All before 1976
http://www.epicdisasters.com/index.php/site/comments/the_worlds_worst_floods_by_death_toll/
Huang He (Yellow) River, China
1931
Death Toll: 1,000,000 to 3,700,000
The Huang He River is prone to flooding because of the broad expanse of plain that lies around it. One of the major reasons for the flooding is the high silt content that gives the river its yellow tint (and thus its name). The silt—which constitutes as much as 60% of its volume—builds up until the river actually is higher than the surrounding land. The tendency to flood is exacerbated by ice dams which block the river in Mongolia; the dams back up the water, and then release devastating walls of water when they break.
The history of flooding has prompted the Communist Chinese government to embark on a program of building dams for flood control. The dams, however, have not proven entirely effective and have been the target of criticism from environmentalists.
2.
Huang He (Yellow) River, China
1887
Death Toll: 900,000 to 2,000,000
3.
Huang He (Yellow) River, China
1938
Death Toll: 500,000 – 900,000
The 1938 flood of the Huang He was caused by Nationalist Chinese troops under Chiang Kai-Shek when they broke the levees in an attempt to turn back advancing Japanese troops. The strategy was partly successful. By 1940, the Japanese were essentially in a stalemate with Chinese forces.
4.
Huang He (Yellow) River, China
1642
Death Toll: 300,000
Chinese rebels destroy the dikes along the city of Kaifeng, flooding the surrounding countryside.
5.
Ru River, Banqiao Dam, China
1975
Death Toll: 230,000
This flood was caused by the collapse of the Banquia Dam, along with several others, following a heavy rain caused by a typhoon. It is the worst dam related collapse in history.
