A review of hydroecological results of the Northern River Basins Study, Canada. Part 2. Peace-Athabasca delta

The Peace-Athabasca Delta (PAD) in northern Canada is one of the world's largest freshwater deltas. Concern developed over the ecological health of this system in the early 1970s following regulation of its main headwater tributary, the Peace River. Continued drying of the delta into the 1990s resulted in the initiation of two major science programs, the Northern River Basins Study and the Peace-Athabasca Delta Technical Studies. Recognizing the importance of water to restoring and maintaining biological productivity and diversity of the PAD, a series of studies was initiated to explain the reasons for the protracted drying and to design methods to restore flooding. These studies demonstrated that open-water floods from the Peace River were unlikely to flood the ecologically sensitive perched basins within the PAD. Moreover they discovered that most large-scale overbank flooding resulted from ice-jams formed during spring break-up. Increases in freeze-up ice levels due to enhanced winter flows from the reservoir and a decrease in spring snowmelt runoff from downstream tributaries were suggested as being responsible for a decline in the frequency and severity of ice-jam floods. Based on results from numerical modelling studies of ice-jams, a flow augmentation strategy was designed to aid the formation of ice-jams near the PAD. Results of a test trial based on this strategy are presented. An update is also provided about ecological studies conducted since the delta was recharged by floodwaters in 1996. Copyright (C) 2002 Environment Canada. Published by John Wiley Sons, Ltd.