Soil erosion can be classified as natural soil erosion or accelerated erosion. Under normal climate conditions, and with natural ground cover, soil erosion can often balance out with the rate of soil production. This is called 'natural erosion', or 'geological erosion'. Natural soil erosion includes water erosion caused by rainfall and runoff of water, wind erosion, glacial erosion caused by flowing ice, stream erosion occurring during channelized water flow, coastal erosion caused by waves and tides, and erosion occurred by transportation. Erosion occurring at a rate that exceeds the rate of natural erosion is called accelerated erosion. Accelerated erosion can result from certain human land use practices such as surface mining, forestry, agriculture, and construction. Additional natural erosion processes, such as water erosion, are responsible for accelerated erosion of soil. Soil erosion in Korea is primarily caused by rainfall. This rain-splash erosion detaches earth materials from the surface by the impact of water striking the surface and by the force of surface runoff. Winderosion is found in coastal regions and highlands. The intensity and amount of rainfall, soil type, the length and steepness of slope determine the degree of soil erosion by rainfall.
Soil is created by weathering of rocks. Rainfall, temperature and vegetation play key roles in rock weathering. Korea has favorable conditions for rock weathering since it is located in the temperate climate zone and has abundant rainfall. However, severe soil erosion often occurs because most of the rain falls in summer and Korea has a relatively steep slope. Thus, soils in Korea are commonly classified as 'Inceptisols' or 'Entisols' which do not have deep soil development. Estimated annual total soil loss in Korea is 50 million tons. Twenty seven million tons of soil loss occurs on farmlands which occupy less than 10 percent of the total land area in Korea. The following map depicts the annual soil loss from farmlands in Korea. The amount of soil loss is determined by rainfall , soil type, topography, land cover, and soil management practices. The RUSLE (Revised Universal Soil Loss Equation) was used to assess the effects of rainfall erosivity, soil erodibility, slope length and steepness on the amount of soil loss and the USLE (Universal Soil Loss Equation) was used to determine the effects of crop management.
Higher rainfall erosivities were found in the southern and western coastal regions. The Baekdu Mountain system usually records higher slope-length and steepness but especially high values were found in Pyeongchang region in Kangwon Province and Jiri Mountain region which divides Kyungsang Province and Jeolla Province. Mean annual soil loss is severe in Pyeongchang and Jeongseon in Kangwon Province and Namhae, Geoje, and Geseoung in Kyungnam Province. National mean annual soil erosion of farmlands, rice paddies, and forests are 37.7 ton/ha, 1.0 ton/ha, and 3.5 ton/ha, respectively. This
study does not create national mean annual soil erosion maps for rice
paddies and forests since soil erosion of these areas are not significant. The following table illustrates the classification of soil erosion and the total areas within each grade.
(Source: Korean Rural Development Administration, National Institute of Agricultural Science and Technology, 2007)
| - Soil Erosion Grade (Based on the Yearbook of Agricultural Statistics (2004)) |
|
| Soil Erosion Grade |
slight |
light |
moderat |
heavy |
Severe |
Extremely severe |
Annual soil
loss (ton/ha)
|
0-6 |
6-11
|
11-22 |
22-33 |
33-50 |
50 |
Area of farmland
(1000 ha)
|
126 |
99 |
159 |
82 |
85 |
168 |
OECD soil erosion grade
|
Tolerable |
Low |
Moderate |
High |
Severe |
|
|
| # Farmland includes orchards |
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