Subject: RDII Initial Abstraction in SWMM 5
The initial abstraction in each of the three components of RDII in SWMM 5 are updated at each time step. The initial abstraction (ia) is:
ia = iaMax - iaUsed
based on the maximum amount of ia, the ia used (iaUsed), the recovery rate (iaRecov) and the month and class of RDII. You can enter a value for iaMax, iaInit and iaRecov for each month.
The iaUsed at the beginning of the simulation is set equal to iaInit
and if there is no rainfall