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31 DECEMBER VARIABLE FLOOD CONTROL DRAFT FOR LIBBY RESERVOIR

31 DECEMBER VARIABLE FLOOD CONTROL DRAFT FOR LIBBY RESERVOIR. U.S. Army Corps of Engineers Northwestern Division, North Pacific Region. HISTORICAL OVERVIEW. Several studies have been conducted by the Corps to investigate flood control relaxation in the Columbia basin

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31 DECEMBER VARIABLE FLOOD CONTROL DRAFT FOR LIBBY RESERVOIR

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  1. 31 DECEMBER VARIABLE FLOOD CONTROL DRAFT FOR LIBBY RESERVOIR U.S. Army Corps of Engineers Northwestern Division, North Pacific Region

  2. HISTORICAL OVERVIEW • Several studies have been conducted by the Corps to investigate flood control relaxation in the Columbia basin • CRT-63 (1991) examined relaxation throughout entire Columbia basin • System Operation Review (1995) identified potential for VARQ at Libby and Hungry Horse Dams • 1999 Status Report • 2002 EA for interim implementation • EIS scheduled for completion in 2005 • This study (December 2003) evaluates the potential for relaxing Libby’s end-of-December flood control draft

  3. NMFS 2000 BiOp on FCRPS • NMFS BiOp, Action 36: “…the Corps shall develop and, if feasible, implement a revised storage reservation diagram for Libby Reservoir that replaces the existing fall draft to a fixed end-of-December elevation. One option is to evaluate variable drafts based on the El Nino Southern Oscillation Index (SOI) predictions or other forecast methodologies of runoff volume. To implement this change, the Corps shall complete successful coordination with Canada under the Columbia River Treaty”

  4. USFWS 2000 BiOp on FCRPS • USFWS BiOp, RPA 8.1.h: “…the action agencies shall evaluate the feasibility of a variable December 31 flood control target of 2411 feet at Libby Dam, based on various alternative long range forecasting procedures (such as the procedures developed by USGS, Tacoma, for western Washington), and any opportunities arising from operational or configuration changes (additional turbines or spillway flow deflectors) addressed elsewhere in this biological opinion. These factors would be used at Libby Dam to increase the probability of storage during less than average water years. ”

  5. REVISED FORECAST PROCEDURE • A new forecast procedure for Libby runoff volume was developed in 2003 & implemented in WY 2004. • The new procedure uses principal components regression, and incorporates the Southern Oscillation Index (SOI) for early season (November & December) forecasts. • 1 Nov 2003 forecast: 6533 KAF (105% of normal) • 1 Dec 2003 forecast: 6445 KAF (103% of normal) • Forecasts are posted on the web each month • The 1 December forecast is used to determine the 31 December draft requirement

  6. LIBBY DAM – THE BASICS • Flood control requirement based on seasonal volume forecasts (Apr-Aug) • Provides local and system flood control • Max. flood control draft = 4.98 MAF (El. 2287 ft.) • Fixed end-of-December draft = 2.0 MAF (El. 2411 ft.) • Full pool is El. 2459 ft.

  7. LIBBY DAM – THE BASICS 2.0 MAF El. 2411 ft. 2.98 MAF El. 2287 ft. DEAD STORAGE

  8. STEP 1:DETERMINE MAXIMUM RELAXATION AMOUNT • Fixed end-of-Dec draft is 2.0 MAF • To relax the 2.0 MAF requirement, must consider: • Maximum water volume that must come out of Libby Dam • Maximum water volume that can come out of Libby Dam

  9. 2.0 MAF El. 2411 ft. 2.98 MAF JAN-MAR INFLOW VOLUME El. 2287 ft. DEAD STORAGE WHAT IS THE MAXIMUM VOLUME OF WATER THAT WOULD HAVE TO COME OUT OF LIBBY?

  10. WHAT IS THE MAXIMUM VOLUME OF WATER THAT WOULD HAVE TO COME OUT OF LIBBY? 2.0 MAF El. 2411 ft. 2.98 MAF JAN-MAR INFLOW VOLUME El. 2287 ft. DEAD STORAGE MAXIMUM VOLUMEOF WATER THATWOULD HAVE TOCOME OUT OF LIBBY 2.98 MAF JAN-MAR INFLOW VOLUME

  11. WHAT IS THE MAXIMUM VOLUME OF WATER THAT COULD COME OUT OF LIBBY? WITH ALL 5 GENERATING UNITS RUNNING, LIBBY HAS A POWERHOUSE CAPACITY OF ABOUT 25,000 CFS.

  12. WHAT IS THE MAXIMUM VOLUME OF WATER THAT COULD COME OUT OF LIBBY? MAXIMUM VOLUMEOF WATERTHAT COULDCOME OUT OF LIBBY X 25,000 CFS 3 months

  13. MAXIMUM ALLOWABLE RELAXATION VOLUME MAXIMUMRELAXATIONVOLUME MAXIMUM VOLUMEOF WATERTHAT COULDCOME OUT OF LIBBY MAXIMUM VOLUMEOF WATER THATWOULD HAVE TOCOME OUT OF LIBBY

  14. X 3 months 25,000 CFS JAN-MAR INFLOW VOLUME 2.98 MAF MAXIMUM ALLOWABLE RELAXATION VOLUME MAXIMUMRELAXATIONVOLUME MAXIMUM VOLUMEOF WATERTHAT COULDCOME OUT OF LIBBY MAXIMUM VOLUMEOF WATER THATWOULD HAVE TOCOME OUT OF LIBBY

  15. Average permissible relaxation (all years considered) = 500 KAF BUT, IF WE EXCLUDE THE HIGHER WATER YEARS (runoff > 6 MAF) Permissible relaxation becomes 600 KAF MAXIMUM ALLOWABLE RELAXATION AMOUNT

  16. VARIABLE DRAFT 1.4 MAF El. 2426.7 ft. 0.6 MAF El. 2411 ft. 2.98 MAF El. 2287 ft. DEAD STORAGE STEP 1:MAXIMUM RELAXATION AMOUNT = 600 KAF FIXED DRAFT 2.0 MAF El. 2411 ft. 2.98 MAF El. 2287 ft. DEAD STORAGE

  17. STEP 2:MODELING TO TEST RELAXATION STEP 2A: MODELING TO TEST 600 KAF RELAXATION WITH STANDARD FLOOD CONTROL STEP 2B: MODELING TO TEST 600 KAF RELAXATION WITH VARQ FLOOD CONTROL

  18. STEP 2A: TEST 600 KAF RELAXATION WITH STANDARD FLOOD CONTROL • Relaxation tested for water year with the LOWEST 1 December forecast: 1953 1953 has 1 December forecast of 4410 KAF (forecast is 71% of normal).

  19. RESERVOIR REGULATION SIMULATION SHOWS RELAXATION WITH STANDARD FC INCREASES TRAPPED STORAGE SIMULATED ELEVATION RULE CURVE OUTFLOW INFLOW

  20. RESERVOIR REGULATION SIMULATION SHOWS RELAXATION WITH STANDARD FC INCREASES TRAPPED STORAGE SIMULATED ELEVATION LIBBY CAN’T RELEASE ENOUGH WATER TO MEET FC BECAUSE OF KOOTENAY LAKE. LIBBY HAS TRAPPED STORAGE RULE CURVE INFLOW

  21. STEP 2B: TEST 600 KAF RELAXATION WITH VARQ FLOOD CONTROL • Relaxation tested for water years in order of increasing 1 December forecast: 1953, 1988, 2001, 1977, 1994, 1980, 1973, 1970, 1979, 1955, 1993, 1992, 1983, 1957 • Stopped testing when flood control violation occurred in water year 1954

  22. 600 KAF RELAXATION WITH VARQ FLOOD CONTROL • AUTOREG simulations show relaxation acceptable in: 1953, 1988, 2001, 1977, 1994, 1980, 1973, 1970, 1979, 1955, 1993, 1992, 1983, 1957 • This is 25% of all years – there is a 1 in 4 chance that any given year will have a relaxed end-of December draft requirement. • Examination of results reveals that full 600 KAF relaxation is not needed in all these years.

  23. 600 KAF RELAXATION WITH VARQ FLOOD CONTROL • AUTOREG simulations show relaxation acceptable in: 1953, 1988, 2001, 1977, 1994, 1980, 1973, 1970, 1979, 1955, 1993, 1992, 1983, 1957 • This is 25% of all years – there is a 1 in 4 chance that any given year will have a relaxed end-of December draft requirement. • Examination of results reveals that full 600 KAF relaxation is not needed in all these years. What does this mean?

  24. El. 2411 ft. on 31 Dec During Jan, Libby releases minimum flow and is still below the end-of-Jan FC target. El. 2426.7 ft. on 31 Dec During Jan, Libby releases 11 kcfs to meet the end-of-Jan FC target. The end-of-Jan FC target governs. CONSIDER 1955 SIMULATIONS

  25. CONSIDER 1955 SIMULATIONS El. 2411 ft. on 31 Dec During Jan, Libby releases minimum flow and is still below the end-of-Jan FC target. El. 2426.7 ft. on 31 Dec During Jan, Libby releases 11 kcfs to meet the end-of-Jan FC target. The end-of-Jan FC target governs.

  26. 600 KAF RELAXATION WITH VARQ FLOOD CONTROL • Conclusion: • Relax 600 KAF if forecast < 5500 KAF • No relaxation if forecast > 5900 KAF • Between 5500 & 5900 KAF, interpolate

  27. STEP 2:MODELING TO TEST RELAXATION • No relaxation permitted with STANDARD flood control • With VARQ flood control, relax as follows: Relax 600 KAF if forecast < 5500 KAF (88% of normal) No relaxation if forecast > 5900 KAF (94% of normal) Between 5500 & 5900 KAF, interpolate

  28. IMPACT OF RELAXATION ON RESERVOIR STORAGE

  29. SUMMARY • Can relax the 31 December flood control draft requirement (with VARQ) as follows: Relax 600 KAF if forecast < 5500 KAF (88% of normal) No relaxation if forecast > 5900 KAF (94% of normal) Between 5500 & 5900 KAF, interpolate • This means the draft requirement will be relaxed in about 25% of all years. • This relaxation increases the probability of storage in the spring during less than average water years.

  30. THE END

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