| In the Ishikari River, riverbed degradation has been caused by bedrock erosion. Local bedrock erosion leads to insufficient embedded depth of bridge piers and the damage of revetments. Bedrock that is completely covered by alluvium cannot undergo erosion. So, we are planning to be covered the bedrock by gravel in order to suppress the riverbed degradation in the Ishikari River. However, gravel bars formed on the alluvial bed often cause partial bedrock exposure. The purpose of this work is to understand the mechanisms underlying the bedrock re-exposure by a large-scale flume experiment. The results suggest that; 1)bedrock of river banks neighborhood is re-exposed continuously in the longitudinal direction; 2) gravel bars are formed, and the bar height affects partial bedrock exposure; 3) in the straight channel zone, bedload moves over the exposed bedrock patches; 4) in the meandering zone, secondary flow prevents the intrusion of bedload into the exposed bedrock patches. |
