Structures¶
Structures represent building footprints or other solid obstacles within the domain. They modify both the elevation and the friction of the mesh.
How structures work¶
When structures are present, two things happen during mesh setup:
-
Elevation burn — Building footprints are rasterised onto the DEM with a height of 5.0m added (using
gdal_rasterize). This raises the ground surface to prevent water flowing through buildings. -
Friction override — Building polygons receive a Manning's roughness coefficient of 10.0, further impeding any flow that does reach the raised elevation.
Methods¶
Each structure feature has a method property:
| Method | Behaviour |
|---|---|
Mannings |
Applies high friction (n=10) to the polygon |
Holes |
Removes the polygon from the mesh entirely |
Reflective |
Creates a reflective internal boundary |
Note
The Holes and Reflective methods are experimental. For most use cases, the default Mannings method with elevation burn is recommended.