THE INFLUENCE OF CHANNEL WIDTH AND BANK ROUGHNESS ON RIVERBED STABILITY IN MOUNTAIN STREAMS

Abstract

We investigate the influence of the channel width and the bank roughness on the riverbed stability of mountain streams by the flume experiment. The experiment results show the following. The reduction of the channel width raises the bed sheer stress for the same flow rate and increases the sediment runoff amount. The amount of sediment runoff is not as large as expected by the bed load transport equation for mixed-size sediment. It is considered that the hiding function is exhibited and the runoff of sediment is suppressed by the stabilized large diameter stones and the progress of coarsening. Riverbank roughness has a clear effect on the control of sediment runoff. By the video analysis, it became clear that the stabilization of the rock near the riverbank makes it difficult to move many stones and stabilizes the riverbed. It was shown that the existence of the riverbank roughness increases the rate at which stones near the riverbank act as keystone. However, the effect seems to be limited if the channel width is narrow.