Yellowtail Dam & Bighorn Lake Water Supply & Operations Meeting Billings, Montana October 9, 2008 RECLAMATION Managing Water in the West

Purpose of Meeting  Public outreach / education regarding Yellowtail Dam & Bighorn Lake  Recap operations during water year 2008  Present operation scenarios for fall / winter  Obtain feedback / comment from public & interested parties

Meeting Agenda 6:00 pmDoors open 6:30 pm Introductions, Welcome, and Meeting Objectives 6:40 pmRecap of Water Year :15 pmFall & Winter Reservoir Operation Scenarios 8:00 pmFacilitated Public Discussion 8:30 pm Adjourn

The Montana Area Office is responsible for managing the water supplies and administering Reclamation programs for Reclamation projects located in Montana east of the continental divide.

The Montana Area Office monitors hydrologic and climatic conditions, prepares inflow projections and operation plans, and directs water releases and lake level management at Yellowtail Dam & Bighorn Lake.

Yellowtail Dam, Bighorn Lake and Afterbay

Yellowtail Dam and Bighorn Lake Visitor Center Powerplant Bighorn Lake Spillway Inlet

Yellowtail Dam, Bighorn Lake and Afterbay Visitor Center Yellowtail Dam Substation Yellowtail Afterbay Dam

Yellowtail Afterbay Dam and Afterbay Bighorn Canal Radial Gates Sluice Gates Afterbay Dam Afterbay Sewage Lagoons

Bighorn Lake Annual Inflow Distribution (based on data) Bighorn Gain 30% Buffalo Bill Release 28% Boysen Release 42%

OPERATIONS - Balancing the needs of the competing interests

Mountain Snowpack Precipitation Inflow to Bighorn Lake Bighorn River Releases Bighorn Lake Storage Conditions Recap of Water Year 2008

Peaked on 110% of average

Recap of Water Year Annual Inflow = 2,132.7 kaf (90% of average) Historic Average Inflow = 2,372.7 kaf

Recap of Water Year April-July Inflow = 1,298.3 kaf (117% of average) Historic Average Inflow = 1,192.8 kaf

Recap of Water Year 2008

April-July Inflow – 1,298.3 kaf (117% of average) Annual Inflow – 2,132.7 kaf (90% of average) Oct-March Inflow – kaf (57% of average) 10/07 Oct-Mar Forecast – kaf (54% of average)

Recap of Water Year 2008 Average River Release = 2,728 cfs (87% of average) Average River Release = 1,922 cfs Historic Average River Release = 3,135 cfs

Recap of Water Year 2008

Peaked on 7/13 at feet Ended year at 0.2 feet below full pool Ended year 10.3 feet higher than in 2007

Summary of Water Year 2008 Water year started out with good precipitation – October well above average but dropped to well below average during November. Fall & winter releases were scheduled and maintained at 1,900 cfs. Mountain precipitation above average during December-March. Precipitation dropped to below average in April but well above average in May. October-March inflows were 57% of average totaling kaf. April-July inflows were 117% of average totaling 1,298.3 kaf. On May 6 releases were reduced to 1,500 cfs to conserve storage. Bighorn Lake reached a low level at elevation on May 8. Bighorn Lake rose nearly 35 feet from May 8 to June 13, reaching a peak elevation of Record rains began around May 21 and continued into early June. The rain accompanying the mountain snowmelt caused inflows to reach a peak of 14,130 cfs on May 24. On May 24 releases were gradually increased from 1,500 cfs to nearly 9,700 cfs by June 18. By the middle of July, releases were reduced from 6,200 cfs to 3,000 cfs and to 2,500 cfs by August 1. Releases are currently 2,700 cfs. Since June 13, storage has slowly declined to elevation 3640 by August 12 and has essentially remained full until present. Annual inflows were 90% of average totaling 2,132.7 kaf. Storage in Bighorn Lake ended the water year at elevation which is 0.2 foot below full.

Bighorn Lake Conditions (as of October 1, 2008) Elevation ft = 0.18 feet below full pool Storage 1,067,800 af = 100% full Inflows = 2,550 cfs Total Outflow = 2,700 cfs River = 2,700 cfs Canal = 0 cfs

Boysen Reservoir Conditions (as of October 1, 2008) Elevation ft = 6.12 feet below full pool Storage 628,800 af = 85% full Inflows = 550 cfs Total Outflow = 700 cfs

Buffalo Bill Reservoir Conditions (as of October 1, 2008) Elevation ft = feet below full pool Storage 484,400 af = 75% full Inflows = 275 cfs Total Outflow = 1,740 cfs River = 1,290 cfs Heart Mtn. Canal = 450

Water Supply Forecasts Fall forecasts rely heavily upon statistical information and analysis Reclamation monitors snow pack data each month from mid-October through May By about February 1 snow pack becomes a major factor Monthly plans are adjusted as needed based on snow data & anticipated normal spring precipitation Significant changes to operation plans may be needed

Bighorn Lake Inflow Forecast – Water Year 2009

10/08 Oct-Mar Forecast – kaf (74% of average) Bighorn Lake Inflow Forecast – Water Year 2009

10/08 Oct-Mar Forecast – kaf (74% of average) 2008 Actual Oct-Mar Inflows – kaf (57% of average)

Bighorn Lake Operation Scenarios

Most Probable Inflow October – March Inflow forecast at kaf (74% of average) Maintain fall and winter release at 2,500 cfs through March Reservoir level expected to drop to elevation 3618 by the end of March (typical flood control target is 3605 to 3614). Power generation during October – March would total GWHrs.

Most Probable Inflow & 2500 cfs Release

Bighorn Lake Operation Scenarios Minimum Probable Inflow October – March Inflow forecast at kaf (69% of average) Maintain fall and winter release at 2,500 cfs through March Reservoir level expected to drop to elevation 3613 by the end of March (typical flood control target is 3605 to 3614). Generation during October – March would total GWHrs.

Minimum Probable Inflow & 2500 cfs Release

Most and Minimum Probable Inflow & 2500 cfs Release

Most & Minimum Probable Inflow & 2500 cfs Release

Bighorn Lake Operation Scenarios Maximum Probable Inflow October – March Inflow forecast at kaf (82% of average) Maintain fall and winter release at 2,500 cfs through March Reservoir level expected to drop to elevation 3628 by the end of March (typical flood control target is 3605 to 3614). Generation during October – March would total GWHrs.

Maximum Probable Inflow & 2500 cfs Release

All 3 Probable Inflow Scenarios & 2500 cfs Release

Question: What is the effect of a release rate other than 2500 cfs ? Response: We looked at the most probable runoff condition with release rates of 2400, 2500, and 2600 cfs.

Most Probable Inflow with 3 Release Rates

Discussion & Comments

The information presented at this meeting can be found on the Montana Area Office website at: Please mail comments to: Ms. Paula A. Holwegner Bureau of Reclamation th Avenue North, Suite 501 Billings, MT fax your comments to: or your comments to: by October 13, 2008 Comments ?

Reclamation’s Internet Website near real-time data available through the HYDROMET data system summaries and plots of historical data annual reservoir operating plan publication monthly water supply reports project data snow plots links to related internet sites