Page 86 - Soil Degradation, Conservation and Remediation

3.3 Types of Water Erosion 73

Fig. 3.3 A sloping soil surface affected by interrill erosion (Photo courtesy of USDA-NRCS)

In addition to soil particles, sheet erosion removes (i) organic residues accu-
mulated on the surface soil and (ii) soluble and easily dissoluble matter, matter
made soluble by weak acids in rainwater. Zachar ( 1982 ) states that sheet erosion
represents microerosion, that is, the eroding and washing of the soil to produce
small- scale forms which may encompass raindrop erosion, laminar erosion, rillet

erosion, and layer erosion. The first phase of sheet erosion, specific with regard
to form, is soil removal by raindrop action – raindrop erosion. In raindrop ero-
sion, the surface is acted upon selectively so that small holes, micropyramids,
and other forms occur, raindrop erosion thus becoming a part of pedestal erosion,
pinnacle erosion, etc. The second subtype in sheet erosion is laminar erosion. It
occurs in any fl ow of water on an inclined soil surface where the kinetic energy
of the water is small and only the finest soil particles are consequently washed

away in a strongly selective manner. By virtue of the accumulation of sheet run-
off water, rill erosion develops, causing small rills with the dimensions of a few
centimeters diameter in cross section, and with a depth not exceeding that of the
arable layer. The rillets that develop in rows and furrows, with the effect of
increasing their dimensions and conspicuousness, are removed during cultiva-
tion. In this form of erosion, soil and particles displaced by water may be inten-
sively separated and sorted. In layer erosion, the soil is washed away neither in
laminae nor in rillets, but in a layer up to several meters wide and 10–25 cm deep
from a tilled surface, that is, in apparent strips from which the topsoil has been
entirely removed.