1990 Fiscal Year Final Research Report Summary
Sedimentation of Tidal Currents
| Project/Area Number |
01540624
|
|---|
| Research Category |
Grant-in-Aid for General Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Research Field |
地質学一般
|
|---|
| Research Institution | Ibaraki University |
|---|
Principal Investigator |
MAKINO Yasuhiko Ibaraki Univ., Fac. of Education, Associate Prof., 教育学部, 助教授 (00100983)
|
|---|
| Project Period (FY) |
1989 – 1990
|
| Keywords | Tide / Intertidal deposits / Wave ripple / Intertidal sandbar / Ariake Sea / Step sediments |
|---|
| Research Abstract |
In the last year of my project, I did research on sedimentation of intertidal sandbars in the Ariake Sea, and Pleistocene intertidal sediments near Ajigaura beach along the Pacific coast.
1. In the Ariake Sea (Bay), muddy tidal flat sediments are widely distributed at the inner part, and sandy tidal flat sediments are developing along the coast of the outer part in Kumamoto Prefecture. At Toguchiura beach, the Uto Peninsula, we can see ten and more ridges of intertidal sandbars. Their ridges are sinuous in phase and subparallel to the beach. Many wave ripples are constructed on the intertidal sandbars by waves in a wind during high tide. The crest line of wave ripples is oblique to the ridge of these sandbars.
The peaked crests of wave ripples on a seaward slope of these bars are eroded with weak wave action just before emergence of wave ripples, and become rounded or flattened. Wave ripples on a landward slope are very little deformed by waves. As the result, the attitude of wave ripples is characteristics at the position of intertidal sandbars. Their difference is very important as a criterion for discriminating the seaward direction.
2. We found out Pleistocene step sediments at Ajigaura beach. When a longshore bar moves to the beach under fair weather, it becomes a beach-attached (welded) bar. The backrushing water sliding down the surface of the beach deforms welded bar sediments to make step. We can know the step-base depth (h) from the step depth (Z : the thickness of step sediments) at that time ; h=1.8 Z. As description on step sediments is very few, I am going to describe on step sediments.
|
