between the two cells on either side of the structure is not a good represent- 

 ation of the local shoreline orientation. Instead, the shoreline orientation 

 on the updrift or upwave side is used for calculating the transport rate. If 

 the groin is on a boundary, the transport rate is calculated as a boundary 

 condition as described in Part IV. Thus, the groin must be placed either on a 

 boundary or at least two calculation cells away from it. This message will 

 appear if a groin is placed one calculation cell away from either end of the 

 numerical grid. The error is remedied by moving the groin at least one cell 

 away from the end of grid or by moving the end of the grid at least one cell 

 away from the groin. (See Line D.4 for nondiffracting groins and Line E.4 for 

 diffracting groins.) 



23. ERROR. GROINS MUST BE SEPARATED BY AT LEAST TWO CALCULATION CELLS. 

 The longshore sand transport rate depends on the angle between the wave crests 

 and the shoreline. To calculate the shoreline orientation, the shoreline 

 location in two adjacent calculation cells is needed. At the location of 

 groins, a straight line between the two cells on either side of the structure 

 is not believed to be a good representation of the local shoreline orienta- 

 tion. Instead, the shoreline orientation on the updrift or upwave side is 

 used for calculating the transport rate, requiring at least two cells separat- 

 ing each pair of groins. This message will appear if two groins are placed 

 with only one calculation cell between them and is remedied by moving one of 

 the groins at least one cell farther away from the other groin. (See Line D.4 

 for nondiffracting groins and Line E.4 for diffracting groins.) 



24. ERROR IN CALCULATION OF BREAKING WAVE HEIGHT. THE WAVE DID NOT 

 BREAK. The undiffracted breaking wave conditions are found by a search method 

 that normally converges within 6 to 8 iterations. However, to avoid the risk 

 of being trapped in an infinite loop, the search is stopped after 20 itera- 

 tions . This error message will appear if the search procedure has not 

 converged within 20 iterations and may be remedied by changing what is 

 probably an unphysical wave height with respect to the nearshore depth (or 

 vice versa). If the error persists, it probably signals a significant flaw in 

 the wave, depth, or structure configuration input. 



25. ERROR. INCORRECT FORMAT FOR BEACH FILL DATES. The dates when 

 beach fills start are specified values of BFDATS entered on Line 1.4 in the 



C8 



