Define Boundaries¶
Watch this step (4:45) in the overview video.
Boundaries close the simulation domain. Each boundary line carries a type that controls how water behaves where it meets the edge.
Draw the boundary¶
- Open the Inputs panel from the left toolbar and find the Boundaries section
- Click the pencil icon
on the Boundaries layer's row to open the editor - The editor lists the boundary lines already drawn, with a + Add new row underneath. Click + Add new. On a layer with nothing drawn yet there is no list: the pencil starts drawing straight away, and the list appears from the second line on
- Draw the line on the map: click to add vertices, double-click to finish
- Fill in the form that opens, then click Save
For the tutorial, draw one closed ring of line work around the part of the Msimbazi floodplain you want to model, staying inside the terrain's coverage.
Boundary types¶
The form's Boundary type field offers four types, and a new line starts on Dirichlet:
| Type | Behaviour |
|---|---|
| Dirichlet | Holds a fixed water level at the edge (stage 0). The default for a new line |
| Reflective | Water is reflected back, so the edge acts as a solid wall |
| Transmissive | Water passes freely out through the edge |
| Time | The level varies over time. Choosing it reveals a Boundary value field where you supply either a Constant or a TimeSeries |
The form also has a Location field, External or Internal, which is External for the ring that closes your domain.
Tip
For a first model, use Transmissive on the downstream edge where water should leave, and Reflective along the sides and upstream. Leaving a reflective edge on the outlet is the usual reason water piles up against the domain boundary in the results.
Next steps¶
Next: build a design storm in the Hydrology panel.