ECO-SYSTEM BASED BEACH EROSION CONTROL BY BERM NOURISHMENT COMBINED WITH BURIED SAND TUBE

Abstract

Miyazaki Coast is a 10 km stretch sandy beach between the Miyazaki Port and the Hitotsuse River, located south of Japan facing the Pacific Ocean. Significant beach erosion has been observed owing to the entrapment of sand in the harbor area and the blockage of longshore sand transport by the river mouth jetties. Sato et al. (ICCE 2010) estimated that the direction of the long-term longshore sand transport is to the southward on the basis of thermo-luminescence measurement of beach sediments. Continuous bathymetry surveys indicated the southward longshore sand transport rate at 200 thousand m3/year. However, a large variability of the incident wave direction suggested the variability in the direction of the longshore transport. Occasional attacks of typhoon storms appeared to accelerate the erosion. As a countermeasure to mitigate the erosion, sand nourishment has been introduced since 2008 with the amount of 50 to 80 thousand m3/year. Three groins were constructed to decrease the longshore transport. However, further erosion has been observed by typhoon storms even on the nourished area. This paper describes the results of on-site monitoring of waves, currents and topography change to understand the role of typhoon storms in beach erosion and to investigate the performance of eco-system based erosion control works.