How Does the Green Ampt Initial Moisture Defiict Work in InfoSWMM and SWMM 5?

Subject:   How Does the Green Ampt Initial Moisture Defiict Work in InfoSWMM and SWMM 5?

This graph shows the values of the internal SWMM 5 parameters for Green Ampt Infiltration for the pervious area of a Subcatchment during a simulation.  The parameters are:

·         Soil Moisture = IMD Max – (FUMax – FU)/Upper Soil Zone Depth
·         FU or current moisture content of the upper zone of the of the soil
·         FUMax which is the saturated moisture content of the upper zone in feet and stays constant during the simulation
·         IMD Max is the user defined Initial soil moisture deficit and is a fraction

Figure 1.  How Soil Moisture changes over time.

Figure 2.  Soil Moisture and IMD are related – the Soil Moisture has a maximum of IMDMax.