What Is A French Drain?

French drains also known as agricultural (agi) drains, trench drains, blind drains and many other names are some of the most common landscape drainage systems on Earth. Henry F. French originally popularised French (later named after him) drains through his book, Farm Drainage The Principles, Processes, and Effects originally released in 1859 the same year Melbourne and Geelong Football Clubs were formalised nearly 200 years ago. Since then they have been widely used in agricultural and residential stormwater drainage in Australia and worldwide as they are cost-effective and incredibly effective at managing soil and surface water. But how do they work?

How do French Drains Work?

French drains work on the simple premise that water likes the easy route out, but before we get into the nitty-gritty let's quickly talk about what the drain looks like. A French drain is made up of a ditch running through your yard on the lower area or an area prone to flooding.

A perforated pipe is then laid in the ditch just off the bottom. Yep, that's right, this may sound counterintuitive but stay with me. The pit is then filled with river rocks or sand depending on the water flow needs. The bigger the aggregate the higher the water flow and vice versa. If the soil around the drain is fine or has a high sand content you can lay a filter membrane along the sides of the ditch or wrap it around the pipe this prevents silt and soil from blocking the drain pipe.

How Do They Drain?

You may be confused as to how a pipe with holes in it is good for drainage. Wouldn't the water just drain out the bottom? Well, that is where science comes in! Water is lazy and wants to take the easiest path possible. Therefore, by placing this pipe with holes in it in the ditch it creates a cavity of minimal resistance that is sloped towards where you want the water to go. Then as it rains the water flows into the ditch through the gravel and into the pipe where it then travels to its endpoint as the resistance within the pipe is less than the gravel outside the pipe.

As they are built in the ground they allow for water to drain not only from the surface but also from the soil through the walls of the ditch. This makes them perfect for managing soil water levels and preventing your gardens and lawns from becoming waterlogged.

French drains are the drainage system chosen by farmers worldwide. This is the proven way to keep your gardens and lawns dry and manage soil water levels. If you need any help with your stormwater drainage systems in Melbourne contact our team of expert plumbers today on 0434 022 483.