Up to twelve Runoff Surfaces can be associated with each subcatchment in the InfoWorks network by listing the Runoff Surfaces in a Land Use which is in turn associated with one or more subcatchments.
Runoff Surfaces are divided into two main categories:
- Impervious (for example roads or roofs)
- Pervious (for example grass)
For each surface type individual characteristics can be defined that determine how runoff of rainfall occurs on that surface, the volume of runoff and the rate at which it enters the drainage system.
Runoff Modelling Restrictions
The restrictions on what surface types can appear in a network are as follows:
- All surfaces for a land use must use the same runoff routing model.
- A surface with the New UK (Variable) PR runoff volume model must be the last surface defined for a land use, and the Default area for the last surface in the land use should be greater than 0. This is because the simulation engine disregards a 0 surface area, and the New UK model requires one. In such a case, we recommend that the Default area is set to 0.001 rather than 0.
- A surface with the Green-Ampt runoff volume model must be the last surface defined for a land use.
- If a Wallingford (Fixed PR) runoff volume is used on a surface in a land use then all surfaces in that land use must use the Wallingford (Fixed PR) runoff volume model.