31 DECEMBER VARIABLE FLOOD CONTROL 31 DECEMBER VARIABLE FLOOD CONTROL DRAFT FOR LIBBY RESERVOIRDRAFT FOR LIBBY RESERVOIR

U.S. Army Corps of Engineers

Northwestern Division, North Pacific Region

HISTORICAL OVERVIEWHISTORICAL 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

NMFS 2000 BiOp on FCRPSNMFS 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”

USFWS 2000 BiOp on FCRPSUSFWS 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. ”

REVISED FORECAST REVISED FORECAST PROCEDUREPROCEDURE

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

LIBBY DAM – THE BASICSLIBBY DAM – THE BASICS

Flood control requirement based on seasonal volume forecasts (Apr-Aug)

Provides local and system flood controlMax. 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.

LIBBY DAM – THE BASICSLIBBY DAM – THE BASICS

El. 2411 ft.

El. 2287 ft.

2.0 MAF

2.98 MAF

DEADSTORAGE

STEP 1:STEP 1:DETERMINE MAXIMUM DETERMINE MAXIMUM RELAXATION AMOUNTRELAXATION AMOUNT

Fixed end-of-Dec draft is 2.0 MAF To relax the 2.0 MAF requirement, must

consider:1. Maximum water volume that must come out

of Libby Dam

2. Maximum water volume that can come out of Libby Dam

WHAT IS THE MAXIMUM VOLUME WHAT IS THE MAXIMUM VOLUME OF WATER THAT WOULD HAVE OF WATER THAT WOULD HAVE

TO COME OUT OF LIBBY?TO COME OUT OF LIBBY?

El. 2411 ft.

El. 2287 ft.

2.0 MAF

2.98 MAF

DEADSTORAGE

JAN-MARINFLOW VOLUME

WHAT IS THE MAXIMUM VOLUME WHAT IS THE MAXIMUM VOLUME OF WATER THAT WOULD HAVE OF WATER THAT WOULD HAVE

TO COME OUT OF LIBBY?TO COME OUT OF LIBBY?

El. 2411 ft.

El. 2287 ft.

2.0 MAF

2.98 MAF

DEADSTORAGE

JAN-MARINFLOW VOLUME

JAN-MARINFLOW VOLUME

2.98 MAF

MAXIMUM VOLUMEMAXIMUM VOLUMEOF WATER THATOF WATER THATWOULD HAVE TOWOULD HAVE TO

COME OUT OF LIBBYCOME OUT OF LIBBY

WHAT IS THE MAXIMUM VOLUME WHAT IS THE MAXIMUM VOLUME OF WATER THAT OF WATER THAT COULDCOULD COME COME

OUT OF LIBBY?OUT OF LIBBY?

WITH ALL 5 GENERATING UNITS RUNNING, LIBBY HAS A POWERHOUSE CAPACITY OF ABOUT 25,000 CFS.

WHAT IS THE MAXIMUM VOLUME WHAT IS THE MAXIMUM VOLUME OF WATER THAT OF WATER THAT COULDCOULD COME COME

OUT OF LIBBY?OUT OF LIBBY?

25,000 CFS X 3 months

MAXIMUM VOLUMEMAXIMUM VOLUMEOF WATEROF WATER

THAT THAT COULDCOULDCOME OUT OF LIBBYCOME OUT OF LIBBY

MAXIMUM ALLOWABLE MAXIMUM ALLOWABLE RELAXATION VOLUMERELAXATION VOLUME

MAXIMUM VOLUMEMAXIMUM VOLUMEOF WATEROF WATER

THAT THAT COULDCOULDCOME OUT OF LIBBYCOME OUT OF LIBBY

MAXIMUM VOLUMEMAXIMUM VOLUMEOF WATER THATOF WATER THATWOULD HAVE TOWOULD HAVE TO

COME OUT OF LIBBYCOME OUT OF LIBBY

MAXIMUMMAXIMUMRELAXATIONRELAXATION

VOLUMEVOLUME

MAXIMUM ALLOWABLE MAXIMUM ALLOWABLE RELAXATION VOLUMERELAXATION VOLUME

MAXIMUM VOLUMEMAXIMUM VOLUMEOF WATEROF WATER

THAT THAT COULDCOULDCOME OUT OF LIBBYCOME OUT OF LIBBY

MAXIMUM VOLUMEMAXIMUM VOLUMEOF WATER THATOF WATER THATWOULD HAVE TOWOULD HAVE TO

COME OUT OF LIBBYCOME OUT OF LIBBY

MAXIMUMMAXIMUMRELAXATIONRELAXATION

VOLUMEVOLUME

3 monthsX25,000 CFS

JAN-MARINFLOW VOLUME

2.98 MAF

MAXIMUM ALLOWABLE MAXIMUM ALLOWABLE RELAXATION AMOUNTRELAXATION AMOUNT

Average permissible relaxation (all years considered) = 500 KAF

BUT, IF WE EXCLUDE THE HIGHER WATER YEARS (runoff > 6 MAF)

Permissible relaxation becomes 600 KAF

STEP 1:STEP 1:MAXIMUM RELAXATION MAXIMUM RELAXATION

AMOUNT = 600 KAFAMOUNT = 600 KAF

DEADSTORAGE

2.98 MAF2.0 MAF

El. 2411 ft.

El. 2287 ft.

FIXEDDRAFT

DEADSTORAGE

2.98 MAF

1.4 MAF El. 2426.7 ft.

El. 2287 ft.

0.6 MAF El. 2411 ft.

VARIABLE DRAFT

STEP 2:STEP 2:MODELING TO TEST MODELING TO TEST

RELAXATIONRELAXATION

STEP 2A: MODELING TO TEST 600 KAF RELAXATION WITH STANDARD FLOOD CONTROL

STEP 2B: MODELING TO TEST 600 KAF RELAXATION WITH VARQ FLOOD CONTROL

STEP 2A:STEP 2A: TEST 600 KAF TEST 600 KAF RELAXATION WITH RELAXATION WITH STANDARDSTANDARD

FLOOD CONTROLFLOOD 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).

RESERVOIR REGULATION SIMULATION RESERVOIR REGULATION SIMULATION SHOWS RELAXATION WITH STANDARD FC SHOWS RELAXATION WITH STANDARD FC

INCREASES TRAPPED STORAGEINCREASES TRAPPED STORAGE

INFLOW

OUTFLOW

SIMULATEDELEVATION

RULECURVE

RESERVOIR REGULATION SIMULATION RESERVOIR REGULATION SIMULATION SHOWS RELAXATION WITH STANDARD FC SHOWS RELAXATION WITH STANDARD FC

INCREASES TRAPPED STORAGEINCREASES TRAPPED STORAGE

INFLOW

SIMULATEDELEVATION

RULECURVE

LIBBY CAN’T RELEASEENOUGH WATER TO MEET FC

BECAUSE OF KOOTENAY LAKE.LIBBY HAS TRAPPED STORAGE

STEP 2B:STEP 2B: TEST 600 KAF TEST 600 KAF RELAXATION WITH RELAXATION WITH VARQVARQ

FLOOD CONTROLFLOOD 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

600 KAF RELAXATION WITH 600 KAF RELAXATION WITH VARQVARQ FLOOD CONTROLFLOOD 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.

600 KAF RELAXATION WITH 600 KAF RELAXATION WITH VARQVARQ FLOOD CONTROLFLOOD 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?

CONSIDER 1955 SIMULATIONSCONSIDER 1955 SIMULATIONS

El. 2411 ft. on 31 DecDuring Jan, Libby releases minimum flow and is still below the end-of-Jan FC target.

During Jan, Libby releases 11 kcfs to meet the end-of-Jan FC target. The end-of-Jan FC target governs.

El. 2426.7 ft. on 31 Dec

CONSIDER 1955 SIMULATIONSCONSIDER 1955 SIMULATIONS

El. 2411 ft. on 31 DecDuring Jan, Libby releases minimum flow and is still below the end-of-Jan FC target.

During Jan, Libby releases 11 kcfs to meet the end-of-Jan FC target. The end-of-Jan FC target governs.

El. 2426.7 ft. on 31 Dec

600 KAF RELAXATION WITH 600 KAF RELAXATION WITH VARQVARQ FLOOD CONTROLFLOOD CONTROL

1 Dec PCREG forecast 1 Dec PCREG forecast (kaf) (% of normal)

1953 4410 70.6 No benefit from relaxation, the 28 Feb FC target governs1988 4786 76.6 Full 600 kaf relaxation is beneficial1977 5026 80.4 Full 600 kaf relaxation is beneficial1994 5289 84.6 Full 600 kaf relaxation is beneficial1980 5323 85.2 Partial relaxation beneficial, then 31 Jan FC target governs1973 5327 85.3 No benefit from relaxation, the 31 Jan FC target governs1970 5526 88.4 Full 600 kaf relaxation is beneficial1979 5676 90.8 Partial relaxation beneficial, then 31 Jan FC target governs1955 5676 90.9 Partial relaxation beneficial, then 31 Jan FC target governs1993 5717 91.5 Partial relaxation beneficial, then 31 Jan FC target governs1992 5869 93.9 Partial relaxation beneficial, then 31 Jan FC target governs1983 5877 94.1 No benefit from relaxation, the 28 Feb FC target governs1957 5882 94.1 No benefit from relaxation, the 15 March FC target governs1966 5931 94.9 No benefit from relaxation, the 28 Feb FC target governs1954 5952 95.3 Increased trapped storage from relaxation

Effectiveness

Conclusion: •Relax 600 KAF if forecast < 5500 KAF•No relaxation if forecast > 5900 KAF •Between 5500 & 5900 KAF, interpolate

STEP 2:STEP 2:MODELING TO TEST MODELING TO TEST

RELAXATIONRELAXATION 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

IMPACT OF RELAXATION IMPACT OF RELAXATION ON RESERVOIR STORAGEON RESERVOIR STORAGE

Additional Water in Libby Dam on 31 March(resulting from relaxation of the 31 December draft requirement)

0

100

200

300

400

500

600

Ad

dit

ion

al w

ater

sto

red

(K

AF

) .

add'l water stored on 31 March (KAF)due to relaxation of the 31 Decemberdraft requirement

0 597 596 597 94 0 561 87 174 277 48 0 0

1953 1988 1977 1994 1980 1973 1970 1979 1955 1993 1992 1983 1957

SUMMARYSUMMARY

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.

THE ENDTHE END