EFDC Restart Options

Owned by Kester Scandrett
Last updated: 17 Oct, 2022 by Duy Pham
6 min read

EEMS provides the user with a number of options for continuing a model run that has stopped prematurely for some reason, or if it has crashed. These include Continuation runs for carrying on from where the model ended, and Restart, for carrying on the run from another time earlier in the run. The EFDC Restart Options are contained in Timing / Linkage in the Model Control form. After a right-mouse click on the Restart Options, the EFDC Model Restart Options form is displayed as shown in Figure 1. An explanation of the terms used, as well as how to use each option, is provided below in detail. Users of these features should be aware that they cannot change the model BC locations and type from the original model to the model using the restart file. Doing so may result in flows going to the locations in the model that no longer have a valid BC. 

Figure 1. EFDC Model Restart Options

Input Options for Restart Files

  • Cold Start

A Cold Start is the default option for a model run. In this case, EFDC+ generates new output files or overwrites the existing output files (Figure 2).

Figure 2. EFDC Model Restart Options: Cold Start


  • Restart

Restart is applicable when a model has stopped prematurely and has finished the run. 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

If the Use checkbox 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 has selected the Use checkbox before the run, EFDC will have automatically generated the restart file (RESTART.OUT), which is separate from the previous output.

In order to restart the model, the user can use the 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 requirements of the particular model. These files will normally be saved 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 in cases where 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 feature allows the model to begin writing from the exact time where it stopped or from the time selected for restart in case of using date stamp. The settings for this option are shown in Figure 4.

The Continuation is the same as the Restart option except that the output will be appended 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 Date box.

Figure 4. EFDC Model Restart Options: Continuation


The process for using continuation run is as follows:

  1. Before running the model ensure Output 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 the model stopped at T = 218 (Figure 4).
  3. Select the Continuation radial button (this is not enabled if the model is not reloaded). A warning message will be displayed 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.

Figure 5. Continuation Run Warning Message


Note: Whenever a new cold start is run the user should save the model in a new folder. This will prevent restart files from prior runs being available, in which case the Last Date may correspond to that prior run.

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. The Warm Start option is described in the Create Warm Start Model section.

The Restart and Continuation runs are regarded as hot starts. In the nomenclature used here, a warm start is different from a hot start because the momentum is not included. Therefore the model would begin from a quiescent system as velocity values are zero. In contrast, a hot start uses all the existing output files to restart the model.

Output Options for Restart Files

The 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 utilized. 

It is standard practice to always select Use and then 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. The Date Stamp can be left unchecked so that the file is written over each time it outputs.

Figure 7. Output Options for Restart Files