In the Hasaki coast around the Hazaki Oceanographical Research Station (HORS), a spatial investigation concerning the geographical features change and the sediment grain diameter change was executed from 1990 to 2015. The change in the particle size distribution of spatial on beach surface and perpendicular sand with core sample was analyzed. Separately for four areas: backshore, shoreline, wave breaking zone and offshore, the relation among the change of sediment grain size distribution, the geographical features change and the external force of wave and wind was examined.
The spatial distribution of median diameter of sand in the vicinity of shoreline divides into three stages by the state of the wave breaking. As for stage I, the berm shape is eroded by the runup of the long-period wave. Stage II, the wave condition becomes calm and the berm shape is formed in discontinuity along the shoreline. Stage III, the big waves break continuously near the shoreline and the berm shape is formed in continuity along the shoreline. Before October, 2006, the change of the beach profile and the grain size is repeated between stage I and II. After the extra high wave in October, 2006, the stage III continues and the shoreline position is steady.
In the wave breaking zone, a perpendicular structure of the grain size is formed by an alternate formation of the bar and the trough. At the storm, the sand of big diameter is left at the bottom of the trough, at the calm, the sand of small diameter piles up.
In the offshore, the fine sand (0.14mm) piles up slowly. However, the sand (0.18mm) piles up by a temporary storm event. The sand that diffused at construction of the Kashima port is thought as an origin of the coarse sand.
Piling up of the backshore is caused by sand carried from foreshore to dune by wind. The grain size of sand is small before 2006, however, it becomes bigger after 2007, because the sand of foreshore becomes coarser.
The maximum size of the blown sand changes in proportion to the maximum wind velocity while the blown sand is generated.