The Rivers web page, discusses the average annual natural flow volumes for the largest rivers in Alberta and illustrates the range of variability (the maximums and minimums) that we have observed since we began monitoring these rivers.

Typically larger rivers, especially those that originate in the Rocky Mountains, do not vary as much from year to year as smaller prairie-fed rivers. This is because the large accumulations of snowpack at higher elevations, are usually more reliable and provide a more consistent annual flow than the small, highly variable snowpacks generally found in the plains areas. Also, these high elevation snowpacks do not start melting as early, so mountain-fed streams generally flow throughout the summer. Plains rivers have spring runoff events that occur in March or April and last only a few weeks. Many prairie streams actually dry up later into the summer

Recorded streamflow data is the actual data that we collect every day. However, it does not necessarily represent natural streamflow conditions and therefore would not give us a clear picture of what sort of patterns or trends might be emerging in our water supplies. In certain areas, especially in the southern part of the province, streams are highly affected by human activities, and especially by storage reservoirs and large-scale irrigation projects. The volume of water diverted or stored can be substantial, so the amount of water that is recorded or observed in these rivers can be significantly different than what would have occurred naturally - both on a seasonal and annual basis.

Analysis of the recorded streamflow data for the past 20 years (1981-2000), reveals interesting trends which are summarized in the adjacent table and map. Note that the relative rankings of some of the rivers change when compared with their natural sizes, once the impacts of diversions are considered. This is particularly noticeable for the Bow (from number 7 to 11) and Oldman (from 10 to 12) rivers. Also note that some of the river basins that have little man-made alterations and are effectively natural (such as the Athabasca River) were drier in the last 20 years when compared with the historical average. Look at the Natural Flow Table here.

Although the above table indicates that many of the rivers have experienced lower average annual streamflows over the past 20 years when compared to the long-term average, 20 years is not a long time to base a trend analysis on.

Analysis of eight of Alberta's larger rivers, covering all of the major basins and using up to 90 years of naturalized data, showed that no significant long-term trend has yet been detected in the natural streamflow volumes. Natural cycles of above and below-average periods occur in the records with recent extremes, both high and low, tending to be within the range of observed historic variability. Recorded volumes in the South Saskatchewan basin have slowly declined over time, likely due to increasing consumption. Once those impacts have been accounted for, the longer-term trend is relatively stable. One exception is the Beaver River, where a significant negative trend was identified - although with a period of record of less than 50 years, a trend determination is more difficult and less meaningful than for the other rivers.

It is important to determine if there is a natural or climate-related reason for the apparently diminishing streamflows in some areas of Alberta. However, the continually increasing pressures on available supplies due to increasing population and economic growth have to be monitored as human use of water can have significant effects on supply in the short term. Monitoring and regulating the amount of water we use is the first step to ensuring it is available for the future.