The Floods Before 1972
The night of June 9, 1972 is the date most people in the region carry in their memory, and rightly so. More than two hundred people died when a wall of water came down Rapid Creek and through the heart of the city. But the creek had threatened the town many times before that night, and the record of those earlier floods reads now like a series of warnings that were noticed, discussed, and then set aside.
Rapid City was laid out in 1876 along the banks of a creek that drains a large stretch of the central Black Hills. That was the whole point of the location. The water meant gardens, livestock, mills, and a reliable supply for a supply town. What the founders could not see, in the first dry season, was how the same creek behaved when a heavy thunderstorm stalled over the higher country to the west. The Hills gather rain quickly and shed it fast. A storm that drops several inches on the steep upper drainages can send that water downstream in a matter of hours, and the narrow valley through Rapid City offered little room for it to spread.
A creek that rose again and again
High water came early and often. Through the late nineteenth century and into the twentieth, residents grew used to spring runoff overtopping the low ground, washing out footbridges, and flooding cellars and the businesses closest to the channel. Most of these events were nuisances rather than catastrophes, the kind of thing an old-timer would mention to a newcomer who had bought a lot too near the bank.
There were sharper episodes. The 1907 flood was remembered for years as a serious one, with water spreading well beyond the normal channel and damaging property along the creek. Other years brought their own scares, particularly when rapid snowmelt combined with rain. Each time, the town cleaned up, replaced what was lost, and rebuilt in more or less the same places. The flat, fertile, well-watered ground along the creek was simply too convenient to abandon, and so houses, shops, mobile home courts, and parks kept filling the floodplain.
The construction of dams changed the calculation, or seemed to. Canyon Lake, formed by a dam on the western edge of town, became a popular recreation spot and gave many residents a sense that the creek had been tamed. Upstream, the larger Pactola Dam was completed in the 1950s as a federal project, holding back a substantial reservoir and offering real flood control for the water that passed through it. People reasonably assumed the worst was now behind them. The trouble was that the dangerous storms in the Black Hills tend to fall on the lower drainages, below the big upstream reservoir, where the water has no barrier between the storm and the town.
Warnings on the record
Engineers and planners understood the risk in general terms. Studies of the creek had identified the floodplain and noted that building in it was hazardous. There were maps showing where water would go in a large flood. There were recommendations, made more than once over the decades, that the lowest ground be kept clear of homes and that development be pushed back from the channel. These ideas surfaced periodically and then lost out to the ordinary pressures of a growing town, where land along the water was valuable and the memory of the last flood faded with each dry year.
What none of the earlier high water had done was test the valley with the kind of rainfall that fell in June 1972, when a stationary storm system dropped an extraordinary amount of rain on the canyons above the city in a single evening. The earthen dam at Canyon Lake clogged with debris and failed, adding its stored water to a creek already far over its banks. The result was the deadliest flood in South Dakota history.
In the aftermath, the city finally did what the studies had long urged. The floodplain was cleared of homes and converted to a greenway of parks, trails, and golf courses, ground that could take the water without costing lives. That decision, painful and expensive, grew directly out of a century of smaller floods that had said the same thing, more quietly, all along. The creek that built Rapid City and the disaster of 1972 were never really separate stories. They were the same lesson, learned the hard way.