Subject: How does the Infiltration Maximum Time to Drain the Upper Soil Zone Work in SWMM 5 Green Ampt?
You can use the monthly soil recovery factor (Figure 1) in SWMM 5 to change how the Infiltration Maximum Time to Drain the Upper Soil Zone (Figure 2) is computed each month during a continuous simulation.
The depth of the upper soil zone in the internal SWMM 5 units of feet is calculated at the start of the simulation based on the Green Ampt Soil Saturated Hydraulic Conductivity
Upper Soil Zone Depth = 4 * (Soil Saturated Hydraulic Conductivity * 12 * 3600)^0.5 / 12
And the Upper Zone Moisture Depletion Factor and Infiltration Maximum Time to Drain the Upper Soil Zone is calculated at each hydrology time step in SWMM 5.
Upper Zone Moisture Depletion Factor = Upper Soil Zone Depth / 300 * 12 /3600 * Monthly Evaporation Recovery Factor
Infiltration Maximum Time to Drain the Upper Soil Zone = 6 / (100 * Upper Zone Moisture Depletion Factor )
Figure 1. Monthly Soil Recovery Factor
Figure 2. Infiltration Maximum Time to Drain the Upper Soil Zone for a Subcatchment
