SEGMENT-SCALE SEDIMENT PASSAGE TIME USING THE MEAN SEDIMENT TRANSPORT VELOCITY

Abstract

 This study investigates and tests a method to define the "mean transport velocity" of sediment using the bed-load equation and to calculate the time scale required for sediment to pass river sections in gravel-bed rivers with a wide grain size distribution. The average transport velocity is calculated by the method based on the pick-up rate and step length, and the method based on the Ashida- Michiue equation. This method was tested on about 10 km section each of the valley bottom plain and the alluvial fan of the Nagara River in the Kisogawa River system in Mid-Japan. After comparing the methods for calculating the shear stress, a discharge hydrograph for 47 years was given, and the mean transport velocity and its time-integrated distance were calculated from the shear stress against the hourly flow rate in each section. The time required to pass through each section was estimated to be 100 to 101 years for fine gravels, and 103 to 104 years for large cobbles.