Ice regime of the lower Peace River and ice-jam flooding of the Peace-Athabasca Delta

The Peace‐Athabasca Delta (PAD) in northern Alberta is one of the world's largest inland freshwater deltas, home to large populations of waterfowl, muskrat, beaver, and free‐ranging wood bison. Beginning in the mid‐1970s, a paucity of ice‐jam flooding in the lower Peace River has resulted in prolonged dry periods and considerable reduction in the area covered by lakes and ponds that provide a habitat for aquatic life in the PAD region. Using archived hydrometric data and in situ observations, the ice regime of the lower Peace is described and quantified, setting the stage for identification of the conditions that lead to ice‐jam flooding and replenishment of Delta habitat. The first such condition is the occurrence of a mechanical, as opposed to a thermal, breakup event; second, the river flow should be at least 4000 m3/s; and third, an ice jam should form within the last 50 km of the Peace River. The type of breakup event depends on the freeze‐up stage and spring flow. The former has increased as a result of flow regulation, and the latter has decreased owing to changing climatic patterns. Both trends tend to inhibit the occurrence of mechanical breakups and contribute to less frequent ice‐jam flooding. Potential mitigation strategies are discussed. Copyright © 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.