thereby modifying the sand transport rate along the beach and possibly starv- 

 ing the adjacent beach through the elimination of potential littoral material. 

 In an extreme case, if the level of the beach in front of a seawall drops, 

 waves will reflect from the wall instead of dissipating on the beach. Stand- 

 ing waves can cause local scour that may temporarily increase transport along- 

 shore or offshore, until a new, steeper equilibrium profile is achieved. The 

 integrity of the seawall may be threatened when the beach elevation drops. 



8. In the literature, there has been very little discussion on repre- 

 sentation of a seawall in the shoreline model or in other models. Essentially 

 all of the work reported to date has been conducted by engineers associated 

 with coastal engineering in Japan. More than 25 percent of Japan's 34,000-km- 

 long (21,000-mile) coastline is protected by seawalls, coastal dikes, armor 

 blocks, and similar structures (Ogawara 1983). 



9. In the early 1970's, Hashimoto et al. (1971) discussed the behavior 

 of the longshore sand transport rate in front of a seawall armored by blocks. 

 They recommended the longshore transport rate be set to zero if the shoreline 

 reaches the seawall. Ozasa and Brampton (1980) treated the loss of berm in 

 front of a seawall and devised prescriptions for introducing the action of a 

 seawall in the shoreline numerical model. In essence, their procedure also 

 consists of setting the longshore sand transport rate equal to zero at calcu- 

 lation points where the berm has been removed and the shoreline has retreated 

 to the seawall. Hanson and Kraus (1980) gave a procedure in the form of a 

 simple shoreline adjustment, but this alone is unsatisfactory because it does 

 not conserve sand volume. Tanaka and Nadaoka (1982) noted that the procedure 

 of setting the transport rate to zero is not correct. They proposed two al- 

 ternative methods, but unfortunately their methods appear to be arbitrary and 

 incomplete. 



10. Recently, Hanson and Kraus (1985) have given an outline of a well- 

 tested procedure for representing the action of a seawall in balance with the 

 capability of the shoreline numerical model and in accordance with three gen- 

 eral principles. The present report gives a complete description of their 

 method. The physical reasoning behind the method is discussed in Part II. 

 The principles upon which the method is based are: 



a. The shoreline in front of a seawall cannot recede landward of 

 the seawall. 



b. Sand volume must be conserved. 



