Evaluation of approaches to calculate debris-flow parameters for hazard assessment

Many different runout prediction methods can be applied to estimate the mobility of future debris flows during hazard assessment. The present article reviews the empirical, analytical, simple flow routing and numerical techniques. All these techniques were applied to back-calculate a debris flow, which occurred in 1982 at La Guingueta catchment, in the Eastern Pyrenees. A sensitivity analysis of input parameters was carried out, while special attention was paid to the influence of rheological parameters. We used the Voellmy fluid rheology for our analytical and numerical modelling, since this flow resistance law coincided best with field observations. The simulation results indicated that the “basal” friction coefficients rather affect the runout distance, while the “turbulence” terms mainly influence flow velocity. A comparison of the velocity computed on the fan showed that the analytical model calculated values similar to the numerical ones. The values of our rheological parameters calibrated at La Guingueta agree with data back-calculated for other debris flows. Empirical relationships represent another method to estimate total runout distance. The results confirmed that they contain an important uncertainty and they are strictly valid only for the conditions, which were the basis for their development. With regards to the simple flow routing algorithm, this methods could satisfactorily simulate the total area affected by the 1982 debris flow, but it was not able to directly calculate total runout distance and velocity. Finally, a suggestion on how different runout prediction methods can be applied to generate debris-flow hazard maps is presented. Taking into account the definition of hazard and intensity, the best choice would be to divide the resulting hazard maps into two types: “final hazard maps” and “preliminary hazard maps”. Only the use of numerical models provided final hazard maps, because they could incorporate different event magnitudes and they supplied output-values for intensity calculation. In contrast, empirical relationships and flow routing algorithms, or a combination of both, could be applied to create preliminary hazard maps. The present study only focussed on runout prediction methods. Other necessary tasks to complete the hazard assessment can be looked up in the “Guidelines for landslide susceptibility, hazard and risk zoning” included in this Special Issue.     

Understanding historical coastal spit evolution: A case study from Spurn,East Yorkshire,UK

Globally sandy coastlines are threatened by erosion driven by climatic changes and increased storminess. Understanding how they have responded to past storms is key to help manage future coastal changes. Coastal spits around the world are particularly dynamic and therefore potentially vulnerable coastal features. Therefore, how they have evolved over the last few centuries is of great importance. To illustrate this, this study focuses on the historical evolution of a spit at Spurn on the east coast of the UK, which currently provides critical protection to settlements within the Humber estuary. Through the combination of digitized historical mapping and luminescence dating, this study shows that Spurn has been a consistent coastal feature over at least the past 440 years. No significant westward migration was observed for the last 200 years. Results show a long-term extension of the spit and a decrease in its overall area, particularly in the last 50 years. Breaches of the neck cause temporary sediment pathway changes enabling westward extension of the head. Use of digitized historical maps in GIS combined with OSL dating has allowed a more complete understanding of long-term spit evolution and sediment transport modes at Spurn. In doing so it helps inform future possible changes linked to pressures, such as increases in storm events and sea-level rise. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

A study of Brans-Dicke theory in FRW-model

In FRW space time Brans-Dicke theory is developed for two cases: (i) the vacuum and (ii) the perfect fluid model. The field equations are transformed into a much simpler form under a change of time co-ordinates and then the solutions are determined for the above cases. An equation of statep =/3 (radiation) is assumed in the case of perfect fluid.     

Age and growth of redeye round herring Etrumeus whiteheadi off the South African coast

Ages of redeye round herring Etrumeus whiteheadi were estimated with associated errors and used to infer life-history information, such as age composition, age-at-maturity and instantaneous mortality rate. Samples were collected in November 2005 during a research survey aimed at estimating the biomass of spawning pelagic fish off South Africa’s west and south coasts. Replicate age estimates obtained from sagittal otoliths were collected with slight bias and relatively high precision. A von Bertalanffy model describing growth of the combined sexes, including juveniles, was L_t = 20.41(1 ? e^{?0.41(t ? 1.92)}). Kimura’s likelihood ratio test revealed no statistically significant differences between growth parameters of males and females. Results suggested that otolith length is a better predictor of age than otolith weight. Maturity estimates for E. whiteheadi were similar to those previously documented.     

First evidence for episodic flooding events in the arid interior of central Saudi Arabia over the last 60 ka

Although evidence for Quaternary environmental changes in the Arabian Peninsula is now growing, research has mostly been conducted in the United Arab Emirates (UAE) and in the Sultanate of Oman. There have been virtually no recent studies in Saudi Arabia, especially in the central region such as around Al‐Quwaiayh. In this area there are a series of outwash plains developed along the eastern edge of the Arabian Shield that formed in the late Quaternary. Four sedimentary sections, which are representative of the deposits that have accumulated, have been studied and five luminescence ages obtained. These are the first luminescence ages acquired from Quaternary sediments in central Saudi Arabia. The preserved fluvial deposits in the study area have formed during humid events at ca. 54 ka, ca. 39 ka and ca. 0.8 ka. In more recent times aeolian sands have been encroaching on to the distal parts of the outwash plains. Copyright © 2008 John Wiley & Sons, Ltd.     

A new multi‐stage recession model for Proglacial Lake Humber during the retreat of the last British–Irish Ice Sheet

The single most prominent lake associated with the retreat phase of the last British–Irish Ice Sheet (BIIS) was Proglacial Lake Humber. The present research elucidates a revised regional history of Proglacial Lake Humber from its maximum elevation to its demise using a combination of landscape mapping and luminescence dating. The results of mapping multiple Lake Humber strandlines are now best described by an eight‐stage recessional model. Erosional highstands of the lake can be shown to post‐date the BIIS advance that deposited the Skipsea Till at around 17 ka whereas new OSL ages show that Lake Humber was nearing its demise by 15.5±0.8 ka, indicating a possible short‐lived lake. Multiple lake level stands are attributed to the switching of lake outlets from the Lincolnshire Gap to the Humber Gap and to oscillations of the BIIS blocking the latter on more than one occasion and subsequently at a lower elevation with till. The horizontal or near‐horizontal shorelines confirm that isostatic adjustment did not occur during the demise of Lake Humber, indicating that BIIS advances in the North Sea region and Vale of York were not only dynamic but of short duration.     

南海北部陆架和陆坡区小型底栖动物群落的比较研究

为了解南海北部陆架与陆坡区小型底栖动物的群落特征,以及影响群落特征的环境因素,2015年6月对南海北部海域(19.3°—21.4°N, 112.4°—115.1°E)7个站位的小型底栖动物及环境因子进行了采样,并对陆架和陆坡区小型底栖动物群落的丰度、生物量、类群组成和群落结构进行比较。结果表明,在陆架站位,小型底栖动物由13个类群组成,平均丰度为(132±130)ind./10cm2,平均生物量为(169±79)μgdwt/10cm2;在陆坡站位由8个类群组成,平均丰度为(33±14)ind./10cm2,平均生物量为(56±35)μgdwt/10cm2。单因素方差分析结果表明,陆坡区小型底栖动物的总丰度和总生物量以及线虫和多毛类的丰度均显著低于陆架区,但优势类群的相对丰度组成没有显著不同,海洋线虫占总丰度的83%,其次为多毛类和桡足类,分别占7%和3%。环境因子的主成分分析(Principal ComponentsAnalysis,PCA)将陆架和陆坡站位沿第一主分量轴分开,小型底栖生物丰度和生物量与沉积物叶绿素a和脱镁叶绿酸含量以及底层水温呈最大正相关,与水深呈负相关;聚类(Cluster)和排序(non-metric Multidimensional Scaling, MDS),以相似性系数65%将7个站位划分为2组,与按照水深划分的陆架和陆坡组基本吻合;单因素相似性分析(one-way ANOSIM)显示陆架和陆坡区小型底栖动物群落结构差异显著;生物-环境分析(Biota-Environment,BIOENV)表明影响群落结构的最佳环境因子组合为叶绿素a和底层水温。综上可知,随水深增加的食物减少和底层水温的下降是限制南海北部研究海域小型底栖动物丰度和生物量及影响群落组成和结构的主要因素。     

Spawning of major carps in the lower Halda River,Bangladesh

Spawning biology and spawn fishery of three valuable species of Indian major carps,Catla catla, Labeo rohita andCirrhinus mrigala, in the lower Halda River, Bangladesh, were studied in 1978. The major carps spawned only in the Sonairchar oxbow-bend from April to June on or near the dates of the full moon and the new moon. The tide was then at its highest level, and there was heavy flood water runoff from the hill region with sharp increases in water level, turbidity and current velocity, as well as decreases in water temperature, dissolved oxygen, and hydrogen ion concentration. These three heterogeneric species, as a result of parallelism or convergence in evolution, overlap in their environmental requirements for spawning. The nursery ground of the major carp fry spawned in the Halda River was found to be in the Bay of Bengal. The brood stock origin is suspected to be at the Shankha River, 40 miles south of the Karnafuli River. The spawn fishery in the Halda River was intensive but inefficient. Engineering works and water management schemes are threatening the spawning habitat.     

Towards an integrated environmental assessment for wetland and catchment management

This paper develops a decision support system for evaluation of wetland ecosystem management strategy and examines its, so far partial, application in a case study of an important complex coastal wetland known as the Norfolk and Suffolk Broads, in the east of England, UK. Most managed ecosystems are complex and often poorly understood hierarchically organized systems. Capturing the range of relevant impacts on natural and human systems under different management options will be a formidable challenge. Biodiversity has a hierarchical structure which ranges from the ecosystem and landscape level, through the community level and down to the population and genetic level. There is a need to develop methodologies for the practicable detection of ecosystem change, as well as the evaluation of different ecological functions. What is also required is a set of indicators (environmental, social and economic) which facilitate the detection of change in ecosystems suffering stress and shock and highlight possible drivers of the change process. A hierarchical classification of ecological indicators of sustainability would need to take into account existing interactions between different organization levels, from species to ecosystems. Effects of environmental stress are expressed in different ways at different levels of biological organization and effects at one level can be expected to impact other levels, often in unpredictable ways. The management strategy, evaluation methodologies and indicators adopted should also assess on sustainability grounds whether any given management option is supporting, or reducing, the diversity of functions which are providing stakeholders with the welfare benefits they require.     

Mega-blowouts in Qinghai–Tibet Plateau: Morphology,distribution and initiation

Blowouts are wind-eroded landforms that are widely distributed in the north-eastern part in Qinghai–Tibet Plateau (QTP), China. These blowouts are thought to form in response to climate change and/or human activity but little is known about their morphodynamics. Using field surveys, remote sensing and geographic information system (GIS) spatial analysis, the distribution and morphology of blowouts are analysed and their initiation considered. Results show the QTP mega-blowouts are some of the largest in the world. The orientations of the trough shaped blowouts are parallel with the prevailing wind, but the saucer and bowl-shaped blowouts are influenced by bi-directional transport. Whilst regional patterns of blowout shape and size were observed to reflect the extent of aeolian sediments and wind regimes, the relationship between the different morphological parameters showed consistency. During initial stages of development, the length to width ratios of blowouts increase rapidly with area but after they reach a mega size this relationship stabilizes as blowouts widen. Initial luminescence dating shows that blowouts appear to have initiated ~100 to 500 years ago, coinciding with the Little Ice Age (LIA) climate event when northwest winds are known to have intensified. Further work is required to confirm this initiation period and establish the significance of mega blowouts for landscape degradation and human activities. © 2018 John Wiley & Sons, Ltd.