August 8, 1975

1975 Banqiao Dam failure

Failure of Banqiao Dam during the Henan “75·8” flood

At one gauge, 1,005 millimetres — nearly 40 inches — fell in a single day. Sixty-two dams failed by overtopping across the region.

About 1:30 a.m., 8 August 1975

In 1975, floodwater overtopped and eroded the earth-fill Banqiao Dam on the Ru River in Henan in the early hours of 8 August. The U.S. Bureau of Reclamation's reconstruction places complete failure at about 1:30 a.m.; other sources put the breach nearer 1:00.

Workers had stood waist-deep on the crest, passing material along a human chain, as the embankment disintegrated. Reported peak breach flow reached 78,100 cubic metres per second.

Not one dam

Banqiao was part of a regional cascade during the 4–8 August storm: two large, two medium and 58 small dams failed by overtopping, 62 in all. Shimantan was the other major failure, though sources disagree whether it went shortly before or after Banqiao.

The rainfall behind it was extraordinary. Linzhuang gauged 1,605 millimetres over 5–7 August, including 1,005 millimetres on 7 August alone. The ASCE study reports 12,000 square kilometres inundated.

A toll that depends on what you count

Failed communications prevented adequate warning and evacuation before the flood wave crossed downstream farms, villages and towns. Transport and communications collapsed, leaving survivors stranded amid contaminated standing water.

The later official direct-flood figure is about 26,000 deaths. Estimates near 230,000 include deaths attributed to the subsequent famine, epidemics and the wider regional cascade.

Sources

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How this was checked

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What the sources leave uncertain

The event date is firm, but sources place the beginning or completion of the breach between roughly 1:00 and 1:30 a.m.
Death estimates are exceptionally disputed. Approximately 26,000 is the later official direct-flood figure; figures near 230,000 include deaths attributed to famine, disease and the wider regional cascade.
Published water-volume estimates range from roughly 600 million to 701 million cubic metres, depending on whether the figure describes stored water, calculated flood volume or total discharge.
Sources disagree about whether Shimantan failed shortly before or shortly after Banqiao. The secure conclusion is that both failed during the same overnight cascade.