Hello there,

I am trying to set a constant outflow concentration as the result for a treatment-equation, i.e. BOD: C=50.
Unfortunately, setting a constant value for the concentration does not work, the result of the effluent concentration would be just the same. However, I want the concentration to be exactly the value I selected in the treatment-expression. Moreover, it seems like every treament-expression with C=... leads to invalid results... What can I do to fix this? Defining an additional inflow at the correspondent node is not sufficient, as my flow should not change.

Furthermore, I am trying to implement an equation where a pollutant stands in the exponent of a equation, i.e. HRT^(0.75*TSS). With this expression, I would get an error when trying to simulate (invalid expression). Is it not possible to use this kind of expression? What else can I do to solve this issue?

Kind regards (from Germany)


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    I found out that (example):


    can actually be replaced by following expression


    Hope that helps anyone with the same problem.



  • No, that form does not work - it looks like you cannot have HRT raised to another pollutant exponent. I will check this

    This function does work, however


    • Thanks for the quick reply!

      I guess it's a very uncommon approach to raise a variable by a pollutant exponent, but maybe this could still be an option to be implemented in upcoming updates for SWMM. 

      Anyway I will try to adopt to it by changing my expression.

      Kind Regards,


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