All Forums


Has somebody ever try to simulate a green roof with a bio-retention cell?

I can't understand exactly the meaning of some parameters, so if someone has an example on a real case of study, I will be happy to take a look!



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 –


  • Hello Steve,

    This is how the equation is used in the code

       getStorageOutflow(double depth)

       //  Input:   depth = depth of water in storage layer (ft)

       //  Output:  returns outflow from storage layer (ft/s)//

       //  Note:    drain eqn. is evaluated in user's units.

        double delta = depth - theLidProc->drain.offset;


        maxValue = delta * theLidProc->storage.voidFrac / Tstep;

        maxValue = feet  / second

        delta *= UCF(RAINDEPTH);    feet converted to mm

            outflow = theLidProc->drain.coeff *

                      pow(delta, theLidProc->drain.expon);

            outflow in mm = mm/hour * delta in mm ^ drain.expon

            outflow /= UCF(RAINFALL);   mm converted back to feet

            outflow = MIN(outflow, maxValue);  outflow 

    to me the units are correct.

  • Segnalo ottima tesi Enrico Capuccini su uso di SWMM per applicazioni di tecnologie BMP ai sistemi di drenaggio, liberamente scaricabile

    Esemplificazioni e applicazioni a casi di studio

    • Thank you Nevio, that is a very good reference for urban LID's and BMP's!

      • Thank you!! I'm going to study what you gave me!

  • Hello Stefano,

    Here is a sample SWMM 5 LID model with Bio Retention - I hope this helps


    • Hi!

      In the Lid Control Editor for a Bio-Retention Cell there are two parameters who's phisical meaning I can't understand. They are the Drain Coefficient (C) and the Drain Exponent (n).

      According to the Lid Editor the  Drain Coefficient is [mm/hr], but according to the equation  C = 2D1/2/T (from the help) it seems to be [mm^0.5/hr].

      I don't understand what they phisically mean!

      Thank you!!


This reply was deleted.