191. TOYOSHIMA, 0., "Design of a Detached Breakwater System," Troceedings 

 of the 14th Confevenoe on Coastal Engi-neervvg , American Society of 

 Civil Engineers, Vol. 2, 1974, pp. 1419-1431. 



Keywords: Accretion, Armor units, Design guidelines, Detached break- 

 water. Environmental concerns, Hexaleg blocks, Japan (Ishizaki 

 and Niigata) , Littoral transport. Segmented breakwater. Struc- 

 tural dimensions, Tombolo 



As a countermeasure against beach erosion, a serious problem in 

 Japan, many preventive works, such as seawalls and groins, have been 

 constructed during the past 20 or more years. However, seawalls and 

 groins are not always effective in preventing beach erosion; in some 

 cases they accelerate erosion. 



Based on the above, detached breakwater systems were tried as a 

 measure against beach erosion for the last 8 years. The purpose was 

 to develop sand deposition behind the structures. Several experimental 

 works were carried out and most of the tests were successful. The design 

 method of this system was based on the results of field investigations 

 conducted for more than 8 years. 



192. (a) TOYOSHIMA, 0., "Changes of Sea Bed Due to Detached Breakwaters," 



Proceedings of the 15th Conference on Coastal Engineering^ 

 American Society of Civil Engineers, Vol, 2, 1976, pp. 1572- 

 1583. 



(b) TOYOSHIMA, 0., "Countermeasure Against the Beach Erosion on 

 the Kaike Coast," Civil Engineering in Japan^ Japan Society of 

 Civil Engineers, Vol. 15, 1976, pp. 26-37, 



Keywords: Accretion, Detached breakwater, Japan (Ishizaki and Kaike), 

 Littoral transport. Segmented breakwater. Structural dimen- 

 sions, Tombolo, Wave attenuation 



The coastlines of the Japanese Island predominantly face the open 

 sea and are subject to attack by severe wave action. Beach erosion has 

 increased since the 1950 's due to decreased sediment supply from rivers 

 and from interference with longshore sediment transport by manmade struc- 

 tures . 



The shoreline at Kaike has receded about 200 meters since about 

 1920. Attempts to stabilize the beach using groins and seawalls was 

 largely unsuccessful during the period from 1947 to 1971. In September 

 1971, the first of a series of segmented, detached 'breakwaters was con- 

 structed. These have caused the accretion of sediment and several tombo- 

 los have formed. The article describes the development of the Kaike 

 project and presents results of field surveys. 



193. TRATMAN, E.E.R., "Submerged Barriers for Shore Protection," The 

 Engineer J Mar. 1940, pp. 226-228. 



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