Water Supply Outlook for Alberta

May 2008

Bow River Basin - Water Supply Forecasts

As of May 1, 2008, natural runoff volumes for the March to September 2008 period are forecast to generally range from below average to average in the Bow River basin. Natural runoff volumes are expected to be below to much below average for the Bow River at Banff, below average for the Bow River at Calgary, below average to average into the Cascade Reservoir and for the Highwood River, and average into the Spray Lakes Reservoir and for the Kananaskis and Elbow Rivers (Table 4a). Current natural runoff volume forecasts range from 80 to 96% of average in the basin. Most of the current forecasts have decreased by 1% of average since the April 1 forecasts, except the Elbow River forecast did not change, the Spray River forecast rose by 1%, the Cascade Reservoir forecast rose by 2% and the Highwood River forecast decreased 6%. The current forecasted volume for the Bow River at Calgary would rank 28th lowest in 91-years of record (1912-2001).

Significant precipitation of 30 to 80 millimetres on May 7 to 9 in much of the basin should further increase these forecasts next month, depending how much more precipitation occurs during the rest of May. Precipitation during the first twelve days of May has been generally above to much above normal so far, except below normal to normal in the mountains upstream of Banff.

The first two months of the forecast period have been completed, with March-April 2008 recorded natural runoff volumes ranging from 57 to 87% of average. The Cascade and Spray Reservoirs and the Kananaskis River have so far recorded the fifth to eleventh lowest natural runoff volumes in 91 years of record, while other areas recorded below to much below average runoff. Recorded volume data is preliminary, due to ice effects, and is subject to change. March-April volumes typically comprise a small portion of the March to September total. The remaining volume forecast, which is the March to September 2008 forecast minus the recorded volume to date, is available in Table 4b.

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