CU 06-36

Visual Inspection Finds Grassy Island Dikes Sound; Inspection Report Available Online – Congressional Notification

Inspectors from the U.S. Fish and Wildlife Service and the U.S. Army Corps of Engineers found that dikes appear sound at Grassy Island in the Detroit River, a part of the Detroit River International Wildlife Refuge. 

At the Grassy Island Forum on March 9, 2006, the Fish and Wildlife Service and the U.S. Army Corps of Engineers made a joint commitment to conduct a visual inspection of the dikes at Grassy Island.  A visual inspection by the agencies was recently conducted of the island’s exterior dike, interior dike, and weir to determine if there are any physical conditions that would compromise the current dike wall’s integrity or weir structure on the island.  The inspection also served as an opportunity for the Corps of Engineers to demonstrate inspection procedures to the U.S. Fish and Wildlife Service, which manages the island as part of the International Refuge.

Based on observations made during the inspection, the Corps concluded the dikes are structurally stable, safe, and operationally adequate under current conditions.  The Corps made several recommendations regarding dike maintenance to maintain or improve structural integrity.  The Corps’ report states that structural testing would be necessary if any significant changes are made to the structure (e.g. placement of additional fill material or a cap). Additionally, a visual inspection can not determine the physical composition of the dike walls, dike wall porosity, or other geotechnical properties.  

Grassy Island is located in the Detroit River, and originally was a large shoal area with a few low-lying islands.  In 1959, 72 acres of this area were diked by the United States Army Corps of Engineers to create a disposal location for sediments dredged primarily from the Rouge River.  There are 28 contaminants in the soil that exceed state and federal guidelines and criteria. Grassy Island is owned by the U.S. Fish and Wildlife Service, has been part of the National Wildlife Refuge System since 1961, and is now part of the Detroit River International Wildlife Refuge.  The Service is in the process of planning for the island’s remediation and restoration. 

The Army Corp of Engineers’ final inspection report and photographs are available online at http://www.fws.gov/midwest/grassyisland