Fighting floods with 'sponge cities'

Fighting floods with 'sponge cities'

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 kill people, spawn disease, destroy infrastructure and virtually shut down entire economies.

But cities can combat these floods by turning themselves into "sponge cities". By harnessing the power of wetlands -- areas covered by water, such as marsh, ponds or rice fields -- a city can absorb water before it submerges its streets. As we mark World Wetlands Day today, it's time for cities to reinvest in wetlands. It's time for sponge cities to fend off the growing scourge of urban floods.

Bangkok and other Thai cities are seeing serious floods with increasing regularity. Udon Thani, one of the major cities in the northeast region of Isan, has been a prime target. 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 brings increased health risks -- so there is a direct human, as well as a financial, cost to the flooding.

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 resulted in 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 continues to grow 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, as it is known, including wetlands, trees and parks. In a year-long project, landscape architects, engineers and scientists have tested 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 mop up floods before they occur.

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 in 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 -- threatening the poorest residents that are most dependent on the benefits that wetlands provide. In contrast, the government of Sri Lanka now recognises the vital benefits of urban wetlands and are working to conserve and enhance their potential. 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 land forms 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.

In recent years, urban development in Thailand and most of Southeast Asia has largely outpaced proper urban planning. Now is the time to recognise 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. Using wetlands to create "sponge cities" is a crucial step on the way to the greener, healthier and less flood-prone cities of the future.


Ignacio Ortinez is Principal of estudioOCA in Bangkok. Matthew McCartney and Priyanie Amerasinghe are senior researchers with the International Water Management Institute (IWMI) and its CGIAR Research Programme on Water, Land and Ecosystems (WLE). IWMI and WLE are non-profit organisations researching water and ecosystem solutions for sustainable agriculture.

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