PALAEOHYDRAULIC RECONSTRUCTION OF GLACIAL LAKE EDMONTON, ALBERTA, CANADA

Glacial Lake Edmonton was a short-lived proglacial lake that formed in central Alberta as the Laurentide Ice Sheet’s southwestern margin retreated. Although this lake considerably altered the geomorphology of the region, there is a scarcity of research relating to its genesis and the palaeohydraulics of its drainage. This study uses high resolution LiDAR imagery to identify the geomorphic features and reconstruct lake evolution. We identify five stages of lake evolution, the most extensive of which drained catastrophically through the previously identified Gwynne outlet. We use a HEC-GeoRAS/HEC-RAS system along with palaeo-depth indicators to estimate the water surface elevation and palaeo-bed topography of the main Gwynne outlet. We then use previously derived associations between lake volume and peak discharge and compare the results with peak discharges derived from spillway incision. Adjusting for downstream attenuation, results from both methods are concordant. We suggest the most extensive Gwynne stage, covering ~3500 km² with an outburst volume of 44 km³, had an estimated peak discharge of 25,000 - 95,000 m³ sec^-1 and a minimum flow duration of 5-8 days. These data, coupled with a lack of outburst depositional features, suggest sediment supply is a major control on spillway morphology within the Canadian Prairies.