Grey Cloud Restoration
Project Overview
The Grey Cloud Island Slough
The Grey Cloud Island Slough is an offshoot of the Mississippi River, and separates Grey Cloud Island Township from the east bank of the Mississippi River. After several decades, it became clear that the bridge and culvert installed in the 1930s was contributing to water quality and ecological issues. To restore the ecological and practical function of the Grey Cloud Island Slough along the Mississippi River, the Grey Cloud Restoration project was constructed.
History
In the early 1900s, a wooden bridge was built across the Grey Cloud Channel. Later replaced with a culvert, this bridge was one of the few access points for residents of Grey Cloud Island to enter or leave. By the 1930s, the U.S. Army Corps of Engineers constructed Lock and Dam Number near downstream Hastings, MN. In 1965, intense flooding buried the culverts, and resulted in an emergency road raise. While the bridge installed in the 1960s still stood, its construction has resulted in a significant lack of flow, harming water quality and impacting local ecology.
Impact on water quality
The flow of water in rivers is part of what creates a healthy ecosystem. When the bridge was installed in the 1960s, it acted like a dam, creating stagnant conditions in the slough. Over time, conditions worsened, as sediment accumulated with no flow to flush the system, and a constant cycle of algal blooms and internal loading of nutrients. The problem became obvious- by sight the slough was green and swampy, and the smell reflected it. Habitat in the area suffered, and aquatic invasive species (AIS) like Eurasian watermilfoil (Myriophyllum spicatum) grew. The loss of habitat contributed to a decrease in biodiversity for fish and other wildlife.
The Grey Cloud Slough provides important habitat for fish spawning, rearing, and overwintering. But without flow, the backwater habitat needed was nonexistent. By creating backwater and side channels, recreational uses of the area were restored.
What is a slough?
A slough is a side-channel, backwater, or shallow wetland where water moves very slowly or stays still. Often they are connected to larger river bodies.
Solutions
To restore ecological function, support flow, while addressing flooding concerns, a new bridge at Grey Cloud Island Dr S. was constructed. The new bridge is constructed to maintain full hydrological connectivity with the main channel, supporting flow into and out of the slough. The new roadway was raised by a foot, to prevent water from overtopping the bridge during Mississippi River flooding events.
With the flow restored, water quality has improved. There was a decrease in total phosphorus concentrations, and the algal blooms and non-native plant population decreased. The slough improved visually, and recreation was restored in the area.
Kyle Axtell
Staff Contact
Questions? Reach out to Kyle Axtell, Planning & Projects Program Manager, at Kyle.Axtell@swwdmn.gov or call 651.728.6124.