Environmental Engineering Reference
In-Depth Information
Figure 19.16 Morphology of soil profiles in relation to slope
in north-east Scotland. The entire catena is termed a soil
association or hydrological sequence.
SOIL EROSION: THE HUMAN DEGRADATION OF SOIL PROFILES
human impact
Soil erosion is a set of processes which remove soil particles from the surface of soil
profiles. Some soil erosion occurs under natural conditions, but human activities often
speed up the rates of loss to give accelerated erosion . Removal can be by three agencies:
rain splash, running water or wind. In the case of running water, there are three types:
sheet erosion , rill erosion and gully erosion . Sheet erosion involves the even removal of
soil in thin layers over an entire area; it is the least conspicuous and most insidious type
of erosion. Rills are small channels cut into fields by small streams, and they are usually
small enough to be removed by ploughing, whereas gullies are much larger and need
major earth moving to fill them in. The energy needed to detach soil particles and move
them comes from the kinetic energy of the rainfall or wind; this is termed the erosivity .
The susceptibility of the landscape to erosion is called the erodibilty , and is influenced
by vegetation, soil and slope factors.
In England and Wales it has been calculated that 40 per cent of the arable farmland is
at risk of soil erosion above a tolerance level of one tonne per hectare, the level which
approximates to the rate at which new soil is formed
Water erosion can be severe on
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