Optimum Timing for Dredging in Great Lakes Harbors Takes a More Scientific Turn

It can’t happen just any old time. Removing sediment from or adding it to harbors to help ships pass or for construction projects is regulated by state and federal rules designed to lessen impacts to the plants and animals living in both marine and fresh water.

“We used to call them fish windows,” said Gene Clark, Wisconsin Sea Grant coastal engineer. “But we’ve learned that other species can be affected by the timing of dredging as well – things like mussels, amphibians and wild rice. It’s not just a fish window, it’s an environmental window for dredging.”

These timing windows were first created almost 50 years ago, spurred by the passage of the National Environmental Policy Act in 1969. They hardly ever change and are enforced through the permitting process by the U.S. Army Corps of Engineers and state departments of natural resources. The designations of these windows were set by natural resource experts, however specific science-based data to help them was lacking.

According to a white paper on dredging windows in the Duluth-Superior Harbor, a number of new scientific tools are now available to “evaluate the specific impacts of dredging, to more accurately monitor the biological integrity and specific biological functions of different parts of our harbors, and to assess changes due to season variation. In addition, new engineering technologies have resulted in new dredging methods and construction options to reduce the impacts of the dredging process, as well as in-water facilities maintenance and fabrication.”

Bringing dredging windows up to date was one of the most important issues identified by harbor stakeholders when asked where they thought Sea Grant could make a difference, Clark said. At stake is money and time, not to mention the wellbeing of the environment.

“The timing of the dredging windows can be very strict, and they can make projects more costly,” said Clark. “The problem doesn’t just affect our harbor. All dredging projects on the Great Lakes have this issue, too.”

Clark believes that with more information about where critical habitats are in the harbor and when important wildlife activities are going on, such as fish spawning, money can be saved on behalf of taxpayers and the contractors.

Clark has teamed with Dale Bergeron, Minnesota Sea Grant maritime extension educator, and members of the Duluth Seaway Port Authority to work on the issue. They have been working for a year to write a white paper, develop a process for deciding what studies are needed, and provide a template for studies in other ports.

“Our goal is to facilitate discussions between the regulatory agencies, the U.S. Army Corps and the contractors,” Clark said. They also plan to work with academic researchers to find funding for the studies.

One activity is taking place next week on May 30. A select group of people from the Duluth-Superior area have been invited to participate in a scoping meeting to conduct a “Science-based Review of Environmental Windows for Dredging and In-water Construction in the Duluth/Superior Estuary and Harbor.”

On the agenda is the history of dredging windows, and defining biological issues such as locations of high- and low-productivity areas and the impacts of seasons and climate variability, and discussion of new technologies that are available for dredging and reducing turbidity. The resulting tasks will take the form of a pilot project, for which funding will be sought.

“Perhaps in a couple of seasons, we’ll have enough information so we can actually make a difference in when dredging windows are set, and potentially save the corps some money, save the contractor money and save some angst on behalf of the permitting agencies,” Clark said.