The Banqiao Reservoir Dam, located on the River Ru in the Zhumadian Prefecture of the Chinese Henan province, failed in 1975, killing an estimated 171,000 people (although some reports estimate that number to be as high as 230,000) and destroying the homes of 11 million people. It is considered to be the biggest dam failure in history, with more casualties than any other dam failure.
Built between April, 1951 and June, 1952, the Banqiao Reservoir Dam was designed in such a way that would allow it to withstand a large flood. This type of flood, where 300 mm of rain falls per day, is known as a “once-in-1,000-years flood.” The August 1975 flood, however, was what is known as a once-in-2,000-years flood, more massive than the construction of the dam had accounted for, meaning that more than an annual amount of rain fell in only 24 hours. Records indicate that 189.5 mm of water fell every hour, which translates to 1,060 mm per day. That far exceeds the province`s average annual rainfall, which is only around 800 mm.
Chances of the devastating flood happening did not go unnoticed and on August 6, a request was made to open the dam. That request was rejected due to an existing flood in those downstream areas. By August 7, the request was granted by telegrams, which failed to get to the proper authorities. Late on August 7, Unit 34450 of the People`s Liberation Army telegraphed the very first warning for the dam failure, but in a matter of only three hours, the Shimantan Dam broke. Within 30 minutes, the water from that dam crested at the Banqiao Dam.
In the wee hours of August 8, 1975, the 24.5-meter Banqiao Reservoir Dam was breached in the aftermath of the third typhoon that had decimated China that year. Over 700 million cubic meters of floodwater was released over the course of six hours. The Daowencheng Commune located downstream was immediately erased from history and 9,600 people were killed instantly.
Survivors recall that the dam bursting sounded like the sky above had collapsed and that the earth itself was cracking. One after another, the other 61 reservoirs located in the area, including the Shimantan Dam, collapsed. This chain reaction released another six billion cubic meters of floodwater, all to an area measuring 10,000 square kilometers.
In total, 62 dams broke and 11 million people`s lives would never be the same. Anyone who survived the initial flooding was trapped without access to food or clean water and contaminated water caused illness throughout the area. 26,000 deaths were attributed to the floodwaters, while nearly 145,000 people lost their lives because of epidemics and famine. In total, around 5,960,000 structures were destroyed, converting the Chinese landscape into one filled with corpses and disease.
After years of studying the incident, researchers concluded that it was the design of the Banqiao Reservoir Dam and the other reservoirs, along with the principles pertaining to the containment of the river, which should be blamed for the failure and subsequent calamity. While many pointed fingers at the weather forecast all those years ago, researchers are citing that the tragedy was man-made and not entirely a natural disaster.
During the late 1950s, scientists warned that any given reservoir`s flood control was being ignored and that the irrigation functions of those reservoirs were overemphasized during the heat of the construction frenzy. It has been estimated that China continues to have 87,000 reservoirs across the nation that were built during this low standard construction era and most of these have fallen into serious disrepair. On top of sub-par construction standards, the country also lacked any early warning system as well as an evacuation plan that could have saved lives.
In the aftermath of the devastation, the Banqiao Reservoir reconstruction was considered a crucial national project in The Seventh Five-Year Plan of China, which was a series of important economic and social development initiatives. The Huai River Water Resources Commission was in charge of the project with the Changjiang Gezhouba Engineering Bureau heading up the construction contract. The rebuilding project lasted from the end of 1986 to June 5, 1993.
Today, engineering programs throughout the world educate students on the devastating history of dam failures and outline the construction methods that need to be taken in order to prevent such a widespread calamity in the future.