Observation of Sediment Dynamics in the Nearshore Region using Fluorescent Sand Tracers

Abstract

The field observations of cross-shore sediment transport from the swash zone to the offshore side of the outer bar using fluorescent sand tracers were conducted in 2014 and 2015 at the Hasaki coast, Japan facing the Pacific Ocean during storm wave conditions. The topography difference between the two years data set is that outer bar shape existed in 2014 and not existed in 2015. During the observations, wave height and wave period were observed, and sand core samplings were conducted. By using the observed wave data and the analyzed results of collected fluorescent sand tracers from the cores, the sediment movements from the offshore side of the outer bar area to the swash zone during storms were investigated. The results indicate that the sediment movements during the storms were affected by the outer bar shape. If the outer bar existed, the sediment of the onshore side of the outer bar tend to move landward, and it also moves to seaward due to undertow until the outer bar location. The sediment at the offshore side of the outer bar tends to move to onshore ward due to bedload sediment transport. However, the transport rate decrease in the trough region. The beach topography without the bar shape, the bed load sediment transport rate at the trough region was higher than that with the bar shape. Thus, the sediments at the offshore side of the bar also could move until the swash zone.