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Designed to neutralize the impacts produced by heavy rains in urban areas, rain parks are part of a Water-Sensitive Urban Design (WSUD) planning model that enables cities to co-exist with overflows symbiotically. Water flows are managed with green roofs, wetlands, lawns with detention basins, and retention ponds. In restored wetlands located between the outer berm and the sea, this solution enables better soak up and speed down seawater.
Human interventions in natural flooding can often cause more damage than they seek to avoid. Manmade coastal defenses, levees, and dams can easily be overwhelmed by large flood events, releasing large amounts of water at once, or forcing it into narrow, fast-flowing channels to create bottlenecks that cause upstream flooding. Floodplains are natural flood protection, yet building on floodplains inhibits this function. Thus the key is to work with nature to absorb excess water sustainably into built-up environments and ultimately, back into the hydrological cycle. As a result, non-structural, soft, and nature-based solutions to flood adaptation such as Rain Parks are replacing centralized and engineered technologies.
The benefits of increasing urban porosity lie principally in climate resilience: in the UK, flooding and flood management cost the UK £2.2 billion every year. In China, floods in 2020 affected nearly 70 million Chinese citizens and cost $29 billion. All in all, Rain Parks allow urban spaces to accommodate floods and stormwater better, keeping communities safe while also creating recreational areas in urban environments.
Case Studies: Resilient Cities
Bangkok: Thai landscape architect Kotchakorn Voraakhom has created a public park in Bangkok designed to withstand frequent flooding. Many of the city’s canals have been paved over to make way for urban sprawl. The problem is that those waterways acted as conduits for rainwater, which now has nowhere to go. As a result, Bangkok experiences frequent flooding. During rainy seasons, the Chulalongkorn University Centenary Park collects and stores water that is then used for irrigation in dry seasons. It can hold up to one million gallons of water over an area of 11 acres. During the dry season, these tanks will provide enough water to keep the park irrigated for up to 20 days.
Copenhagen's Floodable Parks: Flooding in 2011 overwhelmed Copenhagen's stormwater and sewerage system, causing significant damage. One of the city's largest parks, Enghaveparken, has been redesigned to incorporate retention ponds which can be used for recreation when the park is dry, but will fill up when it rains. A boundary dyke around the park will filter water into nearby community gardens.
In Rotterdam, a 'delta city' at sea level, water storage has been incorporated into city design to manage stormwater and reduce the impacts of flooding. Low-level plazas are designed to fill with water, and an underground parking garage acts as a basin with the capacity of four Olympic sized pools. City authorities already subsidize green roofs, and are considering a tax incentive for residents who collect rainwater.
Rain Park Features
Rain parks combine blue and green infrastructure, in other words, water features such as ponds and floodplains, and trees and parks. Typically, water is stored below ground level in a detention pond, bio-retention basin, or tank. Water may then evaporate, be released slowly into the sewerage system, or percolate, for example through vegetation or synthetic soils. Alternatively, it may be treated via wastewater treatments such as infiltration, filtration, or Nanofiltration, for example with Ceramic Membranes, for recirculation, consumption, or for irrigation when water is scarce, such as during dry seasons.
Other features of Rain Parks may include green roofs, wetlands, and planting specifically designed for erosion prevention and slowing water movement. Water harvesting from impermeable surfaces and structures and Porous Pavements may also be incorporated.
An Integrated Water Management Platform could be used to optimize urban water resources. Additional benefits range from providing quality water for agricultural purposes and storing water in the case of fire.
Besides creating communal spaces, redesigned areas could also embody ecological functions, increase urban biodiversity, and enable economic regeneration for local communities. Instead of being seen as waste, rainwater could become a resource, improving life in urban areas and mitigating climate change impacts.
Even if promising, substantial infrastructure changes may increase the cost-benefit this solution provides. Cities with high population density will need to reallocate citizens to other areas or refurbish current parks with proper groundwork, which could, to a large extent, consume time and resources, setting up a considerable implementation drawback.