Active areas

A Flood Modeller 2D simulation requires an active area(s); polygons within your computational grid where you want to restrict calculations.

Active Area polygons define the areas within your model extent that will be active during a simulation. They allow a model to be made more efficient, i.e. by only computing areas that are known to be at risk of flooding. Flood modeller will calculate output variables that you specify (such as Depth, Elevation, Flow, Velocity) for the area(s) bounded by the active area.

These can be irregular polygons defining a particular area, e.g. just the floodplain on the right bank of a river. Areas outside of your active area might be areas where you know that water will never reach anyway. 2D will not perform calculations in any cells located outside of your active area (it will assign the no data flag to these cells). This enables you to save computation time and make a more efficient model.

Active areas are defined by an ESRI polygon shapefile.

By default the active area is initially defined automatically using the full extent of the computational area.

No specific attributes are required for active areas as Flood Modeller 2D only uses the shape extent to determine which computational cells should be active.