CAE in Media


Closing the floodgates to disaster

  • Published: Nov 3, 2013
  • Source: China Daily
  • Font size: BigMediumSmall

Experts are calling for improvements to drainage systems and emergency response capabilities to prevent China's larger cities from being paralyzed by adverse weather, as Wang Zhenghua reports from Shanghai.

Early in October, a heavy storm ravaged a large swathe of East China as Typhoon Fitow swept across the region. At least 70 percent of Yuyao city in Zhejiang province was submerged under deep floodwaters that left the city of 1.3 million people paralyzed as power supplies, telecoms, tap water and public transport services were crippled. Even the local TV and radio stations were unable to broadcast.

Closing the floodgates to disaster

A bridge leading to Guomu village in suburban Yuyao city, Zhejiang province, submerged by floodwater after Typhoon Fitow hit East China in early October. Gao Erqiang / China Daily

Even though 20 days had passed since the unexpected flood hit Yuyao, Chen Zhenglan was still haunted by memories of the nightmare during which the city was thrown into complete chaos and her family, along with many others, was cut off from food and clean water for days.

Luckily, no deaths or casualties were reported, but an official report estimated the economic loss to the city at more than 20 billion yuan ($3.2 billion).

Residents accused the regional government of lacking the experience and foresight required to respond to such a disastrous situation.

"We should all learn a lesson from that flood," said Chen.

A serious threat to life

Yuyao, a dazzling industrial city in northeastern Zhejiang, is the latest indication of the vulnerability of some Chinese cities when faced with storm-generated floods.

In 2012, 184 cities - including some at county-level - were at least partly submerged as a result of heavy rains, according to the State Flood Control and Drought Relief Headquarters. In 2011, the number was 136, while in 2010 it was 269.

Closing the floodgates to disaster

Research conducted by the Ministry of Housing and Urban-Rural Development shows that even cities prone to drought - for example, Shenyang in the northeastern province of Liaoning and Xi'an in Shaanxi province in the northwest - are becoming increasingly waterlogged as a result of heavy storms.

Not only do flash floods cause immense damage to city infrastructures and the residents' property and livelihoods, but they also pose a serious threat to life.

In July last year, 79 people died as a result of the heaviest downpour to hit Beijing for 61 years. Millions of residents were affected and thousands were evacuated from their homes, leading to an economic loss of as much as 10 billion yuan.

Dealing with climatic extremes will remain a major challenge for cities as China moves forward on the path of urbanization, and it will take time for regional governments to remedy their defective drainage networks, according to officials and experts at the 2013 International Forum on Urban Flood Control held in Shanghai in mid-October.

It's estimated that the urban population will continue to rise by 20 million every year as the urban areas to expand. The international consultancy, McKinsey & Co, estimates that by 2025 China will have 10 to 12 mega-cities with populations of 15 to 20 million, and many more city clusters will arise in due course.

Studies have shown that the design of cities can cause the volume of rainfall to increase and lead to storms occurring more frequently.

According to Zhang Jianyun, president of the Nanjing Hydraulic Research Institute, compared with the period between 1961 and 1980, the number of days of heavy rainfall in the urban areas of Suzhou in Jiangsu province rose by 30 percent between 1981 and 2010. In Nanjing, the figure was 22.5 percent, while Ningbo, in Zhejiang, saw 32 percent. In contrast, the increase was significantly slower in the eastern region's inland areas.

The lack of adequate drainage networks to handle stormwater caused by heavy, prolonged rainfall is one of the primary causes of waterlogging in cities, according to the experts.

In developed economies, excess water left by heavy downpours is dealt with by a dual system that consists of traditional pipelines to handle regular downpours, coupled with a major drainage network, featuring both above ground and subterranean water retention facilities, that deals with the water left by severe storms.

These countries have also developed stormwater management practices that reduce the impact on built-up areas and promote the natural movement of water within an ecosystem or watershed.

For example, the United States has promoted a low-impact approach to land development that works with nature to manage stormwater as close to its location as possible by preserving, or sometimes even recreating, natural landscape features, such as lakes, which can absorb runoff, plus making roads and sidewalks more permeable so that water seeps through and enters the water table.

The approach is innovative in that the surplus water is regarded as a resource and not as waste and is usually channeled to irrigate areas of greenbelt and gardens. In addition, the process includes the use of bio-retention facilities such as rain gardens, vegetated rooftops, collection barrels and permeable pavements.

Closing the floodgates to disaster 

A worker checks a drainage system in downtown Yuyao city. Chen Binrong / for China Daily

However in China, the systems lag far behind. "Urban planning at the top level is defective," said Xie Yingxia, senior engineer at the China Academy of Urban Planning and Design.

He added that the core problem is that the drainage networks in Chinese cities are inadequate and lack a system to handle huge volumes of stormwater beyond the capabilities of the pipelines.

Experts have also pointed to the outdated design of drainage pipelines and the expansion of urban construction that has encroached on, and diminished, natural bodies of water that used to absorb storm runoff.

Meanwhile, there is a mismatch between the drainage capacities of pipelines and river courses in some cities, according to Liu Jun, a professor at Hohai University's Hydrology and Water Resources College. The poor alignment means that during periods of heavy rain, rivers are likely to experience "backflow", preventing water from the pipelines from entering the watercourse, he said.

The continuing reclamation of natural bodies of water in cities, such as rivers, lakes and wetlands, prevents them from helping to reduce the impact of rainstorms.

In Beijing, the process of increased urbanization has gradually resulted in the wetlands and natural bodies of water shrinking from 5 percent of the city's total area to just 2 percent. In Wuhan, Hubei province, the number of lakes is reported to have decreased sharply in recent decades, from more than 100 to 38.

When combined, these factors have resulted in cities becoming fragile in the event of heavy storms, and low-lying areas, underpasses and projects located underground are the hardest hit when the rains come. By the end of 2012, Shanghai alone had 30,000 underground projects, according to the Shanghai Water Engineering Design and Research Institute.

Drainage networks

Earlier this year, the State Council, China's cabinet, issued a notice urging cities to accelerate the construction of drainage networks to prevent or at least reduce flooding.

The notice said that cities should formulate detailed plans by the end of 2014, and that construction of fully functional systems should be completed within 10 years.

Closing the floodgates to disaster 

Debris scattering around Yuyao in the wake of Typhoon Fitow. Gao Erqiang / China Daily

Since 2011, several large cities, including Beijing, Shanghai, Wuhan and Guangzhou in Guangdong province, have announced multibillion-yuan projects to maintain and upgrade their drainage systems.

Despite these moves, experts have urged regional governments to step up their responses to severe weather and called for the use of state-of-the-art technology to improve the accuracy of weather forecasts in the event of impending storms.

Wang Xiang, deputy director of the Office of State Flood Control and Drought Relief Headquarters, said the inadequate emergency response to flash floods by local governments is a problem that requires urgent attention.

Even though China's major cities have established specific offices to coordinate flood control and drought relief efforts, lower level entities, such as communities, businesses and public organizations, are short of personnel, expertise and disaster relief materials, he said.

In addition, emergency response management involves multiple government agencies, including hydraulics, traffic, power, meteorological, construction and the urban management departments. However, although their duties sometimes overlap, their relief efforts are poorly coordinated: "Their duties should be clear and a coordination mechanism should be set up," he said.

Also, specific plans for emergencies, such as waterlogged urban areas, mudslides, traffic congestion, flooded underground projects and the failure of power and tap water supplies, are still not in place, although many cities have put forward contingency plans to deal with swollen rivers, said Wang. "Specific plans should be drawn up to deal with different kinds of flooding," he added.

Better planning urged

Wang Hao, an academician at the Chinese Academy of Engineering, said better urban planning is essential to prevent flooding in cities. "We need a systematic project to address the problem and prevent cities from becoming waterlogged," he said. "A proper network layout needs to be determined during the urban planning period, to dispose of stormwater as close to its location as possible."

He advised the construction of a major drainage system, consisting of tunnels, green land, natural bodies of water, retention facilities and roads to cope with the worst conditions in the coming 50 to 100 years.

"Stormwater runoff could then be carried through the drainage systems both above and below ground," he said. "Different regions should apply different methods, according to the prevailing conditions in their own areas."

Contact the author at wangzhenghua@chinadaily.com.cn 

(From China Daily, 2013-11-01)