Modeling Exfiltration

[Vinnymaster117]

I’ve designed a rain garden that includes both above-ground storage and subsurface storage via a stone bed embedded in a soil media layer. The rain garden itself is not designed as an infiltration system—instead, it is lined in impervious liner with a perforated underdrain within the stone media that routes flow to the primary culvert outlet. The rain garden is also equipped with an overflow device. Given this setup, when adding exfiltration as an outlet device over a surface area to govern the amount of flow to the underdrain, am i required to allow exfiltration for both of the defined storages? Also, how does this change if remove the underdrain and convert the rain garden to infiltrate?

Thanks

 

[psmart]

Since the media layer is generally the outlet control (using exfiltration), the pond storage storage should include only the volume above the media. In other words, you should ignore the storage in the media and underlying stone. For details see www.hydrocad.net/raingarden.htm

 

[Vinnymaster117]

Thank you for getting back to me, that makes sense. I will go ahead and remove the subsurface storage devices where I am using exfiltration.

What would you do in the scenario that you have a "zero storage" device to fill the gap between the culvert invert and the bottom of my pond? Do I even need this?

Thank you for your assistance.

 

[psmart]

Just use an exfiltration outlet, possibly routed to a culvert outlet (if you want to check for possible culvert control.) All in the same pond.