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Chapter 1: Introduction

1.1: Sequential Air Photos of the Junction of the Assiniboine and Little Saskatchewan Rivers

Sequential air photos (taken of the same area at different times) reveal changes that have occurred over time. Many geomorphological processes are so slow that no change can be detected even by comparing very old photos with recent ones (the time span is after all little more that 100 years). However, prairie streams flowing across easily eroded sediments assume a meandering form, the position of the meanders changing relatively quickly.

Figure 1.1a: 1947 Photo

The Little Saskatchewan River 1 flows southward onto the floor of the Assiniboine spillway, bounded roughly by provincial road (PR) 459 2. From that point south, it assumes an indirect meandering course 3 to the Assiniboine River 4. Several previous routes can be seen both west 5 and east 6 of the present course. Note also the dam 7 across the Little Saskatchewan River with a reservoir 8 to the north. This was the location of the first hydroelectric power station in Manitoba. Between 1900 and 1930 it supplied electricity to Brandon during the summer months. The dam was washed away and the reservoir emptied in 1949

Figure 1.1.a: 1947 Photo

Figure 1.1.a: 1947 Photo

Figure 1.1a

Vertical air photo: A11041-201

Flight height: 9,520 feet a.s.l.; lens focal length: 152.4 mm

Scale: 1: 16,700 (approx.)

Date: May 19, 1947

Location: Township 10, Range 20 WI

Map sheets: 1:250,000 62F Virden

1:50,000 62F/16 Alexander


[i] For a ground level photo of the dam see figure 16.26.

Figure 1.1b: 1968 Photo

Twenty years after photo 1.1a was taken, the Little Saskatchewan River 1 takes a more direct route to the Assiniboine River 2 (the 1948 route is indicated by a dashed line) and has deposited sediment 3 in the larger river.

This photograph also illustrates several of the criteria used in air-photo interpretation.

1)  Tone. Tones are in shades of grey, ranging from almost white, to almost black. Fields on which crops have been grown, and at least partly harvested, appear in light tones 4 whereas the relatively clear water of the Little Saskatchewan River is dark toned 5. The Assiniboine River, which carries more suspended sediment than the Little Saskatchewan River, is lighter toned than the latter. Also some deciduous trees, probably aspen (Populus tremuloides) appear light toned 6 because in this fall photo the leaves have changed colour to bright yellow.

2)  Texture. A field east of the Little Saskatchewan River 7, which has been left fallow, exhibits a smooth texture because of its uniform medium grey tone. On the other hand the treed area south of the Assiniboine River 8 has a mottled texture resulting from the various tones of the constituent trees.

3)  Pattern. East of the fallow field are two other fields exhibiting the characteristic pattern of grain crops that have been harvested. The westernmost 9 has a pattern of narrow lines typical of a field that has been swathed whereas the field to its east 10 has wider rows resulting from the fact that it is being combined.

4)  Shape/shadow. Shadows thrown by trees west of the Little Saskatchewan River are rounded 11, indicating that they are deciduous rather than coniferous. South of the Assiniboine River, tree shadows indicate that the trees have lost their leaves so that their branched form can be seen 12.

5)  Location and size. At the north end of the field being combined are eight vehicles 13. Given their location it is a reasonable assumption that they are combine harvesters accompanied by trucks to receive the grain. At least four vehicles can be seen on the Trans-Canada Highway 14, 15, and 16. Given their location it can be assumed that they are trucks or cars; the largest of the four is a truck 16.

Figure 1.1.b: 1968 Photo

Figure 1.1.b: 1968 Photo

Figure 1.1b

Vertical air photo: A20811-97

Flight height: 7,200 feet a.s.l.; lens focal length: 152.07 mm.

Scale: 1:12,000 (approx.)

Date: September 29, 1968

Location: Township 10, Range 20 WI

Map sheets: 1:250,000 62F Virden

1:50,000 62F/16 Alexander