Chapter 1 delves into global urbanisation dynamics, honing in on urban water challenges, notably in the context of China’s accelerating urbanisation. Urbanisation, a transformative global force, triggers societal, economic and environmental shifts, offering opportunities for progress if managed adeptly. However, the chapter underscores the escalating water challenges accompanying this phenomenon. Urban floods, propelled by expanding impervious areas, pose substantial global threats, inducing economic losses. The intensified urbanisation aggravates water scarcity, fuelling conflicts and impacting ecosystems. Urban development contributes to water pollution, upsetting natural balances and escalating pollutant concentrations, resulting in ecological degradation. The urban heat island effect exacerbates these challenges, affecting ecosystems and local weather patterns. This chapter provides a nuanced exploration of the intricate relationship between urbanisation and water challenges, emphasising the urgent need for sustainable urban development practices.

Chapter 3 explores the impacts of urbanisation on the hydrological cycle, specifically the storm hydrograph. The replacement of vegetation with impermeable surfaces and the channelling of water in urban areas contribute to flooding and pollution events. The chapter emphasises the interdependence of flood risk management and water quality improvement in urban environments, stressing the importance of considering both aspects. Structural solutions for sustainable water quality improvements in urban stormwater such as Sustainable Drainage Systems (SuDS) are explored, covering flood resilience, benefits, sustainable drainage approaches, evidence of SuDS efficacy, their maintenance and integration into water-sensitive urban design (WSUD) for the entire city.

This chapter explores the potential of using sediment cores from floodplain lakes to assess contaminant levels in riverine flood deposits. It emphasises the limited knowledge about contaminants carried by floodwaters and their risks due to a lack of long-term monitoring data. Sediment cores offer a solution by preserving historical events, enabling the reconstruction of past contaminant levels. Theoretical background and methods for identifying historical flood deposits in sediment cores are discussed, along with temporal trends in waterway pollution. Case studies from Australia and Canada demonstrate the technique’s contribution to understanding the contamination levels in sediments deposited by river floods. Acknowledging the need for refinement, the chapter calls for a better understanding of uncertainties and the development of models to convert contaminant levels in flood deposits to those in the water column. Despite being in its early stages, the use of sediment cores holds great potential for enhancing flood risk assessment and management.

Floods, encompassing river, pluvial, and coastal types, are global disasters causing fatalities, infrastructure damage and ecosystem disruptions. This book fills a research gap by examining the underexplored facet of floods: their impact on water quality. Addressing the nexus of floods, climate change and water quality, it underscores escalating risks from heavy rainfall events, including pollutant mobilisation resulting to water pollution and coastal salinisation. Focussed on urbanisation, the book explores diverse flood types, offering insights into adaptive strategies such as sustainable urban design and sustainable urban drainage systems (SUDS). It emphasises integrating water quality considerations into flood risk management and introduces an online forecast model for urban flooding, highlighting the importance of early warning systems. Case studies and data from Canada, Australia, India, France and China illuminate real-world impacts. The book significantly advances understanding of floods’ multifaceted effects on water quality, providing practical approaches to mitigate challenges in this changing climate and identifying gaps of knowledge that need to be researched.

Chapter 5 explores the imperative need for early warning systems in predicting pluvial flood events in urban areas, focussing on hydraulic interactions and contaminant transport. Urban regions face increased vulnerability due to high population density and extended impervious surfaces. With pluvial floods occurring suddenly and posing a high risk to life and property, the chapter underscores the importance of real-time forecasting to minimise damages. It addresses the challenges in modelling water fluxes in cities, emphasising the complexity of physically based models and input requirements. The discussion extends to the coupling of urban flow and transport models, highlighting the need for efficient control strategies. The chapter also presents a case study in Oberricklingen, Hannover, Germany, showcasing the application of the developed models and concluding that an ANN-based model is optimal for spatially uniform rain events..

Chapter 4 explores the challenges posed by urbanisation on water quality, particularly during extreme rainfall events. The chapter traces the historical development of sewer systems designed to channel stormwater out of cities and into water bodies, emphasising the subsequent need for wastewater treatment to protect water sources. The proliferation of impervious surfaces in cities has led to increased flooding, prompting the construction of larger sewers, albeit quantity-focussed solutions. This approach, coupled with the misconception that stormwater is uncontaminated, exacerbates environmental pollution. The chapter advocates for comprehensive urban drainage management during floods to minimise water pollutants. Storm water tanks and SUDs are mentioned as means to reduce pollution loads to reach water bodies. It discusses the factors crucial for effective management, ranging from maintenance and short-term rain forecasting to the importance of pollutographs in long-term planning. Emphasising citizen involvement and a shift towards sustainable drainage techniques, the chapter provides insights for preserving urban environments amidst increasing extreme rainfall events and climate change threats.

Chapter 11 concludes a thorough analysis of urbanisation, the urban water cycle, and escalating urban floods. The chapter underscores the global changes and projects a substantial urban population increase by 2050. Emphasising the importance of the urban water cycle, it explores the impact of the COVID-19 pandemic on urban water demand. Addressing urban floods’ rising threat due to climate change, heat island effects and intense rainfall, the chapter advocates differentiated approaches and basin–city linkages for effective flood risk management. Prevention strategies, including early warning systems, SuDS and WSUD, are discussed, promoting a holistic understanding of urban water challenges. The chapter calls for increased research, data collection and interdisciplinary collaboration, highlighting UNESCO’s IHP role in promoting ecohydrology and sustainable urban water management, emphasising science-based solutions and policy development. This book somehow advanced the problems raised during the 2024 Olympics games when good water quality was expected to have in the Seine river for aquatic competitions. Not floods but extreme events episodes made it clear that rainfall conveys pollutions to water bodies from soil and neighbouring urban areas. Water runoff, the invisible sources of pollutants, is real and actions and research need to be undertake for its control, so far and with the current stage if knowledge only once pollution has been produced.

Chapter 2 provides a comprehensive overview within the constraints of urban water management evolution. The chapter navigates through historical periods, including the municipal sanitary engineering period, stormwater quantity regulation period, and sustainable development period, showcasing the transitions in addressing urban water challenges. It delves into the strategies employed during each phase, outlining the progression from traditional approaches to contemporary sustainable practices. The chapter also examines the evolution of terminology related to urban drainage and elucidates various types of urban drainage systems. Furthermore, it explores the significance of low impact development (LID) facilities in controlling urban runoff, emphasising their role in sustainable water management. The management of flood risk is a focal point of the chapter, with insights into strategies and practices employed globally, offering a comparative analysis of flood risk management approaches in selected countries.

Chapter 9 investigates the unprecedented flooding of the Seine and Marne rivers in June 2016. Focussing on the core of Île-de-France, managed by SIAAP, the chapter assesses the flood’s impact on the sanitation system and subsequent effects on the quality of the Seine and Marne rivers. Drawing data from sanitation departments and SIAAP, it details the hydrographic network, rainfall and hydrological situations. The study evaluates the sanitation system’s operation, discharged volumes, sewage treatment plants and environmental impacts, emphasising water quality parameters such as nitrogen, orthophosphates, dissolved oxygen and bacteriology. Despite challenges, the assessment highlights effective management, treatment system performance and the importance of real-time control systems, providing insights for future flood response and urban sanitation planning.

Chapter 8 provides a comprehensive exploration of the challenges posed by urban flooding on water quality, focussing on the case study of Mumbai. With India’s rapid urbanisation, the strain on water infrastructure has led to issues such as dropping water tables, inadequate drainage and contamination of stormwater drains with raw sewage. The chapter delves into the aftermath of the severe flooding in Mumbai, particularly the 2005 mega flood, discussing its impacts on water quality and the outbreaks of diseases such as gastroenteritis, malaria and dengue. Mitigation measures and the government’s initiatives, like the AMRUT mission, are highlighted. The chapter underscores the importance of learning from Mumbai’s experience to develop effective strategies for other cities facing similar challenges in the context of urban flooding and water quality management.