Define Rainfall¶
Watch this step (9:35) in the overview video.
Rainfall is applied over an area: you draw a polygon and every mesh triangle inside it receives rain. This is the rain-on-grid approach, and for a catchment study it is usually the main way water enters the model.
Rainfall is its own input type with its own layer. It is not a kind of inflow, and it is not drawn on the Inflows layer.
Draw a rainfall area¶
- Open the Inputs panel from the left toolbar and find the Rainfall section
- Click the pencil icon
on the Rainfall layer's row to open the editor - The editor lists the areas 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
- Draw the polygon on the map: click to add vertices, double-click to close it
- Fill in the form that opens, then click Save
For the tutorial, draw one polygon covering the whole domain, a little outside your boundary ring.
The form¶
| Field | What to enter |
|---|---|
| Title | A short name for this area, for example Catchment rainfall |
| Data | Either Constant or Hyetograph / Design Storm |
Constant takes one number in mm/hr and applies it unchanged for the whole simulation. It is the right choice for a quick sanity check and the wrong choice for design work, because real storms are not flat.
Hyetograph / Design Storm opens a dropdown of the design storms saved in this project, and applies the chosen one as a rainfall-rate-against-time series. That is what the tutorial uses: pick the one hundred year, three hour storm you built in Build a Design Storm.
If the dropdown is empty, no design storms exist yet in this project. Build one first.
An attached but empty Rainfall layer is not an error
If a Scenario selects a Rainfall layer whose polygons carry no rainfall data, Hydrata says so and the Run still goes ahead with no rain at all. A model that floods nowhere is often this, rather than a solver problem.
What Hydrata does with it¶
Values are in millimetres per hour throughout. A series is applied as a step function rather than a smooth curve: each sample's rate holds until the next sample replaces it. See Rainfall inputs for the units conversion and the operator ANUGA applies.
Next steps¶
With terrain, boundaries, inflows and rainfall defined, your model inputs are complete. Next: set up the Scenario.