Saturday, 15 July 2006

The Impacts of a Severe Rainfall on Soil Properties in Steep-Slope Agricultural Areas.

Byung-Keun Hyun, National Institute of Agricultural Sciences and Technology, #249 Se-Dun Dong KewonSun Gu, Su-Won, 441-707, South Korea

The steep-sloped agricultural areas in Korea are occasionally exposed to heavy rainfalls caused by typhoons, can severely impact rates of soil erosion, land sliding, burying, and flooding . The Korean peninsula is exposed to typhoons every July and August, and the steep-sloped agricultural areas are especially impacted, and have been severely damaged by these seasonal rainfall events. The objective of this study was to identify effects of a heavy rainfall on soil properties of the steep-sloped agricultural areas in Korea. Survey sites were located in the northeast coastal area of South Korea, including the Sacheon Myun area, which was severely damaged from a forest fire in April 2000. Surveys were taken at these sites after two years of severe rainfall events, which in August 2002, included an event that poured 800 mm rainfall in a single day.

One rainfall event exceeded the highest maximum precipitation probability (750 mm) for a 500 yr period. After this event, changes in soil properties, including macro morphological and physical characteristics, were observed at the research sites, including fire-damaged forest areas. Soil erosion, burying, and flooding were observed after this storm.

Similar amounts of soil loss were observed between estimated and measured values for erosion events of grades 2-4. For a grade 5 erosion event (land slide), the measured soil loss was significantly higher than the estimated soil loss. Severe soil loss was found at lower soil-depths, greater slopes, longer slope lengths, and concave landscapes. Land slides were often found at areas having coarser textures, higher bulk densities, lower water retention contents, and lower rates of soil aggregation. Crop growth stagnation was found at the forest restoration site because of lower soil fertility and poor drainage caused by the abrupt textural changes. In conclusion, steep-slope agricultural areas are easily eroded, and need to be managed carefully.

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