 The reservoir's flood storage capacity is 22 cubic kilometres (18,000,000 acre · ft). This capacity will reduce the frequency of major downstream flooding from once every ten years to once every 100 years. The dam is expected to minimize the effect of even a "super" flood. In 1954 the river flooded 193,000 km2 (74,518 sq mi), killing 33,169 people and forcing 18,884,000 people to move. The flood covered Wuhan, a city of eight million people, for over three months, and the Jingguang Railway was out of service for more than 100 days. The 1954 flood carried 50 cubic kilometres (12 cu mi) of water. The dam could only divert the water above Chenglingji, leaving 30 to 40 km3 (7.2 to 9.6 cu mi) to be diverted. Also the dam cannot protect against some of the large tributaries downstream, including the Xiang, Zishui, Yuanshui, Lishui, Hanshui, and the Gan.
