The U.S. Army Corps of Engineers (USACE) and Union County, South Dakota, are conducting a feasibility study to evaluate flood risk along the lower Big Sioux River in partnership with North Sioux City, South Dakota, Sioux City, Iowa, and the Dakota Dunes Community Improvement District, South Dakota. 

The study will examine whether improvements to the existing federal flood risk management system or other flood risk reduction measures could better protect people, homes, businesses, transportation routes, and other critical infrastructure from flooding. 

The existing federal flood control project was constructed between 1977 and 1981 and has generally performed as intended. However, recent flooding events have highlighted changing conditions and new challenges that warrant further evaluation. 

Several major floods (including those in 2014, 2018, 2019, and 2024) have caused significant flooding throughout the lower Big Sioux River corridor. 

During the June 2024 flood:

• Floodwaters overtopped Interstate 29
• The BNSF railroad bridge collapsed 
• More than 100 homes near McCook Lake were damaged
• Roads and public infrastructure sustained extensive damage
• Agricultural lands experienced millions of dollars in crop losses
• Emergency rescues were required in flooded neighborhoods

As development continues and flood patterns evolve, the study will evaluate opportunities to reduce future flood risk throughout the area.