Studies on the Soil Erosion Mechanism for the Agricultural Land Developing - Some Results Obtained in the Observation of Sheet Erosion in a Tributary Zone of Namhankang River, Korea-

The observation of sheet erosion caused by rainfall and sunface water run-off was made in a tributary zone of Namhangang River, Korea, from April, 1974 to March, 1977. This report desrcribes some characteristic features of sheet soil erosion of the agricultural land in Korea. Over 950km^2 of area in Yongin region, Kyonghi-do, were carried out the field investigations, and the surface soils at the main 11 points were sampled and analysed as shown in Table 2.1～2.2. Thus, at first, the general characteristics of surface soil were examined in each site of the mountain area, the farm land, the paddy field and the river side. Moreover, the representative 3 points (Samga-Li, Songmoon-Li, Samgeh-Li) were chosen, where the regular sampling and analyzing of soil were made as shown in Table 1.1～1.2.　On the other hand, as shown in Fig.5, the laboratory experiments on the relation between the rainfall intensity and the sheet erosion were done in use of the same type soils as those of the above mentioned representative 3 points.　The experimental results of the sheet erosion were obtained using the same land slope and rainfall intensity and they are discussed in comparisons with the actual data of the field investigations. In the mountain area of Uichungbu city, Kyonghi-do, simultaneously were made the special observations of the surface run-off, the ground water run-off, and the amounts of sheet erosion by means of the Parshall flume equipped under the cooperations of the Ministry of Agriculture and Forestry of Korea, and the Agricultural College of Seoul National University, Korea.(Photo.6) The obtained results are shown in Table 8.1～8.3, and the general counterplan for thr farm land soil conservation in Korea is discussed and considerd. For this experiment also the reforestation project was carried out by M.A.F.K. The obtained results are described as follows. The soil losses of relatively larger particle were observed in field in Korea, and on the other hand, those of relatively smaller one were observed in the laboratory experiment, as shown in Fig.4 and Table 6, respectively. Thus, there is seen the difference of the eroded ratio of small size particles to the amount of overall soil loss between the cases of the field and the experiment. Accordingly, the study which puts the special point on the soil loss mechanism including such problem will be necessary in future. (Received June 30, 1977)