Surface water erosion

1
Surface water erosion

• Movement of loose materials on the surface (soil)
  by flowing water
• Limited to smaller particles (clays to fine
  gravels)
• Energy for surface water erosion
• Raindrop impact
• Overland flow
• Channeled flow

2
Energy for surface water erosion

• Raindrop impact
• Rainfall intensity
• Soil compaction and crusting
• Particle detachment and flow turbulence
• Overland flow (velocity and depth)
• Rainfall excess over infiltration rate
• Rainfall intensity
• Soil properties
• Vegetation cover
• Flow velocities related to
• Slope gradient
• Flow depth (flow volume)
• Surface roughness (vegetation)

3
Erosion factors

• Rainfall energy intensity x duration
• Slope gradient
• Slope length / contributing area
• Soil erodibility
• Vegetation cover
• Land use practice conservation measures

4
Erosion classes
Gully erosion
No or slight erosion
Sheet erosion
Badland erosion
Sheet rill erosion
River bank erosion
5
Wooded landscape near Harare
6
Land cleared for cultivation
Compacted soils promote surface runoff
7
Different crop types provide different ground
cover
Straw mulch
8
Young maize provides a poor ground cover
Mature maize provides better protection
9
Almond cultivation in southern Spain promotes
soil erosion
Natural cover of matoral
10
Clay soils crack during dry season but swell when
wet
11
Rill erosion
KwaZulu Natal
12
Coastal Transkei
Hedges shorten hillslope
Low soil erodibility allows cultivation on steep
slopes
13
Low grazing pressures maintain vegetation cover
in sub-humid area
14
Gully erosion in heavily grazed area
Hillslope acts as runoff source
15
Landscape in northern Kenya What factors do you
think would promote erosion in this environment?
16
Putting it all togetherRelationship between
weathering, hillslope erosion and river load
Mass movements
Sediment clasts - scree
Steep slopes
mechanical
chemical
WEATHERING
RIVER LOAD
Moderate slopes
chemical
Soil
Surface erosion
Dissolved material - solutes
Groundwater flow
HILL SLOPE EROSION