Search Textbook

Table of Contents

Chapter 3: Geologic Structure and Landforms

3.92: The Assiniboine River, the La Salle River, and the Elm River Palaeochannels East of Portage la Prairie

This larger scale photograph shows more detail of the Assiniboine River and of two palaeochannels than figure 3.91. The Assiniboine River 1 meanders across the centre of the area leaving behind three natural cutoffs 2. There are three other cutoffs 3 which appear artificial. In this area the Assiniboine flows between levees on both north 4 and south 5 sides. These are partly natural but have been heightened to protect agricultural land from flooding. A dike has been built south of the river 6 for the same purpose. Meander scrolls left by the shifting river can be seen north 7 and south 8 of the present channel. The Elm River palaeochannel 9 is visible in the south. It too has left prominent meander scrolls 10, and judging from their configuration at 11, it looks as if the waters of the Elm River palaeochannel once emptied into the headwaters of the La Salle palaeochannel at 12. It is noticeable that although the upper parts of the palaeochannels meander, the lower parts of both Elm River 13 and La Salle River 14 do not. Rannie[i] found that lateral migration occurred where the channels formed in relatively course-grained materials, but further east where the channels are bounded by lacustrine clay “lateral activity is inhibited or absent”.

Near the Assiniboine River, most noticeably to the north, the land is divided into long fields running back from the river 15, using the long lot system, whereas in the south the DLS system of squares is in evidence. The boundary between townships 10 and 11 runs across the area with a quarter mile (0.4 km) correction at the junction 16.

Agriculture in the area is intensive, frequently aided by irrigation with water from either the Assiniboine or from buried palaeochannels. This is most noticeable north of the Assiniboine River 17 where many small fields can be seen, probably supporting vegetables and fruits. The Portage area is the main strawberry growing region of Manitoba,[ii] and it seems likely that strawberries are grown in some of the fields close to the river. Similar intensive growing areas are located in Hoop and Holler Bend 18 and along the Elm River 19.

The twinned Trans-Canada Highway 20 can be seen in the north; it veers off to the south to bypass Portage la Prairie which is just off the photo to the west. PTH 26 21 is north of the Trans-Canada Highway and the CP railway line 22. Between the highway and railway are faint indications of the High Bluff palaeochannel 23. The CN line 24 trends west-northwest/east-southeast crossing the Assiniboine River in the process 25. In the west a road out from Portage la Prairie 26 approaches the Assiniboine River. There is no bridge, but the trend continues south of the river 27. In the extreme southwest are the ends of runways 28 at the Southport airbase (CFB Portage la Prairie). Two Hutterite colonies can be seen, the Elm River Colony 29 and another in the extreme southeast 30.

Figure 3.92: The Assiniboine River, the La Salle River, and the Elm River Palaeochannels East of Portage la Prairie

Figure 3.92: The Assiniboine River, the La Salle River, and the Elm River Palaeochannels East of Portage la Prairie

Figure 3.92

Vertical air photograph: MB89021-6-176

Flight height: 30,800 feet a.s.l.; lens focal length: 152.26 mm

Date: August 7, 1989

Scale: 1:57,600 (approx.)

Location: Townships 10, 11, 12; Ranges 5 and 6 WI

Map sheets: 1:250,000 62G Brandon 

1:50,000 62G/16 Portage la Prairie


[i] Rannie, op. cit., 1990, 183.

[ii] Portage la Prairie claims to be the strawberry capital of Canada and has a strawberry festival each year.