Warning Messages 



38. WARNING. INPUT WAVE ALREADY BROKEN. In the use of GENESIS, wave 

 transformation from deep to shallow water can be performed using an internal 

 or an external wave transformation model. If an external wave model is used, 

 wave transformation over the actual (irregular) bathymetry is calculated 

 starting at the defined offshore depth. Resultant values of wave height and 

 direction alongshore at a depth such that wave breaking has not yet occurred 

 are placed in a file (by external manipulations by the modeler) for input to 

 the internal wave model of GENESIS. These depths (for example, the depths in 

 each wave calculation cell at the nominal 6-m or 20-ft contour) define a 

 "nearshore reference line" from which the internal wave model takes over grid 

 cell by grid cell to bring the waves to the breakpoint. This message is 

 issued if the wave height on the reference line exceeds the depth-limited wave 

 height as given by the relation H b = 7D b . This condition is remedied by 

 either decreasing the input wave height in the WAVES file or by increasing the 

 reference depth in the DEPTH file. 



39. WARNING. THE STABILITY PARAMETER IS . The numerical stabil- 

 ity of the calculation scheme is expressed by the stability parameter R s . 

 The magnitude of the stability parameter also indicates the numerical accuracy 

 of the solution. GENESIS calculates the value of R s at each time step at 

 each grid point alongshore and determines the maximum value. If R s > 5 for 

 any grid point, a message is issued. The condition can be eliminated by 

 either decreasing the time step DT at Line A. 5 or by increasing the grid 

 cell size DX at Line A. 3. Normally the time step is reduced since con- 

 siderable effort is involved in developing a grid. 



40. WARNING. TRANSPORT CALCULATIONS DIFFER. A seawall imposes a 

 constraint on the position of the shoreline since the shoreline cannot move 

 landward of the wall. GENESIS first calculates longshore sand transport rates 

 along the beach based on the assumption that the calculated amount of sand is 

 available for transport. At grid cells where the seawall constraint is vio- 

 lated, the shoreline position and the transport rate are adjusted. Corres- 

 ponding quantities in neighboring cells are also adjusted to preserve sand 



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