Oldman River Basin - Water Supply Forecasts

After receiving near record precipitation this spring, much-above-average natural runoff volumes are forecast for the March to September 2002 period in the Oldman River basin (Table 3a). A major precipitation event in early June has resulted in significant changes to the water supply forecast. The July 1 forecasts are 45 to 64 % higher than last month's forecast due to a major storm in June, which resulted in very high streamflows during the month. In contrast to the previous three consecutive years of low volumes, this year's current forecasted values for the March to September period for the Oldman River at Lethbridge would rank eighth highest in 84-years of record (1912-95). Current runoff volume forecasts in the basin for this year are two to three times greater than the recorded volumes last summer.

Preliminary data indicate that the major storm in early June has resulted in record or near record volumes during the first four months of the forecast period (March-June 2002). The March-June 2002 recorded volumes range from 145 to 159 % of average in the basin. The recorded March-June 2002 volumes rank in the top seven volumes on record (compared to the 1912-95 data) for the forecast locations in the basin. The Belly River near Mountain View set a new record volume for the March-June period this year. Volumes thus far are greater than the recorded volumes in 1995 during the same period for the Belly River, St. Mary River and the Oldman River at Lethbridge locations. The March-June 2002 recorded volumes on the Waterton River and the Oldman River near Brocket are slightly less than those recorded during the same period in 1995. The remaining volume forecast, which is the March to September 2002 forecast minus the recorded volume to date, is available in Table 3b.