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Miyahara L.,Coastal Engineering Laboratory Co. | Uda T.,Public Works Research Center | Serizawa M.,Coastal Engineering Laboratory Co.
Proceedings of the Coastal Engineering Conference | Year: 2014

When waves are incident to a sandy beach from two opposite directions, a cuspate foreland or a land-tied island may develop. A typical land-tied island can be seen offshore of Shodoshima Island in the Seto Inland Sea. Another example is Chiringashima Island located in the south part of Satsuma Peninsula, Kyushu. In both cases, the island and land are connected by an extremely slender sand bar that has been stably maintained for a long time, suggesting that it is stable against wave action from both sides of the sand bar. We developed a numerical model for predicting the elongation of a sand bar of a land-tied island using the BG model (a three-dimensional model for predicting beach changes based on Bagnold's concept). Source


Serizawa M.,Coastal Engineering Laboratory Co. | Uda T.,Public Works Research Center | Miyahara S.,Coastal Engineering Laboratory Co.
Proceedings of the Coastal Engineering Conference | Year: 2014

On a flat shallow seabed, sand spits and cuspate forelands with rhythmic shapes may develop and a barrier island can elongate alongshore, which significantly differs from the beach changes on coasts facing a deep ocean. In this study, the interaction between two circular sandy islands on a flat shallow seabed owing to waves was investigated by numerical simulation, focusing on the wave-sheltering effect of the islands themselves. The topographic changes caused by the interaction between two sandy islands were predicted using the BG model (a three-dimensional model for predicting beach changes based on Bagnold's concept). Source


Serizawa M.,Coastal Engineering Laboratory Co. | Uda T.,Public Works Research Center
Chikei/Transactions, Japanese Geomorphological Union | Year: 2011

The development of a cuspate foreland on a coast with abrupt change in coastline orientation was investigated by a movable bed experiment using a wave basin. After 8-hour wave action, a groin was installed at the cuspate foreland and the effect of obstructing continuous longshore sand transport was also experimentally investigated. The results of the experiment were reproduced using the BG model which was proposed by the present authors. The beach changes around the cuspate foreland were successfully predicted. The experimental and numerical results were in good agreement. The installation of a groin on a coast with abrupt change in coastline orientation and a steep slope induces offshore transport of fine sediment, which results in beach erosion. Source


Serizawa M.,Coastal Engineering Laboratory Co. | Uda T.,Public Works Research Center | Miyahara S.,Coastal Engineering Laboratory Co.
Procedia Engineering | Year: 2015

In a slender water body with a large aspect ratio, the angle of wind waves relative to the direction normal to the shoreline may exceed 45°, resulting in the emergence of cuspate forelands and the subdivision of a lake, because the fetch distance along the principal axis becomes large. The BG model (a three-dimensional model for predicting beach changes based on Bagnold's concept) was used to predict the segmentation of a rectangular lake by wind waves under the conditions with/without the construction of offshore breakwaters that reduce the fetch distance, together with the numerical simulation of the deformation of a circular lake when a straight seawall cutting off a part of the lake was constructed. © 2015 Published by Elsevier Ltd. Source


Uda T.,Public Works Research Center | Onaka S.,Chiyoda Corporation | Serizawa M.,Coastal Engineering Laboratory Co.
Procedia Engineering | Year: 2015

Beach changes near Pengambengan fishing port in the western part of Bali Island, Indonesia, were investigated by the analysis of satellite images and field observations. In this area, northwestward longshore sand transport prevails because of the oblique wave incidence from the Indian Ocean, and this longshore sand transport has been blocked by a fishing port breakwater, resulting in severe downcoast erosion. As a measure, a seawall has been constructed, instead of maintaining the continuity of the natural longshore sand transport. The adoption of this method caused further downcoast erosion. The sand bypassing method should be adopted to mitigate such erosion. © 2015 Published by Elsevier Ltd. Source

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