Generation of streamflow to seasonal high waters in a freshwater delta, northwestern Canada

Shallow lakes and wetlands in the Peace-Athabasca Delta (PAD), one of the world's largest freshwater deltas located in northwestern Canada, are dependent on occasional flooding to replenish evaporated water. The hydrology of the PAD has experienced natural and human induced changes in recent times. Since the early 1970s, there has been a desire to restore water to perched wetlands by managing inundation of the perimeter deltas. Before such plans are implemented, it is important to understand the generation of annual peak ice-induced and open-water floodwaters to this Nordic delta. The hydroclimatology, physiography, size, and relative locations of sub-basins exert a strong control on the runoff response. Ice-jam floods in the lower Athabasca and Peace Rivers are generated by large snowmelt runoff from 'trigger tributaries' located in the downstream (foothills and plains) portions of the basin. Flood flows during the open-water period are primarily generated by heavy rainfall runoff originating from the more elevated foothill/mountain regions where the precipitation process is enhanced by orography. In general, storage of alpine runoff in the headwaters of the Peace River places an increased dependence on downstream tributaries of the system to produce extreme flow events to the delta. Recommendations are made for additional hydrological modelling studies to assess the potential change to generation of extreme events from additional water retention/diversion schemes, land-use change, and a changing hydroclimate within the upstream contributing basins of the PAD. Copyright (c) 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.