he first signs of trouble came from China’s largest freshwater lake, Poyang, which sits along the Yangtze River in Jiangxi Province. On July 10, the Changjiang Water Resources Commission (CWRC) under the Ministry of Water Resources raised the flood alert to red, the highest in the country’s four-tier weather warning system, for Poyang Lake and nearby tributaries. Two days later, the lake’s water level reached a record 22.65 meters - 13 centimeters higher than the 1998 floods which killed 4,150 people.
Poyang Lake is the last major reservoir along the Yangtze River before it hits the lower reaches. Since mid-July, the lake has been at full capacity. According to satellite remote sensing monitoring statistics from the National Satellite Meteorological Center, Poyang Lake and the surrounding waters occupied a surface area of 4,206 square kilometers, a 10-year high.
On July 13, the Ministry of Water Resources warned that many tributaries of the Yangtze River have seen red-alert water levels and are expecting extensive flooding, which would put unprecedented pressures on existing control systems.
The largest freshwater lake in China, Poyang plays an important role in controlling floods along the Yangtze River catchment. The region’s five main tributaries drain into Poyang Lake before flowing into the Yangtze. On July 7, floodwaters in the Yangtze River, however, flowed back into Poyang Lake.
Chen Xianping, deputy director of Emergency Management Bureau of Hukou County, Jiangxi Province, told NewsChina that heavy precipitation is behind the high water levels of Poyang. As of July 11, the flooding had affected 5.21 million people, 430,000 of whom were evacuated. On July 12, Poyang Lake’s Hukou Station detected 22.5 meters, just under full reservoir level. At least 1,500 soldiers arrived in Poyang County on July 11 to combat the flood.
“Severe flooding in the tributaries of the Yangtze is not likely to occur. Datong Station at the lower reaches of Poyang Lake is still one meter below the safety level,” Zhou Jianjun, a water resources researcher at Tsinghua University’s School of Civil Engineering, told NewsChina. But Zhou said his greatest concern is that a sudden storm in the Yangtze’s upper reaches would create a disastrous deluge. If the Three Gorges Dam could not block the flood, he said, there would be grave consequences.
Based on weather data, the CWRC predicted back in April that the entire Yangtze River Valley was likely to see flooding in 2020. In early July, the agency reiterated its prediction.
Cheng Xiaotao, a member of the National Disaster Reduction Committee, told NewsChina that there are two causes of flooding in the Yangtze River region: heavy rains downstream in June and heavyrains upstream in Sichuan Province and Chongqing Municipality in July and August.
“The latter half of July is very important. Floods mainly hit downstream of the Yangtze, so it’s important to stabilize conditions upstream,” he said.
To ease pressure on downstream areas, the Three Gorges Dam had reduced its water outflow from 25,000 to 22,000 cubic meters per second since July 11. According to Chen Guiya, deputy chief engineer of the CWRC, Poyang Lake is relatively far from the Three Gorges Dam, so outflow would not affect lake levels. The dam’s role is to block floodwaters and protect the area around Jinjiang - 360 square kilometers that span the city of Zhicheng in Hubei Province to Yueyang County, Hunan Province.
As of July 12, the Three Gorges Dam reported water levels of around 152 meters, higher than the rainy season flood limit of 145 meters. On June 29, the dam discharged water for the first time this year. July 2 saw the Yangtze River’s first major flood, which brought an inflow of 53,000 cubic meters per second into the dam’s reservoir. A second major flood passed the dam on July 19 as inflow decreased to 46,000 cubic meters per second.
Zhou Jianjun told our reporter the dam’s design allows for inflow below 56,700 cubic meters per second to pass through. “China builds its major hydraulic engineering projects to very high flood control standards that can withhold a 100-year flood or even a 1,000-year flood. However, dams discharge five-year and annual floods,” he said. “Withholding minor and moderate flooding negatively affects rivers downstream.”
Zhou said that local governments in downstream areas had hoped the dam would withhold all floodwaters to reduce their need to conduct regular maintenance of their waterways. Also, withholding minor floods would increase profits for the dam’s hydroelectric plant.
“Withholding minor floods would occupy the storage of the Three Gorges Dam. It’s anybody’s guess whether a major flood in all waterways will come,” he said. “If we had a major one like the 1954 flood, that would challenge the dam’s storage capability.” Among China’s most severe floods of the 20th century, the 1954 Yangtze floods killed 33,000 and affected nearly 20 million people.
Zhou added that holding back minor and moderate floods negatively affect not only the Three Gorges Dam but also downstream waterways. Without regular flooding, local governments have little incentive to maintain waterways. Many turn into farmlands.
Zheng Shouren, chief engineer of the Three Gorges Dam, argued that water outflow of 45,000 cubic meters per second during the rainy seasons would likely lead to waterway shrinkage. The dam should have a water outflow of 55,000 cubic meters per second and routinely discharge water to encourage proper maintenance of downstream waterways.
On July 13, the Jiangxi Provincial Flood Control and Drought Relief Headquarters announced that 2,242 of the 2,545 kilometers of riverside and lakeside embankments saw water levels rise above the warning marks. The agency required that all 185 dikes in Poyang Lake open their gates to store the water.
There are 42 major flood storage areas in the middle and lower reaches of the Yangtze River with a space of 12,000 square kilometers and a storage capacity of 59 billion cubic meters.
Zhou Jianjun told our reporter that these areas are a last defense but are still not up to spec. He said that the Three Gorges Dam falls 28 billion cubic meters short of the required water storage, mainly because of lack of investment.
After a flood lashed Anhui Province in August 2016, Cheng Xiaotao, a member of China’s National Disaster Reduction Committee, investigated the disaster-affected areas and found that local governments and residents lacked flood control awareness as the region had not seen floods in 17 years.
“The waterways were largely occupied and blocked, which affected their water discharge capabilities,” Cheng told NewsChina. “Many storage areas are now farmlands. That was the major cause of the floods that swept Anhui.”
In February 2017, Wei Shanzhong, deputy minister of the Ministry of Water Resources, wrote in an article that the embankments that stretch 34,000 kilometers in the middle reaches and 3,900 kilometers in the lower reaches of the Yangtze River Valley are up to code.
“After decades of construction, local governments built a comprehensive flood control system in the Yangtze River’s middle and lower reaches that includes levees, the Three Gorges Dam and water storage areas,” he said.
Zhong Zhiyu, chief engineer with the CWRC, said during China’s two sessions in 2019 that lack of new planning, poor construction of water storage areas, embankment failures in the middle and lower reaches, and poor management are the main flood control problems in the Yangtze River.
Cheng Xiaotao told our reporter that China urgently needs to revise its Law on Flood Control. “They drafted the law in the 1990s with a traditional rural society in mind,” he said. “It’s outdated, and it’s high time we amend it.”