Fighting floods with ‘sponge cities’

Wednesday, February 7, 2018

 A new vision for Udon Thani transforms the city into a green ‘sponge city’ that uses natural infrastructure to protect a growing population from flooding. 

In an era of rampant land development and increasing climate unpredictability, the world is growing used to alarming images of flooded city streets. Urban floods cost billions of dollars per year. Even the mildest can bring traffic to a standstill and cause economic hardship for merchants and residents. The worst floods drown people, spawn disease, destroy infrastructure and virtually shut down entire economies.

But cities themselves can combat these floods by turning into “sponge cities.” By utilizing wetlands – wet areas such as marsh, swamps or shallow ponds – as well as green spaces and floodplains, a city can absorb large amounts of water before it submerges its streets. As we mark World Wetlands Day on February 2, it’s time for cities to reconsider the power of wetlands and other natural infrastructure. It’s time for sponge cities to fend off the growing scourge of urban floods.

Thai cities have dealt with serious floods in recent years. The flooding of Bangkok in 2011 is estimated to have cost USD 41 billion. Udon Thani, one of the major cities in the northeast region of Isan, has also been impacted. Almost every year during the monsoon, the city’s drainage system is overwhelmed. Large areas are inundated, homes and other buildings are flooded, and roads become impassable. Because sewage mixes with flood waters, city flooding can bring increased health risks – causing direct human, as well as financial, costs. 

Flooding in Udon Thani, 30 July 2016.
Flooding in Udon Thani, 30 July 2016. Photo by estudioOCA

In recent years, economic growth and migration from rural areas has led to rapid population growth in Thai cities like Udon Thani. Increasing population has contributed to dramatic land use changes throughout the city. These changes exacerbate the flooding by increasing the area covered in concrete, asphalt and other impervious surfaces, which prevent rainwater seeping into the ground. This increases water runoff – excess water sitting on the surface of the land. This runoff floods the city.

As with many Thai cities, Udon Thani is growing rapidly and solutions are urgently needed to alleviate the increased flood risk. The Bangkok-based planning and design firm estudioOCA has a vision for the future of Udon Thani as a “green” city, mitigating flooding by using “natural infrastructure,” including wetlands, trees and parks. 

A perspective showing the proposed Green Infrastructure Master Plan combining natural and built infrastructure systems for the Udon Thani area.
A perspective showing the proposed Green Infrastructure Master Plan combining natural and built infrastructure systems for the Udon Thani area. Credit to estudioOCA

In a year-long project, landscape architects, engineers and scientists have worked together, to test the feasibility of natural infrastructure to soak up excess water. Using a hydrological model, in combination with design and engineering tools, they have designed a natural infrastructure network that links green areas across the city.

This work has shown that the wetlands and green areas “buffer” water flows; reducing flooding by slowing water flow during storms and increasing infiltration. In essence, they act as a sponge to soak up water before a flood occurs.

Research in Asia by the International Water Management Institute (IWMI) has highlighted the value of urban wetlands, particularly for the urban and suburban poor. For example, wetlands within the city boundary of Hyderabad, India support the growing of rice, vegetables and cattle fodder that are sold in the city markets – a major contribution to the livelihoods of many subsistence farmers. Similarly in India’s northeast, the wetlands of Kolkata not only help reduce flooding in the city, but also support 32,000 people who fish for a living – all while treating the city’s sewage.

In both cases, haphazard urban sprawl is causing the degradation and loss of these wetlands – up to 50% loss in Kolkata between 2000 and 2012 – thereby threatening the poorest residents that are most dependent on the benefits that wetlands provide.

In contrast, the government of Sri Lanka now recognizes the vital benefits of urban wetlands and are working to conserve and enhance their potential, including for flood mitigation. Colombo aims to be one of the first official “Wetland Cities” accredited by the Ramsar Convention. Planners foresee not only better flood protection, but a more competitive and livable international city.

In Udon Thani, the vision is not only to protect existing wetlands, but also restore lost and create new wetlands, along with other natural infrastructure. The aim is to protect the city from flooding, while also providing additional benefits such as green and recreational spaces. A key goal of the “green infrastructure master plan,” that estudioOCA has proposed, is to increase the diversity of landforms within the city. In Europe and the US such diversity has been shown to fight floods and help cities recover more quickly in their aftermath.

Plans for a new park on a canal in Udon Thani, creating a new wetland to slow the speed of water during storms and increase infiltration during (a) dry, and (b) monsoon seasons.
Plans for a new park on a canal in Udon Thani, creating a new wetland to slow the speed of water during storms and increase infiltration during (a) dry, and (b) monsoon seasons. Credit: estudioOCA

In recent years, urban development in Thailand – and throughout most of Southeast Asia – has largely outpaced proper urban planning. Now is the time to recognize that wetlands are an integral part of urban landscapes; a key component of natural infrastructure that provide numerous benefits. As such they must no longer be neglected. Wetlands must be incorporated explicitly in urban planning.

The vision for Udon Thani illustrates what can and must be done. Planning and wisely using wetlands and other natural infrastructure to create “sponge cities” is a crucial step on the way to the greener, healthier and less flood-prone cities of the future.

This blog was originally published by CGIAR, you can read it here.

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