Corps seeks comments on Orwell Dam maintenance

U.S. Army Corps of Engineers, St. Paul District
Published July 2, 2024
Expiration date: 8/2/2024

1. Project Proponent. St. Paul District, Corps of Engineers, 332 Minnesota Street, Suite E1500, St. Paul, Minnesota 55101.

2. Project Authority. The Orwell Dam is part of a comprehensive flood control plan for the Red River of the North drainage basin authorized by the Flood Control Act of 1948 (Public Law 81-516) and the Flood Control Act of 1950 (PL 85-624). Construction of the dam began in May 1951, and operations commenced in the spring of 1953. Additional recreation facilities were contracted for in August 1971. Recreation is considered an incidental benefit under Public Law 78-634.

3. Project Location. The proposed actions would be located in Otter Tail County, Minnesota.

4. Summary of the Proposed Project.
Dam and Stilling Basin Maintenance: The tainter gate chain currently binds due to excessive friction and would be replaced. This chain is critical to the dam as there is only one tainter gate for the project. Under normal conditions the tainter gate should raise to approximately 28 feet, presently the gate is stopping at 12 feet. The installation would consist of blocking underneath the tainter gate to relieve pressure on the chain. The old chain would then be disassembled and removed and the new chain assembled and installed. Additional maintenance would include pressure washing the tainter gate, rehabilitating the stilling basin floor drains (replacing parts, cleaning screens) and completing small concrete repairs. While the stilling basin is dewatered, an inspection would occur to identify any future work needed.

Relief Well Rehabilitation: Relief wells have been successful in lowering the deeply seated artesian pressures in the area but require repeated maintenance due to bio-fouling and mineralization. The well rehabbing will be some combination of brushing, surging, acid treatments, and possible chlorination.

Lake Drawdown and Stilling Basin Dewatering: Lake Orwell would be drawn down from its conservation pool elevation of 1064 to 1050 feet which is the winter drawdown elevation. The drawdown would begin in early September and take approximately four to five weeks to reach elevation 1050 feet. The drawdown would be at a rate of 0.5 feet per day to avoid sloughing of the banks. The drawdown is needed to accommodate for any inflow or rain that may occur during the proposed construction timeframe. The main concern for dewatering the stilling basin is uplift conditions in the dewatered state, given the high artesian pressures. Lowering thelake to elevation 1050 minimizes the pool’s effect on artesian pressures acting on the stilling basin and the downstream channel. 

Once the lake has been drawn down to elevation 1050 feet, the stilling basin would be dewatered by closing the gates. The end sill would be extended with plywood bulkheads, sealed with poly sheeting, and secured with sandbags to keep the channel water from backing up into the dewatered stilling basin. The stilling basin would be dewatered via large submersible pumps; seepage water flowing into the dewatered structure would be pumped out with smaller pumps.

The Corps has a low-flow agreement with the Minnesota Department of Natural Resources (MNDNR) for a minimum discharge of 80 cubic feet per second (cfs) to the Otter Tail River. While the stilling basin is dewatered, 80 cfs would be maintained by two large pumps placed in the lake to pump water through a pair of bypass pipes to the downstream channel. One day prior to dewatering the stilling basin, fish within the stilling basin would be rescued and returned to the Otter Tail River downstream of the dam. Fish would be netted and placed in a concrete bucket, lifted via a crane, and released into the downstream channel.

5. Construction Schedule. The Proposed Project is expected to occur in early fall of 2024.

6. Coordination.
General. The proposed action has been coordinated with the Minnesota Department of Natural Resources.
Federal. A Draft Environmental Assessment and Finding of No Significant Impact was prepared and coordinated in accordance with the National Environmental Policy Act.

7. Summary of Environmental Impacts. The Proposed Project would have short-term minor effects to air quality, water quality, aquatic habitat and fish and wildlife species. There would be no effect to federally listed species. The Proposed Project would have no adverse effect to architectural resources or historic properties.

8. Report. A Draft Environmental Assessment that describes the project and the environmental impacts in detail is available to the public and can be viewed at https://www.mvp.usace.army.mil/Home/Public-Notices/. The report includes project figures, a Draft Finding of No Significant Impact, and letters of coordination from regulatory agencies.

9. Review and Comment. If you have any comments on the environmental assessment they should be provided before the expiration date of this notice. Persons submitting comments are advised that all comments received will be available for public review, to include the possibility of posting on a public website. Questions on the project or comments on the draft Environmental Assessment can be directed to LeeAnn Glomski at LeeAnn.M.Glomski@usace.army.mil. Please
address all formal written correspondence on this project to District Engineer, St. Paul District, Corps of Engineers, ATTN: Regional Planning and Environment Division North, 332 Minnesota Street, Suite E1500, St. Paul, Minnesota 55101.