Geological factors in the development of streams and their whitewater reaches on the Precambrian Shield, northern Saskatchewan
Robertson, Ray Henry
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The Precambrian Shield of northern Saskatchewan comprises (a) the 'pre-Athabascan' Archean and Proterozoic rocks of the Kazan Upland and (b) the Athabasca Formation, a sandstone of Late Proterozoic age, of the Athabasca Plain. These two major physiographic units differ substantially in lithology, structure, and topography. Analysis of topographic maps and airphotos shows a close relationship between stream trends, stream magnitudes, lithology, and structure. An interdependence also exists between the geology, the geomorphology, and the occurrence of waterfalls and rapids. The present major drainage patterns on the Shield, particularly that of the Churchill River and other large streams flowing from the west to the northeast, developed during Late Cretaceous and Tertiary time. Lakes cover 35 to 40 per cent of the Kazan Upland whereas lakes comprise only 15 to 20 per cent of the Athabasca Plain. Their size and outline can be related to the underlying bedrock geology. Drainage density is greater on the Athabasca Plain than on the Kazan Upland. The drainage pattern on the Athabasca Plain exhibits a roughly radial arrangement of commonly meandering streams which only in a few areas appear to be structurally controlled. Streams on the Kazan Upland, where northeast-southwest structural trends dominate, exhibit a poorly developed trellis pattern. Classifications of streams according to their associated rock types and lithological-structural characteristics make it possible to correlate stream trends and lengths with various geologic factors. Mapping the structural trends illustrates the drainage patterns and their dependence on geologic structure. The Churchill River, which flows across the prevailing structural trend, consists of a series of irregularly shaped lakes interconnected by short reaches of fast water. The largest number of whitewater occurrences is on the 'pre-Athabascan' and Proterozoic rocks of the Kazan Upland, with the highest concentrations of whitewater associated with rivers flowing across the general trend. Complex, composite lithologic contacts and fractures are the dominant types of geologic control on the occurrence of whitewater. Streams and reaches of whitewater are most effectively studied by detailed observation of individual occurrences rather than a statistical analysis of aggregated data. The interdependence between geology, stream trends, and whitewater is of more than purely scientific interest as the knowledge of it is useful for planning optimal use of the land. Note:This thesis contains maps that have been sized to fit the viewing area. Use the zoom in tool to view the maps in detail or to enlarge the text.