Plant & Soil Sciences eLibraryPRO
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Lesson Outline

Lesson Media Objects

Erosion

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How Water and Wind Erosion Occur

Objective

By the end of this section the student/user will be able to:
Describe the mechanisms/processes of how water and wind erosion occur.
Accompanying Exercise: (For Students to print off, complete and turn in for a grade)
How Water and Wind Erosion Occur- Exercise (pdf)

The three steps common to both water and wind erosion:

1. DETACHMENT of soil particles:

  • This action dislodges the particles from the soil by the impact energy of the rain or wind.

2. TRANSPORT of particles:

  • This action carries soil particles in the moving wind or water.

3. DEPOSITION of particles in a new location:

  • This action deposits the sediment when the wind and water energy subsides. Clay or silt size particles can be carried a great distance before deposition, while larger sand-size particles will be carried only a short distance.
The impact of a water droplet dislodges and scatters soil particles. Image by NRCS

The impact of raindrops shatters surface aggregates and detaches soil particles from them. Raindrop impact is the primary cause of particle detachment. Raindrops can splash soil particles, moving them up to three feet away. Some of the detached particles float into soil pore spaces. This can clog and seal soil pores and result in reduced water entry (infiltration) into the soil. If the rainfall rate exceeds the rate at which water can infiltrate the soil, the excess water runs off and often carries the detached soil particles with it.

Detached particles (sediment) are carried with flowing water down the slope. How many particles and how far they are transported depends on the velocity and volume of the running water. As the water velocity slows down it loses the energy needed to continue carrying the detached suspended soil particles, and the soil particles are then deposited in their new location.

Similarly, wind erosion is a world-wide problem that occurs when strong winds blow across dry soil on unprotected surfaces. Wind detaches soil particles from the surface. Once detached these particles are transported by either suspension into air and/or rolling along the soil surface. Fine sands, silt or clay size particles can be transported for great distances by strong winds. While larger particles rolling along the soil surface move shorter distance and also shatter other soil particles along the way. As the wind speed decreases, deposition of soil particles begins. Wind erosion most commonly occurs in arid and semi-arid regions, because of the frequent occurrence of dry and windy conditions.

This video clip explains the three steps in wind erosion (detachment, transport, and deposition). The clip also explains how threshold velocity varies depending on the nature of the soil surface. Video Clip by Dr. John Tatarko, USDA

 

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