Saturday, 15 July 2006

Runoff Potential Risk Map Based on CN Method in Korea.

Suk Young Hong1, Kang Ho Jung1, Yi Hyun Kim1, Yeong Sang Jung2, and Han Kang Kwak1. (1) National Institute of Agricultural Science and Technology, RDA, 249 Seodun-dong, Suwon, 441-707, South Korea, (2) Kangwon National Univ, Division of Biological Environment, Chuncheon, 200-701, South Korea

Curve number indicates the runoff potential of the area. The Soil Conservaion Service Curve Number (SCS-CN ) method is a simple, widely used and efficient method for determining the approxient amount of runoff from a rainfall event in a particular area and also is adopted to estimate effective rainfall for disaster assessment in Korea. The curve number is based on the area's hydrologic soil group, land use, treatment, and hydrologic condition. The two former characters are of greatest importance. Spatial variability from land use/cover and soil hydrological properties including infiltration rate during the crop growing season at a field level in agricultural land should be taken into account to estimate runoff. The watershed of the study is located in Goesan-gun including Sosu-myeon (approx. 7,630 ha), Chungchungbuk-do. Using a digital elevation model(DEM), the watershed and the catchments were delineated. The research classified Korean soils into 4-5 hydrologic soil groups based on infiltration rate measured and an estimation model for the representative soils of the restudy area. Digital soil maps(1:5,000 scale) were used for classifying hydrologic soil groups based on soil series unit. On-screen digitization using high resolution aerial images, each field boundary was delineated as farm land unit. After land use and cover survey was carried out for every field, farm land unit data were used for curve number calculation in the watershed. CN was calculated for estimating runoff in the watershed using the land use/cover map and the hydrologic soil map. CN values of the catchments in the watershed ranged from 35 to 57. CN values of each farm land cells ranged from 20 to 98, in the order of forest, paddy fields, upland, and village or man-built area which showed the highest imperviousness. Runoff potential risk map with consideration of slope will be made for the whole country based on digital landuse/cover map delineated from satellite images and digital soil map at scale 1:25,000.

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