The Banqiao and Shimantan Dam Failures: Factors Affecting the Warning and Evacuation Success

Banqiao Dam, Shimantan Dam, and 60 other dams failed in Henan Province, China in August 1975 during rainfall representing the highest known intensity for the Chinese mainland. In a period of less than 6 hours, 575,000 acre-feet of water was released from Banqiao Dam and 135,000 acre-feet from Shimantan Dam. The peak dam failure outflow from Banqiao Dam was 2,760,000 ft3/s and the peak from Shimantan was 1,060,000 ft3/s. More than 10,000,000 people were impacted by the floods, 5,240,000 houses collapsed and estimates of loss of life ranged from 26,000 to 230,000. No formal emergency action plan or dam failure inundation maps existed for the dams. A government order was issued on the day prior to the failure to evacuate only those people living in the immediate vicinity of Banqiao Dam. No evacuations were carried out in areas further downstream. At Banqiao Dam, red signal flares and guns were fired a few hours before failure in a vain attempt to warn some of the population. Banqiao Dam and Shimantan Dam failed between midnight and 2 a.m. There was blackness all around. Survivors caught floating debris and attempted to remain on it until a safer place could be reached or they could be rescued. Water from the collapsed dams, combined with localized flood waters and the collapse of dikes in downstream areas, formed a huge lake, approximately 20,000 square miles in area. Ensuing health epidemics contributed significantly to the loss of life. The paper contains a discussion of the dam failure scenario(s) that took place, the efforts taken to prevent failure, the attempts to warn people at risk, and the flood characteristics in downstream areas. The factors that affected the warning, evacuation and the loss of life are discussed. Some of the factors were positive while many were negative. The paper contains a discussion of the dam failure scenario(s) that took place, the efforts taken to prevent failure, the attempts to warn people at risk, and the flood characteristics in downstream areas. The factors that affected the warning, evacuation and the loss of life are discussed. 15 pp, 14 references.