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### How can I use a bio-retention cell in order to simulate a green roof?

Hi!

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!

thanks!!

Steve

#### Replies

• 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

http://amslaurea.unibo.it/2032/1/Capuccini_Enrico_Applicazione_di_t...

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!!

Steve