General Vertical Coordinates (GVC) Tab

When using the EPA GVC Model the GVC options are enabled as shown in Figure 1. The user must specify which layering option to use with the GVC model, either a Standard Sigma Vertical Grid (pre-GVC) layering option or a Generalized Vertical Grid (GVC) option that allows the number of layers to vary in the model.

Figure 1. GVC Tab

If the GVC layering option is selected the following sub-options must be specified:

• Use GVC Layer File: Check to manually set the cell by cell layers. When checked the GVCLAYER.INP file is written by EFDC_Explorer and then used by EFDC_GVC during the model run. If not checked, EFDC_GVC automatically assigns the GVC layers using the Surface and Bottom Reference Elevations. EFDC_Explorer can set and display the GVC layering. Use the Initialize Layering button to set the layering automatically, using the Surface and Bottom Reference Elevations. You can then view, modify and reset the layering in the ViewPlan function.
• A GVC grid has two types of cells, Local Sigma or GVC cells. Local Sigma cells use the number of layers specified in the # of Vertical Layers in Sigma Region. The number of layers must be less than or equal to KC.

The Utility Options frame allows the redistribution of the total flow into the active layers for all the flow type Boundary Conditions by pressing the Distribute BC Flows button. When using the GVC Grid, the Initialize Layering button allows the user to initialize the GVC layering using the Surface and Bottom elevations specified in the Reference Elevations form.

The Surface and Bottom Reference Elevations should initially be set to something near the maximum water surface elevation and minimum bottom elevation, respectively. These can be altered at any time and the layering recomputed using EFDC_Explorer to determine their validity. The validity of the layering can be viewed in the ViewPlan function, under Fixed Params viewing option.