Location: Near Barnesville, MN
Client: Buffalo-Red River Watershed District
The Manston Slough, located in Wilkin County, is near the bottom of the beach ridge on very flat topography. Runoff from the east drops quickly through the landscape upstream of the site and then enters the Manston Slough area, spilling into the historic basin. Minnesota drained the area in the late 1800s with the construction of Ditch 15. Because of this, more than 75% of the historic wetland in the area had been completely drained and had limited value to waterfowl and other water-related species.
Over time, the US Fish & Wildlife Service (USFWS) and the Minnesota DNR (MnDNR) started aquiring property in the drained basin in hopes that someday the area could be restored.
Approximately 10 years ago, a group of agencies led by the Buffalo-Red River Watershed District (BRRWD) came together to discuss a possible comprehensive project that could achieve multiple goals. After review of the site by the BRRWD and HEI as their engineer, the BRRWD worked towards an appropriate, feasible and lasting plan to restore the historic basin with the help from their Mediation Project Team, which included the MnDNR, USFWS, USDA Natural Resources Conservation Service (NRCS), the Minnesota Board of Water and Soil Resources (BWSR), the Soil and Water Conservation District (SWCD), the Wilkin County Commissioners, Ducks Unlimited (DU), and local landowners.
The project is approximately eight square miles and drains a 26.5 square mile area. During meetings with personnel from the MnDNR and USFWS, who own large portions of the project area, it became evident that the site also had great potential for wildlife habitat enhancement.
With help from the NRCS and DU, the BRRWD worked with over 30 landowners to gain easements for the project. In 2003, the Governor's Clean Water Cabinet selected this site as one of their Pilot Project Initiatives.
The dam embankment has a maximum height of approximately eight feet and primarily consisted of modifications to existing roads. The principal spillway consists of a reinforced concrete culvert through the dam embankment and a reinforced concrete box drop inlet. Stoplogs allow management of the wetland pool and provide drawdown capability to allow access to the site for project construction and operation and maintenance.
The proposed 300-foot vegetated emergency spillway is designed to convey discharges in excess of the principal spillway capacity at nonerosive velocities. HEI used HEC-HMS and HEC-RAS models to simulate runoff events and aid in the design of spillway features. Wilkin County Ditch 13-Lateral serves as the outlet channel. Construction began in 2008 after securing significant funding and permits.
The project included:
- A low hazard classification dam with 4,340 acre-feet of storage below the emergency spillway crest
- 1,147 acres of wetland restoration
- A water level control structure to manage wetland elevations
- Upland watershed treatment to control erosion
This project earned recognition from several organizations.
Featured in Newsletter
This project was the cover story of HEI's 2015 fall newsletter, which you can read online.