EFDC Restart Options is under the Timing / Linkage. Right-mouse click on the Restart Options, the EFDC Model Restart Options form is shown in Figure 1. An explanation of the terms used, as well as how to use each option, is provided below in detail.

Figure 1. EFDC Model Restart Options

Input Options for Restart Files

• Cold Start

Cold start is the normal start of a model run and EFDC will generate the new output files or overwrite the existing output files. This option is the default setting (Figure 2).

Figure 2. EFDC Model Restart Options: Cold Start

• Restart

The Restart is a previously available feature of EFDC and is applicable when a model has stopped prematurely and is not finished. The user can use it to restart from the point at which it terminated or some other point by selecting the appropriate restart file. In this case, there is a hard restart from the time selected. EFDC will create a whole new set of output files which the user will then need to merge later. Figure 3 shows the Restart option.

Figure 3. EFDC Model Restart Options: Restart

As noted that if Use is not checked for Output Options for Restart Files then EFDC will not create restart files. The restart function is still available but the user needs to load their own restart file.

If the user selects the checkbox Use, EFDC will automatically generate the restart file ( RESTART.OUT) which is separated from the previous output.

In order to restart the model, the user can use  Set files button to navigate to the folder where the output files are located. The user has to select only the RESTART.OUT file and click open, then the other restart files (such as RSTWD.OUT, etc.) will be automatically selected by EE based on the requirement of the EFDC model. These files will normally be in the #output folder, with the file name to be selected shown in the header and bottom left of the open file interface. EE will rename the files automatically and save them to the project directory after each one has been selected.

Some of the restart files that are created include the TEMP.RST and RSTWD.INP files if temperature and wetting & drying are being simulated. The Dye Overwrite is a legacy option. If the checkbox is selected the dye concentrations in the restart file will be overwritten by DYE.INP file. This is useful when restarting a tracer study with a new initial condition.

• Continuation
  

The Continuation is a feature, whereby when restarting a model, EFDC+ can now move to the correct location in the EE linkage files and begin writing from the time the model stopped or from the time selected for restart in case of using date stamp. The settings for this restart option are shown in Figure 4.

The Continuation is the same as the Restart option except that the output will append to an existing run and so is only applicable when there is already model output in the current model directory. If there is no output and a restart file then this option is not enabled. If no date stamp is used EE will display only one restart file without a date label which is the last restart file before EFDC terminated. To create the restart file the Restart Output should be set to continuous (i.e. N=1). EE displays the date range available for the continuation from the most recent binary file output in the Last Datebox.

Figure 4. EFDC Model Restart Options: Continuation

Figure 5. Continuation Run Warning Message

The process for using continuation run is as follows:

1. Before running the model ensureOutput Options for Restart Files is set/checked to Use. If Date Stamp is selected the user may continue from any snapshot as all snapshots are saved, not just the final snapshot. However, this is more memory intensive.
2. Reload the model to update Last Date box. In this case (Figure 4) the model stopped at T = 218.
3. Select the Continuation radial button (this is not enabled if the model is not reloaded). Then a warning message will be popped up as shown in Figure 5.
4. Do not change the time of the start. Save the model in the same folder. If the user wants to save in another folder then they will need to manually copy the output to the new folder.
5. Run the model and select overwrite.

The model will run from the continuation time and automatically merge with the prior output. This removes the necessity of the user having to merge runs as was required in earlier versions of EE. This option is different to the Append feature as it is now possible to restart a model at various user-defined times.

Once the Restart Options is selected, it will be updated to the Model Restart Options report as shown in Figure 6.

Figure 6. Model Restart Options Report

Other options not discussed above include: Warm Start. This function allows the user to create the initial conditions for the model at a specified time. This is useful for diagnostic and sensitivity analyses, allowing the user to understand key processes in the system. A Warm Start option is described in Create Warm Start Model.

Output Options for Restart Files

Output Options for Restart Files frame (Figure 7 )provides options for the creation of restart files. If the Use option has been selected then EFDC will create a RESTART.OUT file automatically. If Date Stamp is not checked then one file called RESTART.OUT will be created at the user-defined Output Frequency, overwriting the previous file each time. If Date Stamp is checked then a file called RESTART_YYYYMMDD_HH.MM.OUT is created at the Output Frequency for each EFDC sub-module being utilized. 

DSI standard practice is to always select Use and set Output Frequency to 1 to be the same as the duration of the reference periods. The user must have this option turned on in order to use restart as this creates the files required for the restart. Date stamp can be left unchecked so that the file is written over each time it outputs.

Figure 7. Output Options for Restart Files