# Drywell - Location of Inlet & Outlet



## lambjere1 (Jul 1, 2015)

Hi - We have a poorly draining back yard (large levels of clay in our soil) and are getting ready to install three trench drains around our patio to improve the drainage. We currently have a 4" PVC drain line that runs from an area drain on one side of our yard to the street where it hooks into the city's storm sewer.

We are planning to tie the three new trench drains into this 4" PVC that runs to the street. We are thinking about installing a dry well to provide a buffer and potentially avoid overloading the line running to the street if we get heavy rains. We would combine the trench drains and run them into the drywell, and have the drywell feed to the 4" PVC that runs to the street.

I had two questions. First, whether the idea of a drywell makes sense. Second, if we use the drywell, can we have the drain lines from the trench drains enter the drywell below the outlet that runs to the street? I'm concerned that if the water level gets above the intlet, then the trench drains may slow or stop draining.

Below is a diagram of what we had in mind for the drywell. Apologize if this is unclear!

Thanks.


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## Ron6519 (Mar 28, 2007)

Are you planning one 55 gal drywell? I'd have 2 or 3 daisy chained together. The inlet and outlet pipes at the same level.
Can you get below the clay layer with these drywells. If you can and the layer beneath is sand, the water will perk down into the sand as well as drain to the street in heavy rains.


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## Bondo (Dec 8, 2007)

Ayuh,.... Use a 6' line to the street, 'n skip the drywells,....


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## AllanJ (Nov 24, 2007)

The useful maximum water level in a drywell is the level of the input. Higher than that and the inlet is going to back up no matter what else you do.

I would say skip the subterranean French drains around the patio. Use surface runoff via land contour and/or swale to a surface grate over the drywell. Now the level of the inlet is much higher giving you more flexibility over the level of the subterranean outlet.


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