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Pacific Northwest Region
Boise, Idaho
Media Contact:
Kate Puckett
(509) 575-5848 x205

Released On: March 06, 2003

Reclamation Announces March Water Supply Forecast for Yakima Basin
The March 2003 forecast of water supply based on snowpack and precipitation data available on the first of March indicates a indicates a water supply shortage for proratable users for the coming irrigation season.

Converting the April 1st runoff forecast (natural flow) to total water supply available (TWSA) gives the following volumes for the April through September use period:

With 50% normal subsequent conditions 2.1 million acre-ft With 80% normal subsequent conditions 2.29 million acre-ft With 120% normal subsequent conditions 2.7 million acre-ft

Total demand to be placed against this supply for irrigation, regulation, and flows passing Sunnyside Dam averages 2.5 million acre-feet in a normal year.

The total water supply available for irrigation is the sum of natural flow, storage and return flow, less residual storage and flow passing Sunnyside dam.

Though specific proration levels will not be determined until available flows below the reservoirs can no longer fully meet demands, the following percentages of proratable entitlements would occur if pro-rationing were to begin on April 1 (based on the forecast) for the respective subsequent precipitation levels:

50% normal subsequent conditions 53% proratable supply 80% normal subsequent conditions 71 % proratable supply (most likely) 120% normal subsequent conditions 99 % proratable supply

Non-proratable users will be fully supplied with their entitlement demands for all subsequent conditions listed above. Only proratable users will receive a prorated supply.

Prorationing is currently not in effect. However given this range of potential prorationing, irrigation districts and water users are urged to apply their own judgement in deciding which level of supply may be realized. Water demands requiring storage releases, even prior to storage control, may be charged to the users total entitlement.

Subsequent precipitation is only one factor affecting the amount of water supply available. Diversion rates and the timing of the run-off are critical in determining the storage control date, the available water for irrigation, and the resulting pro-rationing levels. The start of prorationing can be delayed and the water supply extended if diversions during the April through June run-off period can be voluntarily limited, as long as possible, to less than or nearly equal the amount of available flows below the reservoirs. This can tend to improve the proration level that is eventually implemented. If warm, dryer weather prompts an early run-off, the situation could worsen. The Bureau of Reclamation will announce the adopted pro-rationing level when it is implemented.

Reservoir content is currently 588,171 ac-ft (55% of capacity, 89% of average) as of March 6, 2003. Storage Conditions as of March 1 were as follows:

Reservoir Content (acre-feet) Total Capacity Percent of Capacity Keechelus 52,918 140,3001 34 Kachess 151,400 239,000 63 Cle Elum 219,161 436,000 50 Bumping 21,167 33,700 63 Rimrock 135,720 198,000 69 Totals 580,366 1,065,400 52

1Keechelus capacity is currently restricted to 140,300 acre-feet. Normal capacity is 157,800 acre-feet.

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