Resilient urban drainage – Options of an optimized area-management

There is a need for an integrated approach for all involved stakeholders to adapt urban infrastructures to climate change effects and to take into account uncertainties of future developments. By integrating all relevant planning disciplines, a first step towards implementation of resilient technical and social infrastructures can be achieved. With the major goal of optimizing area-management as part of water sensitive urban design, the water sector and its area requirements build the main focus of this study. After identifying local flood hazards and potential surficial retention areas, the additional usage of decentralized stormwater management facilities for flood protection is tested in selected sectors. The results of the study confirm that the combined usage of decentralized facilities for pluvial flooding is a first step to protect urban infrastructure. It shows that decentralized facilities are more flexible than centralized facilities and, thus, have a higher adaptation capacity which is needed considering the various effects of climate change.     

Design hydrograph and routing scheme for flood mapping in a dense urban area

Definition of flood risk maps is a task to which modern surface hydrology devotes substantial research effort. Their impact on the management of flood-prone, dense, urban areas has increased the need for better investigation of inundation dynamics. The problems associated with the aforementioned topics range from the definition of the design hydrograph and the identification of the surface boundary conditions for the flood routing over the inundation plan, to the choice of the hydrodynamic model to simulate urban flooding. Most of academic and commercial mathematical models, solving the De Saint Venant equations, fail on complex topography. Frequently encountered difficulties concern steep slopes, geometric discontinuities, mixed flow regimes, and initially dry areas. In the present paper, flood routing modelling approaches in urban areas and principles for the definition of the design flood events are outlined. The paper shows how urban flooding can be simulated by a quasi-2D hydrodynamic model that makes use of a network of connected channels and storages to simulate flow, respectively, on the streets and into the building blocks. Furthermore, the paper shows that, when flood hazard is assessed by considering flood extent, water depth and flow velocity, an in-depth analysis of the use of design hydrographs that maximise peak flow or inundation volume is needed.     

增强现实技术于洪水风险沟通中的应用

气候变迁,特别是洪水问题给地处三角洲的城市带来了与日俱增的风险。作为应对手段,提出一种整合性的洪水风险管理方法,该方法确保了洪水风险沟通在洪水风险管理战略中的重要地位。洪水的可视化作为洪水风险沟通的一种工具,在改变人们对洪水风险的观念方面有着强大的作用。它可以通过互动的方式,使当地的利益相关者了解洪水的剩余风险和未来风险。其中增强现实技术作为一种可视化手段,它的快速发展与应用为风景园林设计、规划与教育等领域提供了崭新的交互方式。首先,探讨增强现实技术(AR)在洪水风险沟通中的应用现状,并重点关注增强现实技术的2个关键应用领域:对现场决策的支持和针对高层次设计的可视化与对景观干预的评估。随后,展示一种基于增强现实技术所开发的应用,该款创新性的应用为洪水风险沟通提供了一种轻量化的可视化手段。     

Application of spatial statistics as a screening tool for sustainable flood retention basin management

In the context of climate change and the EU flood directive, this paper analyses and explores sustainable flood retention basins (SFRB) as adaptive structures contributing to water resources management and flood risk control. A dataset of 371 potential SFRB (including many operating reservoirs) characterized by 40 variables have been surveyed across central Scotland. However, the spatial properties of these SFRB, such as water storage (which relates to flooding depth) in different regions, are ambiguous. This paper uses geostatistics on the Scottish dataset. Spatial analysis showed that ordinary kriging, which is a spatial interpolation method, could be successfully applied to estimate numerical values for all key flood control variables everywhere in the study area. Moreover, the probability that certain threshold values relevant to flood control managers were exceeded can also be calculated by using disjunctive kriging. The findings provide an effective screening tool in assessing flood control using SFRB.     

Citywide multi-grid urban flood modelling: the July 2012 flood in Beijing

Global flood management is a major issue for most cities which have to deal with worsening factors such as climate change and fast urban growth. Computer models have been used to model and understand urban flooding on a local scale in cities (25–50 km²). It has been practically impossible to model bigger cities in one go in sufficiently high resolution due to the heavy computations involved.

The present paper describes a new modelling approach for urban flooding which allows modelling on large city scale (1000 km²) while keeping sufficient resolution, e.g. 5 m or 10 m grid. The multicell approach is applied for the city of Beijing for July 21st, 2012 flood event. Model results are compared to testimonials from the 2012 event. Comparison to traditional 2D urban flood computations shows that the multicell approach is much faster than standard detailed models while keeping a suitable level of precision.     

Quantitative fault tree analysis for urban water infrastructure flooding

Flooding in urban areas can be caused by heavy rainfall, improper planning or component failures. Few studies have addressed quantitative contributions of different causes to urban flood probability. In this article, we apply probabilistic fault tree analysis for the first time to assess the probability of urban flooding as a result of a range of causes. We rank the causes according to their relative contributions. To quantify the occurrence of flood incidents for individual causes we use data from municipal call centres complemented with rainfall data and hydrodynamic model simulations. Results show that component failures and human errors contribute more to flood probability than sewer overloading by heavy rainfall. This applies not only to flooding in public areas but also to flooding in buildings. Fault tree analysis has proved useful in identifying relative contributions of failure mechanisms and providing quantitative data for risk management.     

Flooding of municipal solid waste landfills — An environmental hazard?

Municipal solid waste (MSW) landfills pose a long-lasting risk for humans and the environment. While landfill emissions under regular operating conditions are well investigated, landfill behaviour and associated emissions in case of flooding are widely unknown, although damages have been documented. This paper aims at developing a methodology for determining the proportion of MSW landfills endangered by flooding, and at evaluating the impact flooded landfills might have on the environment during a flood event.The risk of flooding of MSW landfills is assessed by using information about flood risk zones. Out of 1064 landfills investigated in Austria, 312 sites or about 30% are located in or next to areas flooded on average once in 200 years. Around 5% of these landfills are equipped with flood protection facilities. Material inventories of 147 landfill sites endangered by flooding are established, and potential emissions during a flood event are estimated by assuming the worst case of complete landfill leaching and erosion. The environmental relevance of emissions during flooding is discussed on the basis of a case study in the western part of Austria. Although environmental hazards need to be assessed on a site- and event-specific basis, the results indicate that flooded MSW landfills represent in general small environmental risks for the period of flooding. The longer term consequences of flooding are discussed in a next paper.     

Urban flood disaster management

Disaster management for urban areas is a growing priority owing to factors such as the relentless migration to cities, unplanned development, changing climate, and increasing operational and maintenance costs. New information and communication technologies offer improved opportunities to address these factors. This paper presents and describes the digital city concept as a means of capturing, analysing and applying (digital) information about the city area, its services, and their design and operation. In particular, the functionality of the digital city can be adapted for managing urban flood disasters. The paper highlights the need to manage the urban stormwater cycle integrated with urban planning. Urban flooding should be mitigated by having a judicious mix of both structural and nonstructural strategies, which are selected with the full participation of all stakeholders. The management of urban flooding is illustrated with application to the tropical island of St Maarten.     

Recognising barriers to implementation of Blue-Green Infrastructure: a Newcastle case study

There is a recognised need for a fundamental change in how the UK manages urban water and flood risk in response to increasingly frequent rainfall events coupled with planned urban expansion. Approaches centred on ‘living with and making space for water’ are increasingly adopted internationally. Nonetheless, widespread implementation of Blue-Green Infrastructure (BGI) is currently hampered by barriers that impede uptake and innovation. We investigate the barriers to implementation of BGI in Newcastle, UK, through a series of semi-structured interviews with professional stakeholders. We identify and categorise 17 types of barrier and identify targeted strategies to overcome the dominant barriers. We recommend promotion of BGI’s capacity to meet the objectives of multiple organisations and Local Authority departments, in addition to managing urban water. We conclude that strong business cases, supported by monetised evidence of benefits, and collaborative, inter-agency working could advance implementation of BGI within the current flood risk management legislation.     

The Governance of Local Urban Climate Adaptation: Towards Participation,Collaboration and Shared Responsibilities

This paper focuses on understanding the institutional determinants of adaptive capacity to illustrate emerging challenges and opportunities for climate adaptation in the context of urban pluvial flood risk management. The paper explores and compares the formal-legal as well as the perceived roles and responsibilities of key actor groups in the context of adaptation to urban pluvial flooding in the Dutch city Arnhem. The concluding section questions the assumed power of formal-legal rules and institutions in motivating key stakeholders to take action. It poses that, in order to stimulate participation and collaboration in local climate adaptation, more attention should be paid to the informal institutional context, in particular to the perception of responsibilities.     

The National Rivers Authority's Need for Models

The Water Resources Act 1991 requires the National Rivers Authority to exercise a general supervision over all matters relating to flood defence. There is need for information in order to manage flood defence – not only as part of the overall management of the catchment but, at a more detailed level, to plan and monitor capital and maintenance programmes.
The information requirements of the National Rivers Authority can be satisfied either by witnessing historic flood events, an approach disadvantaged by the infrequency of flood events, or by modelling the system, i.e. the rivers, coasts and flood plain. Once models are calibrated by specific flood events they can be used to predict the outcome of other events and to assess the response required to alleviate potential flooding. The different needs of the Authority can be satisfied by different modelling techniques using different levels of accuracy. Models can be used to analyse river and coastal systems to assess performance and target resources for maintenance and improvement.
The management of flood defences by specifying and monitoring their performance is considered, and a recent trial in reach specification based on modelling techniques is described.     

LAND USE AND FLOOD RISK THROUGH CATCHMENT FLOOD-MANAGEMENT PLANS

Catchment Flood Management Plans involve a high-level assessment of current flood risk and attempt to demonstrate how this risk could change with time. An influencing factor will be the changes to rural and urban land use on catchment hydraulics. By assessing a range of land use and urban-growth scenarios catchment wide, a 'catchment flood management plan' can demonstrate the cumulative effect on downstream flood-risk areas. 'Catchment flood management plan' methods also indicate how long-term land-use and climate changes can expose new areas to more frequent flooding. Techniques to assess these issues, up to a 50-year horizon, have been established as part of these pilot studies. In addition to briefly describing how land-use concerns are integrated into such concepts, this paper outlines how flood-management planning must evolve as a dynamic tool, to fulfil an on-going requirement for future development assessment.     

COMPENSATING FLOOD RETENTION ON PRIVATE LAND IN AUSTRIA: TOWARDS POLYCENTRIC GOVERNANCE IN FLOOD RISK MANAGEMENT?

Flood retention, in particular controlled flood retention, plays an increasingly prominent role in the portfolio of flood risk management strategies. Though a highly effective measure to reduce the risk of flooding for vulnerable areas, flood retention is land-intensive and infringes on landowners’ property rights. Implementation efforts are thus often hampered by the lack of availability of land as well as by the growing demands of (agricultural) landowners for compensation of flood retention services. The proliferation of flood retention not only changes riparian land uses but also results in a shift of authority, power, and agency to lower levels of government as well as to non-governmental actors, including the private landowners who provide the land for flooding but also those who benefit from flood retention. By the example of a compensation scheme for the controlled flood retention in Altenmarkt, an alpine municipality in Austria, this paper explores these nascent forms of governance through the lens of polycentricity. Along five core propositions in polycentric theory, the paper evaluates the governance implications of flood retention compensation in Austria and discusses the possibilities and limitations of flood retention for enhancing landscape resilience in riparian areas.     

Validating a rapid assessment framework for screening surface water flood risk

This research evaluates performance of a rapid assessment framework for screening surface water flood risk in urban catchments. Recent advances in modelling have developed fast and computationally efficient cellular automata frameworks which demonstrate promising utility for increasing available evidence to support surface water management, however, questions remain regarding trade‐offs between accuracy and speed for practical application. This study evaluates performance of a rapid assessment framework by comparing results with outputs from an industry standard hydrodynamic model using a case study of St Neots in Cambridgeshire, UK. Results from the case study show that the rapid assessment framework is able to identify and prioritise areas of flood risk and outputs flood depths which correlate above 97% with the industry standard approach. In theory, this finding supports a simplified representation of catchments using cellular automata, and in practice presents an opportunity to apply the framework to develop evidence to support detailed modelling.     

Developments in the management of flood defences and hydraulic infrastructure in the Netherlands

This article highlights recent developments in flood risk management in the Netherlands and presents approaches for reliability analysis and asset management for flood defences and hydraulic infrastructure. The functioning of this infrastructure is of great importance for the country as large parts of it are prone to flooding. Based on a nationwide flood risk assessment, new safety standards for flood defences have been derived in the form of maximal acceptable failure probabilities. A framework for the reliability-based analysis of the performance of hydraulic infrastructure is introduced. Within this context, various challenges are discussed, such as the dynamic nature of loads, resistance and reliability requirements over time. Various case studies are presented to highlight advances and challenges in various application fields. The first case illustrates how structural health monitoring contributes to a better characterisation of the reliability of the defences and how innovative measures can enhance the reliability. The second case discusses how the river system can be managed in the context of the new safety standards. The third case shows how upgrades and reinforcements of hydraulic structures can be evaluated taking into account (uncertain) future developments, such as sea level rise.     

A new experiments-based methodology to define the stability threshold for any vehicle exposed to flooding

A vehicle exposed to flooding, after losing stability, becomes buoyant and may be washed away with potential injuries and fatalities. Such vehicles cause additional disruption to traffic that is already affected by flooding, which may lead to substantial indirect economic impact, especially in urban areas. Therefore, the analysis of the stability of vehicles exposed to flooding is important in order to make decisions to reduce damages and hazards. In this research, based on an experimental campaign that included a range of twelve car models, a new methodology to obtain the stability threshold for any real vehicle exposed to flooding is developed. A stability coefficient (SC_mod) is derived with which the vehicles can be sorted by stability against water flows and their stability functions may be determined. The experiments were conducted with three different model scales (1:14, 1:18 and 1:24) and involved analysis of both friction and buoyancy effects, which made this the most comprehensive research study to date. This methodology enables the definition of a stable area in the flow depth-velocity domain for any real vehicle. A tool is provided that decision-makers in the field of urban flood risk management can employ and after defining a design vehicle they can obtain its corresponding stability threshold.     

基于景观地形的小流域单元减灾调控评价研究

近年来,中国诸多大中城市内涝灾害频发。武汉市作为城市内涝频发的典型城市,其建成区地表高度(20.0~24.0 m)大多低于外江常年所处的洪水位高度(23.9 m),在区域性暴雨条件下,极易引发内涝灾害。武汉由于其内涝典型性,2013年被列为全国31个重点防洪城市之一,2015年被列入首批海绵城市试点城市之一。从城市内涝发生机理出发,以水文角度的小流域单元作为内涝风险区划的基本单元,利用小流域单元分析武汉市景观地形要素(地表高程、地表起伏度、地表粗糙度)与城市内涝积水密度的相关性及其影响程度,量算统计出小流域单元的内涝风险等级。基于此,提出武汉市小流域单元减灾地形调控评价。以武汉市作为城市内涝问题的研究案例,以期为武汉市内涝缓解提供新的思考路径,具有典型性和必要性。     

Flood damage assessment in urban areas. Application to the Raval district of Barcelona using synthetic depth damage curves

This paper presents a detailed flood damage assessment in the Raval district of Barcelona. The implementation of a new 1D-2D coupled model is used to obtain flood depths, and new stage damage curves are developed to estimate the direct tangible damages. The curves have been validated using data from surveys and actual reported damages to the Spanish re-assurance. Finally, combining hazard and vulnerability levels by using a GIS-based toolbox, the expected annual damage of the area is obtained. This enables the determination of the critical points of the district in terms of flooding impacts, and highlights the need to implement strategies to cope with these impacts.     

基于SWMM模拟上海市区排水及地面淹水过程

针对上海市城区排水系统的水文水力学特性，以SWMM（Storm Water Management Model）为基础开发出适合上海市区产流及排水特点和防汛管理要求的城市雨洪模型。模拟结果表明，该模型的计算结果较为理想、可靠，可在实时和规划条件下动态模拟各排水片和街区的地面积水全过程，并能满足市区防汛预报、水情分析、工程规划与管理等工作的要求。该模型对其他城市的类似工作具有较好的参考价值和指导意义。     

A new flood risk assessment framework for evaluating the effectiveness of policies to improve urban flood resilience

To better understand the impacts of flooding such that authorities can plan for adapting measures to cope with future scenarios, we have developed a modified Drivers-Pressures-State-Impact-Response (DPSIR) framework to allow policy makers to evaluate strategies for improving flood resilience in cities. We showed that this framework proved an effective approach to assessing and improving urban flood resilience, albeit with some limitations. This framework has difficulties in capturing all the important relationships in cities, especially with regards to feedbacks. There is therefore a need to develop improved techniques for understanding components and their relationships. While this research showed that risk assessment is possible even at the mega-city scale, new techniques will support advances in this field. Finally, a chain of models engenders uncertainties. However, the resilience approach promoted in this research, is an effective manner to work with uncertainty by providing the capacity to cope and respond to multiple scenarios.