The French Drain basics

Managing the water on your property is often overlooked and can lead to a lot of problems.
In this article we explore what a French drain is and how it works.

What is a French drain?

From my research the name of the French drain comes from a Henry French from Concord, Massachusetts.
He was a farmer in the late 1850s that wrote in a book about farm water management.
(Most people, including myself, assumed it was from the country.)

The French drain operates on the fundamental that water follows the easiest path to the lowest point on a landscape. Using this principle, it channels water away from areas where it would cause damage or pool during rainy periods.
It is also a way to limit the effect of erosion on soil from running water on a slopped area.

How does a French drain work?

Now that we know what a French drain is, lets talk about how it works.

The single biggest function of the French drain serves, is to direct water from on place, in a controlled manner to another place.
There is no need for any specialist equipment. This does mean that care should be taken to understand exactly how it needs to be implemented. It is always a good idea to get advice from a professional. They are usually familiar with the laws and what possible pitfalls to lookout for.

The French drain is a trench that contains gravel and a perforated drainage pipe (on larger implementations).
It can be a large/deep trench or it can be a slot in a concrete slab and filled with gravel.

Composition of a French drain

a Typical French drain usually consists of a trench that is in the ground. a Perforated pipe is laid in the trench and rounded gravel is used to fill the trench.
The gravel should ideally be washed and rounded gravel. The rounded stone will naturally maintain the spaces between the stones when compacted. You can also choose to keep the gravel exposed or put a layer of soil over it.
Drainage fabric should be ideally line the trench. This will prevent soil particulates from clogging up the space between the gravel.

We did not implement it this way. We will need to monitor and see how that performs in a few years. I believe it should not cause blockage in the pipe itself. There is a gutter pipe, feeding into top end of the French drain pipe. The water coming from the roof should keep the pipe clear.

An example of a French drain.

When we bought our home, we moved into the house in winter and just as a really big rain system was moving over our town. Our daughter opened the back door and shouted “Mom, Dad, come look! There is a sea outside!!!”

Our property is slopes and at an angle from the north-west to the south east corner.
This meant that the water’s natural flow was being blocked by the house and water was pooling up in the corner between the garage and the bedrooms.
The water was around 6cm (2inches) deep. The foundations and walls then soak up this water because it has nowhere else to go!
(This caused so many issues but I will leave that topic for another article…)

Luckily our friends at River Construction was there to save the day!
They quickly identified that the water from the gutter down-pipes was not draining away. This required us to put in a stormwater drainage system. This directed the water around the house and out into a field bordering the bottom of our property.

This would take care of a lot of water but we still had water underground coming from the the higher lying properties above us.
This is where we implemented the French drain. The water in the ground would seep through the gravel and into pipe, through holes we drilled. Wrapping the pipe in burlap helps to prevent debris from blocking the holes.
Where the pipes change direction collection pits help to prevent debris from creating blockages and for easy access to clear them out. This makes maintenance a lot easier in the future.

We covered the basics of a French drain and there is so much more that we can talk about on this topic.
So lookout for a follow up article where we go into a bit more detail and a list some of the common mistakes to look out for.

If you enjoyed this topic, please make sure subscribe to our mail list, so we can keep you up to date.