Soft Shoreline Engineering Case Studies
Gibralter Bay Unit, Detroit River Int. Wildlife Refuge - Site #20
Grosse Ile, Michigan
Project Goals and Objectives: Restore a native shoreline and native plant community, promote environmental education through local schools and encourage stewardship and sustainability
Project Description: In the summer of 2003 the Grosse Ile Nature and Land Conservancy, in partnership with the Greater Detroit American Heritage River (AHR) Initiative, rehabilitated 85 meters (280 feet) of shoreline at the Grosse Ile Nature Area using soft engineering techniques. The shoreline is part of the old Nike Missile base and is located in Gibraltar Bay. The missile base was created in the 1950s by filling in a shallow section of the Detroit River. The base was closed in the early 1960s and was dismantled in the early 1990s. Since the shoreline has not been natural for some time, exotic plants species such as Phragmites and purple loosestrife colonized it.
Nativescape LLC designed the new shoreline. The new technology utilized biodegradable plastic tubes (fibersock or Soil Sock) placed at the edge of the shoreline. Clean-composted recycled yard waste and small stone is pneumatically pumped into the tubes along with a mixture of native emergent plant seeds. The fibersock was then placed along the shoreline edge and anchored in place. The compost mixture was back filled into the space between the tube and the old shoreline creating a new aquatic shelf. A geofabric blanket was then placed over this back fill to stabilize the area until the plants grew. A group of Grosse Ile high school students planted about 1,400 emergent plant roots in the resulting aquatic shelf.
Since then, there was a deposition of material in front of the fibersock. The fibersock degraded and resulted in a new natural shoreline with native emergent plants. This technique has generated great interest and has many potential applications. It was first used for stream bank stabilization in the south. By blowing the compost material into stone riprap, the plant seeds took root and vegetated the riprap creating a more natural shoreline.
The second phase of this project involved completing the remaining Detroit River shoreline at the Grosse Ile Nature Area using this soft engineering technique.
Timeframe: Phase 1 – 2003; Phase 2 – 2004-2005
Partners: Grosse Ile Nature and Land Conservancy, Nativescape LLC, Metropolitan Affairs Coalition; U.S. Fish and Wildlife Service, Great Lakes Basin Program for Soil Erosion and Sediment Control; Grosse Ile Schools, Downriver Community Conference, Friends of the Detroit River, Sea Grant, and the Detroit/Wayne County Port Authority
Ecological Effectiveness: Prior to shoreline restoration, the plant community had limited diversity and was dominated by invasive non-native species, i.e., giant reed (Phragmites australis), purple loosestrife (Lythrum salicaria) and reed canary grass (Phalaris arundinacea) with a limited number of native species. A macro-invertebrate study showed a limited number of species using the site. Bull frogs (Rana catesbeianaa) were not present on the site. There were a limited number of species of insects and birds using the area.
After shoreline restoration, a more diverse plant community was present, dominated by native species that are now seeding surrounding areas, i.e., cupplant (Silphium perfoliatum), swamp rose mallow (Hibiscus palustris) and cardinal flower (Lobelia cardinalis). None of these species were present before restoration. A macro-invertebrate study showed an increase in diversity. Bull Frogs are now present on the site and in the area. There has been a dramatic increase in the number and species of insects and birds using the site.
Restoration Contact: Grosse Ile Nature and Land Conservancy
Monitoring Contact: Nativescape LL