Use rainfall-runoff (0D inflow) in 1D models

Rainfall typically descends directly onto surfaces before finding its way into the sewerage system. However, in urban areas, a substantial portion of the rain lands on buildings. This rainwater can either flow into the sewerage system through rain pipes or be retained, a phenomenon known as 0D inflow.

For a detailed understanding of how 0D inflow is computed and guidance on choosing between utilizing the Surface or Impervious surface references, consult Rainfall on 0D node (inflow). Additionally, refer to Inflow objects for an overview of the schematization objects employed.


How to add 0D inflow to a schematisation:

  • In the Global settings table, the parameter use_0d_inflow must be set to 1 (for ‘impervious surface’ 0D inflow) or 2 (for using ‘surface’ 0D inflow). If you do not want to use 0D inflow, set it to 0.

  • If you are using Surface inflow, add a record to the Surface parameters table.

  • Add polygon features to either the Surface or Impervious surface layers. The feature attributes describe the rainfall-runoff process for each surface. If you are using Surface inflow, set the surface_parameters_id to refer to the parameter set you want to use for this surface.

  • Map each surface to a connection node by adding a line feature to the Surface map or Impervious surface map. Draw a line from the (impervious) surface polygon to the connection node. By default, the Percentage is 100, meaning that 100% of the runoff produced by the mapped surface is added to the volume of the target connection node.

  • If you want, you can also divide the runoff from a surface over several connection nodes. Draw (impervious) surface map lines from the same (impervious) surface polygon to several connection nodes. The Percentage attribute of the (impervious) surface map feature determines how the runoff is distributed over the different connection nodes. E.g. if you map as surface to 3 connection nodes, you may want to set the percentages to 25%, 25% and 50%.


Pay attention to the total storage that is available in the target node in relation to the area of the (impervious) surface. The total storage of the node is the sum of the storage in the connection node (storage area multiplied by the difference between bottom and drain level) and half of the volume of all connected pipes, channels and/or culverts. If the total storage in the node is very small relative to the amount inflow that is expected, the water level in the node will rise very quickly, which may lead to unexpected behaviour.

Combining 0D inflow with 2D rain

Combining 0D inflow with and 2D rain can be useful in several cases, for example:

  • Detailed urban water management models that use 0D inflow for the flow of water from roofs to the sewerage and 2D surface for rainfall and discharge over roads

  • Large open water systems in which a small area is modeled in detail while upstream catchments are lumped in 0D inflow.

An explanation of how this can be used is given in Combine direct rainfall and sewerage inflow.


After taking the steps described above, a 3Di model can be generated from the schematisation. Any rain that is forced on the model during the simulation will be used to calculate the runoff from the surfaces. It will be added to the volume of the calculation node to which it is mapped as lateral discharge.