Four previously proposed structures and two other engineering options were evaluated, and an assessment was done on the potential impacts to the Lake Huron to Lake Erie corridor and the Upper Great Lakes. The structures and engineering options examined include a series of submerged sills in the Upper St. Clair River, estimated to cost from $71.1 million-$222.5 million for up to 13 sills; and an adjustable, inflatable flap gate across the river's east channel at Stag or Fawn islands, estimated to cost $134 million-$171.1 million. The report indicates that these structures could achieve a maximum increase of 25 cm in water levels. The analysis found that inflatable rubber weirs have only been tested in small and shallower systems. Further, the analysis found that in-stream turbines for restoration are only in the exploratory stages.
The analysis found that restoration is technically achievable through a combination of engineering solutions, but that there are a mixture of benefits and costs for various sectors. Under economic effects, the report indicates benefits to navigation, but losses to net hydropower generation and shoreline damages for restoration especially greater than 25 cm. A mix of positive and negative environmental impacts also were identified. For the St. Clair and Detroit River system, the analysis found uniformly negative ecological effects, because the system is home to five endangered or threatened aquatic species, including the Lake Sturgeon. Lake Sturgeon spawning and habitat areas are located in the same deep areas where restoration structures would need to be built to raise water levels and still allow ships to continue to pass through the channel. In the Upper Lakes region, the analysis shows positive ecological impacts for Georgian Bay, Ontario, especially for its wetlands. However, negative ecosystem impacts were identified for Lake St. Clair, along with negative wetland impacts for Lake Erie.
The report indicates that one key factor in estimating the impacts of restoration is Glacial Isostatic Adjustment (GIA), which has the effect of gradually tilting the land surface of the Great Lakes basin over time. Additionally, the report says that major works in the St. Clair River are estimated to take decades due to the need for government approvals, environmental assessments, engineering and design.
The exploratory analysis will become part of the Study's final Phase 2 report, which will focus on an improved regulation plan for Lake Superior outflows at Sault Ste. Marie, multi-lake regulation and climate change adaptation. In July and August, IUGLS plans to hold a series of public meetings throughout the Great Lakes basin, to provide a presentation on the status of the Phase 2 findings. Also planned are informational opportunities via traditional mail, email and the Internet. The final, peer-reviewed Phase 2 report is expected to be submitted to the IJC in March 2012. After that time, the IJC may choose to hold public meetings on that Phase 2 report.