Urban stream channel hazards

In managing urban stream channels there are pressures to use soft engineering techniques to restore channels wherever possible, to undertake management within a drainage basin context, to produce sustainable solutions and to consider community views. However, specific methods for characterizing the channel network in terms of possible management options have not been developed explicitly for urban areas. A method of characterizing the entire drainage network of urban areas, based upon segmentation of the stream channel network according to the incidence of road crossings and stormwater outfalls, is proposed together with consideration of ways in which the segments can be characterized, including stream channel hazards as a means of providing one basis for urban channel management.     

A catchment-scale model of mountain stream channel morphologies in southeast Australia

The position of mountain streams high in the channel network and their proportional dominance mean that channel modifications and adjustments within these systems will have important implications for downstream processes and linkages. This study develops an analysis framework for examining the catchment-scale distribution of reach morphologies, and the relationship among reach type, catchment lithology and flow competence in southeast Australian mountain streams. The analysis framework is applied to three catchments which have contrasting proportions of the two dominant lithologies of the region, Devonian granites and Ordovician metasediments.The model successfully delineated 68% of reach types, and the resultant spatial maps allowed the effects of stream network position and catchment specific controls on channel morphology to be evaluated. Maximum lengths of the majority of reach morphology types were in second-order streams and the maximum number of morphology types (six) was present in third-order streams, with dramatic reductions in reach type variability as the network expands. The position of catchment lithology within the channel network structure was recognized as more important than the aerial extent of a particular lithology on the distribution and abundance of reach morphologies. The model provides an important tool in the management of channel networks for the protection or restoration of ecological diversity, by identifying river segments and tributaries with high morphological diversity.     

Urban transformation of river landscapes in a global context

Over the past 50 years considerable progress has been made in understanding the impacts of urban development on river processes and forms. Such advances have occurred as urban population growth has accelerated around the world. Using a compilation of research results from more than 100 studies conducted in a range of areas (58 addressing morphological change), this paper describes how urbanization has transformed river landscapes across Earth’s surface, emphasizing the distribution of impacts in a global comparative context. Urban development induces an initial phase of sediment mobilization, characterized by increased sediment production (on the order of 2–10 times) and deposition within channels, followed by eventual decline that couples with erosion from increased runoff to enlarge channels. Data from humid and temperate environments around the world indicate that channels generally enlarge to 2–3 times and as much as 15 times the original size. Although research has emphasized temperate environments, recent studies of tropical areas indicate a tendency for channel reduction resulting from strong sediment erosion and deposition responses because of intense precipitation and highly weathered soils. Embryonic research in arid environments further suggests variable river responses to urbanization that are characterized by rapid morphological change over short distances. Regardless of location, the persistence of the sediment production phase varies from months to several years, whereas several decades are likely needed for enlarging channels to stabilize and potentially reach a new equilibrium. Urbanizing streams pose particular challenges for management given an inherent changing nature. Successful management requires a clear understanding of the temporal and spatial variations in adjustment processes.     

长江中游武汉-九江河段河道形态及水动力学特征

Based on measured hydrological data by using ship-mounted Acoustic Doppler Current Profiler (ADCP) instrument, we analyzed shapes of river cross sections of the middle Yangtze River basin (mainly focusing on Makou and Tianjiazhen river reach). Hydrodynamic properties of river channels were also discussed. The research results indicate that nonlinear relationships can be identified between river-width/river-depth ratio (W/D ratio), sizes of cross section and mean flow velocity. Positive relations are detected between W/D ratio and mean flow velocity when W/D<1; and negative relations are observed when W/D>1. Adverse relationships can be obtained between W/D ratio and cross-section area. Geomorphologic and geologic survey indicates different components of river banks in the wider and narrower river reaches respectively. These may be the main driving factors causing unique hydrological properties of river channels in the middle Yangtze River basin. Narrower river cross sections tend to raise water level in the upstream river reach near narrower river channel, giving rise to backwater effects. River knots can cause serious backwater effects, which is harmful for flood mitigation. However river knots will also stabilize river channel and this will be beneficial for river channel management. The results of this paper may be helpful for flood mitigation and river channel management in the middle Yangtze River basin. Foundation: National Natural Science Foundation of China, No.40701015; Key Project of National Natural Science Foundation of China, No.40730635 Author: Zhang Qiang (1974–), Ph.D and Associate Professor, specialized in natural hazards and climatic changes, hydrologic statistics, floods and fluvial geomorphology.     

长江经济带铁路客运通达能力空间格局及第三产业发展效应分析

铁路作为长江经济带综合立体交通走廊的基础组成部分,是构建运输大通道、实现要素快速无障碍流动、推动带域经济发展的重要支撑。以经济带内129个城市为研究对象,分析2000~2015年铁路快速化和高速化过程中客运通达能力演化特征,并利用市域面板数据模型分析其对城市第三产业发展的影响,结果表明：铁路客运通达能力随既有线提速增能和高等级新线开通大幅提升,但城市间旅行时间因铁路网建设空间密度和时间梯度差异产生“时空收敛”非均衡性;低旅行时间网络在主要都市区不断强化,向外持续扩张中沿区际联系主通道出现地带间高可达网络融合,铁路走廊以区域中心城市为节点重构经济带交通区位格局,实现城市群整合、地带间网络化交流;铁路客运发展促进第三产业能力提升和要素集聚,空间上表现为东中部高、西部低,铁路枢纽节点城市、传统干线通道沿线城市和新建铁路沿线城市受到较强的正向作用。     

Assessing the morphodynamical complexity of a large river in planning hydroeconomic measures (as exemplified by the Ob’)

Along the entire length of a large river there is taking place a substantial change in the formation conditions and stability of the channel, the rate and character of channel deformations and, accordingly, in the possibilities of water resources utilization, transport and engineering development of the river. By parametrizing the channel processes, it is possible to rank the river sections according to the degree of complexity of the channel processes, forms of their manifestation, and to the regime of channel reconfiguration, which, in turn, determines the possibilities of planning the measures ensuring the water resources utilization. Using the Ob’ as an example, we provide a rationale for the criteria for singling out the river sections differing by the degree of complexity of the channel processes, on the basis of parameters characterizing the forms of their manifestation, the state of the channels, and the intensity of deformations. We have identified eight sections of a different length, sequentially alternating along the length of the river from the confluence of the Biya and Katun’ as far as the mouth. The ranking of the river sections permitted the future planning of the water resources utilization measures.     

武汉都市圈经济联系的空间结构

都市圈空间结构是城市体系中最综合、最富于变化的热点部分。基于武汉都市圈近年来的统计资料,构建经济联系强度模型,定量分析武汉都市圈空间竞争与范围的动态性特征:中心城市对外经济联系存在主要方向,具有时间惯性,空间极化明显;地域空间上经济联系作用强度距离衰减,形成圈层结构分异。从点、线、面组合关系角度,构建节点中心性、通道网络性、范围系统性指标,定量揭示出武汉都市圈经济联系的空间结构等级层次性特征:中心城市中心性等级差异明显,空间分布不均,与交通地理区位紧密相关;主要通道与侍服能力也存在等级层次性,明显形成两城际交通走廊;中心城市腹地范围与自身外向经济联系强度密切相关,受自然地理、行政区划影响明显。     

珠江三角洲网河区水文与地貌特征变异及其成因

采用珠江三角洲网河区数十年来的人类活动和水文特征资料，通过分析人类活动的水文响应特征，发现该地区近10年多来水文情势发生了显著异变。主要表现在河道人工采砂以及大洪水冲刷导致河床下芬，部分断面水位－流量关系异变。部分河段冲淤特征倒转，汊河分水分沙比发生变化。围垦，臾，码头建设以及水闸的不合理调度使得水量集中，蓄滞洪能力减小，河道流量增加。三角洲上部河床剧烈下切，汇流速度加快；而口门多呈淤只状态，加之海平面上升，潮流顶托阻水，三角洲腹地水位抬升，洪涝威胁加剧。剧烈人类活动是珠江三角洲网河区水文与地貌特征变异的直接原因。     

Morphometric and geological conditions for sediment accumulation in the Udava River,Outer Carpathians,Slovakia

The accumulation of sediment in river channels is a phenomenon that is not only influenced by the channel morphology, but also by the physical and geographical characteristics and the endogenous and exogenous processes taking place in the catchment. This paper presents an analysis of the impact the changes in lithological conditions have on the morphological and morphometric parameters of the Udava River channel and their relation to the channel accumulation forms representative of the river’s longitudinal profile as well as of its planform. Results document when accumulation forms occur and what is their spatial distribution within the longitudinal and cross-sectional river profiles. More resistant structures created sections with a lower degree of sedimentation, while in depression segments the degree of sedimentation was higher. With the increase in longitudinal slope, the impact of channel width on the average channel bar size increased. Also a difference in the accumulation was observed between the left and right bank which could be possibly explained by the impact of Coriolis force.     

1980—2020年粤港澳大湾区城镇用地空间格局类型演变及其驱动力多维探测

深入研究1978年改革开放以来粤港澳大湾区城镇用地空间格局类型,探索土地城镇化多维和交互驱动机制,对推进粤港澳大湾区建设,打造世界级城市群具有重要意义。本文基于模糊聚类,从规模、形态和分布3个维度划分和定义粤港澳大湾区城镇用地空间格局类型,利用地理探测器测度城镇用地空间格局多维变化驱动力及其交互作用。结果表明：① 粤港澳大湾区城镇用地空间格局类型包括分形/复杂大面积型、分形小面积型、复杂小面积型、简单小面积型和散布型5种类型,城镇用地规模和形状复杂性具有一定的正相关性,2010年后用地规模趋于稳定,形态的规则性和紧凑性得到优化,分布集中。② 人口、GDP、地方财政收入、固定资产投资额和路网密度等社会经济因素对城镇用地面积和形态变化影响显著,核心城市对城市群发展的牵引作用在2000年后得以显现。2010—2020年各影响因子对城镇用地面积、分布和类型变化的作用差异有所减弱,但社会经济因素对形状特征的影响力上升。③ 城镇用地面积特征变化的影响力交互作用最为多样,表现有非线性增强、协同增强、单因子减弱和非线性减弱4种类型;对形状、分布和空间格局类型变化的影响力交互作用主要表现为协同增强和非线性增强。核心城市牵引力、路网密度、河网密度与多数因子交互产生“1+1>2”的效果,反映出城市群核心区位、交通优势对城镇用地扩展的强烈推动作用。     

Hydrogeomorphology downstream from bridges

Although recent studies have quantified effects upon river channel morphology downstream of reservoirs, urban areas and channelization schemes, consideration has not been given to effects upon channels downstream of road bridges. Engineering literature focuses upon hydrologic considerations involving estimation of peak flow at the bridge site, and upon hydraulic aspects including backwater effects and scour around the bridge and piers. A reconnaissance survey at 19 bridges in the New Forest shows that channel shape changes below many bridges with width-depth ratios increasing substantially to double their value; that apparent channel capacities may increase below the bridge to twice their above-bridge value, due to incision and scour; and that such effects can be evident for distances downstream of the bridge of the order of 10 times channel width. Reference to large-scale topographic maps for one site, and to maps and large-scale aerial photographs for 15 sites in south central England, shows how these sources can be used to provide measurements of channel width above and below bridges and this indicates that the average downstream width is 1.99 times the upstream width. Such channel adjustments should be considered when measuring morphological and ecological characteristics of river channels and when explaining reaches of rapid channel adjustment.     

基于局部聚类的网络Voronoi图生成方法研究

提出一种将网络约束下的Voronoi和空间聚类相结合的方法,通过构造局部的聚类分析方法对网络边进行加权,根据实际的点过程性质可以把权重定义为加权或者乘权,进行标准化后与道路段本身长度融合进行计算,依此生成网络Voronoi图,以期理解城市街道的空间特性。以武汉市江汉区为例,对城市网格管理系统产生的城市事件进行算法验证,结果表明,该方法提供了一种灵活的网络约束下的服务区域划分工具,可用于基于网络空间点过程影响下的服务区划分,也可用于系统性地定量刻画城市管理的动态特性。     

Reconceptualising coarse sediment delivery problems in rivers as catchment-scale and diffuse

This paper assesses river channel management activities in the context of the interaction between coarse sediment delivery, climate change, river channel response and flood risk. It uses two main sources of evidence: (1) an intensive instrumentation of an upland river catchment using both traditional hydrometric and novel sediment sensing methods; and (2) a sediment delivery model that combines a treatment of sediment generation from mass failure with a treatment of the connectivity of this failed material to the drainage network. The field instrumentation suggests that the precipitation events that deliver sediment from hillslopes to the drainage network are different to those that transfer sediment within the network itself. Extreme events, that could occur at any time in the year (i.e. they are not dependent on wet antecedent conditions), were crucial for sediment delivery. However, sustained high river flows were responsible for the majority of transfer within the river itself. Application of three downscaling methods to climate model predictions for the 2050s and 2080s suggested a significant increase in the number and potential volume of delivery events by the 2050s, regardless of the climate downscaling scenario used. First approximations suggested that this would translate into annual bed level aggradation rates of between 0.10 and 0.20 m per year in the downstream main channel reaches. Second, the importance of this delivery for flood risk studies was confirmed by simulating the effects of 16 months of measured in-channel simulation with river flows scaled for climate change to the 2050s and 2080s. Short-term sedimentation could result in similar magnitude increases in inundated area for 1 in 0.5 and 1 in 2 year floods to those predicted for the 2050s in relation to increases in flow magnitude. Finally, we were able to develop an alternative approach to river management in relation to coarse sediment delivery, based upon reducing the rates of coarse sediment delivery through highly localised woodland planting, under the assumption that reducing delivery rates should reduce the rate of channel migration and hence the magnitude of the bank erosion problem. Thus, the paper demonstrates the need to conceptualise local river management problems in upland river environments as point scale manifestations of a diffuse sediment delivery process, with a much more explicit focus on the catchment scale, if our river systems are to become more insulated from the impacts of future climate changes.     

复杂网络视角下的城市人流空间概念模型与研究框架

城市内人流特征研究一直是城市地理学和城市空间研究的重要领域之一.针对已有相关研究存在仅侧重于从人口规模、密度视角分析空间分布及格局特征,而对隐藏于空间分布背后,因人流动而建立的空间交互关系关注不足的问题.本文以流空间理论、复杂网络理论、空间行为交互理论为理论基础,立足基于流、网络剖析城市内部空间中各要素间的相互作用及关...     

基于洪涝情景模拟的城市公共服务灾害应急响应空间可达性评价——以医疗急救为例

在气候变化和城市化背景下,日益频发的洪涝灾害业已成为当前中国城市面临的重大挑战,也是城市灾害管理和应急响应研究的热点问题之一。本文旨在构建一套适用于城市尺度的洪涝灾害应急响应能力评估范式,以上海市外环以内中心城区为研究区,采用洪涝数值模拟与GIS网络分析相结合的研究方法,评估了当前以及未来正常条件和不同重现期洪涝情景下,城市关键公共服务部门（120急救）应急响应的空间可达性。结果显示：洪涝淹没强度（范围和水深）、道路交通状况（车流速度）以及应急服务机构的数量和位置共同决定了城市洪涝灾害医疗急救的服务范围及响应时间;由于上海市中心城区洪涝影响范围主要分布在黄浦江两岸2~3 km以内区域,因此洪涝对整个中心城区应急医疗服务的影响有限,主要是位于滨江地区部分医院的应急响应范围较正常状态下明显减少,120急救车辆无法或延迟达到部分救援点。研究表明基于洪涝情景模拟的城市公共服务应急响应空间可达性定量化评估方法,具有重要的科学价值和实践意义,可为中国城市洪涝灾害应急管理提供决策依据。     

斯洛伐克外喀尔巴阡山脉Udava河泥沙淤积形态和地质条件（英文）

The accumulation of sediment in river channels is a phenomenon that is not only influenced by the channel morphology, but also by the physical and geographical characteristics and the endogenous and exogenous processes taking place in the catchment. This paper presents an analysis of the impact the changes in lithological conditions have on the morphological and morphometric parameters of the Udava River channel and their relation to the channel accumulation forms representative of the river's longitudinal profile as well as of its planform. Results document when accumulation forms occur and what is their spatial distribution within the longitudinal and cross-sectional river profiles. More resistant structures created sections with a lower degree of sedimentation, while in depression segments the degree of sedimentation was higher. With the increase in longitudinal slope, the impact of channel width on the average channel bar size increased. Also a difference in the accumulation was observed between the left and right bank which could be possibly explained by the impact of Coriolis force.     

Geometric properties of river cross sections and associated hydrodynamic implications in Wuhan–Jiujiang river reach, the Yangtze River

Based on measured hydrological data by using ship-mounted Acoustic Doppler Current Profiler (ADCP) instrument, we analyzed shapes of river cross sections of the middle Yangtze River basin (mainly focusing on Makou and Tianjiazhen river reach). Hydrodynamic properties of river channels were also discussed. The research results indicate that nonlinear relationships can be identified between river-width/river-depth ratio (W/D ratio), sizes of cross section and mean flow velocity. Positive relations are detected between W/D ratio and mean flow velocity when W/D<1; and negative relations are observed when W/D>1. Adverse relationships can be obtained between W/D ratio and cross-section area. Geomorphologic and geologic survey indicates different components of river banks in the wider and narrower river reaches respectively. These may be the main driving factors causing unique hydrological properties of river channels in the middle Yangtze River basin. Narrower river cross sections tend to raise water level in the upstream river reach near narrower river channel, giving rise to backwater effects. River knots can cause serious backwater effects, which is harmful for flood mitigation. However river knots will also stabilize river channel and this will be beneficial for river channel management. The results of this paper may be helpful for flood mitigation and river channel management in the middle Yangtze River basin.     

基于路网分割的京津冀城乡空间识别及特征分析

提出一种基于路网分割应用于区域尺度快速识别城乡边界的方法。该方法利用路网与城市空间格局的强耦合联系,通过城乡斑块地理分割与精度计算确定城市斑块的最优解,识别区域城乡空间。以京津冀为例开展方法验证,分析了区域城乡空间格局、路网特征及城市用地经济效率。结果表明,该方法识别精度较高,可用于低成本、快速、高效的区域城乡空间识别;京津冀城市空间格局呈现“大京津、小河北”的差异性,路网密度特征呈现京、津、石3个显著的高密度区域,二者存在高耦合性;2015年该区域城市用地经济效益总体良好,石家庄、保定、和承德3市综合效率值欠佳,需进一步提高土地利用效率。     

珠江河网分形机理研究

以不同时期珠江网河历史地图及遥感影像为基础,进行了河网分形计算,并从河道发育、人为活动等多个角度分析了珠江网河分形机理。在发育过程中,1883-2001年间河网分维值逐渐减小;在空间上,正干水道中潮道分维值大于分汊河道。分析认为,人为活动是导致珠江网河分形变化的主要因素:联围筑闸消灭横向支汊、口门整治及河道固化减小了河道冲决的几率、河道挖沙引起的水沙分流比变化改变了河道冲淤特性。     

广佛都市圈网络外部性的城镇借用规模绩效检验

在城市网络外部性的环境下,借用规模可以使城镇突破地理距离和规模等级限制,通过网络联系实现城镇经济的共同增长。基于理论辨析,以城市网络的借用规模效应为视角,检验网络外部性下城镇借用规模绩效对城镇经济增长的作用。在回顾网络外部性理论的基础上,以广佛都市圈城镇作为研究对象,首先利用偏离均值标准差倍数的方法解析区域绩效、集聚阴影等特征;其次,基于城镇规模、借用规模、交通网络通达性、科技创新外溢性对城镇经济增长的耦合作用,建立多元回归模型检验网络外部性的发生机制。研究发现：① 城镇既有人口规模越小,区域绩效值越低,10万人的人口规模是绩效特征的分界点,大于和小于10万人的城镇分别呈现出借用规模绩效和集聚阴影特征;② 基于新增注册企业数量和企业网络点度的区域绩效均呈现出较为明显的圈层式空间特征,且基于企业网络点度检验的空间分异特征更为突出;都市圈主城区近郊圈层城镇的绩效较明显,而主城区远郊圈层城镇的集聚阴影现象显著;③ 新增注册企业数的绩效与城镇既有规模关系最为紧密,与区域交通枢纽、借用规模、借用绩效、跨镇合作专利等解释变量的弹性系数依次降低;区域交通网络、技术合作网络的提升有利于促进城镇要素集聚,并通过网络外部性效应影响都市圈的城镇化发展。