River Systems and Fluvial Landforms

Big Bend National Park Texas
Big Bend National Park Texas

NPS Photo/Ann Wildermuth

Fluvial systems are dominated by rivers and streams. Stream erosion may be the most important geomporphic agent. Fluvial processes sculpt the landscape, eroding landforms, transporting sediment, and depositing it to create new landforms. Human civilization and ecosystems alike are dependent on fluvial systems. Rivers provide water for hydroelectric power and shipping, as well as supporting stream-side wetlands (riparian areas) that are critical for clean water and provide rich habitat.

The drainage basin is the fundamental landscape unit in a fluvial processes. This is a system of a primary, or trunk, river and its tributaries. These watersheds are separated from their neighbors by a divide; a highpoint where water flows in different directions on either side.

The shape that a stream takes, or its channel morphology, is a function of the sediment carried and deposited by the stream. This divides streams into two general categories,
meandering and braided.

In addition to the streams themselves, the depositional habits of fluvial systems produce striking landforms.

A floodplain is the area at the base of a valley, adjacent to the river or stream, covered with unconsolidated sediment deposited by fluvial processes. The river will be immediately flanked by a buildup of sediment that forms natural levees. These provide some defense against flooding, but are occaisionally breached in select areas producing crevasse splays--coarse sediment deposited during high flow events.

Alluvial fans represent one end of an erosional-deposition system linked by a river--the deposition end. Most commonly, in cases where sediment is brought downstream from a mountain and deposited as an alluvial fan, spreading out from the mountain's intersection with the floodplain. Neighboring alluvial fans that coalesce are called bajadas.

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Fluvial Landforms

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