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Megaflooding generated from Glacial Lake Missoula (GLM) during the late Pleistocene, swept across the Columbia Plateau and Columbia Basin regions of the northwestern U.S., producing the Channeled Scabland, an assemblage of landforms comprising a regional anastomosing complex of overfit stream channels scoured into basalt bedrock. This region provides the best-studied example of a landscape created by catastrophic flooding. Using DEM data and the HEC-RAS 2-D hydraulic model, we analyzed the GLM flood propagation from the Clark Fork in northern Idaho to the eastern Pacific Ocean, and the GLM flood simulation generally covers the tracts of the Channeled Scabland and captures the paleohydraulic conditions that have been inferred in the field and documented by previous hydraulic studies. A test simulation on the Columbia Gorge suggest the other sources of water besides Lake Missoula may have been involved in producing the megaflooding. Initial hydraulic analyses for the megafloods and their relations to the field evidence provide important insights into cataclysmic flood processes and associated landforms.