Yellowtail Dam & Bighorn Lake 2010 Operation Review

Billings, MTJanuary 2011

RECLAMATIONManaging Water in the West

2010 Bighorn Lake OperationsUsing the Draft Criteria

“A Yo Yo Year”

November – March Period

Nov-Mar parameters used for calculating release rate

April-Oct. gain = 265,000 AF

End of Oct. storage = 1,064,000 AF (Elev. 3639.5)

Boysen planned release = 900 CFS

Buffalo Bill planned release = 360 CFS

Based on above Nov-Mar Release set at 2750 cfs

      Bighorn River Release Rate      

        NOVEMBER - MARCH      

A B C D E F G H I

ENTER CALCULATED ENTER ENTER ENTER Initial CALCULTED CALCULATED TARGET ELEV

Bighorn Lake Nov-Mar Bighorn Lake Buffalo Bill Boysen Res 31-Mar Release to River Release 31-Mar

Apr-Oct Gain Forecasted Gain Oct. 31 Storage Planned Nov-Mar Planned Nov-Mar Stor Target Afterbay From Afterbay Reservoir

acre-feet acre-feet acre-feet Release Avg cfs Release Avg cfs acre-feet cfs cfs Target Elevation

                 

265,000 247,339 1,064,000 360 900 858,442 2705 2775 3620.6

      3639.5            

    Sample Data     Water Year

-183,920   799,574 200 500 2007

37,096   991,906 150 400 2008

237,341   1,060,300 372 700 2009

265,425   1,063,770 368 900 2010

DIRECTIONS: Enter appropriate data under A, C , D, and E (Yellow Cells A10, C10, D10 and E10).

RIVER RELEASE: The release to the river for November - March. is calculated under H (cell H10)

TARGET ELEVATION: The March 31 taget elevation is shown under I (cell I10)

Forecasted Nov. – Mar. Inflow

acre-feet

Forecasted Actual Forecast % of Actual

2010 625,900 646,500 97%

2009 560,600 580,500 97%

• 382,600 382,571 100%

February– March Period“Down It Goes”

February 1 Apr-Jul Forecast 634,200 AF 57%

March 1 Apr-July Forecast 591,000 AF 53%

Minimum Forecast for Rule curve 719,000 AF 64%Under minimum rule curve a release of 2,000 cfs is needed

Apr-July Rule Curve Analysis“Up She Goes”

• Apr 1 April-July Inflow Forecast 625,000 AF 56%

• Apr 15 April-July Inflow Forecast 730,000 AF 65%

• Based on the April 15 Forecast being greater than 719,000 AF a rule curve was prepared

Spring Runoff Forecasts April-July Inflow % of

Date Forecast (ac-ft) Average

Feb. 1 634,000 57%Mar. 1 591,000 53%Apr. 1 625,000 56%Apr. 15 730,000 65%May 1 900,400 81%May 15 1,121,400 101%June 1 1,263,300 113%

Actual 1,504,354 135%

August-October Period“and Down Again”

• Inflows dropped sharply during the 2nd haft of July and continued to drop and remain low through the end of October.

Since most of the snow occurred in the spring it melted rapidly reducing snowpack to supply late summer flows.

August –October were unusually dry and warm reducing runoff and increasing irrigation depletions.

August –October gains to Bighorn Lake were -53,000 AF compared to an average of 35,800 AF, 88,800 AF less than average.

August-October Gains

• Actual 2010 Aug-Oct Gains = -53,000 AF

• Average Aug-Oct Gains = 35,800 AF

• Difference = 88,800 AF

• In CFS this difference is 490 CFS

• Lowest Gains of Record

November – March 2011

Nov-Mar Parameters used for calculating Release Rate

2011 2010April-Oct. Gain = 201,000 AF 265,000 AF

End of Oct. Storage = 938,000 AF 1,064,000 AF

Boysen Planned Release 800 CFS 900 CFS

Buffalo Bill Planned Release 355 CFS 360 CFS

Nov-Mar Release 2,370 CFS 2,750 CFS

QUESTIONS & COMMENTS

March 31 Target Elevation

• Target elevation determined on November 1 prior to accumulation of snowpack in the mountains.

• Target elevation is set at a level that will handle both high and low spring runoff

• Reservoir level is adjusted by March 31 based on forecasts to deal with expected runoff. Reservoir allowed to gradually fill with average to below average forecasts and to be further drafted with above average forecasts

Target Elev. 3620 Compared to 3610

Lake Elevation Storage af

3620 873,600 af3610 803,200 af

Diff. 10 70,400 af

3645.2 1,140,399 af3640.0 1,070,029 af

Diff. 5.2 70,370 af

QUESTIONS

PEAK BIGHORN RIVER DISCHARGE

Year Actual Peak Est. With Rule Curve

1995 14,000 CFS 12,000 CFS

1997 11,000 CFS 12,000 CFS

1999 10,000 CFS 12,000 CFS

2009 12,500 CFS 11,000 CFS

PEAK BIGHORN LAKE ELEVATION

Year Actual Est. With Peak Rule Curve Difference

1995 3646.3 3645.6 -0.7

1997 3651.7 3643.9 -7.81999 3649.3 3641.5 -7.8

2009 3647.9 3645.5 -2.4

PROPOSED RESERVOIR TARGETS

Date Existing Proposed Difference _______ Targets Targets (feet)

Oct 31 3635 3638-40 +3-5 ft

Nov 30 3630 Eliminated +5-7 ft Mar 31 3605-14 3617-21 +7-13 ft

July 31 3640 3640 Same

Nov.-Mar. Operations

• Bighorn River release rate - 2775 cfs

• River discharge 275 cfs above 2500 cfs

• March 31 Bighorn Lake target level – 3620.6 feet

• Current Lake Level – 36??

2010 Forecasted Rule Curve

QUESTIONS & COMMENTS