Running water, aided by mass wasting, is the most important geologic agent in eroding, transporting, and depositing sediment. Almost every landscape on earth shows the results of stream erosion or deposition. Although other agents - groundwater, glaciers, wind, and waves - can be locally important in sculpturing the land, stream action and mass wasting are the dominant processes of landscape development.
The first part of this chapter deals with the various ways that streams erode, transport, and deposit sediment. The second part describes landforms produced by stream action, such as valleys, flood plains, deltas, and alluvial fans, and shows how each of these is related to changes in stream characteristics. The chapter also includes a discussion of the causes and effects of flooding, and various measures used to control flooding.