Water Supply Outlook for Alberta

May 2006

Oldman River Basin - Water Supply Forecasts

As of May 1, 2006, natural runoff volumes for the March to September 2006 period are forecast to be average for the Oldman and Waterton Rivers, while Lethbridge and the Belly and St. Mary Rivers are forecast to be below average to average (Table 4a). Current forecasted values for the March to September 2006 period for the Oldman River at Lethbridge would rank 44th lowest in 91-years of record (1912-2001). Current natural runoff volume forecasts range from 88 to 98% of average. In comparison to April 1 forecasts, this represents a decrease of 1 to 3% of average in the Waterton and St. Mary Rivers and at Lethbridge, and an increase of 1 to 2% in the Belly River and Oldman River at Brocket. The March to September 2006 forecast volumes are 6 to 15% higher than those recorded during the same period last year for the Belly, Waterton and St. Mary Rivers, and 17 to 34% lower than last year at Lethbridge and Brocket, where flooding was more prevalent.

The first two months of the forecast period have been completed, with March-April 2006 recorded natural runoff volumes ranging from 102 to 126% of average. Runoff was above average in the Oldman River at Brocket and Lethbridge and in the Belly River, and average in the Waterton and St.Mary Rivers. Recorded volume data is preliminary, and is subject to change. The remaining volume forecast, which is the March to September 2006 forecast minus the recorded volume to date, is available in Table 4b.

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