Restoring Ice-jam Floodwater to a Drying Delta Ecosystem

Abstract

Overbank flooding is essential to the ecological health of riparian landscapes, particularly river deltas. One of the world's largest freshwater deltas, the Peace-Athabasca Delta (PAD) in northern Canada, has experienced a series of wetting and drying cycles because of inter-annual variations in flooding. Recent research has found that most of the major floods affecting this system are produced by spring ice jams. For approximately two decades, however, the combination of climatic and flow-regulation effects precluded significant ice-jam flooding of the PAD. Resultant drying caused major changes to the ecology of the delta and led to the evaluation of a number of methods to restore water flows. Since most of delta is contained within a national park (Wood Buffalo National Park), a major goal was to employ non-structural measures. Hence, in an effort to manage the water problems of this delta, the final report of a multi-agency “Northern River Basins Study” made the recommendation that the spring flow-release strategy of the upstream hydro electric reservoir be modified to increase the probability of ice-jam flooding near the PAD. This was to be conducted in years when downstream hydrometeorological conditions (snowpack magnitude and ice-cover strength) appeared conducive to ice-jam formation. Such favourable conditions developed in the spring of 1996, a natural ice jam began to develop, and regulated flows were increased to assist in potential flooding. As a result, the PAD experienced its first major flood in over 20 years. This paper reviews the hydrometeorological conditions that led to the ice-jam formation, compares the conditions to historical events, analyzes the spatial extent of the flood, and evaluates the effectiveness of the flow release.