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SWMM 5.0 CN Values

I am trying to determine if I am using the proper CN Values for input parameters in SWMM 5.0.  I've used the NRCS runoff curve numbers in the input for each subbasin determined from weighted CN based on landcover.  Should the impervious be removed from this since it is accounted for separately in the SWMM input parameters?

 

Thanks for the clarification in advance.

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Replies

  • Hi, The CN value that you use is for the pervious area infiltration and does not involve either the surface runoff or the impervious area runoff. If you are using a composite CN then it would be best to not use the composite CN for the pervious area only runoff. You should still use the impervious / pervious are separation to get a good estimate of the subcatchment runoff flow.
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