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Jun 24, 2024 / 16:25

Hanoi to build retention ponds and underground water tanks in urban areas

The move is seen as a viable solution to enhance drainage capacity and reduce inundation in the city.

Hanoi is implementing various solutions to manage flooding during rainfall, including the development of retention ponds and underground rainwater storage tanks. This sustainable drainage solution not only helps manage water but also enhances the urban landscape and architectural space of the capital city.

 A retention pond in Hanoi. Photo: Pham Hung/The Hanoi Times
Multi-benefit solutions
In recent years, Hanoi has devoted significant resources to improving the city's water drainage capacity. This has included the construction of numerous new retention ponds. However, the complex weather patterns, rapid urbanization, and deteriorating drainage infrastructure have made flood control and water drainage increasingly challenging.
Climate change, characterized by extreme weather and rising sea levels, exacerbates these issues. Extreme weather manifests itself in unpredictable patterns of rain, storms, heat, and cold. Heavy rains can lead to severe flooding, while prolonged dry spells cause serious droughts. In this context, developing a system of retention ponds and underground rainwater storage tanks in urban areas is essential to address these challenges.

According to the Hanoi Sewerage and Drainage Company, before the installation of rainwater storage tanks, streets like Nguyen Khuyen would flood when it rained less than 50mm. However, since these tanks were installed, flooding on this street and in the surrounding areas has significantly decreased.

“ When precipitation was between 50-100mm, Nguyen Khuyen Street used to flood up to 0.5-0.7 meters. Since the rainwater tanks became operational, the water level during inundation has been reduced to 0.2-0.3 meters,” a representative from the company shared.

Associate Professor Dr. Nguyen Lam Quang, Deputy Director of the Vietnam Institute for Urban and Industrial Environment, told The Hanoi Times that sustainable urban drainage solutions involve utilizing and optimizing natural water flow through surface runoff. This is achieved by reducing the speed and volume of runoff via natural and artificial water storage systems, which help prevent flooding, replenish groundwater, and utilize rainwater for fire fighting, irrigation, and street cleaning, among other purposes.

This approach aligns with the Government's Decree 80/2014/ND-CP on drainage and wastewater treatment, as well as the specific conditions of Hanoi.

“Therefore, Hanoi must urgently implement measures to develop retention ponds and underground water tanks to enhance drainage capacity and reduce flooding in the city,” said Quang.

Rainwater regulation required
According to Quang, sustainable drainage solutions have been researched and piloted in several Vietnamese cities. Notably, projects funded by the German Development Cooperation Agency (GIZ) have explored and applied sustainable drainage models in some coastal cities in Central Vietnam and the Mekong Delta.
However, sustainable drainage solutions have not yet been widely adopted in urban planning, construction, and drainage management. This is particularly true in the design process of technical preparation plans. The lack of legal frameworks and regulatory documents is a primary reason for this situation. To enhance drainage efficiency and mitigate flooding in Hanoi and across Vietnam, it is necessary to develop a stormwater drainage service fee mechanism and related policies, including the formulation and enactment of a Rainwater Management Law.

Associate Professor Dr. Dang Minh Hai, Deputy Head of the Water Resources Engineering Department at Thuy Loi University, believes that for projects involving changes in land use or drainage direction, developers must implement solutions to prevent increased rainwater runoff into the drainage system, thus avoiding localized flooding.

Specifically, developers looking to build residential or urban areas must obtain rainwater drainage permits and pay for rainwater drainage services. This requirement should be mandatory, said Hai.

Many experts shared the view that sustainable drainage, or slow drainage, involves managing rainwater to extend the of its flow so that urban runoff patterns more closely resemble natural ones. To achieve this, Hanoi should focus on source control, surface control, and area-wide control.

For source control, Hanoi should encourage the use of underground storage systems and rainwater reuse in homes and office buildings. The development of green roofs can significantly retain rainwater in vegetation and soil layers, reducing runoff into the urban drainage system and minimizing localized flooding during heavy rainfall.

According to the drainage plan for Hanoi up to 2030, with a vision towards 2050, approved by the Prime Minister in Decision No. 725 on May 10, 2013, the urban drainage system is divided into four basins: To Lich, Left Bank of the Nhue River, Right Bank of the Nhue River, and Long Bien.
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