SWMM fundamental question

[hansbenford]

When modeling a drainage area in SWMM that is completely impervious using curve numbers. A CN of 98 is put in but also the percent impervious is set to 100%. In this case, is any rainfall lost as initial abstractions or does the 100% impervious imply that all rain contacting it will become runoff (equivalent of CN=100)?

 

[francesca]

In most circumstances, some loss will occur due to storage (depressions in asphalt) and evaporation, hence CN=98 and not 100.

 

[hansbenford]

I understand this. But I am asking if SWMM accounts for that loss even if it is designated 100 % impervious.

 

[RWF7437]

Yes, SWMM does account for this loss, i believe. But you can easily check it yourself. Does the total runoff equal the total rainfall ? If so, then CN=100. If not, then CN = 98.
Try it.

 

[tsgrue]

.

SWMM5 methodologies are generally implemented in the same conceptual manner as in SWMM4.

I suggest you download and review the EPA SWMM4 Manual.

This can be downloaded from "

http://eng.odu.edu/cee/resources/model/swmm.shtml".

I also suggest looking through the SWMM5 Manual and help file.

.



tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation

http://hhwq.blogspot.com