MECHANISM OF SAND-GRAVEL BEACH MORPHOLOGY INVESTIGATED BY BEACH TRENCH SURVEY

Abstract

 Beach trench survey was conducted on Kochi Coast, where long-term erosion of sand-gravel beach was significant. Three trenches with width and depth of about 2 m were excavated perpendicular to the beach spanning from the updrift Niyodo River mouth to the downdrift Katsurahama. The analysis of the trench surface demonstrated the presence of stratified sediment layers inclined landward and a clear erosion line probably developed by typhoons in 2018. Sorting of sediments and change of gravel property were observed in the direction of longshore transport.