Urbanization impacts on flood risks based on urban growth data and coupled flood models

Natural Hazards - Urbanization increases regional impervious surface area, which generally reduces hydrologic response time and therefore increases flood risk. The objective of this work is to...     

GIS-based estimation of flood hazard impacts on road network in Makkah city, Saudi Arabia

Makkah city, Saudi Arabia, is periodically exposed to flash floods that result in major human and economical damages. That is due to several factors including its rugged topography and geological structures. Hence, precise assessment of floods becomes a more vital demand in development planning. A GIS-based methodology has been developed for quantifying and spatially mapping the flood characteristics. The core of this new approach is integrating several topographic, metrological, geological, and land use data sets in a geographic information system (GIS) environment that utilizes the curve number method of flood modelling for ungauged arid catchments. Based on the estimated flood volume of sub-basins, a hazard factor has been developed to quantify the expected hazard level for each road. Applying this proposed approach reveals that 21?% of the road network in Makkah city is subjected to low flood hazards, 29?% is facing medium hazards, and 50?% of roads are exposed to harsh flood impacts. The developed approach may be considered a digital precise method that can be easily re-run, in other situations or regions, to estimate flood hazards on roads.     

GIS支持下的洪水淹没范围模拟

洪水淹没范围的确定是洪灾损失评估的核心环节。采用地理信息系统 (GIS)与水力演进模型,结合三维模拟技术和对象关系模型数据库,对浙江奉化江流域洪水淹没范围进行模拟。该方法能够准确地模拟洪水淹没范围,为快速评估洪灾损失和防洪决策服务提供了科学的依据。     

基于自组织映射神经网络的水库洪水过程分类

针对传统洪水分类方法中洪水特征提取时存在信息损失和主观性强的问题,本文基于洪水全过程构建自组织映射神经网络(Self-Organizing Map, SOM),综合考虑代表性和拓扑性等评价指标以优选网络规模,实现洪水全过程的拓扑逻辑关系挖掘及分类。以三峡水库洪水过程为研究对象,研究结果表明：(1) 2×3维SOM覆盖率达到56.7%,与3×3维SOM相比,仅有约2%的覆盖率差距,具有良好代表性;2×3维SOM输出层仅有1处翻转,拓扑结构比3×3维SOM更优,更适合三峡水库洪水过程分类。(2) 2×3维SOM将洪水过程划分为6类,其神经元拓扑结构可有效刻画各分类的差异与联系,说明SOM可基于可视化拓扑逻辑关系实现高维洪水数据的可靠客观分类。(3)与传统方法的历史典型洪水分类结果相比,SOM能提供可靠且丰富的分类信息。     

基于太湖流域模型的城市内涝过程高效模拟

城市内涝的高效模拟对于降低内涝灾害影响、制定防灾减灾措施具有极其重要的意义。本文提出了基于雨篦子耦合地表与管网的城市降雨-产汇流-内涝全过程高效模拟方法,结合常州市双桥浜城市产汇流与内涝试验基地监测数据,分别构建了基于高效模拟算法和二维水动力算法的城市内涝模型。根据监测数据对所构建的模型进行了率定与验证,并分析对比了2种算法在不同降雨事件中的精度与可靠性。结果表明：太湖流域模型中基于雨篦子的城市水文特征单元高效模拟方法能够较为真实地反映城市内涝的具体特征,且在模型参数一致的前提下,其计算效率约为二维水动力算法的780～1 275倍,能够对城市内涝情况进行快速模拟。     

有限数据条件下边坡可靠度分析的Bootstrap方法

基于Bootstrap抽样技术提出了有限数据条件下边坡可靠度分析方法。简要介绍了传统的边坡可靠度分析方法。采用Bootstrap方法模拟了抗剪强度参数概率分布函数的统计不确定性。以无限边坡为例研究了抗剪强度分布参数和分布类型不确定性对边坡可靠度的影响规律。结果表明：基于有限数据估计的样本均值、样本标准差和AIC值具有较大的变异性,这种变异性进一步导致了抗剪强度参数概率分布函数存在明显的统计不确定性。在考虑抗剪强度参数概率分布函数的统计不确定性时,边坡可靠度指标应为具有一定置信度水平的置信区间,而不是传统可靠度分析中的固定值。边坡可靠度指标的置信区间变化范围随安全系数的增加而增大,同时考虑分布参数和分布类型不确定性计算的可靠度指标具有更大的变异性和更宽的置信区间变化范围。Bootstrap方法为有限数据条件下抗剪强度参数概率分布函数统计不确定性的模拟以及边坡可靠度的评估提供了一条有效的途径。     

基于试桩试验的桩侧注浆抗拔桩承载变形特性的荷载传递法

依托上海虹桥综合交通枢纽工程开展了4组桩侧注浆抗拔桩的现场试桩试验,得到了各试桩各土层的桩侧摩阻力与桩土相对位移关系曲线（?-w曲线）。首先,对前述现场试桩试验得到的?-w曲线以及文献[1]中通过桩土接触面大型直剪试验得到的?-w曲线进行归一化处理,归一化参数为各土层极限侧摩阻力?ult及其相应的临界桩土相对位移wult;然后采用双曲线函数拟合归一化后的各土层?/?ult-w/wult曲线,得到一个统一的?/?ult-w/wult函数关系式;最后,将该双曲线函数应用到荷载传递法中,用于分析预测桩侧注浆抗拔桩的承载变形特性,可求得桩侧注浆抗拔桩桩身各处的荷载-位移曲线、桩身轴力分布曲线以及桩侧摩阻力分布曲线。通过工程案例的验证表明,其计算结果与工程案例实测值较接近,在上海地区具有一定的适用性。     

基于WCA2D与SWMM模型的城市暴雨洪涝快速模拟

为探讨计算高效的元胞自动机模型(WCA2D)与传统一维管网模型耦合的机制以及计算效果,尝试将WCA2D与SWMM模型耦合(SWMM/WCA2D),以广州市长湴片区为例探究一种暴雨洪涝快速二维模拟技术,对比实测积水数据以及SWMM/LISFLOOD-FP模拟,结果表明:SWMM/WCA2D模拟结果与"20180607"实测积水数据相近,表明模型精度良好;根据多指标评估结果,综合考虑主干渠道淤积以及建筑物阻挡情景的R_TPR、R_PPV、F₁值分别达到0.8、0.6、0.7,模拟精度最高,最能反映区域实际情况;通过与SWMM耦合,WCA2D和LISFLOOD-FP的模拟结果差异小(最大水深差值基本低于0.1 m)、相关性强(相关系数基本超过0.7),但前者计算效率是后者的3～5倍,表明WCA2D能够耦合SWMM且计算效率更高,为复杂城市化地区暴雨洪涝快速模拟提供了一种新方法。     

盾构隧道下穿城市道路的路面沉降计算方法研究

随着我国城市化进程的不断推进,地下空间的开发和利用越来越受重视,特别是盾构隧道已成为工程建设的重要技术手段。而城市地下环境日趋复杂,市政隧道下穿既有道路的项目愈发常见,研究与之对应的土体位移预测方法对地下空间安全评估至关重要。借助弹性力学中薄壁圆筒的平面模型,构建相应的边界条件,推导出适用于有重地层浅埋圆截面土体沉降变形计算方法。以澳门纯钢纤维混凝土盾构隧道下穿友谊大马路工程为实例,并与不同收敛模式下随机介质理论进行对比验证。研究结果表明：理论公式与土体位移实测值吻合度较高,且略优于随机介质理论的计算结果。理论公式综合考虑了路基土体参数、隧道深径比及施工技术水平等因素的影响,计算结果合理可靠,可为盾构隧道下穿施工诱发土体位移预测提供重要的理论支持。     

基于汇水区分级划分的城市洪涝模拟

为了有效提高城市暴雨洪涝模拟的精度, 针对城区复杂下垫面和雨水井数据缺失情况, 分别提出雨水井节点数据的确定方法和基于空间信息的汇水区分级划分方法。以武汉市青山区为研究区域, 选取2场典型降水过程, 开展SWMM模型的参数率定和验证工作, 并将基于不同方法划分的汇水区模拟结果与实际渍水数据进行对比。结果表明: ①提出的雨水井节点数据确定方法, 在雨水井实测数据缺失的城市洪涝模拟中具有一定的可靠性和适用性。②基于空间信息分级划分法、水文分析结合泰森多边形法和泰森多边形法所划分的汇水区, 模拟的最大积水深度中分别有100%、63%和75%的典型验证点与实际渍水程度相符, 模拟的溢流点中分别有80.0%、76.4%和77.4%的溢流点位置与5年一遇降雨渍水风险图相符。基于空间信息分级划分法所得的汇水区比较符合真实汇水情况, 且模拟结果比其他2种方法更加准确。③ 5年一遇降雨重现期下, 3种方法划分的汇水区所模拟的积水对研究区域影响程度相对较小, 但遇到高于此重现期的暴雨会出现不同程度的内涝。本研究可为城市暴雨洪涝模拟中雨水井节点数据确定与地表空间离散化提供新方法, 模拟结果可为城市防洪减灾提供参考。     

Vulnerability assessment of an urban flood in Nigeria: Abeokuta flood 2007

The paper presents the result of a vulnerability assessment of urban dwellers to a major flood hazard in Abeokuta, southwestern Nigeria in July 2007. This was achieved by means of questionnaire survey administered to 248 flood area residents. Flood vulnerability was assessed by examining exposure, susceptibility, and coping indicators in the study area. Findings of the study show that although about 50% of respondents had experienced floods, in Abeokuta or elsewhere in the past, majority (66%) did not anticipate a flood event of such magnitude to occur despite its location on a flood plain and, therefore, were unprepared for such hazard. Pre-warning of the flood event was generally lacking among flood area residents as only 8% of respondents indicated pre-warning, which was based on personal observations. Response to the flood hazard was mainly reactive for both private and public agents as flood risk reduction measures were not in place.     

Projected impacts of land use and road network changes on increasing flood hazards using a 4D GIS: A case study in Makkah metropolitan area,Saudi Arabia

Makkah City, west of the Kingdom of Saudi Arabia, is considered the third main highly populated metropolitan area in the Kingdom of Saudi Arabia. It exhibits two unique features that increase the hazardous flood consequences: (1) its topography is very complex and (2) about three million Muslims are gathered annually in Makkah to perform Hajj over a 2-week period. Floods are natural returning hydrological phenomena that have been affecting human lives. The objectives of the current study are: (1) identification of land use types and road networks in Makkah, (2) hydrological modeling of flood characteristics in Makkah based on precise up-to-date databases, (3) examination of the relationship between land use, land cover changes, transportation network expansion, and the floods' prosperities and hazards, and (4) development of digital hydrological maps for present and near future flood hazards in Makkah. The attained results show that the mean runoff depth and the total flood volume are significantly increased from 2010 to 2030. Additionally, it has been found that a great part of the road network in Makkah City is subjected to high dangerous flood impacts. The overall length of flood danger-factor roads is increased from 481 km (with almost 37 %) to 1,398 km (with 74 % approximately) between 2010 and 2030. Thus, it is concluded that urbanization has a direct strong relationship with flood hazards. Consequently, it is recommended that the attained results should be taken into account by decision makers in implementing new development planning of the Makkah metropolitan area.     

Ecological impacts of air pollution from road transport on local vegetation

Motor vehicles emit a cocktail of pollutants and are a major contributor to ground-level air pollution, but little is known regarding the ecological impacts of air pollution from roads on the surrounding vegetation. Data are presented on vegetation at three sites adjacent to two major motorways in the UK, comprising two woodland sites and one blanket bog site. Surveys of oak and beech tree health (at the woodland sites) and species composition (at the blanket bog site) were undertaken along transects away from the motorway.     

基于渐近展开法的脆性岩石双尺度方法初步研究

将渐近展开法与细观统计模型相结合,研究了脆性岩石双尺度计算方法。该方法在细观尺度定义材料属性,假定材料参数符合Weibull分布,采用弹性－理想脆性本构模型,脆断标准采用修正的Mohr-Coulomb准则和最大拉应力准则,通过宏细观尺度耦合计算,得到细观尺度材料损伤演化及其对结构宏观性状的影响。方法包括确定材料统计参数、确定细观尺度代表性体积单元（RVE）及求解边值方程等步骤。数值模型采用商业软件ABAQUS及其内嵌的UMAT用户子程序实现。该方法适用于岩石单轴受压或低围压应力状态,考虑到计算效率,计算时宜采用混合尺度,即模型重点（关键）部位采用双尺度,而其他区域采用单尺度计算。宏观尺度材料软化后未采用正则化方法,此时的计算结果有网格依赖性。     

A method for flood hazard mapping based on basin morphometry: application in two catchments in Greece

Basin morphometric parameters play an important role in hydrological processes, as they largely control a catchment’s hydrologic response. Their analysis becomes even more significant when studying runoff reaction to intense rainfall, especially in the case of ungauged, flash flood prone basins. Unit hydrographs are one of the useful tools for estimating runoff when instrumental data are inadequate. In this work, instantaneous unit hydrographs based on the time-area method have been compiled along the drainage networks of two small rural catchments in Greece, situated approximately 25 km northeast of its capital, Athens. The two catchments drained by ephemeral torrents, namely Rapentosa and Charadros, have been subject to flash flooding during the last decades, which caused extensive damages at the local small towns of Marathon and Vranas. Hydrograph compilation in numerous locations along the catchments’ drainage networks directly reflected the runoff conditions across each basin against a given rainfall. This gave a holistic assessment of their hydrologic response, allowing the detection of areas where peak flow rates were elevated and therefore, there was higher flood potential. The resulting flood hazard zonation showed good correlation with locations of damages induced by past flood events, indicating that the method can successfully predict flood hazard spatial distribution. The whole methodology was based on geographic information software due to its excellent capabilities on storing and processing spatial data.     

基于传递-反射矩阵法的层状公路结构动力响应研究

利用传递-反射矩阵方法和叠加原理推导了双轮胎振动荷载作用下弹性层状公路结构的动力响应解,并利用Hankel数值逆变换技术进行了数值求解。弹性层状结构的传递-反射矩阵同时具有单个矩阵尺寸小、矩阵元素只含有负指数项2个优点,计算结果不受土层单元厚度与荷载频率大小的影响,可以大幅提高计算效率和精度。通过将数值计算与室内模型试验结果进行比较,验证了方法的正确性。在此基础上,分析了面层厚度及模量对层状公路结构动应力、动位移的影响程度和规律,得出了一些有意义的结论。研究结果可为公路路面、路基结构设计提供参考。     

A method of analyzing polymodal distributions in orientation data

A method of cluster analysis for orientation data is described. The method enables vector statistics to be applied to polymodal distributions. Similar results to those found by modal analysis are obtained.     

城市江堤外移工程对防洪影响研究

以浙江省温州市瓯江江堤外移工程为例,应用二维潮流数学模型研究了堤线外移的不同工程方案对城市防洪的影响。该模型能够模拟瓯江与楠溪江交汇引起的复杂水流运动,以及多岛屿对水流流场的影响。验证计算表明,计算的潮位及18条垂线流速及断面流量过程与实测值吻合较好,误差均小于10%。因堤线外移的部分大多位于河道岸线的凹囊,适当外移可使河道岸线更趋平顺。100年一遇洪水时,瓯江大桥至鱼旗山堤线外移曲线方案1与直线方案2分别使屿头山-梅岙河段最高潮位壅高0.03～0.04m及0.04～0.08m。多年平均流量450m3/s时,方案2使塔山至鱼旗山断面垂线平均流速增加6%～22%,工程段以外河段流速变化较小;方案1缩窄的河宽和拦截过水面积明显小于方案2,相应引起流速变化也较小。     

A multi-agent-based model for sustainable governance of urban flood risk mitigation measures

Natural Hazards - Consequences of urban floods increased and diversified in terms of social, economical and environmental effects, due to the dense and unplanned urbanization in areas at risk of...     

Integration of stress testing with graph theory to assess the resilience of urban road networks under seismic hazards

Transportation networks daily provide accessibility and crucial services to societies. However, they must also maintain an acceptable level of service to critical infrastructures in the case of disruptions, especially during natural disasters. We have developed a method for assessing the resilience of transportation network topology when exposed to environmental hazards. This approach integrates graph theory with stress testing methodology and involves five basic steps: (1) establishment of a scenario set that covers a range of seismic damage potential in the network, (2) assessment of resilience using various graph-based metrics, (3) topology-based simulations, (4) evaluation of changes in graph-based metrics, and (5) examination of resilience in terms of spatial distribution of critical nodes and the entire network topology. Our case study was from the city of Kathmandu in Nepal, where the earthquake on April 25, 2015, followed by a major aftershock on May 12, 2015, led to numerous casualties and caused significant damage. Therefore, it is a good example for demonstrating and validating the developed methodology. The results presented here indicate that the proposed approach is quite efficient and accurate in assisting stakeholders when evaluating the resilience of transportation networks based on their topology.