FLOOD09931

• County: Statewide
• Community: Urbanizing Areas of Colorado
• Basin: Statewide
• Title: A Guide for Erosion & Sediment Control in Urbanizing Areas of Colorado
• Date: 1/1/1973
• Prepared For: State of Colorado
• Prepared By: USDA Soil Conservation Service
• Floodplain - Doc Type: Educational/Technical/Reference Information

The Erosion and Sedimentation Process

Soil erosion is the removal and loss of soil by the action
of water, ice, gravity, or wind. The types of erosion are
listed and defined in figure 1.

The water erosion process includes both the detach-
ment and transport of soil particles. The force of rain-
drops falling on bare or sparsely vegetated soil detaches
soil particles. Water running along the ground surface
picks up these particles and carries them along as it
flows. As runoff gains in velocity and concentration, it
detaches more soil particles, cuts rills and gullies into
the soil surface, and adds to its sediment load,

Stream bank and channel erosion occur when water
undercuts unprotected banks and erodes channel bot-
toms.

Wind erosion occurs when soil particles are displaced
and transported from unprotected surfaces by wind
action.

Sedimentation is the settling out of the soil particles
which are transported by water. Sedimentation occurs
when the velocity of water in which soil particles are
suspended'is slowed to a sufficient degree, and for a
sufficient period of time, to allow the particles to settle
out of suspension. Heayier particles, such as sand and

I WIND EROSION

2 RAINDROP EROSION

3 SHEET EROSION

4 RI LL AND GULLY EROSION

5 STREAM AND CHANNEL EROSION

gravel, settle out more rapidly than do fine particles
such as clay and silt.

FIGURE 1

I. Wind Erosion: Soil is displaced and transported
from unprotected areas by wind action.

2. Raindrop Erosion: Erosion resulting from the direct
impact of rain on soil particles. This impact dis-
lodges soil particles and splashes them into the air.
The dislodged soil particles can then be easily
transported by the flow of surface runoff.

3. Sheet Erosion: The removal of a layer of exposed
surface soil by the action of raindrop splash and
runoff. The water moves is broad sheets over the
land and is not confined in small depressions.

4. RiU and Gully Erosion: As runoff flows it concen-
trates in rivuLets, cutting several inches deep into
the soil surface. These grooves are called rills.
Gullies may develop in unrepaired rills or in other
areas where a concentrated flow of water moves
over the soil.

5. Stream and Channel Erosion: Increases in the vol-
ume and velocity of runoff may cause erosion of the
stream or channel banks and bottom.

TYPES OF EROSION

2