Evaluation Of Retrofitting Options In Urban Drainage Systems Based On Flexibility: A Case Study For Nhieu Loc - Thi Nghe Basin In Ho Chi Minh City

Inherent uncertainties are the primary constraints and concerns for any robust urban flood management programme. Selection of better retrofitting options to tackle uncertainties involves the process of evaluating the technical and financial feasibility of a wide range of options. In this paper, we present a case study of a catchment in Ho Chi Minh City, Vietnam, where we apply evolutionary methods to search for optimal retrofitting opportunities to cope with uncertainties. Flexible options such as detention storage at nodes and provision of sustainable drainage systems have been identified. The optimal storage volumes for detention storage at the nodes and optimal coverage areas for sustainable drainage options to prevent flooding in Nhieu Loc – Thi Nghe basin, have been arrived at by integrating optimization techniques and a storm water management model. This case study demonstrates and paves the way for considering combined hydraulic modelling along with an optimization approach as the first step towards incorporating flexibility into urban drainage systems. A Real in Option framework to assess the flexibility is also presente

Flexibility in adaptation planning: when, where and how to include flexibility for increasing urban flood resilience; Dissertation, UNESCO-IHE Institute for Water Education, Delft and TU Delft.

“பய ேகாட ஆ யாைன ெவஉ தா .” - Verse 599, Tirukural (Thiruvalluar 31 BC) “Huge bulk of elephant with pointed tusk all armed, when tiger threatens shrinks away alarmed!” - Translation based on Pope et al. (1886) Flooding has impacts on human activity. The positive impacts contribute to increased water availability and alluvium which increases agricultural productivity in flood plains. The negative impacts are associated with damage to life, property and productivity. The recent increased damage of flooding compared with the past is due to population growth and accumulation of assets in flood prone areas; more flooding incidents; and, changes in climate. For example, two-thirds of the population of The Netherlands lives in areas that are flood prone from rivers and the sea. According to the Organization for Economic Co-operation and Development, worldwide flooding caused USD 40 billion in losses and affected about 250 million people globally in the year 2015. Many mega-cities such as Bangkok, Jakarta, Paris, Mumbai, New Delhi and New York have been affected by floods in the last decade. Climate change has led to altered precipitation patterns and increase in sea levels, contributing to an increase in flooding. For example, the Australian Government`s Bureau of Meteorology has stated that the sea levels have risen between 2.6 and 2.9 mm every year since 1993 around Australia, and the rise in mean sea level amplifies the effects of high tides and storm surges. The increase in urbanisation, together with the effects of climate change complicate the ways for managing flooding in urban areas. However, there is a range of flood risk management strategies or adaptation measures across countries to mitigate the consequences (e.g., the year 2007 European Union Directive on assessment and management of floods). Combinations of flood risk management strategies or adaptation measures are seen as the way forward to tackle uncertainties faced by flood risk managers that arise out of climate change and urbanisation, amongst others. Uncertainties cannot be fully resolved. Postponing the decisions under the premise that new insights may emerge and hence reduce uncertainty. The opportunity to increase the resilience of the urban systems in order to minimise negative impacts of uncertainty and maximise positive impacts can be considered as the positive outcome of uncertainty. Resilience is the ability to: (i) withstand or recover from disturbances; and (ii) anticipate and adapt to change. Resilience towards climate and urban change can be increased by means of flexible adaptation measures. Flexibility in this context can be defined as the presence of opportunities arising from the number of alternative ways to provide services and respond to changing circumstances. As an example, in 2010 the Australian Government released a position paper on adapting to climate change, which considers uncertainty as an opportunity to introduce flexibility and creativity through adaptive measures. Cities such as Melbourne and the State of Victoria have already started including flexibility in their adaptation planning. In contemporary adaptation planning, climate resilience measures are considered together with objectives such as sustainability, productivity and transformations (e.g., transformative adaptation, water sensitive cities). A transformative approach aims to change urban design and supporting structures; the way of living, working and commuting; and the way services are provided in urban areas. Transformation often refers to a system change as opposed to incremental changes, which is the norm in most of the adaptation approaches. Though radical in nature, the transformative approach recommends the use of flexibility and resilience to achieve and sustain the transformation. The concept of ‘Water Sensitive City’ – i.e. a city being liveable, resilient, sustainable and productive whilst managing all aspects of the water cycle – is gaining popularity among policy makers and planners especially in developed economies. This concept also promotes flexibility as an essential attribute to convert uncertainty into opportunity. The nature of uncertainties and opportunities prevailing in the financial markets are similar to the uncertainties and risks in urban flood risk management systems. Considering uncertainty as an opportunity to maximise the return on investments is a well-established practice in finance domains. For example, “Options” is an instrument that is used to adjust to fluctuating market prices by engaging in a contract in the present. The contract provides the user the right to buy or sell a product in the future at a price decided in the present. As the option provides a right but not an obligation, the user can decide whether or not to exercise the option based on how the situation unfolds during the course of time. The two pre-requisites for profiting when trading with options are: (i) possessing options - i.e., creating a chance to work with uncertainty; (ii) exercising the option, i.e., converting the option into an opportunity at the time of convenience. Hence, there is scope for converting the (flood) risk into opportunities or favourable outcomes in managing the risk by a priori creating two prerequisites. Firstly, opportunities can be created by pre-planning in the form of pre-defined optional adaptation measures for propitious implementation in future. Secondly, the performance of these measures can be assessed under plausible future scenarios to know when best to implement the measures. This is called managerial flexibility. Adaptation pathways and real options are among the methods that enable managerial flexibility in urban flood risk management. Adaptation pathways and real options are sequential decision making approaches. They foresee the outcomes of the current and future decisions that might affect the flexibility of a measure or set of measures. An adaptation pathways approach builds flexibility by sequencing the implementation of adaptation measures, so that the urban flood risk management system can adapt to changing climatic, social, economic and environmental conditions. A real options approach values the sequenced adaptation measures in financial terms and helps in determining the sequence of adaptation measures that has the best value for money, which is based on the probability of scenarios. A modified form of the real options approach known as “real in Options” focusses on providing value for the flexibility inherent in having the options in engineered systems such as dikes or drainage systems. This is accomplished by identifying a design configuration that would incur minimum construction, operation, modification and maintenance cost but with the maximum avoided flood damages across a range of scenarios in the future. Real in options is an approach that has been used in the planning and design of large scale infrastructure systems such as high rise buildings, roads and telecommunication network. The scientific community has tested adaptation pathways and real in options approaches in order to make flood risk and other management strategies flexible in case studies across many countries. Further, these approaches are now finding their way into the planning documents that are addressing flood risk and asset management in the UK and The Netherlands. However, these applications consider only the relationship between the adaption measure and the driver of adaptation such as sea level rise, rainfall or urbanisation. The inter-relationship between the adaptation measures such as measures taken at city level and measures taken at household level are not typically taken into account. Further, the interrelationships between the adaptation drivers are also not typically considered in the current adaptation planning context. It can be concluded therefore that there is a lack of comprehensive framing of the adaptation responses to take into account the relationships between the adaptation measures and the drivers of adaptation. This lack of comprehensiveness in framing the adaptation responses during planning can also lead to implementation issues. Appropriate structuring of an adaptation response or opportunity in a local context is critical, as this influences the nature and effectiveness of the adaptation. This research focuses on: (i) increasing the knowledge on incorporating flexibility into urban flood risk management systems; (ii) understanding the various aspects of climate and urban adaptation responses; and (iii) development of flexible implementation practices. The research presented here has developed a generic framework for structuring a multiple perspective approach as a way to increase flexibility in selecting and timing the implementation of adaptation measures. This framework is different from the traditional ‘portfolio of measures’ approach as it helps to establish the relationship between measures in an adaptation context. The framework has been used to structure the adaptation responses to flood risk in Can Tho city, Vietnam, in order to ascertain the applicability in a practical adaptation context. A context specific adaptation grammar based on ‘Systems Engineering’ concepts has been used to analyse the structured adaptation responses in Can Tho. The application of context specific adaptation grammar has revealed that a generic framework, such as that presented here, can be used to structure context specific adaptation responses, and it is possible to generate adaptation pathways based on the relationships between the measures. By demonstrating that flexibility can be enhanced by mapping the relationships between the measures, the scope of the research has been further broadened to create a flexible adaptation planning process. This flexible adaptation planning process identifies where flexibility can be embedded in urban flood risk management systems. The process for this has been developed by drawing on knowledge and procedures used by the automobile and aerospace industries, where flexible adaptation planning is everyday practice. The identification of a flexible water sensitive design component is based on change propagation; i.e. the adaptation measure’s ability to minimise or maximise negative and positive impacts in the urban system. This process has been applied here to identify flexible adaptation measures for managing and adapting to flood risk in Elster creek, an urban catchment in Melbourne, Australia. From the application of the process it was found, during the course of this research, that rainwater harvesting systems and flood proofing measures at the household scale are the best measures for incorporating flexibility to tackle the challenges due to flooding; and ensure effective and efficient flood risk management in the future. It was found that the identification of flexible components for urban flood risk management systems based on change propagation can enhance adaptation of cities. Hence, through this research it has been established that context specific adaptation responses can be structured using a generic framework. However, operational challenges persist in implementing the adaptation measures in managing flood risks, even after identifying flexible components based on change propagation concepts. Add ressing the operational and implementation challenges whilst adapting is especially significant in rapidly developing cities where there is a competition for funds between improving the current infrastructure (adaptation) deficits and future adaptation needs. Hence, there is a need to align adaptation actions that lead to improved liveability, sustainability and resilience. The nature of the adaptation responses is similar, at an abstract level, to any other ‘complex problem’ identified in various domains like software development, manufacturing and supplychain management. The widely accepted ‘agile principles’ as identified in these domains are used here for developing equivalent practices in urban adaptation for flood risk management and a set of twelve principles is proposed for operationalising responses in order to adapt to urban flooding. These agile principles have been used to set out four objectives of urban adaptation – flexible incremental measures; common understanding of an adaptation problem; equal importance to adaptation gaps and deficits, i.e., the competition for funds between improving the current infrastructure needs and adaptation to future changes; and stakeholders working together – that can help to translate these principles into tangible outcomes. This research presented here has focused on increasing the knowledge on incorporating flexibility into urban flood risk management systems by developing and testing: (i) a framework for structuring adaptation responses in a local adaptation context; (ii) a flexible adaptation planning process to identify the flexible adaptation components; and (iii) an agile urban adaptation process to address the operational challenges while implementing flexible adaptation measures. A framework for structuring an adaptation problem in a local adaptation context has been defined, and using this the adaptation problem in Can Tho, Vietnam, have identified. A process for identifying flexible adaptation components in urban flood risk management systems has been developed and tested in Elster creek in Melbourne, Australia. Incorporating flexibility into adaptation planning and operationalising it through an urban agile process can pave the way for efficient and effective management of urban floods. been structured and the adaptation measures that are suitable for the changing context ther

Structuring Climate Adaptation through Multiple Perspectives: Framework and Case Study on Flood Risk Management

Adaptation to climate change is being addressed in many domains. This means that there are multiple perspectives on adaptation; often with differing visions resulting in disconnected responses and outcomes. Combining singular perspectives into coherent, combined perspectives that include multiple needs and visions can help to deepen the understanding of various aspects of adaptation and provide more effective responses. Such combinations of perspectives can help to increase the range and variety of adaptation measures available for implementation or avoid maladaptation compared with adaptations derived from a singular perspective. The objective of this paper is to present and demonstrate a framework for structuring the local adaptation responses using the inputs from multiple perspectives. The adaptation response framing has been done by: (i) contextualizing climate change adaptation needs; (ii) analyzing drivers of change; (iii) characterizing measures of adaptation; and (iv) establishing links between the measures with a particular emphasis on taking account of multiple perspectives. This framework was demonstrated with reference to the management of flood risks in a case study Can Tho, Vietnam. The results from the case study show that framing of adaptation responses from multiple perspectives can enhance the understanding of adaptation measures, thereby helping to bring about more flexible implementation practices

Effectiveness of Runoff Control Legislation and Active, Beautiful, Clean (ABC) Waters Design Features in Singapore

Storm water management in Singapore has always been a challenge due to intense rainfall in a flat, low-lying and urbanised catchment. PUB’s (Singapore’s National Water Agency) recent runoff control regulation limits the runoff coefficient to 0.55 for developments larger than or equal to 0.2 ha. The use of Active, Beautiful, Clean (ABC) Waters design features are encouraged to attain peak runoff reduction. Hence the paper focuses on (i) determining the actual hydrological response regime of Singapore using the relationship between runoff coefficient (C), land use and slope; and (ii) investigating the effectiveness of ABC Waters design features in delaying and reducing peak runoff using a modelling approach. Based on a Storm Water Management Model (SWMM) model and using elevation, land use and soil data as inputs, the peak C-values were obtained for 50 m × 50 m grid cells. The results show that for the same land use, the one with steeper slope resulted in a higher runoff coefficient. Simulations were carried out in two study areas, Green Walk District and Tengah Subcatchment, where ABC Waters design features (such as porous pavements, green roofs, rain gardens) and detention tanks were incorporated to reduce C-values. Results showed that peak C-values can be reduced to less than 0.55 after increasing the green areas and constructing detention facilities. Reduction in peak discharge (22% to 63%) and a delay in peak discharge by up to 30 min were also observed. Hence, it is recommended to consider the relationship between slope and land use while determining runoff coefficients; and to incorporate ABC Waters design features in urban design to reduce the peak flow and runoff coefficient (C)

Enhancing the Economic Value of Large Investments in Sustainable Drainage Systems (SuDS) through Inclusion of Ecosystems Services Benefits

Although Sustainable Drainage Systems (SuDS) are used in cities across the world as effective flood adaptation responses, their economic viability has frequently been questioned. Inclusion of the monetary value of ecosystem services (ES) provided by SuDS can increase the rate of return on investments made. Hence, this paper aims at reviewing the enhancement of the economic value of large-scale investments in SuDS through inclusion of ecosystem services. This study focuses on the flood reduction capacity and the ES benefits of green roofs and rain barrels in the combined sewerage network of Montevideo Municipality in Uruguay. The methodology comprises a cost–benefit analysis—with and without monetised ES provided by SuDS—of two drainage network configurations comprising: (i) SuDS; and (ii) SuDS and detention storage. The optimal drainage design for both these drainage configurations have been determined using SWMM-EA, a tool which uses multi-objective optimisation based evolutionary algorithm (EA) and the storm water management model (SWMM). In both design configurations, total benefits comprising both flood reduction and ES benefits are always higher than their costs. The use of storage along with SuDS provides greater benefits with a larger reduction in flooding, and thus is more cost-effective than using SuDS alone. The results show that, for both of the drainage configurations, the larger investments are not beneficial unless ES benefits are taken into account. Hence, it can be concluded that the inclusion of ES benefits is necessary to justify large-scale investments in SuDS

Scoping for the Operation of Agile Urban Adaptation for Secondary Cities of the Global South: Possibilities in Pune, India

Urban areas, especially in developing countries, are adapting to deficits in infrastructure and basic services (Type I adaptation) and to adaptation gaps in response to current and future climatic, societal and economic change (Type II adaptation). The responses to these adaptations needs can be integrated and implemented using an “agile urban adaptation process”, i.e., an adaptive planning process quickly adapting to change in a flexible manner in short planning horizons, where the requirements and responses evolve through evolutionary development, early delivery, continuous improvement and collaboration between self-organizing and cross-functional teams. This paper focuses on how to move from the current conceptual stage to developing practical knowledge for the operation of agile urban adaptation. Scoping methodology comprises (i) understanding and structuring the adaptation context; (ii) exploring the four agile elements—balancing type I & II adaptation needs, flexibility, range of scenarios and involvement of stakeholders—in the adaptation context; (iii) a detailed SWOT analysis (strength, weakness, opportunities and threat) of adaptation responses; (iv) mapping relationships and synergies between the adaptation responses; and (v) preparing agility score cards for adaptation responses. The scoping exercise revealed that the agile adaptation process can move from concept to operation in Pune, India where the city is improving the basic services and adapting to climate change. For example: conventional adaptation responses such as city greening and check-dams across the rivers have agile characteristics; these responses are synergetic with other adaptation responses; and, there is a possibility to compare conventional adaptation responses based on agile characteristics. This scoping exercise also reveals that urban agile adaptation is not about implementing novel adaptation responses but understanding, planning and implementing conventional adaptation responses using an agile perspective. Urban agile adaptation is also about mainstreaming agile ideas using traditional adaptation responses. Hence, it is possible to apply agile the urban adaptation process using conventional adaptation responses in urban areas which address adaptation deficits related to infrastructure development as well as climate and socio-economic adaptation

Instant flood risk modelling (Inform) tool for co-design of flood risk management strategies with stakeholders in Can Tho city, Vietnam

Flood risk reduction strategies play an important role in flood risk management (FRM) and these strategies are being co-designed with the engagement of the stakeholder through multiple consultations and co-designing sessions. Effective participation of stakeholders in interactive work sessions requires fast and accurate modeling systems with a user-friendly interface, which can simulate the impact due to various flood reduction measures selected by the stakeholders and also generate outputs that can be understood by all stakeholders, especially those who are not FRM specialists. Presenting an easy-to-understand tool with easy inputs and outputs for a variety of stakeholders and at the same time providing reliable and accurate results for a range of scenarios and interventions is a challenge. Seven requirements that are essential for a user-friendly flood risk tool were used to develop an instant flood risk modeling tool. This paper presents a web-based hydraulic tool, i.e., instant flood risk model (Inform), to support FRM in the urban center of Can Tho city (Ninh Kieu district), Mekong Delta, Vietnam. Inform was developed based on (i) a simplified 1D model for the entire Mekong Delta; and (ii) flood hazard and damage maps, and estimated flood damage for Ninh Kieu district in Can Tho city obtained directly from the 1D/2D coupled model for Ninh Kieu district. Inform rapidly generates flood levels, flood hazard and damage maps, estimated damages. Pilot testing with experts confirmed that Inform qualifies as a reliable co-design tool for developing FRM strategies as it features an inbuilt input library, comprises flexible options, easy to use, produces quick results and has a user-friendly interface. With the help of an interactive web-based tool such as Inform presented here, it is possible to co-design FRM strategies for Can Tho or any other city that is subject to flood risk

Effectiveness of ABC Waters Design Features for Runoff Quantity Control in Urban Singapore

Active, Beautiful, Clean Waters (ABC Waters) design features—natural systems consisting of plants and soil that detain and treat rainwater runoff—comprise a major part of Sustainable urban Drainage Systems (SuDS) in Singapore. Although it is generally accepted that ABC Waters design features are able to detain runoff and reduce peak flow, their effectiveness in doing so has not been studied or documented locally. This research aims to determine their effectiveness in reducing peak flow based on a newly constructed pilot precinct named Waterway Ridges. Four types of ABC Waters features have been integrated holistically within the development, and designed innovatively to allow the precinct to achieve an effective C-value of 0.55 for the 10-year design storm; the precinct-wide integration and implemented design with the aim of substantially reducing peak flow are firsts in Singapore. The study is based on results from an uncalibrated 1D hydraulic model developed using the Storm Water Management Model (SWMM). Identification of key design elements and performance enhancement of the features via optimisation were also studied. Results show that the features are effective in reducing peak flow for the 10-year design storm, by 33%, and allowed the precinct to achieve an effective C-value of 0.60

Simulating flood risk under non-stationary climate and urban development conditions - Experimental setup for multiple hazards and a variety of scenarios

A framework for assessing economic flood damage for a large number of climate and urban development scenarios with limited computational effort is presented. Response surfaces are applied to characterize flood damage based on physical variables describing climate-driven hazards and changing vulnerability resulting from urban growth. The framework is embedded in an experimental setup where flood damage obtained from combined hydraulic-urban development simulations is approximated using kriging-metamodels. Space-filling, sequential and stratified sequential sampling strategies are tested. Reliable approximations of economic damage are obtained in a theoretical case study involving pluvial and coastal hazards, and the stratified sequential sampling strategy is most robust to irregular surface shapes. The setup is currently limited to considering only planned urban development patterns and flood adaptation options implemented over short time horizons. However, the number of simulations is reduced by up to one order of magnitude compared to scenario-based methods, highlighting the potential of the approach