Enhance a 2D mesh by adding roughness zones

Step-by-step guide

In ICM, a mesh can be edited using various objects to provide more detail and improve the representation of the underlying topography. These mesh editing objects can be manually added or taken from external files, layers displayed in the GeoPlan view, or objects within the network.

Roughness zones are one type of mesh editing object. Often, the surface of a 2D zone can be made up of many different land covers with different associated roughness values. To account for this variation, roughness zones can be imported to spatially distribute and vary the surface roughness of 2D elements within the 2D zone.

This example investigates several roughness zones previously defined to override the 2D zone roughness. The default roughness for the 2D zone is set to 0.013, representing a typical manning’s n value for asphalt.

One way to define a roughness zone is to use a roughness value:

1. Double-click the first roughness zone, which represents a building.

In the Properties window, this roughness polygon has a Roughness of 0.1 set to represent the high restriction the building would represent to flow. This may be something to use in less detailed areas of the model.

2. Select the second roughness zone to open its Properties.

Notice that it has no Roughness value set, but instead uses a Roughness definition. This allows the roughness to be defined as a function of depth.

3. Click the down arrow and select Open Roughness definition to view these settings.

Alternatively, access the Roughness definition tab using a new polygon window:

4. From the Windows toolbar, expand the Grid windows drop-down and select New polygons window.
5. In the polygons window, open the Roughness definition tab.

The roughness definition with multiple roughness values is defined as a smoothed step function. Here, the values represent tall grass that flattens at Depth threshold 1, and therefore, has a reduced Roughness 2 value.

6. Return to the Roughness zone Properties window.
7. Ensure Exclude roughness zone boundary when creating 2D mesh is enabled. This option is set by default and recommended to help prevent geometry conflicts.

A Priority field was added in version 2023.2. If a zone overlaps another roughness zone, the overlapping part of the zone with the lowest priority value has precedence over a zone with a higher priority value.

8. If changes were made to roughness zones, regenerate the mesh.

Once the mesh is loaded into the network, view the roughness as a color-coded theme:

9. Right-click the GeoPlan and select Properties & Themes.
10. In the GeoPlan Properties and Themes dialog box, in the 2D zone row, Themes column, click Edit.
11. In the Layer Theme Editor, click Add New.
12. Expand the Field drop-down and select 2DTriangle.Roughness_value.
13. Expand the Range drop-down and select Individual, which allows different colors to be selected for different roughness values.
14. Under Ranged Themes, use the Fill Color drop-downs to select each color, or click Auto-Theme repeatedly to browse through color schemes.

15. When finished, click OK to close the Layer Theme Editor.
16. Click OK again to close the GeoPlan Properties and Themes dialog box.

The GeoPlan now shows a color-coded distribution of the different roughness values.