The capital city of Denmark, Copenhagen, has adopted the concept of sponge city to address annual flood issues. The Northern European country incorporated this concept into the Cloudburst Management Plan in 2012.
"The goal of the Cloudburst Management Plan is to reduce the impact of flood events caused by heavy rain, which is anticipated to increase in frequency due to climate change," quoted from the Interlacehub website updated on Tuesday, July 25, 2023.
The background of designing the sponge city came after the major flood that occurred on July 2, 2011. The damage from the disaster amounted to billions of kroner or around US$ 1 billion.
Quoting from the University of Copenhagen, the weather at that time was known as a cloudburst, with over 15 millimeters of rain within 30 minutes. Even during the disaster 14 years ago, 135.4 millimeters of rain fell in the Copenhagen Botanical Garden, 31 millimeters fell in the outskirts of Ishj, and more than 5,000 lightning strikes were recorded within 3 hours.
Heavy rain and hail caused traffic to come to a halt in several parts of the metropolitan area as roads turned into rivers. Some roads were closed for 1-3 days.
Within the Cloudburst Management Plan, 300 projects are planned to be implemented over 20 years. The plan is carried out and funded jointly by the City of Copenhagen, the Greater Copenhagen Utility Company, and private actors such as private landowners.
Urban areas targeted include semi-natural urban parks and green areas, blue areas, green areas for water management, and urban green spaces connected to gray infrastructure.
The project funding comes from the budget of public local authorities, corporate investments, and utility companies. The expenditure amounts to 1.5 billion euros, with details for surface solutions at 700 million euros, cloudburst pipes at 358 million euros, disconnection or connection outside property boundaries at 134 million euros, and home protection at 320 million euros.
The City of Copenhagen can collaborate with water utilities on a comprehensive restructuring of the drainage system (including separating rainwater from wastewater) and street landscapes to turn streets into rivers during extreme rain and direct water to outlets and retention basins.
"This is complemented by greenscaping, particularly through the implementation of Sustainable Urban Drainage Systems - the construction of green parks, roofs, and bioswales to prevent rainwater from flowing directly into drainage channels," quoted from Interlacehub.
As an example in the design, Lake Sankt Jrgens S becomes a public open space in the summer. Then when a flood arrives, more than 70 percent of the lake area is submerged in water and only a path in the middle can be passed through. Subsequently, the water will seep underground and become a water reserve.
The sponge city concept was introduced by Chinese architect
Chinese landscape architect Kongjian Yu researched the sponge city concept in the late 1998. Natural wetlands will absorb water during floods and fill water reserves during droughts.
Quoting from World Economic Forum, this concept was also inspired by traditional irrigation management in China. It has become a characteristic of the rural landscape in the Bamboo Curtain Country and has proven effective in slowing and retaining water, preventing floods, and preserving biodiversity.
Yu's design combines modern urban planning that includes sidewalks, parks, and underground water storage tanks. "These elements work together to absorb excess rainwater, purify water, and replenish groundwater, creating a more resilient urban landscape."
This flood management solution has also been adapted into the planning of the development of the National Capital of Indonesia (IKN), East Kalimantan. The implementation of the sponge city has already been planned within Law Number 3 of 2022 concerning the State Capital. Last year in 2023, the IKN Authority visited Deltares-a research institute in The Hague, Netherlands, for the development of the city.
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