Seeking a Cure Cities are upgrading drainage systems to battle chronic flooding

By Li Li

People in many cities across China have experienced disruptions due to urban drainage failures since the beginning of summer.

Kunming, capital of southwest China’s Yunnan Province, was forced to grapple with urban flooding after the heaviest rainfall of the year hit the city on July 18. During the next three days, flooding of local roads submerged cars and taxis and rendered more than 200 inundated buses unusable.

In the wake of a tropical storm that swept southeast China’s Fujian Province, the coastal city of Xiamen, was severely flooded on July 19.In some areas of the city, water reached waisthigh levels, while pedestrians caught fish that had escaped from ponds and aqua farms.

While reading such reports, citizens in Beijing may be reminded of the city’s most deadly rainstorm from one year ago. The heaviest rain in six decades struck the capital on July 21,2012. The 16 hours of nearly constant downpour wreaked havoc on Beijing’s infrastructure and left 79 people killed in rain-triggered disasters and accidents.

The primary reason for urban flooding is that drainage systems often lag behind overall urban development, said Xu Ke, a senior engineer with the Beijing Tsinghua Tongheng Urban Planning and Design Institute.

He said that another major cause is that some roads are built higher following maintenance projects, leaving lower-lying roads more vulnerable to flooding in heavy rainfall.

Mounting risks

In recent years, frequent urban drainage failures have forced governments of many cities to establish emergency plans.

Rainstorms brought by typhoon Krosa slammed Hangzhou, capital of east China’s Zhejiang Province, in 2007. Streets wereflooded to such an extent that many residents resorted to using canoes for transportation.

Starting in 2008, the local government began raising standards for drainage pipelines used in new projects and applying these in old city areas. Meanwhile, for ident ified vulnerable areas, municipal authorities have established an emergency plan to designate personnel and pumps to key spots during downpours to prevent waterlogging.

But this method has shown only limited effectiveness. During a rainstorm on June 24,Hangzhou was still paralyzed by floods in spite of drainage workers being assigned at 18 key stretches of roads and 14 residential communities beforehand.

The failure of Hangzhou’s emergency drainage plan during this year’s flood season highlights the need for a national effort to solve this problem once and for all. In April, the State Council issued a notice on upgrading urban drainage facilities. Accordingly, China will achieve a drainage network upgrade to separate rainwater from wastewater within the next five years and build sound urban drainage systems within the next 10 years.

On June 18, the Ministry of Housing and Urban-Rural Development (MOHURD) issued a guideline for local urban governments to formulate plans on improving their drainage systems.It says that by 2017 drainage facilities in downtown areas across the 36 largest cities would be upgraded to handle torrential rain occurring once every 50 years; drainage facilities in downtown areas of all other prefecture-level cities would be able to withstand heavy rain occurring once every 30 years, and drainage facilities of all other downtown areas would be able to cope with heavy rain occurring once every 20 years.

According to a survey conducted by the MOHURD in 2010, between 2008 and 2010, 62 percent of cities in China experienced severeflooding at least once; 137 cities reported this problem three times or more and real estate or other facilities were submerged more than 12 hours in 57 cities.

Data from the Office of State Flood Control and Drought Relief Headquarters show 258 cities in China suffered from heavy inundation during 2010, mostly caused by urban flooding in the wake of torrential rains.

Cheng Xiaotao, Executive Deputy Director of the Water Hazard Research Center under the Ministry of Water Resources, told newspaper China Business News that urban flooding has posed a more prominent threat to cities in China than externally sourced floods while laws,regulations and emergency plans on flood control have yet to differentiate responses to both types of disaster. “A clear understanding of the different causes for such water hazards is the key to reducing urban flooding,” he said.

A crumbling system

Cheng said that the most direct cause for worsening urban flooding in China is its relatively poor drainage infrastructure.

Experts with the MOHURD ident ified more spec ific problems such as the low coverage rate of drainage networks and inadequate drainage capacity. According to the ministry, although Beijing’s built-up urban area has doubled over the past decade, the construction of an underground network has not kept pace.

The revised Code for Design of Outdoor Wastewater Engineering, issued by the MOHURD in 2011, stipulates that a drainage system for general areas in cities should withstand high-intensity rainfall once every one to three years, while design for important areas should withstand rainfall once every three to five years.

Cheng said that most cities have taken advantage of the flexible description of precipitation in the regulation and built the weakest drainage systems possible.

Along with his team, Cheng has spent the last three years conducting field surveys in cities across the country, compiling a report entitled Flood Control in Chinese Cities: Current situations, Problems and Solutions. According to their findings, more than 70 percent of cities in China, including Beijing and Wuhan in central China’s Hubei Province, have designed their drainage systems based on handling highintensity rainfall occurring once a year, while old areas in 90 percent of cities have poor drainage facilities.

The report also ident ified the less-than-satisfactory coverage of drainage networks across cities, even in Shanghai.

Cheng attributes this handicap in drainage development to rapid urbanization. “Suburban areas have been turned into urban areas on an unprecedented scale over the past two decades,” he said.

Cheng said that in other countries, where urbanization progressed at a much slower pace,the government had enough time to finish constructing infrastructure before selling land to real estate developers. But this is not the case in China, and the situation is worsened by the fact that the country is yet to establish a sound legal framework to avoid such infrastructure loopholes.

Another important reason is that during the development of large cities in China, open soil, wetland and lakes, which could store water during rapid precipitation, have shrunk enormously. Take Beijing for example. Cheng’s research team discovered that the number of lakes across the capital had plummeted from more than 200 to around 50 over the past six decades.

Many experts have suggested that cities must fully tap storage potential among existing water bodies to alleviate urban flooding.However, widening rivers has become almost impossible in Beijing because of high-density construction on their banks.

A FLOODED CITY: Drivers struggle to pass through downtown areas of Kunming, Yunnan Province, after a torrential rain on July 21

Another typical city suffering from the consequences of land reclamation from lakes and ponds is Wuhan.

Wuhan has been hit by severe urban flooding at least once every summer since 2008.After torrential rains on June 18, 2011, 82 stretches of roads were severely flooded and traffic paralyzed, forcing the highest level of response to deal with the problem.

Nicknamed “city of 100 lakes,” Wuhan used to have more than 100 lakes in its city center during the 1950s and was famed for its lakeside scenery. By 2012, the total number of lakes had dropped to 40 following waves of land reclamation over the past three decades.

Although the local legislature adopted a regulation on protecting lakes and ponds from random land fill and pollution, shrinkage has not be effectively checked until recently. According to official statistics, Wuhan’s built-up urban area grew from 455.06 square km in 2006 to 507.54 square km in 2011, up 11.53 percent during five years.

“To prevent ‘urban flooding’ from devastating Wuhan as a manmade disaster, related laws and regulations must be perfected and more strictly enforced,” Liao Hua, an associate professor at the Law School of South-Central University for Nationalities in Wuhan, told newspaper Legal Weekly. ■