material described in this paper was gained by experience in applying GENESIS 

 and its predecessor model on numerous projects. 



SHORELINE CHANGE MODEL 

 Uses 



The shoreline change model is best suited to situations in which a system- 

 atic trend exists in long-term change of shoreline position, such as retreat 

 downdrift of a groin or jetty, and advance of the shoreline behind a detached 

 breakwater. The dominant cause of shoreline change in the model is related to 

 changes in the sand transport rate along the coast produced by waves and wave- 

 induced currents. Cross -shore transport processes such as storm- induced 

 erosion and cyclical movement of the shoreline produced by seasonal variations 

 in wave climate are assumed to cancel or to average out over a long simulation 

 period. 



Figs. 2a-c show an example of shoreline change which is well suited for 

 modeling (Kraus and Harikai 1983, Kraus , Hanson, and Harikai 1984). The site 

 is Oarai Beach, located about 180 km north of Tokyo on the Pacific Ocean coast 

 of Japan. A 500-m long groin was constructed to protect a fishing harbor from 

 infiltration by sand carried by the longshore current (long groin located at 

 x = in Fig. 2). Figs. 2a and 2b show that the shoreline had a clear 

 tendency to advance on the updrift side of the long groin independent of 

 season if the interval between compared surveys is one year. Fig. 2c gives a 

 plot of shoreline positions surveyed during each season of one year. The 

 tendency of the shoreline to advance is partially obscured because the 

 relatively short interval of 3 months includes the effect of individual storms 

 and other seasonal variations in wave climate, such as changes in predominant 

 direction and wave steepness, on shoreline position. 

 Duration of Simulation 



The duration of the simulation depends on the wave and sand transport 

 conditions, characteristics of the project, and whether the beach is close to 

 or far from equilibrium. Immediately after completion of a project, the beach 

 is far from equilibrium, and changes resulting from longshore sand transport 

 dominate over storm and seasonal changes. Shoreline change calculated over a 

 short interval will probably be reliable in such a case. As the beach ap- 

 proaches equilibrium with the project, the simulation interval must usually be 



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