Soil Infiltration (SWMM)

In SWMM networks, the following methods can be used to model the infiltration of rainfall into the upper soil zone of a subcatchment:

• Horton
• Modified Horton
• Green Ampt
• Modified Green Ampt
• Curve number

Further information about the infiltration models can be found in the SWMM5 Reference Manual, Volume 1 - Hydrology.

As default, the Horton infiltration model is set for the whole network. However, this can be changed using the model parameters Options properties that are displayed by selecting the Model Parameters | Options option from the Model menu. It is also possible to choose which infiltration model is to be used for each subcatchment using the Infiltration model parameter in the applicable subcatchment properties.

The parameters required to model the infiltration methods can be defined as infiltration data for different soil types that are assigned to percentage areas of the subcatchment.

Soil type infiltration parameters are defined using the Soil tab of the Subcatchment Grid Window, and can be edited in the grid or the Soil Property Sheet. Soils can be associated with any number of subcatchments.

Infiltration parameters can also be specified as part of the subcatchment properties. If no defined soils are assigned to any areas of the subcatchment, then the applicable infiltration parameters, specified as part of the subcatchment's properties, will be used.

Similarly, if the assigned soils apply to less than 100% of the subcatchment area, and if any applicable infiltration parameters are specified in the subcatchment's properties, then these will be applied to the remaining area.