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New Libby Dam Forecast Procedure and Impacts to Operations

New Libby Dam Forecast Procedure and Impacts to Operations. Libby WSF Procedure. Reasons for new WSF Last update was in 2004 A snow course used was lost due to a forest fire Then lost the replacement snow course Re-evaluate the variables used in the monthly equations

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New Libby Dam Forecast Procedure and Impacts to Operations

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  1. New Libby Dam Forecast Procedure and Impacts to Operations

  2. Libby WSF Procedure • Reasons for new WSF • Last update was in 2004 • A snow course used was lost due to a forest fire • Then lost the replacement snow course • Re-evaluate the variables used in the monthly equations • Lost a precipitation gage in 2009 (Fortine 1N, MT) • 2009 recommendation to review WSF • Reduce month to month forecast variability

  3. Libby WSF Procedure, cont. • Review results in proposed new procedure for implementation in 2010 • Key changes from previous procedure developed in 2004 are: • Snow site are Snotel not snow courses – easier and more efficient access to the data • Fall precipitation variables drop out of the equations in the winter fall forecasts. (Fall precipitation was the the main driver of the 2010 overforecast) • Added Alberta Snotel sites along continental divide that have a high correlation to Libby’s WSF

  4. 2004 vs. 2010 Equation Dry Years

  5. 2004 vs. 2010 Equation

  6. Libby Dam End of December Variable Draft target • The draft target is a function of the 1 December forecast for the inflow volume from 1 Apr – 31 Aug • If the forecast is >= 5900 KAF target 2411 ft (2.0 MAF of Space) • If the forecast is <= 5500 KAF target 2426.7 ft (relax to 1.4 MAF or 600 KAF) • If the forecast is between 5500 KAF and 5900 KAF relax draft by interpolating between 600 and 0 kaf

  7. Libby Dam SRD • If the forecast is >= 5900 KAF target 2411 ft (2.0 MAF of Space) • If the forecast is <= 5500 KAF target 2426.7 ft (relax to 1.4 MAF or 600 KAF) • If the forecast is between 5500 KAF and 5900 KAF relax draft by interpolating between 600 and 0 kaf

  8. Libby Dam SRD • If the forecast is >= 5900 KAF target 2411 ft (2.0 MAF of Space) • If the forecast is <= 5500 KAF target 2426.7 ft (relax to 1.4 MAF or 600 KAF) • If the forecast is between 5500 KAF and 5900 KAF relax draft by interpolating between 600 and 0 kaf

  9. Libby Dam SRD • If the forecast is >= 5900 KAF target 2411 ft (2.0 MAF of Space) • If the forecast is <= 5500 KAF target 2426.7 ft (relax to 1.4 MAF or 600 KAF) • If the forecast is between 5500 KAF and 5900 KAF relax draft by interpolating between 600 and 0 kaf

  10. Probability of Relaxation 2004 vs 2010 Equation • 2004 Equation • No relaxation = 80% of years • Partial 5900 KAF = ~20% of years • Full 5500 KAF = ~15% of years • 2010 Equation • No relaxation = 47% of years • Partial 5900 KAF = ~53% of years • Full 5500 KAF = ~41% of years

  11. 2004 vs. 2010 Equation

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