Calculate Separate Pervious/Impervious setting

[pjhealy]

I am modelling a subcatchment where there is a parking lot and roadway adjacent to the collection point (catch basin), but a large wooded area, Hydrologic Group A soils, contributing flow to the same point. Using the default calculation setting, this option on the advanced tab being un-checked, the runoff is extremely low, such that I do not believe the results are accurate, as the pavement alone would generate a higher rate and volume of runoff to the catch basin. If I check this option, I get a reasonable runoff result. This setting is a global calculation setting, though, and I would just like to use it for this one subcatchment. Is that possible?
Thanks,

 

[pjhealy]

BTW, I am using Hydrocad 8.50.

 

[psmart]

As your example illiustrates, using a weighted CN value is not appropriate in all cases.

If you don't want to average the pervious and impervious CN values, just model them as separate subcatchments.


Peter Smart
HydroCAD Software

http://www.hydrocad.net