External Wave Model

Owned by Duy Pham
Last updated: 09 Jul, 2024 by Kester Scandrett
6 min read

This external wave model option allows the user to import wave parameter fields from other common wave models. There are two options that can be selected from the drop-down list for the External Wave Model: SWAN Model and Other Model as shown in Figure 1 and Figure 2.

Figure 1  External Wave Model: SWAN Model.

Figure 2  External Wave Model: Other Model.


External Wave Model: SWAN Model

When this option is selected, SWAN Model frame will appear with three options buttons including Generate Inputs Files, Run SWAN, Use Existing SWAN Results.

Generate Inputs Files: Click on this button to generate an input file for the SWAN model, the Create SWAN Input form pops up as shown in Figure 3.

Generate SWAN Input frame: There are several optional check-boxes

Time Options frame: Define the beginning day, end day, and time step for the SWAN model, this time period should be in the range of the EFDC Model running time.

SWAN Settings: Click on that button to show the SWAN settings as shown in Figure 4.

Boundary Conditions: If the Open Boundary Conditions check-box on the Generate SWAN Input frame is checked then the Boundary Conditions button is enabled, click on that button, form of SWAN Boundary Conditions appears as shown in Figure 5. There are three options to set Forcing Type from existing boundary conditions of the model as No wave (Figure 5), Constant (Figure 6), Time-Varying (Figure 7).

Export SWAN Input Directory: As default, the SWAN input file (swan_inp.swn) will be created and saved in the #analysis folder.


Figure 3  Create SWAN Model Input.

Figure 4  SWAN Input Parameters.

Figure 5  SWAN Boundary Conditions: No Wave.

Figure 6  SWAN Boundary Conditions: Constant.

Figure 7  SWAN Boundary Conditions: Time-Varying.

Run SWAN

After the SWAN input file has been created, the user now can run SWAN by clicking on Run SWAN button (Figure 1), the SWAN Run Options form pops up as shown in Figure 8.

SWAN Model Input: Click the Browse button to browse to the input file in the #analysis folder (swan_inp.swn)

SWAN Executable Path: Click the Browse button to browse to the executable file in SWAN folder of the EEMS installation folder.

Finally, click Run button in Figure 8 to run SWAN model. Figure 9 shows a running SWAN model window.

Figure 8  Run SWAN model.

Figure 9  SWAN model Running.

Use Existing SWAN Result

Click on that button, the Import SWAN Results form will appear as shown in Figure 10. The user must define the type of SWAN model (Steady or Unsteady Wave) from the drop-down list. In the Get SWAN Results frame, the user select For Same Grid option (if the SWAN model and EFDC model have the same grid of model domain) or For Locations option ( if the SWAN model and EFDC model have a different grid of model domain) then browse to wave time file (wavetime.inp) and SWAN output file (swan_grp.out). In case the For Locations option is selected, the user needs to location file (swan_loc.inp) as shown Figure 11. Finally, click OK button to come back the Wave form. Note that the user needs to save the model again then the wave.inp file for the current model will be created.


Figure 10  Import SWAN Results: For Same Grid.

Figure 11  Import SWAN Results: For Locations.

External Wave Model: Other Model

When this option is selected, Wave Forcing from Other Wave Model frame will appear with two options buttons including Import from Existing WAVE. INP and Manual Assign Wave Parameters.

Import from Existing WAVE.INP: EE imports an available WAVE.INP file from another project into the current project (Note: two projects have exactly the same grids). When clicking on this button, a message will be popped up as shown in Figure 12. Click Yes button to proceed.



Figure 12  Message confirmation to import WAVE.INP


The Import WAVE.INP file form will appear, select the wave.inp then click Open button as shown in Figure 13. After clicking Open button, it comes back to the Wave form. Note that the user needs to save the model again then the wave.inp file for the current model will be created.

Figure 13  Import WAVE.INP file.

Manually Assign Wave Parameters

This option is not advised to be used due to the longer time required to prepare the input data. When this option is selected, an Interpolate Classed Data form will appear as shown in Figure 14. In the Grid Options frame, select one of two options: All grid cells or Only grid cells inside polygon (when this option is selected, the Add File button in the Polygon Files frame below will be enabled). There are three options for Interpolation Options frame (Replacement, Max and Min values). In the Values to Set frame, select Constant if the user wants to set wave parameters in grid cells with constant values. Select From Scatter (XYZ) Data if the user has a wave data file ( the file has three columns, the two first columns are coordinates, the third column is wave parameter value). When this option is selected, the Add File of Data File frame will be enabled). Next, select wave parameter from the drop-down list of the Parameters. Finally, Click Apply Defined Condition button then OK button. Note that the user needs to save the model again to create the wave.inp file for the current model.

Figure 14 Interpolate Classed Data form.

Note that EFDC+ calculates the wave number using the equation: k = 2pi/wave_length. This means that if the wavelength at some cells in the wave.inp is zero, then the run will crash a “floating divide by zero” error. 

The wavetime.inp contains a time series in days for the application of the wave just like a boundary condition. For each day in Julian time, information about wave parameters such as wave length and wave height is written in the wave.inp file. These values of the wave parameters are needed for every grid cell at every time introduced in the wavetime.inp file. To generate the wave parameters for use in the External Wave Model option in EEMS, there are different tools available, including:

  • STWAVE (Steady State Spectral Wave Model)
  • MIKE 21 SW
  • WAVEWATCH III
  • SWAN (Simulating Waves Nearshore)

If a user needs to write the script to determine the parameters, it is recommended that they SWAN directly from EEMS.