Canyon Lake Dam Breach
Coordinates: 44 ° 3 '28 " N , 103 ° 17' 12.5" W.
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The breach of Canyon Lake (also known as the "Black Hills flood" ) in Rapid City , South Dakota occurred on June 9, 1972 and caused a tidal wave that devastated Rapid City. Up to 238 people were killed in the flood disaster.
The reservoir
Canyon Lake is a reservoir on Rapid Creek in Rapid City, a city in South Dakota , USA with a population of around 43,000 at the time . Rapid Creek rises in the Black Hills , a foothill of the Rocky Mountains , where the presidential monuments carved into the rock can be found on Mount Rushmore .
The 1933-1938 built dam above Rapid City is six meters (20 feet) high (according to other sources, only three meters); the reservoir holds several million cubic meters of water. According to other information, only 863,000 m³ of water were released.
The catastrophe
On June 9, 1972, there was heavy rainfall in the Black Hills in the early evening. The precipitation of 250 mm was limited to a narrow area. At 9:00 p.m. the rain intensified; now 150 mm fell in two hours. The rainwater runoff caused a flash flood in Rapid Creek for which there was no advance warning. The flood caused the reservoir to overflow, and the dam was also overflowed because the flood relief was blocked by floating debris. The peak inflow into the reservoir was around 1220 m³ / s, the peak outflow from the lake 1420 m³ / s.
Rapid Creek had flooded the whole day. In the evening from 10:30 p.m., radio and television warnings of a dam breach were given. At 10:45 p.m. the dam no longer held and broke. The Rapid Creek water level rose 12 feet (3.6 m) as a result. The tidal wave rushed through the place and devastated everything on its way. The balance was 238 dead, 3057 injured, at times up to 2000 missing, 770 destroyed and probably 1,335 damaged houses, 36 destroyed and 236 damaged shops, seven destroyed bridges, 5000 destroyed cars and $ 160 million in property damage. About half the city was destroyed.
In order to prevent a repetition of such an event, levels and measuring devices were then installed to warn of similar floods in the future. The dam was rebuilt.
literature
- A. Hoffmann: The dam breach near Rapid City, USA , in: Wasser und Boden 9, 1974, p. 261 ff