Environmental Change of Suspended Sediment Discharge by Human Action

인간활동으로 인한 부유토양유출의 환경변화

The problem of supply and transport of sediment from a mountainous catchment is very important in explaining dynamic geomorphology and the hydrological cycle. The discharge of suspended sediment is determined by a morphological system. Human interference to environment Is also an important, not negligible factor in sediment production. Moreover, growing concern in recent years for the problems of nonpoint pollution and for the transport of contaminants through terrestrial and aquatic ecosystems has highlighted the role of sediment-associated transport in fluvial systems. This study was conducted in forested and quarried catchments in order to clarify the different discharge process and the mechanism of suspended sediment dynamics for each catchment. As a forested catchment, the Yamaguchi River catchment which drains a $3.12km^2$ area was chosen. On the other hand, the Futagami River basin which is formed by three subbasins (1.07, 1.59 and $1.78km^2$), as a quarried catchment was selected. These catchments are situated to the north and east of Mt. Tsukuba, Ibaraki, Japan. The discharge pattern of suspended sediment from the Futagami River basin is more unstable and irregular than that from forested catchment, the Yamaguchi River catchment. Under the similar rainstorm conditions, suspended sediment concentration from quarried catchment during a rainstorm event increases from 43 to 27,340 mg/l. However, in the case of the forested catchment it changes only from nearly zero to 274 mg/l. Generally, the supply source of suspended sediment is classified into two areas, the in-channel and non-channel source areas. As a result of field measurements, in the case of the forested catchment the in-channel (channel bed, channel bank and channel margin) is the main source area of suspended sediment. On the other hand, remarkable sediment source area on the Quarried catchment is the non-channel that is unvegetated ground.

산지유역에서 토사공급과 이동에 관한 문제는 동적지형학뿐만 아니 수문학적 순환의 입장에서 매우 중요하다. 토사유출 자연의 개변정도등 지형학적 요인에 크게 지배된다. 본 연구에서는 강우시 자연의 개변정도가 서로 다른 유역에서 유출되는 부류토량을 비교하여 부류토사 유출과정과 메타니즘을 알아 보았다. 강우강도가 유사한 30mm의 비가 내렸을때 채석장이 분포하고 있는 인공개변유역의 부유토사농도는 최고 27,000mg/l인 반면, 백연유역의 부유토사농도는 270mg/l에 불과해 100배 정도의 농도차이가 나타났다. 또 인공개역중에서도 인공개변도에 따라 최대부유토사양도 6,400mg/l에서 27,000mg/l까지 다양하게 관측되었다. 일반적으로 부유토사 공급원은 자연유역의 경우 하상, 하안, 그리고 하도주변하도입이며, 인공개변유역은 사면등의 하도외 지역이다.