North Saskatchewan River Basin - Water Supply Forecasts

Recorded March to September 2008 natural runoff volume in the North Saskatchewan River basin was average at Lake Abraham, above average at the Brazeau Reservoir and average to above average at Edmonton. Natural volume forecasts produced for the North Saskatchewan River basin were within 11.4% of recorded values, on average (Table 1).

Volumes at the Bighorn Reservoir were lower than the other areas of the basin since mountain snowpack was normal this year and the major storms in May and June did not reach into the back mountain ranges. These two storms affected other areas of the North Saskatchewan River basin such as the middle Brazeau River, Clearwater and Ram Rivers, which resulted in the higher volumes into the Brazeau Reservoir and at Edmonton.

The six monthly (February to August, excluding June) forecasts of March through September 2008 natural volumes produced for the North Saskatchewan River basin were within 11.4% of recorded values, on average. No forecasts were produced in June this year due to flood events. Large amounts of runoff in several sub-basins of the Brazeau Reservoir and Edmonton in May and June resulted in some forecasts issued beforehand (April, May) being too low for these areas. July forecasts were also low for all three basins and August forecasts were high.

Natural runoff volumes measured during the month of September were below average at the Bighorn and Brazeau Reservoirs, and much below average at Edmonton, ninth lowest in 85 years of record (Table 1).

North Saskatchewan River at Bighorn Dam (Lake Abraham)

The March to September 2008 recorded natural volume for the North Saskatchewan River at Bighorn Dam was average at 2,119,200 dam³ or 98% of average and ranks 14th lowest in thirty years of record (1973-2001 data) (Table 1).

Six monthly (February to August, excluding June) natural volume forecasts were produced for the Bighorn Reservoir for the March to September period. The monthly forecast accuracies ranged from 3.3% to 7.3%, for an overall average of 5.3%. Volume was underestimated in July, as the recorded volume was greater than the upper quartile forecast. In August, volume was overestimated, as measured March - September natural volume ended up tracking lower than the lower quartile forecast.

Brazeau River at Brazeau Dam

The March to September 2008 recorded natural volume for Brazeau Reservoir inflow was above average at 1,513,000 dam³ or 106% of average and ranks 23rd lowest in 41 years of record (1962-2001 data) (Table 1).

Six monthly (February to August, excluding June) natural volume forecasts were produced for the Brazeau Reservoir for the March to September period. The monthly forecast accuracies ranged from 12.4% to 17.4%, for an overall average of 15.5%. Volume was underestimated in May and July, as the recorded volume was greater than the upper quartile forecast. In August, volume was overestimated, as measured March - September natural volume ended up lower than both the lower quartile and minimum forecasts. North Saskatchewan River at Edmonton

The March to September 2008 recorded natural volume for the North Saskatchewan River at Edmonton was average to above average at 5,965,000 dam³ or 102% of average and ranks 52nd lowest in 91 years of record (1912-2001 data) (Table 1).

Six monthly (February to August, excluding June) natural volume forecasts were produced for Edmonton for the March to September period. Forecasts ranged within 16.2% to 18.8% of the recorded volumes for the first four monthly forecasts, and 2.7% to 8.7% for July and August's forecasts. The forecasts were on average, within 13.3% of the recorded March to September volume. Volume was underestimated in April, May and July, as the recorded volume was greater than the upper quartile forecast. In August, volume was overestimated, as measured March - September natural volume ended up tracking lower than the lower quartile forecast.