All Forums

Negative flow problem


I am currently using SWMM 5 to model the Upper Bukit Timah catchment in Singapore for my master thesis. I have already tested several events of precipitation to model the flow on the outfall node. The results were reasonable, the modeled flow was closed to the observed one. Now, I am trying to model the flow for exceptional events (eg. 19Nov09: 90,64mm/h) for which I know the basin was flooded. And I have just realized that I get a negative flow for link C4 and other ones - see attached file. Consequently, the model does not show any flood in my basin...

Could someone help me with that? :-(

Thanks for your answer,


You need to be a member of SWMM 5 or SWMM or EPASWMM - (not formally associated with EPA) to add comments!

Join SWMM 5 or SWMM or EPASWMM - (not formally associated with EPA)

Email me when people reply –


  • Thanks for your answer. The problem is that I do not have a lot of data on the catchment so I have done the model with all the information available.

    Anyway I think I have solved the problem. Link C4 is to short and with a bigger lenght, it seems to work...

    thank you!

  • Hi, Emile.  You might have to model the flooded flow with surface ponding or a major / minor system.  Let us look at your model.
This reply was deleted.