5.14 Materials

5.14.1 Command Status

Required.

5.14.2 Description

Cell materials are used to define the spatial distribution of hydraulic and bed properties such as bottom roughness or horizontal eddy viscosity. The process to assign model materials is outlined as follows.

  1. Set a spatially constant default material for the model domain
  2. Optionally define spatially varying materials using GIS vector layers
  3. Define material blocks for each material defined in Steps 1 and 2 that link the spatial location of materials with hydraulic and bed properties

If an unstructured mesh is used (Section 5.12.3), material data sourced directly from the .2dm may be used and Steps 1 and 2 above can be ignored. However, due to the dependence on mesh topology it is recommended that .2dm materials be overridden using mesh independent TUFLOW FV material spatial layering commands. If a structured mesh is used material spatial layering commands are required.

Supported material model implementations are summarised in Table 5.25, with links to the relevant implementation sections below. Material commands are provided in Table 5.26. Example syntax for spatially defining materials and material properties are provided in the following sections.

Spatial material commands follow TUFLOW’s command layering approach, as described for bathymetry (Section 5.13.3.1). The final material set used by the simulation can be reviewed within the _mesh_check_R file if Write Check Files has been set.

Table 5.25: Material Model Implementations
Model Implementation Description
Spatially Constant Single material assignment across the domain.
Spatially Varying GIS based material mapping with one or more layers.
Table 5.26: Material Commands
Command Description
Set Mat Optional - Sets all material in the domain to a single user specified value.
Read GIS Mat Optional - Spatially vary cell materials using a GIS layer of polygons.
Material Required - Instantiates a material block for a given material ID.
Bottom Roughness Optional - Assigns a material specific bottom roughness. Overrides the Global Bottom Roughness.
Horizontal Eddy Viscosity Optional - Assigns material specific horizontal eddy viscosity value or coefficient. Overrides the Global Horizontal Eddy Viscosity command.
Horizontal Eddy Viscosity Limits Optional - Assigns material specific horizontal eddy viscosity limits. Overrides the Global Horizontal Eddy Viscosity Limits command.
Bed Elevation Limits Optional - Assigns material specific bed elevation limits. Overrides the Global Bed Elevation Limits command.
Spatial Reconstruction Optional - Used to revert an area to first order calculations where the model is otherwise a second order model. If a first order model is being used then this flag will have no effect.
End Material Required - Closes the material block.

Figure 5.8 shows the use of spatially varying material polygons to define the landcover and instream bed type for a coastal estuary analysis. The polygons are coloured according to the material ID assigned to each polygon which is labelled for each polygon.

Material ID Spatial Definition

Figure 5.8: Material ID Spatial Definition

5.14.2.1 Material Properties

Material properties are specified within a material block. Material blocks begins with the Material command and end with End Material. Each material ID used in the model must be referenced in a material block. A single block can reference multiple material IDs for example Materal == 1,2,3. Multiple material properties commands (e.g. bottom roughness, horizontal eddy viscosity, bed elevation limits etc.) can be used within a single material block.

Example material blocks are provided as follows.

Bottom Roughness

This example shows a global bottom roughness that is modified locally by three materials.

! Global Settings - ks Bottom Drag Model
Bottom Drag Model == ks ! {Manning} | ks
Global Bottom Roughness == 0.10 ! {1.0E-6} Nikuradse roughness length (m)

! Local Materials
! Sandy Bed
Material == 10 ! {0} Material ID
  Bottom Roughness == 0.05 ! {Global value} Nikuradse roughness length (m)
End Material

! Overbank
Material == 2 ! {0} Material ID
  Bottom Roughness == 0.15 ! {Global value} Nikuradse roughness length (m)
End Material

! Reeds
Material == 8 ! {0} Material ID
  Bottom Roughness == 0.25 ! {Global value} Nikuradse roughness length (m)
End Material

This example shows a global bottom roughness that is locally modified within materials 3 and 4 using the same material block.

! Global Settings - Manning Bottom Drag Model
Bottom Drag Model == Manning ! {Manning} | ks
Global Bottom Roughness == 0.04 ! {1.0E-6} Manning’s n roughness (s / m^1/3)

! Material block
! Riparian veg
Material == 3,4 ! {0} Material ID - two material IDs referenced
  Bottom Roughness == 0.08 ! {Global value} Manning’s n roughness (s / m^1/3)
End Material

Horizontal Eddy Viscosity

This example shows material specific updates of eddy viscosity coefficients and limits.

! Locally Increase Horizontal Eddy Viscosity
Material == 11 ! {0} Material ID
  Horizontal Eddy Viscosity == 1.0 ! {Global value} Smagorinksy coefficient
  Horizontal Eddy Viscosity Limits == 100., 99999. ! {Global value} Minimum eddy viscosity (m2/s), {Global value} Maximum eddy viscosity (m2/s)
End Material

Bed Elevation Limits

This example shows how bathymetry can be locally updated using a material block. Any bathymetry above -10 mRL is set to -10 mRL. The value -99999. is used to define a lower limit that will never be reached in practice. This means elevations below -10 mRL are not modified. Specifying -99999. is therefore equivalent to applying no truncation to bathymetry below -10 mRL.

! Local Overrides
! Truncate below -10 mRL
Material == 11 ! {0} Material ID
  Bed Elevation Limits == -99999., -10. ! {Global value} zbmin (mRL or ftRL), {Global value} zbmax (mRL or ftRL)
End Material

Material Block With Multiple Properties

This example shows multiple bed properties being updated within a single material block.

! Multiple Material Properties

! Local Materials
! Sandy Bed
Material == 10 ! {0} Material ID
  Bottom Roughness == 0.05 ! {Global value} Nikuradse roughness length (m)
  Bed Elevation Limits == -10, 9999 ! {Global value} zbmin (mRL or ftRL), {Global value} zbmax (mRL or ftRL)
End Material

5.14.3 Spatially Constant

The Set Mat command is used to set a spatially constant material ID. This is typically used to define the default landcover type.

! Spatially constant material ID
Set Mat == 1 ! {0} Material ID

5.14.4 Spatially Varying

GIS polygon layers can be used to set a the material ID for any cell centroids located within the polygon’s extent using the Read GIS Mat command.

During model initialisation (Section 5.2), template layers prefixed with ‘2d_mat_’ are generated for use in defining materials. ‘2d_mat_’ layers require the assignment of a single ‘MATERIAL’ attribute as shown in Table 5.27.

Table 5.27: 2D Mat (2d_mat_) Attribute Description
Attribute Name Description Type
Material Cell Material ID Integer

! Spatially varying material definition

Read GIS Mat == ..\model\gis\2d_mat_BedMapping_001_R.shp ! Materials for offshore
Read GIS Mat == ..\model\gis\2d_mat_GovLanduse_001_R.shp ! Overland landuse mapping
Read GIS Mat == ..\model\gis\2d_mat_Design_OPT_001_R.shp ! Design channel bed type