CNSWMM Model
The CNSWMM runoff volume model is based on the SWMM (Storm Water Management Model) Curve Number infiltration model developed by the US Environment Protection Agency (EPA), and is intended for use in multiple storm simulations.
It is similar to the SCS method, which is a widely accepted model for predicting storm flow volumes from rural catchments. The SCS model combines together all losses due to interception, depression storage and infiltration, to predict the total rainfall excess from a rainfall event.
The SWMM Curve Number model uses a modified, incremental form of the method that accounts only for infiltration losses, since the other abstractions are modelled separately. It is described in the SWMM5 Reference Manual, Volume 1 - Hydrology.
To use the CNSWMM runoff volume model in an InfoWorks network, ensure that the Runoff volume type field of the Runoff Surface is set to CNSWMM and that the following parameters are set for each subcatchment that is to be modelled using CNSWMM method:
- Curve number. A comprehensive list of curve numbers is included in the Setting Runoff Coefficients from GIS Data topic.
- Drying time.
