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United States. Federal Energy Regulatory Commission

Tacoma Power Reports Ramping Rate Excursion at Cushman Hydroelectric Project

Strategic Insights

— 1 min read

Tacoma Power has submitted a notification to the Federal Energy Regulatory Commission (FERC) regarding a ramping rate excursion at the Cushman Hydroelectric Project on October 8, 2025. The incident occurred when a planned spill gate test required the operation of the spill gate, causing a brief increase in flow into the North Fork Skokomish River. The resulting flow rate of -2.04 inches per hour exceeded the allowable ramping rate of -1 inch per hour, triggering a notification to the FERC and the Fisheries & Habitat Committee (FHC).

Key Takeaways:

  • The ramping rate excursion was caused by a planned spill gate test required by the FERC as part of Dam Safety and Inspections.
  • The test resulted in a single reading of -2.04 inches per hour at USGS Gage No. 12058790, exceeding the allowable daytime ramping rate of -1 inch per hour.
  • The drop in flow at the dam was attenuated downstream and not registered at the lower USGS Gage No. 12059500, located approximately 7 miles downstream.
  • Staff biologists conducted spawning ground surveys on October 8, 2025, and did not observe adverse environmental impacts or impacts to fish or other aquatic organisms.
  • The incident will be reported in the FERC License Article 406 Annual Report for Water Year 2026.
  • Tacoma Power notified the FHC of the event on October 9, 2025, as required by Section 6 of Article 407.
  • The incident was not preventable and was beyond the control of staff as the spill gate test was a required dam safety exercise mandated by FERC.

Statistics:

  • The ramping rate excursion lasted for approximately 25 minutes.
  • The drop in flow at the dam was short in duration and small in magnitude.
  • The flow rate exceeded the allowable ramping rate by 204%.
  • The incident occurred at approximately 10:00 AM on October 8, 2025.
  • The spill gate test was completed by 9:15 AM.

Sources:

  • [Federal Energy Regulatory Commission (FERC) Official Notification: Cushman Hydroelectric Project, FERC No. 460 Article 407(1) Ramping Rate Excursion Notification]
  • [Letter from Teresa Loo to Debbie-Anne A. Reese, Federal Energy Regulatory Commission (dated October 15, 2025)]

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