French Drain or Surface Drain, Surface Water or Sub-Surface Water, Oklahoma City, Norman, Edmond, Mustang

Posted: February 8, 2021 in Drain Repair, french drain, French Drain Information, French Drain Photos, French Drain Repair
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A “French Drain” Moves “surface water” away from a low lying problem drainage area. What flows over the ground.  Sub surface water  which runs underground  is not considered  when a drainage system is being installed.  People only think about what they can see and don’t think much about what they can’t see.

channel drain driveway
Channel Drain set in Driveway is one type of Surface Drain

Sub Surface water is water that is underground and saturated in the soil.  Just like water above ground (Surface Water) moves.  Water under ground moves too and is a very big part of any drainage problem.

Water flows over the surface into the area that floods and is a problem.  A big mistake that is made be the casual eye, is that all the water in a swampy problem area got there by running over the surface.  Yes, it probably did, but it also got there by moving there underground as well.  This is called SUB SURFACE WATER MOVEMENT, and it is important to any kind of Drainage System that might be installed.

If your problem water is partially Sub-Surface water, and you install a Drainage System that uses Surface Drains only, then you just wasted a lot of money!

Surface Drain install
Surface Drain Installed by sidewalk

Water can only be drained away that is on the surface.  It goes into the top of the Drain on the Surface.  It’s Name is ” A Surface Drain.”  It Drains Surface Water ONLY!

A French Drain can drain Surface water and Sub Surface water both.  It water is in the problem area by means of Sub – Surface movement, then it will enter the French Drain Laterally, under ground,  and be drained away along with the surface water.

New French Drain
French Drain with very little fall

When Installing a Drainage System, What kind of Drain Pipe do you use and what size Drain Pipe Do you need?

For a Drainage System you have 3 Choices of Drain Pipe.  You can use ADS,  Or Sewer and Drain, or Thick Walled Pvc Pipe.

ADS is Black and Flexible.  It is used in a majority of Drainage Systems.  It works well and is the easiest to install.


connecting down spout

Connecting Gutter Down Spout to French Drain Under Sidewalk


Covering ADS Drain Pipe

ADS is available in 3 inch , 4 inch, and 6 inch for residential and small business Drainage Applications.

Sewer and Drain Pipe is white, green, or grey and is thin walled.  It is used for cheap plumbing applications such as sewer lines.  It is also used for inexpensive Drainage Systems.  A Drainage System using Sewer and Drain Pipe is slightly cheaper than ADS.   It is rigid and harder to install than ADS. It takes more time to install and more digging is required at the joints or connections.  It is very difficult attaching a rigid Drain Pipe to a Curb outlet because the Pipe does not flex at the connection.  The pipe hits the curb outlet at a downward angle and does line up straight with the connection.  Many Drain Installation Companies use a piece of ADS on the end of the Sewer and Drain pipe and then connect it to the curb outlet.  Many times there is no other way to connect them depending on your downward slope.


Sewer and Drain

Green or White Sewer and Drain Pipe

Sewer and Drain is brittle after a short amount of time.  You can break it with a hammer.   Tree roots, many times squeeze the pipe and crack it causing it to leak.   It is not a good long term solution for anything.

Old Sewer and Drain Pipe

Old Sewer and Drain Pipe

Thick walled PVC is superior to ADS and Sewer and Drain.  It will last a lifetime.  It won’t crack under normal circumstances.

That being said, It is The most difficult of all to install.  It is not for weekend warriors or your brother-in-law who says he knows what he is doing.  Someone with a lot of experience is needed to install a Thick Walled PVC Drainage System.

SD and 40 schedule

40 Schedule PVC Drain Pipe on the right, Sewer and Drain on the left.

Oh, by the way, 40 Schedule or 200 Class PVC is by far the most expensive.

If money is no object, then absolutely hire an Expert to install a Thick walled PVC System.

There are two types of Thick Walled Pvc Pipe available for Drainage Systems, 40 Schedule and 200 class.

Forty Schedule is always the same thickness at a particular size pipe.

Two Hundred Class gets thicker as the pipe gets bigger.

Forty Schedule is thicker in pipes smaller than 2 inch.

Two hundred Class is thicker in pipes over 2 inch.

Typically 4 inch pipe is most commonly used in a Drainage Systems.  Forty Schedule and 200 Class are both very good in the 4 inch Size.


The size of Drain Pipe you use in your Drainage System is fairly simple.  You can use 3 Inch, 4 Inch, or 6 Inch.  Sometimes 2 inch can be used on a small single drain but it is easily overwhelmed by too much water.

Four Inch, as stated earlier is the most common size used in a Drainage System.

If your system is a Drainage System and not a Flood Prevention System, then 4 Inch Should be fine for most applications.

If your drainage system must handle a lot of water in a hurry and is designed intercept water to protect property then two 4 inch pipes may be needed or one 6 inch Pipe.  It can vary.

In 2015 we installed a Flood Prevention System that had two 6 inch pipes in the same trench.  Our customer never had water in her garage again.

If you can afford larger Drain Pipe or more than one Drain Pipe in the same trench, your Drainage System should do its job well.

If you connect 5 large Surface Drains to one small 3 inch pipe, be prepared for poor performance.  I’ve seen a large French Drain connected to a 3 inch pipe.  The water shot out of the exit point like a cannon and the problem drainage area stayed flooded for a long time.

I try not to use 3 inch at all for a Drainage System and I am very careful not to attach too large or too many drains to 4 inch.

Gutter to French Drain
Connecting Gutter to French Drain

Surface Drains look nice but they have limited applications.  They must be installed in situations that they are designed for.  Surface Water only in smaller volume applications.  Surface Drains don’t move as much water as French Drains.

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