六甲山系における山地河川の浮遊砂の計測と特性

抄録

The Rokko mountain streams and their basins have undergone vast changes during their history. Throughout the Meiji (1868-1912), this area was not vegetated. In 1938 and 1967, heavy rainfall and flooding occurred in these causing great landslide and debris flow disasters. Currently the mountains are covered by forest. In this study, wash load was observed and measured at each mountain stream, and turbidity propagation experiments were in a longitudinal direction along the Sumiyoshi River Basin. The relationship between the wash load amount, s(m³/s), and the discharge, Q(m³/s), is expressed by the equation Qs=α Q². The spatiotemporal variations in the value and the reasons for such variation were studied. The following results were clarified and observed : 1) Currently, the alue of α of the mountain stream in the Rokko Mountains varies with every flood, but it does not vary by orders of The value α is expressed as a relationship between the product of the average gradient in the basin, D, and area of the basin, A. It is expected that the relationship will depend on the geology of every region. 2) The current for the generation and loss of wash loads in the mountain streams of the Rokko Mountains are thought to based on the discharge of wash load components in riverbed sediment when stream water rises and the capture of components when the water recedes. 3) When the environments that generate sediment in the basins change and he bare land ratio ra increases, α changes by orders of magnitude. 4) When slope failure and sediment discharge occur, he bare land ratio ra increases. However, when a riverbed gravel wash load capture mechanism is held, α does not Conversely, it is predicted that when the wash load floating capture mechanisms are saturated, α increases.