What is a French Drain?
The French drain is basically a trench filled with gravel. This trench is meant to keep the water runoff from a sloping piece of land to be rerouted in a productive manner. It was invented in Concord by the farmer/judge Henry French (Harvard Graduate). When surface water (such as heavy rain) is invading any given area where there is a serious drainage problem, this could be the key to recovering flooded areas.
The French drain first came into the public eye in the year 1859 when Mr. French first published his book on farm drainage, in Concord, Massachusetts. The whole beauty of his idea came from careful observation. For it was not his diploma in law that showed him the ways of the land, it was his keen eye for observation and the ways of Mother Nature. He knew, like all simple farmers do, that water runs downhill, and just loves to accumulate in the most inconvenient of locations. Suffering from constant flooding, Henry French kept paying attention to water behavior until he figured out the best way to make sure water would run in the direction he wanted, without trying to go against Nature’s natural laws. Thus he figured out the concept of what we now call a French drain.
Not only did Mr. French discover this interesting style of drainage he also came up with many other drainage solutions and strategies for an ongoing problem. But what makes the French drain stand out from all the others? The fact that it is a drain that needs little to no upkeep. Most drains suffer from the same problem, over and over. His system design was developed around the idea of a common ditch/trench or gutter/pipe system of drainage that had already previously existed. The problem with a trench or ditch system is that they backup and get clogged easily. But gravel… Yes gravel, small stones from broken boulders. Gravel works like a screen filter would. Usually, there should be at least one foot of slope in the trench for every 100 feet of horizontal catchment (which means it gets deeper, the closer to the drain pipe it gets). It keeps the surface water flowing without the other stuff that comes along with it in really heavy rain. The bigger the rocks, the faster the water will flow.
Speed is not all there is to an efficient drain design. If the water runoff is effecting the foundation of a house, by constantly accumulating for long periods until such time as it evaporates or seeps down into the ground, this could seriously compromise the structural integrity, such as with wet basements. Digging a sloping trench and merely filling it with gravel, won’t solve this problem, in fact, it could worsen such problems. So in order to fix any possible situations, the best thing to do would be to put down a layer of flexible landscape fabric (usually polyethylene), over the channel, or pipe being used for drainage. In the case of a pipe system (characteristic of this style), the landscape fabric will ensure that all the water gets into the pipe, without debris clogging the pipe entrance, as in the case of pipe screens (or kitchen sinks).
Ensuring that the French drain will not create seepage or water damage to any other nearby structures, there is also the factor of clean and well kept drains. In other words, is it going to go with the rest of the yard? This factor is what determines the way a French drain looks after it is all done. By just placing a layer of coarse sand over the top of the gravel and then turf grass over that, it is possible to make it almost invisible to the human eye, unless showing off is the point, in which case the top layer is chosen in accordance to taste (perhaps multi colored river pebbles).
By adding sand to the layers of gravel in a French drain, the water not only gets through the pipe drain (initial reason for this style), but also lends to purifying it for domestic consumption (bath, hose, cloths… etc.). Putting a top layer, gives the whole system a final look (which may or may not be important) for that given system’s design. French drain’s most important feature is the way they filter surface water without requiring daily maintenance. The pipes’ in French drains rarely, if ever get filled with debris, and water flows freely, keeping the water clean while recovering flooded areas.