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Independent regulatory commissions

Deviation in Minimum Instream Flow at Bear River due to Debris Clogging Waste Gate

Strategic Insights

— 2 min read

A deviation in minimum instream flow at compliance gage YB-198 in the Bear River occurred on July 11, 2025, due to debris clogging the Drum Canal waste gate at YB-137. This deviation resulted in a drop in flow below the required minimum instream flow (MIF) of 5 cfs to approximately 4 cfs for a period of over an hour. The event was not intended but occurred as a result of flushing debris from the Spaulding lower intake during return to service testing of the Spaulding No. 1 Powerhouse. The deviation had no significant impact on aquatic species within the affected Bear River Reach, given the short duration of the event and its occurrence in the evening when water temperatures are typically cooler.

Key Takeaways:

  • The deviation in minimum instream flow at compliance gage YB-198 in the Bear River occurred on July 11, 2025, due to debris clogging the Drum Canal waste gate at YB-137.
  • The flow dropped below the required minimum instream flow (MIF) of 5 cfs to approximately 4 cfs for a period of over an hour.
  • The event was not intended but occurred as a result of flushing debris from the Spaulding lower intake during return to service testing of the Spaulding No. 1 Powerhouse.
  • PG&E staff noticed the drop in flow at YB-198 and opened the South Yuba Canal waste gate at YB-139 to provide supplemental water to the Bear River above YB-198.
  • The Drum Canal waste gate at YB-137 was partially open throughout the event but had become clogged with debris, unable to pass sufficient supplemental flows to maintain flow above the 5 cfs minimum.
  • PG&E's aquatic biologists reviewed the deviation and evaluated the potential for adverse effects to aquatic resources, finding no significant impact on aquatic species within the affected Bear River Reach.
  • The deviation occurred during a short period of over an hour, with the flow decreasing by approximately 1 cfs below the MIF of 5 cfs.
  • The events occurred in the evening when water temperatures are typically cooler, which reduced the potential impact on aquatic species.
  • PG&E has taken corrective actions to mitigate the likelihood of this occurring again during testing, by stationing a staff member near the Drum Canal waste gate at YB-137 to flush debris as needed.

Statistics:

  • The minimum instream flow at compliance gage YB-198 in the Bear River is required to be 5 cfs.
  • The flow at YB-198 dropped to approximately 4 cfs for a period of over an hour due to debris clogging the Drum Canal waste gate at YB-137.
  • The total duration of the recession below 5 cfs lasted approximately an hour and twelve minutes.
  • The flow decreased by approximately 1 cfs below the MIF of 5 cfs during the deviation.
  • The deviation occurred on July 11, 2025, during the return to service testing of the Spaulding No. 1 Powerhouse.
  • PG&E's aquatic biologists surveyed the affected reach of the Bear River during relicensing and found no listed fish species, but did find brown trout and rainbow trout.
  • The stretch of stream surveyed was approximately 7.5 miles downstream from the Drum Afterbay.

Sources:

  • Pacific Gas and Electric Company (July 21, 2025): Deviation in Minimum Instream Flow at Compliance Gage YB-198 in the Bear River due to Debris Clogging Waste Gate (Washington: Federal Energy Regulatory Commission).

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