MsDDC
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Location: Washington, DC; 7A by the map but 7B by local urban temps

Water Management in Low-Lying Yard

As I've said elsewhere around the forums, my yard is at the bottom of two hills, and all the drainage from my roof ends up in my back yard (only one downspout off my 600 square foot (footprint) house. When it rains normally and we get moderate to heavy rains, the yard floods a bit. Last summer (2018), I terraced the hill from the back, which improved, but didn't eliminate the flooding. I can't really install a rain barrel because I don't have a spot to connect it to my downspout (long story, complicated arrangement of my yard).

So, I had a company out today to investigate installing a french drain in the yard to get the water below ground. The rep said, yeah, a french drain is the right solution, but it needs more than that. I can either install a sump pump and shoot the water out to the alley, which he didn't recommend (it's uphill, that's a big project given that my yard is deep, you're really not supposed to discharge rainwater onto city property, and an outdoor sump pump tends to fail in cold weather), and I agree with that. His recommendation was for a cistern, he thinks about 64 cubic feet (a 4x4 chamber, 4 feet deep). I generally agree, but think that might be a little bigger than necessary. That's almost 500 gallons, and after heavy rains in the spring, I estimated that my yard had around 175 gallons of water standing in it (I measured the depth and size of the puddle).

I'm still waiting for the estimate, but wanted to solicit some opinions so I don't get taken for a ride. What he specifically recommended was a french drain across the yard, 20 feet, that handles the low part of the yard with 2 surface drains; plus another smaller one, 7 feet, with one surface drain where the downspout empties. And then the 4x4 cistern where the pipes meet. From what I could tell from the brochure for the cisterns, they are 1x1x4 feet. My thought was that 2 of them plus the drain length would be enough (~120 gallons in the cistern plus what the pipes can hold), but maybe there's reason to want more space in the cistern and not rely on the pipe capacity? Not my area of expertise beyond being able to do the math.

imafan26
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French drains will improve flow in the yard, however the drains must drain down hill. The outlet needs to be in the lowest spot but still be higher than where it is draining to.

The down spout can be connected into an underground drainage system.

Even though your yard is between two hills, the pooling in the back yard for most people is because they changed the grade somehow. The usual cause is putting in retaining walls and filling in swales to level the yard.

My backyard used to flood every time with heavy rain when I was a kid. I would have to wade out in water higher than my ankles to rescue my dog who was sitting on top of her dog house because she was so afraid of the water. Our house was on a kind of terrace. the house above us was about four feet higher and the one behind and below was lower. Concrete walls were built on all sides and that created the swimming pool as the water was trapped and could not go down to the lower properties and the dirt from excavating for the walls was used to level the yard.

To avoid that issue, I made sure my new house was sitting high so no water would sit in the yard. Our neighbors put in walls and they both had swimming pools in their back yard after a heavy rain. We had no walls and a fairly steep grade into the ravine behind us. We planted a hibiscus hedge for privacy and that did not stop water from flowing. We also made sure not to disturb the swale. Actually a corner of a small garden did partially go into the swale and there was some pooling there. The neighbor on one side of us put soil on our side of their wall that blocked our side yard drainage. The way they built their wall, when their yard flooded we had fountains of water spewing from the spaces between their tiles into our yard. I remember we had to go out and dig a trench on the side yard to remove the extra dirt so the water could exit our property.

The house on one side of us put in a drain, but it was a surface drain, not a french drain. I was good enough to get the water from the back yard to the street.

My current neighbor extended his house to the back yard and had drainage issues after that and he did put in a proper French drain but there is an electrical box on a corner of his lot so he asked permission to run his drain outlet through my hedge to avoid flooding the electrical box. My hedge covers it and it drains into the street.

French drains can clog over time. It does take a long time. I actually prefer to use surface drains like swales, but that means grading the property properly and not having obstructions like solid walls on the perimeter. The other way would be to put in a drainage trench or something like a rain garden that can capture and hold some of the runoff. Rain gardens would have to be big enough to accommodate an average amount of rain. It still could not handle a hundred year flood. It is an environmentally friendly option and reduces pollutants from washing off. It can be a major undertaking depending on the size. A small one is doable.

https://www.tenthacrefarm.com/permaculture-swale/

SQWIB
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I feel your pain!

Vanisle_BC
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MsDDC:

You speak of a 4x4x4 cistern, then 1x1x4 cisterns, plural, so I'm confused (not unusual :). The concept would be underground storage, gravity fed & either concrete lined or of made of prefabbed plastic? Are the 1x1x4 cisterns individual tanks or some sort of modular units? And what happens to the stored water next; pumped out, maybe for removal by truck, or for garden irrigation?

I'm wondering if your calculation of the amount ponding on the surface ignores the underlying goundwater, so it could tend to be self-replenishing. I know it sounds simplistic, but just creating a pond or swimming pool leaps tp mind!

BUT "To every problem there is a simple solution, which is usually wrong"

Good luck.

MsDDC
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Location: Washington, DC; 7A by the map but 7B by local urban temps

To answer a bunch of questions at once:

The biggest hill comes from the back of my yard toward the house. The alternative to having proper grading away from the house is all that water ending up in my basement. So, my yard slopes steeply from the back to the middle, that area is now terraced to slow the water down. Then there's a low spot in the middle of the yard, then a slight gradient up to the house so the water doesn't reach the house. It did reach the house once before I put in the terraced garden.

The second hill comes from the left, is slight, and ends at my yard. The neighbor to the right's yard is ever-so-slightly higher than mine. The amount of water collecting from that would be small.

Here's photos:

Before:
20180603_145639 copy.jpg
After:
20180706_181817 (2).jpg
The french drains would go across the yard (left to right at the low point, with two surface drains running into it from the left and in the middle at the official low point) and from the downspout (which will be cut to the end of the patio) out several feet, and meet at some kind of collection container underground on the right-ish side of the yard, just about the lowest spot (within inches so the trench can just be dug to account for those inches.

The container they want to install underground is a modular system with 1x1x4 containers that can be joined together in whatever configuration you need. They drain into the ground. Vanisle may be onto something there where they have to account for some groundwater seeping up into them, so they need far more capacity than just want comes off my roof. I'd love to do something where I could use the water to water my garden, and I'll ask, but I suspect that is a very expensive solution (would need to attach a pipe with a hose hookup, and a pump).

MsDDC
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Location: Washington, DC; 7A by the map but 7B by local urban temps

Will also note that, since the terraced garden went in, the water that does sit on the surface absorbs into the ground within, at most, 24 hours (that was after 2.5 inches of rain in just over an hour, that event where downtown DC flooded, if anyone saw it on the news). While the topography of my lot has me at a low point for the neighborhood, the neighborhood itself is at a high elevation for the overall area, continuing to slope down pretty substantially just across the street, so the water table is fairly far down here. Just getting the water underground so I don't have to wade it while it soaks in should be sufficient.

MsDDC
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Okay, I have some more information now. This is what the "containers" look like: https://www.yelp.com/biz_photos/vm-drai ... 8oXu4qJnBQ

$2900 all-in, including re-sodding over the cuts (which is a nice inclusion I didn't expect). They say the total capacity of the system is 500 gallons, which should be able to remove an inch of rain per 24 hours from both the yard and the roof, which seems sufficient. Not all the rain that hits the yard ends up in the low spot (grass has grown in nicely from that after photo, so the water doesn't all run). If my neighbor to the left didn't keep their lawn so short, it would be better, but I can't control that (he decries my 3" long, not burned out grass as "unruly"). It's a small amount of water coming in from that side, anyway.

Any thoughts on the reasonableness of this? I secretly hate my neighbors that discharge water on public space (houses without as good of grading, with sump pumps in the basement that just spew out on the sidewalk...real nice when it's winter!), plus that hill would be a big challenge for pumping the water up it, so keeping the water *under* my yard until it can naturally soak into the ground seems the only option.

SQWIB
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It looks like your also getting run off from both neighbors on either side, I would at the least level your yard with theirs.

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rainbowgardener
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I can't say anything about the cistern issue. But one thing to think about in addition would be to add some plantings to your green area -- small trees, shrubs, hedges, perennials. It would be pretty, but trees and shrubs will suck up a lot of water, especially if you get moisture loving ones and have some mulchy areas surrounding them. Sweetshrub, button bush, summersweet are good for wet areas.

Image

MsDDC
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Location: Washington, DC; 7A by the map but 7B by local urban temps

To rainbow: I actually have plans for that once the disturbing of the yard is done. I was going to put at least 2 smallish crape myrtles just past the patio (Zuni, should get to be about 9-12 feet...tall enough for some visual interest, but not so tall they block light out to the garden since it's on the far north end of the yard). I may add some shorter things between them as I go.

To SQWIB: really just from the left. The neighbors to the right have a rain barrel their down spout empties into (and it's on the far side from me), don't maintain their yard at all (which presents its own issues, but their "jungle" keeps water from tumbling my way), and have a lot of trees that soak up water well. The difference between the yards side-to-side is just a couple inches, so a good layer of grass or something similar can do wonders (I wish I had a pic of how badly the neighbor to the left damaged the "lawn" (it's all weeds, but it's at least ground cover) by over-cutting in the minor drought we had this summer and fall). This is what it looks like now with the grass grown in except for the low spot (where my little doggy is sitting and grass can't grow well because that's where water stands the longest).
20190604_192552.jpg

MsDDC
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Location: Washington, DC; 7A by the map but 7B by local urban temps

And if anyone can help me rotate pics, that would be great! If you click on it, it comes up in the proper orientation!



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