Black Hills Flood

Record flows were reported on Rapid, Battle, Bear Butte, and Boxelder Creeks. On June 9 a stationary front, with moderate southeast surface flow, moved though high pressure aloft. A strong flow of warm, moist air near the surface fed the storms and anchored them against the Hills for 6 to 8 hours. An average of 6 inches of rain fell with up to 15 inches reported. Rainfall intensities of 2 to 6 inches/hour were common. Canyon Lake breached, adding to the wall of water that poured through Rapid City. Flow on Rapid Creek in Rapid City was estimated at 50,000 cfs. After the flood, 750 acres near Rapid Creek were designated as a floodway. $164 million in damages and 238 deaths were reported.

http://www.crh.noaa.gov/unr/?n=history