The Effects of Offshore Wave Energy Flux and Longshore Current Velocity on Medium-Term Shoreline Change at Hasaki, Japan

Abstract

The relationships between medium-term shoreline fluctuations, offshore wave energy flux and longshore current velocity were investigated on the basis of data sets from 1987 to 2001 (15years). In this analysis, the spectral density of the data was calculated, and the frequency components from the investigated period (15 years) to 1000 days were recomposed and defined as the medium-term fluctuation. A multiple linear regression analysis was performed to evaluate the associations between the medium-term fluctuations of shoreline change rate and that of the major dependent variables, which are the offshore wave energy flux and the longshore current velocity. The results suggested that a medium-term fluctuation of the shoreline change rate at the field was affected by both the medium-term fluctuations of the offshore wave energy flux and the longshore current velocity at approximately the same rate. The fluctuation range of the medium-term shoreline fluctuation was nearly the same range of the seasonal shoreline fluctuation, i.e. approximately 20 m. This indicates that for beach management, not only seasonal shoreline fluctuation but also medium-term shoreline fluctuation is needed to be considered.