Corps lowers impact to fish spawning near Soo Locks

SAULT STE. MARIE, Mich. (March 5, 2021) – U.S. Army Corps of Engineers (USACE) officials will use dry blasting during New Lock at the Soo construction to avoid or drastically minimize impacts to fish larvae and adult fish spawning near the Soo Locks.

The Soo Locks on the St. Marys River allow vessels to navigate the 21 ft elevation change between Lake Superior and the lower Great Lakes. A new Poe-sized lock being built will provide necessary redundancy in the Great Lakes Navigation System’s critical infrastructure.

To build the New Lock, deepening the channel on the upstream side (west) of the Poe lock is necessary. Dredging is scheduled to occur in 2021-2022. Drilling and blasting are required to fragment the bedrock and concrete for dredging.

Ground vibration, underwater shockwaves from blasting, and the potential physical impacts to nearby fish and fish eggs in the St. Mary’s River are concerns for USACE and Michigan Department of Natural Resources.

The U.S. Army Engineer Research and Development Center (ERDC) conducted an assessment on dry and underwater blasting and its impacts on fish spawning. The team found nine data sources and reviewed them to determine the upper limit of vibrations and sudden change in water pressure brought on from blasting. The team developed estimated thresholds to protect fish spawning habitat in the immediate dredging area.

To remove existing concrete floor and underlying bedrock for the New Lock construction, blasting is expected to occur out of water, called dry blasting, in the current Sabin Lock between upstream and downstream cofferdams.

The ERDC assessment notes, “potential impacts from dry blasting to the local fish population are dependent on a number of site specific factors ranging from the blasting details (type and amount of explosive charge, blast confinement method, water depth, substrate type, charge delay, etc confinement, etc.) and the size, life-stage (e.g., eggs, larval, adult), and morphology of the fish”.

Based on New Lock blasting plans details, ERDC engineers and scientists determined dry blasting as an alternative to underwater blasting will effectively minimize the sudden change in water pressure to species a primary means for injury to fish.

“Shock waves generated by in-water blasting have greater lethal effects as compared to those propagated from ground to water due to the sharper pressure-time signature, the ERDC assessment says. For dry blasting, part of the blasting energy is reflected and lost at the ground-water interface.”

The results indicate vibrations and water overpressures from dry blasting will be sufficiently protective of fish spawning habitats for fish eggs, according to the ERDC assessment.

Dr. Andrew McQueen, an ERDC research biologist involved in this study said, “the St. Marys rapids near the new Soo Locks construction serve as a spawning ground and habitat for a variety of ecologically and recreationally important fish species, and our goal is to provide science-informed risk management to protect these resources”.

USACE strives to achieve environmental sustainability of USACE civil works projects and operations by evaluating project proposals for environmental soundness, making recommendations for project modifications that reduce environmental impacts and/or provide environmental enhancements.