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

Released On: May 09, 2003

Reclamation Announces May Water Supply Forecast for Yakima Basin
The May 2003 forecast of the Yakima Basin water supply, based on snowpack and precipitation data available on the first of May, indicates a slight shortfall to the proratable water rights holders for the coming irrigation season.

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

With 50% normal subsequent conditions 2.28 million acre-ft With 100% normal subsequent conditions 2.44 million acre-ft (most likely) With 150% normal subsequent conditions 2.60 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 May 1 (based on the forecast) for the respective subsequent precipitation levels:

50% normal subsequent conditions 88% proratable supply 100% normal subsequent conditions 98% proratable supply 150% normal subsequent conditions 100% proratable supply

Non-proratable water rights 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 May 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 865,908 ac-ft (81% of capacity, 104% of average) as of May 9, 2003:

Reservoir Content acre-feet) Total Capacity Percent of Capacity Keechelus 92,180 157,800 58 Kachess 200,729 239,000 84 Cle Elum 324,754 436,900 74 Bumping 30,244 33,700 90 Rimrock 191,360 198,000 97 Totals 839,267 1,065,400 79

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

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