In August of 1975, typhoon Nina pelted the region with the heaviest rains ever recorded in the area. More than a year’s worth of water fell in 24 hours. The previous record was 800 mm of rain, and the stalled typhoon Nina dropped a new record of 1060 mm in one day.

The rainfall caused massive downstream flooding and, because of the flooded downstream areas, one request to open the dam was rejected on August 6. On August 7, the request to open the dam was accepted but this information did not reach the dam, as the storm had brought down the telegraph wires.  The under-designed sluice gates were unable to handle the water volume. The water crested on August 8 at 0.3 m. higher than the protection wall on the dam, which failed.  Shimantan Dam and 62 other smaller dams in the Huai river basin also failed.     The Banqiao Dam failure caused a huge wave, 10 kilometers wide and 3-7 meters high to rush downstream at 50 kilometers per hour,  inundating the lower area. One estimate is that 26,000 people died from flooding and another 145,000 died afterward as a result of epidemics and famine. [1]. Some 5,960,000 buildings collapsed and 11 million residents were affected. Unofficial estimates of the number of people killed by the disaster have run as high as 230,000 people. The  Chinese government tried their best to keep the accident a secret. By 1993 the dam was rebuilt, several meters taller. Since the Banquiao disaster the Chinese government became very focused on surveillance, repair, and consolidation of reservoir dams.

============================================  Seven county seats, Suiping, Xiping (西平), Ru'nan (汝南), Pingyu (平舆), Xincai (新蔡), Luohe (漯河), and Linquan (临泉) were inundated, as were thousands of square kilometers of countryside and countless communities. Evacuation orders had not been fully delivered due to weather conditions and poor communications. Telegraphs failed, telephones were rare, and some messengers were caught by the flood. While only 827 out of 6,000 people died in the evacuated community of Shahedian just below Banqiao Dam, half of a total of 36,000 people died in the unevacuated Wencheng commune of Suipin County next to Shahedian, and the Daowencheng Commune was wiped from the map, killing all 9,600 citizens. It has been reported that 90,000 - 230,000 people were killed as a result of the dam breaking. [2]

The dam was designed to survive a once-in-1000-years flood (300 mm of rainfall per day) but a once-in-2000-years flood occurred in August 1975, following the collision of Typhoon Nina and a cold front. The typhoon was blocked for two days before its direction ultimately changed from northeastward to westward. As a result of this near stationary thunderstorm system, more than a year's worth of rain fell within 24 hours (1060 mm), exceeding the average annual precipitation of about 800 mm. The Banqiao Reservoir was designed with a capacity of only 492 million cubic meters but it had to accommodate more than 697 million cubic meters of floods, with half the recommended gates.

The cascade of dams that had been built on the Huai River and its tributaries to reduce flood risks ultimately made the flooding deadlier and the rescue effort more difficult. "Henan Flood Disaster in August 1975", the government-sponsored book, records the deadly flood with stark figures. “Two large dams, Banqiao and Shimantan, plus two medium-sized and 58 small ones were broken down by the flood. Nearly 10 billion cubic meters of water created 10-meter-high waves and ravaged the whole Zhumadian area in a matter of hours. More than four million people in 30 counties were trapped in the water, with five million houses and one million animals washed away" [4]