boundaries are open and the type boundary condition to be imposed on each. 

 The program can be run in an interactive mode from a terminal, allowing errors 

 in the input data to be corrected efficiently and changes made to the 

 parameters. 



2. Computational Unit (CU) . 



The CU is the program that does the actual calculations of the water level 

 and x,y components of the water velocity along each gridline at every time 

 step. It is submitted as a batch job with the user having no control as opposed 

 to the lU, which is interactive. The CU uses the data prepared by the lU and 

 produces a simulation through the time period specified. The printout of water 

 level and velocity components can be obtained at specified time increments. 

 Results also can be stored at specified time increments for use later in plot- 

 ting the water levels and currents in one, two, or three dimensions at a given 

 time or versus time at specified points. 



3. Example Application . 



The System 21 Mark 8 model is applied to an area around the CERC Field 

 Research Facility at Duck, North Carolina. Contours of the bathymetry in the 

 region modeled are shown in Figure 2. A 60 by 130 grid with a uniform spacing 



llOOr- 



1000 



900 



^ 800 



E 



£ 700 



g 600 



< 



S 500 



S 400 



300 



200 



100 







200 400 600 



Distonce Offshore ( m ) 



800 



1000 



Figure 2. Contours of bathymetry near the pier (October 1980 survey). 



The rectangular boundary near the pier is the region modeled. 

 The contour interval is 1 meter. 



