102. Line 1300 (970): This program segment is an error checking calcu- 

 lation to verify that sand volume was conserved. It also accounts for sand 

 that may have entered the system at the boundaries. 



Programs CORRE and CORRI 



103. Subroutines CORRE and CORRI are called by YSEXP and YSIMP, respec- 

 tively. They recalculate the transport rate due to the possible limited vol- 

 ume of sand in front of a seawall and adjust the position of the shoreline 

 accordingly. 



104. Line 200 (190): A branch is made according to whether the trans- 

 port rate Q, is less than, greater than, or equal to zero. A branch is nec- 

 essary because the corrections must be performed in the direction of sand 

 transport. 



105. Line (200): This and similar lines correspond to Equation 5. 



106. Line 260: Corresponds to Equation 20. 



107. Lines 270-310 (260-310): If the intermediate shoreline position 

 YC (for the explicit scheme, position Y) is seaward of the seawall, no correc- 

 tion is necessary. If not, the downstream transport rate Q i+ -| must be cor- 

 rected in order to conserve sand volume. The position YC (Y) is then set to 

 the corresponding position of the seawall. 



108. Lines 540-680 (540-680): Calculate as described above, but for 

 the reversed transport direction. 



109. Lines 700-800 (700-800): Corrections at a minus point are com- 

 puted. Sand cannot be generated in a minus cell located at a seawall. There- 

 fore, the transport rates at both cell faces are corrected so that the shore- 

 line will not move landward of the seawall. 



110. Lines 820-950 (820-970): This program segment operates in the same 

 manner as similar segments previously described, except that here the calcula- 

 tion is done in order of decreasing index since the transport is in the nega- 

 tive x-direction. Calculation starts at the point to the left (lower i-values) 

 of the minus cell and continues downstream until a plus cell is encountered. 



111. Lines 970-1100: After corrections are completed for grid points 

 within the domain of the seawall, the same procedure must be carried out for 

 the unprotected (unstructured) parts of the beach, if any. This step is nec- 

 essary for the implicit scheme, since all values of Q are solved at once. 

 It is not required in the explicit scheme, for which corrections are com- 

 pletely determined point by point, at the present time step. 



40 



