FORMATIVE CONDITION OF BARS AND STREAMS WITH VEGETATION GROWTH UNDER UNSTEADY WATER AND SEDIMENT SUPPLY CONDITION

Braided streams and alternate bars under unsteady water and sediment supply conditions were reproduced via flume tests and numerical analysis, and the effects of the unsteady characteristics of water and sediment supply on the geometric characteristics of streams and bars are discussed. The results show that sediment deposits in smaller channels at higher locations during floods and bed at riffles is eroded during low flows. These phenomena force water to flow into larger streams. As a result, the bed elevation in streams decreases. Furthermore, the presence of vegetation enhances sediment deposition at higher locations and contributes to a decrease in the number of streams. These results also indicate that the unsteady condition of water and sediment supply and vegetation growth in rivers are absolutely essential for formation of single thread meandering channels.