Strategies for Restoring Spring Flooding to a Drying Northern Delta

Delta ecosystems are often comprised of a myriad of channels and lakes, the latter of which can be subdivided according to the level of their connection with the main flow system. The dynamics of such lakes, in terms of their overall biological structure and productivity, depend on flooding and flushing during high-stage events. Major flooding of the Peace–Athabasca Delta—one of the world's largest and most productive deltas—has not occurred since 1974. Before this, the delta also experienced an extensive drying period from 1968 to 1971 as one of its main rivers became regulated. As a result, extensive changes have occurred in the vegetation regime and associated wildlife habitat. Two methods used in attempts to restore water to these systems are reviewed: rockfill weirs and artificial ice jams/dams. Recorded data since 1976 suggest that the weirs have been effective in restoring water on the large delta lakes to levels which would have occurred under an unregulated river regime. The weirs have not, however, replenished water in most of the perched basins. Moreover, even an historically high flow event in 1990 failed to flood them. Analysis of historical water level data revealed that ice-jam backwater is the only method by which these areas of the delta can be flooded. Although hydrometeorological conditions have not been conducive for the formation of major ice jams since 1974, attempts have been made to artificially induce an ice jam. The strategies, field trials and future applications of such an approach are reviewed.