Oldman River Basin - Water Supply Forecasts

As of June 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 92 to 99% of average. In comparison to May 1 forecasts, this represents an increase of 1 to 2% of average in the Waterton and St. Mary Rivers, and a decrease of 2% in the Belly River and Oldman River at Brocket, which results in no change for Lethbridge. The March to September 2006 forecast volumes are 4 to 16% higher than those recorded during the same period last year for the Belly, Waterton and St. Mary Rivers, and 14 to 36% lower than last year at Lethbridge and Brocket, where flooding was more prevalent.

The first three months of the forecast period have been completed, with March-May 2006 recorded natural runoff volumes ranging from 95 to 106% of average. Runoff was above average in the Waterton River, and average in the Oldman, Belly 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. Below average to average natural runoff volumes are forecast for the June - September period for Lethbridge and the Belly and St. Mary Rivers, and average natural runoff volumes are expected for the Waterton River and the Oldman River near Brocket.