River Systems and Fluvial Landforms

Big Bend National Park Texas
Big Bend National Park Texas

NPS Photo/Ann Wildermuth

[Site Under Development]

Introduction

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.

illustration of river system showing 3 part upper, middle, and lower courses.

Source:  Trista L. Thornberry-Ehrlich, Colorado State University.

The drainage basin or watershed is a fundamental landscape unit in fluvial geomorphology. A dranage basin contains a primary, or trunk, river and its tributaries. Watersheds are separated from their neighbors by a divide; a highpoint where water flows in different directions on either side.

  • Upper Basin
    Headwaters
  • Mid-basin
    Low gradiant valleys and flood plains
  • Lower Basin
    Depositional Zone

Floodplain Landforms

In addition to the streams themselves, the depositional habits of fluvial systems produce striking landforms. Fluvial deposits are sediments deposited by the flowing water of a stream.

Illustration of channel features
Illustration of channel features from Chaco Culture National Historical Park geologic report.

Source: Trista L. Thornberry-Ehrlich, Colorado State University.

A floodplain is the relatively flat surface adjacent to the river or stream. During floods, when the stream overflows its banks, water flows over the floodplain and deposits sediment. Through fluvial processes, streams construct floodplains that accommodate their maximum flood capacity. Geomorphic features of the floodplain include:

  • Natural Levees—River may be immediately flanked by a buildup of sediment that forms natural levees. These provide some defense against flooding, but are occaisionally breached in areas producing flood-plain splays—coarse fan-shaped deposit of sediment created during high flow events.
  • Oxbows and oxbow lakes—See below, features of a Meandering Stream Channel.
  • Point Bars—See below, features of a Meandering Stream Channel.
  • Terraces

Channel Morphology

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

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      Fluvial Landforms in Parks

      Alsaka

      Contiguous U.S.

      Last updated: August 6, 2019

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