Natural Resources Canada
www.nrcan.gc.ca
The Red River is a single-channeled, meandering river. It is 880 km long by length of channel or 456 km long in a straight line, from the confluence of the Bois de Sioux and Otter Tail rivers in southern North Dakota/Minnesota, to Lake Winnipeg, Manitoba, in the north. The watershed encompasses an area of about 290 000 km2, including the Assiniboine River basin (163 000 km2) which joins the Red River at Winnipeg. About 16% of the Red River basin, excluding the Assiniboine basin, is located in Canada; the remainder is within the states of North Dakota, Minnesota and South Dakota. In Manitoba, the river has an average valley gradient of 0.0001.
The Red River flows northward along the very flat Red River Valley, where natural topographic variations are subtle, aside from incised stream courses and gullies. The valley is oriented north-south and aptly described by Warren Upham as "being a vast plain" 40 to 50 mi [64 to 80 km] wide and more than 300 mi long [the distance is about 530 km], stretching from Lake Traverse to Lake Winnipeg" (Upham 1895 p. 20). Within Manitoba, the Manitoba Escarpment forms the western edge of the valley, but to the east the margin is much less distinct.
Despite a name that suggests a direct link to the river, the Red River Valley predates the establishment of the river. The basic form and slope of the valley were shaped by the gradual erosion of Mesozoic bedrock during the Tertiary and Quaternary Periods. This erosion exposed underlying and more resistant Paleozoic bedrock, creating a lowland surface between the Manitoba Escarpment to the west and the Precambrian shield to the east. The bedrock surface of the lowland has moderate relief and a gradual northward slope. Along the central Red River Valley, the lowland bedrock is buried beneath late Pleistocene glacial sediments that, in turn, are capped with a clay-rich veneer of glaciolacustrine sediments deposited within glacial Lake Agassiz. Lake Agassiz was a large, ever-changing glacial lake that at one stage or another occupied most of Manitoba, eastern North Dakota, northwestern Minnesota, northwestern Ontario and east-central Saskatchewan during the late Pleistocene and early Holocene. Collectively, the surficial deposits create the flat, gently northwards sloping plain of the present day Red River Valley.
Upham, W.
1895: The Glacial Lake Agassiz; United States Geological Survey Monograph 25, 658 p.
The Red River is a very young river. In southern Manitoba it became established on the bed of glacial Lake Agassiz between 8200 and 7800 radiocarbon years ago, as the final stages of the lake waned and receded northward. The river eroded a shallow stream-cut valley, up to 15 m deep and 2500 m wide, into the surface of the Red River Valley plain. The shallowness of the river valley originates from the flat topography and low northward gradient of the Red River Valley plain between Fargo, North Dakota and Lake Winnipeg. There are no major reductions in topography along this course that the river could exploit through headward erosion and thereby significantly deepen the valley. A slight drop in the river profile occurs just north of Winnipeg at Lister Rapids, where the river flows across an outcrop of resistant carbonate bedrock that controls the baselevel of the river upstream. The decrease in bed elevation across Lister Rapids is only about 7 m over 15 km, but relative to the gentle gradient of the river this is a significant drop in the profile.
