Assela Pathirana

Impacts of climate change on rainfall extremes and urban drainage systems: a review

A review is made of current methods for assessing future changes in urban rainfall extremes and their effects on urban drainage systems, due to anthropogenic-induced climate change. The review concludes that in spite of significant advances there are still many limitations in our understanding of how to describe precipitation patterns in a changing climate in order to design and operate urban drainage infrastructure. Climate change may well be the driver that ensures that changes in urban drainage paradigms are identified and suitable solutions implemented. Design and optimization of urban drainage infrastructure considering climate change impacts and co-optimizing these with other objectives will become ever more important to keep our cities habitable into the future.

Impacts of Climate Change on Rainfall Extremes and Urban Drainage Systems

Impacts of Climate Change on Rainfall Extremes and Urban Drainage Systems provides a state-of-the-art overview of existing methodologies and relevant results related to the assessment of the climate change impacts on urban rainfall extremes as well as on urban hydrology and hydraulics. This overview focuses mainly on several difficulties and limitations regarding the current methods and discusses various issues and challenges facing the research community in dealing with the climate change impact assessment and adaptation for urban drainage infrastructure design and management. ISBN: 9781780401256 (Print) ISBN: 9781780401263 (eBook)

Developing the evidence base for mainstreaming adaptation of stormwater systems to climate change

In a context of high uncertainty about hydro-climatic variables, the development of updated methods for climate impact and adaptation assessment is as important, if not more important than the provision of improved climate change data. In this paper, we introduce a hybrid method to facilitate mainstreaming adaptation of stormwater systems to climate change: i.e., the Mainstreaming method. The Mainstreaming method starts with an analysis of adaptation tipping points (ATPs), which is effect-based. These are points of reference where the magnitude of climate change is such that acceptable technical, environmental, societal or economic standards may be compromised. It extends the ATP analysis to include aspects from a bottom-up approach. The extension concerns the analysis of adaptation opportunities in the stormwater system. The results from both analyses are then used in combination to identify and exploit Adaptation Mainstreaming Moments (AMMs). Use of this method will enhance the understanding of the adaptive potential of stormwater systems. We have applied the proposed hybrid method to the management of flood risk for an urban stormwater system in Dordrecht (the Netherlands). The main finding of this case study is that the application of the Mainstreaming method helps to increase the no-/low-regret character of adaptation for several reasons: it focuses the attention on the most urgent effects of climate change; it is expected to lead to potential cost reductions, since adaptation options can be integrated into infrastructure and building design at an early stage instead of being applied separately; it will lead to the development of area-specific responses, which could not have been developed on a higher scale level; it makes it possible to take account of local values and sensibilities, which contributes to increased public and political support for the adaptive strategies.

Multi-objective optimisation of cost–benefit of urban flood management using a 1D2D coupled model

This paper presents a multi-objective optimisation (MOO) tool for urban drainage management that is based on a 1D2D coupled model of SWMM5 (1D sub-surface flow model) and BreZo (2D surface flow model). This coupled model is linked with NSGA-II, which is an Evolutionary Algorithm-based optimiser. Previously the combination of a surface/sub-surface flow model and evolutionary optimisation has been considered to be infeasible due to the computational demands. The 1D2D coupled model used here shows a computational efficiency that is acceptable for optimisation. This technological advance is the result of the application of a triangular irregular discretisation process and an explicit finite volume solver in the 2D surface flow model. Besides that, OpenMP based parallelisation was employed at optimiser level to further improve the computational speed of the MOO tool. The MOO tool has been applied to an existing sewer network in West Garforth, UK. This application demonstrates the advantages of using multi-objective optimisation by providing an easy-to-comprehend Pareto-optimal front (relating investment cost to expected flood damage) that could be used for decision making processes, without repeatedly going through the modelling-optimisation stage.

EPANET2 DESKTOP APPLICATION FOR PRESSURE DRIVEN DEMAND MODELING

The fixed demand hydraulics engine of EPANET software in its original form is not suitable for analysis of water distribution networks with low operating pressures. A modification of EPANET desktop for pressure driven demand analysis, employing emitter modeling of demands, is presented. The introduced version is able to work in a fully transparent way with standard EPANET network files and could be developed into other EPANET-toolkit based applications following the exact procedure as with standard EPANET. A simple network example used to demonstrate the operation of the system. Finally an illustrative case study of the model application is presented.

Spatial Analysis Tool for Development of Leakage Control Zones from the Analogy of Distributed Computing

Development of a methodology, rational and zoning scheme for the demarcation of complicated water distribution networks is important for making the zone demarcation process more accurate, economical, less time consuming, fast, repeatable, generic and optimal with respect to the cost of flow meters required. A new water distribution zone demarcation method is presented that uses the analogy of graph theoretic and graph partitioning principles used in distributed computing to distribute workloads among processors to suggest optimal zoning schemes based on balancing length, demand or flow within zones with the objective of monitoring of unaccounted for water. The method is developed into an automated prototype optimal zoning tool using C++ programming language, a graph partition tool used in distributed computing (METIS) and the EPANET tool kit. The tool is operated by a user interface written in the Python. Case studies are presented to demonstrate how the zoning tool is applied to the zone demarcation problem for the developed zoning schemes. The developed zone demarcation tool was observed to be an efficient and effective approach for the optimal demarcation of complicated water networks into optimal zones based on balancing length, demand or flow within zones. However the tool is sensitive to the number of partitions, the topology of the Water distribution network and the partitioning algorithms used. The tool can be used as a decision support tool for the optimal development and reduction of uncertainties in development of leakage control zones by decision makers. This will enable water companies to increase their productivities and also optimise resource allocations by reduction of the time to monitor, discover leaks and partition zones. This will lead to improved operating revenues

Coping capacities for improving adaptation pathways for flood protection in Can Tho, Vietnam

The planning and phasing of adaptation responses are essential to tackle uncertainties and ensure positive outcomes while adapting to changing circumstances. Understanding the evolution of coping and adaptation responses and their capacities is a prerequisite for preparing an effective flood management plan for the future. The aim of this paper is to determine the effect of coping capacity on longer term adaptation responses in a flood risk management system. The objectives, requirements, targets, design, and performance of flood protection measures will have to be determined after taking into account, or in conjunction with, the coping capacities. A methodology has been developed and demonstrated based on an adaptation pathway approach to account for coping capacities and to assess the effect of these on flood protection measures. Application of this methodology for flood protection measures in Can Tho City in the Mekong Delta shows the effect of considering coping capacity for flood protection measures and the value in delaying the occurrence of tipping points. Coping measures such as elevating property floor levels can postpone the tipping points when dikes are no longer effective. Consideration of coping capacity in the system improves adaptation responses and leads to better adaptation outcomes.

Managing urban water systems with significant adaptation deficits—unified framework for secondary cities: part I—conceptual framework

The lack of resilience of urban systems to weather and climate variability—termed type I adaptation—and also to climate change—type II adaptation—are both major challenges to the livability and sustainability of cities in the Global South. However, there is often competition and conflict in these cities between actions that address existing adaptation deficits (type I) and projected adaptation gaps (type II). Extending the concept of the environmental Kuznets curve, this paper argues that synergistic action on type I and type II adaptation is essential in order for these cities to maintain their livability and build resilience to climate variability and climate change in the face of growing urban populations. A proposed unifying framework has been demonstrated in Can Tho, Vietnam, where there are significant adaptation deficits due to rapid urbanization and adaptation gaps due to climate change and socioeconomic changes. The analysis in Can Tho reveals the lack of integration between type I and type II measures that could be overcome by closer integration between various stakeholders in terms of planning, prioritizing, and implementing adaptation measures.

Managing urban water systems with significant adaptation deficits—unified framework for secondary cities: part II—the practice

Adaptation gaps are shortcomings of a system responding to climate change, whereas adaptation deficits are shortcomings in providing services. These two drivers for adaptation are often in conflict in many secondary cities in the global south (SCGS). It is possible to align these seemingly conflicting drivers into a productive unity, a conceptual alignment, which is the first step in achieving harmony while implementing adaptation actions. This paper focuses on the practical aspects of implementing aligned adaptation action that leads to improvements in liveability, sustainability, and resilience of SCGS. At an abstract level, the nature of the adaptation problem is similar to the complex problems identified in various domains, such as software development, manufacturing, and supply chain management. The widely accepted “agile principles”—used in the above domains—is the basis for developing a set of twelve principles for urban adaptation, which are synthesized from numerous recent studies that have implicitly proposed or applied most of these principles to climate change adaptation in urban settings. These principles lead to four essential objectives appertaining to the process of sustainable urban adaptation. The urban agile principles are used to analyze the current state of adaptation of Can Tho City in Vietnam and to ascertain the agile ways of addressing its adaptation challenges. Analysis of the outcomes shows that harmonized approaches can simultaneously address both adaptation deficits and gaps.

Coupled 1D-2D hydrodynamic inundation model for sewer overflow: Influence of modeling parameters

Abstract This paper presents outcome of our investigation on the influence of modeling parameters on 1D-2D hydrodynamic inundation model for sewer overflow, developed through coupling of an existing 1D sewer network model (SWMM) and 2D inundation model (BREZO). The 1D-2D hydrodynamic model was developed for the purpose of examining flood incidence due to surcharged water on overland surface. The investigation was carried out by performing sensitivity analysis on the developed model. For the sensitivity analysis, modeling parameters, such as mesh resolution Digital Elevation Model (DEM) resolution and roughness were considered. The outcome of the study shows the model is sensitive to changes in these parameters. The performance of the model is significantly influenced, by the Mannings friction value, the DEM resolution and the area of the triangular mesh. Also, changes in the aforementioned modeling parameters influence the Flood characteristics, such as the inundation extent, the flow depth and the velocity across the model domain.