Nashville French Drains which, despite their name, originated in the United States, essentially work by providing invasive groundwater with a path of least resistance by means of which it can be redirected away from a structure or low-lying section of lawn. They are named for a new Hampshire man, Henry Flagg French, who, in 1860, published a book with the intriguing title: Farm Drainage - The Principles, Processes, and Effects of Draining Land with Stones, Wood, Plows, and Open Ditches, and Especially with Tiles.
Nowadays, Nashville French Drains are generally used to combat flooding problems caused by surface and/or groundwater that a home owner may be having, especially affecting their lawn, foundation or basement. They are also sometimes used to drain off liquid effluent from septic tanks.
The basic design, a gravel-filled trench, is simple but for it to continue working over the long haul, it's important that it be well executed. French Drain Installation Nashville
Flooding problems are usually associated with sloping ground, non-porous clayey soil, or a combination of the two. For example, if your property is built on a slope with your neighbors' house occupying a lot higher up the slope, heavy rainfall can precipitate an accumulation of groundwater rushing down from their property and onto your own. If your soil is not able to absorb all that water, you could very well experience damage to your house's foundation, or leakage into a crawlspace or basement below the ground floor of the house.
A linear French drain is a simple, cost-effective solution to such a problem. In this scenario, it acts as a moat that protects your house by intercepting the groundwater rushing down the slope and directing it around and away from your house's foundation.
A linear French drain is a doable D.I.Y. project, if you don't mind doing some backbreaking work (this does involve digging a trench, which after all is a thing closely akin to a ditch) and you have the proper tools and materials (1" round washed gravel, 4" PVC pipe with drainage holes, a trenching spade or power trencher and a builder's level)
So, let's get down to the nitty-gritty both of how to build a French drain, and how it works. First of all, you'll need to dig an L-shaped or U-shaped trench system, 6" wide and 24" deep, four to six feet from the house. It's important not to build the drain too near the house because, if you do, you'll be bringing water up against the foundation, which is exactly what you don't want.
The main leg of the trench system should be dug up the slope from the house. For a U-shaped French drain, it should be level and connected to two pipes on either side of the house with 90 degree PVC elbow joints. For an L-shaped drain, the main leg should slope down, at a pitch of at least 1/8 inch per foot of fall, to the second leg which will run alongside the house, also connected by means of a 90 degree PVC elbow joint.
When you are designing your drain system, you want to make gravity work for you. Just like a river, groundwater flows downhill, so you'll have to work with the natural slope of your property and, if possible, have the exit pipe come out above ground to give the groundwater an easy exit point.