SEAWALL BOUNDARY CONDITION IN NUMERICAL 

 MODELS OF SHORELINE EVOLUTION 



PART I: INTRODUCTION 



Overview 



1 . This report provides potential users with a complete description of 

 the method developed by Hanson and Kraus (1985) for implementing the seawall 

 boundary condition in the shoreline change numerical model. Example runs are 

 included so that users may test their programs. Computer programs written in 

 FORTRAN 77 are given and explained for both explicit and implicit finite- 

 difference numerical solution schemes. 



2. The governing principles for the seawall boundary condition are sum- 

 marized in Part I. The physical basis of the seawall boundary condition is 

 discussed in a general and descriptive way in Part II. Parts I and II provide 

 background material and can be understood without knowledge of numerical model- 

 ing. Technical details of the shoreline numerical model and implementation of 

 the seawall boundary condition are given in Part III. Two example calculations 

 and a discussion of numerical accuracy and efficiency are given in Part IV. 



The computer programs are described in Part V and listed in Appendix A. 



Purpose of Seawalls 



3. Chronic erosion is found along many portions of the coast of the 

 United States and other coasts of the world. Coastal erosion is caused by di- 

 verse factors. These include rise in mean sea level, increase in severity of 

 incident waves, change in local magnitude and direction of incident waves (as 

 produced, e.g., by a newly installed coastal structure), loss of sediment sup- 

 ply from rivers and cliffs, and interruption of the local littoral drift by 

 structures. If the cause of undesirable erosion in an area cannot be elimi- 

 nated or corrected, then buildings, roads, and other resources will eventually 

 become endangered, and some degree of shore protection must be undertaken. 

 Chapter 1 of the Shore Protection Manual (SPM 1984) contains a detailed dis- 

 cussion of the causes of coastal erosion and their remedial measures. 



