units as significant wave height. Wave angles are expressed in degrees, and 

 wave period is expressed in seconds. 



304. The number of data lines contained in WAVES does not have to 

 correspond to the total number of calculation time steps. However, the WAVES 

 input file must be designed to provide the data at the specified time step. 

 WAVES is automatically rewound if the end of the file is reached, and wave 

 data are again read from the start of the file. A simple way to represent a 

 constant wave climate through time (for testing and scoping purposes, for 

 example) is to place only one line of data in WAVES. In this case, the 

 variable DTW at Line B.6 in the START file is recommended to be set equal to 

 or greater than the number of time steps to be used, as determined by the 

 values entered at Lines A. 6 and A. 7. Otherwise, the WAVES file will be 

 rewound numerous times, increasing required computer time. 



305. NWD = 1 . If an external wave transformation model was used 



(NWD = 1 in Line B.3 of the START file), at each time step WAVES must contain: 



a. The wave period (assumed to be constant over the calculation 

 reach during the time step) . 



b. The wave height and wave direction at one offshore location 

 (at the depth DZ specified at Line B.2 of the START file). 



c. The wave height and the wave direction for each point on the 

 nearshore depth reference line. 



306. The three offshore quantities of wave period, height, and direc- 

 tion are placed on the same line and may be entered in "free format," i.e., 

 with or without a decimal. Individual entries must be separated by either a 

 blank space or a comma (or both). If the period is negative, GENESIS will not 

 calculate for the particular time step. This capability is a convenient means 

 to represent a calm wave condition for which there will be no longshore sand 

 transport. 



307. The total set of values of wave height and direction at each grid 

 point alongshore on the nearshore grid for each time step of the simulation 

 comprise a considerable amount of data. Therefore, these data are held in 

 "compressed format" in the WAVES file to minimize storage space. Thus, values 

 of individual pairs of wave height H and wave direction Z (called "6" in 

 the main text) at nearshore grid points are held in a quantity IZH and read 

 in the integer format 1017, in which IZH is calculated as 



127 



