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Black Hills Disaster of 1972 One of the most detrimental floods in the history of South Dakota took place on June 9th-10th 1972 (Nair, Hjelmfelt, and Pielke 1753). This flood was the 1972 Black Hills Flood, taking place in the Black Hills of Rapid City, South Dakota. The Black Hills Flood also known as the Rapid City Flood, not only hit Rapid city although the main object, it caused flooding in “Battle Spring Creek, Rapid, and Boxelder Creeks” (Carter, Williamson, and Teller). *The occurrence of such a devastating flood was caused by the excessive and rare amount of rainfall the area received. A few days before the happening of the Rapid City Flood “earlier rains had left the soil saturated, increasing the amount of runoff of the flood to come” (Cater, Williamson, and Teller).*On the afternoon of the 9th substantial rains began to fall on the area, caused by “an almost stationary group of thunderstorms” (Carter, Williamson, and Teller). The unusual amounts of rain were caused by: A strong low- level easterly flow which forced the moist unstable air upslope on the hills. This sustained orographic effect helped the air to rise, cool, and release its moisture in repeating thunderstorms. Another contributing factor was the unusually light winds at a higher atmospheric levels which did not disperse the moist air nor move the thunderstorms along to prevent an extreme concentration of rainfall. (Carter, Williamson, and Teller)

• According to Thompson the air pattern causing this storm was noticed in big measure over the Great Plains, with a minor scale to the east of the Rockies. There were only what appeared to be light winds, so nothing indicated that there was a huge storm underway. Thompson further indicates that a cold high pressure region was pushed from Canada into the Great Lakes region leading into the western part of South Dakota. A “metro-scale cloud mass” from Colorado also moved towards Rapid City (164). One of the cloud masses amplified the “mid-level moisture over Rapid City,” while the other mass caused the pressure to stay, as the high pressure pushed downward, thus creating the right conditions to produce rainfall (Thompson 164-165). The rainfall from the upper “cloud mass” above the Black Hills formed into new smaller masses downwind which reprocessed the rain allowing for the constant rainfall (Nair, Hjelmfelt, Pielke 1756). The storm was categorized by Nair, Hjelmfelt, and Pielke as “convective cells of high precipitation efficiency a characteristic of tropical precipitation systems (1753). The immense precipitation was based over the “Rapid, Boxelder, Spring, and Battle Creeks,” creating run-off, along these creeks which lead to flooding throughout the surrounding areas (Nair, Hjelmfelt, and Pielke 1753).

The intense rain began on the afternoon of June 9th and continued until after midnight on June 10th. The immense amount of rain the Black Hills received during the thunderstorms ranged from 4 to 15 inches (Carter, Williamson, and Teller). Causing Rapid City Creek and surrounding creeks to overflow, along with massive amounts of runoff resulting in flood waters. The run-off carried rubble to the Canyon Lake Dam creating a barrier in front of its spillway (Carter, Williamson, and Teller). This resulted in the “increase in depth of water behind the dam of 11 to 12 feet,” which caused the release of more water adding to the already moving floodwaters (Thompson 167). The flash flood hit Rapid City the hardest around midnight on June 9th; the flood waters also hit the small town Keystone nearby (Carter, Williamson, and Teller). ?Being as this was one of the worst floods in the history of South Dakota it caused a tremendous amount of damage. The flood waters displaced large rocks, trees, trailers, vehicles, and carried homes away (Thompson166). In Rapid City the flood resulted in the deaths of “238 including 5 missing,” 14 of the deaths were trained professionals (Rapid City). *The flood resulted in over 3,000 people being injured. A total of 1,335 homes were ruined, and 2,820 homes were damaged. More than 200 businesses were ruined, and around “5,000” cars were demolished. The damages in Rapid City totaled 66 million dollars in 1972 dollar value (Rapid City). As for Keystone “eight people were killed and much of the town was washed away,” (Carter, Williamson, and Teller). The damage in Keystone totaled around $1.5 million (Rapid City). The total cost of the 1972 Black Hills flood totaled $165 million, including infrastructure, and utilities. The total amount of rain the Black Hills received was “800,000 acre feet” equal to “1 billion metric tons of water,” (Rapid City). With all of these conditions and circumstances the 1972 Black Hills flood proves to be one of the worst floods in the history of South Dakota.

Works Cited Carter, Janet M., Joyce E. Williamson, and Ralph W. Teller. “The 1972 Black Hills-Rapid City Flood Revisited.” USGS Science for a Changing World. U.S. Geological Survey, Apr.2002. Web 11 Oct. 2012. Nair, U.S., Hjelmfelt R. Mark, and Pielke A. Robert, Sr. “Numerical Simulation of the 9-10 June 1972 Black Hills Storm Using CSU RAMS.” Monthly Weather Review 125. (1997): 1753-1766. Print “Rapid City Flood of 1972.” RCPL-Rapid City Flood of 1972. Rapid City Library, n.d. Web. 12 Oct. 2012 Thompson, Herbert J. “The Black Hills Flood” Weatherwise 08 Jul. 2010:162-173. Print.