Planning Continues for Cat Islands Restoration

UW Sea Grant Provides Technical Assistance

A chain of four small islands once formed the backbone of extensive wildlife habitat in southern Green Bay. Known as the Cat Islands, they were washed away in the 1970s by high water levels, storm waves, and ice shoves. Today, UW Sea Grant is working with numerous other organizations to rebuild the islands and restore the many ecological functions they once provided for the bay.

Those functions were complex and wide-ranging, according to Vicky Harris, UW Sea Grant’s habitat restoration specialist. Rich aquatic vegetation once surrounded the Cat Islands, providing habitat for a wide variety of fish, turtles, frogs, and birds. These plants also protected the islands themselves from the erosive forces of pounding waves. The islands, in turn, sheltered additional wetland habitat around the shores of the southern bay.  

Harris says the islands became vulnerable to erosion when sediment from farm fields, construction sites, and other exposed land in the river’s watershed clouded the water in the bay, reducing the depth to which sunlight could penetrate. This choked out much of the near-shore vegetation that buffered the islands from erosive waves.

Meanwhile, the city of Green Bay and shoreline property owners had hardened shorelines with riprap to protect them from rising lake levels and storm floods, Harris said. As a result, wave energy was reflected back into the bay instead of being absorbed by gradually sloping shorelines and dense aquatic vegetation. With larger waves pounding on their shores and less vegetation to protect them, the islands eroded away—and with them went the trees, grasses, aquatic vegetation, and wildlife they supported.

Harris has been working with many groups for over a decade to restore the islands. The project is a collaboration with the Brown County Port, the U.S. Army Corps of Engineers (USACE), the U.S. Fish and Wildlife Service, the Wisconsin Department of Natural Resources, and other organizations.

In her previous capacity as coordinator of the Green Bay Remedial Action Plan and a member of its Biota and Habitat Work Group, Harris worked with Brown County to draft early versions of a proposal that led to a $5 million grant in 1996 from the USACE under the Water Resources Development Act.

“The purpose of the grant is to restore aquatic ecosystems and to find beneficial ways to use dredged sediments rather than simply land filling,” Harris said. “Dredged sediments from the outer bay will be used to replace critical habitats that were lost to Green Bay over the past several decades.”

The grant is paying for 75 percent of the project, with the remainder coming from local sources. It is expected to take about eight years to dredge enough sediments from the outer channel to complete the first of three planned islands. Completing the second two may take decades, Harris said.

The sediments from the outer bay contain barely detectable levels of PCBs, Harris said. Nevertheless, some groups worry that using those sediments to build the island will endanger fish and wildlife. However, Harris says the sediments from the outer channel actually have lower PCB concentrations than those currently in the area where the islands are to be built. The Biota and Habitat Work Group has recommended that sediments used to restore the islands not exceed 0.1 parts per million (ppm), less than half the proposed 0.25 ppm cleanup target for the Fox River, Harris said.

Phil Keillor, UW Sea Grant’s coastal engineer, adds that the sediments used to build the islands will be capped with clean sand.

Working with the Biota and Habitat Work Group,  Keillor provided concept drawings for the first of the three islands. These called for a sloping backside that would provide natural habitat for shore birds. However, concern about the dredged sediments escaping from the island has led to preliminary designs that resemble typical, armored containment facilities, Keillor said.

“There’s a desire to guarantee that no sediment will wash back into the bay,” he said. “But, you can’t guarantee that and provide habitat at the same time. If we want an island that looks somewhat natural and provides habitat, we have to run a small risk that some of these minimally contaminated sediments will wash away. Such a small risk is acceptable,” he said.

Harris is currently focusing on explaining the project to the public and answering questions that people may have. She may be reached at (920) 465-2795 or at harrisv@uwgb.edu.

- John Karl

Last updated 14 June 2001 by Karl
All contents copyright 2000 University of Wisconsin Sea Grant Institute

http://www.seagrant.wisc.edu/Communications/news/LD_stories/2001/CatIslands.html