Tuflow and estry manual Version 3

3.16Initial Water Levels (IWL) and Restart Files

3.16.12D Domains

Initial water levels (IWL) are set globally as a constant using the Set IWL (.tcf file) or Set IWL (.tgc file) command. IWLs can also vary spatially using one or more GIS layers. This is particularly useful for setting initial water levels in lakes, dams, etc.

To set a gradually varying water surface, the best approach is to start the simulation “cold” or “dry” and create a restart file to set initial water levels and flow velocities – see Write Restart File at Time, Write Restart File Interval and Read Restart File.

The easiest way to set up a GIS IWL layer is to:

1. 
   Create a 1d_iwl layer using an empty layer created by Write Empty MI Files.
   
2. 
   Digitise regions, lines or points and assign each object an initial water level value.
   
3. 
   Export the GIS layer as a MIF/MID.
   
4. 
   Use the Read MI IWL command to read in the IWL values.
   

Alternatively, the Read MID command can be used as follows:

1. 
   Select the relevant grid cells or ZC points from a 2d_grd or 2d_zpt GIS layer.
   
2. 
   Save the selection as another layer named 2d_iwl_.
   
3. 
   Modify the 2d_iwl attributes (see Table 4 .19) so that you:
   
   1. 
      keep the first two columns as the row (n) and column (m) grid references;
      
   2. 
      remove all other columns;
      
   3. 
      add a (third) column as one named “IWL” defined as a float or decimal.
      
4. 
   Using the GIS to set the IWL value(s) as required.
   
5. 
   Other grid cells or ZC points can be copied and pasted into 2d_iwl if required and the IWL value(s) allocated.
   
6. 
   Export the GIS layer as a MIF/MID.
   
7. 
   Use the Read MID IWL command to read in the IWL values (see Section 10.1.1.1.1.1A.8 or 10.1.1.1.1.1C.3).
   

Any number of IWL layers may be used, noting that if a cell’s IWL occurs more than once, the last occurrence prevails, ie. TUFLOW overwrites any previous IWL already set.

The Read MID IWL command maybe used in the .tcf and .tgc files, noting that the .tgc file is processed before the .tcf file. Note: At present, the Read MI IWL command can only be used in the .tgc file (this will be extended to the .tcf file in a future release). Using the IWL command in the .tcf file allows the initial water levels to be set independently of the geometry file. This is useful where several simulations of different events use the same .tgc file but have different initial conditions, by removing the need to not have separate geometry files for each event.

Table 4.19 2d_iwl Attributes