Quenching the Peace Athabasca Delta

The Peace Athabasca Delta in northern Alberta is one of the world's largest inland freshwater deltas, and a wetland of international importance under the Ramsar Convention. Home to some of the largest undisturbed grass and sedge meadows in North America, it provides habitat for large populations of waterfowl, muskrat, beaver and free-ranging wood bison.

Over the past 25 years, however, this complex and dynamic region has undergone several prolonged dry periods that have turned some basins from aquatic into terrestrial ecosystems. The first came after the construction and initial filling of the W.A.C. Bennett hydroelectric dam at the headwaters of the Peace River, between 1968 and 1971, and the second after the retreat of a major spring flood in 1974. Scientists at Environment Canada's National Water Research Institute investigated these trends, and found that the effects of flow regulation, combined with variations in climate, had reduced the number of massive ice jams that cause flooding.

Unlike urbanized areas to the south, where spring flooding caused by river ice jams often wreaks havoc on property and the economy, flooding in this remote northern part of Canada spurs the high biological productivity for which the Delta is famous. Flooding is vital, especially to the perched ponds and lakes that are separated from the open-water channel system. Without it, all sorts of changes occur to the ecosystem, from shifts in dominant vegetation to dramatic declines in small-mammal habitats and populations.

Knowing why these drying periods occurred has enabled scientists to develop a strategy that maximizes the potential for flooding by timing flow releases from the dam to coincide with favourable natural conditions, such as the size of the snowpack. In spring 1996, hydrological and climatic conditions were appropriate, and a timed flow release by dam managers increased the magnitude of an ice-jam flood—bringing water to areas that had been dry for more than two decades.

These images--taken at the same location one month apart--show the extreme differences
in water levels in the Peace Athabasca Delta before and after flooding.

There is still much to be learned about the hydro-climatology and ecology of the Delta if the region's productivity and biological diversity are to be sustained. However, gathering information about such a huge and remote region poses many problems for researchers. To meet these challenges, Environment Canada scientists are developing innovative tools to learn more about the spatial dimension of floods, water levels and changing flow regimes in the region.

One such tool is satellite imagery. During the years when the Delta was drying out, willow grew extensively, contributing to a thick cover of vegetation that could not be penetrated by traditional remote-sensing methods. Using a combination of traditional satellite technology and the newer RADARSAT microwave system, scientists have been able to "see" through this cover and track the boundaries of the 1996 flood.

Analysis of historical satellite imagery showing past water-level fluctuations will further improve understanding of evapotranspiration and other hydrological processes, and provide data for water-balance models that help predict future changes. These models, along with a hydraulic model of the region, are now being applied in ongoing research into the potential impacts of climate change on water resources in this unique and important region of the country.

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