Big Sioux River History: Rejected Dam Delivered Other Benefits
By Pete Carrels
As industrial agriculture changed the landscape of the Big Sioux River watershed, so too did it change the hydrology of the Big Sioux River. Perennial prairie was replaced by annually planted grains. Topsoil eroded from cultivated farm fields and migrated to the river, settling onto the channel floor and diminishing the river’s carrying capacity. Runoff to the river and its tributaries increased because there was less prairie to absorb rainfall and snow melt. By the 1960s, flooding issues along the river had dramatically escalated.
To the rescue came the U.S. Army Corps of Engineers. Their solution reflected their preferred response to such circumstances: Build big dams. The agency also enjoyed channelizing rivers and had proposed that tactic in 1962 for the lower Big Sioux. Anglers and hunters vigorously opposed the plan, and it was abandoned.
The Corps of Engineers was, in that era, one of the leading river-altering forces on earth. The agency had dammed and channelized rivers across the country, including the Missouri River. Maintaining and expanding commercial navigation and providing flood control were key goals as the Corps sought to fulfill its particular dream for a better America. No opportunity was too challenging for the Corps. Consider their 1957 proposal to transform the James River into a barge-floating navigation canal linking the Missouri River near Yankton, SD, north to Jamestown, ND, and then west to the Missouri River. Officials in Huron, SD were ecstatic at the prospect of becoming a commercial port. The absurdity of this fantasy was obscured by the day’s lack of environmental sensibilities. Fortunately, common sense prevailed, and the shipping lane was not built.
No doubt, the Corps has had reasonable successes. Sioux Falls benefits from the agency’s riverengineering expertise. And in recent years, the Corps has positively responded to evolving public wishes to protect the environment rather than subdue or erase it.
But 60 years ago, the agency targeted the Big Sioux. The genuine causes of worsened flooding—land use practices in the watershed—weren’t addressed by anyone. Instead, the agency issued a plan to gain control of the Big Sioux basin by building six new dams; two would be on the river’s mainstem, near Canton and Flandreau. These would be formidable structures of the rolled-earth variety, like the Oahe Dam. The Flandreau dam would measure 8,300 feet long and 79 feet high. Land needed for the dam and its reservoir would total 27,730 acres. The height of the Canton dam would be 75 feet. That dam would require the acquisition of 13,850 acres.
Altogether, forty thousand acres of prime riparian habitat and floodplain farmland would be drowned behind these two dams. Other large dams were proposed on Skunk Creek and the Rock River. Farmers, not surprisingly, weren’t pleased with this proposal, and many fought dam construction during a political conflict lasting from 1969 to 1973. Local opponents finally prevailed, quieting dam promotions. But not for long.
In 1974, the Corps added a new and tantalizing justification for the Flandreau dam. Not only would the dam provide flood control, but it would also serve as a water source for Sioux Falls. That city supplied its water needs by siphoning the Big Sioux aquifer, and concerns had arisen regarding the aquifer’s long-term reliability. In stepped the Corps with a handy solution. Farmers again rose to protest.
Officials in Sioux Falls realized it was a mistake to ask their rural neighbors to give up land for Sioux Falls’ water needs, and they gazed south to the Missouri River as a potential source. In 1974, Senator George McGovern helped secure funding to study the feasibility of a pipeline from the Missouri River to Sioux Falls. That funding was an early expression of interest in what would later become the Lewis and Clark Regional Water System. This pipeline network now provides water to half of Sioux Falls. Eventually, more than 300,000 people living in rural areas and communities in three states will benefit.