Measure 8: Spill Management at Grizzly Forebay and Lower Bucks Lake
In order to minimize the impact of unavoidable spills on Grizzly Creek, Grizzly Forebay shall be drawn down to the extent practical in advance of forecast spill events.
The duration of this measure applies to spills caused or influenced by powerhouse (PH) load changes, herein referred to as “managed spills”. Load changes are the only method of significantly affecting rate of change of Project spills at Grizzly Forebay and Lower Bucks, which have uncontrolled spillways and small low-level outlets designed for minimum instream flow releases.
The following requirements do not apply to spills during periods when the applicable powerhouses are held at constant load for the duration of the spill (i.e. “block loaded” achieving a natural rate of change in flow); nor do they apply to spills at Grizzly Forebay when load changes are made in parallel at both Grizzly PH and Bucks PH such that flows through the powerhouses are as equivalent as possible (i.e. “paired schedules” achieving a natural rate of change in flow).
At no time shall managed spills that affect flows on Grizzly Creek be scheduled during the first five days or the last two days of the prescribed daily steps of the Rock Creek-Cresta Project (FERC Project No. 1962) North Fork Feather River Cresta Reach 21-day spill recession (CSR)*. Preferentially, managed spills that affect flows on Grizzly Creek shall be scheduled prior to the CSR; however, if that is impractical they may be scheduled during the fifteen days of constant flow within the CSR (i.e. Days 6-20).
For additional protection of the foothill yellow-legged frog population in the Cresta Reach, extended outages greater than two weeks on Bucks PH and Grizzly PH shall not be scheduled during April through July in order to avoid potential resultant spills on Grizzly Creek during that ecologically sensitive period. Outages during August and September are unlikely to result in spills; however, no outages shall be scheduled for these months if they will cause a spill.
For down-ramping of managed spills that occur from April through September, the load change over 24 hours shall not exceed the MW value in Tables 1, 2, or 3 corresponding to the applicable powerhouse and instantaneous spill flow at the beginning of that 24-hour increment.
For down-ramping of managed spills that occur from October through March, anyload changes over 60 minutes shall not exceed the MW value in Tables 1, 2, or3 corresponding to the applicable powerhouse and instantaneous spill flow at the beginning of that 60-minute increment.
During extended spills of greater than 350 cfs that occur from October through March, flexible schedules and bidding are allowed, but load changes shall not exceed the MW value in Tables 1, 2, or 3 corresponding to the applicable powerhouse and instantaneous spill flow at the beginning of that increment. For spills at Grizzly Forebay, this flexibility applies only when flows on the North Fork Feather River exceed 3,500 cfs at NF56.
Table 1: Grizzly Powerhouse load changes for Spills at Grizzly Forebay Dam(Changes in powerhouse flows result in corresponding changes in instream flows – i.e., powerhouse flows are decreasing, instream flows will decrease at a similar magnitude)
Initial flow at NF22(cfs) / Allowable change
(MW) / Approximate powerhouse flow change per step (cfs)
> 800 / N/A / N/A
551 - 800 / 12.0 / 203 - 209
351 - 550 / 8.0 / 135 - 140
150 - 350 / 4.0 / 67 - 70
< 150 / 2.0* / 33 - 35
*Depending on the 9 – 11 MW no-run zone, may require a 3 MW step
Table 2: Bucks Powerhouse load changes for Spills at Grizzly Forebay Dam(Changes in powerhouse flows result in corresponding changes in instream flows – i.e., powerhouse flows are increasing, instream flows will decrease at a similar magnitude)
Initial flow at NF22(cfs) / Allowable change
(MW) / Approximate powerhouse flow change per step (cfs)
> 800 / N/A / N/A
551 - 800 / 40.0 / ~207
351 - 550 / 24.0 / 119 - 158
150 - 350 / 12.0 / 58 - 86
< 150 / 6.0 / 29 - 45
Table 3: Grizzly Powerhouse load changes for Spills at Lower Bucks Dam(Changes in powerhouse flows result in corresponding changes in instream flows – i.e., powerhouse flows are increasing, instream flows will decrease at a similar magnitude)
Initial flow at NF12(cfs) / Allowable change
(MW) / Approximate powerhouse flow change per step (cfs)+
> 800 / N/A / N/A
551 - 800 / 12.0 / 203 - 209
351 - 550 / 8.0 / 135 - 140
150 - 350 / 4.0 / 67 - 70
< 150 / 2.0* / 33 - 35
*Depending on the 9 – 11 MW no-run zone, may require a 3 MW step
River stage shall be monitored in Bucks Creek downstream of Lower Bucks Lake Dam and in Grizzly Creek downstream of Grizzly Forebay Dam for the first 5 years of the License, or until all three ramping scenarios are implemented, whichever may come first. After License Year Five,the Licensees shall compile a reportthat documents the effects of implementation of the measure on instream flow conditions in Bucks Creek, Grizzly Creek, and the North Fork Feather River. The report shall also providerecommendations to improve the Licensees’ compliance with this measure.
Based on the report and associated hydrologic data, the Licensees, in consultation with the Forest Service, USFWS, CDFW, SWRCB and interested stakeholders, shall review, update, and revise the measure, as needed, when significant changes in the existing conditions occur.
Sixty days shall be allowed for the Forest Service, USFWS, CDFW, SWRCB and interested stakeholders to provide written comments and recommendations. After consultation and agreement with the Forest Service and SWRCB, the Licensees shall work with the Forest Service and SWRCB to file the updated measure with FERC. The Licensees shall include all relevant documentation of coordination and consultation with the updated measure filed with FERC. If the Licensees do not adopt a particular recommendation by the Forest Service, USFWS, CDFW, SWRCB, or interested stakeholder, the filing shall include the reasons for not doing so. The Licensees shall implement the measure as approved by FERC.
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