Bow River Basin - Water Supply Forecasts

Recorded March to September 2008 natural runoff volumes in the Bow River basin varied from above average to much above average at all locations except the Bow River at Banff, where it was 13th lowest in 91 years of record (1912 to 2001 data). Mountain snowpack upstream of Banff was below normal this year and the major storms in May and June that created large runoff volumes in other areas of the Bow River basin did not reach into the back mountain ranges upstream of Banff. Due mainly to these two storms, natural runoff volumes into the Cascade Reservoir and in the Elbow River at Bragg Creek and Highwood River at the mouth were 11th, 12th and 20th highest in 91 years of record, respectively. Natural runoff volumes were above average this year for the Spray Reservoir, Kananaskis River, and Bow River at Calgary, between 105% and 107% of average (Table 1).

The six monthly (February to August, excluding June) forecasts of March through September 2008 natural volumes produced for the Bow River basin were within 16.4% of recorded values, on average. No forecasts were produced in June this year due to flood events. Large amounts of runoff in several basins in May and June resulted in forecasts issued beforehand (February through May) being too low.

Natural runoff volumes measured during the month of September were below average at Banff, average for the Kananaskis and Highwood Rivers, above average for the Elbow River, Spray Lake and Calgary, and much above average for the Cascade Reservoir. (Table 1).

Bow River at Banff

The March to September 2008 recorded natural volume for the Bow River at Banff was much-below-average at 907,800 dam³ or 85% of average and ranks 13th lowest on record (based on the 1912-2001 data) (Table 1).

Six monthly (February to August, excluding June) natural volume forecasts were produced for Banff for the March to September period. The monthly forecast accuracies ranged from 0.1% to 6.6%, for an overall average of 4.1%. The recorded volume was within the probable forecast range and greater than the reasonable minimum forecast for all six forecasts.

Lake Minnewanka (Cascade Reservoir) Inflow

The March to September 2008 recorded natural volume for the inflow to Lake Minnewanka was much above average at 233,300 dam³ or 136% of average and ranks 81st lowest (11th highest) in 91 years of record (1912-2001 data) (Table 1).

Six monthly (February to August, excluding June) natural volume forecasts were produced for Lake Minnewanka for the March to September period. Volumes were underestimated in the first four forecasts, indeed the upper quartile forecasts were exceeded, as major storms in May and June radically increased runoff volumes. The recorded volume was within the probable range and greater than the reasonable minimum for the July and August forecasts.

Forecasts ranged within 31.4% to 36.1% of the recorded volumes for the first four monthly forecasts, and 0.0% to 2.2% for July and August's forecasts. The forecasts were on average, within 23.2% of the recorded March to September volume.

Spray Reservoir near Banff

The March to September 2008 recorded natural inflow volume for the Spray Reservoir near Banff was above average at 393,000 dam³ or 107% of average and ranks 61st lowest on record (based on the 1912-2001 data) (Table 1).

Six monthly (February to August, excluding June) natural volume forecasts were produced for the Spray Reservoir for the March to September period. The monthly forecast accuracies ranged from 2.9% to 12.4%, for an overall average of 8.3%. The recorded volume was within the probable forecast range and greater than the reasonable minimum forecast for all six forecasts.

Kananaskis River at Barrier Lake Reservoir

The March to September 2008 recorded natural volume for the Kananaskis River was above average at 436,900 dam³ or 107% of average and ranks 56th lowest on record (based on the 1912-2001 data) (Table 1).

Six monthly (February to August, excluding June) natural volume forecasts were produced for the Kananaskis River for the March to September period. The monthly forecast accuracies ranged from 1.4% to 11.4%, for an overall average of 7.3%. The recorded volume was within the probable forecast range and greater than the reasonable minimum forecast for all six forecasts.

Bow River at Calgary

The March to September 2008 recorded natural volume for the Bow River at Calgary was above average at 2,545,300 dam³ or 105% of average and ranks 60th lowest on record (based on the 1912-2001 data) (Table 1).

Six monthly (February to August, excluding June) natural volume forecasts were produced for Calgary for the March to September period. The monthly forecast accuracies ranged from 8.4% to 15.0%, for an overall average of 12.0%. The recorded volume was within the probable forecast range for all six forecasts and greater than the reasonable minimum forecast for all but August's forecast.

Elbow River at Bragg Creek

The March to September 2008 recorded natural volume for the Elbow River at Bragg Creek was much above average at 302,300 dam³ or 139% of average and ranks 80th lowest (12th highest) on record (based on the 1912-2001 data) (Table 1).

Six monthly (February to August, excluding June) natural volume forecasts were produced for the Elbow River at Bragg Creek for the March to September period. Volumes were underestimated in the first four forecasts, as the upper quartile forecasts were exceeded, due to major storms in May and June that radically increased runoff volumes. The recorded volume was within the probable range and greater than the reasonable minimum for the July and August forecasts.

Forecasts ranged within 43.9% to 44.9% of the recorded volumes for the first four monthly forecasts, and 0.2% to 0.8% for July and August's forecasts. The forecasts were on average, within 29.8% of the recorded March to September volume.

Highwood River

The March to September 2008 recorded natural volume for the Highwood River was above to much above average at 802,000 dam³ or 128% of average and ranks 72nd lowest (20th highest) on record (based on the 1912-2001 data) (Table 1).

Six monthly (February to August, excluding June) natural volume forecasts were produced for the Highwood River for the March to September period. Volumes were underestimated in the first four forecasts due to major storms in May and June that radically increased runoff volumes, especially in April and May as the upper quartile forecasts were exceeded these two months. July and August forecasts were high, as the recorded volume was less than the lower quartile forecast, and less than August's minimum forecast.

Forecasts ranged within 36.8% to 47.7% of the recorded volumes for the first four monthly forecasts, and 8.5% to 5.3% for July and August's forecasts. The forecasts were on average, within 30.0% of the recorded March to September volume.