Oldman River Basin - Water Supply Forecasts

Below-average to much-below-average natural runoff volumes are forecast for the March to September 2002 period in the Oldman River basin (Table 3). Current forecasts range from 66 to 82 % of average. Current forecasted values for the March to September period for the Oldman River at Lethbridge would rank seventeenth lowest in 84-years of record (1912-95). The March 1 forecasts are 2 to 3 % higher than last month's forecast as a result of a snowstorm in the latter part of February, which resulted in above-normal precipitation being recorded during the month. Current runoff volume forecasts for this year are 12 to 27% higher than recorded runoff volumes last summer.

Despite near average snow accumulations at the higher elevations, below-average to much-below-average runoff is forecast for the March to September period because of the lack of snow below 6000 feet. The foothills area of the southern tributaries (Waterton, Belly and St. Mary) did receive significant snowfall in February, however remain below-average for the most part. Given the low soil moisture conditions, most of the snowmelt from the foothills is not expected to runoff. This year, the March to September water supply forecasts are heavily dependent on rainfall during the spring and early summer (May and June) months. Water supply from the higher elevations, given the current snow accumulations, is assured. If above-normal precipitation occurs at the lower elevations, the forecast water supply will improve dramatically.