What to do with torrents off the roof?
dsmcn
| Posted in GBA Pro Help on
Zone 4A, East TN, annual rainfall >50″ and downpours can be significant. Upslope lot.
Downspouts will tie into 4″ pipe to daylight, but then what? Seems responsible to NOT discharge it down the driveway. But if I discharge it onto the slope it would soon create a local grand canyon.
There will be a 3′ garden wall to provide a level grade in front of the house. The 4″gutter drains will exit through that wall in two or three places.
Any tried and true remedies?
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Replies
Some people terminate the pipe into a drywell filled with stones. A lot depends on your local conditions. How permeable is your soil? How steep is the land? How much room do you have?
My roof has no gutters. Rain pours off the roof into a three foot wide trench filled with 3/4" stone. We put perforated pipe, wrapped with landscape cloth, in the trench under the stone. We have very sandy soil, so a lot of the water just gets absorbed by the ground. The rest flows through the pipes. The pipes eventually terminate on a pretty steep slope that we filled with 6 -8" stones. The large stones help to avoid any erosion.
I assume you are concerned about dumping water into the municipal wastewater system. Where does your water go after it enters the sewer? If your area has an old combined system, then adding water probably isn't a good idea. If it's a dedicated storm water system and not overcapacity, I'm not sure I would worry about it.
Stephen's large dry well placed down slope and well away from the house is an appropriate solution. That re-charges the ground water, and doesn't contribute to storm run-off contamination/erosion issues.
Without seeing the topo and site plan on your list and existing adjacent properties, how can we tell? Also from the sounds of it, a pipe that terminates into a gravel filled dry well can be overwhelmed and may back up if th etorrents are so great as to fill the well faster than it cam perculate. If you could create a swale or detention area for the water with a safety damn that would allow some water out of it was overwhelmed, that might work better. I created an excavated low area for detention, and then ran a 12" pipe sixty feet under the drive way to a lower area lined with round gravel. That retention area then has an overflow of gravel lined swale that runs it to a vegetated meadow then tothe woods. We had one storm in 18 months that had wtaer runs great in that swale into a vegetated area. Every other time it perculated away before it rose that high. I learned to do this when during construction we had frozen ground, the weather warmed and all of a sudden we had torrential rain. The driveway which was a foot higher was almost overtaken. So that is why I lower the grade for the pounding area and diverted almost all my roof water and driveway water to that pounded area. Always bear in mind that when you have frost conditions in late winter, the ground won't perc if you get downpours. That is often overlooked in these situations and here in upstate NY, we have had rainier and wetter winters with less snow and more rain/wintry mix than in the past. Some of these winter rainstorms with frozen ground can be significant.
Where I live, all roof water is required to be piped into drywalls, the volume determined based on the square footage of the roof. Additionally, we have to put trench drains in the driveways that are connected to the same drywalls. There is a grate on top of the drywall in case of overflow.
"Rain garden" may provide you with a solution.
If you search for that phrase online, you'll find a lot of information. Better information tends to come from extension services, or from city websites, as opposed to Pinterest, etc. As a bonus, a rain garden can reduce the amount of area that needs regular maintenance (i.e., mowing), and can serve as a butterfly/bee refuge. This is of course lot dependent, but it's often a good solution.
Jonathan, in my area there are dilapidated houses that direct water from the roof into the walls, soaking the drywall, especially when ice dams form. But I think you typed "dry well" and it got autocorrected to drywall.
Hah! Good catch Charlie. Funny how many times autocorrect turns into auto mistake!
Our local code requires 250cf of detention for every 1000sf of impervious area.