1997 Fiscal Year Final Research Report Summary
A field experiment on the formation of beach cusps
| Project/Area Number |
08680183
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
自然地理学
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| Research Institution | Osaka University (1997)
University of Tsukuba (1996) |
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Principal Investigator |
SUNAMURA Tsuguo Graduate School of Science, Osaka University, Professor, 大学院・理学研究科, 教授 (00011164)
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| Project Period (FY) |
1996 – 1997
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| Keywords | beach cusps / shingle beaches / edge wave theory |
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| Research Abstract |
The study aims to conduct a field experiment on a pebble-cobble beach called Banbaura, located near th tip of the Manasuru Peninsula, Kanagawa Prefecture, in order to examine the initiation of beach cusps on a shingle beach paying a special attention to the temporal changes in swash/backwash movement associated with the cusp formation. The experiment started with a manually flattened foreshore zone as the initial boundary condition. The swash patterns and the cusp development were continuously secorded by a suspended video-camera system that is newly developed in this study.
This recording system is composed of a small, light-weight CCD camera module, and a video tape recorder with an LCD monirtor. The camera module is suspended in the air from the top of a carbon rod which will be stood at a high angle. The recording system is portable and very easy to set up.
The analyzes of the video images showed that there exixted the Bagnold type flow pattern on the swash zone of the cusp field, i.e., swash water flow deflected by the cusp horn concentrates in the embayment to flow down inhancing the backwash flow. The presence of this circulation pattern suggested that synchronous edge waves were responsible for the cusps appreared in the experiment ; so that the cusp spacing by use of the edge wave theory was conducted. Comparison between the calculation and the measurement indicated that the former (11.8m) was much greater than the latter (2.3-2.9m). This concludes that the edge wave theory cannot be applied to the present result.
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