SCS Hydrology In InfoSWMM and H2OMap SWMM Initial Abstraction Values

If you are using one of the SCS Options in InfoSWMM and H2OMap SWMM (Bullet 1 in Figure 1) then you should:
1. The CN, Time of Concentration and an optional Initial Abstraction in the Subcatchment DB Table (Bullet 2)
2. If the Initial Abstraction is zero then the default SCS Storage Equation or S = 0.2 (1000/CN - 10)
3. The losses from the Subcatchment occur the start and during the simulation (Bullet 3) and the Runoff is delayed compared to the Rainfall.   
4. If you do not want to use S = 0.2 (1000/CN - 10) then a positive value based on alternatives such as S = 0.1 (1000/CN - 10) or S = 0.05 (1000/CN - 10)

Figure 1. SCS Hydrology In InfoSWMM and H2OMap SWMM


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