The century-old Island Lake Dam not only regulates water levels and supports recreation on the Island Lake Reservoir, but also supports generating power for Minnesota’s largest hydropower system. When Minnesota Power identified a critical problem—five leaking sluice gates causing a reduction in power generation and posing operational, environmental, and safety risks—it turned to Barr for assistance.
Designing and implementing dam repairs called for special precision. The gates’ location, 50 feet below the water’s surface meant divers couldn’t safely access the gates for repairs. An additional complication was that the dam’s original design called for partial drainage of the reservoir to access the gates, and this option was no longer feasible.
Barr performed an options study for a replacement design that would improve gate integrity and reliability. Once a design was selected, close collaboration among Minnesota Power, Barr, and construction contractor J.F. Brennan Company, Inc., along with the use of a three-dimensional model, enabled development of a final design and detailed construction plans.
The design configuration extended the end walls and piers vertically by 30 feet. New bracing and framing were added to distribute loads. Bulkhead slots accommodated steel bulkheads for dewatering. Finite-element models were used to assess load stresses and size new elements to help assure structural integrity and stability. As gate design was developed, Barr also conducted a potential failure mode analysis (PFMA) to help assess the risks associated with the design’s construction, operation, and long-term maintenance.
This repair and restoration project received a 2021 Grand Award in Engineering Excellence from the American Council of Engineering Companies of Minnesota.