Page 488 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

15
452 part III The Earth–Atmo
sphere Interface
River Systems
concepts
KEy LEARnIng
After reading the chapter, you should be able to:
• Sketch a basic drainage basin model, and identify different types of drainage patterns by visual examination.
• Explain the concepts of stream gradient and base level, and describe the relationship between stream velocity, depth, width, and discharge.
• Explain the processes involved in fluvial erosion and sediment transport.
• Describe common stream channel patterns, and explain the concept of a
graded stream.
• Describe the depositional landforms associated with floodplains and alluvial fan environments.
• List and describe several types of river deltas, and explain flood probability estimates.
William River flows northward through boreal forest as a meandering channel toward Lake Athabasca in northern Saskatchewan. About 20 km south of the lake, it encounters the Athabasca sand dunes, first the West Field (shown here,
on the left) and then the East Field about
7 km further downstream. Sand from the
30 000 hectare dune fields, predominantly from the West Field, is blown into the river channel, which consequently experiences a dramatic change in character. In response to the progressive infusion of sand as the river passes through the dune fields, the channel widens and becomes shallow and braided, dominated by bedload sediment transport. At the shoreline of Lake Athabasca, William River deposits the newly acquired sediment to build a delta into the lake. [Robin Karpan.]