Home improvement: french drain or dry well?

Questions on how we spend our money and our time - consumer goods and services, home and vehicle, leisure and recreational activities
Post Reply
User avatar
Topic Author
Monk
Posts: 168
Joined: Sat Nov 28, 2009 4:17 pm
Location: RDWHAHB

Home improvement: french drain or dry well?

Post by Monk »

Ah, the joys of home ownership...

We recently purchased a home in a delightful midwestern college town. After a heavy rain, we discovered the sump pump discharge creates a magnificent water feature in our backyard, about 20 feet from the basement wall. The four year old boy in me thinks our personal freshwater spring is kind of cool, but the middle aged schlub knows it needs fixing. In digging out the discharge pipe I discovered it is connected to a completely clogged section of perforated drain tile, leaving the water nowhere to go but to the surface. Unfortunately, we have a pancake-flat lot and very thick clay. My percolation test might as well been dug in a cereal bowl. Connecting the sump discharge to the sewer is verboten under local code.

The drainage contractors who have come through have recommended everything from carrying the discharge 40 ft from the house and out a pop-up valve ("because it won't drain into the ground anyway") to a 3 cubic yard catchment "system" requiring removal of half the backyard landscaping. I'm more inclined to go with the contractors who recommended either a 3'x3'x3' dry well or a 20 ft french drain well away from the house. The price for either the dry well or the french drain is effectively the same, but I have no idea which would be more effective in this situation, or if we'll simply be moving the mud hole from the middle of the yard to the back corner.

Any Bogleheads successfully resolve a similar drainage issue?
User avatar
retiredjg
Posts: 53989
Joined: Thu Jan 10, 2008 11:56 am

Re: Home improvement: french drain or dry well?

Post by retiredjg »

I can't help with your basic question, but see if a rain garden might be part of your solution, maybe in combination with what you are already considering. Lots of info about rain gardens on google.

They are becoming common here in the NC mountains where heavy afternoon thundershowers can be almost daily and it can rain an inch in half an hour.
User avatar
Topic Author
Monk
Posts: 168
Joined: Sat Nov 28, 2009 4:17 pm
Location: RDWHAHB

Re: Home improvement: french drain or dry well?

Post by Monk »

retiredjg wrote:I can't help with your basic question, but see if a rain garden might be part of your solution, maybe in combination with what you are already considering. Lots of info about rain gardens on google.
Indeed - I'm planning to dig a rain garden in the front yard to help handle some of the water making its way into our footing drains and eventually into the sump. But for this area, I'm trying to keep as much open grass as possible for the kids to play on. Certainly a good suggestion, though.
User avatar
tyrion
Posts: 1423
Joined: Fri Feb 08, 2008 2:33 pm

Re: Home improvement: french drain or dry well?

Post by tyrion »

This is probably not applicable since I'm in a different low-rain environment, but I have all our downspouts directed in to rain barrels. The barrels each have an overflow valve connected to a hose that directs water to the edge of our property line where it can safely find its way to the storm drain rather than creating an enormous puddle in a low spot in the back yard. This all works great until the rainfall exceeds a certain intensity level where the overflow valves are unable to keep up with demand and the water overflows the rain barrels. Which is where the downspouts are anyway, so not a huge deal.
Glomar
Posts: 78
Joined: Sun Oct 19, 2014 1:27 pm

Re: Home improvement: french drain or dry well?

Post by Glomar »

I'm not sure I totally understand your situation - a little confused how the water is making its way to the surface, although that is certainly preferable than in your basement!

So take this all with a grain of salt, but we've got an exterior French drain that has an amazing capacity. Ours runs around the house to intercept stormwater runoff before it runs down toward the house. The amount of water coming out of the outlet during heavy rains is nuts - like its own creek.

I had brought up the idea of a dry well with a couple of folks more knowledgeable than me and they both said basically the same thing - that they are a drop in the bucket and really don't hold a whole lot of water. Once they are full that's it, whereas with a French drain it just keeps going.

French drains do get clogged over time, though. I think a normal lifespan is maybe 5-10 years? Although if the drain is set up properly they won't have to re-do entirely from scratch.

Good luck!
User avatar
Doom&Gloom
Posts: 5398
Joined: Thu May 08, 2014 3:36 pm

Re: Home improvement: french drain or dry well?

Post by Doom&Gloom »

It sounds like we had a similar situation in the southeastern US--very flat lot with runoff from one neighbor's backyard flowing directly toward our house. The topography of our backyard had been changed over a several year period by a variety of (mostly natural) events. Our biggest problem was that even though we have nearly two acres, we really had no "good" low spot to terminate a French drain.

We ended up having a French drain installed (about 120 feet) to the lowest spot on the other side of the yard where a "pop-up" terminated the drain. We have three grates about six feet apart near the house where the French drain begins which feed into the actual drain "pipe." The rest of the length along the drain is 8-10 inches of large rocks on top of the drain (no grates). It was a very minimal drop, so I didn't expect much. I was very surprised how much water it handled. However, during extremely heavy rains, it still wasn't quite enough, so we did have a small berm added to re-direct some of the water runoff toward the same low spot. After a year or so, our grass has covered the length of the drain except for the grates and the pop-up. So far, it has been maintenance-free except for keeping the grates free of leaves. I couldn't be happier with the result.
MathWizard
Posts: 6542
Joined: Tue Jul 26, 2011 1:35 pm

Re: Home improvement: french drain or dry well?

Post by MathWizard »

We just have a grassed swale which moves water from the backyard to the storm drain, keeping it way away from the house.
The sump pump dumps into the swale.

This would be about as cheap and aesthetically pleasing as you can get.

French drains can plug up eventually. Since you have non-permeable soil, it would be better to get the water
on top of the ground and moving away from your house toward the storm drain.
User avatar
Topic Author
Monk
Posts: 168
Joined: Sat Nov 28, 2009 4:17 pm
Location: RDWHAHB

Re: Home improvement: french drain or dry well?

Post by Monk »

Glomar wrote:I'm not sure I totally understand your situation - a little confused how the water is making its way to the surface, although that is certainly preferable than in your basement!
I think the water table was just that high - after digging out the discharge pipe, the hole filled to the brim and stayed that way for several days. In spite of this, the basement stayed tolerably dry.
Glomar wrote: So take this all with a grain of salt, but we've got an exterior French drain that has an amazing capacity. Ours runs around the house to intercept stormwater runoff before it runs down toward the house. The amount of water coming out of the outlet during heavy rains is nuts - like its own creek.

I had brought up the idea of a dry well with a couple of folks more knowledgeable than me and they both said basically the same thing - that they are a drop in the bucket and really don't hold a whole lot of water. Once they are full that's it, whereas with a French drain it just keeps going.

French drains do get clogged over time, though. I think a normal lifespan is maybe 5-10 years? Although if the drain is set up properly they won't have to re-do entirely from scratch.

Good luck!
I'm leaning in the direction of a french drain as well - dissipates the water over a much larger area, and should allow it to infiltrate into the soil so much faster. Thanks for the input.
User avatar
Topic Author
Monk
Posts: 168
Joined: Sat Nov 28, 2009 4:17 pm
Location: RDWHAHB

Re: Home improvement: french drain or dry well?

Post by Monk »

Doom&Gloom wrote: We ended up having a French drain installed (about 120 feet) to the lowest spot on the other side of the yard where a "pop-up" terminated the drain.
Any idea how often the "pop-up".... erm... pops? Is that area noticeably more soggy than the rest of the french drain? It sounds like you have a larger version of what I'm considering installing.
User avatar
Doom&Gloom
Posts: 5398
Joined: Thu May 08, 2014 3:36 pm

Re: Home improvement: french drain or dry well?

Post by Doom&Gloom »

Monk wrote:
Doom&Gloom wrote: We ended up having a French drain installed (about 120 feet) to the lowest spot on the other side of the yard where a "pop-up" terminated the drain.
Any idea how often the "pop-up".... erm... pops? Is that area noticeably more soggy than the rest of the french drain? It sounds like you have a larger version of what I'm considering installing.
Our pop-up doohickey only pops up when there is enough water in the "pipe" part of the drain to force it open. That area is certainly the last area of the yard to dry out--but it always had been anyway because it is the lowest spot in a fairly flat yard.

One of the totally unexpected effects of our French drain was that except for the lowest area near the terminus, the rest of the yard near the French drain now dries out much faster and more thoroughly than it had before. I wouldn't expect to see a similar effect if your yard is mostly clay, but it was certainly a pleasant surprise to us. And I'm not sure that all French drains are similar to ours which is designed for water not only to flow to the low spot through the pipe but around the pipe in what is essentially a rock-filled, grass-covered, 6-inch wide ditch as well.
john94549
Posts: 4638
Joined: Tue Jul 26, 2011 8:50 pm

Re: Home improvement: french drain or dry well?

Post by john94549 »

I'd lean to the French drain. Make sure it's sized properly and remember "perfs down". The drain pipe has perforations to allow the introduction of water. Many "DIY"ers install the pipe with "perfs up", which defeats the whole purpose*.

You want the water to rise in the trench up to the bottom of the pipe, then go into the pipe via the perforations, then be carried away. Stated another way, "perfs down." A proper gravel base is important. You might also consider filter fabric. You do not want the perfs to get clogged.

I'd be wary of a "dry well". Water collected therein has to go "somewhere" (evaporation aside), and the water might end up where you least want it.

*Funny story. I was in a Home Depot several years back, and some company came out with French drain pipes with perfs all the way around. I guess they were trying to protect us from ourselves.
WhyNotUs
Posts: 2606
Joined: Sun Apr 14, 2013 11:38 am

Re: Home improvement: french drain or dry well?

Post by WhyNotUs »

How deep is the clay? If you get down a foot or two or three do you get to cobble? If so, I would go with a dry well. You dig below the clay level, fill with gravel and create a place for water to perc.
I own the next hot stock- VTSAX
woodenpelican
Posts: 36
Joined: Thu Sep 25, 2014 11:33 am

Re: Home improvement: french drain or dry well?

Post by woodenpelican »

Look for boring/well logs near your house on your state's department of ecology website to see if there is any permeable soil beneath the clay. If the clay goes down more than 10 feet, a dry well will likely not be as effective as a french drain.
User avatar
Topic Author
Monk
Posts: 168
Joined: Sat Nov 28, 2009 4:17 pm
Location: RDWHAHB

Re: Home improvement: french drain or dry well?

Post by Monk »

Much thanks to all who contributed - I'm putting down a deposit this afternoon on the french drain installation (terminated with a pop-up).

-Monk
SpideyIndexer
Posts: 850
Joined: Thu Apr 02, 2015 10:13 pm

Re: Home improvement: french drain or dry well?

Post by SpideyIndexer »

How well did it work?
forgeblast
Posts: 585
Joined: Fri Oct 13, 2017 8:45 am
Location: PA
Contact:

Re: Home improvement: french drain or dry well?

Post by forgeblast »

When we ran our gutters and the drainage I hit a spot where It was a shelf of rock. I had to make a mini-dry well. Basically dug a 3x3 hole, ran the pipe to it and filled it with gravel.
Post Reply