Abstract
River sand bar may become a barrier of smooth release of flood flow from the river channel into the sea until it is flushed. On the other hand, it prevents intrusion of sea water and transmission of high waves in to the channel. If flushing and recovery processes of the river sand bar are understood well, a sophisticated river management can be achieved. In this context, this study examines river sand bar flushing processes from eight years observation with X-band radar at the River Tenryu. 23 flushings of the river sand bar was analyzed and categorized into three patterns: (1) washed by the flood flow, (2) eroded by high waves, and (3) by the combination of flow and waves. The width of the river mouth before the flood is and important factor that determines the magnitude and pattern of the river sand bar flushing. Flushing and widening of the river mouth of 100 m or larger can be expected by flood of approximately 3 years return period. Further, the location of the river sand bar during the observation period was tracked: the mean location of the river sand bar migrated gradually and intermittently to the river side. During the migrations, erosion at the sea side of the river sand bar was observed frequently, while the area of itself increased slightly.
