Background
Lake Redwood was created in 1902 by installing a dam structure to power a grist mill on the west side of the lake. 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 2007, the RCRCA hired HEI when the project was originally initiated. We were then retained in 2018 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.
The Project
The RCRCA hired HEI to complete this project in two phases.
Phase I
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, which does not include land acquisition cost. The dredged materials are transported via pipeline to the CDF. Once sediments settle in the CDF, clean water is returned to the Minnesota River through a private ditch and creek to the northeast.
Phase II
Phase II began in the fall of 2021 with the placement of the disposal pipeline from Lake Redwood to the CDF.
As part of the dredging phase, three islands had vegetation that needed to be removed. This ended up being the biggest challenge for our contractor, J.F. Brennan Company, Inc. of La Crosse, WI, by causing several delays.
Only one area on the lake required changes to the proposed lake bottom grades as a result of changed conditions. An outcropping of rock negated the removal of approximately 5,000 CY of anticipated sediment. When initially encountered, residents adjacent to the lake communicated with the RCRCA that they observed vibrations in their homes. Operations were then discontinued in the area once crews determined the extent of the rock outcropping.
Despite these challenges, the lake was opened to use in the fall of 2022 for approximately $4.5 million.
In total, 682,330 CY were dredged from the lake, which is 25,000 CY more than anticipated. Water quality has improved greatly in the lake. The pre-project water depth averaged approximately 3-feet with virtually no water clarity. Prior to the 2022 fall freeze-up, the water clarity had improved to a depth of 5-6 feet.
Despite the anticipation to find numerous treasure(s) only a few random items were discovered:
- An iron ice/log hook
- Ring with no center stone
- “Old Timer” brand pocket-knife
- Old/large Steel Tractor Wheel
- Two flashlights
- Goggles
- Snowmobile seat cover
- Keys
- Oil lamp wick holder
- Golf Club
- Pristine Schlitz beer can
- Two John Deer Mud Flaps
- Most surprisingly…not a single tire!
Client Benefits
- 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.