EFDC Restart Options

Owned by Kester Scandrett
Last updated: 15 Sept, 2021 by Duy Pham
5 min read

The bottom frame of Figure 1 shows the EFDC Restart Option. An explanation of some of the terms is provided below, as well as how to use each option.

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.

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 1  Timing/Linkage: EFDC Restart Options.

EFDC Restart Option (Output)

EFDC Restart Options (Output) check box provides options for creation of restart files. If the Use option has been selected then EFDC will create a RESTART.OUT file. 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. Note that if Use is not checked it is not possible to create a restart file should the model stop or crash for some reason.

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.

EFDC Restart Option (Input)

As noted that if Use is not checked for EFDC Restart Option (Output) then EFDC will not create restart files and restart function is not available. If it has been checked then the user should select the Restart radial button in the EFDC Restart Option (Input) frame. The output will be separate from the previous output. In this case EFDC has generated the restart file and EE will copy it for the user. Use the Set files button to select the restart files to hot start. Set files is used to navigate to the folder where the output files are located. EE will automatically copy and rename the EFDC restart files to the current project directory. 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 EFDC model (prior to EE7.2 the user had to select each restart file applicable to that model run in turn). These files will normally be in the #output folder, with 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 Run

From the release of EE7.2, a number of updates have been provided for restart options. A new option is Continuation, 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 1.


A Continuation Run 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 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 Dates box.

The process for using continuation runs is as follows:

  1. Before running the model ensure EFDC Restart Options (Output) 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 2) the model stopped at T = 142.75.
  3. Select the Continuation radial button (this is not enabled if the model is not reloaded).
  4. Do not change the time of 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.

Figure 2  Timing/Linkage: EFDC Restart Options.

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.
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.

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 maybe created using either the ViewPlan or View3D. The user goes to the desired time and saves the current model conditions by selecting the highlighted button, shown in Figure 3 below. In this case, the new Warm Start model would begin with the water column and sediment bed conditions at 271.042. A Warm Start model is different from a Hot Start model because the momentum is not included. Therefore model would begin from a quiescent system as all velocity values are zero.



Figure 3  EFDC Restart Options: Warm Start.

Hot Start means using the existing output files to restart the model.