in front of a seawall, thus allowing the beach to recover. 



31. In the shoreline model, it would be incorrect to set the transport 

 rate equal to zero at a location where the shoreline makes contact with a sea- 

 wall, as done in most previous treatments. Rather, the transport rate should 

 be adjusted to allow calculation cells in contact with a seawall to transfer 

 sand in order to conserve total sand volume and preserve the direction of its 

 transport. 



32. On real beaches, sand is not always transported in the same direc- 

 tion over the full length of the beach. Changes in the direction of transport 

 may be produced, for example, by longshore variations in wave direction and 

 wave height as caused by refraction over an irregular bottom, or by diffrac- 

 tion at structures and headlands. Therefore, at one or more areas along a 

 beach, it is possible that a net amount of sand is moving out of the area. 

 The ways in which this can occur, and implications for shoreline change in 

 the presence of a seawall, are described in the section Model Input Require- 

 ments and Boundary Conditions, in Part III. 



14 



