How to create a Rain area

When using the Water Overlay to perform rain calculations, it may be desirable to define one or more specific regions of the Project area in which the amount of rainfall differs from another. To configure this, a Rain area can be added to define a specific amount of rainfall in a specific region of the Project area.

How to create a Rain area for the Water Overlay:

1. Either draw a new Area, or import an area.
2. Ensure the new Area has a RAIN_M Attribute. Its value is not yet important.
3. Open the Water Overlay Wizard.
4. Ensure in the step regarding Weather, that the rain mode is set to allow Areas to override the Weather's Rain.
5. In the step to override rain with areas, select the Area you created or imported.
6. To set a single amount of rainfall which should fall in the Rain area across the entire simulation period, select "Fixed" and enter the amount of rainfall to fall in total in the Rain area.
7. To set a varying amount of rainfall, so that during the simulation the amount or intensity of rain varies in the Rain area, select "dynamic", and import a CSV to define the exact amounts of rainfall.

Notes

• It is also possible to configure the RAIN_M Attribute manually as an Attribute Array, but this is not recommended because the values (in seconds and meters) are not the same magnitude as is natural for working with rainfall use cases.
• A CSV for dynamic rainfall defines a time sequence(end-time), and should be structured as follows:

time, rain
3600, 0.03
7200, 0
9000, 0.03
10800, 0.06

The first number indicates time, the second number the amount of rain in mm. During import, you are prompted to specify the unit of time (seconds, minutes, days), and whether the separator is a comma or a semicolon.