<img src="https://d5nxst8fruw4z.cloudfront.net/atrk.gif?account=iA1Pi1a8Dy00ym" style="display:none" height="1" width="1" alt="" />
Dismiss
Skip Navigation

9.12: Deposition by Streams

Difficulty Level: Basic Created by: CK-12
Atoms Practice
Estimated5 minsto complete
%
Progress
Practice Deposition by Streams
 
 
 
MEMORY METER
This indicates how strong in your memory this concept is
Practice
Progress
Estimated5 minsto complete
%
Estimated5 minsto complete
%
Practice Now
MEMORY METER
This indicates how strong in your memory this concept is
Turn In

Why is there a pile of cobbles in that stream?

A river meanders causing erosion on one side of its bank. On the other side, sediments are deposited. On this photo of a meander, where is there erosion and where is there deposition?

Sediment Transport

The size of particles determines how they are carried by flowing water. This is illustrated in Figure below.

How Flowing Water Moves Particles. How particles are moved by flowing water depends on their size.

Sediments are carried as:

  • Dissolved load: Dissolved ions are carried in the water. These ions usually travel all the way to the ocean.
  • Suspended load: Sediments carried as solids as the stream flows are suspended load. The size of particles that can be carried is determined by the stream’s velocity (Figure below).

The Connecticut River is brown from the sediment it carries. The river drops the sediment offshore into Long Island Sound.

  • Bed load: Some particles are too large to be carried as suspended load. These sediments are bumped and pushed along the stream bed as bed load. Bed load sediments do not move continuously. This intermittent movement is called saltation. Streams with high velocities that flow down steep slopes cut down into the stream bed. The sediments that travel as bed load do a lot of the downcutting.

Deposition by Streams and Rivers

When a stream or river slows down, it starts dropping its sediments. Larger sediments are dropped in steep areas, but smaller sediments can still be carried. Smaller sediments are dropped as the slope becomes less steep.

Alluvial Fans

In arid regions, a mountain stream may flow onto flatter land. The stream comes to a stop rapidly. The deposits form an alluvial fan, like the one in Figure below.

An alluvial fan in (A) Death Valley, California, (B) Nile River Delta in Egypt.

Deltas

Deposition also occurs when a stream or river empties into a large body of still water. In this case, a delta forms. A delta is shaped like a triangle. It spreads out into the body of water. An example is shown in Figure above.

Deposition by Flood Waters

A flood occurs when a river overflows it banks. This might happen because of heavy rains.

Floodplains

As the water spreads out over the land, it slows down and drops its sediment. If a river floods often, the floodplain develops a thick layer of rich soil because of all the deposits. That’s why floodplains are usually good places for growing plants. For example, the Nile River in Egypt provides both water and thick sediments for raising crops in the middle of a sandy desert.

Natural Levees

A flooding river often forms natural levees along its banks. A levee is a raised strip of sediments deposited close to the water’s edge. You can see how levees form in Figure below. Levees occur because floodwaters deposit their biggest sediments first when they overflow the river’s banks.

This diagram shows how a river builds natural levees along its banks.

Vocabulary

  • alluvial fan: Curved, fan-shaped, coarse-sediment deposit that forms when a stream meets flat ground.
  • bed load: Sediments moved by rolling or bumping along the stream bed.
  • delta: A triangular-shaped deposit of sediments that forms where a river meets standing water.
  • dissolved load: The elements carried in solution by a stream.
  • floodplain: The flat area around a stream where water flows when the stream is in flood.
  • saltation: The intermittent movement of bed load particles.
  • suspended load: Solid particles that are carried in the main stream flow.

Summary

  • Streams carry dissolved ions and sediments. The sizes of the sediments a stream can carry, its competence, depend on the stream's velocity.
  • Particles that are too large to be suspended move along the stream bed by saltation.
  • Rivers deposit sediments on levees, floodplains, and in deltas and alluvial fans.

Practice

Use this resource to answer the questions that follow.

Running Water: How it Erodes and Deposits at http://www.youtube.com/watch?v=_HFmxRicX4o (2:56)

  1. What is laminar flow?
  2. What is turbulent flow?
  3. What is jet flow?
  4. Where does jet flow occur?
  5. What is water velocity?
  6. What factors can influence the stream velocity?

Review

  1. If the amount of water in a stream in flood starts to go down, what will happen to sediments the stream is carrying? What will be deposited and where?
  2. Describe what happens when a river floods? How are natural levees created?
  3. How do alluvial fans form?

    Notes/Highlights Having trouble? Report an issue.

    Color Highlighted Text Notes
    Please to create your own Highlights / Notes
    Show More

    Vocabulary

    alluvial fan

    Curved, fan-shaped, coarse-sediment deposit that forms when a stream meets flat ground.

    bed load

    Sediments moved by rolling or bumping along the stream bed.

    delta

    Triangular-shaped deposit of sediments that forms where a river meets standing water.

    dissolved load

    Elements carried in solution by a stream.

    floodplain

    Flat area around a stream where water flows when the stream is in flood.

    saltation

    Intermittent movement of bed load particles.

    suspended load

    Solid particles that are carried in the main stream flow.

    Image Attributions

    Show Hide Details
    Description
    Difficulty Level:
    Basic
    Grades:
    6 , 7
    Date Created:
    Jan 04, 2013
    Last Modified:
    Aug 29, 2016
    Files can only be attached to the latest version of Modality
    Please wait...
    Please wait...
    Image Detail
    Sizes: Medium | Original
     
    SCI.ESC.431.3.L.1
    Here
    Add Note
    Please to create your own Highlights / Notes