LONG-TERM CHANGE IN LONGSHORE SAND TRANSPORT AT POINT IRAGO WITH SHORELINES MEETING AT ACUTE ANGLE

Abstract

 Long-term changes in longshore sand transport around Point Irago were investigated. When multiplying the area of the coastal lowland of Nishino-hama Beach northeast of Point Irago by the thickness of the sand layer of 27 m of this lowland, and divided by 6000 years after the Jomon transgression of the sea, the rate of deposition of sand became 7.4×10⁴ m³/yr. This is equal to the rate of longshore sand transport turning around the tip of Point Irago which is the only source of sand to this lowland. On the other hand, the depth of closure was estimated to be 6 m from the bathymetry around Irago Port measured in 1956, and longshore sand transport was estimated to be 6.9×10⁴ m³/yr given this depth of closure. Thus, longshore sand transport estimated in geomorphological and engineering time scales was in good agreement.