Urban fluvial flood modelling using a two‐dimensional diffusion‐wave treatment,part 1: mesh resolution effects

High‐resolution data obtained from airborne remote sensing is increasing opportunities for representation of small‐scale structural elements (e.g. walls, buildings) in complex floodplain systems using two‐dimensional (2D) models of flood inundation. At the same time, 2D inundation models have been developed and shown to provide good predictions of flood inundation extent, with respect to both full solution of the depth‐averaged Navier–Stokes equations and simplified diffusion‐wave models. However, these models have yet to be applied extensively to urban areas. This paper applies a 2D raster‐based diffusion‐wave model to determine patterns of fluvial flood inundation in urban areas using high‐resolution topographic data and explores the effects of spatial resolution upon estimated inundation extent and flow routing process. Model response shows that even relatively small changes in model resolution have considerable effects on the predicted inundation extent and the timing of flood inundation. Timing sensitivity would be expected, given the relatively poor representation of inertial processes in a diffusion‐wave model. Sensitivity to inundation extent is more surprising, but is associated with: (1) the smoothing effect of mesh coarsening upon input topographical data; (2) poorer representation of both cell blockage and surface routing processes as the mesh is coarsened, where the flow routing is especially complex; and (3) the effects of (1) and (2) upon water levels and velocities, which in turn determine which parts of the floodplain the flow can actually travel to. It is shown that the combined effects of wetting and roughness parameters can compensate in part for a coarser mesh resolution. However, the coarser the resolution, the poorer the ability to control the inundation process, as these parameters not only affect the speed, but also the direction of wetting. Thus, high‐resolution data will need to be coupled to a more sophisticated representation of the inundation process in order to obtain effective predictions of flood inundation extent. This is explored in a companion paper. Copyright © 2005 John Wiley & Sons, Ltd.     

CO2注气压力对瓦斯扩散系数影响规律实验研究

煤层CH₄解吸效率低、扩散慢的特点严重制约着煤层瓦斯抽采的效率,为解决低透气性煤层瓦斯抽采困难的问题,选取晋城赵庄煤矿煤样,研究不同注气压力对驱替CH₄过程的影响以及驱替过程中CH₄扩散系数的变化规律,利用自主研发的CO₂驱替CH₄试验平台,在0.6、0.8、1.0 MPa等不同注气压力条件下分别进行CO₂驱替CH₄实验。结果表明:驱替压力越大,达到最大CH₄排放量的时间越短,CO₂突破时间越快,置换效率越大,驱替效果越好;CH₄气体驱替过程分为3个阶段,先急剧增加再缓慢增加最后保持平稳;在同一注气压力下,瓦斯扩散系数随时间呈先增大后减小的变化规律,注气压力为0.6、0.8、1.0 MPa时,瓦斯扩散系数的最大值分别为2.27×10-5、3.36×10-5、4.62×10-5 cm2/s。从实验结果可知,不同注气压力下,CO₂对CH₄主要起到驱替作用、置换吸附-解吸作用及稀释驱替作用;每个阶段的CH₄气体运移情况不同,根据实验阶段合理调整注气流量、压力等参数,使注驱技术搭配更高效。研究结果对CO₂深埋与瓦斯（煤层气）高效抽采具有理论指导意义。      

Chemical spots and oscillatory diffusion modes in magnetic stars

The stars of the middle main sequence often have spot‐like chemical structures at their surfaces. We consider diffusion caused by electric currents and argue that such current‐driven diffusion can form chemical inhomogeneities in a plasma. The considered mechanism can contribute to a formation of element spots in Hg‐Mn and Ap‐stars. Due to the Hall effect, diffusion in the presence of electric currents can be accompanied by the propagation of a particular type of magnetohydrodynamic modes in which only the impurity number density oscillates. Such modes exist if the magnetic pressure is much greater than the gas pressure and can be the reason for variations of the abundance peculiarities in stars. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Volunteered Geographic Information constructions in a contested terrain: A case of OpenStreetMap in China

The recent explosive growth of user-generated geographic information has drawn significant attention from GIS scholars and human geographers. Volunteered Geographic Information (VGI) here refers to a key component of such a phenomenon, comprising both a range of practices of geographic information production and dissemination by volunteers as well as new forms of geospatial data produced and curated through various interactive online platforms and mobile devices such as OpenStreetMap (OSM) and Google Maps. VGI constructions have raised questions on spatial knowledge, power, and context. Through a study that examines social constructions of OSM in China, this paper makes two contributions to the existing literature: providing a political economic account of VGI constructions in China and exploring legalities in VGI research. Informed by research in critical GIS, this paper traces political economic transitions in relation to OSM constructions and examines OSM contributors' experiences and how these experiences constitute OSM development and usage. Drawing upon law and society research, this paper investigates how OSM mappers encounter the state's regulatory scheme of online mapping. This legality perspective of spatial data production and usage is a topic rarely explored in VGI studies. With interview data and document analysis, this paper unravels processes of powerful state institutional arrangements to control and invest in VGI simultaneously, entrepreneurs' interest in developing location-based services using VGI data, and experiences from a tech-savvy group in exploring and making VGI. While individual experiences vary, they show efforts of questioning embedded power relations shaping spatial data production in these continuously evolving, contested technoscientific and social landscapes.     

Quantifying the influence of rainfall,vegetation and animals on soil erosion and hillslope connectivity in the monsoonal tropics of northern Australia

Erosion of soil by water is facilitated by both diffusive and fluvial processes. Here we examine three different soil redistribution processes operating at very different spatial and temporal scales in the monsoonal tropics of northern Australia. The first process, rainsplash, operates across the entire catchment. This process, while subject to annual and seasonal variations in rainfall amount and intensity, can be considered a constant forcing and redistributes on average 9 t ha⁻¹ year⁻¹ (range −0.9 to 19 t ha⁻¹ year⁻¹). The second process, bioturbation, where in this study soil is disturbed by feral pigs (wild boar), occurs in selected areas throughout each year. Pigs exhume 3 to 36.0 t ha⁻¹ year⁻¹ (average ~11 t ha⁻¹ year⁻¹). The effect of this disturbance may last for many years afterwards. The third process is the disturbance of the soil surface by tree throw and creation of pit–mound topography (also a form of bioturbation), together with the resultant placement of the tree superstructure (above ground biomass) on the ground, which may form debris dams. Tree throw at the scale examined here is likely to occur only once every 50–100 years, with the influence of this single event lasting for at least 10 years post event. Tree throw in a single event exhumed ~5 t ha⁻¹ (1.1–9.5 t ha⁻¹) of soil. In contrast to rainsplash, pig disturbance and tree throw events are largely point-based phenomena. Field observation suggests that it takes many years for the disturbance from both pigs and tree throw to be removed. We find here that in terms of relative soil redistribution, rainsplash has the largest influence, with any erosional disturbance by pigs and tree throw being within the variability of rainsplash. However, the disruption of surface flow by the pig digs and tree throw disrupts sedimentological and hydrological connectivity.     

省级国土资源网上交易系统建设研究

将互联网在线交易技术、地理信息系统技术和信息安全技术整合应用到国土资源的权属交易领域,推进国有资源交易活动的公平、公正、公开原则,营造良好的市场环境已经成为推动国土资源市场建设的趋势,也成为地理信息系统技术向公众应用领域延伸的一个重要方向。文章以广西壮族自治区国土资源网上交易系统的建设为背景,研究国土资源网上交易系统开发的目标、功能以及关键技术,有效地解决了传统土地、矿业权交易受地域、时间的限制和私下串标、围标等问题,为省级国土资源部门开展网上交易系统建设提供了解决方案和思路。     

用于地震预警的P波震相到时自动拾取

P波震相的自动拾取可用于地震预警中地震事件判别和地震定位,是实现基于地震台网地震预警的首要条件.针对地震预警中P波震相拾取的特点,本文发展了一套基于长短时平均(STA/LTA)和池赤准则(AIC)算法的多步骤P波自动拾取技术,应用Delaunay三角剖分提出了一种非几何相关的干扰信号剔除方法,并应用福建省数字地震台网记录对方法进行了验证,目前方法已经用到了福建省地震预警试验系统中.     

Mapping potential areas for groundwater storage in the High Guir Basin (Morocco):Contribution of remote sensing and geographic information system

Identification of water potential areas in arid regions is a crucial element for the enhancement of their water resources and socio-economic development. In fact, water resources system-planning can be used to make various decisions and implement management of water resources policies. The purpose of this study is to identify groundwater storage areas in the high Guir Basin by implementing Geographic Information System (GIS) and Remote Sensing methods. The required data for this study can be summarized into five critical factors: Topography (slope), lithology, rainfall, rock fracture and drainage. These critical factors have been converted by the GIS into thematic maps. For each critical parameter, a coefficient with weight was attributed according to its importance. The map of potential groundwater storage areas is obtained by adding the products (coefficient × weight) of the five parameters. The results show that 50% to 64% of the total area of the High Guir Basin is potentially rich in groundwater, where most of fracture systems are intensely developed. The obtained results are validated with specific yield of the aquifer in the study area. It is noted that there is a strong positive correlation between excellent groundwater potential zones with high flows of water points and it diminishes with low specific yield with poor potential zones.     

不同固化材料垫层在黄土中隔水能力及其垂直扩散特性

黄土作为地基材料时由于其湿陷性容易出现失稳现象,利用固化剂垫层改良黄土地基水稳性和强度的技术被广泛使用。本文主要通过在黄土中分别加入石灰、水泥和粉煤灰固化剂垫层的方法进行加固,测定了在垂直方向上各处的含水率、密度、干密度、土颗粒比表面积(SSA)及阳离子交换能力(CEC)的变化。试验表明石灰、水泥和粉煤灰垫层可以影响10～15cm范围内相邻土层含水率、密度、比表面积和阳离子交换能力,改变土质结构,提高土体的水稳性。改性后的土体越靠近固化剂垫层,含水率、SSA和CEC越小而密度越大。其中,石灰垫层效果最好,它能将黄土中含水率减小超过4%,密度增加1.0～1.5g cm-3,粉煤灰作用次之,水泥最弱。此外,试样土颗粒比表面积(SSA)与阳离子交换能力(CEC)存在线性递增的关系,本次试验中,3个试样中SSA与CEC之比均稳定于6.5～7.5之间。