32. Slopes and Streams

Photo 55: The junction of Whitemud Creek and Blackmud Creek. Edmonton, Alberta. 2011-05-04

Rivers

Photo 55 shows the joining of Edmonton’s Whitemud Creek and Blackmud Creek, to continue as the Whitemud Creek. In this case, the Blackmud Creek is a tributary of the Whitemud Creek. Rivers start as rain on a field, flowing towards the lowest area, which is called sheet flow. Too much sheet flow or sheet wash can cause sheet erosion, the removal of the nutrient-rich topsoil. Sheet flow accumulates into small channels called rills, which merge into gullies, and gullies into streams. The Whitemud Creek tributary drains into the North-Saskatchewan river, which can be labeled as a trunk of the Saskatchewan river watershed. The system of trunk and tributaries is called a drainage basin or watershed. The Athabasca glacier and river, discussed in a few other blog posts, drains into the Mackenzie River drainage basin. Drainage basins are separated by continental divides, high continual ridges in the continent that determine water flow.

Photo 56: Various rocks, eroded through various processes, at our new pond behind our house. Lacombe, Alberta. 2011-06-26

River transportation

Photo 56 shows the recently built pond in our back yard. We used some rocks from our agricultural fields, the rocks with sharp corners, which over time make their way to the surface of the land. The other rocks in the photo are round and have probably been transported by rivers. Rivers transport sediment of many varieties. Clay, silt, and sand are often suspended in the water due to the river’s velocity. These materials are also most easily deposited. Rocks are pushed along by rolling over the river’s bed (bottom), which is called traction. Lighter rocks are sometimes suspended and roll at other times, they jump through a river, which is called saltation.