variation in order to estimate the shore protection capabilities of the 

 breakwater system. Perlin (1979) investigated geometric parameters determin- 

 ing the influence of a breakwater on the shoreline by using a numerical 

 simulation model of a single shore-parallel structure. Kraus (1983) obtained 

 good agreement in a comparison of breaking wave height and direction and 

 shoreline change behind a detached breakwater calculated with a numerical 

 model and measured in a physical model. Kraus and Harikai (1983), Kraus, 

 Hanson, and Harikai (1984), and Hanson and Kraus (1986a) modeled waves and 

 shoreline change behind large breakwaters in the field, and Hanson (1987, 

 1989) modeled shoreline change measured behind three detached breakwaters at 

 Lakeview Park, Lorain, Ohio. 



All of the aforementioned numerical modeling studies reproduced correct 

 trends in shoreline evolution behind detached breakwaters. However, an 

 important process absent in these works was wave transmission through the 

 breakwaters. Wave transmission is a decisive factor in most practical appli- 

 cations, since it is economical and often advantageous from the perspective of 

 beach change control to build low and/or porous structures which allow a 

 portion of the incident wave energy to penetrate directly behind them. The 

 shoreline change model GENESIS (Hanson 1987, 1989; Hanson and Kraus 1989) has 

 recently been enhanced to include wave transmission at detached breakwaters, 

 and the purpose of the present paper is to demonstrate this new capability. 

 Technical details will be given in Hanson and Kraus (in prep). 



DETACHED BREAKWATER PROCESSES 



The most obvious shore protection property of detached breakwaters is the 

 wave sheltering afforded to the beach (Fig. 1). The wave height and longshore 

 current speed are reduced behind these structures, and sand carried by the 

 longshore current is deposited in the calm "shadow zone," resulting in seaward 

 progression of the shoreline. If a detached breakwater is placed too far 

 offshore, its sheltering effect will be inoperative, whereas if it is placed 

 too close to the shore, the beach will prograde excessively, forming a tom- 

 bolo. 



Typically, the most desired structure placement is such that the resultant 

 cuspate- shaped equilibrium beach form, called a salient (Dally and Pope 1986), 



41 



