Seminary Fen Ravine Restoration and Stabilization

Seminary Fen is a 600-acre calcareous fen complex in Carver County. Calcareous fens are a rare wetland type characterized by discharge of relatively cold, calcium-rich groundwater that sustains unique plant communities. Only 500 calcareous fens are currently identified in the world, several of which exist in the Lower Minnesota River Watershed Districts (LMRWD). Seminary Fen is one of the highest quality calcareous fens in southern Minnesota. It has been characterized as one of the most significant natural areas in the Twin Cities Metropolitan Area and is part of the Minnesota Department of Natural Resources Scientific and Natural Areas program. The fen's unique hydrology, soils, plants, and habitats are highly sensitive to water quality and sedimentation stress. Erosion from concentrated flow to Seminary Fen created a ravine and discharged sediment to the northern portion of the fen. Without stabilization, the ravine would continue to transport sediment to Seminary Fen.

In 2009, the City of Chaska restored a wetland outlet for rate control to the ravine. The LMRWD applied for and received a Clean Water Fund Grant in 2012. Ravine assessment was completed in 2013 and 2014. It is estimated that 5.3 acres of the Seminary Fen wetland at the end of the ravine had been covered with as much as four feet of sediment, requiring stabilization to reduce the transport of sediment to the fen’s wetland complex. The project stabilized approximately 2,150 linear feet of the ravine. Stabilization techniques included reshaping eroding slopes, reducing erosive flow velocity with riffle pools, raising the channel bed closer to historic elevations, and stabilizing the channel bottom with a cobble channel-pool system.

As Seminary Fen supports dozens of rare animal and plant species that are sensitive to sedimentation stress, reducing the sediment load to the fen is critical to maintain the unique fen wildlife. Throughout the stabilization invasive species were removed and replaced with native vegetation, further maintaining fen wildlife. This project represented a 63% reduction in sediment load to Seminary Fen.

Seminary Fen Ravine Restoration and Stabilization Final Report - July 2016