TAILIEUCHUNG - Erosion control in the tropics - Part 3

3 The erosion process Some understanding of the way in which the erosion process takes place is needed to appreciate the usefulness of preventive measures. A few factors will be mentioned which together determine how much and what type of erosion is likely to occur. | 3 The erosion process Some understanding of the way in which the erosion process takes place is needed to appreciate the usefulness of preventive measures. A few factors will be mentioned which together determine how much and what type of erosion is likely to occur. Splash-erosion and stream-erosion Within water-erosion there are two types of erosion splash erosion and stream erosion. Certainly they do occur at the same time but for clarity we will discuss them separately. Splash erosion In splash erosion the falling raindrops break off small parts of the soil aggregates see Glossary . The loosened small soil particles fill the gaps between the larger particles and a so-called crust is formed see figure 7 . This layer or crust is not easily penetrated by water and air Water cannot easily infiltrate in the soil and is not available to the plant- roots hence crop growth is hindered and the water will run-off. Figure 7 Splash erosion and crusting In splash erosion the force of the falling raindrops is determined by the size and the falling velocity of the raindrop. Both these factors are of course closely related to the type of rainstorm from which the droplets fall. If the raindrops are first intercepted by a cover crop before The erosion process 17 falling on the soil their impact will be less. Those falling from a greater height will have more impact. Stream erosion Water that cannot penetrate the soil runs off to lower lying areas choosing the path of least resistance. This process causes the danger of stream erosion. In stream erosion the particles that were loosened by the turbulence in the water are carried away by the streaming water see figure 8A B . Figure 8 Stream erosion Where the water stream collects the scouring action of the water is greater and rills may be formed there. These become bigger through collapsing of the sidewalls and scouring until a gully of several metres deep is formed. The amount of erosion that occurs depends mainly on the force

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