The time, volume and flooded rate shown in the SWMM 5 Report File Node Flooding Summary (Figure 2) are calculated as follows (Figure 1):
For All Nodes NOT Outfalls ( this includes Junctions, Storage Nodes, Dividers)
If the New Volume is greater than the Full Volume of the or there is Overflow then at each time step the Time Flooded is increased
If the New Volume is greater than the Full Volume of the or there is Overflow then at each time step the Volume Flooded is increased by the Overflow * Time Step
If the New Volume is greater than the Full Volume of the or there is Overflow AND Surface Ponding is Used then the Ponded Volume is New Volume – Full Volume
If the Node Depth Plus the Node Invert Elevation is above the Node Crown Elevation then at each time step the time surcharged is increased.
Figure 1. Levels of Surcharged and Flooding in SWMM 5.
Figure 2. SWMM 5 Node Flooding Summary