LONGITUDINAL DISPERSION IN SEDIMENT-LADEN OPEN CHANNEL FLOWS

Laboratory experiments on longitudinal dispersion in clear-water and sediment-laden open channel flows are reported. Data from these experiments and those available from previous studies indicate that the suspended sediment present in the flow affects the longitudinal dispersion process. The observed velocity distributions over the depth of sediment-laden flows indicate that the velocity deviates from the mean velocity more in sediment-laden flows than in clear-water flows. The velocity distributions over the cross section and secondary flow in the channel are also expected to be altereddue to the presence of suspended sediments in the flow. For these reasons, more dispersion is found in sediment-laden flows than in corresponding clear-water flows. A predictor for the dispersion coefficient in sediment-laden flows is proposed.     

近50多年来澜沧江流域农业灌溉需水的时空变化

利用澜沧江流域云南境内8 个气象站1950s-2007 年的逐月气象数据,现状作物种植、农业耕作、田间水分管理等资料,应用Mann-Kendall 法和R/S 分析法,探索50 多年来流域区的干湿变化、农业灌溉定额转折变化趋势及分布规律。结果表明：年、季平均温度普遍地显著升高,降水量干季增加、湿季减少;大部分地区的参照作物腾发量ET0在年度及干、湿季都呈增加趋势,仅在流域中段大理、剑川、耿马的部分时段为减少,干湿指数大多数地区都是降低;水稻及农业综合灌溉需水定额从流域上游到下游逐渐呈减少、增-减并存到增加的趋势。气象因子、ET0、干湿指数、水稻灌溉及农业综合灌溉定额发生转折变异现象都集中在澜沧江中下段的耿马、思茅、景洪、勐腊等地,且时间系列的转折变异点在1960s-1990s 的各个时期均有出现。水稻灌溉定额随纬度方向变化的相关系数为0.513,随海拔高程变化为0.610,最高值出现在维西,最低值为勐腊;农业综合灌溉定额受作物种植结构和水稻种植面积的影响较大,二者相关系数达到0.826,但其与纬度、海拔的变化规律不明显,最高值在大理,最低值在维西。灌溉定额在小范围内的多样性变化,表明在纵向岭谷特殊环境对地表水汽输送、气温和气流场分布等的“通道-阻隔”作用下,澜沧江河谷农业灌溉需水量时空变化的复杂性。     

基于InSAR形变数据分析台湾纵谷断层南段现今运动特征

本文利用2007—2010年花东纵谷南段区域的InSAR形变数据作为约束, 采用分段断层模型和层状介质模型, 反演中国台湾东部纵谷断层南段滑动速率空间分布, 并据此分析断层运动特征。 研究结果表明, 纵谷断层南段整体以逆冲运动为主, 兼具左旋走滑运动。 纵谷断层南段的滑动速率具有空间非均匀性, 在空间上可以细分为深浅两个极值区, 浅部(0~15 km)最大滑动速率为10 cm/a, 位于深度2.5 km左右; 深部(15~30 km)最大滑动速率为21 cm/a, 位于深度25 km左右。 反演结果与用重复地震估算的深部滑动速率基本吻合。     

GIS支持下的澜沧江流域云南段土壤侵蚀空间分析

利用ArcView3.2和ARC/INF08.1软件,通过图层叠加、统计分析和缓冲区分析等,提取西南纵向岭谷区澜沧江流域云南段的不同类型和强度的土壤侵蚀与地形坡度、土地利用/土地覆盖现状、土壤类型和分布、大雨日数以及河流、道路两侧的缓冲区等的相应数据,计算出土壤侵蚀综合度。结果表明,研究区不同坡度等级中,15°²5°坡度上的土壤侵蚀最强,其次为8°¹5°坡地和4°⁸°坡地;>25°坡地上则较小;不同用地类型的土壤侵蚀程度不同,总体上,旱耕坡地的土壤侵蚀较草地严重,而草地又较林地严重;在各种土壤类型中,黄壤和石灰土的土壤侵蚀最为突出,其次为红壤、黄棕壤和南方水稻土等;河流两侧和道路两侧的土壤侵蚀都较整个流域要严重,而河流两侧又略重于道路两侧;当多年平均大雨日数小于20日时,土壤侵蚀程度基本上随大雨日数的增加而增加;当大雨日数大于20日时,土壤侵蚀程度反而较小,原因在于前期大雨冲刷侵蚀,带走了地表的疏松物质。研究结果可为有针对性地防治水土流失、减少河流泥沙和水库淤积提供依据。     

LONGITUDINAL STREAM-PROFILES AS INDICATORS FOR GEOMETRIC SEGMENTATION OF THE LANGSHAN- HUANGBAISI FAULT ZONE, NORTHWEST BEIJING

The Langshan-Huangbaisi fault zone in northwest Beijing is the southwestern part of the normal fault zone on the northern margin of the Yanqing basin, 35.5km long and NNE-NEE-trending in general, on which two major 130°- 140° bends separate it into three segments with different strikes.Using the Hack's method, 71 longitudinal stream-profiles along the fault zone are analysed, shawing a well geomorphic response to the fault geometry. On these two major bends the gradient indices,K value     

Runoff generation in a sandy area—the nizzana sands,Western Negev,Israel

This paper presents the results of sprinkling experiments conducted over the lower part of vegetated and crusted linear dunes as well as over flat playa surfaces that appear in the interdune corridors. Data obtained show that these two surface units respond quickly to rainstorms. Runoff generation can be expected for any storm exceeding 2-3 mm and runoff coefficients are high. When the topsoil algal crust, 1 to 2 mm thick, is removed from the surface of the dune, infiltration increases drastically and eliminates any possibility of runoff generation under present-day rainfall conditions. This data may be of great help in the understanding of the geomorphology and sedimentary sequence of the corridors separting linear dunes.     

Operationalizing longitudinal approaches to climate change vulnerability assessment

The past decade has seen a proliferation of community-scale climate change vulnerability assessments globally. Much of this work has employed frameworks informed by scholarship in the vulnerability field, which draws upon interviews with community members to identify and characterize climatic risks and adaptive responses. This scholarship has developed a baseline understanding of vulnerability in specific places and industries at particular times. However, given the dynamic nature of vulnerability new methodologies are needed to generate insights on how climate change is experienced and responded to over time. Longitudinal approaches have long been used in sociology and the health sciences to capture the dynamism of human processes, but their penetration into vulnerability research has been limited. In this article, we describe the application of two longitudinal approaches, cohort and trend studies, in climate change vulnerability assessment by analyzing three case studies from the Arctic where the authors applied these approaches. These case studies highlight how longitudinal approaches can be operationalized to capture the dynamism of vulnerability by identifying climate anomalies and trends, and how adaptations develop over time, including insights on themes such as social learning and adaptive pathways.     

Environmental controls on food web regimes: A fluvial perspective

Because food web regimes control the biomass of primary producers (e.g., plants or algae), intermediate consumers (e.g., invertebrates), and large top predators (tuna, killer whales), they are of societal as well as academic interest. Some controls over food web regimes may be internal, but many are mediated by conditions or fluxes over large spatial scales. To understand locally observed changes in food webs, we must learn more about how environmental gradients and boundaries affect the fluxes of energy, materials, or organisms through landscapes or seascapes that influence local species interactions. Marine biologists and oceanographers have overcome formidable challenges of fieldwork on the high seas to make remarkable progress towards this goal. In river drainage networks, we have opportunities to address similar questions at smaller spatial scales, in ecosystems with clear physical structure and organization. Despite these advantages, we still have much to learn about linkages between fluxes from watershed landscapes and local food webs in river networks. Longitudinal (downstream) gradients in productivity, disturbance regimes, and habitat structure exert strong effects on the organisms and energy sources of river food webs, but their effects on species interactions are just beginning to be explored. In fluid ecosystems with less obvious physical structure, like the open ocean, discerning features that control the movement of organisms and affect food web dynamics is even more challenging. In both habitats, new sensing, tracing and mapping technologies have revealed how landscape or seascape features (e.g., watershed divides, ocean fronts or circulation cells) channel, contain or concentrate organisms, energy and materials. Field experiments and direct in situ observations of basic natural history, however, remain as vital as ever in interpreting the responses of biota to these features. We need field data that quantify the many spatial and temporal scales of functional relationships that link environments, fluxes and food web interactions to understand how they will respond to intensifying anthropogenic forcing over the coming decades.     

Effect of fluid column dynamics on longitudinal vibrations of an ultra deepwater riser covered by an orifice plug

The paper studies longitudinal vibrations of an ultra-deepwater drilling riser whose bottom end is disconnected from the sea floor and covered by a plug (a blind one or the one with a hole). An elastic shell is used as a model of a riser pipe. The fluid column motion in the riser is described by the Navier–Stokes equation for a compressible fluid. Losses of fluid pressure during its flowing through a hole in the plug are taken into account. Solution of the riser equations is carried out in the frequency domain. Analysis of the effect which the riser length, wave period and height, and the plug-hole diameter on the amplitude of the riser's tension vibrations is conducted. A riser manufactured of strong aluminium alloys, some of prospective materials for ultra deepwater drilling, was considered as a prototype. It has been shown that risers 2000–4000 m long, plug-hole, and a riser 6000 m long with plug-hole of 0.087 m in diameter can withstand wave height of >15 m throughout the frequency range.     

“Natural cycles” in lay understandings of climate change

This article analyses lay understandings of climate change elicited through a longitudinal population-based survey of climate change, place and community among 1162 residents in the Hunter Valley, Southeast Australia. We explore how older residents in contrasting rural and coastal geographic areas perceive climate change information in terms of culturally relevant meanings and values, lived experiences and emotional responses to seasonal cycles, temperature fluctuations and altered landscapes. Thematic analysis of comments given by 467 interviewees to an open-ended question identified a significant subset for whom the concepts of “nature” and “science” express competing views about changing climatic conditions. For them, the idea of “natural cycles” is a significant cultural construct that links nature and humans through time in a way that structures stable and resilient understandings of environmental change, drawing on established cosmological frameworks for contemplating the future in relation to the past. In contrast to other studies that postulate scepticism and denial as individuals’ fear management strategies in the face of climate change threat, we found that the natural cycles view is founded on a reassuring deeper conviction about how nature works, and is linked to other pro-environmental values not commonly found in sceptical groups. It is a paradox of natural cycles thinking that it rejects the anthropocentrism that is at the heart of science-based environmentalism. By contrast, it places humans as deeply integrated with nature, rather than operating outside it and attempting with uncertain science to control something that is ultimately uncontrollable.