Great River Hydro Reports Deviations from Stabilization Limit

Strategic Insights -

Great River Hydro, LLC, licensee for the Deerfield River Project No. 2323, has submitted a document to the Federal Energy Regulatory Commission (FERC) informing them of two deviations from the required stabilization limit at Somerset Development. The deviations occurred due to heavy rain events that dropped up to two inches of water to the region, causing the maximum water surface elevation (WSE) to be exceeded by up to 0.13 feet (approx. 1.5 inches) in the second event. The company's operators increased project discharge to its maximum of 940 cfs prior to the exceedance and continued releasing maximum flow until after the elevation returned to compliance levels.

Key Takeaways:

  • Great River Hydro, LLC has reported two deviations from the required stabilization limit at Somerset Development due to heavy rain events.
  • The deviations occurred on May 31, 2025, and June 7, 2025, with the maximum WSE being exceeded by up to 0.09 feet (approx. 1 inch) and 0.13 feet (approx. 1.5 inches) respectively.
  • The company's operators increased project discharge to its maximum of 940 cfs prior to each exceedance and continued releasing maximum flow until after the elevation returned to compliance levels.
  • The loon nesting stabilization target WSE for 2025 is 2129.00 feet msl, with the maximum WSE (+ 3 inches) being 2129.25 msl.
  • The Vermont Department of Fish and Wildlife and Great River Hydro had mutual agreement to temporarily modify the stabilization target WSE for project maintenance purposes.
  • The company is expected to provide an update on the status of the loon pairs nesting on the reservoir in their annual report.

Statistics:

  • Maximum project discharge: 940 cfs
  • Maximum WSE exceedence: up to 0.13 feet (approx. 1.5 inches)
  • Duration of first deviation: 15 hours, 9 minutes
  • Duration of second deviation: 14 hours, 37 minutes
  • Rainfall drop: up to two inches

Sources:

  • Great River Hydro Jennifer Griffin Director, FERC License Compliance Great River Hydro, LLC 2 Killeen Street North Walpole, NH 03609 603-966-0477 jgriffin@greatriverhydro.com June 10, 2025
  • TransCanada Hydro Northeast, Inc., 159 FERC P 62,188 (2017)