Bow River Basin - Water Supply Forecasts

Recorded March to September 2004 natural runoff volume in the Bow River basin varied widely from above average at the Cascade Reservoir to below to much-below-average at Banff. Recorded natural runoff volumes ranged between 77% and 108% of average, from 20th lowest to 32nd highest on record (1912 to 2001 data) (Table 4). The seven monthly natural volume forecasts produced for the Bow River basin were within 11.9% of recorded values, on average, for the March through September runoff period.

Going into last winter, basin soil moisture was below average after last year ended with August-September volumes ranking among the ten lowest on record, with some being historical lows. Winter snow accumulation was below average, but early melt in March (April in the higher elevations) reulted in average or above average runoff during these months. Above to much above normal summer precipitation steadily improved runoff volumes as soils wettened. By the end of the season, August-September natural runoff volumes ranked between the ninth and fifteenth highest in 91 years of record at all forecast basins except Banff, which recorded below average runoff. For the runoff year (March through September), volumes in 2004 were higher than in 2003, by 3 to 22%.

Bow River at Banff

The March to September 2004 recorded natural volume for the Bow River at Banff was below to much-below-average at 933,000 dam³ or 87% of average and ranks 20th lowest on record (based on the 1912-2001 data) (Table 4). Natural runoff volume this year was 3% higher than last year.

Seven monthly (February to August) natural volume forecasts were produced for Banff for the March to September period. Initial forecasts were low due to the lack of snow accumulation and dry antecedent conditions, and steadily declined as below normal precipitation fell during the April-July period. Precipitation during August-September, after the final forecast was issued, was much above normal, however with dry conditions persisting, only below average runoff was recorded. As illustrated in Figure 9, the recorded March to September 2004 natural volume at Banff (dark blue line) was below the forecasted values (brown triangles) for the first four months, and above for the final three months. The recorded volume was within the probable range and greater than the reasonable minimum for all seven forecasts.

Forecasts ranged within 0.9% to 7.3% of the recorded volume, with May being the most accurate forecast and six of the seven forecasts within five percent of the recorded value. Monthly forecasts were, on average, within 3.1% of the recorded March to September volume.

Lake Minnewanka (Cascade Reservoir) Inflow

The March to September 2004 recorded natural volume for the inflow to Lake Minnewanka was above-average at 203,000 dam³ or 108% of average and ranks 32nd highest in 91 years of record (1912-2001 data) (Table 4). This year's inflow volume was 15% higher than last year.

Seven monthly (February to August) natural volume forecasts were produced for Lake Minnewanka for the March to September period. As illustrated in Figure 10, the forecasted values (brown triangles) were much lower than the recorded March to September 2004 natural volume (dark blue line) for all seven months of forecasts. Initial forecasts were low due to below average snowpack, but above normal precipitation fell during March through September. As a result, a total inflow volume of 108% was recorded, corresponding to the upper range forecasts which averaged 112% over the year. The recorded volume was within the probable range for six of the seven forecasts (all but June) and was greater than the reasonable minimum for all seven forecasts.

Forecasts ranged within 9.2% to 27.9% of the recorded volumes, with August's being the most accurate and the only one of the forecasts within ten percent of the recorded value. The forecasts were on average, within 21.6% of the recorded March to September volume.

Spray Reservoir near Banff

The March to September 2004 recorded natural inflow volume for the Spray Reservoir near Banff was average to above average at 383,000 dam³ or 104% of average and ranks 39th highest on record (based on the 1912-2001 data) (Table 4). This year's inflow volume was 20% higher than last year.

Seven monthly (February to August) natural volume forecasts were produced for the Spray Reservoir for the March to September period. Volumes were underestimated, as is evident in Figure 11, where the forecasted values (brown triangles) were much lower than the recorded March to September 2004 natural volume (dark blue line) for all seven months of forecasts. Rapid early melting of the snowpack resulted in near-record runoff volume in April, but other than that, volumes, and forecasts, remained at consistently below average levels with the normal precipitation that occurred. However, after the final forecast was issued, nearly twice the normal precipitation during August-September resulted in the 11th highest runoff volume of record for this period. As a result, the total March-September recorded volume was within the forecasted probable range for only February and April's forecasts, but greater than the reasonable minimum for all forecasts.

Forecasts ranged within 13.1% to 21.3% of the recorded volume, with February's being the most accurate, but none of the seven forecasts were within ten percent of the recorded value. The forecasts were on average, within 17.6% of the recorded March to September volume.

Kananaskis River at Barrier Lake Reservoir

The March to September 2004 recorded natural volume for the Kananaskis River was average at 395,000 dam³ or 95% of average and ranks 40th lowest on record (based on the 1912-2001 data) (Table 4). Natural runoff volume this year was 15% higher than last year.

Seven monthly (February to August) natural volume forecasts were produced for the Kananaskis River for the March to September period. Early melting of the below average snowpack resulted in above average runoff volume in April, but other than that, volumes, and forecasts, remained at consistently below average levels with the normal precipitation that occurred. However, during the August-September period following the final forecast, much above normal precipitation resulted in the 15th highest runoff volume of record for this period. As illustrated in Figure 12, recorded March to September 2004 natural volume for the Kananaskis River (dark blue line) was above all seven forecasted values (brown triangles). Six of seven forecasts were within the forecasted probable range (all but August) and all seven were greater than the reasonable minimum.

Forecasts ranged within 5.7% to 13.0% of the recorded volume, with February's being the most accurate and three of the forecasts (February, April, July) within ten percent of the recorded values. Monthly forecasts were, on average, within 9.8% of the recorded March to September volume.

Bow River at Calgary

The March to September 2004 recorded natural volume for the Bow River at Calgary was below-average at 2,245,000 dam³ or 92% of average and ranks 31st lowest on record (based on the 1912-2001 data) (Table 4). Natural runoff volume this year was 11% higher than last year.

Seven monthly (February to August) natural volume forecasts were produced for the Bow River at Calgary for the March to September period. The February 1 forecast was lowered slightly in March following an extremely dry February in which approximately 15% of normal precipitation was recorded in the basin. The remainder of the forecasts were similar, but thereafter, heavy August-September precipitation led to the 15th highest natural runoff volume on record for those two months. As illustrated in Figure 13, the forecasted values (brown triangles) were lower than the recorded March to September 2004 natural volume at Calgary (dark blue line) for all but February. The recorded volume was within the probable range for six of seven forecasts (all but August) and was greater than the reasonable minimum for all seven forecasts.

Forecasts ranged within 0.2% to 7.8% of the recorded volumes, with February's being the most accurate and four of the seven forecasts within six percent of the recorded value. The forecasts were on average, within 5.2% of the recorded March to September volume.

Elbow River at Bragg Creek

The March to September 2004 recorded natural volume for the Elbow River at Bragg Creek was average at 211,000 dam³ or 96% of average and ranks 39th highest on record (based on the 1912-95 data) (Table 4). Natural runoff volume this year was 22% higher than last year.

Seven monthly (February to August) natural volume forecasts were produced for the Elbow River for the March to September period. As illustrated in Figure 14, the recorded March to September 2004 natural volume for the Elbow River (dark blue line) was above the forecasted values (brown triangles) for all seven forecasts. Initial forecasts were low due to much below average snowpack, which melted early resulting in normal runoff during March despite below average soil moisture conditions. Forecasts thereafter for below average runoff remained consistent, mirroring the recorded volumes, as normal precipitation fell during the March-September period. However, much above normal precipitation in August produced much more runoff than was expected, with August-September volume being the ninth highest on record. The basin soil conditions are wetter than in neighboring basins. The recorded volume was within the probable range for five of the seven forecasts (all but July and August) and was greater than the reasonable minimum for all seven forecasts.

Forecasts ranged within 12.4% to 22.5% of the recorded volume, with February's being the most accurate, but none of the seven forecasts were within ten percent of the recorded value. The forecasts were on average, within 18.1% of the recorded March to September volume.

Highwood River

The March to September 2004 recorded natural volume for the Highwood River was below-average to average at 486,000 dam³ or 77% of average and ranks 33rd lowest on record (based on the 1912-2001 data) (Table 4). Natural runoff volume this year was 5% higher than last year.

Seven monthly (February to August) natural volume forecasts were produced for the Highwood River for the March to September period. Initial forecasts were low due to the lack of snow accumulation, and steadily dropped as each month less volume than expected was recorded despite normal precipitation over the March through July period. Twice normal precipitation in August however, resulted in August-September volume being the ninth highest on record. This raised the year's total volume back towards the initial forecasts. As illustrated in Figure 15, the recorded March to September 2004 natural volume for the Highwood River (dark blue line) was below the forecasted values (brown triangles) for the first month and above for the following six forecasts. The recorded volume was within the probable range for all but the final two forecasts (July and August) and greater than the reasonable minimum for all seven forecasts.

Forecasts ranged within 0.1% to 17.0% of the recorded volume, with March being the best forecast and four of the forecasts within six percent of the recorded value. The forecasts were on average, within 7.6% of the recorded March to September volume.