Abstract
The construction of breakwaters and other shoreline structures on the part of a coast influences drift sand transport in the bay, and causes comprehensive topographic changes on the beach. This study was designed to investigate and assess sediment dynamics and land use transformation at Shiraragahama Beach in Miiraku where located in the northwestern end of Fukue Island, Nagasaki, Kyushu, Japan. This are is designated as Saikai National Park and has a rich natural environment and a mediaeval historical port. Because of the rapid development of breakwaters for a fishing harbor in recent years, the original shore environments of this sandy beach have changed to tidal sandy flats. First, we evaluated land use patterns in the basin of river flows into the site to fully understand the status of a supply source about deposited sediment. Secondly, we measured the altitude by using RTK-GPS through a year from 2017 and calculated the altitude between traverse lines on Arc-GIS. Finally, we examined the sediment deposit distribution on the site by grain size analysis. The results show, abandoned farmlands in the river basin are increased and it is considered that sediment yield from these grounds is possibly increased as well. The altitude of the site were found not significantly different through a year, but the seasonal changes of rainfall and wind wave were found responsible for the spatial dynamics of sediment in Shiraragahama. Ecosystem, landscape and community use of Shiraragaham are good status which should be conserved.
