North Saskatchewan River Basin - Water Supply Forecasts

Recorded March to September 2004 natural runoff volume in the North Saskatchewan River basin was average at Lake Abraham, below-average to much-below-average at Edmonton, and below-average to average at Brazeau Reservoir (Table 6). Natural volume forecasts produced for the North Saskatchewan River basin were within 9.5% of recorded values, on average.

Going into last winter, the lower elevations and plains areas of the basin were dry. Winter snow accumulations ranged from average in the foothills to much above average in the plains. The snow then melted earlier than usual this spring, producing near-average March runoff in several areas despite dry soils. However, with little snow left in April and May and below normal to normal precipitation during this period, March through May recorded natural runoff volumes were the lowest in 41 years of record at the Brazeau Dam and second lowest in 91 years of record at Edmonton. Summer precipitation was generally normal, resulting in steadily improving, but still low amounts of runoff as the soil wettened. The season ended with much above normal precipitation during August and September, resulting in natural flow volumes that ranged from 115 to 210% of average in September.

In the mountainous Bighorn Reservoir drainage basin, initial conditions were wetter as last year volumes were near average. The snowpack was much below average, but early melt and average precipitation improved March and April volumes to much above average levels, ranking eighth highest in 30 years of record. Summer precipitation was generally normal, until August-September which was much above normal. Runoff for the summer was below average to average, resulting in an overall average runoff year.

North Saskatchewan River at Bighorn Dam (Lake Abraham)

The March to September 2004 recorded natural volume for the North Saskatchewan River at Bighorn Dam was average at 2,173,000 dam³ or 103% of average and ranks 16th lowest on record (based on the 1973-2001 data) (Table 6). This is 5% higher than the volume recorded during the same period last year.

Seven monthly (February to August) natural volume forecasts were produced for Bighorn Dam for the March to September period. Initial forecasts were low due to lack of snow, and remained fairly steady through the summer with the normal precipitation, until being raised in August. As illustrated in Figure 18, the forecasted values (brown triangles) were below the recorded March to September 2004 natural volume at Bighorn Dam (dark blue line) for the first six months, and slightly above during August. The recorded volume was above the forecast probable range for six of seven forecasts (all but the last forecast in August), and greater than the reasonable minimum in all seven forecasts.

Forecasts ranged within 0.1% to 11.3% of the recorded volumes, and were on average within 8.6% of the recorded March to September volume. August's forecast was the most accurate, and three of seven forecasts were within 10% of the recorded value.

Brazeau River at Brazeau Dam

The March to September 2004 recorded natural volume for the Brazeau River at Brazeau Dam was below-average to average at 1,260,000 dam³ or 88% of average and ranks 16th lowest on record (based on the 1962-2001 data) (Table 6). The March to September 2004 recorded volume is 11% higher than the volume recorded over the same time period last year.

Seven monthly (February to August) natural volume forecasts were produced for Brazeau Dam for the March to September period. Initial forecasts were low due to dry antecedent conditions, but increased slowly as the soils wettened. There was an extreme improvement in runoff this year, from the lowest volume on record from March to May, to the tenth highest runoff volume during August-September. Much above normal August-September precipitation resulted in dam inflows which were 118% of average, which raised the year's volume above the forecasts to the upper limit of 117% forecast for this two month period. As illustrated in Figure 19, the forecasted values (brown triangles) were below the recorded March to September 2004 natural volume at Brazeau Dam (dark blue line) for all seven months. The recorded volume was above the forecast probable range for six of seven forecasts (all but the final forecast in August) and greater than the reasonable minimum in all seven forecasts.

Forecasts ranged within 11.8% to 18.1% of the recorded volumes, and were on average within 15.9% of the recorded March to September volume. August's forecast was the most accurate, but none of the seven forecasts were within 10% of the recorded value.

North Saskatchewan River at Edmonton

The March to September 2004 recorded natural volume for the North Saskatchewan River at Edmonton was below to much-below-average at 4,720,000 dam³ or 80% of average and ranks 18th lowest on record (based on the 1912-2001 data) (Table 6). The 2004 recorded volume is 11% lower than the volume recorded over the same time period last year.

Seven monthly (February to August) natural volume forecasts were produced for Edmonton for the March to September period. Initial forecasts were low due to dry antecedent conditions, decreased steadily through spring as precipitation was lacking, then steadied as summer precipitation was normal. Heavy August-September precipitation in the basin raised the year's volume back toward the initial forecasts issued in February and March. As illustrated in Figure 20, the forecasted values (brown triangles) were above the recorded March to September 2004 natural volume at Edmonton (dark blue line) for the first two months and below during April-August. The recorded volume was within the probable range and greater than the reasonable minimum for all seven forecasts.

Forecasts ranged within 0.2% to 5.9% of the recorded volumes, and were on average within 4.1% of the recorded March to September volume. March's forecast was the most accurate, with three of the seven forecasts (February, March, and July) within 5% of the recorded value.