using redundancy analysis(RDA) and variation partitioning methods. The distribution of vegetation types was related to both environmental and spatial fractions, with a set of 17 variables retained(e.g. rockiness, grass cover and temperature seasonality as the most important variables). There was an association between the floristic composition of each vegetation type and the elevation range. Although the identified vegetation types are floristically related, they are distinguished by exclusive and habitat-specialist woody species. This uniqueness of vegetation types should be considered in terms of complementarity for the conservation of campos rupestres.  相似文献   

Sequence stratigraphic framework of Proterozoic successions in eastern Brazil   总被引：1，自引：0，他引：1  

Marcelo A. Martins-Neto 《Marine and Petroleum Geology》2009

First-order regional unconformities separate Proterozoic supracrustal rocks of the gas-bearing São Francisco craton and surrounding thrust-and-fold belts (eastern Brazil) into four genetic stratigraphic units, which constitute 1st-order basin-fill sequences (Espinhaço, Canastra–Paranoá–Vazante, Macaúbas and Bambuí sequences).  相似文献   

A nonlinear model of parametric rolling stabilization by anti-roll tanks     

Marcelo A.S. Neves  Jorge A. Merino  Claudio A. Rodríguez 《Ocean Engineering》2009,36(14):1048-1059

The present paper describes a mathematical model in which the fluid motion inside a U-tank is nonlinearly coupled to the heave, roll and pitch motions of the ship. The main purpose of the investigation is centred on the control of roll motion in the case of parametric resonance in longitudinal waves. A transom stern small vessel, known to be quite prone to parametric amplification, is employed in the study. Four tank designs are employed in order to study the influence of tank mass, tank natural frequency and tank internal damping on the control of parametric rolling at different head seas conditions. Additionally, the influence of the vertical position of the tank is also investigated. The main results are presented in the form of limits of stability, with encounter frequency and wave amplitudes as parameters. Distinct dynamical characteristics are discussed and conclusions are drawn on the relevant parameters for the efficient control of the roll amplifications in head seas.  相似文献   

Drivers of peatland water table dynamics in the central Andes,Bolivia and Peru     

David J. Cooper  Jeremy Sueltenfuss  Eduardo Oyague  Karina Yager  Daniel Slayback  E. Marcelo Cabero Caballero  Jaime Argollo  Bryan G. Mark 《水文研究》2019,33(13):1913-1925

Cushion plant dominated peatlands are key ecosystems in tropical alpine regions of the Andes in South America. The cushion plants have formed peat bodies over thousands of years that fill many valley bottoms, and the forage produced by the plants is critical for native and nonnative domesticated mammals. The sources and flow paths of water supporting these peatlands remain largely unknown. Some studies have suggested that glacier meltwater streams support some peatlands, and that the ongoing loss of glaciers and their meltwaters could lead to the loss or diminishment of peatlands. We analysed the hydrologic regime of 10 peatlands in four mountain regions of Bolivia and Peru using groundwater monitoring. Groundwater levels in peatlands were relatively stable and within 20 cm of the ground surface during the rainy season, and many sites had water tables 40–90 cm below the ground surface in the dry season. Topographic and groundwater elevations in the peatlands demonstrated that the water source of all 10 peatlands was hillslope groundwater flowing from lateral moraines, talus, colluvium, or bedrock aquifers into the peatlands. There was little to no input from streams, whether derived from glacier melt or other sources, and glacier melt could not have recharged the hillslope aquifers supporting peatlands. We measured the stable water isotopes in water samples taken during different seasons, distributed throughout the catchments, and the values are consistent with this interpretation. Our findings indicate that peatlands in the study region are recharged by hillslope groundwater discharge rather than stream water and may not be as vulnerable to glacial decline as other studies have indicated. However, both glaciers and peatlands are susceptible to changing thermal and precipitation regimes that could affect the persistence of peatlands.  相似文献   

Numerical study on the effect of rigid inclusions on existing railroads     

Dong Wang  Marcelo Sánchez  Jean-Louis Briaud 《国际地质力学数值与分析法杂志》2019,43(18):2772-2796

Railroad track problems have been exacerbated by the continuous increase in freight loads and train traffic. The need to implement soil improvement technique in a relatively short window-time (ie, to minimize train-traffic disruption) is a key aspect to be considered when adopting a convenient remedial solution to control settlements in railroads constructed on problematic subgrades. Rigid inclusions are selected in this paper because they are reliable solutions relatively easy to implement. Furthermore, they can be used in different ground conditions and are suitable for short construction times (eg, do not require a curing time, as in grouting methods). Typical (analytical) methods for the design of rigid inclusions are adopted in this paper to define an optimal distribution of piles for the case of existing railroads. The selected layout is then analyzed in detail by means of a 3-D dynamic finite element simulator using both, elastoplastic and elastic models. The performance of rigid inclusions is studied considering different operational scenarios, with dynamic and static loads, as well as involving subgrades with different plasticity index values. It is found that the predictions from the analytical design methods for rigid inclusion tend to be unconservative when compared against the finite element results. As for the numerical solutions, the most unfavorable stress condition is associated with the dynamic elastoplastic finite element solution. It is estimated that the rigid inclusions will contribute to a reduction in the ground settlements of around 15% to 20%, depending on the subgrade plasticity index.  相似文献   

General relativity with variable speed of light and Pioneers anomaly     

Marcelo Samuel Berman 《Astrophysics and Space Science》2011,336(2):327-329

We consider a General Relativistic RW’s metric, with variable speed of light, and find a field of Universal acceleration, numerically coincident with the value of the Pioneers anomalous one. This deceleration may decrease with time, as we calculated. This is relevant to understand the Physics that may be involved in the Cosmological approach to the Pioneers anomaly.  相似文献