The U.S. Army Corps of Engineers Louisville District gave the go-ahead for the second phase of the Rough River Dam Safety Modification Project in southwestern Kentucky that aims to restore the dam’s long-term structural integrity and safeguard downstream communities in the largely rural area.
The $320 million fixed-price Phase 2 firm contract to Thalle-Bauer LLC., Hillsborough, N.C., includes options that could increase its total value to $655 million, according to the Corps. Groundbreaking on the project, 95 miles southwest of Louisville, will take place this spring and construction would take up to seven years.
Thalle-Bauer will build a new outlet work on the left abutment of the dam, which will include a new control tower and a stilling basin connected by a tunnel. Once the new outlet works are operational, a cutoff wall will be constructed across the crest of the dam, varying in depth from 75 feet to 180 feet. The final part of the project moves Kentucky State Highway 79 upstream of the dam.
Built between 1955 and 1961, the Corps-maintained 1,590-foot-long, 135-foot-high embankment dam creates Rough River Lake, a 5,100-acre recreational lake that is the centerpiece of a state park. After a 2012 report highlighted an unacceptable risk due to building the dam’s base on karst geology, the Corps launched a multi-phase rehabilitation effort.
Karst geology is a type of landscape formed when water dissolves soluble rock, most commonly limestone, but also dolomite or chalk. Over long periods of time, rainwater and slightly acidic groundwater eat away at the rock, creating distinctive landforms both above and below ground such as sinkholes, caves and caverns, disappearing streams, springs, and thin, rocky soils.
Phase 1, completed in May 2017, included road relocation across the dam crest and exploratory drilling and grouting across the centerline of the structure.
According to the Corps’ project page, instrumentation and subsequent visual observations indicated continued deterioration of the foundation, leading to the implementation of interim risk reduction measures in 2023, such as lowering reservoir water levels to relieve pressure on the dam, pending completion of long-term repairs.
Extreme flooding in April 2025 caused water from the dam to flow into the spillway, but the Corps said it was monitoring the event.
“Due to known concerns with the foundation of the dam, the reduction in the frequency of events [such as flooding] that stressing the structure is our goal,” Jackie Henn, director of the Corps’ dam safety program, said at the time.
He said automated instrumentation systems allow the Corps to monitor dam integrity at all times.
