Author(s): Takuya Inoue; Tomoo Ushiyama; Kazutake Asahi; Mitsuaki Yonemoto
Linked Author(s):
Keywords: Flume experiment; Mixed alluvial-bedrock river; Alternate bar; Alluvial cover
Abstract: A weakly bedrock layer is partially exposed in the middle reaches of the Ishikari River (Hokkaido, Japan) .Local bedrock erosion has led to insufficient embedded depth of bridge piers and damage to revetments. As those problems are becoming more serious, we are planning to be covered the bedrock by gravel in order to suppress the bedrock local erosion. However, the formation of gravel bars often cause partial bedrock exposure. The purpose of this work is to understand the mechanisms of the bedrock re-exposure using a large-scale flume experiment. We conducted an experiment using 1/50-scale model of the Ishikari River. The flume bed was non-erodible mortar bed, and was covered with sand of average diameter 1. 1mm. The thickness of sand layer was 20mm. The experiment was bank-full flow with discharge of 35. 5L/s. Sediment feed rate was equal to the sediment transport capacity. The experimental results showed that; 1) the bedrock was re-exposed by the bar formation near the flume banks; 2) in the straight channel zone, bedload moves over the exposed bedrock patches; 3) in the meandering zone, the secondary flow prevents the intrusion of bedload into the exposed bedrock patches.
Year: 2015