A TRIAL ON LONG-TERM OBSERVATION OF LONGSHORE CURRENT BY A DOPPLER RADAR VELOCIMETER

Abstract

 Longshore currents are one factor that determines the fate of sandy beaches. If we have a better understanding of the behavior of longshore currents, we can achieve a better prediction. In this respect, instruments are installed in shallow waters with considerable efforts to measure the longshore current. In this study, a Doppler radar velocimeter was installed at the research pier HORS, Hasaki Ocean Research Station, to measure the longshore current remotely for five months. We verified the measurement results with wave observation and float drift observation. The direction of the longshore current was looking to the downwave direction of the incident waves. It changed by the incident wave angle. The longshore current velocity's magnitude increased proportionately to the wave power but saturated when the wave power exceeded a specific value. This may depend on the evolution of the surf zone: During high wave periods, the breaking point locates far from the velocimeter.