7.10 Initial Conditions

7.10.1 Command Status

Optional.

7.10.2 Description

Initial conditions are recommended for salinity, temperature and each tracer, where simulated. Supported initial condition model implementations are summarised in Table 7.21, with links to the relevant implementation sections below. Commands are listed in Table 7.22.

Table 7.21: Initial Conditions Implementations
Model Implementation Description
Spatially Constant Sets initial conditions using spatially constant fields in 2D or as horizontal uniform profiles in 3D.
Spatially Varying Sets initial constituent values using 2D or 3D cell based CSV inputs.
Ocean Circulation Model Sets initial conditions using an ocean circulation model inputs.
Restart File Reads initial conditions from a previous simulation restart file.
Table 7.22: Initial Conditions Commands
Command Description
Initial Salinity Optional - Sets a spatially constant initial salinity concentration for all water depths.
Initial Temperature Optional - Sets a spatially constant initial water temperature for all water depths.
Initial Tracer Concentration Optional - Sets a spatially constant tracer concentration for each simulated tracer. This value is also constant for all water depths.
Initial Scalar Profile Optional - Used to assign spatially constant but depth varying 3D initial condition profiles.
Initial Condition 2D Optional - Used to specify spatially varying depth averaged initial constituent fields.
Initial Condition 3D Optional - Used to specify spatially varying 3D initial constituent fields.
Initial Condition OGCM Optional - Used to specify initial sea surface height, velocity, salinity and temperature fields from an ocean circulation model.
Initial Condition Quiescent Optional - Sets the initial u and v velocity fields to zero when used in combination with the Initial Condition OGCM command.
Restart File Optional - Used to initialise salinity, temperature and tracer fields from a prior simulation.

7.10.3 Spatially Constant

7.10.3.1 Two Dimensional

This method sets a single value across the entire model domain for each simulated constituent.

! Spatially Constant Tracer Initial Conditions
Initial Tracer Concentration == 100.0 ! {0.0} Trace_1 concentration (g/m^3)

If multiple tracers are simulated, initial concentrations are specified as comma separated values as shown below.

Initial Tracer Concentration == 100., 20., 0.0 ! {0.0} Trace_1 concentration (g/m^3), {0.0} Trace_2 concentration (g/m^3), {0.0} Trace_3 concentration (g/m^3)

Other spatially constant initial conditions for salinity and temperature are listed as follows.

! Spatially Constant Salinity Initial Conditions
Initial Salinity == 35.0 ! {0.0} Salinity (psu)

! Spatially Constant Temperature Initial Conditions
Initial Temperature == 24.0 ! {0.0} Temperature (C)

7.10.3.2 Three Dimensional

This method sets a single horizontally constant value for each vertical layer across the entire model domain for each simulated constituent using the Initial Scalar Profile command.

! Spatially Constant 3D Initial Profile
Initial Scalar Profile == ..\model\bc_dbase\IC_Profile_001.csv ! IC profile filepath

To set tracer, salinity and temperature initial conditions as a laterally uniform profile, the referenced csv file requires the following columns.

  • DEPTH: Depth values (m) from the surface downwards (positive downward) for assigning concentrations
  • SAL: Corresponding salinity (psu) values at each of the depths in the DEPTH column
  • TEMP: Corresponding temperatures (C) at each of the depths in the DEPTH column
  • TRACE_1: Corresponding tracer 1 concentrations (g/m\(^3\)) at each of the depths in the DEPTH column
  • TRACE_2: Corresponding tracer 2 concentrations (g/m\(^3\)) at each of the depths in the DEPTH column
  • etc.

Columns listed above can be omitted for constituents that are not simulated.

Example initial scalar profile CSV.

IC_Profile_001.csv
DEPTH, SAL, TEMP, TRACE_1, TRACE_2
 0.0, 35.0, 25.0, 12.0, 100.0
 5.0, 35.0, 18.0, 12.0, 100.0
10.0, 35.0, 11.0, 20.0, 150.0

7.10.4 Spatially Varying

7.10.4.1 Two Dimensional

Initial conditions can be set as spatial varying (depth averaged) across the model domain for salinity, temperature and tracers within a 2D model with the Initial Condition 2D command.

! Spatially Varying 2D Initial Conditions
Initial Condition 2D == ..\model\bc_dbase\IC_ML_2D_001.csv ! 2D IC filepath

This command was previously described in Section 5.15.4. To set salinity, temperature and tracer initial conditions, the referenced csv file requires an additional column for each as follows.

  • ‘SAL’ (psu) for salinity
  • ‘TEMP’ (C) for temperature
  • ‘TRACE_X’ (g/m\(^3\)) for tracers, where X is the tracer number up to the number of tracers simulated

Not all 2D cell IDs need be included in the csv file, so if this command is issued after any of the three commands listed in Section 7.10.3 then this Initial Condition 2D will overwrite only those cells specified. This command can be issued in either 2D or 3D simulations.

Example initial condition 2D file.

IC_ML_2D_001.csv - This lake resides over six TUFLOW FV cells
ID, WL, U, V, SAL, TEMP, TRACE_1
23, 1.1, 0.0, 0.0, 1.6, 50.0
28, 1.1, 0.0, 0.0, 2.3, 60.0
29, 1.1, 0.0, 0.0, 1.8, 55.0
42, 1.1, 0.0, 0.0, 1.2, 50.0
45, 1.1, 0.0, 0.0, 2.4, 45.0
66, 1.1, 0.0, 0.0, 2.3, 40.0

7.10.4.2 Three Dimensional

Initial conditions can be set at every three dimensional cell across the model domain for tracers, salinity and temperature within a 3D model (only) with the Initial Condition 3D command.

! Spatially Varying 3D Initial Conditions
Initial Condition 3D == ..\model\bc_dbase\IC_ML_3D_001.csv ! 3D IC filepath

This command was previously described in Section 6.8.3. To set salinity, temperature and tracer initial conditions, the referenced csv file requires an additional column for each as follows.

  • ‘SAL’ (psu) for salinity
  • ‘TEMP’ (C) for temperature
  • ‘TRACE_X’ (g/m^3) for tracers, where X is the tracer number up to the number of tracers simulated

Not all 3D cell IDs need be included in the csv file, so if this command is issued after any of the three commands listed in Section 7.10.3 then this Initial Condition 3D will overwrite only those cells specified. This command can only be issued in 3D simulations.

IC_ML_3D_001.csv - This lake resides over 18 3D cells (6 2D cells x 3 layers deep)
ID, WL, U, V, SAL, TEMP, TRACE_1
69, 1.1, 0.0, 0.0, 0.0, 1.20, 20.0
70, 1.1, 0.0, 0.0, 0.0, 1.28, 22.0
71, 1.1, 0.0, 0.0, 0.0, 1.35, 24.0
84, 1.1, 0.0, 0.0, 0.0, 1.42, 26.0
85, 1.1, 0.0, 0.0, 0.0, 1.48, 28.0
86, 1.1, 0.0, 0.0, 0.0, 1.55, 30.0
87, 1.1, 0.0, 0.0, 0.0, 1.63, 32.0
88, 1.1, 0.0, 0.0, 0.0, 1.70, 34.0
89, 1.1, 0.0, 0.0, 0.0, 1.77, 36.0
126, 1.1, 0.0, 0.0, 0.0, 1.84, 38.0
127, 1.1, 0.0, 0.0, 0.0, 1.90, 40.0
128, 1.1, 0.0, 0.0, 0.0, 1.97, 42.0
135, 1.1, 0.0, 0.0, 0.0, 2.05, 44.0
136, 1.1, 0.0, 0.0, 0.0, 2.12, 47.0
137, 1.1, 0.0, 0.0, 0.0, 2.20, 49.0
198, 1.1, 0.0, 0.0, 0.0, 2.28, 52.0
199, 1.1, 0.0, 0.0, 0.0, 2.38, 55.0
200, 1.1, 0.0, 0.0, 0.0, 2.50, 60.0

7.10.5 Ocean General Circulation Model

If using the Ocean circulation model boundary implementation (see Section 7.11.7), initial water level, velocity, salinity and temperature can be mapped from the OBC_GRID boundary type via Initial Condition OGCM. A second command, Initial Condition Quiescent, can then be optionally used to zero initial currents and reduce transient startup shocks. These initial conditions should only be used with the OBC_GRID boundary type.

! Use OBC_GRID derived fields 3D spatially varying initial conditions
Initial Condition OGCM ! {no default} Use OBC_GRID to assign 3D initial conditions
Initial Condition Quiescent ! {no default} Set initial currents to zero

7.10.6 Restart File

Restart files can be used to provide initial conditions for salinity, temperature and tracers in the same manner as described in Section 5.15.5. The combination of simulated salinity, temperature and tracers must be the same in the restart file and restarted simulation. Advection dispersion properties (such as scalar diffusivities or material distributions) may change between simulations.

! Read Restart File For AD Initial Conditions
Restart File == .\log\CC_20251201_20260101_WU_001.rst ! Restart filepath