Bow River Basin - Water Supply Forecasts

Recorded March to September 2006 natural runoff volumes in the Bow River basin varied widely from average at the Spray Reservoir to much-below-average at Banff. The Elbow, Highwood and Kananaskis Rivers were below average and Calgary and the Cascade Reservoir were below to much below average. Recorded natural runoff volumes ranged between 71% and 98% of average, from 13th lowest to 41st highest on record (1912 to 2001 data) (Table 4). The seven monthly natural volume forecasts produced for the Bow River basin were within 8.9% of recorded values, on average, for the March through September runoff period.

Going into last winter, soil moisture was much above average and river flows were high due to much above normal summer and fall precipitation. Mountain snowpacks were generally below average for much of the winter. Initial natural runoff volume forecasts in February were generally below average to average.

By May 1, snowpack had improved to average, except at lower elevations and in the Highwood River basin which were below to much below average. Forecasts for the Highwood were lowered in May and steadily decreased each month thereafter as precipitation and runoff declined as summer progressed. After much below normal precipitation during May, Elbow River basin forecasts decreased for June 1. Spray Reservoir forecasts rose significantly on June 1 as volumes were much higher than expected, probably due to extra snow in unmeasured areas of the basin. As a result, Calgary forecasts also rose slightly. After heavy precipitation in early June, Spray and Kananaskis forecasts, and in turn Calgary's, rose in July. Otherwise, forecasts were fairly steady from February to July.

After much below normal precipitation in July final forecasts in August were significantly lowered for all areas, as July typically comprises a large portion of the year's precipitation. Natural runoff volumes for the month of July ranged from third lowest on record at the Cascade Reservoir to 15th lowest in the Kananaskis River, while southern parts of the basin (Elbow and Highwood) ranged from 22nd to 25th lowest. August was again a very dry month, with natural runoff volumes that month being lowest on record at Banff, Spray Reservoir, and in turn, Calgary. The southern basin again fared much better in August, at 19th to 34th lowest on record. September precipitation was generally above normal, except below normal upstream of Banff and the Spray Reservoir. As a result, natural runoff volumes for the year (March through September) ended up very close to August's forecasted values except at Spray Lake. Recent corrections to flow data at Banff by Water Survey of Canada resulted in the natural runoff volume for the year being closer to forecasted volumes.

Volumes were much lower than in 2005 due to flooding last year, but slightly lower at Banff, where high flows were much less prevalent.

Soil moisture is currently near normal in most of the basin.

Bow River at Banff

The March to September 2006 recorded natural volume for the Bow River at Banff was much-below-average at 903,000 dam³ or 84% of average and ranks 13th lowest on record (based on the 1912-2001 data) (Table 4). Natural runoff volume this year was 6% lower than last year.

Seven monthly (February to August) natural volume forecasts were produced for Banff for the March to September period. As illustrated in Figure 9, the recorded March to September 2006 natural volume at Banff (dark blue line) was below the forecasted values (brown triangles) until August. The recorded volume was within the probable range and greater than the reasonable minimum for all seven forecasts.

Forecasts ranged within 0.4% to 9.9% of the recorded volume, with August being the most accurate forecast (within 0.4%) and the previous six forecasts ranged within 6.2 to 9.9% of the recorded value. Monthly forecasts were, on average, within 7.1% of the recorded March to September volume.

Lake Minnewanka (Cascade Reservoir) Inflow

The March to September 2006 recorded natural volume for the inflow to Lake Minnewanka was below to much below average at 144,000 dam³ or 77% of average and ranks 17th lowest in 91 years of record (1912-2001 data) (Table 4). This year's inflow volume was 52% lower than last year.

Seven monthly (February to August) natural volume forecasts were produced for Lake Minnewanka for the March to September period. Volumes were overestimated, as is evident in Figure 10, where the forecasted values (brown triangles) were much higher than the recorded March to September 2006 natural volume (dark blue line) for all but August's forecast. The recorded volume of 77% better follows the lower range of forecasts which averaged 78.9% over the year. The recorded volume was within the probable range and greater than the reasonable minimum for five of seven forecasts (all but June and July).

Forecasts ranged within 0.3% to 15.4% 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 11.5% of the recorded March to September volume.

Spray Reservoir near Banff

The March to September 2006 recorded natural inflow volume for the Spray Reservoir near Banff was average at 360,000 dam³ or 98% of average and ranks 41st lowest on record (based on the 1912-2001 data) (Table 4). This year's inflow volume was 9% lower than last year.

Seven monthly (February to August) natural volume forecasts were produced for the Spray Reservoir for the March to September period. As illustrated in Figure 11, the forecasted values (brown triangles) were lower than the recorded March to September 2006 natural volume (dark blue line) for the first four months of forecasts, and higher for the last three. The total March-September recorded volume was within the forecasted probable range and greater than the reasonable minimum for all but the final two forecasts.

Forecasts ranged within 1.9% to 14.5% of the recorded volume, with March's being the most accurate, and all but July's within 5.8%. The forecasts were on average, within 5.3% of the recorded March to September volume.

Kananaskis River at Barrier Lake Reservoir

The March to September 2006 recorded natural volume for the Kananaskis River was average at 361,000 dam³ or 88% of average and ranks 29th lowest on record (based on the 1912-2001 data) (Table 4). Natural runoff volume this year was 25% lower than last year.

Seven monthly (February to August) natural volume forecasts were produced for the Kananaskis River for the March to September period. As illustrated in Figure 12, recorded March to September 2006 natural volume for the Kananaskis River (dark blue line) was below all seven forecasted values (brown triangles). The final recorded natural volume was within the forecasted probable range for four of seven forecasts (all but May, June, July) and was greater than the reasonable minimum for all seven.

Forecasts ranged within 2.6% to 11.4% of the recorded volume, with August's being the most accurate and all but July's within 5.9 to 7.3% of the recorded values. Monthly forecasts were on average within 6.6% of the recorded March to September volume.

Bow River at Calgary

The March to September 2006 recorded natural volume for the Bow River at Calgary was below to much below average at 2,020,000 dam³ or 83% of average and ranks 21st lowest on record (based on the 1912-2001 data) (Table 4). Natural runoff volume this year was 28% lower 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. As illustrated in Figure 13, the forecasted values (brown triangles) were higher than the recorded March to September 2006 natural volume at Calgary (dark blue line) for all seven forecasts. The recorded volume of 83% better follows the lower range of forecasts which averaged 81.7% over the year. The recorded volume was within the probable range for five of seven forecasts (all but June and July) and was greater than the reasonable minimum for all seven forecasts.

Forecasts ranged within 5.2% to 14.8% of the recorded volumes, with July's being the least accurate, August's being the most accurate and the other five forecasts within 8.3 to 12.6% of the recorded value. The forecasts were on average, within 10.2% of the recorded March to September volume.

Elbow River at Bragg Creek

The March to September 2006 recorded natural volume for the Elbow River at Bragg Creek was below average at 174,000 dam³ or 80% of average and ranks 31st lowest on record (based on the 1912-2001 data) (Table 4). Natural runoff volume this year was 63% lower than last year, when major flooding occurred.

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 2006 natural volume for the Elbow River (dark blue line) was below the forecasted values (brown triangles) for all seven forecasts. The recorded volume of 80% better follows the lower range of forecasts which averaged 77% over the year. The recorded volume was within the probable range for six of the seven forecasts (all but July) and was greater than the reasonable minimum for all seven forecasts.

Forecasts ranged within 1.2% to 14.9% of the recorded volume, with February's being the least accurate, and August's being the most accurate. The forecasts were on average within 9.7% of the recorded March to September volume.

Highwood River

The March to September 2006 recorded natural volume for the Highwood River was below average at 446,000 dam³ or 71% of average and ranks 29th lowest on record (based on the 1912-2001 data) (Table 4). Natural runoff volume this year was 126% lower than last year, when major flooding occurred.

Seven monthly (February to August) natural volume forecasts were produced for the Highwood River for the March to September period. As illustrated in Figure 15, the recorded March to September 2006 natural volume for the Highwood River (dark blue line) was below the forecasted values (brown triangles) for all but August's forecast. The recorded volume at 71% better follows the lower range of forecasts which averaged 67.9% over the year. The recorded volume was within the probable range and greater than the reasonable minimum for all seven forecasts.

Forecasts ranged within 0.6% to 20.3% of the recorded volume, with August's being the best forecast, July within 4.7%, June within 7.8% and the first four of the forecasts being within 13.2 to 20.3% of the recorded value. The forecasts were on average, within 11.7% of the recorded March to September volume.