Assela Pathirana

IHE Delft Institute for Water Education | UNESCO-IHE

The increasing global population and in-country migration have a significant impact on global land use land cover (LULC) change, which reduces green spaces and increases built-up areas altering the near-surface radiation and energy budgets, as well as the hydrological cycle over an urban area. The LULC change can lead to a combination of hazards su...

Microbial pathogens in urban floodwaters pose risks to human health, potentially causing diseases such as diarrhea. However, the disease burden related to urban traffic exposure from citizens passing through floodwaters is not easily quantified and therefore not included in many studies. Notably, this problem has received little attention in low-to...

Over the next three decades–the typical planning period for large infrastructure–the world will have changed into a place that is predominantly water-scarce, yet also subject to more extreme flooding. The water world's disjointed project-based approach to knowledge and capacity building needs to be replaced with a programmatic and professionalised...

Risk-informed flood risk management requires a comprehensive and quantitative risk assessment, which often demands multiple (thousands of) river and flood model simulations. Performing such a large number of model simulations is a challenge, especially for large, complex river systems (e.g., Mekong) due to the associated computational and resource...

Many deltaic regions around the world are exploring or adopting planning initiatives to address the complex challenges associated with future economic development and climate change. A key feature is their adaptive nature, also coined as adaptive delta management (ADM). ADM refers to the development of strategies and measures that allow us to adapt...

Water rationing contributes to inequalities in the water supply. Household storage tanks complicate the performance and the hydraulic modelling of these systems. Rationing is often not based on insights into system performance and fails to achieve equity and the operators struggle to explain the rationing tactics to the stakeholders. Understanding...

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...

Infrastructure Asset Management (IAM) is the process by which decisions are made and resources allocated to ensure organisational or societal assets continue to deliver, as required. IAM is an evolving field. We discuss this evolution and present our perspectives on the future direction of IAM. IAM was born as a response to the poor state of mainte...

Urbanization is changing land use–land cover (LULC) transforming green spaces (GS) and bodies of water into built-up areas. LULC change is affecting ecosystem services (ES) in urban areas, such as by decreasing of the water retention capacity, the urban temperature regulation capacity and the carbon sequestration. The relation between LULC change a...

North Sea Region countries depend heavily on flood protection infrastructure, such as dikes, dams, sluices and flood gates. Knowledge on where, when and how much to invest to ensure functioning is of crucial importance for asset owners and operators. This requires asset management approaches that are adaptable, respond to feedback and function with...

Deterioration of water quality due to economic development, climate change and other factors has become a challenge to human beings and the ecosystem. Most countries have recognized this problem and have resorted to actions for improving water quality. However, the effect on water quality improvements due to these actions is uncertain due to the pl...

Flood risk management and planning decisions in many parts of the world have historically utilised flood hazard or risk maps for a very limited number of hazard scenarios (e.g. river water levels), mainly due to computational challenges. With the potentially massive increase in flood risk in future due to the combination of climate change effects (...

The expense and logistical difficulties of groundwater assessment in geographically dispersed, small landmasses, prevent it from being widely applied in small island developing countries. We propose a survey-based approach for screening groundwater quality using crowd-sourced information. A household-level survey was conducted in 45 selected inhabi...

This paper investigates the contamination of floodwaters in the urban center of Can Tho city, Vietnam. We sampled water from sewers, surface water bodies, and flood, before, during, and after specific flooding events. Total nucleic acid was extracted from the samples and subjected to a quantitative polymerase chain reaction (qPCR) to detect specifi...

Microbial pathogens in urban flood waters have showed high risk to human health, however, there is lacking of health risk assessment in urban flood waters in low-to-middle income countries (LMICs) regarding the microbial pollutants. To that aim, our study assessed health risk related to enteric pathogens in flood water in Can Tho city – an urban ar...

Sustainable urban development at the global level results from sustainable actions undertaken at city, neighbourhood and household levels with the right balance of environmental, economic and social aspects, achieved through initiatives such as water sensitive cities, sponge cities and “active, beautiful and clean waters ” (ABC waters). Green infra...

Resilience towards climate and socio-economic changes can be increased by means of flexible adaptation. In contemporary adaptation planning, building resilience is considered together with objectives such as sustainability, productivity and transformations. An adaptation planning process (termed water-sensitive city adaptation planning process (WSC...

Urbanization continues to trigger massive land-use land-cover change that transforms natural green environments to impermeable paved surfaces. Fast-growing cities in Asia experience increased urban temperature indicating the development of urban heat islands (UHIs) because of decreased urban green space, particularly in recent decades. This paper i...

Upgrading urban services and maintaining their functionality, such as drainage systems, in a sustainable manner to keep up with the increasing demand and changing needs, like climate adaptation and socio-economic conditions, is a planning, implementation and management challenge. Retrofitting urban infrastructure is a socio-technical process like p...

Traditional infrastructure asset management is about maintaining the status quo of service levels in a resource-restricted, sometimes risk-increasing environment. Infrastructure asset management (IAM) is effective in addressing resource-deprived situations and in maximizing the benefits of the utility in these contexts. This makes IAM a very approp...

At present, the Sponge City Concept (SCC) is gaining ground, Sponge Cities technologies are becoming more and more accepted by Chinese city governments, and the first best practices are being shared. However, there are still many challenges ahead which hamper effective implementation and upscaling. This paper presents an overview of some opportunit...

This paper is the introduction to the special issue on Climate change adapatation in the Mekong river basin. The papers in this issue focus on four interrelated themes: (1) impacts of climate change and human interferences on water, nutrient, and sediment flows (Shrestha et al. 2018); (2) climate change adaptation in urban centers (Radhakrishnan et...

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 adaptat...

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...

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 a...

Probabilistic flood forecasting requires flood models that are simple and fast. Many of the modelling applications in the literature tend to be complex and slow, making them unsuitable for probabilistic applications which require thousands of individual simulations. This article focusses on the development of such a modelling approach to support pr...

In the context of climate adaptation planning there are relationships between adaptation drivers and adaptation measures, which makes the selection and implementation of the adaptation measures a challenging task. This challenge may be addressed by: structuring the adaptation problem using a multiple perspective adaptation framework; and applying a...

Climate change and urbanization have led to an increase in the frequency of extreme water related events such as flooding, which has negative impacts on the environment, economy and human health. With respect to the latter, our understanding of the interrelationship between flooding, urban surface water and human health is still very limited. More...

Cities have started adapting to uncertain climate drivers such as temperature and sea level rise, and some cities are also transitioning towards concepts such as Water Sensitivity. In adaptation planning, flexibility is considered as an important characteristic to respond to changing circumstances. This paper develops a novel approach to identify w...

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 adap...

Public health risks from urban flooding are a global concern. Contaminated floodwater may expose residents living in cities as they are in direct contact with the water. However, the recent literature does not provide much information about this issue, especially for developing countries. In this paper, the health risk due to a flood event occurred...

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 en...

D eveloping countries in Southeast Asia, are facing the challenge of the ASEAN Vision 2020 to produce quality agricultural products that will cater not only to its local consumers but to approximately 600 million people across ten ASEAN nations. Agricultural expansion through land conversion was intensified in developing countries experiencing rapi...

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 desig...

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 eff...

Water pollution associated with flooding is one of the major problems in cities in the global South. However, studies of water quality dynamics during flood events are not often reported in literature, probably due to difficult conditions for sampling during flood events. Water quality parameters in open water (canals, rivers, and lakes), flood wat...

Water pollution associated with flooding is one of the major problems in cities in the global South. However, studies of water quality dynamics during flood events are not often reported in literature, probably due to difficult conditions for sampling during flood events. Water quality parameters in open water (canals, rivers, and lakes), floodwate...

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 understandi...

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 understandi...

The study involves water quality assessment of the surface waters of Can Tho City, Vietnam. Water samples were obtained in six strategic sites. The mean pH values were within set Vietnam standards. The mean conductivity and Total Dissolved Solids (TDS) values were higher in low tides and in densely populated urban districts of An Hoa and An Cu. The...

Addressing the 17 Sustainable Development Goals (SDG) in a developing country like Vietnam is not easy. The study aimed to address at least three of the 17 SDG, namely, good health, clean water and sanitation and life below water. This study conducted microbiological analysis on surface waters of flood vulnerable communities and concurrently done h...

Social learning concepts of developed countries are often recommended for implementing strategies for climate change adaptation in developing countries. The effectiveness of these replications is questionable, because it is necessary to align the set-up of learning processes with the social, economic and environmental conditions of the local contex...

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 su...

Water lies at the heart of human development but the global challenges for meeting demands, coupled with increasing urbanisation, land degradation and human population growth, make the challenges of water use in the developing world particularly acute. Capacity development is crucial for creating and strengthening the knowledge base to address wate...

Urban water systems are often designed using deterministic single values as design parameters. Subsequently the different design alternatives are compared using a discounted cash flow analysis that assumes that all parameters remain as-predicted for the entire project period. In reality the future is unknown and at best a possible range of values f...

This paper reports about the use of a binary salt based gel polymer electrolyte (GPE) for dye sensitized solar (DSS) cells. The two salts are Tetrapropylammonium Iodide(Pr4NI) and Zinc Iodide(ZnI2) which has not been considered commonly. The GPEs consist with Polyacrylonitrile (PAN) as the polymer and Ethylene Carbonate (EC) / Propylene Carbonate (...

At present, many approaches and models have been developed to perform spatially explicit simulations that mimic observed land use and land cover changes (LULC) for a given area. Calibration of such models is often performed using comparatively standard ‘off-the-shelf’ machine-learning algorithms that are not necessarily suited to perform effectivel...

It is widely accepted that Integrated Water Resources Management (IWRM) is the way forward to respond to efficient, equitable and sustainable development and management of water resources. Additionally, IWRM has also strong linkages with variability in climate conditions which causes various challenges for IWRM approaches. Besides the annual climat...

Inherent uncertainties are the main matter of constrain and concern for any fool proof urban flood management programme. Selection of better retrofitting options to tackle uncertainties involves the process of evaluating the technical and financial feasibility of wide range of options. In this paper, we present a case study of a catchment in Ho Chi...

Achieving resilient water systems requires a combination of technological, spatial and social interventions. Amongst other factors, the implementation of such interventions depends on stakeholder collaboration. The importance of collaborative learning amongst groups of diverse stakeholders for enhancing urban flood resilience is increasingly highli...

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...

More than half of the humanity lives in cities and many cities are growing in size at a phenomenal rate. Urbanisation-driven landuse change influences the local hydrometeorological processes, changes the urban micro-climate and sometimes affects the precipitation significantly. Understanding the feedback of urbanisation driven micro-climatic change...

The water sensitive city is a term within urban water management in which the concept of resilience to extreme climatic events and climate change plays a key role and represents the interaction between different branches of water science, engineering, and other domains such as urban planning and design. In this context, resilience is the ability of...

Future uncertainties are a matter of concern for urban flood management. This calls for an integrated urban flood risk management approach that is adaptive to changing circumstances in the future. Emerging approaches in urban flood risk management such as Water Sensitive Urban Design, living with water, and room for water try to address the flood i...

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...

Under the umbrella of the IWA/IAHR Joint Committee on Urban Drainage, the International Working Group on Urban Rainfall (IGUR) has reviewed existing methodologies for the analysis of long-term historical and future trends in urban rainfall extremes and their effects on urban drainage systems, due to anthropogenic climate change. Current practices h...

A major cause of increasing flood risk of cities is the increasing population and value of domestic and commercial buildings and growing interdependency on infrastructure networks. Contemporary flood risk analyses generally include only direct economic damages and fail to consider other flood risks, such as disruption to the economy or the loss of...

Urban development increases flood risk in cities due to local changes in hydrological and hydrometeorologi-cal conditions that increase flood hazard, as well as to urban concentrations that increase the vulnerability. The relationship between the increasing urban runoff and flooding due to increased imperviousness is better perceived than that betw...

Urban development increases flood risk in cities due to local changes in hydrological and hydrometeorologi-cal conditions that increase flood hazard, as well as to urban concentrations that increase the vulnerability. The relationship between the increasing urban runoff and flooding due to increased imperviousness is better perceived than that betw...

We analyse the implementation of Sustainable Drainage Systems (SuDS) as a solution to better manage storm water runoffs and reduce urban flooding, and at the same time provide significant Ecosystem Services (ES). ES vary from temperature control at urban and building scale to main water savings, depending on the type of SuDS considered. The general...

This paper presents an adaptation process for flooding systems that can be applied whatever analytical method is used to account for climate change uncertainty. The process is aimed at providing flood risk infrastructure that is more resilient to climate change, where resilience is considered as the ability of the system as a whole to function as e...

Solving today's complex hydrological problems requires originality, creative thinking and trans-disciplinary approaches. Hydrological education that was traditionally teacher centred, where the students look up to the teacher for expertise and information, should change to better prepare hydrologists to develop new knowledge and apply it in new con...

Assessing the impact of climate change in an urban drainage context requires the use of tools and methodologies that work at the local scale and fine temporal resolution. This paper aims to provide a methodology for the downscaling of an ensemble of Global Circulation Models (GCMs) output in order to produce synthetic point urban scale rainfall ser...

A growing body of evidence suggests that it is unwise to make the a-priori assumption that university students are ready and eager to embrace modern online technologies employed to enhance the educational experience. We present our opinion on employing Wiki, a popular Web 2.0 technology, in small student groups, based on a case-study of using it cu...

Concerns have been raised regarding disinfection by-products (DBPs) formed as a result of the reaction of halogen-based disinfectants with DBP precursors. In order to appreciate the chemical and biological tradeoffs, it is imperative to understand the formation trends of DBPs and their spread in the distribution network. However, the water at a poi...

In order to enable estimation of flood damage due to sewer overflow, a Sewer Network Model (SWMM) was coupled with an Inundation Model (BreZo) based on irregular triangular meshes. SWMM uses a ID explicit finite difference solver that handles the full shallow water equations. BreZo employs a Godunov-type finite volume algorithm to explicitly solve...

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 climat...

Solving today's complex hydrological problems requires originality, creative thinking and trans-disciplinary approaches. Hydrological education that was traditionally teacher centred, where the students look up to the teacher for expertise and information, should change to better prepare hydrologists to develop new knowledge and apply it in new con...

A growing body of evidence suggests that it is unwise to make the a-priori assumption that university students are ready and eager to embrace modern online technologies employed to enhance the educational experience. We present an opinion on employing Wiki, a popular Web 2.0 technology, in small student groups, based on a case-study of using it cus...

Infrastructure for water, urban drainage and flood protection has a typical lifetime of 30–200 years and its continuing performance is very sensitive to climate change. Investment decisions for such systems are frequently based on state-of-the-art impact assessments using a specified climate change scenario in order to identify a singular optimal a...

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...

Urban development increases flood risk in cities due to local changes in hydrological and hydrometeorological conditions that increase flood hazard, and also to urban concentrations that increase the vulnerability. The relationship between the increasing urban runoff and flooding due to increased imperviousness better perceived than that between th...

The increasing number of people living in urban areas has influenced performance of the urban water system. Inadequacy of drainage systems generate urban floods resulting in material loss, public health hazard and environmental deterioration. The harmful pollutant concentrations often found in surface water during urban flood events raise many publ...

Cities exhibit unique spatial patterns, and thus a distinctive heterogeneity. At different scales of influence, they introduce changes in the physical properties of the natural environment, as the diffusion of impervious surfaces. While climate change is expected to increase the frequency of hazards, patterns of urbanization might be critical in ba...

The consequences of urban growth on the exposure, sensitivity but also as a driver of flooding are often underexposed. Yet, the rate of current urbanization is unprecedented and might increase future flood risk dramatically. To gain insight in this issue, a study on urban development has been performed using 3 case study areas: the megacities of Be...

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 f...

The consequences of urban growth on the exposure, sensitivity but also as a driver of flooding are often underexposed. Yet, the rate of current urbanization is unprecedented and might increase future flood risk dramatically. To gain insight in this issue, a study on urban development has been performed using 3 case study areas: the megacities of Be...

UNESCO-IHE's students are unique in several aspects: they are mid-career professionals separated from their last university experience by a number of years in the profession, they are from diverse social and cultural backgrounds, and they often have relatively clear understanding on the diverse problems in the practice of engineering in their respe...

World's urban centers are growing rapidly causing the impact of extreme rainfall events felt much more severely due to relatively well unerstood phenomena like decreased infiltration and flow resistance. However, an increasing set of evidence (e.g. heavy rainfall event observed at Nerima, central part of Tokyo metropolitan area, on 21 July 1999) su...