BEACH EROSION CAUSED BY OBSTRUCTION OF CONTINUOUS LONGSHORE SAND TRANSPORT

AN EXAMPLE OF COASTLINE BETWEEN MONBETSU PORT AND LAKE SAROMA IN HOKKAIDO

Abstract

The shoreline changes along the 64-km-long coast facing Ohotsuku Sea were investigated through the comparison of aerial photographs taken in 1947 and 2001. In this area, predominant direction of longshore sand transport is east. Port breakwaters and jetties were constructed, resulting in the disruption of continuous longshore sand transport. Severe downcoast erosion was triggered by the construction of these structures. Seawalls and concrete armor units had been installed to prevent erosion locally, but it failed to accelerate further downcoast erosion. Comprehensive measures are required to change this situation.