Water management (SDG 6)

Sri Lanka faces multiple natural hazards, including tropical storms, flash floods, and landslides. As the country's urban population has grown, development projects have encroached on wetlands, compromising their natural flood protection, air and water purification, and carbon storage capabilities. Additionally, hilly regions are at risk of landslides, particularly during the monsoon season, posing significant threats to vulnerable communities (4).
To address these challenges, the World Bank and the Sri Lankan government collaborated on the Metro Colombo Urban Development Project. This initiative focused on nature-based solutions (NBS) as cost-effective and sustainable approaches to risk management (4). By strengthening natural processes and ecosystem services, the project aimed to mitigate hazards such as floods, erosion, and landslides (4). Technical assessments by the World Bank highlighted the importance of wetlands in flood protection, leading to efforts to protect and restore 20 square kilometres of freshwater lakes, wetlands, and swamps (1, 4).
The project supported the Sri Lankan government in reducing flooding in the Colombo Water Basin and enhanced local authorities' capacity to manage infrastructure and services. It prioritised metropolitan investments to mitigate the physical and socioeconomic impacts of flooding and aimed to build long-term capacity for urban management and local service delivery (6).

To reduce the risk of urban flooding, the city of Seville, through its metropolitan water company Emasesa, established several "sustainable urban drainage systems". One of the pilot locations is on the Avenida de las Ascociaciones de Vecinos, where a rain garden complemented by an infiltration zone was established. The main aim of the project is to reduce the risk of flooding, but the system can also improve the urban landscape by offering green space, preventing desertification and reducing pollutants carried by runoff [Ref. 1-4]. After implementation, the project was shown to be effective during heavy rain [Ref. 5]. The system can store up to 34 m2 of water and reduce flow rates to the sewage network by 69 % and the total runoff to sewage by 93 % [Ref. 3-5]. The project was initiated and led by Emamesa, while two different companies were employed to design and construct the system [Ref. 1, 2, 6, 7]. The total budget of the project, which also included some renovations of grey infrastructure along the street, was 165000 EUR [Ref. 1].

The Waliwa project, launched in 2017 by the municipality of Sainte-Luce, is a collaborative effort dedicated to restoring marine biodiversity, enhancing the ecological balance of the bay area, revitalizing the local ecosystem and supporting sustainable economic activities. By focusing on marine biodiversity conservation, Waliwa addresses several critical environmental challenges. The project helps mitigate coastline erosion, support the blue economy through artisanal fishing and tourism, and foster an environmentally friendly culture among the local community.
So far, the Waliwa project has implemented three initiatives: it restored the Gros Raisin backshore to address erosion and provide nesting sea turtles with protected space (Ref 4). The project also intervened to restore the Pont Café pond, which was covered in Salvinia Molesta, preventing the intake of oxygen and hampering its role as a water filter, habitat for species and flood regulator .
Furthermore, the project has conducted studies and raised awareness about the challenges posed by wastewater management on the health of municipal water bodies. Through these efforts, Waliwa is working to create a more sustainable and resilient marine environment for future generations. (Ref 4, 5, 6; 12)

Assemini, a municipality in Cagliari, has long grappled with hydrogeological instability, marked by major floods in 1999 and 2002. To mitigate future risks, the municipality launched a series of interventions focused on improving the hydraulic management of its waterways. These projects are part of a broader strategy to address recurring flood hazards exacerbated by the effects of rapid urbanization in the 1970s, which disrupted the natural water drainage systems (1,3). The central goal of the project is to reduce the risk of flooding by enhancing the functionality of existing waterways. This includes both preventative measures and structural improvements to the canal system to manage stormwater more effectively. These efforts aim to safeguard urban and rural areas from severe meteorological events. The project development involved a multi-phased approach starting in 2013, focusing on cleaning and maintaining minor waterways such as the Gutturu Lorenzu, Sa Nuxedda, and Giaccu Meloni streams. These efforts expanded over time, culminating in an agreement with the Land Reclamation Consortium of Southern Sardinia in 2015, securing both local and regional financial support. The interventions have covered over 24 kilometers of canals and streams, targeting key flood-prone areas (1,2).
Key interventions include the cleaning and maintenance of over 35 km of canals and streams, in partnership with the Land Reclamation Consortium of Southern Sardinia, supported by regional funding. A separate, large-scale intervention in Truncu Is Follas involves constructing an open-air diversion canal, a retention basin (44,500 m³), and new pipelines to redirect floodwaters, thus reducing risk for residents downstream in both Assemini and Elmas.

The project focused on implementing multilayer blue-green roofs in four Italian cities—Cagliari, Palermo, Perugia, and Viterbo—as part of a broader European initiative to address climate change impacts in urban environments (1,3). Spearheaded by a collaboration between multiple Italian universities and the Dutch company Metropolder, the project began in 2019 (1,3). The primary goal is to enhance urban resilience by integrating green infrastructure capable of mitigating climate-related urban hazards such as flooding and heat waves, which are increasingly severe due to climate change and urbanisation (2,3).
The multilayer blue-green roofs combine the ecological benefits of traditional green roofs with an added water storage layer, allowing them to retain rainfall and manage runoff effectively (2,3). This dual function helps reduce pluvial flooding and the urban heat island effect, while also improving thermal insulation in buildings (2,3). Each installation was planted with low-maintenance, climate-adapted vegetation, and equipped with sensors to monitor ecohydrological and thermal performance over several years (1,3). These roofs are capable of retaining up to 100% of rainfall from significant events, thereby easing the burden on urban drainage systems and contributing to climate adaptation in Mediterranean cities (2,4).

The Cagliari Canal project is an initiative aimed at revitalizing and transforming the urban and natural landscape of the Cagliari Metropolitan Area in Sardinia. The project is rooted in the city's strategic metropolitan plan and seeks to restore and enhance the navigability of the Terramaini-La Palma canal, which had become disused and neglected over time​ (3,4). The primary goal of the Cagliari Canal project is to develop a connected, innovative, and sustainable urban environment by re-establishing the canal as a green and blue infrastructure​ (2). It aims to provide alternative, sustainable mobility options, improve connectivity between municipalities, and enhance the natural and urban environments. It strives to foster a sense of community by creating a shared space for residents and integrating modern amenities that align with environmental sustainability (1,4). It involved a highly participatory process, emphasizing community involvement from the initial planning stages. The Metropolitan Authority of Cagliari, in collaboration with local stakeholders, launched a series of consultations to gather public input on the canal's design and function​(3). These consultations were part of a broader initiative called LabMet, the Metropolitan Laboratory for Innovation, which facilitated the collection of ideas and feedback (1). The project was partly developed in response to the increasing environmental challenges faced by Cagliari, including the need to adapt to climate change. The canal's revitalization is seen as a key measure for enhancing the city's resilience to climate-related risks, such as flooding and heat waves​(1). By restoring the canal and its surrounding areas, the project aims to mitigate these risks through improved water management, reducing pollution, and the creation of green spaces that can absorb excess rainwater and provide cooling effects​ (2)

Located between the Rotes Rathaus, Karl-Liebknecht-Straße, Nikolai Quarter, Spreeufer and the television tower, the old founding centre of Berlin is one of the capital's most important urban open spaces. This open space between the TV tower and the Spree is being redesigned on the basis of an international open space planning competition and many years of public participation. With further development, this touristically significant location in the historic centre of Berlin will undergo a climate-resilient redesign and upgrade with great design and functional quality. (Ref. 1)
The listed areas of the Rathausforum and the Marx-Engels-Forum will in future be connected to form a continuous ribbon of open space that runs from Alexanderplatz to the Spree. Central areas will be unsealed and green spaces will be created that can be used in a variety of ways, which will also be attractive places to spend time and improve the microclimate. Trees and shrubs will be planted on already existing and new green areas. The aim is to respectfully consider the numerous visible and hidden historical references and at the same time transform the site into a sustainable urban open space that combines a high quality of recreation, sustainability and culture. Next to plants, a new rainwater management system is being implemented that stores rainwater and uses the created green spaces to evaporate water. Playgrounds and a water fountain are further additions to a new recreational area. (Ref. 3; Ref. 4; Ref. 5)
The project is characterized by a years-long participation process. Around 10.000 citizens participated in feedback rounds, workshops, dialogues, and information sessions in which they could voice they wishes and ideas for the area. The project is implemented and organized by the state-owned company Grün Berlin, which engage with various stakeholders since 2015. Preparations for the construction start in late 2024 and the project is expected to be finished in 2030. (Ref. 5; Ref. 9)

Booterstown Marsh, the only remaining saltmarsh on the south shore of Dublin Bay, plays a crucial role in the Dublin Bay Protection Plan. As part of South Dublin Bay's protected landscape, this unique 4.3-hectare brackish water marsh provides vital environmental and educational value within an urban setting. It supports three key habitats, ranging from freshwater to saltwater, creating essential feeding and roosting grounds for an array of migratory birds. The marsh attracts numerous bird species, including Moorhen, Reed Bunting, Sedge Warbler, Teal, Snipe, Lapwing, Oystercatcher, Redshank, Dunlin, and Brent Geese, establishing it as the only bird sanctuary in South Dublin Bay.
Booterstown Marsh’s ecological significance is underscored by its inclusion in the Dún Laoghaire-Rathdown County Council’s Biodiversity Action Plan 2021-2025: Nature Recovery, Restoration & Reconnection. Managed by the Biodiversity Section of the council, this initiative focuses on protecting and enhancing Booterstown Marsh as part of a broader effort to restore natural habitats across the area. The council’s project addresses key factors in biodiversity loss—such as land use pressures, climate change, and invasive species—by implementing an annual monitoring program to prevent deterioration of critical EU Annex habitats and species.
An Taisce, a local NGO has managed the marsh reserve since the 1970s, dedicating efforts to conservation and public education. This habitat, along with other local ecosystems like the wetlands at Ballycorus and woodlands at Loughlinstown, serves as an essential natural defense against climate change, removing carbon dioxide from the atmosphere and helping stabilize local landscapes by slowing floodwaters in catchment areas.(1-6)

The former Kulturpark Plänterwald, once the only permanent amusement park in the GDR, closed in 2001 due to declining visitor numbers. Over time, the 23-hectare site became a ‘lost place,’ falling into disrepair. In 2014, the state of Berlin reacquired the area, and two years later, Grün Berlin initiated its redevelopment with a sustainable development concept that places significant emphasis on rainwater management.
The project’s goal is to avoid discharging rainwater into the sewer system and instead manage all precipitation on-site. This approach addresses both heavy rainfall events and extreme drought conditions, creating a sustainable rainwater management system. A central element of this concept is the historic but dried-up water basin located near the iconic Ferris wheel. Plans include redesigning and reactivating the basin, incorporating terraces and a shallow water zone, transforming it into a key part of the rainwater cycle while providing an attractive recreational and adventure area. (Ref. 1; Ref. 2)
In the future, the water basin will no longer be purely decorative but will serve as a critical artificial water reservoir. To support this function, it will be equipped with a natural horizontal filter system featuring reeds for rainwater purification. Pre-treated water will flow into the newly designed 3,000-square-metre basin near the Ferris wheel. Rainwater collected in the basin, along with water stored in cisterns throughout the park, will irrigate the site’s vegetation. This innovative approach ensures sustainable water use and contributes to the ecological revitalization of the park. (Ref. 1; Ref. 3)
By integrating sustainable rainwater management into its redevelopment, the former Kulturpark Plänterwald is being transformed into a resilient and environmentally conscious space, combining historical preservation with modern ecological practices.

The Far West Detroit neighborhood faces significant challenges with its aging infrastructure. The neighborhood’s stormwater and sewer systems are combined into a single system that is only capable of handling a limited volume. During heavy rain events, the system's capacity is exceeded, causing excess stormwater and untreated sewage to overflow into the Rouge River, which negatively impacts the environment (Ref. 1).
Detroit is investing $40 million in a transformative stormwater management system in the Far West neighborhood near Rouge Park. Described by the Detroit Water and Sewerage Department as the largest project of its kind, it will redirect 98 million gallons of rainwater and snowmelt into two new detention basins and a renovated sewer system. The new wastewater system is expected to significantly reduce water volumes in Detroit’s combined sewer system during heavy rainfall and to provide flood relief for approximately 1,200 homes that have experienced flooding in recent years. This expansion, informed by community feedback, marks one of the city's most notable investments in green infrastructure to improve its overextended wastewater management system.
The project has been planned through extensive studies and community coordination since 2016, with construction set to occur in three phases, extending through 2026. Crews broke ground on the South Basin, North Basin, and sewer overhaul in July 2022, and progress is reportedly on track. In addition to the basins, the stormwater management initiative includes neighborhood improvements to enhance recreational opportunities for residents and visitors alike. Planned enhancements in Rouge Park will introduce wetland spaces with native flora, creating greener, more inviting areas in the community for residents to enjoy (Ref. 2).