Define Boundaries

Boundaries define the extent of your simulation domain. Each boundary line segment has a type that controls how water behaves at the edge.

Drawing boundaries

1. Select the Boundaries layer
2. Click the pencil icon to enter edit mode
3. Click Add New Feature
4. Draw a polygon around your domain on the map
5. Click Save Changes

Boundary types

Type	Behaviour
Reflective	Water is reflected back — acts as a solid wall
Transmissive	Water passes freely through the boundary
Dirichlet	Maintains a fixed water level (stage = 0)

Tip

For most models, use Transmissive boundaries on the downstream edge where water should flow out, and Reflective boundaries on the sides and upstream.