[HGM03-P04] The River-Bed Slope Discontinuity in Alluvial River Channels
Keywords:river-bed slope discontinuity , bed surface sedimentary structure, The Kiso River, open-work gravel layer, The Sendai River, The Yahagi River
We conducted following investigations in 3 rivers (the Kiso River, the Nagara River and the Sendai River) where the slope discontinuity occurs and the Yahagi River where doesn’t. According to Kodama (1994), we classified surface sedimentary structures into 4 types and surveyed them by a line grid method with 5 m intervals. Gravel particles on bar surfaces are often in contact with one another, forming an open-work gravel layer (Type1). Surface gravel particles rest on matrix-supported gravel layers (Type2 or 3) and sand-covered areas(Type4).
In the 3 slope discontinuity rivers, Type1 existed upstream but decreased rapidly downstream, while Type2~4 increase rapidly downstream. On the other hand, in the Yahagi River, only Type2~4 existed and Type1 didn’t.
Considering these facts, the slope discontinuity which occurs within a gravel-bed reach was and confirmed in the 3 rivers. As bed-load mobility depends strongly on the surface sedimentary structures, slope discontinuity occurs in gravel bed reach in sand starved rivers.