Building a French drain

[Hilary]

I have a section of a field that fills up with water in the spring. I also suspect that it contributes to my cellar river in the spring. It would be better for the field if this didn’t happen - if it doesn’t outright kill the hay grass it never grows well so I am going to just go ahead and put in a French drain to the lower edge of the field.

Do I need a pipe? Or can I just dig the trench, and fill it with a riprap type of rock and then put the soil back?

I live in NH next to a granite quarry, so I know the bedrock is right below the grass most of the time, but I think if I can find a channel to drain this seasonal swamp, it will improve several things.

[Bluey]

You could ask your Soil Conservation Agency, that are part of the USDA Farm Service Agency in your county.
They will have the proper maps and can flag where you can put your ditch and may even cost share with you.

Here, we use 2"-5" rock gravel for french drains.
You can drive even big trucks thru that and it will still make good drainage ditches.
That may be different where you are, each region can be different.

[Color_of_Light]

@Hilary

I have a section of a field that fills up with water in the spring. I also suspect that it contributes to my cellar river in the spring. It would be better for the field if this didn’t happen - if it doesn’t outright kill the hay grass it never grows well so I am going to just go ahead and put in a French drain to the lower edge of the field.

Do I need a pipe? Or can I just dig the trench, and fill it with a riprap type of rock and then put the soil back?

I live in NH next to a granite quarry, so I know the bedrock is right below the grass most of the time, but I think if I can find a channel to drain this seasonal swamp, it will improve several things.

Hello! The reason for the pipe is to carry the water away from the effected area. How many feet of water does your field collect? So yes, I would absolutely use a pipe if I had your situation. You will also need an area to where all of that collected water will be moved to. When digging the ditch, you will need to put some degree of slope into the bottom of the ditch. The ditch is usually 2’ deep. Possibly more if you have a major flood problem. The degree of slope will depend upon the volume of water flooding the field. A 2 percent slope might do, or maybe more. You will also want to protect your french drain from filling up with silt that will come with all of the flooding water. After digging the ditch, line the bottom of the ditch with some filtering fabric, then add the pipe. You can use a sock covered flexible perf pipe, or you can use a rigid perforated pipe (often is white). The diameter of pipe will depend on the amount of water, too. If your field is really filling up, you might need a 3", 4" or larger perf pipe to quickly carry that water away.

[gumtree]

Good advise from Color of Light. But every situation can be different and require it’s own unique design. You should get a storm water management engineer to take a look. If not designed and installed correctly you could just be throwing good money after bad. IMO there is no “quick, cheap fix”.

[WildandWickedWarmblo]

Good ideas on this thread. I want to have a french drain put in on one sloping paddock.

[Gemma23426]

Pvc Pipe is cheaper and quick solution but you can consider concrete drainage, but it adds more cost.

[Color_of_Light]

@gumtree

Good advise from Color of Light. But every situation can be different and require it’s own unique design. You should get a storm water management engineer to take a look. If not designed and installed correctly you could just be throwing good money after bad. IMO there is no “quick, cheap fix”.

Yes, a storm water management engineer, or a well seasoned and highly reputable excavator with a long history of creating drainage for clients in your area. Or, if you’re handy, you could build it yourself.
The principles behind french drains are all the same:

• capture ground and surface water
• prevent water from overtaking a specific area
• carry unwanted water away from specific area and displace it elsewhere

Specific design varies by site location, rate of water accumulation, water volume, length of travel for diverting water…

• depth of trench
• degree of slope of trench
• diameter and type of perf pipe

The concept is pretty easy. You could rent a track hoe or back hoe (there even some small ones available), dig the ditch yourself, shoot the grade with a laser, add fabric, pipe, drain rock yourself. Just make sure you have a destination for all of that captured water. The trench and pipe have to go down hill the entire length. Any hump in your trench grade will mean water will get stuck on either side of that hump. Depending upon the lay of your land, the end of the pipe could daylight somewhere drain out on the surface, or it could require a large dry well filled with rock.

[Color_of_Light]

@Gemma23426

Pvc Pipe is cheaper and quick solution but you can consider concrete drainage, but it adds more cost.

Both require a trench (usually at least 2’, if not more below the surface) with a continuous grade, and both need to be covered with drain rock. I’m not sure there’s an advantage in using concrete perf pipe. My property had some concrete and clay pipe on it when we bought it. Both were broken and pieces eventually came to the surface. We put in french drains around outdoor arena and few other places. Used both sock covered perf, as well as rigid perf. The oldest are 15 years old and they have all been trouble free. Built a few more french drains in recent years the same way.

[danacat]

@Color of Light

The reason for the pipe is to carry the water away from the effected area. You will also need an area to where all of that collected water will be moved to. When digging the ditch, you will need to put some degree of slope into the bottom of the ditch. The ditch is usually 2’ deep. Possibly more if you have a major flood problem. The degree of slope will depend upon the volume of water flooding the field. A 2 percent slope might do, or maybe more. You will also want to protect your french drain from filling up with silt that will come with all of the flooding water. After digging the ditch, line the bottom of the ditch with some filtering fabric, then add the pipe. You can use a sock covered flexible perf pipe, or you can use a rigid perforated pipe (often is white). The diameter of pipe will depend on the amount of water, too. If your field is really filling up, you might need a 3", 4" or larger perf pipe to quickly carry that water away.

^^^^^^^^ absolutely correct. I just put some french drains in – 100’s of feet – and that ^^^^ is exactly how my contractor did it. All the water goes to my pond.

[Color_of_Light]

@Color of Light

Used both sock covered perf, as well as rigid perf.

Realized I need to explain this a little better…You can’t just throw rigid perf into a trench and cover with rock, especially if you have large volumes of water. Sludge has to be kept out of your trench, otherwise it will get clogged and not work. You don’t want to clog up that drain rock or the drain pipe, believe me. This would require digging the entire project up and re-doing it. This is why fabric is laid down to line the entire trench -before- adding the perf pipe and the drain rock. You make a giant burrito of fabric, perf pipe, and drain rock. Some just make a a taco, with the fabric only lining 3 sides, and fill it with rock. Other situations (possibly OP’s situation where it sounds like there is more than just ground water running horizontal, but also surface water pouring into the top of the trench) require a burrito with overlapping fabric on the top side. The burrito stops maybe 6’ below the top of the trench, then more rock is added on top to hide the fabric. This way if you have to clean some sludge out, it’s just sitting on top of that fabric 6" down. If you really do have the potential to have a giant sludge problem, there are other ways to design the french drain for easier clean out.

The type of soil (soil analysis) will help determine the potential amount of sludge.

[ToTheNines]

Did you know you can get socks for rigid (pvc) perforated pipe? I got some and that is what I am planning to use.

It’s called Drain-Sleeve and comes in 100’ lengths.

[danacat]

@Color of Light

You can’t just throw rigid perf into a trench and cover with rock, especially if you have large volumes of water. Sludge has to be kept out of your trench, otherwise it will get clogged and not work. .

I forgot to mention that we used geo tech fabric – lined the bottom and sides of the trench with it (one continuous piece as much as possible) to prevent sludge/mud from eventually clogging the trench. We get a lot of rain in NY, snow melt etc, so the fabric was a must especially since I opted to NOT put gutters on my new barn. The french drain catches all the roof water too.

[Hilary]

Thank you all! The area seems to trap the water due to a natural dip in the field which is mostly the high point of the area. Before I put in the ring, it was a bit of a problem. but the water didn’t seem to linger as much because it could drain south and east. . The south edge has a decent slope so the plan is to trench towards that - basically give the water better chance to go south, since the east side has the ring and the north side has a road. The west side is just high.

[Gemma23426]

@Color of Light

The oldest are 15 years old and they have all been trouble free. Built a few more french drains in recent years the same way.

Wow that’s outstanding. Really out of my expectation.