Oldman River Basin - Water Supply Forecasts

As of April 1, 2006, natural runoff volumes for the March to September 2006 period are forecast to be average for the Oldman, Waterton and St. Mary Rivers, while the Belly River is 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 94 to 100% of average. In comparison to March 1 forecasts, this represents an increase of 0 to 3% of average in the Oldman, Waterton and St. Mary Rivers and at Lethbridge, and a decrease of 2% in the Belly River. The March to September 2006 forecast volumes are 4 to 18% higher than those recorded during the same period last year for the Belly, Waterton and St. Mary Rivers, and 12 to 35% lower than last year at Lethbridge and Brocket, where flooding was more prevalent.

Despite generally above average snowpack in the mountains and wet soil conditions due to heavy summer and fall precipitation last year, below average snowpack at lower elevations has resulted in the runoff forecasts being only average.

The first month of the forecast period has been completed, with March 2006 recorded natural runoff volumes ranging from 72 to 120% of average. Runoff was above average in the Oldman River at Brocket and Lethbridge, average to above average in the Belly River, average in the Waterton River, and below average to average in the St.Mary River. Recorded volume data is preliminary, due to ice effects, and is subject to change. March volumes typically comprise a small portion of the March to September total. The remaining volume forecast, which is the March to September 2006 forecast minus the recorded volume to date, is available in Table 4b.