Minnesota Power Exceeds Lower Operating Limit at Birch Lake Reservoir

Strategic Insights -

Minnesota Power, a subsidiary of Allete, Inc., has reported to the Federal Energy Regulatory Commission that Birch Lake Reservoir's hourly-average elevation exceeded its lower operating limit on October 10, 2025, due to insufficient inflow. This marks the fourth time since 2008 that the reservoir has fallen below the specified limit. To manage the situation, Minnesota Power consulted with resource agencies and implemented an adaptive management plan, allowing the pond elevation to fall below the lower band, similar to a natural lake. The company set discharge to the minimum allowable as defined by License Condition 8, releasing seasonal minimum flows or inflow, whichever is less, into the South Kawishiwi River.

Key Takeaways:

  • On October 10, 2025, Birch Lake Reservoir's hourly-average elevation exceeded its lower operating limit, which is set at 1418.49 feet on September 1 and increases to 1419.49 feet on November 15.
  • This marks the fourth time since 2008 that the reservoir has fallen below the specified limit.
  • Minnesota Power consulted with resource agencies and implemented an adaptive management plan to manage the situation.
  • The company set discharge to the minimum allowable, releasing seasonal minimum flows or inflow into the South Kawishiwi River.
  • No adverse environmental impacts were observed or reported as a result of the deviation.
  • The event was reported to the Winton Collaborative Team, with no comments received.
  • Daily data was provided for the deviation, including garden elevation, Birch elevation, White Iron elevation, Birch discharge, and USGS data for the South Kawishiwi River.
  • The Licensee is required to operate Birch Lake Reservoir within the established upper and lower operating limits, with the ability to deviate from the limits under specific circumstances.

Statistics:

  • October 10, 2025: Site elevation 1385.14 feet, Birch lake elevation 1419.01 feet, White Iron elevation 1385.33 feet, and Birch discharge 235 cfs.
  • The reservoir's lower operating limit is set at 1418.49 feet on September 1 and increases to 1419.49 feet on November 15.
  • Four instances since 2008 where the reservoir has fallen below the specified limit.
  • No adverse environmental impacts observed or reported as a result of the deviation.

Sources:

  • Minnesota Power, Correspondence to the Federal Energy Regulatory Commission, RE: Winton Hydroelectric Project # 469, Birch lake Reservoir Development.
  • United States Geological Survey (USGS) Data, SOUTH KAWISHIWI RIVER NEAR ELY, MN.