The 1972 Black Hills-Rapid City Flood

The 1972 Black Hills-Rapid City Flood Revisited

Can the 1972 Flood Happen Again?

Today’s Flood Protection and Warning

Rapid Creek Hydrograph - June 9, 1972 through June 10, 1972

The 1972 Black Hills-Rapid City Flood Revisited

On June 9-10, 1972, extremely heavy rains over the eastern Black Hills of South Dakota produced record floods on Rapid Creek and other streams in the area. Nearly 15 inches of rain fell in about 6 hours near Nemo, and more than 10 inches of rain fell over an area of 60 square miles. According to the Red Cross, the resulting floods left 238 people dead and 3,057 people injured. In addition to the human tragedy, total damage was estimated in excess of $160 million (about $664 million in 2002 dollars), which included 1,335 homes and 5,000 automobiles that were destroyed.  Runoff from this storm produced record floods (highest peak flows recorded) along Battle, Spring, Rapid, and Boxelder Creeks. Smaller floods also occurred along Elk Creek and Bear Butte Creek.

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Can the 1972 Flood Happen Again?

The answer is yes. The 1972 flood has an estimated recurrence interval of 500 years (Burr and Korkow, 1996), which means that a flood of this magnitude will occur on average once every 500 years. Every year there is a 0.2 percent chance (1 in 500) of experiencing a similar flood. Because of the short period of record for Rapid Creek gaging stations, the recurrence interval of 500 years may be revised substantially as additional data are collected. "Floods are natural and normal phenomena. They are catastrophic simply because man occupies the flood plain, the highway channel of a river (Bue, 1967)."

Today’s Flood Protection and Warning

In the aftermath of the 1972 flood, interim and long-range programs were initiated and millions of federal dollars were spent in Rapid City and the surrounding stricken communities (Rahn, 1984). Rapid City approved a flood-plain management program, known as the "greenway" concept, whereby most of the flood plain was converted into large parks. However, Rapid City and the surrounding communities are susceptible to extreme flooding because of their location in and around the Black Hills. Most floods in the Black Hills area are caused by intense rainfall over very steep watersheds, which allows little time for warning residents of flood threats.

In 1997, a flood-warning system was implemented by the USGS in cooperation with the Rapid City-Pennington County Emergency Management and the National Weather Service (NWS). Combination precipitation/streamflow-gaging stations monitor rainfall and subsequent rises in stream stage on a continuous basis during the flood season (April-October). This real-time information is relayed via a satellite network to the NWS, where forecasters can send warning to the public when streams rise to threatening levels. Rapid City-Pennington County Emergency Management can then coordinate emergency response, public safety services, and local governmental agencies as needed. Currently (2002), the USGS collects data at 20 flood-warning sites in the Black Hills area, which are located along Battle, Spring, Rapid, Victoria, Boxelder, Spearfish, and Bear Butte Creeks and their tributaries.

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The USGS currently (2002) operates a network of about 120 continuous-record streamflow-gaging stations and 35 high-flow partial-record gages in South Dakota. Miscellaneous annual streamflow measurements also are made at several additional sites throughout the State. When flooding occurs, the USGS mobilizes personnel to collect streamflow data in affected areas. Streamflow data improves flood forecasting, provides additional data for USGS flood-frequency analysis that is used by the South Dakota Department of Transportation for bridge design, and provides information for use by emergency management agencies before, during, and after flooding.

Rapid Creek Hydrograph - June 9, 1972 through June 10, 1972

Although Pactola Reservoir was effective in storing runoff that originated upstream of Pactola Dam, the heaviest rainfall occurred downstream of the dam. Most of the flow that passed through Rapid City via Rapid Creek originated in the 51 square mile drainage between Pactola Dam and Canyon Lake. Flood waters that reached Rapid City above Canyon Lake Dam between 9:30 and 10:00 p.m. on June 9 carried large amounts of debris that clogged the spillway of Canyon Lake Dam. The dam at Canyon Lake failed at about 10:45 p.m. However, the effect of this dam failure on the subsequent flood wave into urban Rapid City (figure 1) has been difficult to assess because the amount of water coming down Rapid Creek and several tributaries (accounting for 86 percent of the peak flow) far over-shadowed the amount of water in the small lake (Swartz and others, 1975). The peak discharge of 50,000 cubic feet per second (ft³/s) was carried through Rapid City via Rapid Creek at about midnight on June 9, while many people were asleep and unaware of the impending flood (figure 1, Rapid Creek at Rapid City).

The floods struck quickly and forcefully, but did not last long nor did they make much impact further downstream in the basins. Water in Rapid Creek was back within the banks of the stream by 5:00 a.m. on June 10. As the peak flows moved into less-steep terrain, the flows spread out over a wide area and much of the water was stored in the flood plains (figure 1, Rapid Creek near Farmingdale).

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References

Bue, C.D., 1967, Flood information for flood-plain planning: U.S. Geological Survey Circular 539, 10 p.

Burr, M.J., and Korkow, K.L., 1996, Peak-flow frequency estimates through 1994 for gaged streams in South Dakota: U.S. Geological Survey Open-File Report 96-202, 407 p.

Driscoll, D.G., Hamade, G.R., and Kenner, S.J., 2000, Summary of precipitation data for the Black Hills area of South Dakota, water years 1931-98: U.S. Geological Survey Open-File Report 00-329, 151 p.

National Oceanic and Atmospheric Administration, 1972, Black Hills Flood of June 9, 1972: Rockville, Maryland, U.S. Department of Commerce, Natural Disaster Survey Report 72-1, 20 p.

Rahn, P.H., 1984, Flood-plain management program in Rapid City, South Dakota: Geological Society of America Bulletin, v. 95, p. 838-843.

Schwarz, F.K., Hughes, L.A., Hansen, E.M., Petersen, M.S., and Kelly, D.B., 1975, The Black Hills-Rapid City Flood of June 9-10, 1972—A description of the storm and flood: U.S. Geological Survey Professional Paper 877, 47 p.

Teller, R.W., Huse, T.L., and Owens, Park, 2000, Development and operation of a cooperative flood-warning system, in Strobel, M.L., and others, eds., Hydrology of the Black Hills—Proceedings of the 1999 Conference on the Hydrology of the Black Hills: Rapid City, South Dakota School of Mines and Technology Bulletin no. 20, p. 59-62.

U.S. Army Corps of Engineers, 1973, Flood Plain Information—Rapid Creek, Rapid City, South Dakota: Omaha, Nebraska, Department of the Army, 48 p., 16 pl.

Schwarz, F.K., Hughes, L.A., Hansen, E.M., Petersen, M.S., and Kelly, D.B., 1975, The Black Hills-Rapid City Flood of June 9-10, 1972—A description of the storm and flood: U.S. Geological Survey Professional Paper 877, 47 p