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French Drain Question

Posted on 2/5/25 at 8:31 am
Posted by LSUTiger23
Madisonville, LA
Member since Jun 2010
1284 posts
Posted on 2/5/25 at 8:31 am
Hey Everyone,

I am planning a French drain system for my backyard to divert water toward the front of my house. I want to have a combination of a French drain system with perforated pipe and solid pipe that will collect the downspout water. My thoughts were to join the system together with the perforated pipe system tying into the solid pipe system down stream. At the transition point, maybe I dig a "dry well" that is deeper then the trench and fill with gravel to allow the water to wick through the rock and any residual water can go into the solid pipe?

I am hoping someone with experience with these would be able to tell me if this is a mistake, and if so, what recommendations could you give me.

See my plan that I drew up here. French Drain Plans

As always, the advice is greatly appreciated.
Posted by Screaming Viking
Member since Jul 2013
5272 posts
Posted on 2/5/25 at 8:56 am to
judging by the drawing you created, you are quite the detailed guy. very nice.

My $.02. And I am in the drainage business, but not an engineer (full disclosure).

Whatever size pipe you are planning to use....go the next size up. Sticks, leaves, crawfish pot stuff, etc. tend to get stuck over time.

Never use any 90 bends in drainage. use 45 degree bends, or wyes, or wyes + 45's. Main reason is that you will need to be able to make use of a clean out to flush the system on occasion.

I personally believe that the sumps you are planning are unnecessary. The perforated pipe french drain system should be enough. Water follows water.
Posted by crewdepoo
Hogwarts
Member since Jan 2015
10492 posts
Posted on 2/5/25 at 8:56 am to
I installed a smaller French drain in my yard a couple years ago and did a lot of research.

Don't see any issue with your design. Although in Louisiana soils a dry well may not be worth it.
Posted by crewdepoo
Hogwarts
Member since Jan 2015
10492 posts
Posted on 2/5/25 at 8:58 am to
quote:

Never use any 90 bends in drainage
I used a catch basin box on my 90s that allowed me to clean them out when needed.
Posted by LSUTiger23
Madisonville, LA
Member since Jun 2010
1284 posts
Posted on 2/5/25 at 9:17 am to
quote:

I personally believe that the sumps you are planning are unnecessary.


When you say sumps, do you mean the # of Inlets/grates i am showing?
Posted by Geauxld Finger
Baton Rouge
Member since Jan 2005
32249 posts
Posted on 2/5/25 at 9:43 am to
quote:

I used a catch basin box on my 90s that allowed me to clean them out when needed


This. Try to avoid blind tie ins. That’s where build up happens
Posted by crewdepoo
Hogwarts
Member since Jan 2015
10492 posts
Posted on 2/5/25 at 9:44 am to
(no message)
This post was edited on 2/5/25 at 9:45 am
Posted by Screaming Viking
Member since Jul 2013
5272 posts
Posted on 2/5/25 at 10:36 am to
quote:

I used a catch basin box on my 90s that allowed me to clean them out when needed.


perfect solution. depending upon the depth of the pipe. you may have to install risers to attain the required depth.
Posted by Screaming Viking
Member since Jul 2013
5272 posts
Posted on 2/5/25 at 10:38 am to
quote:

When you say sumps, do you mean the # of Inlets/grates i am showing?


no. i said sumps in describing what you called "dry wells". unless you have some serious ground water (IE the lowest lot anywhere around) then this is probably unnecessary.
Posted by doubleb
Baton Rouge
Member since Aug 2006
40067 posts
Posted on 2/5/25 at 11:50 am to
Let me echo your advice in sizing the pipes.

Never run 4” UG horiz. Lines should be a minimum of 6”

Posted by Tree_Fall
Member since Mar 2021
829 posts
Posted on 2/6/25 at 11:40 am to
I have 3 gutter downspouts emptying into catch basins then 6" solid pipe to a popup at the lower curb. There is an 18" drop over 40'. The contractor's alternative was to run downspouts directly into the solid pipe. I was worried about leaves and picked the catch basin option. I initially put a coarse filter in the basins, then switched to a diy cone of 1/8" hardware cloth. Five years along, and all is well.
Posted by SundayFunday
Member since Sep 2011
9619 posts
Posted on 5/6/25 at 12:34 pm to
Glad to find a relatively recent post on this topic. Ill be planning something very similar in the near future.

I have a similar design in mind to OP but without the dry wells (our yard isnt that large to justify it)

Question: For the endpoint of the pipe, what is the best way to let it drain toward the street. My yard has a sidewalk that intersects the direction of the pipe toward the street (obviously) so I imagine the pip would have to stop just before the sidewalk. My main question is, 'is that fine/normal to do?' Its probably a dumb obvious question but I just wanted to be sure. My yards slope isnt very significant so itll be a nice challenge to get the lions share of the pipe to be angled correctly but mainly I just didnt want to be getting cited if letting the pipe drain onto the sidewalk was against a vague code or anything.

Any advice is appreciated
Posted by tigerfoot
Alexandria
Member since Sep 2006
58947 posts
Posted on 5/6/25 at 1:12 pm to
I didnt think I had enough drop at my road from my trouble spot at the front of my house, so I called a company, they said they could do it, put in the drain with like a 6inch perf pipe wrapped in some type of black fabric.......it sucks water out like crazy, best money I ever spent on my home. Good luck with your project.
Posted by jose
Houma
Member since Feb 2009
29371 posts
Posted on 5/6/25 at 1:42 pm to
I put in a french drain system at my house this weekend. Hell of a project. I was a cheapo and decided to not rent the ditch digger, big mistake

I put 2 square catch basins by my back patio and then sent that to the fence and then connected that to a low spot in my back yard with another catch basin.

The hard part was that the low spot in the corner was so low, that I had to leave the damn sticking up out of the yard so much, but I went back and tried to raise the area around it with the dirt that I dug up the trenches with. Hell of a project.
Posted by jose
Houma
Member since Feb 2009
29371 posts
Posted on 5/6/25 at 1:43 pm to
quote:

what is the best way to let it drain toward the street.


I ran my pipe under my fence and used a Pop-Up emitter valve. Fingers crossed it works as it should.
Posted by Cage Fighter Trainee
Member since Aug 2024
114 posts
Posted on 5/6/25 at 1:45 pm to
quote:

I imagine the pip would have to stop just before the sidewalk


If you're going to do all that work, I'd rather have the water drain to the street. You can easily tunnel under the sidewalk with a hose nozzle. Just dig a pit to the depth you need on either side of the sidewalk and let the hose/water pressure do the work. You'll be able to slide a section of pipe all the way to the street. I also sawcut the curb on mine so my pipe sits right at street level.
Posted by SundayFunday
Member since Sep 2011
9619 posts
Posted on 5/6/25 at 1:58 pm to
Nice! Appreciate the advice from everyone.

Ill likely dig under the sidewalk if I can and just make it a whole weekend project sometime when we arent getting flooded and/or 100% humid summer weather.
Posted by jose
Houma
Member since Feb 2009
29371 posts
Posted on 5/6/25 at 1:59 pm to
I found some great youtube videos on this. I just didn't feel like doing that because I am pretty sure you need to notch out your curb as well correct?
Posted by Cage Fighter Trainee
Member since Aug 2024
114 posts
Posted on 5/6/25 at 2:08 pm to


Yes. I made two cuts using one of these blades and chiseled the rest of the concrete to allow the pipe to fit. It may sound difficult but it's very easy, just wear safety glasses.
Posted by jose
Houma
Member since Feb 2009
29371 posts
Posted on 5/6/25 at 2:22 pm to
Ok good to know for if/when I decide to do all that. If the pop-up valve works, then I ride with that, but I know I can always come back and dig further and go under my sidewalk.
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