Monday, February 15, 2016
Constructed spawning reefs – essentially beds of loose rock placed on the river bottom – can re-create rocky fish habitat that has been degraded, destroyed, or made inaccessible in a river system. In the St. Clair and Detroit Rivers, a multi-disciplinary team of academic and agency scientists has learned to site and build reefs that attract desired fish species during spawning season and successfully incubate their eggs. However, some constructed reef projects have accumulated sand and silt, which limits their value to fish over time.
To help predict and avoid sediment issues, two U-M engineers have partnered with the Water Center and the reef restoration team to study the hydrodynamics related to simulated reefs. Aline Cotel from the Department of Civil and Environmental Engineering has been testing potential reef shapes in a water tunnel using dye and particle image velocimetry to visualize the structure of water flow and quantify the velocity and vorticity fields. Laura Alford from the Department of Naval Architecture and Marine Engineering has been modeling water flow over potential reef designs for a proposed restoration site using computational fluid dynamics. Their research finds that the angle of the upstream edge of a reef determines whether eddies and turbulence develop that could trap sediment. They also find that water velocities are fairly steady over a flat but somewhat bumpy reef shape, and the added expense of a more complicated ramp or airfoil shape does not seem to be necessary for the proposed restoration site.
This new research combined with on-going monitoring from state and federal agency scientists is informing the design of a reef that will likely be built upstream of Belle Isle, located in the Detroit River, in 2016. This site has a small and oddly shaped potential restoration area, and the hydrodynamic modeling has helped select a design that will maximize benefits for fish and minimize the risk of sediment in-filling. Research and restoration efforts are funded by the Great Lakes Restoration Initiative.
These and other restoration lessons have been summarized in new practitioner-oriented publication developed by Water Center specialists. The team’s diverse experiences will also be shared in a webinar on March 9 at 11 am (EST). For more information see:
• Science in Action: Lessons Learned from Fish Habitat Restoration in the St. Clair and Detroit Rivers (PDF, 44 pages)
• A Home for Lake Sturgeon (slideshow)