as a seaward boundary or :i channel exiting ti>! grid, eitlier the water eleva- 

 tion or the flow velocities can be specified ::d an open boundary-condition. 

 This infornacion can be input to K'TKM as tabular data, or constituent tides 

 can be calculated within the code during the time-stepping process. Open 

 boundaries for a grid can be snved from a specitied internal boundary of 

 another S''-a so that computational pvids can be linked togetlier. Grid linking 

 is used in this study in order to model large coastal areas inexpensively and 

 to supply correct boundar}' conditions to the shore-processes grid. 

 Land-water boundaries 



18. WII->1 allows land-water boundaries to be either fixed or variable to 

 account for flooding in low-lying terrain. Fixed boundaries specify a no-flow 

 condition at the cell face between land and water. The position of a variable 

 boundary is determined by the relationship of the water elevation at a "wet" 

 cell to the land elevation at a neighboring "dry" cell. Once a water eleva- 

 tion rises above the level of adjacent land height, water is initially moved 

 onto the "dry" cell by using a broad-crested weir formula (Reid and Bodine 

 1968). Wien the water level on the dry eel] exceeds some small value, the 

 boundary face is treated as open and computations for n , u , and v are 

 r.iade at the now "wet" cell. Drying is the inverse process, and mass is con- 

 served in these procedures. 



Thin-wall barriers 



19. These barriers are defined along cell faces and are of three 

 types: exposed, submerged, and overtopping. Exposed barriers allow no flow 

 across a cell face. Submerged barriers control flow across a cell face by 

 using a time-dependent friction coefficient. Overtopping barriers are dynamic: 

 they can be completely exposed, completely submerged, or they can act as 

 broad-crested weirs. The barrier character is determined by its height and the 

 water elevations in the two adjoining cells. 



Grid Connections 



20. Application of the embedded grid concept employed in th.'s study 

 requires a transfer of hydrodynamic information frcm one grid to another. 

 Specifically, data are transferred from the offshore grid to the nearshore 

 grid and thence to the shore process grid. In .Tactice, the shore process 

 mode] was always driven by a nearshore model simulation, and the offshore 



17 



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