USING ICE TO FLOOD THE PEACE-ATHABASCA DELTA, CANADA

Flooding of deltas on large, northern rivers is usually the result of spring ice-jam events, as opposed to high flows during the open-water season. Some of the most sensitive components of such ecosystems are t he perched basins: small ponds and lakes that are hydraulically isolat ed from the main flow system. The biological structure and productivit y of these basins are highly dependent on flooding and flushing associ ated with high stage events. Major flooding of the Peace-Athabasca Del ta, one of the world's largest and most productive deltas, has not occ urred since 1974, the time of the last major ice-jam event. Prior to t his, the Delta also experienced an extensive drying period, from 1958- 1971, as one of its main rivers became regulated. As a result, extensi ve changes have occurred in the vegetation regime and associated wildl ife habitat. Recognizing the historical role of ice-jam flooding, atte mpts are being made to induce flooding through regulation of the natur al flow system using ice. The changing hydroecology of this flood-depe ndent ecosystem, common approaches related to regulation effects and r iver ice covers, and the unique strategies used to construct artificia l ice darns and/or initiate ice jams, are all reviewed.