Location: Redwood Falls, MN
Client: Redwood Cottonwood Rivers Control Area
Lake Redwood was created in the early 1900s by installing a dam structure to provide recreational opportunities to the community. Redwood County is one of a handful of counties in Minnesota that have no natural lakes. Initially, the lake’s recreational benefits made it a staple for the City of Redwood Falls and the surrounding community. Additionally, the City added a hydroelectric plant to supplement the electrical power supply for residents.
However, by the 1980s, this 65-acre man-made lake was almost entirely filled with accumulated sediment. The once vibrant lake could no longer support recreational activities (water skiing, fishing, and swimming). To resolve this issue, the Redwood Cottonwood Rivers Control Area (RCRCA) was formed in 1983 to restore the functions and services of the lake and improve water quality within the surrounding area to mitigate sediment transport. The project was first initiated in 2007. However, the project was not constructed due to insufficient funding.
In 2018, the RCRCA hired HEI to renew the project permits and construction documents to hydraulically dredge approximately 650,000 cubic yards (CY) of accumulated sediment from the lake to increase the average depth from just 2 feet to 10 feet, with a maximum of 20 feet. This project will also improve the lake’s water quality by lowering its turbidity, resulting in a higher quality fishery and aquatic plant communities. Also, the deeper/cleaner lake will increase the hydroelectric plant’s productivity.
This project is being constructed in two phases.
For Phase I, HEI designed and supported the construction of a confined disposal facility (CDF) located approximately 3 miles northwest of Lake Redwood. The CDF was constructed in 2020 for $930,000. The dredged materials will be transported via pipeline to the CDF. After sediments have settled in the CDF, clean water will be returned to the Minnesota River through a private ditch and creek to the northeast of the CDF.
Phase II consists of the lake dredging activities. This work includes placing the disposal pipeline from Lake Redwood to the CDF, placing the booster pumps along the disposal pipeline route, and hydraulically dredging the lake. Phase II will be completed over the 2021 and 2022 construction seasons for approximately $4.5 million.
- Restoration of an important recreational waterbody for the City of Redwood Falls and its surrounding communities.
- Increased average lake depth of 10 feet with a maximum of 20 feet.
- Improved water quality, fishery, and aquatic habitat.
- Improved productivity for hydropower from the dam, giving city residents more renewable energy.