Urban flood risk assessment using sewer flooding databases

Sustainable water management is a global challenge for the 21st century. One key aspect remains protection against urban flooding. The main objective is to ensure or maintain an adequate level of service for all inhabitants. However, level of service is still difficult to assess and the high-risk locations difficult to identify. In this article, we propose a methodology, which (i) allows water managers to measure the service provided by the urban drainage system with regard to protection against urban flooding; and (ii) helps stakeholders to determine effective strategies for improving the service provided. One key aspect of this work is to use a database of sewer flood event records to assess flood risk. Our methodology helps urban water managers to assess the risk of sewer flooding; this approach does not seek to predict flooding but rather to inform decision makers on the current level of risk and on actions which need to be taken to reduce the risk. This work is based on a comprehensive definition of risk, including territorial vulnerability and perceptions of urban water stakeholders. This paper presents the results and the methodological contributions from implementing the methodology on two case studies: the cities of Lyon and Mulhouse.     

英国的洪水风险管理

为了减少洪水造成的破坏和损失，近年来世界各国的洪水管理已从单一的防洪工程向洪水风险管理转变。除了能进行有效的洪水防御外，洪水风险管理还被认为是维持生物多样性、河流及海岸生态系统的重要手段。回顾了英国的洪水风险管理及其组成体系，并分析讨论了未来可能面临的问题及应对措施。结果表明，随着全球气候变化及社会经济发展，洪水发生的频率及其影响正在增加。因此，如何全面综合考虑降雨、径流、河流、洪泛区以及人类活动、社会经济规划、发展和管理等诸多因素是实施洪水风险管理面临的重要课题。     

The efficiency of asset management strategies to reduce urban flood risk

In this study, three asset management strategies were compared with respect to their efficiency to reduce flood risk. Data from call centres at two municipalities were used to quantify urban flood risks associated with three causes of urban flooding: gully pot blockage, sewer pipe blockage and sewer overloading. The efficiency of three flood reduction strategies was assessed based on their effect on the causes contributing to flood risk. The sensitivity of the results to uncertainty in the data source, citizens' calls, was analysed through incorporation of uncertainty ranges taken from customer complaint literature. Based on the available data it could be shown that increasing gully pot blockage is the most efficient action to reduce flood risk, given data uncertainty. If differences between cause incidences are large, as in the presented case study, call data are sufficient to decide how flood risk can be most efficiently reduced. According to the results of this analysis, enlargement of sewer pipes is not an efficient strategy to reduce flood risk, because flood risk associated with sewer overloading is small compared to other failure mechanisms.     

Floodplain management strategies for flood attenuation in the river Po

This paper analyses the effects of different floodplain management policies on flood hazard using a 350 km reach of the river Po (Italy) as a case study. The river Po is the longest Italian river, and the largest in terms of streamflow. The middle‐lower Po flows East some 350 km in the Pianura Padana (Po Valley), a very important agricultural region and industrial heart of Northern Italy. This portion of the river consists of a main channel (200–500 m wide) and a floodplain (overall width from 200 m to 5 km) confined by two continuous artificial embankments. Floodplains are densely cultivated, and a significant portion of these areas is protected against frequent flooding by a system of minor dykes, which impacts significantly the hydraulic behaviour of the middle‐lower Po during major flood events. This study aims at investigating the effects of the adoption of different floodplain management strategies (e.g. raising, lowering or removing the minor dyke system) on the hydrodynamics of the middle‐lower Po and, in particular, on flood‐risk mitigation. This is a crucial task for institutions and public bodies in charge of formulating robust flood risk management strategies for the river Po. Furthermore, the results of this study are of interest for other European water‐related public bodies managing large river basins, in the light of the recent European Directive 2007/60/EC on the assessment and management of flood risks. The analysis is performed by means of a quasi‐2D hydraulic model, which has been developed on the basis of a laser‐scanning DTM and a large amount of calibration data recorded during the significant flood event of October 2000. Copyright © 2010 John Wiley & Sons, Ltd.     

Using water management infrastructure to address both flood risk and the urban heat island

Abstract

Two important environmental challenges for many cities are to prevent flooding after heavy rain, and to minimize warming due to the urban heat island effect. There is a close link between these two phenomena, as rainfall intensity increases with rising air temperature. The two problems of flood management and urban warming therefore need to be tackled together. In particular, management strategies that contribute to reducing urban temperatures should be recognized as a means of reducing flood risk, especially in regions prone to intense rainfall.     

城市排水防涝基础设施应对能力的三个阈值

城市排水管网、沟渠、河湖水系是承纳、转输、调蓄暴雨径流的重要基础设施，在应对城市暴雨内涝中发挥着至关重要的作用。城市排水防涝基础设施受设计标准、运行维护水平、城市下垫面环境变化等多重因素的影响，其自身应对暴雨的能力差异较大。科学量化城市排水防涝设施的应对能力对城市洪涝预报、预警和应急调度十分必要。本文提出了城市排水防涝基础设施应对能力的三个阈值，即：雨水管渠排水能力阈值、内涝防治系统应对能力阈值和应急设施防御上限阈值。这三个阈值通俗讲就是“不积水”阈值、“不内涝”阈值和“不失防”阈值。基于郑州2021年“7·20”特大暴雨灾害的调研结果，对三个阈值的表征指标和确定方法进行了初步探讨。结合文献调研，对北京、东京、深圳等城市对应阈值进行了分析量化，对暴雨量级超过不同阈值标准后的防控策略进行了探讨，提出了城市排水防涝阈值协同提升途径，可为城市极端暴雨的防控提供决策参考。     

Integrated flood management.

While there have been a number of international initiatives centred around hydrological sciences and technical approaches, the social, economic, environmental, and legal and institutional aspects of flood management have been dealt with sporadically and in a limited manner. WMO and the Global Water Partnership have established the Associated Programme on Flood Management (APFM) to address these issues and developed a concept of Integrated Flood Management (IFM) in 2002. This article is the result of the integrated flood management approaches through pilot projects and multi-disciplinary approaches launched by the initiative since the establishment of the IFM concept. This approach seeks to integrate land- and water-resources development in a river basin, within the context of Integrated Water Resources Management (IWRM) and aims at maximizing the benefits from floodplains and at the same time reducing loss of life from flooding. This approach identified the key elements of IFM and recommended that these can be put in place by: adopting a basin approach to flood management; adopting a multi-disciplinary approach in flood management; reducing vulnerability to and risks from flooding; enabling community participation; and preserving ecosystems; and addressing climate change and variability, supported by enabling mechanism through appropriate legislation and regulations.     

Catchment Flood Management

Abstract

In recent years, there has been a growing concern worldwide about climate change and the corresponding apparent increase in the risk and frequency of flooding and about the implications for a wide range of river basin management issues. This paper describes the United Kingdom government's approach to implementing Catchment Flood Management Plans (CFMPs), which will provide a large-scale strategic planning framework for the integrated management of flood risk to people and the development of the natural environment in a sustainable manner. This unified approach is to be adopted across England and Wales, with a view to establishing a unified framework to study flood management in each major catchment. Following on from this introduction to the U.K. approach to high-level flood management, details are given of a study where better water quality management during flood flow conditions has been shown to require a catchment-wide approach to reducing diffuse source pollution from agricultural regions. This study also shows that without this holistic approach to water management, a major cause of non-compliance with an EU Directive would not have been established for this river basin.     

国外有关洪水保险的实践及对我国的启示

洪水保险是一项重要的非工程防洪措施,是行之有效的洪灾风险管理手段,已被越来越多的国家所重视.美国是最早以立法形式将洪水保险作为洪水风险管理系统,制定并实施全国性洪水保险计划的国家,经过艰难曲折的探索,闯出了一条成功之路.英国是成功地采用市场化洪水保险模式的国家之一.我国20世纪80年代末开始洪水保险尝试,目前还处于探索阶段.分析英、美两国不同的洪水保险制度,可以为我国提供借鉴.     

Floodplain Inundation Analysis Combined with Contingent Valuation: Implications for Sustainable Flood Risk Management

This study presents the results of open-ended contingent valuation method (CVM) to estimate the residents’ maximum willingness to pay (WTP) for flood insurance and structural flood control measures in the Neka River Basin in Northern Iran. Flood inundation analysis and floodplain risk mapping were conducted by applying the HEC-RAS model combined with GIS analysis. A calibrated 100-year flood risk inundation map was considered as a basis for this research. This paper demonstrates applicability of CVM combined with flood inundation analysis to understand public participation for flood risk management, and their perception of flooding, considering associated socioeconomic and environmental factors. The results have shown that stated WTPs significantly varies with household income, distance people live from the river and the land use type of properties. Findings of this study suggest that the majority of respondents view flood hazard as the most important natural disaster. Furthermore, WTPs are significantly higher for those who have high level of flood risk perception. Three policy options for flood risk management are discussed, which include flood zoning and land use regulation, flood insurance program, and structural measure of levee construction. The advantages and disadvantages of each option are explored. It was concluded that a combination of possible mitigation options should be considered in order to achieve sustainable flood risk management in the Neka River Floodplain.     

Predicting Flood Hazard Indices in Torrential or Flashy River Basins and Catchments

Flood hazard maps are one of the main components of any flood risk management strategy. It is predicted that the degree of flood risk is going to significantly increase in the future due to climatic and environmental changes, and hence it is increasingly important that state-of-the-art methods are implemented for assessing human stability in floodwaters. Therefore, this paper focuses on proposing more accurate and detailed guidelines for predicting flood hazard indices in small and steep river basins or catchments, prone to the occurrence of flash flooding. The results obtained in this study indicate that for river basins with an average bed gradient greater than 1% (i.e. torrential or flashy river basins or catchments), then the flood hazard indices should be predicted using criteria which are based on the physical interpretation of the processes that affect the human stability in floodwaters, i.e. mechanics based and experimentally calibrated flood hazard assessment methods.     

The political economy of flood management reform in China

Abstract

This article examines the political economy factors that are likely to shape China’s attempts to reform its approach to managing floods, particularly by implementing integrated flood risk management (IFRM). IFRM emphasizes the use of structural and non-structural measures to reduce flood risk, rather than simply seeking to control flooding. For China, reducing flood risk is increasingly important in light of urbanization and climate change. However, a number of political economy issues, especially the division of power between central and local levels of government, create considerable challenges for flood management reform. This article examines China’s approach to implementing IFRM in light of existing political economy constraints and the institutional framework for flood management. It argues that effective flood management reform requires addressing common challenges, including interjurisdictional and intersectoral coordination and stakeholder participation.     

A Decentralized Bi-Level Fuzzy Two-Stage Decision Model for Flood Management

Flood, as a serious worldwide environment problem, can lead to detrimental economic losses and fatalities. Effective flood control is desired to mitigate the adverse impacts of flooding and the associated flood risk through development of cost-effective and efficient flood management decisions and policies. A bi-level fuzzy two-stage stochastic programming model, named BIFS model is developed in this study to provide decision support for economic analysis of flood management. The BIFS model is capable of not only addressing the sequential decision making issue involving the two-level decision makers, but also correcting the pre-regulated flood management decisions before the occurrence of a flood event in the two-stage environment. The probabilistic and non-probabilistic uncertainties expressed as probability density functions and fuzzy sets are quantitatively analyzed. The overall satisfaction solution is obtained for meeting the goals of the two-level decision makers by compromising, reflecting the tradeoffs among various decision makers in the two decision-making levels. The results of application of the BIFS model to a representative case study indicate informed decision strategies for flood management. Tradeoffs between economic objectives and uncertainty-averse attitudes of decision makers are quantified.     

基于MIKE FLOOD的中小河流溃堤洪水风险分析

近年来洪水引发的中小河流堤防溃决等洪水灾害风险问题凸显,因此进行溃堤洪水风险分析对于加强中小河流的洪水管理及减少溃堤洪水带来的损失具有十分重要的意义。以江西省罗塘河为例,借助MIKE软件中的MIKE 11、MIKE 21及其耦合模块对罗塘河遭遇10a一遇及20a一遇洪水进行溃堤洪水演进模拟。然后依据灾害系统理论从洪水的危险性和易损性两方面选择淹没水深、淹没流速、淹没历时等7个指标构建溃堤洪水风险评价指标体系。最后利用GIS技术与层次分析法对罗塘河洪水风险进行了评价。结果表明:洪水危险区面积为0.19 km~2,占研究区总面积的2.18%,主要分布在地势低洼的富港地区;重灾区和中灾区面积为1.25 km~2,占研究区总面积的14.37%,主要分布在重文和蒋元乐家;安全区为研究区域内洪水没有到达并且地物覆盖价值较低的地区,包括游家店、下胡、大塘杨家和马山等处。研究成果可为中小河流防洪规划、避洪转移等提供参考依据。     

Urban and river flooding:Comparison of flood risk management approaches in the UK and China and an assessment of future knowledge needs

Increased urbanisation,economic growth,and long-term climate variability have made both the UK and China more susceptible to urban and river flooding,putting people and property at increased risk.This paper presents a review of the current flooding challenges that are affecting the UK and China and the actions that each country is undertaking to tackle these problems.Particular emphases in this paper are laid on(1) learning from previous flooding events in the UK and China,and(2) which management methodologies are commonly used to reduce flood risk.The paper concludes with a strategic research plan suggested by the authors,together with proposed ways to overcome identified knowledge gaps in flood management.Recommendations briefly comprise the engagement of all stakeholders to ensure a proactive approach to land use planning,early warning systems,and water-sensitive urban design or redesign through more effective policy,multi-level flood models,and data driven models of water quantity and quality.     

城市洪涝灾情评估与风险管理初探

快速城市化背景下城市洪涝问题日趋严重,城市洪涝已成为制约经济社会可持续发展的重要瓶颈。聚焦城市洪涝灾情评估与风险管理,从城市洪涝灾情评估方法、城市洪涝风险分析与区划和城市洪涝风险管理与对策3个方面开展研究,预期成果可为城市洪涝灾害防治提供科学支撑和技术保障。     

基于HEC-RAS及HEC-GeoRAS的溃坝洪水分析

洪水漫顶、渗漏等原因引起的垮坝失事,将会给下游人民带来巨大的生命财产损失,因此,对溃坝洪水引起的淹没范围的准确预测至关重要。通过对大渡河上22座梯级水电站进行对比分析,选定长河坝电站水库大坝为研究对象,分析洪水漫顶引起的长河坝溃坝,及由其引起的下游黄金坪、泸定水电站的连续溃坝对泸定县的淹没范围。首先利用HEC-GeoRAS和Google地球提取研究区域的地形数据,然后将建好的模型导入到一维溃坝洪水计算工具HEC-RAS中进行溃坝洪水演进模拟,最后通过HEC-GeoRAS分析研究区域的洪水淹没范围及流速分布。结果表明:由长河坝溃坝引起的下游泸定县的洪水淹没范围为左右岸平均漫堤宽度约200 m,已经淹没到了城区;从流速分布图得出河道中心的流速均较大,最大流速为16.217 m/s。研究结果可为洪水风险图的制作及防洪决策提供一定的技术支持。     

Calibration of a 1D/1D urban flood model using 1D/2D model results in the absence of field data

Recently increased flood events have been prompting researchers to improve existing coupled flood-models such as one-dimensional (1D)/1D and 1D/two-dimensional (2D) models. While 1D/1D models simulate sewer and surface networks using a one-dimensional approach, 1D/2D models represent the surface network by a two-dimensional surface grid. However their application raises two issues to urban flood modellers: (1) stormwater systems planning/emergency or risk analysis demands for fast models, and the 1D/2D computational time is prohibitive, (2) and the recognized lack of field data (e.g. Hunter et al. (2008)) causes difficulties for the calibration/validation of 1D/1D models. In this paper we propose to overcome these issues by calibrating a 1D/1D model with the results of a 1D/2D model. The flood-inundation results show that: (1) 1D/2D results can be used to calibrate faster 1D/1D models, (2) the 1D/1D model is able to map the 1D/2D flood maximum extent well, and the flooding limits satisfactorily in each time-step, (3) the 1D/1D model major differences are the instantaneous flow propagation and overestimation of the flood-depths within surface-ponds, (4) the agreement in the volume surcharged by both models is a necessary condition for the 1D surface-network validation and (5) the agreement of the manholes discharge shapes measures the fitness of the calibrated 1D surface-network.     

海河蓄滞洪区洪水资源利用的水污染风险分析

海河蓄滞洪区的洪水资源利用是提高流域水资源利用效率，缓解水资源供需矛盾的措施之一。但由于海河流域水污染严重，洪水资源利用时存在水污染风险，须在利用过程中谨慎考虑。本文分析了海河大黄浦洼蓄滞洪区洪水资源利用的水源水质问题，应用建立的蓄滞洪区水质预报模型，计算分析了各种分洪条件下的水质情景。阐述了洪水资源利用时水污染问题的不确定性以及相应的水污染风险，并结合大黄浦洼的实际水环境条件，提出了减缓水污染风险的措施建议。     

Assessing the legitimacy of flood risk governance arrangements in Europe: insights from intra-country evaluations

Legitimacy has received comparatively less attention than societal resilience in the context of flooding, thus methods for assessing and monitoring the legitimacy of flood risk governance arrangements are noticeably lacking. This study attempts to address this gap by assessing the legitimacy of flood risk governance arrangements in six European countries through cross-disciplinary and comparative research methods. On the basis of this assessment, recommendations to enhance the legitimacy of flood risk governance in Europe are presented.