STUDY ON THE MEASUREMENT AND INDICATION METHOD OF SEDIMENT DISCHARGE TAKING ACCOUNT OF PA RTICLE SIZE

摘要

Due to the distinctive geology, topography and climate of Japan, much sediment is carried down the rivers. However, due to gravel mining, check dams and dam construction, sediment discharge began decreasing and scouring of riverbed and coastal erosion occurred in many rivers and along the coasts from the 1960s. To prevent such scouring and erosion, it is important to study the present status of sediment discharge and consider measures against them throughout the sediment flow system. Sediment in rivers is classified by particle size according to tractive force, and it deposits as the tractive force reduces, and then forms the geomorphology of the river. Channel section can be divided into segments by particle size of the bed material. We could find the amount of sediment discharge for each particle size in each segment by proper method determined by estimating sediment transport types, such as wash-load, suspended-load and bed-load. We gauged the amount of wash-load and suspended-load by measurement. When analyzing the sediment discharge throughout the sediment flow system, it is necessary to clarify the size and discharge of sediments composing the river geomorphology in the studied segment. In this study, we created and used a "River geomorphological map", which is a flow chart composed of the sediment supply area and sediment flow for each particle size. By using this map, the sediment discharge for each particle size throughout the sediment flow system can be determined as the flux of sediment. Such maps are useful for recognizing the outline of sediment discharge throughout the sediment flow system.