Pacific Gas and Electric Company Submits Notification of Ramping Rate Modification

Strategic Insights -

Pacific Gas and Electric Company (PG&E) has submitted a notification to the Federal Energy Regulatory Commission (FERC) regarding a ramping rate modification that occurred at the Tiger Creek Afterbay Dam on July 4, 2025. The modification resulted from an equipment malfunction in the automated feedback system, which caused an increase in flow rates exceeding the allowable limit.

The incident occurred when the West Point powerhouse was out of service, and the MIF control system was operating in automatic mode. The system received incorrect data indicating a drop in flow, prompting the spill gates to open, resulting in a ramping rate modification. Despite the brief adjustment, the event exceeded the allowable ramp-up rate limit of 25 cfs/hr, reaching 35.33 cfs/hr. However, the incident did not result in any minimum instream flow (MIF) violations, personal injuries, property damage, or known impacts to biological or cultural resources.

Key Takeaways:

  • The ramping rate modification occurred on July 4, 2025, due to an equipment malfunction in the automated feedback system.
  • The modification exceeded the allowable ramp-up rate limit of 25 cfs/hr, reaching 35.33 cfs/hr.
  • The incident did not result in any negative environmental impacts, including MIF violations, personal injuries, property damage, or known impacts to biological or cultural resources.
  • PG&E notified the ERC and Forest Service by email on July 14, 2025, as required by Condition No. 9 of the Project license.
  • The incident remains within the 1% non-compliance threshold allowed by the Ramping Rate Variability Plan.
  • PG&E has taken corrective action to prevent recurrence, including operating the gates in manual mode whenever West Point is out of service.

Statistics:

  • The ramping rate modification exceeded the allowable ramp-up rate limit by 10.33 cfs/hr.
  • The flow data indicates that the effective ramp-up rate limit at M59 is 35 cfs/hr (25 cfs/hr base + 40% variability).
  • The incident occurred between 00:45 and 01:45 on July 4, 2025.
  • PG&E notified the ERC and Forest Service within 10 days of the incident, as required by Condition No. 9.

Sources:

  • PG&E, "Notification of Modification - Ramping Rate Modification at M59, Tiger Creek Afterbay Dam, on July 4, 2025"
  • Federal Energy Regulatory Commission, "Notice of Condition No. 9 - Ramping Rates of the project license"
  • PG&E, "Ramping Rate Variability Plan, approved by FERC June 15, 2009"