Project Overview: Challenges with Ice and Debris
The Lower St. Anthony Falls Lock and Dam is a hydroelectric facility on the Mississippi River in downtown Minneapolis, Minnesota. It generates 8.98 megawatts of power and plays a vital role in regional energy production.
The site features a 275-foot concrete spillway on the river’s north side. A single operating lock sits on the southern bank, with a 56-foot-wide auxiliary lock chamber between them.
“The Mississippi River is the reason why Minneapolis and St. Paul were built where they are. People have lived in this area for thousands of years, drawn by the life-sustaining gifts of the river and the power of St. Anthony Falls, or Owámniyomni. Learn more about Dakota homelands. St. Anthony Falls is the only major waterfall on the entire Mississippi River, and as it moved over thousands of years, it carved the only gorge on the river, a beloved place for many residents.” (Source: Meet our Twin Cities locks and dams)
Downstream from the auxiliary lock, sixteen matrix turbine-generator units sit in a stacked configuration. Each unit includes an integrated trash screen to protect against floating ice and debris. However, the existing trash boom system failed to prevent large volumes of debris and ice from reaching the screens. This often led to clogging, which caused frequent turbine shutdowns.
Impact of Shutdowns
These shutdowns resulted in significant power generation losses. Over time, the facility lost thousands of megawatts in production. In addition, operations and maintenance costs increased due to repeated cleanups and repairs.
Brookfield Renewable Takes Action
In June 2018, Brookfield Renewable U.S.—a global leader in renewable energy—sought a solution. They partnered with Pacific Netting Products to design a reliable boom system that could protect the facility year-round.
Custom MultiFunction Boom Solution
Pacific Netting Products delivered a custom-engineered MultiFunction Boom. This solution protects the hydropower units from both surface debris and submerged debris as well as ice.
Debris Boom Features
- Total Length: 225 feet
- Boom Type: 36-inch Class 1, rated for 346,000 pounds safe working load
- Shape: Nine sections arranged in a “V” formation for debris funneling
- Connections: Flange-bolted joints for durability and strength
- Flow Design: Built to withstand up to 10 feet per second flow
- Safety Features:
- Fitted with both debris skirt and splashguard
- Custom swimmer safety ladder
- Walkway grate on one boom section
- Anchored by heavy-duty in-river cored concrete pile, flush to riverbed, connected by chain to 8 ft x16 ft anchor buoy
- Weather-resistant: Year-round deployment
Ice and Debris Management
The boom includes a debris skirt to intercept floating and submerged material. A splash guard helps deflect water and smaller debris, improving screen protection.
These features reduce clogging and keep the hydropower units operational during normal and adverse conditions.
Built-In Safety Features
Safety played a major role in the boom design. On the lock side, engineers added a custom swimmer self-rescue ladder. A steel walkway grate on one boom section allows safe maintenance access for personnel.
Secure Anchoring System
A heavy-duty in-river concrete pile, cored and flush with the riverbed, anchors the boom. It connects to an 8-foot by 16-foot anchor buoy made of foam-filled composite. This buoy is unsinkable and designed to absorb impacts without shifting.
Year-Round Performance
The boom system remains deployed throughout all seasons, including during harsh winter conditions. It delivers year-round protection with minimal maintenance.
Key Benefits
- Reduces shutdowns
- Minimizes energy loss
- Lowers operations and maintenance costs
- Improves safety and reliability
A Long-Term Investment in Reliability
The new MultiFunction Boom has significantly improved performance at the Lower St. Anthony Falls facility. Since its installation, turbine interruptions have dropped, and power output has become more stable.
Brookfield Renewable’s investment in this advanced system reflects their commitment to clean, reliable energy for the region.
