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Dworshak SOR # 2009-02Transition to Refill

Stephen Hall P.E., Reservoir Regulation

Walla Walla District USACE

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SOR #2009-02Requested full power-house discharge from

Dworshak from May 12th 2009 to May 17th 2009 as needed to achieve 100 kcfs flow at Lower Granite Dam.

The COE response was a compromise between requested SOR flows and minimum discharge for a higher probability of refill.

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Time Line of TMT Meetings• April 8th TMT Meeting – April 1st forecast = 99% normal (2.66 MAF), estimated discharge during refill = 5 to 6 kcfs. Discharging maximum amount (110% TDG) for flood control based on Grand Coulee Flood control shift and increasing water supply forecast

• April 22nd TMT Meeting – Initiated discussion on transition to refill with two options. Salmon Managers requested maximum discharge through the end of April. COE accepted the Salmon Manager request.

• April 29th TMT Meeting – Based on a decline in National Weather Service Ensamble Streamflow Prediction forecasted volume (2.4 MAF) COE expressed concern regarding refill. The Flood Control Refill Curve (FCRC) was intersected on April 18th. FCRC provides 95% chance of refill by 30 June. Salmon Managers request maximum discharge through April 30th then a reduction to full powerhouse (10.6 kcfs) through May 6th. COE accepted the Salmon Manager request.

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Time Line of TMT Meetings cont.• May 5th RCC Communication with Salmon Managers – COE reduced discharge from 10.6 kcfs to 7.5 kcfs per agreement with Salmon Managers with a further plan to make further reductions on May 6th.

• May 6th TMT Meeting – COE expressed increasing concern with refill flexibility (little remaining volume above minimum discharge). Based on ESP and other data, with Salmon Manager agreement, COE reduced to minimum discharge on May 6th.

• May 12th @ 15:23 SOR sent to Reservoir Control Center (RCC) by Salmon Managers

• May 13th TMT Meeting – COE present ESP refill information, explained the significant departure from FCRC curve, and historical analysis of similar years/conditions to express significant concern regarding refill based on the SOR. COE decided to implement a compromise operation resulting in a gradual reduction in discharge over the next 5 days.

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The next few slides are the information presented at TMT including:

Water Supply Forecast

ESP Traces with refill volumes

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Forecast Uncertainty = +/- 400 KAF

ESP Forecast change= + 170 KAF

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COE Decision was based on:

• Fish Needs – described in SOR

• Risk to Refill– ESP Trace information– Flood Control Refill Curve computations– Historical Analysis – 4 of 12 similar years

would not refill– Water supply forecast uncertainty

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Lessons from SOR & JTS Memo • Balance between refill and spring augmentation

is difficult, especially with high uncertainty in future events.

• Raises valid question “If we could go back in time, would we do anything different based on what we did know or could have known?”

• We cannot use 20-20 hind sight (observed runoff) to question real-time decisions.

• We need to communicate forecast AND the uncertainty associated with the forecast

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Questions