Help me stop flooding my neighbors yard with my sump pump when it rains!

February 12, 2020 8:42 PM

I live in an house in the south that is on a street that is a hill. My house is almost at the bottom of the hill. There is a basement with a sump basin that fills up and drains a lot whenever it storms, and empties into the neighbors (unused) yard. Trying to figure out where the heck storm water can go that is legal and not a dick move.

I've drawn a diagram that shows why this is slightly complicated. Basically, there is a driveway down from street level that terminates in my neighbor's yard (which they are currently not using for anything so it is dirt and concrete). Because we are at the bottom of a hill, the sump pump is extra busy with everyone else's runoff (like emptying once every 10-15 minutes or so). Needless to say, the neighbors are not thrilled, though they haven't made a fuss mostly because it doesn't happen other than during storms and the yard is not anything they have immediate plans to use.

Complicating factors:
- The house is old so there is no drain to the sewer beneath it that i can tell.
- There is a dirt hill between the bottom of the driveway and our yard, putting our yard about 4-5 feet above their yard.
- The top of the sump basin is on the same plane as the bottom of the driveway.
- there is a 14ft deck attached to the back of the house
- There is only about 3ft of room between the outside wall of the house and the start of the concrete driveway, and the same on their side.
- We have clay dirt.

I've done the research and according to this it does not appear that Georgia:

1) allows pumps to be attached to the sewer line going away from the house.
2) allows pumps to deliver water into the street (which seems like it could be dangerous)


I'm ideally trying to figure out a solution that minimizes there being a ton of standing water in anyone's yard, since we get crazy amounts of mosquitoes in the spring.

There doesn't seem to be any place where i can actually direct this water! What do other people do? Am I just f-ed?

posted by softlord to Home & Garden (21 answers total)

Response by poster: (this should be obvious but the drawing and positioning of things within it is very much not to scale or especially accurate)
posted by softlord at 8:51 PM on February 12, 2020

Is you are still in Atlanta, maybe call these people. Most areas have regular sewers and storm sewers for runoff.
posted by Yorrick at 8:52 PM on February 12, 2020 [1 favorite]

Response by poster: (done threadsitting after this). There is a sewer grate thing three houses further down the hill but the water would have to go out up the driveway hill and out into the street in order to get there (And also be pushed out with enough force that it wouldn't just run back down the driveway). The block gets rushing water whenever it storms.
posted by softlord at 9:01 PM on February 12, 2020

My home has a similar situation. Our sump pump exits to the curb where the water runs down the gutter of the street past neighbors homes to a storm drain near the bottom of the hill.
Where is the nearest storm drain?
posted by artdrectr at 9:07 PM on February 12, 2020

Could you perhaps install a retention tank under your deck, redirect the sump pump outlet to that, and arrange for the tank to empty slowly via a small-diameter hose so that most of the flow out of the retention tank happens while it's not raining?
posted by flabdablet at 10:59 PM on February 12, 2020 [2 favorites]

To what extent, if any, are you receiving stormwater from other neighbours above you? Here in NZ it is illegal in many jurisdictions to shed water to your neighbours, and it can be one way to reduce your own stormwater burden. It's by no means a complete solution but a part of the package I get involved in here sometimes.

Is there a permeable layer beneath the clay? I've seen a few cases where puncturing the surface is a solution - but sometimes it becomes a whole new disaster if soil type is wrong.

flabdablet's tank and timer is a solution at a house I just visited last week. I haven't got my law hat on but that 712.1 seems a bit circular.

What is the largest volume you have to deal with?
posted by unearthed at 11:43 PM on February 12, 2020 [1 favorite]

I've seen a few cases where puncturing the surface is a solution - but sometimes it becomes a whole new disaster if soil type is wrong

Tunnel erosion is a thing in many of the clay-dominated soil profiles in my region and it does indeed turn disastrous, quite sneakily and non-visibly for years and then very very suddenly and dramatically.
posted by flabdablet at 1:38 AM on February 13, 2020 [4 favorites]

This is probably a bigger project than you’re up for, and I don’t know if it’d be practical in your soil conditions, but hire someone to design and install a rain garden in your yard that can handle the outflow from the sump?

The general idea is that you create an area of permeable soil/artificial medium that’s capable of retaining water at the scale of what you need to deal with, planted with vegetation that doesn’t mind getting swamped and will be able to take up the water load so that you’re ready for the next rainstorm.

This is a professional design problem, I think — you’d need to find someone who does this for a living, not figure it out yourself. And probably more trouble and expense than you want to go to. But I thought I’d bring it up because I think they’re neat, and they’re astonishingly effective in an urban setting. Something twice the size of an ordinary tree pit can make a whole lot of water just go away.
posted by LizardBreath at 2:44 AM on February 13, 2020 [4 favorites]

A retention tank to gather the flash flooding. The tank itself is drained by a low power pump to a hose that heads into your regular drains (with an air-gap, like your washing machine). The tank should have an overflow hose that goes away from your house, of course, and in all but the worst situations would never be used.
posted by seanmpuckett at 6:39 AM on February 13, 2020

The tank itself is drained by a low power pump to a hose that heads up to street level and into the sewers

or a thin hose off a drainage tap that goes straight out to a tree or shrubs. As long as the flow rate out of that hose is kept quite slow, it doesn't need anything as fancy as pumps and timers; it can just keep on draining by gravity for as long as there's water left in the tank.

Even running in a rainstorm and even on clay soils, a slow hose is going to make a negligible difference to the amount of water on the ground, especially if it runs into a shallow mulch-filled ground basin or swale with plenty of roots nearby.
posted by flabdablet at 6:51 AM on February 13, 2020

Response by poster: OK some clarifications

- The basin is 30 gallons. In heavy storms it will empty about every 10 minutes or so for the duration and sometimes for a few days afterward, such is the runoff below grade.
- Tunnel erosion is definitely a thing here
- I'm not actually sure it rains enough here to make a rain garden feasible and is currently outside our budget (or rather would not be the first place we would want to spend money at the moment though it is definitely a worthwhile investment ecologically)
- The yard is mostly just grass for now and not really used as a garden
- not sure what you mean by "regular drains", @seanmpuckett. there are not any man-made holes in the ground through which water passes on the property and only a sewer drain several houses down. Unless i'm misinterpreting.
posted by softlord at 7:04 AM on February 13, 2020

I think a rain garden or a permeable paver area, which basically creates a holding area for water, could be at least an improvement. These allow water to be absorbed more gradually into the ground.

Some municipalities are actively encouraging residents to create these, and offer a subsidy if you engage their trained and vetted installers. You might search the Philadelphia Water Department and PHS, the Pennsylvania Horticultural Society for user-friendly descriptions. They have partnered here and are leaning hard with paired advertising and free workshops for interested residents. They offer several options from rainbarrels, rain gardens, to larger permeable paver installations. In my city the subsidy is $2000 per address which was enough to entice me.

I took advantage, and now have a puddle-free backyard after monsoon-like downpours. The Water Department is also committing millions of dollars to retropaving miles of city roads with permeable concrete to improve drainage and slow stormwater near intersections - the city installed one enormous paving project two blocks from my home and is now working on the intersection closest to me. This might be seen as a very expensive undertaking for a city, but water drainage and municipal infrastructure is attracting new attention as sea levels rise. By slowing water in neighborhoods, they are able to reduce the pace at which drain water floods the sewers and stormwater systems. Encouraging homeowners with a subsidy also defrays some municipal expense, since a large project will usually cost a homeowner more than the amount of the subsidy.
posted by citygirl at 7:05 AM on February 13, 2020

The basin is 30 gallons. In heavy storms it will empty about every 10 minutes or so for the duration and sometimes for a few days afterward, such is the runoff below grade.

So, 180 gallons per hour in a heavy storm. How long does a typical heavy storm last where you are, what sort of emptying rate are you seeing during post-storm runoff periods, and how much under-deck volume could you feasibly devote to a tank?
posted by flabdablet at 7:27 AM on February 13, 2020

If you had a hose that went past the neighbors house, could it empty into a safer place?
posted by nickggully at 9:09 AM on February 13, 2020

Response by poster: @nickggully said hose would have to travel up to street level and past the driveway but yes technically it could do that i suppose.
posted by softlord at 10:40 AM on February 13, 2020

From your drawing it appears that the sump empties on to the driveway and flows to the neighbors in a steady stream. Can you extend the drain down the side of the house to empty onto you back lawn. The will still flow down hill but the grass should allow it to disperse rather then flowing in a stream. You could also bury perforated pipe in the back lawn which would help disperse the water. Just make sure the water does not flow back toward your house or you will be just circulating the water.
posted by tman99 at 12:03 PM on February 13, 2020

Atlanta is exactly the right climate for a rain garden. They work best and make the biggest difference with occasional heavy storms like we used to have mostly in the summer but now seem to be having weekly (daily in February) year round. Speaking as your local friendly stream ecologist, you need a better solution so that you are not increasing peak flows in your local stream or eroding away your neighbor's soil into the stream, as sediment is one of the biggest threats to water quality in the Atlanta area.

Atlanta Watershed has some great local info about rain gardens. To help in the construction, you can get very inexpensive compost and mulch from DeKalb County. (you'll have to dig out the clay in the hole because rain gardens need functional, draining soil, not our clay). Your closest Ace Hardware has garden experts who can give you good advice about plants.
posted by hydropsyche at 4:49 PM on February 13, 2020

The yard is mostly just grass for now and not really used as a garden

Plant a couple trees and/or a few decent size shrubs out there now, and by the time your neighbour does care about flooding into their yard, your plantings will be established enough for their roots to be capable of removing useful amounts of water.

Digging a fair bit of gypsum into the topsoil around the planting sites will usually give roots a good head start on breaking clay, though it would be worth testing yours first; if what's in your yard is the kind of sodic clay that promotes tunnel erosion then gypsum will do it less good and you'd be better off going straight for vast quantities of plant-based mulch. Which will, incidentally, act as a water sponge in its own right.

None of the above will be expensive.
posted by flabdablet at 8:31 PM on February 13, 2020

Keep in mind that these drainage issues are not your fault and are a natural consequence of having houses at the bottom of a hill. Odds are that if your house wasn't there, nearly all that water would still be draining into your neighbor's yard. The house and sump pump have probably been there for decades. So don't guilt yourself into thinking this is your urgent problem that needs to be fixed right now.

You can probably call your city's watershed management department and they can help you figure out what your options are, if any.
posted by Blue Genie at 10:52 PM on February 13, 2020

A variation on a retention tank and a rain garden is a dry well. This is basically a big hole in the ground filled with gravel. Water is collected in the spaces between the gravel bits and eventually soaks into the ground. The theory is similar to various ways to dispose of water from a septic tank.
posted by SemiSalt at 9:09 AM on February 14, 2020 [1 favorite]

I have an ongoing job solving stormwater on a 10hectare industrial site with no possibility of drainage. So my only option is to maximise evaporation and plant transpiration - I may also pump some water to roofs and evaporate directly.

Some solutions will work at any scale:

Change all surfaces to porous so water can both be absorbed into them and evaporate out again. Where possible extend this porous layer as deep as possible. Using plants - per flabdablet above - is a natural way to increase soil porosity and waterholding as the roots open up the soil and enable soil to hold more water. A planted gravel drive can be part of this solution and is low-cost.

You want the most water-hungry and water-wasteful plants you can find. Such plants will also penetrate hard, low-oxygen soils. Some of these will get too big for your place so hedging them or scrub-cutting every few years is what I would do with them. Given room I may make a hedge maze or similar sinuous shape based on a continuous mound to retain and transpirae as much as possible.

You want a mix of evergreen and deciduous with groundcovers, low and medium shrubs and trees\hedges\large shrubs, that way there's some redundancy in the uptake system and good performance across the year. Also the more plants layers you have the better as more water is held there and evaporated directly.
posted by unearthed at 3:55 PM on February 14, 2020