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

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.     

云南德钦白马雪山岩体热历史及其对青藏高原三江地区构造地貌演化的指示意义

青藏高原三江地区高程缓降、河流及深切峡谷发育,重建其构造-热年代时空演化为把握该地区地形地貌发育演化的内在驱动力提供科学依据。本研究以云南德钦白马雪山岩体为研究对象,开展磷灰石(U-Th)/He及裂变径迹年代学分析,结合已发表的U-Pb和Ar-Ar年代学结果来重塑该地区的构造-热演化历史和地形演化。研究表明,该地区经历了多期快速冷却事件:三叠世的岩浆侵位活动,早白垩世和中-晚始新世的快速冷却,以及中新世和上新世以来的快速剥蚀。青藏高原隆升致使全球气候变化的同时也导致其周缘地区经受强烈侵蚀:中新世以来(21~11Ma)快速冷却速率为10℃/Myr,而上新世以来(ca.5Ma)冷却速率从10℃/Myr增至15℃/Myr。假定区域现今地温梯度为25~35℃/km,河谷剖面不同位置的侵蚀速率及剥蚀量的空间分布特征进一步表明(靠近澜沧江主干道处侵蚀速率远高于其支流,且对应的年龄相对年轻),河流下切及溯源侵蚀的多重效应导致该地区快速剥蚀、剥露,地形起伏加大的瞬态地貌演化规律。     

Local and temporal variations in near‐shore macrobenthic communities associated with submarine groundwater discharges

The influence of submarine groundwater discharges (SGD) on the dynamics of coastal ecosystems is receiving increasing scientific attention, although our knowledge of this issue still remains insufficient. Understanding the ecological response of coastal ecosystems to SGD dynamics is important in order to evaluate and predict changes in coastal communities. The aim of the present study was to characterize the effect of groundwater discharge on subtidal soft‐bottom macrofaunal assemblages in the south coast of Portugal (Algarve) at different times of the year and under different discharge regimes. Sediment macrofauna was sampled twice per season in spring and summer 2011 in two locations: one under influence of SGD (Olhos de Água) and one not under that influence (Arrifes). The results showed that differences in community structure between locations occurred mainly during spring, when the magnitude of groundwater discharge was higher. Several individual taxa were strongly associated with the SGD, particularly during spring: the polychaete families Magelonidae and Oweniidae; the isopod Cyathura carinata; and the bivalves Tellimya ferruginosa and Tellina fabula. Some of these taxa are already considered indicators of SGD, whereas others merit further investigation. The average similarity among samples was consistently larger in the location with SGD and the average similarity between the two locations was generally higher during spring, indicating that SGD promote stability in macrobenthic communities across time and space. SGD were also associated with higher values of Chlorophyll a (Chl a), fine sediments and total abundance of organisms (particularly suspension feeders). This suggests that differences between locations are associated with SGD and mediated by nutrient fluxes and sediment transport, or their interaction.     

Experimental Study of An Aquaculture Net Cage in Waves and Current

Model experiments of a floating fish cage subjected to waves and current have been performed. The objective was to study the dynamic behaviour of the fish cage model in waves and current. The fish cage model was composed of a model net, a flexible floating collar of the circular plastic type and a weight system. It was found that there are many wave periods in which cancellation of the wave-induced forces on the model occur. These cancellation wave periods are within the range of dimensioning wave periods commonly used for testing of fish farm structures and hence are important to be aware of. Large deformations of the net under realistic wave and current conditions were observed, where contact between the net and other parts of the structure were identified. This may cause damages to the net due to abrasion.     

Secular and tidal evolution of circumbinary systems

We investigate the secular dynamics of three-body circumbinary systems under the effect of tides. We use the octupolar non-restricted approximation for the orbital interactions, general relativity corrections, the quadrupolar approximation for the spins, and the viscous linear model for tides. We derive the averaged equations of motion in a simplified vectorial formalism, which is suitable to model the long-term evolution of a wide variety of circumbinary systems in very eccentric and inclined orbits. In particular, this vectorial approach can be used to derive constraints for tidal migration, capture in Cassini states, and stellar spin–orbit misalignment. We show that circumbinary planets with initial arbitrary orbital inclination can become coplanar through a secular resonance between the precession of the orbit and the precession of the spin of one of the stars. We also show that circumbinary systems for which the pericenter of the inner orbit is initially in libration present chaotic motion for the spins and for the eccentricity of the outer orbit. Because our model is valid for the non-restricted problem, it can also be applied to any three-body hierarchical system such as star–planet–satellite systems and triple stellar systems.     

Gully-head morphology and implications for gully development on abandoned fields in a semi-arid environment,Sierra de Gata,southeast Spain

In this paper we examine whether gully-head morphology can be used as an indicator for gully development and, hence, for sediment production. A survey was conducted at five hillslopes in the Sierra de Gata where different types of channel heads occur close to each other. The survey included measurements of morphologic and pedologic properties, ground surface, channel and catchment characteristics of every gully head present (n = 59). On the basis of the observed morphologies, the heads were subdivided into four types: gradual, transitional (a short inclined section), abrupt and rilled-abrupt. The analyses showed that it is possible to explain the differences of gully heads and the role of some environmental factors on the basis of their morphologies, at least for the gradual and the abrupt types. The results suggested that steep headcuts (abrupt) were formed from secondary headcuts in the channel, which migrated upstream. The abrupt headcuts were always formed in more than one soil layer of which one was a resistant (stony) layer. However, shear strength measurements (at saturation) showed that the top layer was not always the most resistant one. Width–depth relationships indicated that gradual type headcuts were controlled by fluvial processes and abrupt headcuts by a combination of fluvial and mass-wasting processes. Gradual types occurred more downslope than the abrupt types suggesting that the incisions started by fluvial processes and migrated upwards when knickpoints developed in the channel. The rilled-abrupt types are still actively retreating. Thus, the abrupt types correspond to slower retreat rates. Abrupt gully heads may deteriorate into transitional types when plunge-pool erosion becomes less effective. The conceptual model is supported by data from ephemeral gullies in two other study areas (Sierra de la Torrecilla, Spain, and Alentejo, Portugal). Copyright © 1999 John Wiley & Sons, Ltd.     

Unstably stratified geophysical fluid dynamics

The linear dynamics of the unstably stratified geophysical flows is investigated with a two-layer formulation. A ‘convective’ deformation radius classifies the dynamics into three regimes:

• 1. 

  1. the scales smaller than the deformation radius: the dynamics characterized by unstable inertial-gravity modes;

• 2. 

  2. the scales larger than the deformation radius: a quasi-geostrophic regime;

• 3. 

  3. the scales close to the deformation radius, where the dynamics transits from the inertial-gravity regime to the quasi-geostrophic regime.

The Rossby wave can propagate eastward in the unstably stratified quasi-geostrophic regime. The baroclinic instabilities are basically realized as a larger-scale extent of the inertial-gravity instabilities, but the former can be isolated from the latter in a limit of small β-effect, with a very deep lower layer. The results suggest that the convectively unstable Jovian atmospheric dynamics can be well described as a quasi-geostrophic system.     

Clay minerals in fluvial shaley sandstone of upper Triassic reservoir (TAGS)—Toual field SE Algeria: identification from wireline logs and core data

The creep property of rock under cyclic loading is very important in civil engineering. In order to establish a novel constitutive equation for rock under cyclic loading, a fractional-order viscoplastic body under cyclic loading was constructed based on fractional-order viscous element. A fractional-order visco-elastoplastic model (FVEPM) for rock was established by connecting constructed fractional-order viscoplastic body with Burgers model. The model was a Burgers model when the maximum value of cyclic loading was less than the critical strength of rock; otherwise, it was a FVEPM which can be used to reflect the transient, steady-state, and tertiary creep phases of rock. The cyclic loading was decomposed into a static load and a cyclic loading with a zero average stress. According to rheological mechanics theory, the rheology constitutive equation of rock under the static load can be derived. According to viscoelastic mechanics theory, the constitutive equation under cyclic loading with a zero average stress was established by introducing the variation parameters of energy storage and energy dissipation compliance caused by rock damage and fracture. Finally, a new dynamic constitutive equation of rock cyclic loading can be obtained by superimposing the constitutive equation under static load and cyclic loading with a zero average stress. Compared with existing test results of rock under cyclic loading, the proposed constitutive model can be used to describe the creep characteristics of rock under cyclic loading and reflect the presented fluctuation of strain curve of rock under cyclic loading.