Reprinted from: 



Proceedings of Coastal Zone '89 . 

 American Society of Civil Engineers, 

 pp. 568-582, 1989. 



SHORELINE CHANGE BEHIND TRANSMISSIVE DETACHED BREAKWATERS 

 Hans Hanson 1 , Nicholas C. Kraus 2 , and Lindsay D. Nakashima 3 



ABSTRACT 



This paper describes simulations of shoreline evolution behind 

 detached breakwaters performed by using the shoreline change numerical 

 model GENESIS. The model was recently enhanced to include wave trans- 

 mission through breakwaters. Results of sensitivity tests are first 

 presented, showing that GENESIS provides qualitatively reasonable 

 predictions. Shoreline change at Holly Beach, Louisiana, site of six 

 detached breakwaters of different transmissivities , is then success- 

 fully simulated in this first demonstration of the new capability. 



INTRODUCTION 



Detached breakwaters provide an attractive and important shore protection 

 alternative possessing different properties than groins and beach nourishment. 

 Detached breakwaters may be used by themselves (either singly or in shore- 

 parallel sections separated by gaps) or in combination with the traditional 

 shore protection methods of groins and nourishment. Detached breakwaters 

 reduce wave energy incident on the beach and impede the offshore transport of 

 sand, neither of which properties are possessed by groins. Despite the ad- 

 vantages of detached breakwaters, they have been little utilized in the United 

 States as compared to other countries, in particular, Japan, Spain, and 

 Israel . 



The planning and design of a detached breakwater system requires consider- 

 ation of many factors, including structure length, distance offshore, crest 

 height, composition of the core of the breakwater, and gap width in the case 

 of segmented breakwaters. These parameters must then be related to the 

 average and extreme wave heights, wave direction, profile shape, and tidal 



(1) Associate Professor, Dept. of Water Resources Engineering, Institute of 

 Science and Technology, University of Lund, Box 118, Lund, Sweden S- 221-00. 



(2) Senior Research Scientist, Coastal Engineering Research Center, U.S. Army 

 Engineer Waterways Experiment Station, 3909 Halls Ferry Road, Vicksburg, 

 Mississippi 39180-6199. 



(3) Assistant Research Professor, Louisiana Geological Survey, Coastal 

 Geology Section, Box G, University Station, Baton Rouge, Louisiana 70893. 



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